@conference { ISI:000238284200016, title = {Density functional response approach for electric properties of molecules}, booktitle = {International Conference on Computational Methods in Sciences and Engineering (ICCMSE 2005)}, series = {LECTURE SERIES ON COMPUTER AND COMPUTATIONAL SCIENCES}, volume = {3}, year = {2005}, note = {International Conference on Computational Methods in Sciences and Engineering (ICCMSE 2005), Corinth, GREECE, OCT 21-26, 2005}, month = {OCT}, pages = {142-151}, publisher = {Vsp BV-C/o Brill Acad Publ, Po Box 9000, 2300 Pa Leiden, Netherlands}, organization = {Vsp BV-C/o Brill Acad Publ, Po Box 9000, 2300 Pa Leiden, Netherlands}, address = {Corinth, Greece}, abstract = {

We review in this paper an implementation of the response approach to the Kohn-Sham (KS) density functional theory (DFT) for obtaining the linear and non-linear electric response properties of molecules using Gaussian type orbital basis centered on atoms. We have made a formulation in which the response of the electron density through the solution of the coupled perturbed Kohn-Sham (CPKS) equations has to be obtained only once, instead of iteratively as in the case of completely analytic procedure. Our method is based on a numerical finite-field solution of derivative KS operator, followed by analytic solution of CPKS equation. Further, using the response of the electron density, the dipole moment, polarizability and first-hyperpolarizability of the molecules are evaluated. The method is particularly useful for large systems. We tested our method using HF, BH, H2O and CO as test molecules, for which, high quality ab initio results are available. Further, our study of possible incorporation of non-dynamical electron correlation by studying BH and HF at several internuclear distances is discussed.

}, keywords = {Density functional theory, molecular properties, polarizability, Response approach}, isbn = {90-6764-442-0}, issn = {1573-4196}, author = {Pal, Sourav and Sophy, K. B.}, editor = {Maroulis, G and Simos, T} } @conference { ISI:000238054400287, title = {Reactivity descriptors: conceptual and computational developments}, booktitle = {International Conference on Computational Methods in Sciences and Engineering (ICCMSE 2005)}, series = {LECTURE SERIES ON COMPUTER AND COMPUTATIONAL SCIENCES}, volume = {4A-4B}, year = {2005}, note = {International Conference on Computational Methods in Sciences and Engineering (ICCMSE 2005), Corinth, GREECE, OCT 21-26, 2005}, month = {OCT}, pages = {1172-1174}, publisher = {Vsp BV-C/o Brill Acad Publ, Po Box 9000, 2300 Pa Leiden, Netherlands}, organization = {Vsp BV-C/o Brill Acad Publ, Po Box 9000, 2300 Pa Leiden, Netherlands}, address = {Corinth, Greece}, isbn = {90-6764-443-9}, issn = {1573-4196}, author = {Pal, Sourav}, editor = {Simos, T. and Maroulis, G.} } @article { ISI:000241574500031, title = {Analytically continued fock space multi-reference coupled-cluster theory: application to the shape resonance}, journal = {Chemical Physics}, volume = {329}, number = {1-3, SI}, year = {2006}, month = {OCT}, pages = {283-289}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

The Fock space multi-reference coupled-cluster (FSMRCC) method is used for the study of the shape resonance energy and width in an electron-atom/molecule collision. The procedure is based upon combining a complex absorbing potential (CAP) with FSMRCC theory. Accurate resonance parameters are obtained by solving a small non-Hermitian eigen-value problem. We study the shape resonances in e(-)-C2H4 and e(-)-Mg. (c) 2006 Elsevier B.V. All rights reserved.

}, keywords = {complex absorbing potential, correlated independent particle potential, Fock space multi-reference coupled-cluster theory, shape resonance}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2006.07.002}, author = {Pal, Sourav and Sajeev, Y. and Vaval, Nayana} } @article { ISI:000241168600010, title = {Constrained variational response to Fock-space multi-reference coupled-cluster theory: Some pilot applications}, journal = {Journal of Molecular Structure-Theochem}, volume = {768}, number = {1-3}, year = {2006}, month = {AUG}, pages = {91-96}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Fock space (FS) multi-reference (MR) coupled-cluster (CC) has been established to be state-of-the-art method for energies of open-shell radicals, ionized, electron attached states and excited states. Due to the multi-root nature of the method, the linear response of MRCC, however, is non-trivial. Constrained variation approach (CVA) makes it plausible to calculate response of the MRCC method efficiently. However, the approach is used for only one root of the problem at a time. In the present article, we make first implementation of the approach and present test results of dipole moments of small radicals. (c) 2006 Elsevier B.V. All rights reserved.

}, keywords = {constrained variation, coupled-cluster, Dipole moment, Multi-reference, response}, issn = {0166-1280}, doi = {10.1016/j.theochem.2006.05.022}, author = {Manohar, Prashant Uday and Vaval, Nayana and Pal, Sourav} } @article { ISI:000242646200011, title = {Interaction induced shifts in O-H stretching frequency of water in halide-ion water clusters: a microscopic approach with a bond descriptor}, journal = {Journal of Chemical Physics}, volume = {125}, number = {21}, year = {2006}, month = {DEC}, pages = {Article No. 214304}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

Based on conceptual density functional theory, two new descriptors, the normalized atom-condensed Fukui functions (NFFs) and bond deformation kernel (BDK), are proposed to describe the O-H stretching frequency shifts in water halide-ion clusters by including local polarizations in the system. NFF, along with BDK, can be successfully used to describe interactions between different atoms, especially in cases where polarizations are quite important. (c) 2006 American Institute of Physics.

}, issn = {0021-9606}, doi = {10.1063/1.2400225}, author = {Tanwar, Akhilesh and Bagchi, Biman and Pal, Sourav} } @article { ISI:000239573100068, title = {Minimum magnetizability principle}, journal = {Journal of Chemical Physics}, volume = {125}, number = {5}, year = {2006}, month = {AUG }, pages = {Article No. 056101}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, issn = {0021-9606}, doi = {10.1063/1.2227381}, author = {Tanwar, Akhilesh and Pal, Sourav and Roy, Debesh Ranjan and Chattaraj, Pratim Kumar} } @article { ISI:000239884300028, title = {Theoretical study of N2O reduction by CO in Fe-BEA zeolite}, journal = {Chemphyschem}, volume = {7}, number = {8}, year = {2006}, month = {AUG}, pages = {1795-1801}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Article}, address = {PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY}, abstract = {

Quantum mechanical (QM) and QM/molecular mechanics (MM) studies of the full catalytic cycle of N2O reduction by CO in Fe-BEA zeolite, that is, oxidation of BEA-Fe by NO and reduction of BEA-Fe-alpha O by CO, is presented. A large QM cluster, representing half of the channel of the BEA zeolite, is used. The contribution of the MM embedding to the calculated activation energies is found to be negligible. The minimum-energy paths for N2O decomposition and reduction with CO are calculated using the nudged elastic bond (NEB) method. Calculated band experimental activation energies ore in good agreement The two possible orientations for the gaseous molecules adsorbing on the Fe site that ore found lead to different activation energies.

}, keywords = {Density functional calculations, iron, nitrogen oxides, reaction mechanisms, zeolites}, issn = {1439-4235}, doi = {10.1002/cphc.200600228}, author = {Fischer, Gerd and Goursot, Annick and Coq, Bernard and Delahay, Gerard and Pal, Sourav} } @conference { ISI:000252146200027, title = {Constrained variational response to fock-space multi-reference coupled-cluster theory: formulation for excited-state electronic structure calculations and some pilot applications}, booktitle = {Computational Methods in Science and Engineering Vol 1: Theory and Computation: Old Problems and New Challenges}, series = {AIP CONFERENCE PROCEEDINGS}, volume = {963}, year = {2007}, note = {International Conference on Computational Methods in Science and Engineering, Corfu, GREECE, SEP 25-30, 2007}, month = {SEP}, pages = {337-344}, publisher = {European Soc Computat Methods Sci \& Engn; Minist Natl Educ \& Religious Affairs; E4 Comp Engn}, organization = {European Soc Computat Methods Sci \& Engn; Minist Natl Educ \& Religious Affairs; E4 Comp Engn}, address = {2 Huntington Quadrangle, Ste 1no1, Melville, NY 11747-4501 USA}, abstract = {

Fock-space (FS) multi-reference (MR) coupled-cluster (CC) method has emerged as compact tool to account for electronic structure of open-shell systems and molecules in low-lying excited states. Development of linear response (LR) has been one of the challenging problems in FSMRCC due to multiple-root nature of effective Hamiltonian. The recently developed constrained variational approach (CVA) has opened up a promising tool for efficient evaluation of analytic response properties. In this article, we present formulation of the method for excited state calculations. We discuss the decoupling of equations as a result of spin-adaptation and present some preliminary results for analytical dipole moments and polarizabilities of some molecules in low-lying triplet excited states.

}, keywords = {CVA, Dipole moment, excited states, FSMRCC, polarizability}, isbn = {978-0-7354-0477-9}, issn = {0094-243X}, author = {Manohar, Prashant Uday and Pal, Sourav}, editor = {Maroulis, G and Simos, TE} } @article { ISI:000246282600007, title = {Density functional static dipole polarizability and first-hyperpolarizability calculations of Na-n (n=2, 4, 6, 8) clusters using an approximate CPKS method and its comparison with MP2 calculations}, journal = {Journal of Chemical Theory and Computation}, volume = {3}, number = {3}, year = {2007}, month = {MAY}, pages = {716-727}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

{We report the static dipole polarizability and first-hyperpolarizability of the sodium atom clusters, Na-n

}, issn = {1549-9618}, doi = {10.1021/ct6003627}, author = {Sophy, K. B. and Calaminici, Patrizia and Pal, Sourav} } @article { ISI:000249329300010, title = {Deprotonation of 1,2-dialkylpyridinium ions: a DFT study of reactivity and site selectivity}, journal = {Journal of Physical Chemistry A}, volume = {111}, number = {36}, year = {2007}, month = {SEP}, pages = {8823-8828}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

A site-selectivity model, based on the Fukui function as a local reactivity descriptor, has been applied to 1.2-disubstituted pyridinium ions incorporating two competing sites of similar reactivity, i.e., 1-methylene and 2-methylene, which may undergo deprotonation depending on the nature of substituent present on these moieties. Applicability of the local HSAB rule, in context with the Li-Evans{\textquoteright} generalized HSAB principle suggesting the hard-hard interactions to be controlled by minimum Fukui function, has been illustrated. Global and local reactivity descriptors have been computed by carrying out DFT calculations at B3LYP/6-31++G** level using Mulliken and NPA methods for charge analysis. A comparison with the calculated deprotonation energies involving two sites indicates that the observed site selectivity in differently substituted pyridinium ions is better explained by the Li-Evans rule of minimum Fukui function for hard-hard interactions.

}, issn = {1089-5639}, doi = {10.1021/jp072812o}, author = {Gupta, Neelima and Garg, Reena and Shah, Kirti Kr. and Tanwar, Akhilesh and Pal, Sourav} } @article { ISI:000246060000033, title = {Dipole moments and polarizabilities of some small radicals using constrained variational response to fock-space multi-reference coupled-cluster theory}, journal = {Chemical Physics Letters}, volume = {438}, number = {4-6}, year = {2007}, month = {APR}, pages = {321-325}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

In this Letter, we present dipole moments and polarizabilities of some open-shell doublet radicals, obtained analytically using constrained variational response to Fock-space (FS) multi-reference (MR) coupled cluster (CC) theory. These radicals can be treated as electron attached (EA) states of the corresponding closed-shell cations. Additionally, we also report analytical polarizabilities of some doublet radicals, which can be considered as ionized (IP) states of the corresponding anions. We compare our results with finite field FSMRCC response and the available benchmark results. (c) 2007 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2007.02.075}, author = {Manohar, Prashant Uday and Pal, Sourav} } @article { ISI:000249667400056, title = {Electronic structure of spherical quantum dots using coupled cluster method}, journal = {Journal of Chemical Physics}, volume = {127}, number = {11}, year = {2007}, month = {SEP}, pages = {114708}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

2, 6, 12, and 20 electron quantum dots have been studied using coupled cluster at singles and doubles level and extensive multireference coupled cluster (MRCC) method. A Fock-space version of MRCC (FSMRCC) containing single hole-particle excited determinants has been used to calculate low-lying excited states of the above system. The ionization potential and electron affinity are also calculated. The effect of correlation energy on excitation energy and charge density is shown by calculating them at the high density region (low value of density parameter r(s)) and at the low density region (high value of density parameter r(s)). (c) 2007 American Institute of Physics.

}, issn = {0021-9606}, doi = {10.1063/1.2768523}, author = {Heidari, Ideh and Pal, Sourav and Pujari, B. S. and Kanhere, Dilip G.} } @article { ISI:000243388500023, title = {Influence of electric field on the global and local reactivity descriptors: reactivity and stability of weakly bonded complexes}, journal = {Journal of Physical Chemistry A}, volume = {111}, number = {2}, year = {2007}, month = {JAN}, pages = {375-383}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The response of the global and local reactivity density-based descriptors (chemical potential, hardness, softness, Fukui function, and local softness) in the presence of external electric field has been studied for some of the simple prototype molecular systems. In addition to the analysis on the reactivity of these systems, the influence of the electric field on the interaction energy of the complexes formed by these systems has also been studied using the recently proposed semiquantitative model based on the local hard-soft acid-base principle. By using the inverse relationship between the global hardness and softness parameters, a simple relationship is obtained for the variation of hardness in terms of the Fukui function under the external electric field. It is shown that the increase in the hardness values for a particular system in the presence of external field does not necessarily imply that the reactivity of the system would be deactivated or vice versa.

}, issn = {1089-5639}, doi = {10.1021/jp065580m}, author = {Kar, Rahul and Chandrakumar, K. R. S. and Pal, Sourav} } @article { ISI:000254309400007, title = {Shape resonance in electron molecule scattering using coupled cluster method}, journal = {Indian Journal of Physics and Proceedings of the Indian Association for the Cultivation of Science}, volume = {81}, number = {10}, year = {2007}, month = {OCT}, pages = {1061-1067}, publisher = {INDIAN ASSOC CULTIVATION SCIENCE}, type = {Article}, address = {INDIAN J PHYSICS, JADAVPUR, KOLKATA 700 032, INDIA}, abstract = {

The Fock space multi-reference coupled-cluster (FSMRCC) method along with the complex absorbing potential (CAP) is used for the study of the shape resonance energy and width in an electron molecule collision. We study the shape resonances in e(-) -H2CO and e(-) -CO.

}, keywords = {electron-molecule scattering, multi-reference coupled-cluster}, issn = {0973-1458}, author = {Pal, Sourav and Vaval, Nayana and Sajeev, Y.} } @article { ISI:000259876700012, title = {Calculation of vibrational energy of molecule using coupled cluster linear response theory in bosonic representation: convergence studies}, journal = {Journal of Chemical Physics}, volume = {129}, number = {13}, year = {2008}, month = {OCT}, pages = {134111}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

Vibrational excited state energies have been calculated using vibrational coupled cluster linear response theory (CCLRT). The method has been implemented on formaldehyde and water molecule. Convergence studies have been shown with varying the cluster operator from S(4) to S(6) as well as the excitation operator from four bosons to six bosons. A good agreement with full configuration interaction results has been observed with S(6) truncation at coupled-cluster method level and six bosonic excitations at CCLRT level. (C) 2008 American Institute of Physics.

}, issn = {0021-9606}, doi = {10.1063/1.2982502}, author = {Banik, Subrata and Pal, Sourav and Prasad, M. Durga} } @article { ISI:000253511900004, title = {Comparative study of structural, acidic and hydrophilic properties of Sn-BEA with Ti-BEA using periodic density functional theory}, journal = {Journal of Physical Chemistry B}, volume = {112}, number = {9}, year = {2008}, month = {MAR}, pages = {2573-2579}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Periodic density functional theory has been employed to characterize the differences in the structural, Lewis acidic and hydrophilic properties of Sn-BEA and Ti-BEA. We show that the incorporation of Sri increases the Lewis acidity of BEA compared to the incorporation of Ti. Hence, the present work gives insight into the role of Sn in increasing the efficiency of the oxidation reactions. The results also justify that the percentage of Sri substituted in BEA is less than Ti. The structural analysis shows that the first coordination shell of Sri is larger than that of Ti. However, the second coordination of both sites remains the same. The water adsorption properties of these substituted zeolites are quantified. Moreover, we explain the higher Lewis acidity of Sn than the Ti site on the basis of the Fukui functions and charge population analysis.

}, issn = {1520-6106}, doi = {10.1021/jp709846s}, author = {Shetty, Sharan and Kulkarni, Bhakti S. and Kanhere, Dilip G. and Goursot, Annick and Pal, Sourav} } @article { ISI:000255704100017, title = {Density functional investigations of electronics structure and dehydrogenation reactions of Al- and Si-substituted magnesium hydride}, journal = {ChemPhysChem }, volume = {9}, number = {6}, year = {2008}, month = {APR}, pages = {928-934}, publisher = {WILEY-V C H VERLAG GMBH}, type = {Article}, address = {PO BOX 10 11 61, D-69451 WEINHEIM, GERMANY}, abstract = {

{The effect on the hydrogen storage attributes of magnesium hydride (MgH2) of the substitution of Mg by varying fractions of Al and Si is investigated by an ab initio plane-wave pseuodopotential method based on density functional theory. Three supercells, namely, 2 x 2 x x 3 x 1 x 1 and 5 x 1 x 1 are used for generating configurations with varying amounts (fractions x=0.0625, 0.1, and 0.167) of impurities. The analyses of band structure and density of states (DOS) show that, when a Mg atom is replaced by Al, the band gap vanishes as the extra electron occupies the conduction band minimum. In the case of Si-substitution, additional states are generated within the band gap of pure MgH2-significontly reducing the gap in the process. The reduced band gaps cause the Mg-H bond to become more susceptible to dissociation. For all the fractions, the calculated reaction energies for the stepwise removal of H-2 molecules from Al- and Si-substituted MgH2 ore much lower than for H-2 removal from pure MgH2. The reduced stability is also reflected in the comparatively smaller heats of formation (Delta H-f) of the substituted MgH2 systems. Si causes greater destabilization of MgH2 than Al for each x. For fractions x = 0.167 of Al

}, keywords = {band structure, Density functional calculations, hydrides, Hydrogen storage, Thermodynamics}, issn = {1439-4235}, doi = {10.1002/cphc.200700860}, author = {Kelkar, Tuhina and Pal, Sourav and Kanhere, Dilip G.} } @article { ISI:000256765900007, title = {Electric field response of molecular reactivity descriptors: a case study}, journal = {Theoretical Chemistry Accounts}, volume = {120}, number = {4-6}, year = {2008}, month = {JUL}, pages = {375-383}, publisher = {SPRINGER}, type = {Article}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

In the present article, we study the influence of external electric field on the density-based global and local reactivity descriptors using examples of some planar nonlinear polyatomic molecules with C-2V point group symmetry. The study mainly involves the application of weak electric field in a direction along the principal axis and along its perpendicular direction. We also discuss the strength of the electric field studied in this work in terms of the strength of the molecular interaction. The work is expected to throw light on the effect of interactions within the above range on reactivity descriptors. Results are presented for a few prototype molecules.

}, keywords = {electric field, molecular interaction, planar nonlinear polyatomic molecules, Reactivity descriptors}, issn = {1432-881X}, doi = {10.1007/s00214-008-0437-4}, author = {Kar, Rahul and Pal, Sourav} } @article { ISI:000256005300018, title = {First principles calculations of thermal, equations of state and thermodynamical properties of MgH2 at finite temperatures}, journal = {Computational Materials Science}, volume = {42}, number = {3}, year = {2008}, month = {MAY}, pages = {510-516}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

We present the first principles calculations of the thermodynamical properties of magnesium hydride (MgH2) over a temperature range of 0-1000 K. The phonon dispersions are determined within the density functional framework and are used to calculate the free energy of MgH2 within the quasiharmonic approximation (QHA) at each cell volume and temperature T. Using the free energies the thermal equation of state (EOS) is derived at several temperatures. From the thermal EOS structural parameters such as the equilibrium bell volume (V-0) and elastic properties, namely, bulk modulus (K-0) and its pressure derivative (K-0({\textquoteright})) are computed. The free energies are also used to calculate various thermodynamical properties within QHA. These include internal energy E, entropy S, specific heat capacity at constant pressure C-P, thermal pressure P-thermal(V,T) and volume thermal expansion Delta V/V (\%). The good agreement of calculated values of S and Cp with experimental data exhibits that QHA can be used as a tool for calculating the thermodynamical properties of MgH2 over a wide temperature range. P-thermal(V,T) increases strongly with T at all the volumes but it is a slowly varying function of volume for T = 298-500 K. According to Karki [B.B. Karki, Am. Miner. 85 (2000) 1447] such volume based variations can be neglected and so it is possible to estimate the thermal EOS only with the knowledge of the measured P-thermal(V,T) versus temperature at ambient pressure and isothermal compression data at ambient temperature. Temperature dependence of Delta V/V(\%) shows that V-0 increased with increase in temperature. However, the percentage decrease in K-0 superseded this percentage increase in V-0 even at temperatures moderately higher than 298 K. Therefore, we suggest application of temperature (T \> 298 K) as an approach to enhance the hydrogen storage capacity of MgH2 because of its better compressibility at these temperatures. (C) 2007 Elsevier B.V. All rights reserved.

