Correlations and free energies in restricted primitive model descriptions of electrolytes.

The pair and triplet correlations of a restricted primitive model (RPM) description of aqueous NaCl solutions have been computed in the concentration regime 0.5–4 M via Monte Carlo simulations, using both the method of configuration statistics and the particle insertion (chemical potential) method. Comparison of the triplet data to Kirkwood’s superposition approximation and the Abe and convolution approximations shows that deviations occur only for distances close to contact. The entropy computed via the entropy expansion including terms up to third order and the insertion method is dominated essentially by packing effects. The pair correlations and thermodynamic properties derived from the simulations were compared to the hypernetted chain (HNC) approximation which was found to be very good corroborating the conclusions drawn from earlier RPM studies. [ABSTRACT FROM AUTHOR]