Theory and simulation of jump dynamics, diffusion and phase equilibrium in nanopores

Abstract

We review theory and simulation of rare event dynamics, diffusion and phase equilibrium in nanopores, focusing on benzene in Na-X and Na-Y zeolites because of persistent experimental discrepancies. We discuss transition state theory and its application to zeolite-guest systems, suggesting that calculations on flexible lattices and at finite guest loadings are important areas for future research. We consider many-body adsorption and diffusion in zeolites, focusing on the coupling between rare event dynamics and strong guest-guest interactions. We explore the possibility that benzene can undergo phase transitions from low to high sorbate density in Na-X, and find that this type of phase transition might explain intriguing loading dependencies of water and ammonia diffusion in terms of a subcritical droplet picture of adsorption in zeolites. We discuss various formulations of non-equilibrium diffusion through finite lattices, and describe a tracer counter-permeation simulation technique. We find that transport in finite single-file systems is characterized by a diffusivity that decreases monotonically with file length, but that this transport is otherwise completely described by Fick's laws. We conclude by speculating on the prospect for cross-fertilization between zeolite science and other fields.