Molecular simulation of loading-dependent diffusion in nanoporous materials using extended dynamically corrected transition state theory

Abstract

A dynamically corrected transition state theory method is presented that is capable of computing quantitatively the self-diffusivity of adsorbed molecules in confined systems at nonzero loading. This extention to traditional transition state theory is free of additional assumptions and yields a diffusivity identical to that obtained by conventional molecular-dynamics simulations. While molecular-dynamics calculations are limited to relatively fast diffusing molecules, our approach extends the range of accessible time scales significantly beyond currently available methods. We show results for methane, ethane, and propane in LTL-and LTA-type zeolites over a wide range of temperatures and loadings, and demonstrate the extensibility of the method to mixtures.

Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

“…To obtain a correct diffusion coefficient, all these effects should be taken into account. For a more elaborate discussion on interparticle and time correlations, we refer to the paper of Ala-Nissila et al 35 C. Diffusion Regimes and the Reed-Ehrlich Model. The starting point for our explanation of diffusion on a molecular scale is the Reed-Ehrlich model, which is often used to describe diffusion phenomena.…”

“…κ is the contribution to the diffusion of interparticle collisions, which in general have a lowering effect on the diffusion. For more details about the dcTST method, we refer the reader to ref 35.…”

Dynamically Corrected Transition State Theory Calculations of Self-Diffusion in Anisotropic Nanoporous Materials

“…26,29 We used the velocity Verlet integration scheme with a time step of 0.5 fs. The relative energy drift was smaller than 10 -4 .…”

Molecular Simulations of Zeolites: Adsorption, Diffusion, and Shape Selectivity

“…Applications of these simulations have been reviewed by Keil et al 28 A rigorous extension of transition theory beyond high loadinghasbeenproposedbyDubbeldamandco-workers. [285][286][287] In this technique one computes the free energy barrier of a tagged particle. The contributions of the other particles in the systems are included in this free energy barrier and in the recrossing rate.…”