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Abstract: We present density functional theory (DFT) calculations using B3LYP/6-31++G∗∗ method to show relaxation in geometry of base pairs on cation radical formation. The changes in hydrogen bond length and angles show that in the cationic radical form the structure of the base pairs relaxes due to the distribution of charge. According to a recent study, it has been found that, upon excitation hole transfer from base to sugar occurs which results in sugar radical formation and leads to strand breakage [A. Kumar, M.D. Sevilla, J. Phys. Chem. B 110 (2006) 24181]. One hydrogen bond increases, while the other decreases in Adenine–Thymine (AT) base pair and in case of Guanine–Cytosine (GC) base pair, one bond increases and other two decrease. Same is the case with bond angles for both the base pairs. Analysis of the electron density map of Singly Occupied Molecular Orbital (SOMO) reveals that electron is transferred mainly from adenine and guanine bases in the cationic radical formation of AT and GC base pair, respectively. The reactive sites of bases have been analyzed using condensed Fukui functions in a relaxed and frozen core approximation. The effects of relaxation on the reactivity indices are also analyzed. [Copyright &y& Elsevier]

Abstract: We consider a series of dipolar organic molecules where the donor groups and the acceptor groups are separated by π-conjugation like phenyl ring or alkene chains. We have performed extensive quantum chemical calculations based on density functional theory (DFT) to calculate their linear and non-linear optical coefficients. We show that though DFT is known to overestimate the polarizabilities of quasi-linear systems, the results with proper inclusion of exchange correlation compare well with the experimental studies. On increasing the π-conjugation length, the coefficients increase non-linearly. We also vary the donor and the acceptor groups and study the role of chemical modifications on the response properties. Herein we suggest experimental methods by which the molecules may be arranged in non-centrosymmetric fashion in the bulk for device integration. [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]

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. [Copyright &y& Elsevier]