}, keywords = {equation of state, Hydrogen storage, lattice dynamics, magnesium hydride, Thermodynamic properties}, issn = {0927-0256}, doi = {10.1016/j.commatsci.2007.08.014}, author = {Kelkar, Tuhina and Kanhere, Dilip G. and Pal, Sourav} } @article { ISI:000260533000029, title = {Noniterative density functional response approach: application to nonlinear optical properties of p-nitroaniline and its methyl-substituted derivatives}, journal = {Journal of Physical Chemistry A}, volume = {112}, number = {44}, year = {2008}, month = {NOV}, pages = {11266-11272}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We report the effect of substitution, position of the substituent, and the symmetry on the nonlinear optical properties of p-nitroanline (PNA) and its derivatives using our implementation of the noniterative approximation of couple-perturbed Kohn-Sham (CPKS) equation in the deMon2k. Dipole moment, static polarizability, and first hyperpolarizability of these pi-conjugated donor-acceptor organic derivatives of PNA and its methyl-substituted analogs are calculated using our method at different exchange correlation functionals, namely, BP86, BPW91, and BLYP, using 6-31++G** basis set. A comparison of results obtained by our method with those obtained by MP2 (finite-field perturbation) method is presented in this paper. The effect of optical gap on charge transfer and subsequently on polarizabilities has been illustrated.

}, issn = {1089-5639}, doi = {10.1021/jp806204q}, author = {Sophy, K. B. and Shedge, Sapana V. and Pal, Sourav} } @article { ISI:000273349000001, title = {Bond length variations: electron number profiles and transferable atomic sizes}, journal = {Journal of Molecular Structure}, volume = {936}, number = {1-3}, year = {2009}, month = {NOV}, pages = {1-8}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

A profile of the number of electrons with distance along the M-X bond in gas-phase diatomic molecules has been obtained from electron density plots calculated using DFT B3LYP 6-311G** method for some representative molecules. This {\textquoteleft}{\textquoteleft}number profile{\textquoteright}{\textquoteright} is compared with that expected from the partitioning of the 1D bond-distance into atom-specific transferable {\textquoteleft}{\textquoteleft}hub{\textquoteright}{\textquoteright} or core atomic sizes of the M and X atoms and another {\textquoteleft}{\textquoteleft}axle{\textquoteright}{\textquoteright} size which is associated with a pair of (bonding) electrons. The {\textquoteleft}{\textquoteleft}hub{\textquoteright}{\textquoteright} size is proportional to a core atom-specific size, r(nZ)(c) with r(nZ)(c)(M) \>= r(nZ)(c)(X). For {\textquoteleft}{\textquoteleft}single bonds{\textquoteright}{\textquoteright}, the {\textquoteleft}{\textquoteleft}hub{\textquoteright}{\textquoteright} size for M atom is C(M)r(nZ)(c)(M) and for X atom is C(X)r(nZ)(c)(X). The {\textquoteleft}{\textquoteleft}axle{\textquoteright}{\textquoteright} size, DMX, is usually the ordinary (similar to 4a(H)/3 where a(H) is the Bohr radius of the hydrogen atom) or elongated (similar to 2a(H)) bond length of the hydrogen molecule. The {\textquoteleft}{\textquoteleft}hub{\textquoteright}{\textquoteright} and {\textquoteleft}{\textquoteleft}axle{\textquoteright}{\textquoteright} sizes could be characterized {\textquoteleft}{\textquoteleft}charge-transfer{\textquoteright}{\textquoteright} (C(M) = pi(2/3) = 2.144; C(X) = pi(4/3)/2 = 2.300 and D(MX) = 4a(H)/3) or {\textquoteleft}{\textquoteleft}neutral{\textquoteright}{\textquoteright} (CM or C(X) = 1, 2, ... and D(MX) = 2a(H)). We use a new {\textquoteleft}{\textquoteleft}static{\textquoteright}{\textquoteright} or {\textquoteleft}{\textquoteleft}peripatetic{\textquoteright}{\textquoteright} classification for the core sizes which is derived from a new condition for metallization in elements based on atomic size. The charge-transfer distance, d(MX)(+/-), is usually found for {\textquoteleft}{\textquoteleft}static{\textquoteright}{\textquoteright} conditions while the {\textquoteleft}{\textquoteleft}neutral{\textquoteright}{\textquoteright} description is usually found when X = F or for {\textquoteleft}{\textquoteleft}peripatetic{\textquoteright}{\textquoteright} conditions. Such a partitioning is seen to agree with that from the plot of the total number of electrons, N(el), vs r along a bond axis. The Nel vs r plots from each atom are described by a simple hydrogen-atom-like function which differ away ({\textquoteright}{\textquoteright}out{\textquoteright}{\textquoteright}) or towards ({\textquoteright}{\textquoteright}in{\textquoteright}{\textquoteright}) the M-X bond. Thus N(in,out)(M, X) = (Z(M,X) +/- 1) exp (-r/B(in,out)) where the minus sign is associated with M and plus sign with X and Bin, out being related inversely to the Slater orbital exponent. (C) 2009 Elsevier B.V. All rights reserved.

}, keywords = {B3LYP, Bond length, Bond-stretch isomer, DFT, Diatomic molecule}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2009.07.007}, author = {Ganguly, Parthasarathy and Kulkarni, Bhakti S. and Pal, Sourav} } @article { ISI:000266989800010, title = {Computational study of electronic structure, thermodynamics and kinetics of hydrogen desorption from Al- and Si-doped alpha-, gamma-, and beta-MgH2}, journal = {Journal of Materials Chemistry}, volume = {19}, number = {25}, year = {2009}, month = {APR}, pages = {4348-4355}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

First principles calculations of pure and Al-and Si-doped alpha-, gamma-, and beta-MgH2 were performed to investigate the influence of Al and Si as impurities and the presence of high pressure phases on the properties of hydrogen sorption of magnesium hydride. The ab initio plane wave pseudopotential method based on density functional theory within the generalized gradient approximation was used in the present study. The total energies of the considered systems were calculated as a function of cell volume to obtain material properties such as bulk modulus K-0, equilibrium cell volume V-0 and minimum energy E-0(V-0). From the density of states (DOS) analysis, it was shown that doping MgH2 with Al and Si caused a reduction in the band gaps of each of the three phases. The diminished band gaps made the Mg-H bond more susceptible to dissociation. The destabilization of the hydrides was reflected in the decreased heats of formation of the doped hydrides, with the following Delta H-f order: Si \< Al and beta \< gamma \< alpha. A 30.5\% reduction in the activation energy barrier E-act for H-2 desorption was calculated for the Al-doped alpha-MgH2(001) surface and a 15.5\% decrease in E-act of the Si-doped gamma-MgH2(001) surface was deduced, while doping with Al and Si increased the activation energy barrier for the beta-MgH2 (001) surface drastically.

}, issn = {0959-9428}, doi = {10.1039/b901115c}, author = {Kelkar, Tuhina and Pal, Sourav} } @article { ISI:000265529700034, title = {Density functional investigation of relativistic effects on the structure and reactivity of tetrahedral gold clusters}, journal = {Journal of Physical Chemistry C}, volume = {113}, number = {17}, year = {2009}, month = {APR}, pages = {7101-7106}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The influence of relativistic effects on the structure, vibrational modes, and reactivity of recently discovered tertrahedral gold clusters (Au(19) and Au(20)) are investigated using density functional methods. The intramolecular reactivity of the clusters was analyzed using density functional-based reactivity descriptors. The work shows that whereas the structural properties and vibrational modes are considerably affected by the relativistic effects, the reactivity trends based on Fukui function calculation on various atoms within this cluster remain unaffected by the absence or presence of relativistic effects. The reactivity descriptors reveal that the vertex atoms are the most reactive ones in Au(20) toward a nucleophilic attack. On the other hand, atoms connecting the missing vertex edge with the pyramid base along with the vertex atom are the most reactive for a nucleophilic attack in Au(19). The atoms lying at the center of each face are favorable for an electrophilic attack in both cases. Interestingly, the atoms with a missing cap in Aulg are highly favorable for electrophilic attack, and Au(20) has more sites for a favorable nucleophilic attack.

}, issn = {1932-7447}, doi = {10.1021/jp9001884}, author = {De, Himadri Sekhar and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000267983100004, title = {First- and second-order electrical properties computed at the FSMRCCSD level for excited states of closed-shell molecules using the constrained-variational approach}, journal = {Journal of Chemical Physics}, volume = {131}, number = {2}, year = {2009}, month = {JUL}, pages = {024102}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

Fock space multireference coupled-cluster (FSMRCC) method emerged as an efficient tool to describe the electronic structure of nearly degenerate cases. Development of linear response has been one of the challenging problems in FSMRCC due to the multiple-root nature of the effective Hamiltonian. A response from any of the roots would span the space for getting the properties. Hence, all roots perturbed by the external field would proliferate the excited states. We recently developed the FSMRCC method for the efficient evaluation of analytic response properties using a constrained variation approach. In this paper, we present analytic dipole moments and polarizabilities of H2O, O-3, and CH+ molecules in low-lying excited states along with brief discussion of singlet triplet decoupling of (1,1) sector of FSMRCC resulting from spin adaptation. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3167796]

}, issn = {0021-9606}, doi = {10.1063/1.3167796}, author = {Bag, Arijit and Manohar, Prashant Uday and Vaval, Nayana and Pal, Sourav} } @article { ISI:000269926200012, title = {Intermediate hamiltonian hilbert space coupled cluster method: theory and pilot application}, journal = {International Journal of Quantum Chemistry}, volume = {109}, number = {13}, year = {2009}, month = {NOV}, pages = {2909-2915}, publisher = {JOHN WILEY \& SONS INC}, address = {111 RIVER ST, HOBOKEN, NJ 07030 USA}, abstract = {

The intermediate Hamiltonian state universal (Hilbert-space) coupled-cluster method is presented, using a formalism similar to that developed for the valence universal (Fock-space) approach. The method is expected to be applicable to many states not accessible by traditional multiroot multireference all-order size-extensive approaches. A pilot application to excited states of atomic beryllium shows good convergence and agreement with experiment and full CI values. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 2909-2915, 2009

}, keywords = {coupled cluster, Hilbert space, intermediate Hamiltonian}, issn = {0020-7608}, doi = {10.1002/qua.22155}, author = {Eliav, Ephraim and Borschevsky, Anastasia and Shamasundar, K. R. and Pal, Sourav and Kaldor, Uzi} } @article { ISI:000265804300014, title = {Ionization potential and structure relaxation of adenine, thymine, guanine and cytosine bases and their base pairs: a quantification of reactive sites}, journal = {Journal of Molecular Structure-Theochem}, volume = {902}, number = {1-3}, year = {2009}, month = {MAY}, pages = {96-102}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

We present density functional theory (DFT) calculations using B3LYP/6-31++G** method to show relaxation in geometry of base pairs on cation radical formation. The changes in hydrogen bond length and angles show that in the cationic radical form the structure of the base pairs relaxes due to the distribution of charge. According to a recent study. it has been found that, upon excitation hole transfer from base to sugar occurs which results in sugar radical formation and leads to strand breakage 145] [A. Kumar, M.D. Sevilla, J. Phys. Chem. B 110 (2006) 24181]. One hydrogen bond increases, while the other decreases in Adenine-Thymine (AT) base pair and in case of Guanine-Cytosine (GC) base pair. one bond increases and other two decrease. Same is the case with bond angles for both the base pairs. Analysis of the electron density map of Singly Occupied Molecular Orbital (SOMO) reveals that electron is transferred mainly from adenine and guanine bases in the cationic radical formation of AT and CC base pair, respectively. The reactive sites of bases have been analyzed using condensed Fukui functions in a relaxed and frozen core approximation. The effects of relaxation on the reactivity indices are also analyzed. (C) 2009 Elsevier B.V. All rights reserved.

}, keywords = {Base-pairs, DNA bases, Fukui function, H-bond length, Ionization potential}, issn = {0166-1280}, doi = {10.1016/j.theochem.2009.02.018}, author = {Mishra, Deepti and Pal, Sourav} } @article { ISI:000267086900013, title = {Magnetizability of doublet radicals using fock space multi-reference coupled cluster method}, journal = {International Journal of Quantum Chemistry}, volume = {109}, number = {10, SI}, year = {2009}, month = {AUG}, pages = {2191-2198}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

In this article, we report the first implementation of the recently developed Fock space multi reference Coupled cluster (FSMRCC) response approach for magnetizabilities. The FSM-RCC treats dynamic and static correlation in a very extensive manner. We report pilot application of the diarnagnetizability of NO, NO2, OH, and BH2 radicals. We also report preliminary applications of the paramagnetic magnetizability of the NO radical. Standard atom-centered Gaussian basis functions have been used, and this allowed US to Study the gauge dependence of the magnetizabilities. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 2191-2198, 2009

}, keywords = {Fock space, magnetizability, multireference}, issn = {0020-7608}, doi = {10.1002/qua.22093}, author = {Ravichandran, Lalitha and Vaval, Nayana and Pal, Sourav} } @article { ISI:000282840600020, title = {Calculation of dipole transition matrix elements and expectation values by vibrational coupled cluster method}, journal = {Journal of Chemical Theory and Computation}, volume = {6}, number = {10}, year = {2010}, month = {OCT}, pages = {3198-3204}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

An effective operator approach based on the coupled cluster method is described and applied to calculate vibrational expectation values and absolute transition matrix elements. Coupled cluster linear response theory (CCLRT) is used to calculate excited states. The convergence pattern of these properties with the rank of the excitation operator is studied. The method is applied to a water molecule. Arponen-type double similarity transformation in extended coupled cluster (ECCM) framework is also used to generate an effective operator, and the convergence pattern of these properties is compared to the normal coupled cluster (NCCM) approach. It is found that the coupled cluster method provides an accurate description of these quantities for low lying vibrational excited states. The ECCM provides a significant improvement for the calculation of the transition matrix elements.

}, issn = {1549-9618}, doi = {10.1021/ct1003669}, author = {Banik, Subrata and Pal, Sourav and Prasad, M. Durga} } @article { ISI:000280708400025, title = {CDASE-A reliable scheme to explain the reactivity sequence between Diels-Alder pairs}, journal = {Physical Chemistry Chemical Physics}, volume = {12}, number = {32}, year = {2010}, month = {JUL}, pages = {9328-9338}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The reliability of the Comprehensive Decomposition Analysis of Stabilization Energy (CDASE) scheme, proposed recently (Phys. Chem. Chem. Phys., 2009, 11, 8306), has been demonstrated in the present study. Reactivity sequence among more than 100 pairs, taking part in Diels-Alder (DA) reaction, is successfully generated by this scheme. The diene series consisted mainly of cis-1,3-butadiene and different substituted butadienes whereas dienophiles are mainly ethylene and its different substitutions. Both the positive energy component (i.e., the energy parameter defined as {\textquoteleft}internal assistance{\textquoteright}) and the negative energy component could generate the expected reactivity trend among the chosen DA pairs, which is also supported by the global electrophilicities of dienes and dienophiles and the corresponding charge-transfer values (Delta N). The numerical values of these components are capable of predicting even the {\textquoteleft}normal electron demand{\textquoteright} (NED) and {\textquoteleft}inverse electron demand{\textquoteright} (IED) nature of the corresponding DA reaction. The method is also capable of reproducing the lower reactivity of acetylene as dienophile when compared to that of ethylene. The reason for the success of CDASE-scheme in explaining intermolecular reactivity sequence is also analysed.

}, issn = {1463-9076}, doi = {10.1039/b925441b}, author = {Saha, Soumen and Roy, Ram Kinkar and Pal, Sourav} } @article { ISI:000274355800017, title = {Comparison of the auxiliary density perturbation theory and the noniterative approximation to the coupled perturbed kohn-sham method: case study of the polarizabilities of disubstituted azoarene molecules}, journal = {Journal of Physical Chemistry A}, volume = {114}, number = {6}, year = {2010}, month = {FEB}, pages = {2357-2364}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We present a theoretical study of the polarizabilities of free and disubstituted azoarenes employing auxiliary density perturbation theory (ADPT) and the noniterative approximation to the coupled perturbed Kohn-Sham (NIA-CPKS) method. Both methods are noniterative but use different approaches to obtain the perturbed density matrix. NIA-CPKS is different froth the conventional CPKS approach in that the perturbed Kohn-Sham matrix is obtained numerically, thereby yielding a single-step solution to CPKS. ADPT is an alternative approach to the analytical CPKS method in the framework of the auxiliary density functional theory. It is shown that the polarizabilities obtained using these two methods are in good agreement with each other. Comparisons are made for disubstituted azoarenes, which give support to the push-pull mechanism. Both methods reproduce the same trend for polarizabilities because of the substitution pattern of the azoarene moiety. Our results are consistent with the standard organic chemistry {\textquoteleft}{\textquoteleft}activating/deactivating{\textquoteright}{\textquoteright} sequence. We present the polarizabilities of the above molecules calculated with three different exchange-correlation functionals and two different auxiliary function sets. The computational advantages of both methods are also discussed.

}, issn = {1089-5639}, doi = {10.1021/jp909966f}, author = {Shedge, Sapana V. and Carmona-Espindola, Javier and Pal, Sourav and Koster, Andreas M.} } @article { ISI:000278112200007, title = {Effect of solvents having different dielectric constants on reactivity: a conceptual DFT approach}, journal = {International Journal of Quantum Chemistry}, volume = {110}, number = {9}, year = {2010}, month = {AUG}, pages = {1642-1647}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

Conceptual density functional theory is exploited to understand the reactivity in a medium of solvents with increasing dielectric constants. Aprotic as well as protic solvents are used for this study. It is found that the global parameters, such as chemical potential and hardness, decrease from gas phase to solvent phase with increasing dielectric constant. However, it is observed that the Fukui functions of the reactive atoms increase significantly with the dielectric constants of the aprotic solvents while for the protic solvents the variation of the reactivity indices is insignificant. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 1642-1647, 2010

}, keywords = {COSMO, DFT, dielectric constant, Reactivity descriptors, solvent effect}, issn = {0020-7608}, doi = {10.1002/qua.22333}, author = {Kar, Rahul and Pal, Sourav} } @article { ISI:000284635100022, title = {Fock space multi-reference coupled-cluster method for energies and energy derivatives}, journal = {Molecular Physics}, volume = {108}, number = {21-23, SI}, year = {2010}, month = {OCT}, pages = {PII 927961714}, publisher = {TAYLOR \& FRANCIS LTD}, address = {4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLAND}, abstract = {

In this article, the development of Fock space multi-reference coupled-cluster method is reviewed. Molecular applications of the method for excitation and ionisation energies which took place at Quantum Theory Project have been discussed. Later developments of the method for energy derivatives have been presented along with pilot applications of molecular properties of radicals and excited states.

