Canonical ensemble molecular dynamics simulations of Lennard-Jones methane and ethane were performed for an atomistic model of AIPO4-5; a molecular sieve having approximately cylindrical channels of diameter 7-3Å. Methane molecules were able to pass each other in the nanopore and exhibited unidirectional but otherwise ordinary diffusion along the channel axis, with the mean-squaredisplacement directly proportional to time, and a diffusion coefficient calculated at a loading of 0.7 molecules per unit cell at 295K of 4-70 x 10-4cm2/s. Ethane molecules could not pass each other easily in the nanopore and for short times exhibited single-file diffusion. That is, the mean-square displacement was proportional to the square root of the time. At longer times, contributions of ordinary unidirectional diffusion were observed due to the non-zero probability of passing. A slightly larger molecule exhibited pure single-file diffusion. The single-file mobility for the large molecule at 0.7 molecule per unit cell and 295K was 1.57 x 10-9cm/s0.5. The density dependence of the single-file mobility was in agreement with one-dimensional hard rod predictions.

Unidirectional and Single-File Diffusion in AlPO4-5: Molecular Dynamics Investigations. Keffer, D., Mccormick, A.V., Davis, H.T.: Molecular Physics, 1996, 87[2], 367-87