Diffusion anomaly from analytical formula

An analytic expression is derived for the diffusion coefficient of a sorbate in a crystalline porous solid with bottlenecks. The diffusion coefficients obtained from the analytic expression is found to agree well with the molecular dynamics results. It is also found to reproduce the temperature dependence of the levitation effect for zeolites Y and A. The present calculations provide a strong theoretical support for the levitation effect obtained so far purely from molecular dynamics calculation