Ion-specific excluded-volume correlations and solvation forces.

Realistic ion-ion and ion-surface potentials from explicit-water simulations are used in implicit-solvent Monte Carlo simulations to study the ionic structure and double-layer forces in a nanometer slab confinement. The highly salt-specific results can be reproduced and rationalized by a simple nonlocal Poisson-Boltzmann theory of a nonadditive primitive model, in which effective hard-sphere radii are obtained from the short-ranged part of the pair potentials. Steric corrections to solvation forces are mainly repulsive and strongly coupled to the ion-surface interactions.