}, keywords = {coupled-cluster, difference energies, energy derivatives, Fock space, Multi-reference}, issn = {0026-8976}, doi = {10.1080/00268976.2010.522205}, author = {Pal, Sourav} } @article { ISI:000273051800057, title = {Influence of plane wave cut-off on structural and electronic properties in Sn-BEA and Ti-BEA zeolite water molecule interaction}, journal = {Chemical Physics Letters}, volume = {484}, number = {4-6}, year = {2010}, month = {JAN}, pages = {374-379}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Periodic systems are best described by the pseudo-potential methods. However, the accuracy of its description depends on the cut-off of plane wave basis. This is much more critical in the case of weak interactions, where a clear understanding on the influence of plane wave cut-off on the structural and electronic properties is not readily available in the literature. In the present work, we have taken a metal substituted beta zeolite-H2O complex for understanding this objective. Our studies show that while a lower cut-off of 500 eV is sufficient for the convergence of the structural parameters, description of energy-dependent properties necessitates a high cut-off value. (C) 2009 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2009.11.041}, author = {Kulkarni, Bhakti S. and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000284743900017, title = {Model study of effect of M = Li+, Na+, Be2+, Mg2+, and Al3+ ion decoration on hydrogen adsorption of metal-organic framework-5}, journal = {International Journal of Hydrogen Energy}, volume = {35}, number = {23, SI}, year = {2010}, month = {DEC}, pages = {12846-12857}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

The effect of light metal ion decoration of the organic linker in metal organic framework MOF 5 on its hydrogen adsorption with respect to its hydrogen binding energy (Delta B E) and gravimetric storage capacity is examined theoretically by employing models of the form MC6H6 nH(2) where M = Li+ Na+ Be2+ Mg2+ and Al3+ A systematic investigation of the suitability of DFT functionals for studying such systems is also carried out Our results show that the interaction energy (Delta E) of the metal ion M with the benzene ring Delta B E and charge transfer (Q(trans)) from the metal to benzene ring exhibit the same increasing order Na+ \< Li+ \< Mg2+ \< Be2+ \< Al3+ Organic hnker decoration with the above metal ions strengthened H-2 MOF 5 interactions relative to its pure state However amongst these ions only Mg2+ ion resulted in Delta B E magnitudes that were optimal for allowing room temperature hydrogen storage applications of MOF 5 A much higher gravimetric storage capacity (6 15 wt \% H-2) is also predicted for Mg2+ decorated MOF 5 as compared to both pure MOF 5 and Li+ decorated MOF (C) 2010 Professor T Nejat Veziroglu Published by Elsevier Ltd All rights reserved

}, keywords = {Binding energy, Hydrogen adsorption, Hydrogen storage, Metal organic frameworks}, issn = {0360-3199}, doi = {10.1016/j.ijhydene.2010.08.054}, author = {Maark, Tuhina Adit and Pal, Sourav} } @article { ISI:000274432400021, title = {Molecular electric dipole moments using the GVVPT2 variant of multireference perturbation theory}, journal = {Chemical Physics Letters}, volume = {487}, number = {1-3}, year = {2010}, month = {FEB}, pages = {116-121}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

A Lagrangian approach for electric dipoles within second order Generalized Van Vleck Perturbation Theory (GVVPT2) is presented. The Lagrangian approach for this response property requires that only one, perturbation-independent, set of simultaneous equations needs to be solved. The presented formulation is demonstrated numerically on several well studied molecules at their equilibrium bond lengths and on the complete potential energy curves of the ground and first excited states of LiH. Numerical corroboration of the expected continuity for molecular properties for the GVVPT2 method is observed. It is seen that the GVVPT2 electric dipoles are in good agreement with experiment and with other high accuracy theoretical methods. (C) 2010 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2010.01.003}, author = {Theis, Daniel and Khait, Yuriy G. and Pal, Sourav and Hoffmann, Mark R.} } @article { ISI:000281321000006, title = {Probing lewis acidity and reactivity of Sn- and Ti-beta zeolite using industrially important moieties: a periodic density functional study}, journal = {Journal of Molecular Catalysis A-Chemical}, volume = {329}, number = {1-2}, year = {2010}, month = {AUG}, pages = {36-43}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

The Lewis acidic nature and reactivity of two industrially important catalysts, viz.. Sn and Ti substituted beta zeolite (T-BEA) are analyzed using a unique combination of structural parameters, energetics and reactivity descriptors. To achieve this purpose, we adsorb the industrially important moieties (L) namely NH(3), H(2)O, CH(3)OH, CH(3)CN on the active sites of T-BEA. The calculations were performed using a periodic density functional method where the valence electrons are described using a plane wave basis set in conjunction with pseudo-potentials for the core electrons. The analysis of the structural properties of these complexes reveals that TO(4) shows typical characteristic splitting 120 degrees/90 degrees, close to bipyramidal geometry as compared to tetrahedral symmetry observed in the bare T-BEA. This is associated with small variations in the framework bond lengths (\>= 0.08 angstrom) and a substantially large variation of bond angles (\<= 10 degrees) in all the ligand-zeolite complexes. Further in both cases of Sn and Ti substituted beta zeolite, ligand interacts at optimum inter-atomic bond distance. Our interaction energies show that adsorption of all ligand moieties is stronger at Sn center than that of Ti. In general, the order of stability of the different T-BEA adducts is NH(3) \> H(2)O \> CH(3)OH \> CH(3)CN. The ligand interaction is associated with the corresponding bond elongation and bond reduction of the adsorbed molecules on catalyst active site, which can be taken as measure of red or blue shifted frequencies. Finally, the global descriptors of reactivity justify the fact that soft acid, Sn-BEA, interacts strongly with soft bases following the Pearson{\textquoteright}s HSAB principle. However, hard acid, Ti-BEA interacts with soft bases to form a stable Lewis adduct. Furthermore, the HOMO-LUMO gap of all Sn-BEA-L adducts is lower than that of Ti-BEA-L adducts indicating to its higher Lewis acidic nature compared to Ti-BEA. (C) 2010 Elsevier B.V. All rights reserved.

}, keywords = {Beta zeolite, Lewis acidity, Ligand-zeolite complex, Periodic-DFT, Reactivity descriptors}, issn = {1381-1169}, doi = {10.1016/j.molcata.2010.06.014}, author = {Kulkarni, Bhakti S. and Krishnamurty, Sailaja and Pal, Sourav} } @proceedings {42678, title = {On some aspects of fock-space multi-reference coupled-cluster singles and doubles energies and optical properties}, volume = {11}, year = {2010}, month = {APR}, pages = {375-393}, publisher = {Springer}, address = {Netherlands}, author = {Manohar, Prashant Uday and Shamasundar, K. R. and Bag, Arijit and Vaval, Nayana and Pal, Sourav} } @article { ISI:000276341700068, title = {Understanding the reactivity properties of Au-n (6 <= n <= 13) clusters using density functional theory based reactivity descriptors}, journal = {Journal of Physical Chemistry C}, volume = {114}, number = {14}, year = {2010}, month = {APR}, pages = {6690-6703}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

{Relativistic density functional theory (DFT) based calculations have been performed on gold clusters with six to thirteen atoms (Au-n

}, issn = {1932-7447}, doi = {10.1021/jp1004852}, author = {De, Himadri Sekhar and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000295235200041, title = {Ab initio and periodic DFT investigation of hydrogen storage on light metal-decorated MOF-5}, journal = {International Journal of Hydrogen Energy}, volume = {36}, number = {17}, year = {2011}, month = {AUG}, pages = {10816-10827}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

The effect of light metal (M = Li, Be, Mg, and Al) decoration on the stability of metal organic framework MOF-5 and its hydrogen adsorption is investigated by ab initio and periodic density functional theory (DFT) calculations by employing models of the form BDC:M-2:nH(2) and MOF-5:M-2:nH(2), where BDC stands for the benzenedicarboxylate organic linker and MOF-5 represents the primitive unit cell. The suitability of the periodic DFT method employing the GGA-PBE functional is tested against MP2/6-311 + G* and MP2/cc-pVTZ molecular calculations. A correlation between the charge transfer and interaction energies is revealed. The metal-MOF-5 interactions are analyzed using the frontier molecular orbital approach. Difference charge density plots show that H-2 molecules get polarized due to the charge generated on the metal atom adsorbed over the BDC linker, resulting in electrostatic guest-host interactions. Our solid state results show that amongst the four metal atoms, Mg and Be decoration does not stabilize the MOF-5 to any significant extent. Li and Al decoration strengthened the H-2-MOE-5 interactions relative to the pure MOF-5 exhibited by the enhanced binding energies. The hydrogen binding energies for the Li- and Al-decorated MOF-5 were found to be sensible for allowing reversible hydrogen storage at ambient temperatures. A high hydrogen uptake of 4.3 wt.\% and 3.9 wt.\% is also predicted for the Li- and Al-decorated MOF-5, respectively. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

}, keywords = {ab initio calculations, Density functional theory, Hydrogen binding energies, Hydrogen storage, Metal-Pi-Arene interactions}, issn = {0360-3199}, doi = {10.1016/j.ijhydene.2011.05.165}, author = {Dixit, Mudit and Maark, Tuhina Adit and Pal, Sourav} } @article { ISI:000289315700010, title = {Effect of triples to dipole moments in fock-space multireference coupled cluster method}, journal = {Journal of Chemical Theory and Computation}, volume = {7}, number = {4}, year = {2011}, month = {APR}, pages = {876-883}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

In this paper, we present the new implementation of partial triples for the dipole moment of doublet radicals in Lagrangian formulation of Fock-space multireference coupled cluster (A-FSMRCC) response method. We have implemented a specific scheme of noniterative triples, in addition to singles and doubles schemes, which accounts for the effects appearing at least at the third order in dipole moments. The method is applied to the ground states of OH, OOH, HCOO, CN, CH, and PO radicals.

}, issn = {1549-9618}, doi = {10.1021/ct1007263}, author = {Ravichandran, Lalitha and Vaval, Nayana and Pal, Sourav} } @article { ISI:000294386000007, title = {Finite temperature behavior of gas phase neutral Au-n (3 <= n <= 10) clusters: a first principles investigation}, journal = {Journal of Physical Chemistry C}, volume = {115}, number = {35}, year = {2011}, month = {SEP}, pages = {17278-17285}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

{Relativistic density functional theory (DFT) based molecular dynamical simulations are performed on gold clusters with 3-10 atoms (Au-n

}, issn = {1932-7447}, doi = {10.1021/jp2023605}, author = {De, Himadri Sekhar and Krishnamurty, Sailaja and Mishra, Deepti and Pal, Sourav} } @article { ISI:000293192100022, title = {Size- and shape-sensitive reactivity behavior of Al-n(n=2-5, 13, 30, and 100) clusters toward the N-2 molecule: a first-principles investigation}, journal = {Journal of Physical Chemistry C}, volume = {115}, number = {30}, year = {2011}, month = {AUG}, pages = {14615-14623}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Reactivity of aluminum clusters has been found to exhibit size-sensitive variations. N-2 reduction is a hard process, and its dissociation on the Al surface is one of the few chemical methods available under nonhazardous conditions. In this context, we attempt to understand the adsorption behavior of N-2 molecules as a function of varying size and shape of Al clusters using a Density Functional Theory (DFT) based method. During the complex formation, various N-2 adsorption modes are examined. The results clearly demonstrate that, while the interaction energy does not vary with respect to the cluster size, shape of the cluster is highly contributive toward the chemisorption (a prerequisite for the reactivity) of the N-2 molecule. The underlying electronic and structural factors influencing the adsorption of N-2 molecules on the Al clusters are analyzed with the help of the Electron Localization Function (ELF) and Frontier Molecular Orbitals. As an illustration, the activation barrier calculations on various Al-13 conformations are calculated, and results confirm the experimental propositions that high-energy structures (depending upon their geometrical and electronic orientation) are more favorable for N-2 reduction.

}, issn = {1932-7447}, doi = {10.1021/jp203452a}, author = {Kulkarni, Bhakti S. and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000294340300007, title = {Understanding the molecular conformations of Na-dimyristoylphosphatidylglycerol (DMPG) using DFT-based method}, journal = {Molecular Simulation}, volume = {37}, number = {11}, year = {2011}, month = {AUG}, pages = {953-963}, publisher = {TAYLOR \& FRANCIS LTD}, address = {4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLAND}, abstract = {

The molecular conformations of phospholipids comprising a lipid bilayer determine the physico-chemical properties of the latter. In this study, we attempt to understand the various possible conformations available for an anionic lipid molecule dimyristoylphosphatidylglycerol (DMPG) with Na as its charge-compensating cation. The various possible molecular orientations available for lipid molecule are analysed using a density functional theory-based method. Our study reveals a rich conformational space with two different types of glycerol body orientations, more commonly known as rotamers. Interestingly, this is in agreement with the molecular conformations proposed earlier by NMR studies on lipid monomer solutions. We demonstrate that these conformations are an outcome of delicate balance of electrostatic and van der Waals forces along with intra-molecular hydrogen bonds achieved by a critical combination of torsion angles. Na(+) ions are seen to interact predominantly with the oxygen atoms of the glycerol groups in tail and head along with that of phosphate oxygen atoms leading to a cage-like orientation of lipid molecule around the Na(+). Following the conformational analysis, we attempt to evaluate the electronic properties of few low-lying conformations. This study shows that though the water molecules screen the Na-O(lipid) interactions, they do not dramatically modify the Na-O(lipid) bond distances. The lipid conformation retains the cage-like structure around the Na(+) in the presence of water molecules. Some amount of charge transfer from the water molecules to Na ion is noted. The water molecules modify the phosphate-tail glycerol group interactions leading to a more stable Na-DMPG-H(2)O and Na-DMPG-4H(2)O complexes.

}, keywords = {DFT, DMPG, molecular conformations, rotamer and hydration energy}, issn = {0892-7022}, doi = {10.1080/08927022.2011.582105}, author = {Mishra, Deepti and Pal, Sourav and Krishnamurty, Sailaja} } @article { ISI:000292022700003, title = {Validation and application of auxiliary density perturbation theory and non-iterative approximation to coupled-perturbed Kohn-Sham approach for calculation of dipole-quadrupole polarizability}, journal = {Chemical Physics Letters}, volume = {510}, number = {4-6}, year = {2011}, month = {JUL}, pages = {185-190}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Recently, two non-iterative approaches have been proposed to calculate response properties within density functional theory (DFT). These approaches are auxiliary density perturbation theory (ADPT) and the non-iterative approach to the coupled-perturbed Kohn-Sham (NIA-CPKS) method. Though both methods are non-iterative, they use different techniques to obtain the perturbed Kohn-Sham matrix. In this Letter, for the first time, both of these two independent methods have been used for the calculation of dipole-quadrupole polarizabilities. To validate these methods, three tetrahedral molecules viz., P-4; CH4 and adamantane (C10H16) have been used as examples. The comparison with MP2 and CCSD proves the reliability of the methodology. (C) 2011 Elsevier B. V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2011.05.032}, author = {Shedge, Sapana V. and Pal, Sourav and Koester, Andreas M.} } @article { ISI:000302296000032, title = {Behaviour of density functional theory for electric response properties at distorted geometries of molecules}, journal = {Theoretical Chemistry Accounts}, volume = {131}, number = {2}, year = {2012}, month = {FEB}, pages = {1094}, publisher = {SPRINGER}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

The role of exchange-correlation is well known for accurate calculations of electric response properties. The exchange-correlation functional in density functional theory (DFT) has been well studied for ground state equilibrium geometry. However, the behaviour of these functional in stretched geometries, where static correlation play an important role, has not been studied systematically, particularly for response electric properties. Thus, we present here the rigorous calculation of electric response properties at distorted geometries of the molecules. We have considered dipole polarizability and dipole-quadrupole polarizability for description of role of static and dynamic correlation for electric response properties. The calculations are performed with our new approach, noniterative approximation to coupled-perturbed Kohn-Sham method. These DFT results are compared with higher level ab initio such as coupled perturbed singles and doubles and fully correlated full CI. We have studied single, double and triple-bonded systems at different inter-nuclear separation. We report here the dipole polarizability and dipole-quadrupole polarizability of HF, BH, H2CO, CO and NO+. We also present the effect of basis and functional on polarizability and dipole-quadrupole polarizability.

}, keywords = {DFT, Dipole-dipole polarizability, Dipole-quadrupole polarizability, Distorted geometry, NIA-CPKS}, issn = {1432-881X}, doi = {10.1007/s00214-012-1094-1}, author = {Shedge, Sapana V. and Joshi, Sayali P. and Pal, Sourav} } @article { ISI:000310215400007, title = {Conformational modulation of Ant-Pro oligomers using chirality alteration of proline residues}, journal = {Organic \& Biomolecular Chemistry}, volume = {10}, number = {42}, year = {2012}, month = {SEP}, pages = {8426-8433}, publisher = {ROYAL SOC CHEMISTRY}, type = {Article}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Structural modulation of Ant-Pro (anthranilic acid-proline) oligomers has been carried out by chirality alteration of the proline residues. The results suggest that the chirality altered oligomers show well-defined helical conformation featuring nine-membered hydrogen bonding interactions - without compromising conformational rigidity.

}, issn = {1477-0520}, doi = {10.1039/c2ob26132d}, author = {Kale, Sangram S. and Kotmale, Amol S. and Dutta, Achintya Kumar and Pal, Sourav and Rajamohanan, P. R. and Sanjayan, Gangadhar J.} } @article { ISI:000304915100006, title = {Constrained variational approach for energy derivatives in Intermediate hamiltonian fock-space coupled-cluster theory}, journal = {Chemical Physics}, volume = {401}, year = {2012}, month = {JUN}, pages = {45-49}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Fock-space multi-reference coupled cluster theory is an efficient method for electronic structure of nearly degenerate cases. However, it suffers from the intruder state problem for large model space. The intermediate Hamiltonian formulation eliminates intruder state problem and helps in the convergence of equations. In this paper we have implemented intermediate Hamiltonian approach in Fock-space coupled cluster method for the response properties. We test our method for the dipole moments of doublet radicals. We report dipole moments of CN, SF and NS radicals. (C) 2011 Elsevier B. V. All rights reserved.

}, keywords = {Constrained variational approach, Fock-space multi-reference coupled cluster, Intermediate Hamiltonian theory, Response approach}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2011.10.018}, author = {Ghosh, Aryya and Gupta, Jitendra and Pal, Sourav and Vaval, Nayana} } @inbook { ISI:000321629100005, title = {Descriptors as probes for inter-molecular interactions and external perturbation}, booktitle = {Applications of Density Functional Theory to Chemical Reactivity}, series = {Structure and Bonding}, volume = {149}, year = {2012}, pages = {131-158}, publisher = {Springer}, organization = {Springer}, address = {233 Spring Street, New York, NY 10013, United States}, abstract = {

In this article, different reactivity descriptors have been reviewed. Conceptual density functional theory is an important area where a lot of interesting developments in terms of descriptors and molecule interactions have taken place in recent years. This review will highlight our own work on such development of descriptors and their applications to characterise stability and reactivity in molecule systems.

}, keywords = {Conceptual density functional theory, Electric field effect, Global reactivity descriptors, HSAB, Local HSAB, Local reactivity descriptors}, isbn = {978-3-642-32753-7; 978-3-642-32752-0}, issn = {0081-5993}, doi = {10.1007/978-3-642-32753-7_4}, author = {Pal, Sourav}, editor = {Putz, M. V. and Mingos, D. M. P.} } @article { ISI:000306066600010, title = {Equation-of-motion coupled-cluster method for the study of shape resonance}, journal = {Journal of Chemical Physics}, volume = {136}, number = {23}, year = {2012}, month = {JUN}, pages = {234110}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

The equation-of-motion coupled-cluster method (EOM-CC) is applied for the first time to calculate the energy and width of a shape resonance in an electron-molecule scattering. The procedure is based on inclusion of complex absorbing potential with EOM-CC theory. We have applied this method to investigate the shape resonance in e(-)N(2), e(-)CO, and e(-)C(2)H(2). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729464]

}, issn = {0021-9606}, doi = {10.1063/1.4729464}, author = {Ghosh, Aryya and Vaval, Nayana and Pal, Sourav} } @article { ISI:000306111900003, title = {Extended coupled cluster for Raman and infrared spectra of small molecules}, journal = {Chemical Physics}, volume = {403}, year = {2012}, month = {JUL}, pages = {25-32}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

In this paper we study the harmonic vibrational frequencies, infrared (IR) intensities, Raman intensities and depolarization ratio using extended coupled cluster method. Raman and IR intensities are mixed derivatives of energy with respect to the electric field and geometric perturbation whereas vibrational frequencies are derivatives of energy with respect to geometry. We use semi-numerical approach to obtain these derivatives. We have studied the effect of electron correlation and basis set for the above properties. We compare our results with non-variational coupled cluster and experimental values, wherever available. We have studied HF, BH, CH+, CO and H2CO molecules in different basis sets. For HF molecule, benchmarking is done with full CI values and basis set convergence is studied for this molecule. Effect of triples is studied for all the molecules. (C) 2012 Elsevier B.V. All rights reserved.

}, keywords = {Extended coupled cluster, IR and Raman spectroscopy, Mixed derivatives}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2012.04.017}, author = {Joshi, Sayali P. and Dutta, Achintya Kumar and Pal, Sourav and Vaval, Nayana} } @article { ISI:000311350000015, title = {First principle investigation on the thermal stability of a golden fullerene: a case study of Au-32}, journal = {Catalysis Today}, volume = {198}, number = {1, SI}, year = {2012}, month = {DEC}, pages = {106-109}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Structural and electronic properties of Au-32 cluster are analyzed using relativistic density functional theory (DFT) based methods. Further, DFT based molecular dynamical (MD) simulations are performed on Au-32 golden fullerene with an aim of understanding its thermal stability at various working temperatures. Various conformations being populated at different temperatures of a cluster are analyzed. The study shows that the ground state icosahedral conformation is stable only up to 300 K and structure remains in a hollow conformation only up to 400 K. This clearly explains the reasons for failure by experimentalists in trapping the unique fullerene conformation in spite of the theoretical predictions of it being a very stable one. The above MD study also indicates that the bare fullerene Au-32 cluster (without any stabilizing ligands) can be used for potential catalytic applications only around room temperatures. (C) 2012 Elsevier B. V. All rights reserved.

}, keywords = {Au-32 cluster, Born-Oppenheimer molecular dynamics, Density functional theory, Golden fullerenes, Relativistic effects}, issn = {0920-5861}, doi = {10.1016/j.cattod.2012.04.072}, author = {De, Himadri Sekhar and Krishnamurty, Sailaja and Pal, Sourav} } @article {42666, title = {Fock-space multi-reference coupled-cluster response with the effect of triples on dipole moment of ClO and SF radicals}, journal = {Journal of Chemical Sciences}, volume = {124}, year = {2012}, month = {JAN}, pages = {223-232}, doi = {10.1007/s12039-012-0220-x}, author = {Ravichandran, Lalitha and Bhattacharya, Debarati and Vaval, Nayana and Pal, Sourav} } @article { ISI:000307300900016, title = {Helical folding in heterogeneous foldamers without inter-residual backbone hydrogen-bonding}, journal = {Chemical Communications}, volume = {48}, number = {71}, year = {2012}, month = {JUL}, pages = {8922-8924}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

This communication describes a set of hybrid foldamers that do not feature inter-residual, but intra-residual backbone hydrogen-bonding, yet adopt a preferentially folded conformation displaying right-handed helical architecture. Conformational ordering is apparently due to the combined conformational restrictions imposed by the conformationally restricted individual amino acid residues with which the oligomers are made of.

