The tracer diffusion of methane molecules in the unidirectional channels of the phosphate was studied by means of molecular dynamics simulations. A 1-dimensional hop-and-cross model was introduced and was shown to be able to reproduce the molecular dynamics results accurately, as well as shortening the computational time. After eliminating the system-size effect by using the new model, 2 regimes could be identified. One was a short-term regime in which the mean square displacement was proportional to t0.6, and the other was a long-term regime in which the proportionality was linear.

Unidirectional Diffusion of Methane in AlPO4. H.L.Tepper, J.P.Hoogenboom, N.F.A.Van Der Vegt, W.J.Briels: Journal of Chemical Physics, 1999, 110[23], 11511-6