Pseudocontinual model of point dipoles for taking into account solvation in quantum-chemical calculations

A new variant of the point-dipole model has been proposed for taking into account solvation in quantum-chemical calculations by the MNDO and MNDOH methods. The model essentially consists of a dissolved molecule or ion surrounded by point dipoles which are almost continuously and uniformly distributed in space, the dipoles which make significant contributions to the energy of solvation are selected, and the interactions of the selected point dipoles are included in the Hamiltonian. It has been demonstrated in the example of calculations of the energy of hydration of simple ions and several supermolecules consisting of an ion and one or two water molecules that the proposed model provides good quantitative agreement with experiments and that the expenditure of machine time for the performance of calculations with and without consideration of solvation are practically identical. The cross section of the potential-energy surface has been calculated for a model nucleophilic substitution reaction taking place according to an S/sub N/2 mechanism with the consideration of solvation