• Sankar Prasad Bhattacharyya

      Articles written in Journal of Chemical Sciences

    • CNDO bonding parameters in transition metal atoms

      Sankar Prasad Bhattacharyya

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      The method of calculating CNDO bonding parameters developed recently is extended to transition metal atoms. It is shown that one of the approximations introduced earlier can also be deduced by a more complete treatment of the imbalance problem in CNDO-MO theory. The conventionally calibrated bonding parameters indirectly incorporate important contributions from two-particle interactions. The parameters developed are used to compute the coefficients of metal-to-ligand transfer of spin in many hexafluro metallate ions of transition metals. The results are compared with those obtained by conventional CNDO-MO calculation. Comparison of the computed bonding parameters with other available values is also made.

    • Change of molecular structure in the excited states: A (CNDO/2) hole-potential study on phosphine

      Manas Banerjee Sankar Prasad Bhattacharyya

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      Molecular structure of phosphine in a number of excited electronic states is studied using the method of hole-potential within the basic framework of CNDO/2 theory. Effects of including 3d-functions of phosphorus in the basis set on computed molecular geometries, transition energies and inversion barriers in the excited states have been investigated. An attempt is made to rationalise qualitatively the structural changes in the excitedstate in terms of Walsh-type correlation diagram constructed with the eigenvalues of the Fock operator in theVN-1 potential model. A simple orbital model for predicting the nature of structural changes in the excited states is proposed.

    • Applications of a novel algorithm for the calculation ofMCSCF wavefunction: a look into possible avenues of convergence acceleration

      Kalyan Das Kumar Debashis Mukherjee Sankar Prasad Bhattacharyya

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      The efficacy of a method based on the direct inversion in the iterative subspace (DIIS) in accelerating the approach to self consistency in the calculation of theMCSCF wavefunction using a novel algorithm developed earlier, is compared with that of a simple damping technique. Although the ‘damping’ turns out to be ineffective in the ‘quadratic region’, it accelerates remarkably in the rate of descent on the energy hypersurface in the early stages of the iterative process which leads to an impressive overall increase in the rate of approach to self consistency. TheDIIS based procedure turns out to be ineffective when coupled to the present method and is plagued by ill conditioning problems. Calculations are done to compute the equilibrium geometrical parameter, charge density on different atoms, and dipole moment of HNO molecule in the lowest1,3nπ* states at theINDO/2-MCSCF level.

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