Computer simulation of a model 2–2 electrolyte: Multiple time-step molecular dynamics

Abstract

A popular model of a 2–2 electrolyte is simulated using a multiple time-step molecular dynamics algorithm. Many authors have used this particular model to test approximate statistical mechanical theories. The ions are assumed to be the same size, and to interact via a continuous potential which behaves as a Coulomb potential at large distances and as an inverse ninth power repulsion at short distances. The ions are embedded in a dielectric continuum of fixed dielectric constant, here taken to be 78.358 to model water at 25 °C. The multiple time-step algorithm outlined here is essential to the success of the simulation. The structure, thermodynamics, and clustering of ions in the electrolyte are examined over the full range of concentrations. Significant corrections are found to earlier Monte Carlo simulations at the concentration 0.005 M, and new results are presented at the concentration 0.001 M.