Na–Cl ion pair association in supercritical water

Molecular dynamics simulations of supercritical electrolyte solutions with three different ion–water models are performed to study the anion–cation potential of mean force of an infinitely dilute aqueous NaCl solution in the vicinity of the solvent’s critical point. The association constant for the ion pair Na/Cl and the constant of equilibrium between the solvent-separated and the contact ion pairs are determined for three models at the solvent critical density and 5% above its critical temperature. The realism of the aqueous electrolyte models is assessed by comparing the association constants obtained by simulation with those based on high temperature conductance measurements. Some remarks are given concerning the calculation of the mean-force potential from simulation and the impact of the assumptions involved. © 1995 American Institute of Physics.