@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} } @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: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} } @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 {46640, title = {Investigation of bond topological and electrostatic properties of plumbagin molecule: an experimental and theoretical charge density study}, journal = {Journal of Molecular Structure}, volume = {1220}, year = {2020}, month = {NOV}, pages = {128714}, type = {Article}, abstract = {

Plumbagin is a naturally occurring derivative with several medicinal properties including antioxidants, antifungal, antimalarial, leprosy and antitumor properties; their structural and electrostatic properties are yet to be determined. The crystal structure of plumbagin has been solved; it shows that the compound crystallizes in P2(1)/c space group with two molecules in the asymmetric unit. The electron density distribution of both molecules have determined from multipole model refinement. Among all the C-O bonds of both molecules (I \& II), the OH group connected C-O bond and the methyl group connected C-C bond exhibits less electron density and the negative Laplacian of electron density as well. Further, the electrostatic potential (ESP) surface of two plumbagin molecules show some difference in their electronegative regions. The carbonyl O-atoms exhibit high electronegative ESP regions which are the key reactive locations of plumbagin when bind with the active site of target protein and in the ESP map, an aromatic pi-cloud also observed in one of the molecule. The electron density distribution of O-H center dot center dot center dot O intermolecular interactions between the molecules I and II, reveals that these interactions are found very stronger than the other interactions in the crystal. (C) 2020 Elsevier B.V. All rights reserved.

}, keywords = {Dipole moment, Electron density, Electrostatic potential, intermolecular interactions, Plumbagin}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2020.128714}, author = {Kalaiarasi, Chinnasamy and Sivanandam, Magudeeswaran and Suganya, Suresh and Christy, George and Gonnade, Rajesh G. and Hathwar, Venkatesha R. and Kumaradhas, Poomani} }