Diffusion of inert gases in silica sodalite: Importance of lattice flexibility

It is known that some zeolites are able to adsorb sorbates with diameters larger than their pore size. This ability is usually explained by the flexibility of zeolite lattices. In this paper we quantify this explanation by incorporating lattice flexibility into transition state theory to compute transport rates of inert gas molecules (Ne, Ar and Kr) through narrow windows of silica sodalite cages. We find that the diffusion rates obtained with the flexible zeolite lattice are in much better agreement with experiment than those with a rigid lattice, as stretching of the zeolite window considerably reduces the activation barrier.