A new interpretation of the effective Born radius from simulation and experiment

We show, from molecular dynamics simulations of ions of varying charge and size in TIP3P water, that the effective Born radius is an average of Rion, the ionic radius, and Rgmax, the first peak position in the ion–solvent radial distribution function. This relationship has been validated for `realisticʹ ions using experimental Rgmax. It implies that the correct solvation free energy expression is a combination of two Born free energies; one for the bare ion of radius Rion and the other for its associated solvent shell of radius Rgmax. Implications of the new solvation free energy formula are discussed.