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Abstract

The equilibrium structure of aqueous Na-Cl electrolytes in the concentration regime between 1 and 5 mol l-1 is studied by means of a molecular dynamics computer simulation using interaction-site descriptions of water and the ionic components. The electrostatic interactions are treated both with the newly developed charged-clouds scheme and with Ewald summation. In the case of a 5 mol l-1 electrolyte, the results for pair correlations obtained by the two methods are in excellent agreement. However, the charged-clouds technique is much faster than Ewald summation and makes simulations at lower salt concentrations feasible. It is found that both ion-water and ion-ion correlation functions depend only weakly on the ionic concentration. Sodium and chloride ions exhibit only a negligible tendency to form contact pairs. In particular, no chloride ion pairs in contact are observed.