Molecular Dynamics and Hypernetted Chain Equation Studies of Soft Core Repulsions in Electrolyte Solutions

Abstract

Abstract Effects of the repulsive soft core pair potential r−v in 1:1 electrolytes (1 molar concentration) are studied by molecular dynamics (MD) simulations and by the hypernetted chain (HNC) integral equations. Comparisons on the electrolyte structure and dynamical properties are made between a (a) soft ion (SI) model and a (b) soft ion in solution (SIS) model of electrolyte. In the SI model, there is no solvent, whereas the SIS model has ions and neutral solvent molecules at liquid density. Inclusion of the solvent imparts liquid-like structure to the ion-ion pair correlation functions and, if v ≠ ∞, gives rise to substantial back scattering oscillations in the velocity autocorrelation functions with a consequent reduction in the particle self diffusion coefficient. Larger values of v reduce the back scattering in the velocity autocorrelation functions. The dynamical behavior of the ions in the SI model is similar to that of the primitive model electrolyte (θ = ∞) when v ≥ 9. In the SIS fluid, all the ...