Does lattice vibration drive diffusion in zeolites?

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Abstract
A method of estimation of the effect of lattice vibration as a driving force for sorbate diffusion in zeolites is proposed. A realistic lattice model is employed to cut off unrealistic long vibrational modes and eliminate feedback due to lattice periodicity. A generalized Langevin equation for sorbate motion is then derived with the magnitude of the lattice vibration captured by two parameters, μ and ν, which can be readily computed for any system. The effect of lattice vibration is then estimated for a variety of sorbate–zeolite pairs. Lattice vibration is found to be a negligible driving force for some systems (e.g., methane and xenon in silicalite) and an important driving force for other systems. In the latter case, the lattice vibration can provide either linear stochastic Langevin-type force (e.g., for benzene in silicalite) or nonlinear deterministic force (e.g., for argon in sodalite).