A microscopic theory of solvation of monoions

The solvation free energies of ions are often computed using continuum theories, like the Born model. The Born model has the disadvantages that to fit experimental data, ionic radii are taken as adjustable parameters and you need to know the dielectric constant. We present here a more microscopic treatment for computing the free energies of ion solvation in water. Like the Born model, it gives an expression that is simple and can be computed quickly, but unlike the Born model, it uses true ionic radii and does not require inputting a dielectric constant. We show that the present model gives predictions for the free energies of transfer of alkali and halide ions into water that are in excellent agreement with recent experimentally derived estimates.