A theoretical treatment for dealing with the energetics of an arbitrary charge distribution imbedded in a central spherical cavity surrounded by two concentric dielectric continua is described. The results provide a general means for treating environmental effects using the continuum model. The form of the solution is particularly suited to identifying the contributions of the various dielectric regions.

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A theoretical analysis of solvent effects on the conformational stability of a dissolved molecule is presented in terms of statistical thermodynamics. The relationships among the various current approaches to the problem are discussed in this context, together with considerations on their capabilities and limitations. The union of these approaches into a "supermolecule-continuum" model is shown to accommodate the main factors which contribute to solute-solvent interactions. A progression of improved methods for supermolecule-continuum calculations are proposed and the prospects for quantum mechanical calculations in each case are discussed.

The methodology and results of statistical thermodynamic supermolecule-continuum calculations on hydrated ions are described. Configurational averaging is carried out using the site method. Enthalpies, free energies, and entropies are calculated for the tetrahedral and octahedral coordination of the ions Li+, Na+, K+, F~, and Cl-. The calculations utilize accurate quantum-mechanical representations of all interactions in the supermolecular assembly, and include no adjustable parameters. With the exception of the entropies for anions, all values agree satisfactorily with experimental results. The possibility of using extensions of this methodology for theoretical studies of polyatomic molecules in condensed phases is discussed.

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