@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: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:000318320300033, title = {Multipole moments using extended coupled cluster method}, journal = {Chemical Physics Letters}, volume = {568}, year = {2013}, month = {MAY}, pages = {170-175}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Using analytic extended coupled cluster (ECC) response approach quadrupole moments, dipole-quadrupole polarizabilities and dipole polarizabilities are studied. In the current implementation of the functional we have included all the double linked terms within (CCSD) approximation. These terms will be important for the accurate description of properties at the stretched geometries. We report the properties for carbon monoxide and hydrogen fluoride molecules, as a function of bond distance and compare our results for carbon monoxide with the full Cl results. We have also reported the properties of methane, tetrafluoromethane, acetylene, difluoroacetylene, water and ammonia. (C) 2013 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2013.03.013}, author = {Joshi, Sayali P. and Vaval, Nayana} } @article { ISI:000342545900037, title = {Extended coupled cluster method for potential energy surface: a decoupled approach}, journal = {Chemical Physics Letters}, volume = {612}, year = {2014}, month = {SEP}, pages = {209-213}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Extended coupled cluster (ECC) method has been implemented extensively for the calculation of molecular properties. In this Letter we report the potential energy surface (PES) study using coupled and a decoupled approximation of ECC. HF, N-2 and C-2 are studied as test systems. N-2 and C-2 being doubly and triply bonded, are considered to be interesting systems for PES study. We compare our results with full CI (FCI) results wherever available. Decoupled approach within ECC framework shows good convergence for all the molecules. (C) 2014 Elsevier B.V. All rights reserved.

}, issn = {0009-2614}, doi = {10.1016/j.cplett.2014.08.016}, author = {Joshi, Sayali P. and Vaval, Nayana} }