Thermodynamics of electrolyte solutions in the modified mean spherical approximation

Abstract

The exact Ornstein–Zernike formalism for ionic fluids is seen to be equivalent to the dressed-ion theory (DIT), therefore proving the exact character of this mean-field formalism. The modified mean spherical approximation (MMSA) [Varela et al., J. Chem. Phys. 109, 1930 (1998)] is a modified version of the mean spherical approximation, which corrects some of the deficiencies of the original version of this closure relation in the prediction of the effective screening length. The MMSA effective non-Debye decay length, developed in the framework of the dressed-ion transport theory (DIT) of Kjellander and Mitchell, is an improvement on those of other theoretical and numerical schemes, which include self-consistent second moment approaches, asymptotic expansions, and nonlinear Debye–Hückel approximations. The MMSA screening length is used to analyze thermodynamic magnitudes of the charged fluid such as the internal energy and the osmotic coefficient and the results are seen to fit accurately to hypernetted chain calculations.