  The free energy of ion solvation can be decomposed into enthalpic and
entropic contributions. This helps to understand the connection between the
dielectric properties and the underlying forces. We present a simple
linear-response model of screened charge interactions that provides an
alternative understanding of solvation barriers. Moreover, it explains the
"anti-Coulomb" interactions (attraction between like-charged ions and repulsion
between opposite-charged ions) observed in both simulations and experiments. We
show that this is a universal behavior associated to the non-local response
function of any dielectric or metallic system.
