Equilibrium molecular dynamics and grand canonical Monte Carlo simulations were used to compute the diffusivities of CH4 and CF4, adsorbed in a fully atomistic model of silicalite, over a wide range of temperatures and pore loadings. The results provided a direct test of the accuracy of the Darken approximation. The latter was accurate for CH4 in silicalite at 298K, but was less accurate at higher temperatures. On the other hand, CF4 deviated strongly from the Darken approximation at all temperatures.

Direct Tests of the Darken Approximation for Molecular Diffusion and Conduction in Zeolites using Equilibrium Molecular Dynamics. A.I.Skoulidas, D.S.Sholl: Journal of Physical Chemistry B, 2001, 105[16], 3153-4