Distributed polarizabilities derived from induction energies:: A finite perturbation approach

An approach based on finite perturbation theory is proposed for deriving models of distributed polarizabilities from quantum mechanically determined induction energies. It relies on the construction of a grid of points, over which the induction energy resulting from the interaction of a charge with the molecule of interest is evaluated at the desired level of approximation. Distributed polarizabilities of any order are then fitted by solving the normal equations of the least-squares problem, the solution of which provides an optimal description of induction effects. The method is probed by examining several models of distributed polarizabilities of increasing complexity in the case of water, methanol, acetonitrile, and benzene. At a reasonable order of multipole expansion, atomic polarizabilities derived using this approach are found to reproduce the corresponding molecular polarizabilities with an appropriate accuracy. The careful choice of the parameters to be fitted appears to be a key factor for obtaining physically realistic models. (C) 2000 American Institute of Physics. [S0021-9606(00)50704-1].