It was recalled that traditional models of single-file diffusion in zeolites assumed that the adsorbate diffusion at high and dilute pore loadings was identical. Atomistic models of single-file systems had instead shown that clusters of adsorbed molecules could diffuse via concerted motions that were not available to individual adsorbates. Molecular dynamics simulations of CF4 clusters in AlPO4-5 and Xe clusters in AlPO4-31 were reported here. These simulations were used to characterize the diffusion and dissociation mechanisms and rates of the clusters as a function of temperature and cluster size. Using kinetic Monte Carlo simulations of coarse-grained models, pores containing hundreds of interacting clusters were simulated at microsecond time-scales. These simulations offered the first opportunity to examine single-file diffusion in models that accurately accounted for the existence of concerted cluster diffusion. The simulations showed that concerted cluster motions made large contributions to single-file mobility. Deviations of computed single-file mobilities from well-known results for hard-sphere diffusion were considered.

Influences of Concerted Cluster Diffusion on Single-File Diffusion of CF4 in AlPO4-5 and Xe in AlPO4-31. D.S.Sholl, C.K.Lee: Journal of Chemical Physics, 2000, 112[2], 817-24