@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: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: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: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} } @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: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} }