Shells theory of solvation and the long-range Born correction

Abstract

A new solvation model, named shells theory of solvation, is proposed. In this approach, the solvent is divided in two regions, the S1 shell, close to the solute and describing specific solute–solvent interactions, and the S2 shell, representing the remain solvent and accounting for the long-range interaction contribution. A simple theoretical equation can be derived which allows the computation of the solvation free energy using two-point thermodynamic integration and configurations generated from molecular dynamics simulation. The discrete/continuum version of this theory provides rigorous theoretical foundations for the popular long-range Born correction and presents a new reliable expression for including this contribution. Further, it converges to the full discrete representation of the solvent when the number of solvent molecules goes to infinity. The method can be easily applied when the solute–solvent interaction (S1 shell) is treated by full quantum mechanics, while the S2 shell is described by a dielectric continuum solvation method. A simple test of the theory was done for solvation of fluoride ion in benzene solution. The S1 shell was composed of the fluoride ion plus 32 benzene molecules, and the interaction with the S2 shell was calculated at Hartree–Fock level with the MINI basis set and using the polarizable continuum model.