}, issn = {1359-7345}, doi = {10.1039/c2cc33235c}, author = {Priya, Gowri and Kotmale, Amol S. and Gawade, Rupesh L. and Mishra, Deepti and Pal, Sourav and Puranik, Vedavati G. and Rajamohanan, Pattuparambil R. and Sanjayan, Gangadhar J.} } @article { ISI:000305092400004, title = {NOx catalyzed pathway of stratospheric ozone depletion: a coupled cluster investigation}, journal = {Journal of Chemical Theory and Computation}, volume = {8}, number = {6}, year = {2012}, month = {MAY}, pages = {1895-1901}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We report a theoretical investigation on the NOx catalyzed pathways of stratospheric ozone depletion using highly accurate coupled cluster methods. These catalytic reactions represent a great challenge to state-of-the-art ab initio methods, while their mechanisms remain unclear to both experimentalists and theoreticians. In this work, we have used the so-called {\textquoteleft}{\textquoteleft}gold standard of quantum chemistry,{\textquoteright}{\textquoteright} the CCSD(T) method, to identify the saddle points on NOx-based reaction pathways of ozone hole formation. Energies of the saddle points are calculated using the multireference variants of coupled cluster methods. The calculated activation energies and rate constants show good agreement with available experimental results. Tropospheric precursors to stratospheric NOx radicals have been identified, and their potential importance in stratospheric chemistry has been discussed. Our calculations resolve previous conflicts between ab initio and experimental results for a trans nitro peroxide intermediate, in the NOx catalyzed pathway of ozone depletion.

}, issn = {1549-9618}, doi = {10.1021/ct300209s}, author = {Dutta, Achintya Kumar and Vaval, Nayana and Pal, Sourav} } @article { ISI:000307748700004, title = {Scandium-decorated MOF-5 as potential candidates for room-temperature hydrogen storage: a solution for the clustering problem in MOFs}, journal = {Journal of Physical Chemistry C}, volume = {116}, number = {33}, year = {2012}, month = {AUG}, pages = {17336-17342}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Transition-metal-based systems show promising binding energy for hydrogen storage but suffer from clustering problem. The effect of light transition metal (M = Sc, Ti) decoration, boron substitution on the hydrogen storage properties of MOF-5, and clustering problem of metals has been investigated using ab initio density, functional theory. Our results of solid-tate calculations reveal that whereas Ti clusters strongly Sc atoms do not suffer from this problem when decorating MOF-5. Boron substitution on metal-decorated MOF-5 enhances the interaction energy of both the metals with MOF-5. Sc-decorated MOF-5 shows a hydrogen storage capacity of 5.81 wt \% with calculated binding energies of 20-40 kJ/mol, which ensures the room-teniperature applicability of this hydrogen storage material.

}, issn = {1932-7447}, doi = {10.1021/jp302852h}, author = {Dixit, Mudit and Maark, Tuhina Adit and Ghatak, Kamalika and Ahuja, Rajiv and Pal, Sourav} } @article { ISI:000310567800027, title = {Theoretical study of frequency and temperature dependence of dipole-quadrupole polarizability of P-4 and adamantane}, journal = {Chemical Physics Letters}, volume = {552}, year = {2012}, month = {NOV}, pages = {146-150}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

The frequency and temperature dependence of dipole-quadrupole polarizability of tetrahedral P-4 and adamantane molecules have been studied using first-principle all-electron density functional theory calculation. The recently developed time-dependent auxiliary density functional theory is extended for the calculation of dynamic dipole-quadrupole polarizabilities. Temperature effects are incorporated by Born-Oppenheimer molecular dynamics (BOMD) simulations recorded up to 100 ps. The dynamic dipole-quadrupole polarizabilities are calculated along these trajectories. The frequency and temperature effects can be significant for the accurate calculation of dipole-quadrupole polarizability. We have also identified the main reason for the observed discrepancy between experiment and theory in the case of adamantane. (c) 2012 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2012.09.045}, author = {Shedge, Sapana V. and Pal, Sourav and Koester, Andreas M.} } @article { ISI:000309100600009, title = {Vibrational multi-reference coupled cluster theory in bosonic representation}, journal = {Journal of Chemical Physics}, volume = {137}, number = {11}, year = {2012}, month = {SEP}, pages = {114108}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

The vibrational multi-reference coupled cluster method is developed to calculate the vibrational excitation energies of polyatomic molecules. The method is implemented on ozone and formaldehyde molecules and the results are compared with full vibrational configuration interaction (FVCI) method. A good agreement is found between the vibrational multi-reference coupled cluster method and converged FVCI method for lower lying vibrational states. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4753422]

}, issn = {0021-9606}, doi = {10.1063/1.4753422}, author = {Banik, Subrata and Pal, Sourav and Prasad, M. Durga} } @article { ISI:000325400600023, title = {CAP/EOM-CCSD method for the study of potential curves of resonant states}, journal = {Physical Chemistry Chemical Physics}, volume = {15}, number = {41}, year = {2013}, month = {SEP}, pages = {17915-17921}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The equation-of-motion coupled-cluster (EOM-CC) method along with the complex absorbing potential (CAP) is used for the study of resonance in e(-)-N-2 and e(-)-CO. Resonance position and width are studied as a function of bond length. We report the potential curves (PC) of the resonance states.

}, issn = {1463-9076}, doi = {10.1039/c3cp52552j}, author = {Ghosh, Aryya and Karne, Anagha S. and Pal, Sourav and Vaval, Nayana} } @article { ISI:000315874200009, title = {Electronic transition dipole moments and dipole oscillator strengths within fock-space multi-reference coupled cluster framework: an efficient and novel approach}, journal = {Journal of Chemical Physics}, volume = {138}, number = {9}, year = {2013}, month = {MAR}, pages = {094108}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

Within the Fock-space multi-reference coupled cluster framework, we have evaluated the electronic transition dipole moments, which determine absorption intensities. These depend on matrix elements between two different wave functions (e. g., ground state to the excited state). We present two different ways, to calculate these transition moments. In the first method, we construct the ground and excited state wave functions with the normal exponential ansatz of Fock-space coupled cluster method and then calculate the relevant off-diagonal matrix elements. In the second approach, we linearize the exponential form of the wave operator which will generate the left vector, by use of Lagrangian formulation. The right vector is obtained from the exponential ansatz. In order to relate the transition moments to oscillator strengths, excitation energies need to be evaluated. The excitation energies are obtained from the Fock-space multi-reference framework. The transition dipole moments of the ground to a few excited states, together with the oscillator strengths of a few molecules, are presented. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793277]

}, issn = {0021-9606}, doi = {10.1063/1.4793277}, author = {Bhattacharya, Debarati and Vaval, Nayana and Pal, Sourav} } @article { ISI:000319006300007, title = {Extended coupled cluster through nth perturbation order for molecular response properties: a comparative study}, journal = {Chemical Physics}, volume = {417}, year = {2013}, month = {MAY}, pages = {45-51}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

In this paper, we have presented and analyzed the extended coupled cluster (ECC) energy functional, truncated up to nth perturbation order in which expansion is limit to operators of the single and double excitations. The expression for the first order energy derivatives based on the above truncation schemes has been derived and numerically analyzed. We have done a comparative study for dipole moment in various perturbative ECC (n) methods (2 \<= n \<= 5) for three systems (HF, H2O and BH) at equilibrium geometry. We have particularly studied two variants of ECC (4) and ECC (5*) method for stretched geometry. We have analyzed the contribution of important terms present in ECC functional based on perturbative argument. We have compared our results with standard coupled cluster (CCSD) as well as cubic truncated ECC and also benchmarked with the full CI results wherever available. (c) 2013 Elsevier B.V. All rights reserved.

}, keywords = {Dipole moment, Energy functional, Extended coupled cluster}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2013.03.012}, author = {Gupta, Jitendra and Manohar, Prashant Uday and Ghosh, Aryya and Vaval, Nayana and Pal, Sourav} } @article { ISI:000318538100003, title = {Fock space multireference coupled cluster theory: study of shape resonance}, journal = {International Journal of Quantum Chemistry}, volume = {113}, number = {12}, year = {2013}, month = {JUN}, pages = {1690-1695}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

The complex absorbing potential along with correlated independent particle potential (CIP) Fock space multireference coupled cluster method is used for the study of resonances. We have studied shape resonance of e(-) - F-2, e(-) - N2O and e(-) -CO molecules. In particular, we have studied e(-) - F-2 scattering at different bond lengths to know whether F-2(-) is bound at the equilibrium bond length of F-2. (C) 2013 Wiley Periodicals, Inc.

}, keywords = {correlated independent particle potential, Fock-space multireference coupled cluster theory, shape resonance}, issn = {0020-7608}, doi = {10.1002/qua.24387}, author = {Bhattacharya, Sumantra and Vaval, Nayana and Pal, Sourav} } @article { ISI:000323132100073, title = {Highly concise and practical route to clavaminols, sphinganine and (+)-spisulosine via indium mediated allylation of alpha-hydrazino aldehyde and a theoretical insight into the stereochemical aspects of the reaction}, journal = {RSC Advances}, volume = {3}, number = {35}, year = {2013}, month = {JUL}, pages = {15442-15448}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

A conceptually different approach has been employed for the synthesis of 1,2-amino alcohols by proline-catalyzed alpha-amination of aldehyde and one-pot indium mediated allylation of the crude alpha-hydrazino aldehydes. DFT based quantum chemical calculations have been performed to obtain a quantitative explanation of the stereoselectivity of the reaction.

}, issn = {2046-2069}, doi = {10.1039/c3ra43048k}, author = {Pandey, Menaka and Chowdhury, Partha Sarathi and Dutta, Achintya Kumar and Kumar, Pradeep and Pal, Sourav} } @article { ISI:000326366800071, title = {Influence of charge and ligand on the finite temperature behavior of gold clusters: a BOMD study on Au-6 cluster}, journal = {Journal of Physical Chemistry C}, volume = {117}, number = {40}, year = {2013}, month = {OCT}, pages = {20982-20990}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Conformation and electronic charge on a gold cluster are known to determine its catalytic property. However, little is known on the finite temperature behavior of various gold cluster conformations. Much less is known on the role of charge or a ligand in stabilizing a conformation at finite temperatures. In this work, we have carried out relativistic density functional theory (DFT) based molecular dynamical simulations on neutral and charged Au-6 clusters with an aim of understanding the stability of ground state conformations as a function of charge on the cluster. Our simulations reveal that cationic and anionic Au-6 clusters undergo conformational transitions at 500 K where as neutral Au-6 cluster retains its ground state conformation up to a temperature of 1100 K. In order to look into the factors leading to the stabilization of neutral Au-6 cluster (or destabilization of cationic and anionic Au-6 clusters), structural and electronic properties are analyzed. Factors such as charge redistribution within the atoms and composition of molecular orbitals are seen to contribute towards stronger Au-Au bonds in Au-6(0) thereby stabilizing it considerably. Following the analysis, simulations are also extended to neutral, cationic, and anionic Au-6-COn (n = 1,2) complexes. In the case of CO chemisorbed Au-6 clusters, neutral and negatively charged ground state conformations are stable up to nearly 800 K, while the positively charged Au-6 ground state conformation collapses at room temperature. This work, in short demonstrates how charge or even a ligand can be used to moderate the physical properties of a gold cluster.

}, issn = {1932-7447}, doi = {10.1021/jp407081m}, author = {Manzoor, Dar and Pal, Sourav and Krishnamurty, Sailaja} } @article {42654, title = {Interatomic coulombic decay in (HF)n,(n=2-3) clusters using CAP/EOM-CCSD method}, journal = {Molecular Physics}, volume = {112}, year = {2013}, month = {NOV}, pages = {669-673}, type = {Article}, abstract = {

The equation-of-motion coupled-cluster method along with the complex absorbing potential has been applied to study the interatomic Coulombic decay mechanism in hydrogen-bonded clusters. We have applied this method to calculate the lifetime of the F 2s inner-valence ionised state of (HF)(n) (n = 2-3) clusters. The lifetime is found to be very short and decreases substantially with increasing the number of HF monomer.

}, keywords = {complex absorbing potential (CAP), equation-of-motion coupled-cluster (EOM-CC), HF clusters, interatomic Coulombic decay (ICD)}, issn = {0026-8976}, doi = {10.1080/00268976.2013.852263}, author = {Ghosh, Aryya and Pal, Sourav and Vaval, Nayana} } @article { ISI:000323509900012, title = {Lagrange multiplier approach for excited state properties through intermediate hamiltonian formulation of fock space multireference coupled-cluster theory}, journal = {Journal of Chemical Physics}, volume = {139}, number = {7}, year = {2013}, month = {AUG}, pages = {074108}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

In this paper, we present a formulation based on Lagrange multiplier approach for efficient evaluation of excited state energy derivatives in Fock space coupled cluster theory within the intermediate Hamiltonian framework. The formulation is applied to derive the explicit generic expressions up to second order energy derivatives for [1, 1] sector of Fock space with singles and doubles approximation. Its advantage, efficiency, and interconnection in comparison to the Lagrange multiplier approach in traditional formulation of Fock space, which is built on the concept of Bloch equation based effective Hamiltonian, has been discussed. Computational strategy for their implementation has also been discussed in some detail. (C) 2013 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4817943}, author = {Gupta, Jitendra and Vaval, Nayana and Pal, Sourav} } @article { ISI:000326355100005, title = {Performance of the EOMIP-CCSD(2) method for determining the structure and properties of doublet radicals: a benchmark investigation}, journal = {Journal of Chemical Theory and Computation}, volume = {9}, number = {10}, year = {2013}, month = {OCT}, pages = {4313-4331}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We present a benchmark study on the performance of the EOMIP-CCSD(2) method for computation of structure and properties of doublet radicals. The EOMIP-CCSD(2) method is a second-order approximation to the standard EOMIP-CCSD method. By retaining the black box nature of the standard EOMIP-CCSD method and adding favorable N-5 scaling, the EOMIP-CCSD(2) method can become the method of choice for predicting the structure and spectroscopic properties of large doublet radicals. The EOMIP-CCSD(2) method overcomes the typical problems associated with the standard single reference ab initio treatment of doublet radicals. We compare our results for geometries and harmonic vibrational frequencies with those obtained using the standard EOMIP-CCSD method, as well as unrestricted Hartree-Fock (UHF)- and restricted open-shell Hartree-Fock (ROHF)-based single-reference coupled-cluster and second order many-body perturbation theory (MBPT(2)) methods. The effect of the basis set on the quality of the results has been studied using a hierarchy of Dunning{\textquoteright}s correlation-consistent aug-cc-pVXZ (X = D, T, Q) basis sets. Numerical results show that the EOMIP-CCSD(2) method, despite its N-5 scaling, gives better agreement with experimental results, compared to the UHF- and ROHF-based MBPT(2), as well as the single-reference coupled-cluster methods.

}, issn = {1549-9618}, doi = {10.1021/ct400316m}, author = {Dutta, Achintya Kumar and Vaval, Nayana and Pal, Sourav} } @article { ISI:000325392000050, title = {Perturbative approximations to single and double spin flip equation of motion coupled cluster singles doubles methods}, journal = {Journal of Chemical Physics}, volume = {139}, number = {12}, year = {2013}, month = {SEP}, pages = {124116}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

Spin flip equation of motion coupled cluster (EOM-SF-CC) can correctly treat situations involving electronic degeneracies or near degeneracies, e. g., bond breaking, di- and tri-radicals, etc. However, for large systems EOM-SF-CC (even in single and double excitations) is computationally prohibitively expensive. Therefore, earlier approximations to EOM-SF-CC methods such as spin flip configuration interaction singles with perturbative doubles (SF-CIS(D)) have been proposed. In this work, we present a new perturbative approximation to EOM-SF-CC, which has been found to be more accurate than SF-CIS(D). The capabilities, advantages, and timings of the new approach have been demonstrated considering the singlet-triplet gaps in di- and triradicals as well as bond breaking examples. The method is extended to double spin flip EOM-CC and its capabilities have been tested. (C) 2013 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4821936}, author = {Dutta, Achintya Kumar and Pal, Sourav and Ghosh, Debashree} } @article { ISI:000313012200051, title = {Polarizability of few electron quantum dots: extended coupled-cluster response approach}, journal = {Chemical Physics Letters}, volume = {555}, year = {2013}, month = {JAN}, pages = {263-267}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

The dipole polarizability is studied for few electron quantum dots using extended coupled cluster linear response method (ECCLR). The polarizability of pure parabolic quantum dots depends only on the number of electrons and the parabolic confinement strength. We added impurity in a GAUSSIAN form to the external parabolic potential and used ECCLR to calculate polarizability. To examine the effect of external potential, we changed the parabolic confinement to square-well and repeated all calculations. We mainly looked at eigenvalue spectrum and charge density specially when the system shifts towards lower density regions. (C) 2012 Elsevier B. V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2012.10.071}, author = {Heidari, Ideh and Vaval, Nayana and Pal, Sourav and Kanhere, Dilip G.} } @article { ISI:000326296800033, title = {Role of substituents on the reactivity and electron density profile of diimine ligands: a density functional theory based study}, journal = {Journal of Chemical Sciences}, volume = {125}, number = {5}, year = {2013}, month = {SEP}, pages = {1247-1258}, publisher = {INDIAN ACAD SCIENCES}, address = {C V RAMAN AVENUE, SADASHIVANAGAR, P B \#8005, BANGALORE 560 080, INDIA}, abstract = {

In this paper, we study the reactivity of diimines like 2, 2({\textquoteright})-bipyridine, 1, l0-phenanthroline and 1, 2, 4-triazines using density-based reactivity descriptors. We discuss the enhancement or diminution in the reactivity of these ligands as a function of two substituent groups, namely methyl (-CH3) group and phenyl (-C6H5) group. The global reactivity descriptors explain the global affinity and philicity of these ligands, whereas the local softness depicts the particular site selectivity. The inter-molecular reactivity trends for the same systems are analysed through the philicity and group philicity indices. The sigma-donor character of these ligands is quantified with the help of electron density profile. In addition, the possible strength of interaction of these ligands with metal ions is supported with actual reaction energies of Ru-L complexes.

}, keywords = {2, 2 {\textquoteleft}-bipyridine, DFT, diimine, Reactivity descriptors, Ru-ligand interaction, substituent effects}, issn = {0974-3626}, doi = {10.1007/s12039-013-0469-8}, author = {Kulkarni, Bhakti S. and Mishra, Deepti and Pal, Sourav} } @article { ISI:000323177900012, title = {Study of interatomic coulombic decay of Ne(H2O)(n) (n=1,3) clusters using equation-of-motion coupled-cluster method}, journal = {Journal of Chemical Physics}, volume = {139}, number = {6}, year = {2013}, month = {AUG}, pages = {Article No. 064112}, publisher = {AMER INST PHYSICS}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

Interatomic Coulombic decay (ICD) is an efficient and ultrafast radiationless decay mechanism which can be initiated by removal of an electron from the inner-valence shell of an atom or molecule. Generally, the ICD mechanism is prevailed in weakly bound clusters. A very promising approach, known as CAP/EOM-CC, consists of the combination of complex absorbing potential (CAP) with the equation-of-motion coupled-cluster (EOM-CC) method, is applied for the first time to study the nature of the ICD mechanism. We have applied this technique to determine the lifetime of an auto-ionized, inner-valence excited state of the NeH2O, Ne(H2O)(2), and Ne(H2O)(3) systems. The lifetime is found to be very short and decreases significantly with the number of neighboring water molecules. (C) 2013 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4817966}, author = {Ghosh, Aryya and Pal, Sourav and Vaval, Nayana} } @article { ISI:000325389000001, title = {Understanding the orientation of water molecules around the phosphate and attached functional groups in a phospholipid molecule: a DFT-based study}, journal = {Molecular Simulation}, volume = {39}, number = {12}, year = {2013}, month = {OCT}, pages = {937-955}, publisher = {TAYLOR \& FRANCIS LTD}, address = {4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLAND}, abstract = {

The adsorption of water molecules around a polar region (in particular around the phosphate moiety) in the phospholipid molecules is studied in this work. Phospholipid molecules with different functional groups are known to respond differently to the water molecules. Hence, we attempt to study the adsorption of water molecules around the phosphate group as a consequence of the change of functional group attached to the phosphate group, viz. phosphatidyl ethanolamine (PE), phosphatidyl choline (PC) and phosphatidyl glycerol (PG). As the latter is anionic in nature, the charge is compensated by Na+ counterion. Up to seven water molecules are adsorbed around the phosphate groups in model systems mimicking phospholipid molecule. The corresponding changes in the structural and electronic aspects are analysed. The significant difference between the PE and PC model systems is the formation of clathrate-like structure in the latter. Itisnoticed that as the number of water molecules increases to seven, both the hydrogen atoms in the water molecule participate in hydrogen bonding. However, in the PG model system, the charge-compensating counterion prevents the water molecule to form clathrate-like structures. The adsorption sites for water molecules are validated by density functional theory-based reactivity descriptors, viz. Fukui functions in the PE model system.

