Calculations on the ``Restricted Primitive Model'' for 1–1 Electrolyte Solutions

Abstract

This paper concerns the ``restricted primitive model'' of 1–1 aqueous electrolyte solutions at concentrations up to 2.0M. Monte Carlo data are compared with several recent theoretical treatments: those based on the hypernetted-chain (HNC) equation and the Percus—Yevick—Allnatt (PYA) equation, the mean spherical model, and the mode expansion and γ-ordering approaches. Some new theoretical calculations are reported. The hypernetted-chain treatment appears to be the most successful of the integral equation theories. Of particular interest is the observation of charge oscillation in the radial distribution functions in both the HNC and Monte Carlo calculations. It is also noted that the cube-root concentration dependence of the deviation from ideality, previously observed for real systems, occurs also in accurate treatments of the primitive model. When the diameter of the ions is sufficiently large, the thermodynamic properties of the restricted primitive model approach those of the corresponding uncharged system at very moderate concentrations.