The importance of various degrees of freedom in the theoretical study of the diffusion of methane in silicalite-1

The self diffusion coefficient of methane in silicalite-1 is influenced by the flexibility of the lattice unlike the self diffusion coefficient of methane in the cation-free zeolite of type A. In the present paper, besides the influence of lattice vibrations on this process, the influence of internal vibrations of the methane molecule and the applicability of several spherical models of this molecule are examined. The method of moments [Chem. Phys. Lett. 198 (1992) 283] is generalized to anisotropic diffusion.