}, keywords = {cHelpG, DMPC, DMPE, DMPG, Fukui functions, Hydration}, issn = {0892-7022}, doi = {10.1080/08927022.2013.783701}, author = {Mishra, Deepti and Das, Susanta and Krishnamurthy, Sailaja and Pal, Sourav} } @article { ISI:000330145400022, title = {Understanding the site selectivity in small-sized neutral and charged AI(n) (4 <= n <= 7) clusters using density functional theory based reactivity descriptors: a validation study on water molecule adsorption}, journal = {Journal of Physical Chemistry A}, volume = {117}, number = {36, SI}, year = {2013}, month = {SEP}, pages = {8691-8702}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Aluminum clusters are now technologically important due to their high catalytic activity. Our present study on the small-sized aluminum clusters applies density functional theory (DFT)-based reactivity descriptors to identify potential sites for adsorption and eventual chemical reaction. Depending on symmetry, susceptibility of various type of reactive sites within a cluster toward an impending electrophilic and/or nucleophilic attack is predicted using the reactivity descriptors. In addition, the study devises general rules as to how the size, shape, and charge of the cluster influences the number of available sites for an electrophilic and/or nucleophilic attack. The predictions by reactivity descriptors are validated by performing an explicit adsorption of water molecule on Al clusters with four atoms. The adsorption studies demonstrate that the most stable water-luster complex is obtained when the molecule is adsorbed through an oxygen atom on the site with the highest relative electrophilicity.

}, issn = {1089-5639}, doi = {10.1021/jp403109s}, author = {Das, Susanta and Pal, Sourav and Krishnamurty, Sailaja} } @article { ISI:000338486300020, title = {1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU): a highly efficient catalyst in glycerol carbonate synthesis}, journal = {Journal of Molecular Catalysis A-Chemical}, volume = {391}, year = {2014}, month = {SEP}, pages = {144-149}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Transesterification of dimethyl carbonate (DMC) with glycerol (GLY) was investigated using various amines as catalysts. Amidines like 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) were found to be the best catalysts for this reaction. Best results: 98\% conversion of GLY with 96\% selectivity to GC (TON: 9408), were obtained with DBU as a catalyst. Effect of various reaction conditions on activity and selectivity were investigated using DBU as catalyst. The mechanism of the reaction was investigated with the help of H-1, C-13 and N-15 NMR analysis and OFT calculations. (C) 2014 Elsevier B.V. All rights reserved.

}, keywords = {DBU, Glycerol, Glycerol carbonate, transesterification}, issn = {1381-1169}, doi = {10.1016/j.molcata.2014.04.016}, author = {Munshi, Mudassir K. and Gade, Swapna M. and Mane, Manoj V. and Mishra, Deepti and Pal, Sourav and Vanka, Kumar and Rane, Vilas H. and Kelkar, Ashutosh A.} } @conference { ISI:000349165104705, title = {Complex absorbing potential based coupled-cluster methods to metastable states}, booktitle = { 248th National Meeting of the American-Chemical-Society (ACS)}, volume = {248}, year = {2014}, note = {248th National Meeting of the American-Chemical-Society (ACS), San Francisco, CA, AUG 10-14, 2014}, month = {AUG}, pages = {Meeting Abstract: 504-COMP}, publisher = {American Chemical Society}, organization = {American Chemical Society}, type = {Meeting Abstract}, address = {1155 16th ST, NW, Washington, DC 20036 USA}, issn = {0065-7727}, author = {Pal, Sourav} } @article { ISI:000344589700016, title = {Complex absorbing potential based equation-of-motion coupled cluster method for the potential energy curve of CO2- anion}, journal = {Journal of Chemical Physics}, volume = {141}, number = {16}, year = {2014}, month = {OCT}, pages = {Article No. 164113}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {

The equation-of-motion coupled cluster method employing the complex absorbing potential has been used to investigate the low energy electron scattering by CO2. We have studied the potential energy curve for the (2)Pi(u) resonance states of CO2- upon bending as well as symmetric and asymmetric stretching of the molecule. Specifically, we have stretched the C-O bond length from 1.1 angstrom to 1.5 angstrom and the bending angles are changed between 180 degrees and 132 degrees. Upon bending, the low energy (2)Pi(u) resonance state is split into two components, i.e., (2)A(1), B-2(1) due to the Renner-Teller effect, which behave differently as the molecule is bent. (c) 2014 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4899280}, author = {Ghosh, Aryya and Vaval, Nayana and Pal, Sourav and Bartlett, Rodney J.} } @article { ISI:000349902200001, title = {Computational investigation on the catalytic activity of Rh-6 and Rh4Ru2 clusters towards methanol activation}, journal = {Theoretical Chemistry Accounts }, volume = {134}, number = {1}, year = {2014}, month = {DEC}, pages = {1597}, publisher = {SPRINGER}, type = {Article}, address = {233 SPRING ST, NEW YORK, NY 10013 USA}, abstract = {

Catalysis of molecular activation of small molecules through scission of strong chemical bonds is one of the major challenges faced by chemists. More specifically, activation of the strong C-H and O-H bonds of various alcohols, especially methanol, is one of the various important intermediate steps of key organic reactions. Our present work explores a suitable metal cluster catalyst towards methanol dissociation. In particular, we have examined the effect of ruthenium doping (Rh:Ru = 2:1) on the catalytic activity of Rh-6 cluster towards methanol dissociation. Density functional theory-based calculations illustrate two competitive pathways for methanol dissociation, which are via O-H and C-H bond breaking. Both the pathways are found to be energetically favourable in the presence of bimetallic and mono-metallic clusters. Importantly, energy barrier for O-H bond dissociation reduces considerably in doped cluster as compared to pure Rh-6 cluster and is smaller than the values reported for a number of other small metallic clusters.

}, keywords = {Bimetallic Clusters, Density Functional Theory (DFT), Doping, Methanol Activation, Rhodium Clusters}, issn = {1432-881X}, doi = {10.1007/s00214-014-1597-z}, author = {Ghatak, Kamalika and Sengupta, Turbasu and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000341122200039, title = {Dinitrogen activation by silicon and phosphorus doped aluminum clusters}, journal = {Journal of Physical Chemistry C}, volume = {118}, number = {34}, year = {2014}, month = {AUG}, pages = {19869-19878}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

N-2 reduction is crucial for life, and very few catalysts are currently available to carry out this process at ambient temperature and pressure. In the present work, density functional theory based calculations reveal doped aluminum clusters to be highly reactive toward molecular nitrogen and hence are prospective materials for its activation at low temperatures. Calculations on silicon and phosphorus doped aluminum clusters with 5-8 atoms demonstrate an enhanced N-2 activation with respect to their pristine ground state and high energy counterparts. This increased efficiency of N-2 activation by doped ground state Al clusters is corroborated by an increment of the N N bond length, a red shift in N N bond stretching frequency, and adsorption energy (E-ad). Ab initio molecular-dynamics simulations demonstrate consequential efficiency of doped clusters toward dinitrogen activation at finite temperature. The ability of doped clusters toward activation of molecular nitrogen is site and shape sensitive. In short, this theoretical study highlights the critical role of doping foreign impurities for future endeavors in the design of cost-effective and efficient catalysts for N-2 activation at ambient temperatures. This observation may spur further studies in the field of aluminum nanocatalysis by doping silicon and phosphorus atom in aluminum clusters.

}, issn = {1932-7447}, doi = {10.1021/jp505700a}, author = {Das, Susanta and Pal, Sourav and Krishnamurty, Sailaja} } @article {46365, title = {Effect of silicon doping on the reactivity and catalytic activity of gold clusters}, journal = {Journal of Physical Chemistry C}, volume = {118}, year = {2014}, month = {APR }, pages = {7501-7507}, type = {Article}, abstract = {

Doping is known to be an excellent and simple way of catalyst design. Although notable progress has been made in understanding the reactivity and catalytic activity of gas-phase and supported gold clusters, very few studies have been carried out on the doped gold clusters. In the present work, we have carried out density functional theory calculations to investigate the effect of silicon doping on the reactivity and catalytic activity of gold nanoclusters. The present work particularly focuses on the adsorption and activation of molecular oxygen on the pristine and silicon-doped gold clusters. The results confirm that the silicon-doped Au7Si cluster shows considerable binding and activation of the O-2 molecule in comparison to the pristine Au-8 cluster as reflected in the relevant geometrical parameters (O-O and Au-O bond lengths) and O-O stretching frequency. However, silicon doping has no contrasting effect on the reactivity and catalytic activity of the Au-7 cluster. In addition to the stronger binding and activation of the O-2 molecule, the doped Au7Si cluster leads to a significant reduction in the activation barrier (0.57 eV) for the environmentally important CO oxidation reaction in contrast to the catalytically inactive pristine Au-8 cluster (1.22 eV). Thus, our results highlight the critical role of doping foreign impurities for future endeavors in the field of gold nanocatalysis.

}, issn = {1932-7447}, doi = {10.1021/jp501611t}, author = {Manzoor, Dar and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000340530500007, title = {Electronic transition dipole moment: a semi-biorthogonal approach within valence universal coupled cluster framework}, journal = {International Journal of Quantum Chemistry}, volume = {114}, number = {18, SI}, year = {2014}, month = {SEP}, pages = {1212-1219}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

Electronic dipole strengths (square of transition moments) and oscillator strengths are evaluated for various transitions, arising from the ground state to a few valence excited states. Parallel to two other methods of calculating the dipole strength within the Fock-space multireference coupled cluster framework, a new semi-biorthogonal approach is formulated and implemented in this article. This semi-biorthogonal approach can evaluate dipole strengths at a lower computational effort than the biorthogonal approach without compromising on the accuracy. This new method is compared and tested against the previously developed expectation value and biorthogonal approach for various molecular transitions. (C) 2014 Wiley Periodicals, Inc.

}, keywords = {electronic transition dipole, Fock-space, oscillator strength, semi-biorthogonal expectation value}, issn = {0020-7608}, doi = {10.1002/qua.24691}, author = {Bhattacharya, Debarati and Vaval, Nayana and Pal, Sourav} } @article { ISI:000341059100015, title = {Enhanced interaction of molecular oxygen with amino acid complexes of silver and gold clusters}, journal = {Indian Journal of Chemistry Section A-Inorganic Bio-Inorganic Physical Theoretical \& Analytical Chemistry}, volume = {53}, number = {8-9, SI}, year = {2014}, month = {AUG}, pages = {996-1000}, publisher = {NATL INST SCIENCE COMMUNICATION-NISCAIR}, type = {Article}, address = {DR K S KRISHNAN MARG, PUSA CAMPUS, NEW DELHI 110 012, INDIA}, abstract = {

Density functional theory calculations have been carried out to study the effect of amino acid adsorption on the reactivity of silver and gold clusters with molecular oxygen. It is found that the amino acids glycine and alanine form stable complexes with both Ag-4 and Au-4 clusters. However, the extent of interaction is more in the case of the Au-4 cluster, as reflected from the increase in binding energy in the amino acid Au-4 complexes. Our results confirm that the adsorption of amino acids glycine and alanine enhances the reactivity of Ag-4 and Au-4 clusters towards O-2 molecule. The enhanced reactivity of O-2 molecule towards the amino acid metal cluster complexes is manifested by an increase in the O-2 binding energy and a decrease in the M-O (M = Ag, Au) bond length. Moreover, it is found that the co-adsorption of amino acids and O-2 molecule on the Ag-4 and Au-4 clusters is cooperative.

}, keywords = {Amino acid complexes, Density functional calculations, Gold clusters, Metal clusters, Silver clusters, Theoretical chemistry}, issn = {0376-4710}, author = {Manzoor, Dar and Pal, Sourav} } @article { ISI:000334168400024, title = {Ground state of naphthyl cation: singlet or triplet?}, journal = {Journal of Chemical Physics}, volume = {140}, number = {11}, year = {2014}, month = {MAR}, pages = {114312}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {

We present a benchmark theoretical investigation on the electronic structure and singlet- triplet(ST) gap of 1- and 2-naphthyl cations using the CCSD(T) method. Our calculations reveal that the ground states of both the naphthyl cations are singlet, contrary to the results obtained by DFT/B3LYP calculations reported in previous theoretical studies. However, the triplet states obtained in the two structural isomers of naphthyl cation are completely different. The triplet state in 1-naphthyl cation is (pi,sigma) type, whereas in 2-naphthyl cation it is (pi,sigma) type, The S-T gaps in naphthyl cations and the relative stability ordering of the singlet and the triplet states are highly sensitive to the basis set quality as well as level of correlation, and demand for inclusion of perturbative triples in the coupled-cluster ansatz. (c) 2014 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4868485}, author = {Dutta, Achintya Kumar and Manohar, Prashant Uday and Vaval, Nayana and Pal, Sourav} } @article { ISI:000347360200068, title = {Hydrogen atom chemisorbed gold clusters as highly active catalysts for oxygen activation and co oxidation}, journal = {Journal of Physical Chemistry C}, volume = {118}, number = {51}, year = {2014}, month = {DEC}, pages = {30057-30062}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Using oxygen activation and carbon monoxide oxidation as a probe, we have carried out density functional theory (DFT) calculations to investigate the effect of hydrogen atom chemisorption on the reactivity and catalytic activity of gold nanoclusters. In the present work, we particularly focus on the closed shell neutral Au-n (n = 2, 4, 6, 8) gold clusters which are reported to be chemically inert and catalytically less active. The results confirm that the hydrogen atom chemisorption activates the inert clusters, thereby leading to enhanced binding and activation of the O-2 molecule. A significant amount of increase in the O-O and decrease in the Au-O bond lengths together with a pertinent red shift in the O-O stretching frequencies clearly indicates the stronger binding and activation of oxygen molecule in the case of AunH clusters. Further, our results reveal that the hydrogen atom chemisorbed gold clusters are catalytically more active with low activation barriers for the CO oxidation reaction compared to the parent less active closed shell gold clusters. Thus, in short the current theoretical observation provides key inputs for enhancing the reactivity and catalytic activity of inert gold clusters through the adsorption of a small atom or a molecule.

}, issn = {1932-7447}, doi = {10.1021/jp510488v}, author = {Manzoor, Dar and Pal, Sourav} } @article { ISI:000341543000009, title = {Intermediate hamiltonian fock space multireference coupled cluster approach to core excitation spectra}, journal = {Journal of Chemical Theory and Computation}, volume = {10}, number = {9}, year = {2014}, month = {SEP}, pages = {3656-3668}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The Fock space multireference coupled cluster (FSMRCC) method provides an efficient approach for the direct calculation of excitation energies. In intermediate Hamiltonian (IH-FSMRCC) formulation, the method is free from intruder state problems and associated convergence difficulties, even with a large model space. In this paper, we demonstrate that the IH-FSMRCC method with suitably chosen model space can be used for the accurate description of core excitation spectra of molecules, and our results are in excellent agreement with the experimental values. We have investigated the effect of choice of model space on the computed results. Unlike the equation-of-motion (EOM)-based method, the IH-FSMRCC does not require any special technique for convergence and in singles and doubles approximation gives a performance comparable to that of the standard EOMEE-CCSD method, even better in some of the cases.

}, issn = {1549-9618}, doi = {10.1021/ct500285e}, author = {Dutta, Achintya Kumar and Gupta, Jitendra and Vaval, Nayana and Pal, Sourav} } @article { ISI:000347596700001, title = {Molecular recognition pattern of cytotoxic alkaloid vinblastine with multiple targets}, journal = {Journal of Molecular Graphics \& Modelling}, volume = {54}, year = {2014}, month = {NOV}, pages = {1-9}, publisher = {ELSEVIER SCIENCE INC}, address = {360 PARK AVE SOUTH, NEW YORK, NY 10010-1710 USA}, abstract = {

Vinblastine (VLB), a cytotoxic alkaloid is used extensively against various cancer types and the crystal structure of its tubulin complex is already known. Multitarget affinity of vinblastine has been investigated and the nature of binding with biological receptors namely, duplex DNA and Human serum albumin (HSA) has been compared to the binding characteristics of its known complex with natural high affinity receptor tubulin using molecular docking and QM-MM calculations. VLB is found to interact with DNA as well as HSA protein, though, with weaker affinity as compared to tubulin. Analysis of various docked complexes revealed that the H-bonds and cation-pi bonds do not have significant contribution to the binding interactions and despite its large size, VLB remains in relaxed conformation and fits in the hydrophobic regions on the receptors. (C) 2014 Elsevier Inc. All rights reserved.

}, keywords = {Drug-DNA interactions, Drug-protein binding, Human serum albumin, Molecular docking, Multitarget affinity, QM-MM calculation, Vinblastine}, issn = {1093-3263}, doi = {10.1016/j.jmgm.2014.09.001}, author = {Pandya, Prateek and Agarwal, Lokesh Kr and Gupta, Neelima and Pal, Sourav} } @article { ISI:000336020400012, title = {Partitioned EOMEA-MBPT(2): an efficient N-5 scaling method for calculation of electron affinities}, journal = {Journal of Chemical Theory and Computation}, volume = {10}, number = {5}, year = {2014}, month = {APR}, pages = {1923-1933}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We present an N-5 scaling modification to the standard EOMEA-CCSD method, based on the matrix partitioning technique and perturbative approximations. The method has lower computational scaling and smaller storage requirements than the standard EOMEA-CCSD method and, therefore, can be used to calculate electron affinities of large molecules and clusters. The performance and capabilities of the new method have been benchmarked with the standard EOMEA-CCSD method, for a test set of 20 small molecules, and the average absolute deviation is only 0.03 eV. The method is further used to investigate electron affinities of DNA and RNA nucleobases, and the results are in excellent agreement with the experimental values.

}, issn = {1549-9618}, doi = {10.1021/ct4009409}, author = {Dutta, Achintya Kumar and Gupta, Jitendra and Pathak, Himadri and Vaval, Nayana and Pal, Sourav} } @article { ISI:000332999800006, title = {Photoelectrochemical splitting of water with nanocrystalline Zn1-xMnxO thin films: first-principle DFT computations supporting the systematic experimental endeavor}, journal = {International Journal of Hydrogen Energy}, volume = {39}, number = {8}, year = {2014}, month = {MAR}, pages = {3637-3648}, publisher = {PERGAMON-ELSEVIER SCIENCE LTD}, address = {THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND}, abstract = {

Photoelectrochemical splitting of water with nanocrystalline Zn1-xMnxO thin films was investigated. ZnO thin films with 1, 3, 5 and 7\% at. Mn incorporation were synthesized by sol gel method and characterized by X-Ray Diffraction (XRD) analysis, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Photoelectron spectroscopy (XPS), High Resolution Transmission Electron Microscopy (HR-TEM) and UV-Vis spectroscopy. Mn incorporation coupled with variation in sintering temperature led to significant microstructural changes, which tentatively influenced the magnitude of optical absorption and charge carrier mobility, thereby impacting the performance of such systems towards photoelectrochemical splitting of water. Electronic structure computations based on first principle density functional theory (DFT) revealed electronic states of Mn being responsible for the marginally recorded red shift in bandgap energy. Photoelectrochemical measurements using thin films of 1\% at. Mn:ZnO sintered at 600 degrees C yielded 3 times enhanced photocurrent at zero bias due to improved optical absorption. Plausible explanations for the effect have also been offered. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

}, keywords = {Density functional theory, Hydrogen energy, Mn doped ZnO, Optical properties, Photoelectrochemical water splitting}, issn = {0360-3199}, doi = {10.1016/j.ijhydene.2013.12.150}, author = {Sharma, Vidhika and Dixit, Mudit and Satsangi, Vibha R. and Dass, Sahab and Pal, Sourav and Shrivastav, Rohit} } @article {46363, title = {Relativistic equation-of-motion coupled-cluster method: application to closed-shell atomic systems}, journal = {Physical Review Applied}, volume = {89}, year = {2014}, month = {APR }, pages = {042510}, type = {Article}, abstract = {

We report our successful implementation of the relativistic equation-of-motion coupled-cluster (EOMCC) method. This method is employed to compute the principal ionization potentials (IPs) of closed-shell rare-gas atoms, He-like ions, Be-like ions, along with Na+, Al+, K+, Be, andMg. Four-component Dirac spinors are used in the calculations, and the one-and two-electron integrals are evaluated using the Dirac-Coulomb Hamiltonian. Our results are in excellent agreement with available measurements, which are taken from the National Institute of Science and Technology database. The accuracies of the calculations are estimated to be within one half of a percent for He-like and Be-like ions and 1\% for the heavier systems. We also present results using the second-order many-body perturbation theory and random-phase approximation in the EOMCC framework. These results are compared with those of EOMCC at the level of single and double excitations in order to assess the role of the electron correlation effects in the intermediate schemes considered in our calculations.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.89.042510}, author = {Pathak, Himadri and Sahoo, B. K. and Das, B. P. and Vaval, Nayana and Pal, Sourav} } @article {42640, title = {Relativistic equation-of-motion coupled-cluster method for the double-ionization potentials of closed-shell atoms}, journal = {Physical Review A}, volume = {90}, year = {2014}, month = {JUL}, pages = {Article No. 010501}, doi = {10.1103/PhysRevA.90.010501}, author = {Pathak, Himadri and Ghosh, Aryya and Sahoo, B. K. and Das, B. P. and Vaval, Nayana and Pal, Sourav} } @article { ISI:000346385900016, title = {Relativistic equation-of-motion coupled-cluster method for the ionization problem: application to molecules}, journal = {Physical Review A}, volume = {90}, number = {6}, year = {2014}, month = {DEC}, pages = {Article No. 062501}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

We report the implementation of the four-component spinor relativistic equation-of-motion (EOM) coupled-cluster method within the single- and double-excitation approximation to calculate the ionization potential of molecules. We have applied this method to calculate vertical ionization potentials of the molecules XH (X = F, Cl, Br, I) along with Cl-2 and Br-2 in their closed-shell configuration. We have also presented intermediate results using the second-order many-body perturbation-theory level in the EOM framework to understand the role of electron correlation. All the calculated values are compared with the available experimental results. Our results are found to be in good agreement with sophisticated experiments, and relative deviation of less than 1\% is achieved for all the considered systems.

