PREDICTION OF ION SOLVATION FREE-ENERGIES IN A POLARIZABLE DIELECTRIC CONTINUUM

An improved model for the prediction of free energies of ionic solvation has been developed and tested. Dielectric saturation effects have been included in the analysis by solving simultaneously the modified Laplace equation for the electric potential and the Booth equation for the potential-dependent solvent permittivity. The free energy change was determined using the conventional Born cycle with an additional work term to account for the energy which must be added to the solvent to return the aligned solvent molecules to their original state prior to ion charging. In contrast to other free energy theories, the present model has no adjustable parameters. Solvation free energies were computed for alkali metal, alkaline earth, and transition metal cations and simple anions in water and for univalent cations and anions in three nonaqueous solvents (methanol, 1,1-dichloroethane, and acetonitrile). When a Goldschmidt scale radius was used for the ions, predicted free energies were within 14% of experimental values.