  We demonstrate that with two small modifications, the popular dielectric
continuum model is capable of predicting, with high accuracy, ion solvation
thermodynamics in numerous polar solvents, and ion solvation free energies in
water--co-solvent mixtures. The first modification involves perturbing the
macroscopic dielectric-flux interface condition at the solute--solvent
interface with a nonlinear function of the local electric field, giving what we
have called a solvation-layer interface condition (SLIC). The second
modification is a simple treatment of the microscopic interface potential
(static potential). We show that the resulting model exhibits high accuracy
without the need for fitting solute atom radii in a state-dependent fashion.
Compared to experimental results in nine water--co-solvent mixtures, SLIC
predicts transfer free energies to within 2.5 kJ/mol. The co-solvents include
both protic and aprotic species, as well as biologically relevant denaturants
such as urea and dimethylformamide. Furthermore, our results indicate that the
interface potential is essential to reproduce entropies and heat capacities.
The present work, together with previous studies of SLIC illustrating its
accuracy for biomolecules in water, indicates it as a promising dielectric
continuum model for accurate predictions of molecular solvation in a wide range
of conditions.