}, issn = {1050-2947}, doi = {10.1103/PhysRevA.90.062501}, author = {Pathak, Himadri and Sasmal, Sudip and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article { ISI:000341976100014, title = {Relativistic spectroscopy of plasma-embedded Li-like systems with screening effects in two-body Debye potentials}, journal = {Journal of Physics B-Atomic Molecular and Optical Physics}, volume = {47}, number = {17}, year = {2014}, month = {SEP}, pages = {175701}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {

The spectroscopic properties of Li atoms and Li-like Ca and Ti ions in the plasma environment are investigated using a relativistic coupled-cluster (RCC) method. Assuming that the plasma is of low density and very hot, we consider the Debye model with two approximations to account for the screening effects: (i) in the nuclear potential alone and (ii) in both the nuclear and the electron-electron interaction potentials. Also, calculations for the energies and the lifetimes of the atomic states are carried out for plasma-free systems to check their accuracy, after which they are investigated in the plasma environment. It is observed that screenings in the electron-electron interaction potentials stabilize the systems more than when the screenings are present only in the nuclear potential. Similarly, the blue and red shifts in the Delta n = 0 and Delta n not equal 0 transition lines (with the principal quantum number n) of the Li-like ions observed in the (i) approximation are altered in the (ii) approximation. The level crossings among the energy levels are observed for large screening effects and are found to be prominent in the states of higher orbital angular momentum. The lifetimes of many low-lying states of the allowed transitions are estimated by considering different plasma screening strengths.

}, keywords = {atomic Spectroscopy, Debye model, relativistic method}, issn = {0953-4075}, doi = {10.1088/0953-4075/47/17/175701}, author = {Das, Madhulita and Sahoo, B. K. and Pal, Sourav} } @article { ISI:000332188200009, title = {Structure, stability, and properties of the trans peroxo nitrate radical: the importance of nondynamic correlation}, journal = {Journal of Physical Chemistry A}, volume = {118}, number = {8}, year = {2014}, month = {FEB}, pages = {1350-1362}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We report a comparative single-reference and multireference coupled-cluster investigation on the structure, potential energy surface, and IR spectroscopic properties of the trans peroxo nitrate radical, one of the key intermediates in stratospheric NOx chemistry. The previous single-reference ab initio studies predicted an unbound structure for the trans peroxo nitrate radical. However, our Fock space multireference coupled-cluster calculation confirms a bound structure for the trans peroxo nitrate radical, in accordance with the experimental results reported earlier. Further, the analysis of the potential energy surface in FSMRCC method indicates a well-behaved minima, contrary to the shallow minima predicted by the single-reference coupled-cluster method. The harmonic force field analysis, of various possible isomers of peroxo nitrate also reveals that only the trans structure leads to the experimentally observed IR peak at 1840 cm(-1). The present study highlights the critical importance of nondynamic correlation in predicting the structure and properties of high-energy stratospheric NOx radicals.

}, issn = {1089-5639}, doi = {10.1021/jp409218c}, author = {Dutta, Achintya Kumar and Dar, Manzoor and Vaval, Nayana and Pal, Sourav} } @article { ISI:000360653900022, title = {Calculation of P,T-odd interaction constant of PbF using Z-vector method in the relativistic coupled-cluster framework}, journal = {Journal of Chemical Physics}, volume = {143}, number = {8}, year = {2015}, month = {AUG}, pages = {084119}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {

The effective electric field experienced by the unpaired electron in the ground state of PbF, which is a potential candidate in the search of electron electric dipole moment due to some special characteristics, is calculated using Z-vector method in the coupled cluster single-and double-excitation approximation with four component Dirac spinor. This is an important quantity to set the upper bound limit of the electron electric dipole moment. Further, we have calculated molecular dipole moment and parallel magnetic hyperfine structure constant (A(parallel to)) of Pb-207 in PbF to test the accuracy of the wavefunction obtained in the Z-vector method. The outcome of our calculations clearly suggests that the core electrons have significant contribution to the {\textquoteleft}{\textquoteleft}atom in compound{\textquoteright}{\textquoteright} properties. (C) 2015 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4929591}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article { ISI:000356520400003, title = {Computational strategies for understanding the nature of interaction in dioxin imprinted nanoporous trappers}, journal = {Journal of Molecular Recognition}, volume = {28}, number = {7}, year = {2015}, month = {JUL}, pages = {427-437}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

A new computational model capable of understanding the nature of interactions in signature complexes formed between the template(2,3,7,8-tetrachlorodibenzo-p dioxin (TCDD)) and the functional monomers (methacrylic acid (MAA)) using density functional theory (DFT) has been designed. The polymer precursors were optimized for geometries in polymerization media, computing the interaction energies between template molecules and functional monomers of transient pre-polymerized complexes (PPC), and structural and vibrational properties reference to theoretical infrared spectra were computed using DFT of B3LYP/6 311+G(d,p) hybrid functional method. Atom in molecule theory was used to analyze the hydrogen-bonding characteristics of PPC of MAA-TCDD. Considering the theoretical titrations conducted in a virtual solvent box, it was found that the 1:4 molar ratio was required to form the most stable PPC in a given solvent system. The electron density plots indicate strong hydrogen bonding as shown by the 2pz dominant highest occupied molecular orbital (HOMO) character that could be the preferable sites of binding for target molecule, TCDD. Considering HOMO approach, the active adsorption sites in molecularly imprinted polymer was modeled to get insight on molecular recognition property for targeted molecule, TCDD. The proposed computational protocol is simple, accurate, and novel to design the polymer and is useful to predict the properties of polymer systems than the conventional theoretical analysis of template-monomer interactions. Copyright (c) 2015 John Wiley \& Sons, Ltd.

}, keywords = {carcinogenic pollutants, computer simulations, Density Functional Theory (DFT), intermolecular interactions, Molecularly Imprinted Polymers (MIP)}, issn = {0952-3499}, doi = {10.1002/jmr.2459}, author = {Khan, Muntazir S. and Pal, Sourav and Krupadam, Reddithota J.} } @article { ISI:000354238700002, title = {Electron attachment to DNA and RNA nucleobases: an EOMCC investigation}, journal = {International Journal of Quantum Chemistry}, volume = {115}, number = {12}, year = {2015}, month = {JUN}, pages = {753-764}, publisher = {WILEY-BLACKWELL}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

We report a benchmark theoretical investigation of both vertical and adiabatic electron affinities of DNA and RNA nucleobases: adenine, guanine, cytosine, thymine, and uracil using equation of motion coupled cluster method. The vertical electron affinity (VEA) values of the first five states of the DNA and RNA nucleobases are computed. It is observed that the first electron attached state is energetically accessible in gas phase. Furthermore, an analysis of the natural orbitals exhibits that the first electron attached states of uracil and thymine are valence-bound in nature and undergo significant structural changes on attachment of an extra electron, which reflects in the deviation of the adiabatic electron affinity (AEA) than that of the vertical ones. Conversely, the first electron attached states of cytosine, adenine, and guanine are in the category of dipole-bound anions. Their structure, by and large, remain unaffected on attachment of an extra electron, which is evident from the observed small difference between the AEA and VEA values. VEA and AEA values of all the DNA and RNA nucleobases are found to be negative, which implies that the first electron attached states are not stable rather quasi bound. The results of all previous theoretical calculations are out of track and shows large deviation with respect to the experimentally measured values, whereas, our results are found to be in good agreement. Therefore, our computed values can be used as a reliable standard to calibrate new theoretical methods. (c) 2015 Wiley Periodicals, Inc.

}, keywords = {DNA-RNA bases, electron affinity, EOMCC}, issn = {0020-7608}, doi = {10.1002/qua.24892}, author = {Dutta, Achintya Kumar and Sengupta, Turbasu and Vaval, Nayana and Pal, Sourav} } @article { ISI:000356201700008, title = {EOMIP-CCSD(2)*: an efficient method for the calculation of ionization potentials}, journal = {Journal of Chemical Theory and Computation}, volume = {11}, number = {6}, year = {2015}, month = {JUN}, pages = {2461-2472}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

A new approximation within the domain of EOMIP-CC method is proposed. The proposed scheme is based on the perturbative truncation of the similarity transformed effective Hamiltonian matrix. We call it the EOMIP-CCSD(2)* method, which scales as noniterative N-6 and its storage requirement is very less, compared to the conventional EOMIP-CCSD method. The existing EOMIP-CCSD(2) method has a tendency to overestimate the ionization potential (IP) values. On the other hand, our new strategy corrects for the problem of such an overestimation, which is evident from the excellent agreement achieved with the experimental values. Furthermore, not only the ionization potential but also geometry and IR frequencies of problematic double radicals are estimated correctly, and the results are comparable to the CCSD(T) method, obviously at lesser computational cost. The EOMIP-CCSD(2)* method works even for the core ionization and satellite IP, where the earlier EOMIP-CCSD(2) approximation dramatically fails.

}, issn = {1549-9618}, doi = {10.1021/ct500927h}, author = {Dutta, Achintya Kumar and Vaval, Nayana and Pal, Sourav} } @article { ISI:000352195500001, title = {Implementation of the Z-vector method in the relativistic-coupled-cluster framework to calculate first-order energy derivatives: Application to the SrF molecule}, journal = {Physical Review A}, volume = {91}, number = {3}, year = {2015}, month = {MAR}, pages = {030503}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

The molecular dipole moment and magnetic hyperfine-structure constant demand an accurate wave function far from the nucleus and in the near nuclear region, respectively. We, therefore, employ the so-called Z-vector method in the domain of relativistic-coupled-cluster theory to calculate the first-order property of molecular systems in their open-shell ground-state configuration. The implemented method is applied to calculate the molecular dipole moment and parallel component of the magnetic hyperfine-structure constant of the SrF molecule. The results of our calculation are compared with the experimental and other available theoretically calculated values. We are successful in achieving good accordance with the experimental results. The result of our calculation of the molecular dipole moment is in the accuracy of similar to 0.5\%, which is clearly an improvement over the previous calculation based on the expectation value method in the four-component coupled-cluster framework [V. S. Prasannaa et al., Phys. Rev. A 90, 052507 (2014)]. Thus, it can be inferred that the Z-vector method can provide an accurate wave function in both the near and far nuclear region, which is evident from our calculated results.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.91.030503}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {42627, title = {Lifetime of inner-shell hole states of Ar (2p) and Kr (3d) using equation-of-motion coupled cluster method}, journal = {Journal of Chemical Physics}, volume = {143}, year = {2015}, month = {JUL}, pages = {Article No. 024305}, doi = {10.1063/1.4926396}, author = {Ghosh, Aryya and Pal, Sourav and Vaval, Nayana} } @article { ISI:000349018100016, title = {New scheme for perturbative triples correction to (0,1) sector of Fock space multi-reference coupled cluster method: Theory, implementation, and examples}, journal = {Journal of Chemical Physics}, volume = {142}, number = {4}, year = {2015}, month = {JAN}, pages = {Article No. 044113}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {

We propose a new elegant strategy to implement third order triples correction in the light of many-body perturbation theory to the Fock space multi-reference coupled cluster method for the ionization problem. The computational scaling as well as the storage requirement is of key concerns in any many-body calculations. Our proposed approach scales as N-6 does not require the storage of triples amplitudes and gives superior agreement over all the previous attempts made. This approach is capable of calculating multiple roots in a single calculation in contrast to the inclusion of perturbative triples in the equation of motion variant of the coupled cluster theory, where each root needs to be computed in a state-specific way and requires both the left and right state vectors together. The performance of the newly implemented scheme is tested by applying to methylene, boron nitride (B2N) anion, nitrogen, water, carbon monoxide, acetylene, formaldehyde, and thymine monomer, a DNA base. (C) 2015 AIP Publishing LLC.

}, issn = {0021-9606}, doi = {10.1063/1.4906233}, author = {Dutta, Achintya Kumar and Vaval, Nayana and Pal, Sourav} } @article { ISI:000357805700036, title = {Oxidative addition of the C-I bond on aluminum nanoclusters}, journal = {Nanoscale}, volume = {7}, number = {28}, year = {2015}, month = {JUN}, pages = {12109-12125}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Energetics and the in-depth reaction mechanism of the oxidative addition step of the cross-coupling reaction are studied in the framework of density functional theory (DFT) on aluminum nanoclusters. Aluminum metal in its bulk state is totally inactive towards carbon-halogen bond dissociation but selected Al nanoclusters (size ranging from 3 to 20 atoms) have shown a significantly lower activation barrier towards the oxidative addition reaction. The calculated energy barriers are lower than the gold clusters and within a comparable range with the conventional and most versatile Pd catalyst. Further investigations reveal that the activation energies and other reaction parameters are highly sensitive to the geometrical shapes and electronic structures of the clusters rather than their size, imposing the fact that comprehensive studies on aluminum clusters can be beneficial for nanoscience and nanotechnology. To understand the possible reaction mechanism in detail, the reaction pathway is investigated with the ab initio Born Oppenheimer Molecular Dynamics (BOMD) simulation and the Natural Bond Orbital (NBO) analysis. In short, our theoretical study highlights the thermodynamic and kinetic details of C-I bond dissociation on aluminum clusters for future endeavors in cluster chemistry.

}, issn = {2040-3364}, doi = {10.1039/c5nr02278a}, author = {Sengupta, Turbasu and Das, Susanta and Pal, Sourav} } @conference { ISI:000354845400032, title = {Partial triples excitation to the fock space multi-reference singles and doubles: dipole moment of doublet radicals}, booktitle = {Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2010 (ICCMSE-2010)}, series = {AIP Conference Proceedings}, volume = {1642}, year = {2015}, note = {International Conference of Computational Methods in Sciences and Engineering (ICCMSE), Kos, GREECE, OCT 03-08, 2010}, month = {FEB}, pages = {223-226}, publisher = {European Soc Computat Methods Sci, Engn \& Technol}, organization = {European Soc Computat Methods Sci, Engn \& Technol}, address = {2 Huntington Quadrangle, STE 1NO1, Melville, NY 11747-4501 USA}, abstract = {

We present the partial triples effect on the dipole moment of doublet radicals in Lagrangian formulation of Fockspace multi-reference coupled cluster response method(A FSMRCC). This specific scheme uses non-iterative triples, in addition to singles and doubles excitations(A FSMRCCSD(T*)), which accounts for the effects appearing at least at the third order in dipole moment. This method is applied to the ground states of small radicals.

}, keywords = {Dipole moment, Multi-reference, Triples}, isbn = {978-0-7354-1282-8}, issn = {0094-243X}, doi = {10.1063/1.4906657}, author = {Ravichandran, Lalitha and Vaval, Nayana and Pal, Sourav}, editor = {Simos, TE and Maroulis, G} } @article { ISI:000357933400054, title = {Perturbative order analysis of the similarity transformed hamiltonian in fock-space coupled cluster theory: difference energy and electric response properties}, journal = {Molecular Physics}, volume = {113}, number = {13-14, SI}, year = {2015}, month = {JUL}, pages = {2046-2060}, publisher = {TAYLOR \& FRANCIS LTD}, address = {4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLAND}, abstract = {

A perturbative analysis of the ground-state similarity transformed Hamiltonian and its effect on the various Fock-space coupled cluster (FSCC) sectors is presented through calculation of ionisation potential, electron affinity, excitation energies and response properties. Various truncation schemes of the effective Hamiltonian are presented with explicit form of the defining equations. Based on such a truncation, the approximate methods are labelled as FSCC(n), where n represents the correlation energy of the ionised, electron attached or excited states corrected at least up to nth order within coupled cluster singles and doubles scheme (CCSD). A lower scaling CC2 type of approach (abbreviated as FS-CC2) is compared against the group of FSCC(n) methods for energies. Electric response properties have been compared and contrasted for the two lower scaling methods: FSCC(2) and FS-CC2. The various truncated methods are tested for a number of small molecules. The results obtained from a range of truncated methods are compared against full FSCCSD calculations.

}, keywords = {electric response properties, Fock space, perturbative order, similarity transformed Hamiltonian}, issn = {0026-8976}, doi = {10.1080/00268976.2015.1059509}, author = {Bhattacharya, Debarati and Dutta, Achintya Kumar and Gupta, Jitendra and Pal, Sourav} } @article { ISI:000356753600002, title = {Reactivity and catalytic activity of hydrogen atom chemisorbed silver clusters}, journal = {Journal of Physical Chemistry A}, volume = {119}, number = {24}, year = {2015}, month = {JUN}, pages = {6162-6170}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Metal clusters of silver have attracted recent interest of researchers as a result of their potential in different,catalytic applications and low Cost. However, due to the completely filled d orbital and very high first ionization potential of the silver atom, the silver-based catalysts interact very weakly with the reacting molecules. In the current work, density functional theory calculations were carried out to investigate the effect of hydrogen atom chemisorption. On the reactivity and catalytic properties of inert silver clusters Our results affirm that the hydrogen atom chemisorption leads to enhancement the binding energy of the adsorbed O-2 molecule on the inert silver clusters. The increase in the binding energy is also characterized by the decrease in the Ag-O and increase in the O-O bond lengths in the case of the AgnH Silver clusters. Pertinent to the increase in the O-O bond length, a. significant red shift in the O-O Stretching frequency is. also noted in the case,of the AgnH silver clusters. Moreover, the hydrogen atom chemisorbed silver clusters show low reaction barriers and heat Of formation of the final products for the,environmentally important CO oxidation reaction as compared to the parent catalytically inactive clusters The obtained results were compared with those of the corresponding gold and hydrogen atom chemisorbed gold clusters obtained at the same level of theory. It is expected the current computational study will provide key insights for future advances in the design of efficient nanosilver-based catalysts through the adsorption of a small atom or a ligand.

}, issn = {1089-5639}, doi = {10.1021/acs.jpca.5b01987}, author = {Manzoor, Dar and Pal, Sourav} } @article { ISI:000354188800009, title = {Relativistic equation-of-motion coupled-cluster investigation of the trends of single and double ionization potentials in the He and Be isoelectronic systems}, journal = {Journal of Physics B-Atomic Molecular and Optical Physics}, volume = {48}, number = {11}, year = {2015}, month = {JUN}, pages = {115009}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {

We employ a four-component spinor relativistic equation-of-motion coupled-cluster (EOMCC) method within the single-and double-excitation approximation to calculate the single ionization potentials (IPs) and double ionization potentials (DIPs) of the He and Be isoelectronic sequences up to Ne. The obtained results are compared with the available results from the National Institute of Standards and Technology (NIST) database to test the performance of the EOMCC method. We also present intermediate results at different levels of approximations in the EOMCC framework to gain insight of the effect of electron correlation. Furthermore, we investigate the dependence of the IPs and DIPs of these ions on the ionic charge and observe that these follow parabolic trends. Similarities between the trends of IPs and DIPs in both the classes of considered systems are categorically demonstrated.

}, keywords = {coupled-cluster method, double ionization potentials, equation-of-motion theory}, issn = {0953-4075}, doi = {10.1088/0953-4075/48/11/115009}, author = {Pathak, Himadri and Sahoo, B. K. and Sengupta, Turbasu and Das, B. P. and Vaval, Nayana and Pal, Sourav} } @article {42629, title = {Relativistic extended coupled cluster method for magnetic hyperfine structure constant}, journal = {Physical Review A}, volume = {91}, year = {2015}, month = {FEB}, pages = {Article No. 022512}, type = {Article}, doi = {10.1103/PhysRevA.91.022512}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @conference { ISI:000354845400033, title = {Study of molecular vibration by coupled cluster method: bosonic approach}, booktitle = {Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2010 (ICCMSE-2010)}, series = {AIP Conference Proceedings}, volume = {1642}, year = {2015}, note = {International Conference of Computational Methods in Sciences and Engineering (ICCMSE), Kos, GREECE, OCT 03-08, 2010}, month = {FEB}, pages = {227-230}, publisher = {European Soc Computat Methods Sci, Engn \& Technol}, organization = {European Soc Computat Methods Sci, Engn \& Technol}, address = {2 Huntington Quadrangle, STE 1NO1, Melville, NY 11747-4501 USA}, abstract = {

The vibrational coupled cluster method in bosonic representation is formulated to describe the molecular anharmonic vibrational spectra. The vibrational coupled cluster formalism is based on Watson Hamiltonian in normal coordinates. The vibrational excited states are described using coupled cluster linear response theory (CCLRT). The quality of the coupled cluster wave function is analyzed. Specifically, the mean displacement values of the normal coordinates and expectation values of the square of the normal coordinates of different vibrational states are calculated. A good agreement between the converged full CI results and coupled cluster results is found for the lower lying vibrational states.

