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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, O3, 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. [ABSTRACT FROM AUTHOR]

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 S4 to S6 as well as the excitation operator from four bosons to six bosons. A good agreement with full configuration interaction results has been observed with S6 truncation at coupled-cluster method level and six bosonic excitations at CCLRT level. [ABSTRACT FROM AUTHOR]

A thorough study on the nature of Mulliken population analysis (MPA) based condensed Fukui function (FF) indices has been performed. It is claimed analytically that nothing can be predicted about the sign of condensed FF indices, even when evaluated by using very small fractional molecular charge (i.e., approximately following the analytical definition of FF indices). The corresponding numerical demonstrations on different chemical systems confirm our claim. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The correlated static-exchange potential for LiH and H2 molecules has been studied using many-body coupled cluster technique. A general trend has been observed. Its importance to the low energy scattering of electrons from these diatomic targets has been pointed out. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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 2 V 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. [ABSTRACT FROM AUTHOR]

In this article, we present analytical dipole moments and dipole polarizabilities of oxygen monofluoride and nitrogen dioxide using the recently developed constrained variational approach in Fock-space multi-reference coupled-cluster singles and doubles (CVA-FSMRCCSD) method. Both these molecules are important in atmospheric chemistry. The near-degeneracy in low-lying states of these molecules demands for MR description of the wavefunction. We also report our study of variation in the properties of oxygen monofluoride with respect to basis set. Benchmark results, wherever available, have been duly reported for comparison. [ABSTRACT FROM AUTHOR]

A fully relaxed analytic extended coupled cluster response method is presented for molecular properties. The inclusion of orbital relaxation in extended coupled cluster method is expected to improve molecular properties away from equilibrium. A fully relaxed model of extended coupled cluster method is tested using hydrogen fluoride and boron hydride at various geometries. [Copyright &y& Elsevier]

In this paper, we present linear and non-linear electric properties of BH, CO and H2O using a density functional response approach, which is a combination of numerical and analytical technique and is thus a simplification of fully analytic method. In the framework of an analytic response approach using Kohn–Sham (KS) density functional theory, the derivative of the KS operator with respect to external field is evaluated numerically, while the orbital derivatives and the subsequent energy derivatives are obtained fully analytically. The method is tested using three molecules BH, CO and H2O, which are marked by high degree of electron correlation and for which extensive ab initio benchmark results are available. Further, we have made a study of possible incorporation of non-dynamical electron correlation by studying BH at several inter-nuclear distances. [Copyright &y& Elsevier]

Extended coupled-cluster method has emerged as a compact method for study of energies and electric properties of molecules and extended systems. In this Letter, we present a linear response to the above method for study of magnetizabilities of small test molecules. Specifically, we have presented results of diamagnetic and paramagnetic magnetizabilities of HF and CO in appropriate basis sets and studied the gauge dependence and basis set dependence of the properties evaluated through the above method. The results have been compared with SCF and NCC values, as well as experimental values. [Copyright &y& Elsevier]