A non-equilibrium molecular simulation method had been developed that permitted the direct study of interdiffusion in multi-component mixtures. The method combined stochastic insertion and deletion moves characteristic of grand canonical simulations with molecular dynamics to control the chemical potential μi of a species i. Restricting the insertions and deletions to two separate control volumes one could apply different μi in distinct locations, and thus create chemical potential gradients. These methods could be used to study transient phenomena such as the filling of micropores or used in steady-state mode to determine the diffusion coefficients in multi-component fluid mixtures. The effects of molecular interactions were reported and it was demonstrated how, in a sufficiently non-ideal ternary mixture, this could lead to up-hill or reverse diffusion. In addition a novel extension was introduced that was specifically designed for the study of gradient-driven diffusion of molecules that were too large to be inserted and deleted.

Gradient-Driven Diffusion using Dual Control Volume Grand Canonical Molecular Dynamics (DCV-GCMD). Van Swol, F., Heffelfinger, G.S.: Materials Research Society Symposium - Proceedings, 1996, 408, 299-304