Incorporating the Excluded Solvent Volume and Surface Charges for Computing Solvation Free Energy

Gauss's law or Poisson's equation is conventionally used to calculate solvation free energy. However, the near-solute dielectric polarization from Gauss's law or Poisson's equation differs from that obtained from molecular dynamics (MD) simulations. To mimic the near-solute dielectric polarization from MD simulations, the first-shell water was treated as two layers of surface charges, the densities of which are proportional to the electric field at the solvent molecule that is modeled as a hard sphere. The intermediate water was treated as a bulk solvent. An equation describing the solvation free energy of ions using this solvent scheme was derived using the TIP3P water model. (c) 2013 Wiley Periodicals, Inc.