}, keywords = {CCLRT, Expectation values, Watson Hamiltonian}, isbn = {978-0-7354-1282-8}, issn = {0094-243X}, doi = {10.1063/1.4906658}, author = {Banik, Subrata and Pal, Sourav and Prasad, M. Durga}, editor = {Simos, TE and Maroulis, G} } @article { ISI:000362239300030, title = {Systematic comparison of DFT and CCSD dipole moments, polarizabilities and hyperpolarizabilities}, journal = {Chemical Physics Letters}, volume = {635}, year = {2015}, month = {AUG}, pages = {168-173}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

A comparative study of dipole moments, polarizabilities and hyperpolarizabilities of 16 different molecules is performed employing two completely different theoretical approaches namely, density functional theory (DFT) and coupled cluster singles and doubles (CCSD). Both methods include electron correlation. The CCSD method is more accurate but highly expensive. DFT with auxiliary density allows non-iterative solutions which is computational advantage and useful for large molecules. Dipole moments and polarizability calculations from DFT are in very good agreement with CCSD calculations. However, negative hyperpolarizability values from DFT differ significantly from their CCSD counterparts, whereas positive hyperpolarizabilities show reasonable agreement between these methodologies. (C) 2015 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2015.06.046}, author = {Karne, Anagha S. and Vaval, Nayana and Pal, Sourav and Vasquez-Perez, Jose M. and Koester, Andreas M. and Calaminici, Patrizia} } @article { ISI:000361649900037, title = {Systematic comparison of DFT and CCSD dipole moments, polarizabilities and hyperpolarizabilities (vol 635, pg 168, 2015)}, journal = {Chemical Physics Letters}, volume = {636}, year = {2015}, month = {SEP}, pages = {228-229}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, issn = {0009-2614}, doi = {10.1016/j.cplett.2015.08.034}, author = {Karne, Anagha S. and Vaval, Nayana and Pal, Sourav and Vasquez-Perez, Jose M. and Koester, Andreas M. and Calaminici, Patrizia} } @article {43584, title = {Calculation of hyperfine structure constants of small molecules using Z-vector method in the relativistic coupled-cluster framework}, journal = {Journal of Chemical Sciences}, volume = {128}, year = {2016}, month = {OCT}, pages = {1671-1675}, abstract = {The Z-vector method in the relativistic coupled-cluster framework is employed to calculate the parallel and perpendicular components of the magnetic hyperfine structure constant of a few small alkaline earth hydrides (BeH, MgH, and CaH) and fluorides (MgF and CaF). We have compared our Z-vector results with the values calculated by the extended coupled-cluster (ECC) method reported in Phys. Rev. A 91 022512 (2015). All these results are compared with the available experimental values. The Z-vector results are found to be in better agreement with the experimental values than those of the ECC values.}, doi = {10.1007/s12039-016-1174-1}, author = {Sasmal, Sudip and Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {43596, title = {Contriving a catalytically active structure from an inert conformation: a density functionalinvestigation of Al, Hf, and Ge doping of Au-20 tetrahedral clusters}, journal = {Journal of Physical Chemistry C}, volume = {120}, year = {2016}, month = {SEP}, pages = {19636-19641}, abstract = {

The transformation of an inert structure into a catalytically active conformation has immense potential from a structural engineering point of view. In the present work, we explored methods of achieving such a transformation through a density-functional-based study. Au-20 is known be one of the most stable and catalytically inert gold clusters, with a well-known tetrahedral structure. We demonstrate the transformation of the inert Au-20 conformation into a highly active catalytic cluster through selective doping with Hf and Ge atoms. Depending on the dopant, the inert tetrahedral Au-20 cluster evolves into either an endohedral or a hollow-cage-like conformation. The structural changes are manifested in the catalytic properties as well, with the result that the transformed doped cages exhibit extremely low activation barriers for the environmentally important CO oxidation reaction as compared to reported inert Au-20 cluster. The activation barriers for CO oxidation are particularly low (\<0.12 eV) when germanium is directly involved in the CO oxidation. Thus, the current work highlights the importance of engineering structural properties of metal nanoclusters with the help of heteroatom dopants for future applications in efficient catalysis.

}, doi = {10.1021/acs.jpcc.6b04305}, author = {Manzoor, Dar and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000371103000013, title = {Electron detachment and subsequent structural changes of water clusters}, journal = {Journal of Physical Chemistry A}, volume = {120}, number = {7}, year = {2016}, month = {FEB}, pages = {1065-1073}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

A cost-effective equation of motion coupled cluster method, EOMIP-CCSD(2), is used to investigate vertical and adiabatic ionization potential as well as ionization-induced structural changes of water clusters and compared with CCSD(T), CASPT2, and MP2 methods. The moderate N-5 scaling and low storage requirement yields EOMIP-CCSD (2) calculation feasible even for reasonably large molecules and clusters with accuracy comparable to CCSD(T) method at much cheaper computational cost. Our calculations shed light on the authenticity of EOMIP-CCSD(2) results and establish a reliable method to study of ionization energy of molecular clusters. We have further investigated the performance of several classes of DFT functionals for ionization energies of water clusters to benchmark the results and to get a reliable functionals for the same.

}, issn = {1089-5639}, doi = {10.1021/acs.jpca.5b09389}, author = {Das, Susanta and Sengupta, Turbasu and Dutta, Achintya Kumar and Pal, Sourav} } @article { ISI:000371608600013, title = {Endohedrally doped gold nanocages: efficient catalysts for O-2 activation and CO oxidation}, journal = {Physical Chemistry Chemical Physics}, volume = {18}, number = {10}, year = {2016}, month = {MAR}, pages = {7068-7074}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Gold nanocages are the most attractive catalytic materials as all the atoms in the cage type clusters reside on the surface, making them available for chemisorption by reacting molecules. Due to a hollow space at the center, their chemical and catalytic properties can be tuned effectively and easily by endohedral doping. While a significant experimental and theoretical understanding is currently available on the structural and electronic properties of doped gold cages, very little information is available on their reactivity and catalytic behavior. In the present work, with the help of density functional theory calculations we demonstrate that endohedral doping leads to a notable increase in the binding energy of molecular oxygen on the gold nanocages. The enhancement in the O-2 binding energy on the doped gold cages is also confirmed by a significant decrease in the Au-O and an increase in the O-O bond lengths, corroborated by a red shift (similar to 250 cm(-1)) in the O-O stretching frequency as compared to the pristine cage. Furthermore, interestingly, the doped gold cages show very low activation barriers for the environmentally important CO oxidation reaction as compared to the pristine gold cage. Importantly, the decrease in the barrier height is comparatively greater for the rate limiting step of O-O-C-O intermediate formation and as a result the CO oxidation is expected to be more facile on the doped gold cages. Thus, the current study highlights the role of heteroatom doping in imparting new chemical and catalytic properties to gold cages and is expected to spur further research in the design of efficient gold nanocatalysts.

}, issn = {1463-9076}, doi = {10.1039/c5cp05624a}, author = {Manzoor, Dar and Krishnamurty, Sailaja and Pal, Sourav} } @article { ISI:000377203300035, title = {Hydrogen adsorption in ZIF-7: A DFT and ab-initio molecular dynamics study}, journal = {Chemical Physics Letters}, volume = {651}, year = {2016}, month = {MAY}, pages = {178-182}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Primary H-2 adsorption sites in a zeolitic imidazolate framework, ZIF-7, are identified using ab-initio density functional theory (DFT) based molecular dynamics annealing simulations. The simulations suggest several low energy adsorption sites. The effect of light transition metal decoration on hydrogen storage properties was studied. Our ab-intio DFT calculations illustrate that decorating the ZIF with Sc increases both the number of H-2 molecules, as well as the H-2 binding energy. The binding energy (similar to 25 kJ/mol per H-2) at 8H(2) loading in the pore, suggests that Sc-ZIFs can be potential candidates for hydrogen storage. (C) 2016 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2016.03.030}, author = {Dixit, Mudit and Major, Dan Thomas and Pal, Sourav} } @article {43419, title = {Influence of carbon and phosphorus doping on electronic properties of ZnO}, journal = {Journal of Materials Science-Materials in Electronics}, volume = {27}, year = {2016}, month = {DEC}, pages = {12318-12322}, abstract = {ZnO is one of the most promising candidate for photoelectrochemical splitting of water for hydrogen production. To increase the efficiency of ZnO based photoelectrochemical cell, its band-gap and band edges should be tailored to match visible light spectra and water redox potential respectively. In this paper, First-principles density functional theory calculations have been performed to evaluate the effect of non-metal dopants on electronic properties of ZnO. The model structures of X-doped ZnO were constructed using 32-atom 2 x 2 x 2 supercell of wurtzite ZnO with one O atom replaced with X (carbon C, phosphorus P). With respect to the electronic band structure, C (2p), P (3p) states are located above the valence band maximum of ZnO and mixing of these states is feeble to produce significant band gap narrowing. Doping of these non-metals dopants helps in the creation of isolated states which enhances visible light absorption of ZnO. Our theoretical calculations are consistent with the experimental results of C (P) doped ZnO and fully explains its visible light activity on non-metal doping.}, doi = {10.1007/s10854-016-5192-z}, author = {Sharma, Vidhika and Prasad, Mohit and Jadkar, Sandesh and Pal, Sourav} } @article {43446, title = {N-2 activation on Al metal clusters: catalyzing role of BN-doped graphene support}, journal = {Physical Chemistry Chemical Physics}, volume = {18}, year = {2016}, month = {OCT}, pages = {27721-27727}, abstract = {The successful sustenance of life demands an ambient abiotic process for N-2 activation and dissociation. The Bosch-Haber process remains the only abiotic and synthetic means for N-2 activation and its fixation. Metal nanoclusters have been recently reported for activating molecular nitrogen. Interestingly, the metal clusters explored so far for N-2 activation are free clusters and, hence, are practically not applicable by experimental chemists. Using density functional theory (DFT) based methodology, we propose a potential catalytic system for di-nitrogen activation, viz. supported Al clusters. Al clusters supported on BN doped graphene sheets are seen to activate N-2 molecule with a red shift in the N-N stretching frequency up to 874 cm(-1) with activation barriers as low as 1.14 eV.}, doi = {10.1039/c6cp03342c}, author = {Kumar, Deepak and Pal, Sourav and Krishnamurty, Sailaja} } @article { ISI:000381418000084, title = {Radical attached aluminum nanoclusters: an alternative way of cluster stabilization}, journal = {Physical Chemistry Chemical Physics}, volume = {18}, number = {31}, year = {2016}, month = {AUG}, pages = {21746-21759}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The stability and electronic structure of radical attached aluminum nanoclusters are investigated using density functional theory (DFT). A detailed investigation shows good correlation between the thermodynamic stability of radical attached clusters and the stability of the attached radical anions. All other calculated parameters like HOMO-LUMO gap and charge transfer are also found to be consistent with the observed thermodynamic stabilities of the complexes. Investigation of the electronic structure of radical attached complexes further shows the presence of jellium structures within the core similar to the ligated clusters. Comparison with available experimental and theoretical data also proves the validity of superatomic complex theory for the radical attached clusters as well. Based on the evaluated thermodynamic parameters, selected radical attached clusters are observed to be more thermodynamically stable in comparison with experimentally synthesized ligated clusters. Stabilization of small metal clusters is one of the greatest challenges in current cluster science and the present investigation confirms the fact that radical attached clusters can provide a viable alternative to ligated clusters in the future.

}, issn = {1463-9076}, doi = {10.1039/c6cp03601e}, author = {Sengupta, Turbasu and Pal, Sourav} } @article { ISI:000377497000004, title = {Relativistic coupled-cluster study of RaF as a candidate for the parity- and time-reversal-violating interaction}, journal = {Physical Review A}, volume = {93}, number = {6}, year = {2016}, month = {JUN}, pages = {062506}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

We have employed both the Z-vector method and the expectation-value approach in the relativistic coupled-cluster framework to calculate the scalar-pseudoscalar (S-PS) P, T-odd interaction constant W-s and the effective electric field E-eff experienced by the unpaired electron in the ground electronic state of RaF. Further, the magnetic hyperfine structure constants of Ra-223 in RaF and Ra-223(+) are also calculated and compared with the experimental values wherever available to judge the extent of the accuracy obtained with the employed methods. The outcome of our study reveals that the Z-vector method is superior to the expectation-value approach in terms of accuracy obtained for the calculation of ground-state property. The Z-vector calculation shows that RaF has a high Eeff (52.5 GV/cm) and W-s (141.2 kHz), which makes it a potential candidate for the electric dipole moment of the electron (eEDM) experiment. An estimation of uncertainty associated with our final results is made, and it is found that it lies below 10\%.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.93.062506}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {42619, title = {Relativistic equation-of-motion coupled-cluster method for the electron attachment problem}, journal = {Computational and Theoretical Chemistry}, volume = {1076}, year = {2016}, month = {JAN}, pages = {94-100}, abstract = {

The article considers the successful implementation of relativistic equation-of-motion coupled cluster method for the electron attachment problem (EA-EOMCC) at the level of single- and double- excitation approximation. The implemented relativistic EA-EOMCC method is employed to calculate ionization potential values of alkali metal atoms (Li, Na, K, Rb, Cs, Fr) and the vertical electron affinity values of LiX (X = H, F, Cl, Br), NaY (Y = H, F, Cl) starting from their closed-shell configuration. Both four component and exact two-component calculations are done for all the opted systems. Further, we have shown the effect of spin-orbit interaction considering the atomic systems. The results of our atomic calculations are compared with the values from the NIST database and the results are found to be very accurate (\<1\%). (C) 2015 Elsevier B.V. All rights reserved.

}, doi = {10.1016/j.comptc.2015.12.015}, author = {Pathak, Himadri and Sasmal, Sudip and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {42621, title = {Search for parity and time reversal violating effects in HgH: relativistic coupled-cluster study}, journal = {Journal of Chemical Physics}, volume = {144}, year = {2016}, month = {MAR}, pages = {Article No. 124307}, abstract = {

The high effective electric field (E-eff) experienced by the unpaired electron in an atom or a molecule is one of the key ingredients in the success of electron electric dipole moment (eEDM) experiment and its precise calculation requires a very accurate theory. We, therefore, employed the Z-vector method in the relativistic coupled-cluster framework and found that HgH has a very large E-eff value (123.2 GV/cm) which makes it a potential candidate for the next generation eEDM experiment. Our study also reveals that it has a large scalar-pseudoscalar (S-PS) P, T-violating interaction constant, W-s = 284.2 kHz. To judge the accuracy of the obtained results, we have calculated parallel and perpendicular magnetic hyperfine structure (HFS) constants and compared with the available experimental values. The results of our calculation are found to be in nice agreement with the experimental values. Therefore, by looking at the HFS results, we can say that both E-eff and W-s values are also very accurate. Further, We have derived the relationship between these quantities and the ratio which will help to get model independent value of eEDM and S-PS interaction constant. (C) 2016 AIP Publishing LLC.

}, doi = {10.1063/1.4944673}, author = {Sasmal, Sudip and Pathak, Himadri and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {45638, title = {Strategic Preparation of Efficient and Durable NiCo Alloy Supported N-Doped Porous Graphene as an Oxygen Evolution Electrocatalyst: A Theoretical and Experimental Investigation}, journal = {Advanced Materials Interfaces}, volume = {3}, year = {2016}, month = {OCT }, pages = {1600532}, type = {Article}, abstract = {

Development of an efficient and durable water splitting electrocatalyst holds a great commitment for the future energy devices. The real application of oxygen evolution reaction (OER) catalysts mainly suffers from sluggish kinetics and high overpotential except for the Ir and Ru-based systems. However, the high cost and vulnerability of the Ir and Ru metals are the main hostiles to use them for marketization. Herein, a high-performance OER electrocatalyst consisting of NiCo alloy nanoparticles supported on high surface area N-doped porous graphene (NiCo/pNGr(75: 25)) is reported. The importance of the doped-N for achieving the uniform dispersion-cum-effective interaction of the size controlled NiCo alloy nanoparticles has been explicitly investigated by transmission electron microscopy, X-ray diffraction, X-ray photo electron spectroscopy, Raman, density functional theory (DFT) calculations, etc. The electrochemical analysis of NiCo/pNGr(75: 25) shows an overpotential of approximate to 260 mV at 10 mA cm(-2) with a smaller Tafel slope of approximate to 87 mV dec(-1) and long catalytic durability. DFT calculations are done to check the interaction between the NiCo alloy nanoparticles and the defective sites of pNGr and also with the doped-N, which could be attained for maintaining long catalytic durability. Furthermore, NiCo/pNGr(75: 25) is used as an OER catalyst to fabricate an electrolyzer, which works at very low potential of 1.5 V in 1 M KOH.

}, issn = {2196-7350}, doi = {10.1002/admi.201600532}, author = {Singh, Santosh K. and Kumar, Deepak and Dhavale, Vishal M. and Pal, Sourav and Kurungot, Sreekumar} } @article { ISI:000375969000054, title = {Transition metal doped aluminum clusters: an account of spin}, journal = {Journal of Physical Chemistry C}, volume = {120}, number = {18}, year = {2016}, month = {MAY}, pages = {10027-10040}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The influence of spin on the properties of small sized transition metal doped aluminum clusters are investigated in the framework of density functional theory (DFT). Detailed analysis on minimum spin doped aluminum clusters has shown prominent indication of odd even oscillation in various calculated properties, supporting the presence of jellium shell structures within them. However, optimized high spin ground state counterparts, on the other hand, show rather smooth trends consistent with the properties of bulk materials. Resemblance to the bulk transition metals is further reflected in the gradual declining trends of heat of adsorption of CO2 molecule on cluster surface by sequentially changing the dopant atom from scandium to zinc. All the observations are also compared and found to be consistent with the earlier theoretical and experimental findings as obtained in the current literature. The similarities in the properties between atomic clusters and the bulk material is of utter importance and indeed precious considering the promising influence of the acquired information in understanding the process of evolution of nanoparticles from constituent atoms.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.6b00510}, author = {Sengupta, Turbasu and Das, Susanta and Pal, Sourav} } @article {45660, title = {Auger decay rates of core hole states using equation of motion coupled cluster method}, journal = {Chemical Physics}, volume = {482 }, year = {2017}, month = {JAN}, pages = {160-164}, type = {Article}, abstract = {The recent development of Linac coherent light source high intense X-ray laser makes it possible to create double core ionization in the molecule. The generation of double core hole state and its decay is identified by Auger spectroscopy. The decay of this double core hole (DCH) states can be used as a powerful spectroscopic tool in chemical analysis. In the present work, we have implemented a promising approach, known as CAP-EOMCC method, which is a combination of complex absorbing potential (CAP) and equation -of-motion coupled cluster (EOMCC) approach to calculate the lifetime of single and double core hole states. We have applied this method to calculate the lifetime of the single core hole (K-LL) and double core hole (KK-KLL) states of CH4, NH3 and HF molecules. The predicted lifetime is found to be extremely short. (C) 2016 Elsevier B.V. All rights reserved.}, doi = {10.1016/j.chemphys.2016.09.038}, author = {Ghosh, Aryya and Vaval, Nayana and Pal, Sourav} } @article {44123, title = {Dissociative adsorption of molecular hydrogen on BN-doped graphene-supported aluminum clusters}, journal = {Journal of Physical Chemistry C}, volume = {121}, year = {2017}, month = {NOV}, pages = {26493-26498}, type = {Article}, abstract = {The present work demonstrates dissociative adsorption of molecular hydrogen on supported and unsupported aluminum Wclusters (Al-n, n = 4-8, 13) using density functional theory based calculations. The studies reveal that the presence of a BN-doped graphene surface support reduces the dissociative adsorption barrier of the bond in molecular hydrogen on even atom clusters. In particular, supported Al-6 demonstrates a barrier-less dissociative adsorption toward the H-2 molecule. These results demonstrate the excellent potential of supported Al nanoparticles for hydrogen storage and also the potential of doped graphene systems are catalyzing supports.}, doi = {10.1021/acs.jpcc.7b07789}, author = {Kumar, Deepak and Krishnamurty, Sailaja and Pal, Sourav} } @article {43802, title = {Effect of ligand attachment on the C-I bond dissociation process on aluminum nanoclusters: a DFT investigation}, journal = {Journal of Physical Chemistry C}, volume = {121}, year = {2017}, month = {AUG}, pages = {17354-17364}, type = {Article}, abstract = {The influence of the ligand attachment on the activation process of carbon halogen bond on small sized aluminum nanoclusters are investigated using density functional theory. Attaching suitable ligand to metal clusters is among the widely popular techniques often used by experimentalists in order to stabilize metastable clusters. In depth theoretical investigations have shown that based on the jellium configuration of the cluster, attaching an electron withdrawing ligand can either make a cluster more reactive toward the C-I dissociation or may convert the cluster relatively inert. The alteration of the activation barriers and other associated parameters due to ligand attachment are included in this paper along with additional calculations and explanations. The study also shows that even the reaction parameters of specific magic clusters can be significantly altered via ligand attachment. The activation process of small molecules on metal clusters are of crucial importance for the development of material science and cluster chemistry. The present investigation will therefore be useful for better understanding of the properties of the ligated clusters as well as may also aid the experimentalists toward controlling the reactivity of a specific cluster as required.}, doi = {10.1021/acs.jocc.7b05470}, author = {Sengupta, Turbasu and Samanta, Bipasa and Pal, Sourav} } @article {45694, title = {Mechanistic investigation of the carbon-iodine bond activation on the niobium-carbon cluster}, journal = {ACS Omega}, volume = {2 }, year = {2017}, month = {SEP}, pages = {5335-5347}, type = {Article}, abstract = {

The activation process of carbon-iodine (C-I) bond on neutral and cationic niobium metcars (Nb8C12) is investigated using density functional theory and related computational techniques. Metallocarbohedrenes or metcars are a class of stable metal-carbide clusters of specific stoichiometry and of great interest to cluster chemists since their first discovery. The detailed reaction mechanism along with the overall energy profile of the C-I dissociation reaction on niobium metcar and its cations is presented in this paper. The tunneling-corrected rate constants and their related reaction parameters such as the pre-exponential factor are also included alongside. The major differences between the reaction mechanism of the neutral and cationic metcars are also highlighted as well. Despite the available experimental results, the C-I bond dissociation on metcars has remained an unexplored problem in the theoretical and computational domains. Thus, the present investigation can fill in the gap and may also provide new insights provoking further developments in cluster and materials chemistry in future.

