Incorporation of solvent effects into ab initio molecular orbital calculations by the generalized Born formula. Formulation, parameterization, and applications

A recently developed method for incorporation of solvent effects into ab initio SCF calculations using the generalized Born formula was modified by (i) introducing a steric factor which accounts for the exclusion of the solvent shell of an atom in a molecule by the other atoms, and (ii) re-determination of the parameters used to evaluate the atomic radii which are expressed as a function of the atomic charge obtained by Lowdin population analysis. The hydration free energies of neutral molecules, cations, and anions are calculated semi-quantitatively by the new version of the method. The results of its application to the S(N)2 reaction of Cl- and CH3Cl, the S(N)1 ionic dissociation of t-BuCl, and the internal rotation in formamide are presented. (C) 1997 Elsevier Science B.V.