This work demonstrated a general method for simulating multi-component diffusion in concentrated solutions using molecular dynamics. Although there were prior reports of molecular dynamics simulations of diffusion in multi-component systems, no fully rigorous expressions were reported for simulating Stefan-Maxwell diffusivities for an arbitrary number of species. The Green-Kubo approach developed here allowed for the computation of a full diffusion-coefficient matrix for any number of species. The development was applicable to any solution that could be simulated using molecular dynamics; nevertheless, the primary interest was in electrochemical applications. To this end, the method was tested by simulations of aqueous KCl and NaCl salt solutions in the concentration range of 1 to 4m. Intermolecular potentials were parameterized for these transport-based simulations. This work was the first to simulate all three independent diffusion coefficients for these solutions. The results were in semi-quantitative agreement with experiment and showed that Green-Kubo calculations were realizable for concentrated electrolytes and other solutions.

Molecular Dynamics Simulations of Multicomponent Diffusion. 1. Equilibrium Method. Wheeler, D.R., Newman, J.: Journal of Physical Chemistry B, 2004, 108[47], 18353-61