}, doi = {10.1021/acsomega.7b00894}, author = {Sengupta, Turbasu and Khan, Muntazir S. and Pal, Sourav} } @article {44640, title = {Correlation trends in the magnetic hyperfine structure of atoms: a relativistic coupled-cluster case study}, journal = {Physical Review A}, volume = {98}, year = {2018}, month = {AUG}, type = {Article}, abstract = {

The role of electron correlation in the hyperfine structure of alkali metals and alkaline earth metal monopositive ions in their ground electronic configuration is investigated using the Z-vector method in a relativistic coupled-cluster regime within the singles and doubles approximation. The systematic effects of core-correlating functions, polarization of core electrons, and high-lying virtual functions on core electrons correlation are studied. The study reveals that the core-correlating function plays a significant role in core polarization and thus is very important for precise calculation of the wave function near the nuclear region. The inner-core electrons (1s-2p) require very high virtual energy functions for proper correlation. Therefore, the all-electron correlation treatment and the inclusion of higher-energy virtual functions are the key factors for precise calculation of the hyperfine structure constant of atoms. Our calculated values are in excellent agreement with the available experimental values, which also implies that the wave function produced by the Z-vector method is accurate enough for further calculation of the parity- and time-reversal symmetry-violating properties in atoms and molecules.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.98.022507}, author = {Talukdar, Kaushik and Sasmal, Sudip and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {45371, title = {Dissociative chemisorption of hydrogen molecules on defective graphene-supported aluminium clusters: a computational study}, journal = {Physical Chemistry Chemical Physics }, volume = {20}, year = {2018}, month = {NOV}, pages = {26506-26512}, type = {Article}, abstract = {

Using periodic density functional theory-based calculations, in the present study, we address the chemical bonding between aluminium clusters (Al-n, n = 4-8 and 13) and monovacant defective graphene. The adsorption strength of the above-mentioned aluminium clusters is fivefold (approximate to 3 to 5 eV) higher on defective graphene as compared to the earlier reported values on non-defective graphene and BN-doped graphene. The Bader charge analysis and different charge densities reveal that this adsorption is driven by significant charge transfer from the Al clusters to defective graphene. Thus, chemisorbed Al clusters demonstrate high activity towards dissociative adsorption of molecular hydrogen.

}, issn = { 1463-9076}, doi = {10.1039/c8cp05711g}, author = {Kumar, Deepak and Govindaraja, Thillai and Krishnamurty, Sailaja and Kaliaperumal, Selvaraj and Pal, Sourav} } @article {44617, title = {Lower scaling approximation to EOM-CCSD: a critical assessment of the ionization problem}, journal = {International Journal of Quantum Chemistry}, volume = {118}, year = {2018}, month = {JUL}, pages = {e25594}, abstract = {

In this article, we investigate the performance of different approximate variants of the EOM-CCSD method for calculation of ionization potential (IP), as compared to EOM-CCSDT reference values. None of the lower scaling approximations to the EOM-CCSD method give a consistent performance for valence, inner valence, and core ionization, favoring one, or the other depending on the nature of the approximation used. The parent EOMIP-CCSD method gives superior performance for valence IP but can show large errors for inner valence and core ionization. The problem is particularly severe for core-ionization, where even the EOMIP-CCSDT method cannot provide quantitative accuracy.

}, keywords = {EOM-CCSD, Ionization potential, lower scaling}, issn = {0020-7608}, doi = {10.1002/qua.25594}, author = {Dutta, Achintya Kumar and Vaval, Nayana and Pal, Sourav} } @article {45378, title = {Specificity of amino acid-aluminum cluster interaction and subsequent oxygen activation by the above complex}, journal = {Journal of Physical Chemistry C }, volume = {122}, year = {2018}, month = {DEC}, pages = {28310-28323}, type = {Article}, abstract = {Amino acid aluminum cluster complex has been shown to be a promising oxygen molecule activator and has the potential to dissociate O-O bond on the cluster surface. The study of the complex also reveals specificity of amino acid to aluminum cluster in the above complex, which can be used in the detection of amino acid. The results have been obtained by the density functional theory at the B3LYP/6-311++g(d,p) level of calculation.}, issn = { 1932-7447}, doi = { 10.1021/acs.jpcc.8b08396}, author = {Samanta, Bipasa and Sengupta, Turbasu and Pal, Sourav} } @article {45538, title = {Aluminum cluster for CO and O-2 adsorption}, journal = {Journal of Molecular Modeling}, volume = {25}, year = {2019}, month = {JAN}, pages = {2}, type = {Article}, abstract = {

Low temperature oxidation of CO to CO2 is an important process for the environment. Similarly adsorption of CO from the releasing sources is also of major concern today. Whereas the potential of gold and silver clusters is well proven for thecatalysis of the above mentioned reaction, the potential of aluminum (Al) clusters remains unexplored. The present study proves that, similar to the transition metals, Al clusters can also be used for adsorption of gases. We first tested the potential of Al cluster as adsorbents for CO. The high binding energy (BE) values prove that Al clusters can be used for adsorbing both CO and O-2. Since oxygen binding is more facile, we adsorbed oxygen on Al and then checked the effect of this O-2 on the BE of CO. The results were obtained by DFT calculations at M062X/TZVP level of theory.

}, keywords = {Aluminum clusters, Charge decomposition analysis, CO adsorption, DFT, O-2 adsorption, Wiberg bond indices}, issn = {1610-2940}, doi = {10.1007/s00894-018-3869-3}, author = {Samanta, Bipasa and Sengupta, Turbasu and Pal, Sourav} } @article {46172, title = {Nuclear parity- and time-reversal-symmetry violation in the (HgH)-Hg-201 molecule}, journal = {Physical Review A}, volume = {99}, year = {2019}, month = {MAR }, pages = {032503}, type = {Article}, abstract = {

Investigation of the nuclear magnetic quadrupole moment (MQM) is an excellent way to reveal the new physics in the hadron sector of matter. Therefore, we investigate the violation of parity (P) and time-reversal (T) invariance induced by the MQM of the( 201) Hg nucleus in the HgH molecule, which has been proposed as a very promising candidate for the experimental search of the electric dipole moment of electron [M. G. Kozlov and A. Derevianko, Phys. Rev. Lett. 97, 063001 (2006)]. We report the precise value of the molecular parameter, W-M, associated with the P, T-odd nuclear MQM-electron interaction in (HgH)-Hg-201 using the four-component relativistic coupled-cluster method. This parameter is required to interpret the experimental P, T-odd frequency shift in terms of the MQM of nuclei. Furthermore, the magnetic hyperfine structure (HFS) constants of the molecule are computed at the same level of theory. We also study the role of core-correlating functions and the virtual energy functions in the calculations of the HFS constant and W-M. The most reliable value of W(M )in HgH is obtained as 3.22 x 10 (33) Hz/e cm (2) with an uncertainty of around 6\%.

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.99.032503}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46240, title = {Relativistic coupled-cluster investigation of parity (P) and time-reversal (T) symmetry violations in HgF}, journal = {Journal of Chemical Physics}, volume = {150}, year = {2019}, month = {FEB}, type = {Article}, abstract = {

We employ the Z-vector method in the four-component relativistic coupled-cluster framework to calculate the parity (P) and time-reversal (T) symmetry violating scalar-pseudoscalar nucleus-electron interaction constant (W-s), the effective electric field (E-eff) experienced by the unpaired electron, and the nuclear magnetic quadrupole moment-electron interaction constant (W-M) in the open-shell ground electronic state of HgF. The molecular frame dipole moment and the magnetic hyperfine structure (HFS) constant of the molecule are also calculated at the same level of theory. The outcome of our study is that HgF has a high value of E-eff (115.9 GV/cm), W-s (266.4 kHz), and W-M (3.59 x 10(33) Hz/e cm(2)), which shows that it can be a possible candidate for the search of new physics beyond the standard model. Our results are in good agreement with the available literature values. Furthermore, we investigate the effect of the basis set and the virtual energy functions on the computed properties. The role of the high-energy virtual spinors is found to be significant in the calculation of the HFS constant and the P,T-odd interaction coefficients. Published under license by AIP Publishing.

}, doi = {10.1063/1.5083000}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46641, title = {Electronic structure parameter of nuclear magnetic quadrupole moment interaction in metal monofluorides}, journal = {Journal of Chemical Physics}, volume = {153}, year = {2020}, month = {NOV}, pages = {184306}, type = {Article}, abstract = {

The electronic structure parameter (W-M) of the nuclear magnetic quadrupole moment (MQM) interaction in numerous open-shell metal monofluorides (viz., MgF, CaF, SrF, BaF, RaF, and PbF) is computed in the fully relativistic coupled-cluster framework. The electron-correlation effects are found to be very important for the precise calculation of W-M in the studied molecular systems. The molecular MQM interaction parameter scales nearly as Z(2) in the alkaline earth metal monofluorides, where Z is the nuclear charge of metal. Our study identifies (RaF)-Ra-223 as a good candidate for the experimental search of the nuclear MQM, which can help unravel the physics beyond the standard model in the hadron sector of matter.

}, issn = {0021-9606}, doi = {10.1063/5.0028669}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46600, title = {Negative ion resonance states: the fock-space coupled-cluster way}, journal = {Journal of Physical Chemistry A}, volume = {124}, year = {2020}, month = {DEC}, pages = {10407-10421}, type = {Article}, abstract = {

The negative ion resonance states, which are electron-molecule metastable compound states, play the most important role in free-electron controlled molecular reactions and low-energy free-electron-induced DNA damage. Their electronic structure is often only poorly described but crucial to an understanding of their reaction dynamics. One of the most important challenges to current electronic structure theory is the computation of negative ion resonance states. As a major step forward, coupled-cluster theories, which are well-known for their ability to produce the best approximate bound state electronic eigen solutions, are upgraded to offer the most accurate and effective approximations for negative ion resonance states. The existing Fock-space coupled-cluster (FSCC) and the equation-of-motion coupled-cluster (EOM-CC) approaches that compute bound states are redesigned for the direct and simultaneous determination of both the kinetic energy of the free electron at which the electron-molecule compound states are resonantly formed and the corresponding autodetachment decay rate of the electron from the metastable compound state. This Feature Article reviews the computation of negative ion resonances using the FSCC approach and, in passing, provides the highlights of the equivalent EOM-CC approach.

}, issn = {1089-5639}, doi = {10.1021/acs.jpca.0c09148}, author = {Basumallick, Suhita and Sajeev, Y. and Pal, Sourav and Vaval, Nayana} } @article {46788, title = {Relativistic coupled-cluster study of BaF in search of CP violation}, journal = {Journal of Physics B-Atomic Molecular and Optical Physics}, volume = {53}, year = {2020}, month = {JUL}, pages = {135102}, type = {Article}, abstract = {

BaF is one of the potential candidates for the experimental search of the electric dipole moment of the electron (eEDM). The NL-eEDM collaboration is building a new experimental set up to measure the eEDM using the BaF molecule (The NL-eEDM collaboration, 2018 Eur. Phys. J. D 72: 197). To analyze the results of such an experiment, one would require the accurate value of the molecular P, T-odd interaction parameters that cannot be measured from any experiment. In this work, we report the precise value of the P, T-odd interaction parameters of the BaF molecule obtained from the four-component relativistic coupled-cluster calculations. We also calculate the hyperfine structure (HFS) constants of the same molecule to assess the reliability of the reported molecular parameters. The calculated HFS constants show good agreement with the available experimental values. Further, the systematic effects of electron-correlation along with the roles of inner-core electrons and the virtual energy functions in the calculation of the studied properties of BaF are investigated.

}, keywords = {electric dipole moment of the electron, electron-correlation, Relativistic effects}, issn = {0953-4075}, doi = {10.1088/1361-6455/ab84c8}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46927, title = {Relativistic double-ionization equation-of-motion coupled-cluster method: application to low-lying doubly ionized states}, journal = {Journal of Chemical Physics}, volume = {152}, year = {2020}, month = {MAR}, pages = {104302}, type = {Article}, abstract = {

This article deals with the extension of the relativistic double-ionization equation-of-motion coupled-cluster (DI-EOMCC) method [H. Pathak et al. Phys. Rev. A 90, 010501(R) (2014)] for the molecular systems. The Dirac-Coulomb Hamiltonian with four-component spinors is considered to take care of the relativistic effects. The implemented method is employed to compute a few low-lying doubly ionized states of noble gas atoms (Ar, Kr, Xe, and Rn) and Cl-2, Br-2, HBr, and HI. Additionally, we presented results with two intermediate schemes in the four-component relativistic DI-EOMCC framework to understand the role of electron correlation. The computed double ionization spectra for the atomic systems are compared with the values from the non-relativistic DI-EOMCC method with spin-orbit coupling [Z. Wang et al. J. Chem. Phys. 142, 144109 (2015)] and the values from the National Institute of Science and Technology (NIST) database. Our atomic results are found to be in good agreement with the NIST values. Furthermore, the obtained results for the molecular systems agree well with the available experimental values.

}, issn = {0021-9606}, doi = {10.1063/1.5140988}, author = {Pathak, Himadri and Sasmal, Sudip and Talukdar, Kaushik and Nayak, Malaya K. and Veval, Nayana and Pal, Sourav} } @article {46932, title = {Role of electron correlation in the P, T-odd effects of CdH: a relativistic coupled-cluster investigation}, journal = {Physical Review A}, volume = {101}, year = {2020}, month = {MAR }, pages = {032505}, type = {Article}, abstract = {

We investigate the parity (P) and time-reversal (T) symmetry violating effects in the CdH molecule and perform the relativistic coupled-cluster calculation of the molecular parameters-E-eff, W-s, and W-M-related to the electric dipole moment of electron (eEDM) interaction, the scalar-pseudoscalar (S-PS) nucleus-electron neutral current coupling, and the nuclear magnetic quadrupole moment (MQM) interaction with electrons, respectively. We also compute the molecular dipole moment and the magnetic hyperfine structure coupling constant of CdH. The values of E-eff, W-s, and W-M obtained by us in the said molecule are 12.2 GV/cm, 14.0 kHz, and 0.82 x 10(33) Hz/e cm(2), respectively, within an uncertainty of 10\%. Furthermore, we study the trend of electron-correlation in the computed properties of CdH and that of the P, T-odd parameters in the group-12 monohydrides (i.e., ZnH, CdH, and HgH).

}, issn = {2469-9926}, doi = {10.1103/PhysRevA.101.032505}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} } @article {46959, title = {Shape resonance of sulphur dioxide anion excited states using the CAP-CIP-FSMRCCSD method}, journal = {Molecular Physics}, volume = {118}, year = {2020}, month = {AUG }, type = {Article}, abstract = {

We have studied the shape resonance of excited states of sulphur dioxide (SO2) anion by using the correlated independent particle Fock space multi-reference coupled cluster (CAP-CIP-FSMRCCSD) method augmented by complex absorption potential. These resonant states have been trapped experimentally in recent years by electron collision. In particular, we have investigated e(-)-SO2 scattering and computed the negative-ion resonance states of the anion responsible for the two resonances around 4.45 and 6.56 eV and compared the results with the existing experimental observations. From the computational results using the CAP-CIP-FSMRCCSD method, it has been observed that both the resonances near 4.45 and 6.56 eV result from A(1) symmetries. [GRAPHICS] .

}, keywords = {CAP augmented correlated independent particle (CAP-CIP-FSMRCCSD), complex absorption potential (CAP), coupled cluster, Fock space multireference coupled cluster (FSMRCCSD), shape resonance}, issn = {0026-8976}, doi = {10.1080/00268976.2020.1726521, Early Access Date = FEB 2020}, author = {Basumallick, Suhita and Bhattacharya, Sumantra and Jana, Irina and Vaval, Nayana and Pal, Sourav} } @article {47073, title = {Interatomic Coulombic decay in Neon-Helium cluster: a complex absorbing potential based equation-of-motion coupled cluster investigation}, journal = {Molecular Physics}, volume = {119}, year = {2021}, month = {MAY}, pages = {e1884300}, type = {Article}, abstract = {

The interatomic Coulombic decay (ICD) of the Ne(2s(-1)) and Ne(2s(-1)2p(-1)) states in neon-helium dimer is studied using highly accurate complex absorbing potential based equation-of-motion coupled cluster (CAP-EOMCC) method. The ICD decay process for the Ne(2s(-1)) state in neon-helium dimer is closed at its equilibrium bond distance. However, the decay channel is open at large bond distance of 6.2 angstrom. The decay channel for the double ionised Ne(2s(-1)2p(-1)) state is open at 3.46 angstrom. From our calculations, we have noticed that the decay rate of Ne(2s(-1)2p(-1)) state in neon-helium dimer is four times faster compared to the Ne(2s(-1)) state. We have also investigated how the decay rate of Ne(2s(-1)) state in neon-helium cluster varies in the presence of different helium environment. [GRAPHICS] .

}, keywords = {double ionised state, equation-of-motion coupled cluster (EOMCC), He droplet, interatomic Coulombic decay (ICD)}, issn = {0026-8976}, doi = {10.1080/00268976.2021.1884300, Early Access Date = FEB 2021}, author = {Ghosh, Aryya and Pal, Sourav and Vaval, Nayana} } @article {47358, title = {Resonance study: effect of partial triples excitation using complex absorbing potential-based Fock-space multi-reference coupled cluster}, journal = {International Journal of Quantum Chemistry}, volume = {121}, year = {2021}, month = {SEP}, pages = {e26738}, type = {Article; Early Access}, abstract = {

Resonances are metastable states with finite lifetime. They play important role in physics, chemistry and biology. The theoretical calculation of resonance state is a challenging problem. In this paper we have studied the shape resonance of Be, Mg, N-2 and CO. We have used correlated independent particle approximation to the Fock space multi-reference coupled cluster singles-doubles with third-order triples (CAP-CIP-FSMRCCSD(T)) method augmented by complex absorption potential. The resonance energy and decay widths are obtained by solving a non-Hermitian eigen-value problem within FSMRCC framework. The effects of the lowest order triples on the resonance energy and decay are studied.

}, keywords = {complex absorbing potential, electron affinity, Fock\&\#8208, negative ion resonance, partial triples, space MRCC}, issn = {0020-7608}, doi = {10.1002/qua.26738, Early Access Date = MAY 2021}, author = {Jana, Irina and Basumallick, Suhita and Pal, Sourav and Vaval, Nayana} } @article {48334, title = {Relativistic coupled-cluster study of SrF for low-energy precision tests of fundamental physics}, journal = {Theoretical Chemistry Accounts}, volume = {142}, year = {2023}, month = {FEB}, pages = {15}, type = {Article}, abstract = {

SrF, being a laser-coolable molecule, can be an interesting system for spectroscopic tests of fundamental physics. We present an electronic structure study of this molecule within the four-component relativistic coupled-cluster singles and doubles (RCCSD) framework and employ the RCCSD-based methods to compute its molecular-frame dipole moment and core properties such as hyperfine structure coupling constant and molecular P, T-odd electronic structure parameters that are of great importance for the high-precision tests of fundamental physics. The impact of basis set size, Hamiltonian and nuclear model on the property calculation of SrF is also investigated. The computed results are in good agreement with the available experimental values. The present study shows that the SrF molecule could be useful for high-precision molecular experiments to explore physics beyond the Standard Model of elementary particles.

}, keywords = {Coupled cluster theory, CP violation, Hyperfine structure, Molecular spectroscopy, Relativistic effects}, issn = {1432-881X}, doi = {10.1007/s00214-023-02953-6}, author = {Talukdar, Kaushik and Buragohain, Haimyapriya and Nayak, Malaya K. K. and Vaval, Nayana and Pal, Sourav} } @article {49728, title = {Relativistic extended-coupled-cluster calculations of P , T -odd sensitivity parameters for diatomic molecules}, journal = {Journal of Chemical Theory and Computation}, volume = {21}, year = {2025}, month = {MAY}, pages = {5481-5489}, type = {Article}, abstract = {

We demonstrate the first application of the four-component relativistic extended-coupled-cluster (ECC) method, a variational approach, to determine the P , T -odd molecular electronic structure parameters necessary for high-precision spectroscopic measurements on ultracold molecules. We calculate the P , T -odd sensitivity parameters for two moderately heavy, laser-coolable diatomic molecules (SrH and SrF), as well as two relatively lighter open-shell molecules (CaH and CaF) in their ground electronic state, 2 Sigma 1/2. The hyperfine structure constants of 87Sr in the SrF and SrH molecules are also computed and compared with available experimental results to assess the accuracy of our calculations. Furthermore, we examine the roles of electron correlation, relativity, basis set, and virtual spinors in ECC calculations of the sensitivity parameters. Our study reveals that the ECC method is a reliable technique for studying P , T -odd properties of diatomic molecules such as CaH, CaF, SrH and SrF, yielding results in very good agreement with those obtained using two widely employed analytic approaches: the Z-vector technique and the linear expectation-value method within the relativistic single-reference coupled-cluster singles and doubles framework.

}, issn = {1549-9618}, doi = {10.1021/acs.jctc.5c00329}, author = {Talukdar, Kaushik and Nayak, Malaya K. and Vaval, Nayana and Pal, Sourav} }