Solvatons. II. Aqueous dissociation of hydrides in the MINDOS approximation

A simple electrostatic model of solvation is presented which allows the interaction with solvent to be included systematically within semiempirical SCF calculations. Solvent effects are incorporated into the Hamiltonian for a solute molecule through a series of imaginary particles, solvatons, which represent the oriented solvent distribution around the solute.The proposed model is based on an algorithm for approximating the enthalpy of solvation of each atomic center from its charge in the molecular system and the experimental hydration enthalpies of its various ions. The calculated atomic solvation energy of one center is then modified to include the interaction with other charged atomic centers in the molecule. The method, developed here for the MINDO/3 approximation, has been applied to the calculation of the aqueous dissociation of a series of hydrides. In general, it leads to fairly accurate solvation enthalpies andpK_a values when applied to systems with fixed molecular geometries. A general discussion of the problems associated with the development of a solvation model within a semiempirical framework is also presented.