Canonical ensemble molecular dynamics simulations were made of methane diffusion in AlPO4-5 in order to estimate the role of lattice motion in adsorbate diffusivity in straight-pore zeolites. Both a static-lattice model and a fully dynamic lattice model were used at a loading of 1.5CH4/unit-cell at 295K. Although previous simulation work had implied that there should be a difference in behaviour, it was shown that there was little difference in the observed CH4 diffusivity (1.26 x 10-7m2/s) and passing frequency (0.305) when a static lattice approximation was used instead of a fully dynamic lattice model (1.33 x 10-7m2/s, 0.328). A method was introduced for the handling of lattice motion in molecular simulations. This involved the use of the normal vibrational modes in an harmonic crystal approximation.

The Effects of a Dynamic Lattice on Methane Self-Diffusivity Calculations in AlPO4. K.T.Thomson, A.V.McCormick, H.T.Davis: Journal of Chemical Physics, 2000, 112[7], 3345-50