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 rep resenting the halogen molecules and of linear flexible triatomic species mo delling CO2 and CS2 have been carried out in the zeolite silicalite. The ma in purpose was to compare the performance of the random walk model to that of its "two-step'' extension in representing molecular migration inside suc h an interconnected 3-D pore network. The two-step model always gives a bet ter estimate of the elements of the diffusion tensor, and also provides som e interesting insight into the features of the molecular motion of the stud ied species. The analysis of the two-step event probabilities is also appli ed to assess the extent of diffusive memory in each case.