Simulations of phase transitions and free energies for ionic systems

A review of simulation studies of phase equilibria and free energies for systems dominated by coulombic interactions is presented. Phase transitions occur for ionic systems in the strong-coupling limit realized in low-dielectric constant solvents, at low temperatures, or for high charge valences. The majority of simulation results to date are for primitive models that treat the solvent as a uniform dielectric continuum. Transitions involving fluid and solid phases for such models have been studied extensively in the past decade. There is now strong evidence that the vapour-liquid transition is in the Ising universality class. For highly charged colloids the vapour-liquid transition becomes metastable with respect to the fluid-solid transition and the behaviour matches that of charged hard plates. Phase transitions of charged chains illustrate sensitivity of the phase behaviour to the charge pattern. Studies of salt solubilities using models with explicit solvent suggest that reasonable agreement with experiment can be achieved with existing force fields, but there is considerable room for improvement. Areas of future research needs are briefly discussed.