A microscopic model for calculations of chemical processes in aqueous solutions

A new microscopic model for calculations of chemical processes in aqueous solutions is presented. The model, referred to here as the “surface constrained soft sphere dipoles” (SCSSD) model avoids the problems of the continuum models by explicitly including the solvent molecules. Each solvent molecule is represented as a point dipole attached to the center of a soft sphere. The solvation energy is evaluated by minimizing the solute-solvent energy with respect to the orientations and positions of those dipoles while constraining the surface dipoles to have the orientations and positions of the bulk solvent. The model is demonstrated by calculating the energetic of charge separation in aqueous solution and evaluating the corresponding dielectric constant. The SCSSD model can be used for quantitative studies of ionic reactions in solutions. This is demonstrated by calculation of the potential surface for the dissociation of formic acid in aqueous solution.