Application of the two-step model to the diffusion of linear diatomic and triatomic molecules in silicalite

Molecular dynamics simulations of the diffusion of diatomic oscillators representing the halogen molecules and of linear flexible triatomic species modelling CO2and CS2have been carried out in the zeolite silicalite. The main purpose was to compare the performance of the random walk model to that of its "two-step" extension in representing molecular migration inside such an interconnected 3-D pore network. The two-step model always gives a better estimate of the elements of the diffusion tensor, and also provides some interesting insight into the features of the molecular motion of the studied species. The analysis of the two-step event probabilities is also applied to assess the extent of diffusive memory in each case.