Gusev and Suter calculation of the diffusion coefficients of light gases in silicalite-1 membrane and silica-sodalite zeolite

Transition-state theory (TST) as implemented by Gusev and Suter was applied to calculate the zero-loading-diffusion coefficients of 12 gases (He, Ne, Ar, Xe, H-2, N-2, O-2, CO2, SF6, CH4, CF4, and i-C4H10) in two different zeolites, silicalite-1 and silica-sodalite. GuSeV-Suter (GS) model was and is widely and Successfully used for polymeric matrixes. Therefore, the reliability of this method was studied for gas diffusion in silicalite-1 and silica-sodalite using CVFF-aug and CVFF force fields and two simulation cells. The results were compared with diffusion coefficients used to reproduce the permeance in a silicalite-1 membrane. Model limits were also tested comparing the H-2, He and Ne diffusion in silica-sodalite with previous calculations of classical and quantum TST. Gusev-Suter method systematically underestimates the average diffusion coefficients of the considered gases: underestimation was less marked for species larger than methane. The ratio between D-x and D-y components in silicalite-1 was found near one differently from the expected result. The diffusion coefficients obtained using Gusev-Suter approach in silicalite-1 and silica-sodalite can be improved with an appropriate average displacements definition, set in this work equal to 0. Concerning the anisotropy diffusion in silicalite-1, this work shows that correlated jumps in a Gusev-Suter procedure would also be considered. Gusev-Suter computational time for diffusivity estimation of Xe, CF4, CO2 and SF6 is much shorter than the corresponding molecular dynamics (MD) simulation time. (C) 2003 Elsevier B.V. All rights reserved.