AN ADVANCED CONTINUUM MEDIUM MODEL FOR TREATING SOLVATION EFFECTS - NONLOCAL ELECTROSTATICS WITH A CAVITY

The Born-Kirkwood-Onsager (BKO) model of solvation, where a solute mol ecule is positioned inside a cavity cut into a solvent, which is consi dered as a dielectric continuum, is studied within the bounds of nonlo cal electrostatics. The nonlocal cavity model is explicitly formulated and the corresponding nonlocal Poisson equation is reduced to an inte gral equation describing the behavior of the charge density induced in the medium. It is found that the presence of a cavity does not create singularities in the total electrostatic potential and its normal der ivatives. Such singularities appear only in the local limit and are co mpletely dissipated by nonlocal effects. The Born case of a spherical cavity with a point charge at its centre is investigated in detail. Th e corresponding one-dimensional integral Poisson equation is solved nu merically and values for the solvation energy are determined. Several tests of this approach are presented: (a) We show that our integral eq uation reduces in the local limit to the chief equation of the local B KO theory. (b) We provide certain approximations which enable us to ob tain the solution corresponding to the preceding nonlocal treatment of Dogonadze and Kornyshev (DK). (c) We make a comparison with the resul ts of molecular solvation theory (mean spherical approximation), as ap plied to the calculation of solvation energies of spherical ions. (C) 1996 American Institute of Physics.