Structure and thermodynamics in the linear modified Poisson-Boltzmann theories in restricted primitive model electrolytes

TL;DR

This paper evaluates three linear modified Poisson-Boltzmann theories for restricted primitive model electrolytes, demonstrating their high accuracy in predicting thermodynamic and structural properties compared to simulations and other theories.

Contribution

It introduces and compares three recent linear modified Poisson-Boltzmann theories, showing their effectiveness in accurately predicting electrolyte thermodynamics and structure.

Findings

Linear theories predict osmotic and activity coefficients accurately.

Predicted structures match well with formal theories and simulations.

Analytical equivalence of excess energy and activity coefficient in certain theories.

Abstract

Structure and thermodynamics in restricted primitive model electrolytes are examined using three recently developed versions of a linear form of the modified Poisson-Boltzmann equation. Analytical expressions for the osmotic coefficient and the electrical part of the mean activity coefficient are obtained and the results for the osmotic and the mean activity coefficients are compared with that from the more established mean spherical approximation, symmetric Poisson-Boltzmann, modified Poisson-Boltzmann theories, and available Monte Carlo simulation results. The linear theories predict the thermodynamics to a remarkable degree of accuracy relative to the simulations and are consistent with the mean spherical approximation and modified Poisson-Boltzmann results. The predicted structure in the form of the radial distribution functions and the mean electrostatic potential also compare well with the corresponding results from the formal theories. The excess internal energy and the electrical part of the mean activity coefficient are shown to be identical analytically for the mean spherical approximation and the linear modified Poisson-Boltzmann theories.