@article { ISI:000230091400031, title = {Analytically continued Fock space multireference coupled-cluster theory: application to the (2)Pi(g) shape resonance in e-N-2 scattering}, journal = {Journal of Chemical Physics}, volume = {122}, number = {23}, year = {2005}, month = {JUN}, pages = {234320}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

The technique of Fock space multireference coupled-cluster (FSMRCC) is applied for the first time to the correlated calculation of the energy and width of a shape resonance in an electron-molecule collision. The procedure is based upon combining a complex absorbing potential with FSMRCC theory. Accurate resonance parameters are obtained by solving a small non-Hermitian eigenvalue problem. The potential-energy curve of the (2)Pi(g) state of N-2(-) is calculated using the FSMRCC and multireference configuration-interaction (MRCI) level of theories. Comparison with the single-determinant Hartree-Fock theory indicates that correlation effects are important in determining the behavior of the resonance state. (C) 2005 American Institute of Physics.

}, issn = {0021-9606}, doi = {10.1063/1.1938887}, author = {Sajeev, Y and Santra, R and Pal, S} } @article { ISI:000233661000012, title = {Correlated complex independent particle potential for calculating electronic resonances}, journal = {Journal of Chemical Physics}, volume = {123}, number = {20}, year = {2005}, month = {NOV}, pages = {204110}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {CIRCULATION \& FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 USA}, abstract = {

We have formulated and applied an analytic continuation method for the recently formulated correlated independent particle potential [A. Beste and R. J. Bartlett J. Chem. Phys. 120, 8395 (2004)] derived from Fock space multireference coupled cluster theory. The technique developed is an advanced ab initio tool for calculating the properties of resonances in the low-energy electron-molecule collision problem. The proposed method quantitatively describes elastic electron-molecule scattering below the first electronically inelastic threshold. A complex absorbing potential is utilized to define the analytic continuation for the potential. A separate treatment of electron correlation and relaxation effects for the projectile-target system and the analytic continuation using the complex absorbing potential is possible, when an approximated form of the correlated complex independent particle potential is used. The method, which is referred to as complex absorbing potential-based correlated independent particle (CAP-CIP), is tested by application to the well-known (2)Pi(g) shape resonance of e-N-2 and the B-2(2g) shape resonance of e-C2H4 (ethylene) with highly satisfactory results. (c) 2005 American Institute of Physics.

}, issn = {0021-9606}, doi = {10.1063/1.2130338}, author = {Sajeev, Y and Santra, R and Pal, S} } @article { ISI:000231714000001, title = {Electronic spectra and ionization potentials of halogen oxides using the fock space coupled-cluster method}, journal = {Collection of Czechoslovac Chemical Communications}, volume = {70}, number = {7}, year = {2005}, month = {JAN}, pages = {851-863}, publisher = {INST ORGANIC CHEM AND BIOCHEM}, type = {Article}, address = {ACAD SCI CZECH REPUBLIC, FLEMINGOVO NAM 2, PRAGUE 6 166 10, CZECH REPUBLIC}, abstract = {

The ionization potentials and excitation energies of halogen monoxides and dihalogen oxides are studied using fully size-extensive Fock space version of multi-reference coupled-cluster theory. The low-lying excited states of ClO-, FO-, Cl2O and F2O are obtained along with the ionization spectra of Cl2O and F2O. The adiabatic electron affinity of ClO, FO and the vertical detachment energy of ClO- and FO- are also presented.

}, issn = {0010-0765}, doi = {10.1135/cccc20050851}, author = {Vaval, N and Manohar, Prashant Uday and Pal, S} } @article { ISI:000230485700031, title = {General formalism of the Fock space multireference coupled cluster method for investigating molecular electronic resonances}, journal = {Molecular Physics}, volume = {103}, number = {15-16}, year = {2005}, month = {AUG}, pages = {2267-2275}, publisher = {TAYLOR \& FRANCIS LTD}, type = {Article}, address = {4 PARK SQUARE, MILTON PARK, ABINGDON OX14 4RN, OXON, ENGLAND}, abstract = {

Electron correlation and relaxation effects play a substantial role in the formation and decay of resonance states. In this paper we formulate a complex absorbing potential combined with the Fock space multireference coupled cluster method for the correlated calculations of resonance energy and width. This can describe the dynamic and non-dynamic electron correlation efficiently in the ionized or electron attached states.

}, keywords = {electronic resonances, Fock space multireference coupled cluster method}, issn = {0026-8976}, doi = {10.1080/00268970500084158}, author = {Sajeev, Y and Pal, S} } @article { ISI:000230698100036, title = {Optimization of nonlinear optical properties by substituent position, geometry and symmetry of the molecule: an ab initio study}, journal = {Journal of Physical Chemistry B}, volume = {109}, number = {29}, year = {2005}, month = {JUL}, pages = {14093-14101}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Static polarizability and first- and second-order hyperpolarizability tensors are computed at the correlated level for a series of para-nitroaniline derivatives. The importance of including electron correlation effects in the determination of equilibrium structure and the molecular properties is investigated. A qualitative description of the substitution effects, planarity, and symmetric effect of the molecule on the molecular susceptibility is discussed.

}, issn = {1520-6106}, doi = {10.1021/jp051355d}, author = {Davis, D and Sreekumar, K and Sajeev, Y and Pal, S} } @article { ISI:000232909100017, title = {Separability of local reactivity descriptors}, journal = {Journal of Chemical Sciences}, volume = {117}, number = {5}, year = {2005}, month = {SEP}, pages = {497-505}, publisher = {INDIAN ACAD SCIENCES}, type = {Article}, address = {C V RAMAN AVENUE, SADASHIVANAGAR, P B \#8005, BANGALORE 560 080, INDIA}, abstract = {

The size-dependence of different local reactivity descriptors of dimer A(2) and AB type of systems is discussed. We derive analytic results of these descriptors calculated using finite difference approximation. In particular, we studied Fukui functions, relative electrophilicity and relative nucleophilicity, local softness and local philicity. The results are explained using the example of the dimer of BH3NH3.

}, keywords = {condensed Fukai functions, Local reactivity descriptors, molecular interactions, separability}, issn = {0974-3626}, doi = {10.1007/BF02708355}, author = {Tanwar, A and Pal, S} } @article { ISI:000231534100002, title = {On the single-root approach within the framework of coupled-cluster theory in fock space}, journal = {Chemical Physics}, volume = {315}, number = {3}, year = {2005}, month = {AUG}, pages = {240-250}, publisher = {ELSEVIER SCIENCE BV}, type = {Article}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

A thorough formulation of Fock Space Brillouin-Wigner Coupled Cluster method is presented following previous developments [N.D.K. Petraco, L Horny, H.F. Schaefer, I. Hubac, J. Chem. Phys. 117 (2002) 9580]. The new method is designed to avoid the intruder states problem, and introduces the single-root solution feature which has not been considered yet within valence-universal methods. The explicit equations for the (0,1) sector of the Fock space are introduced. (C) 2005 Elsevier B.V. All rights reserved.

}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2005.03.020}, author = {Horny, L and Schaefer, HF and Hubac, I and Pal, S} }