title: Understanding diffusion in confined systems: methane in a ZK4 molecular sieve. A molecular dynamics simulation study.
abstract: The equilibrium probability distribution of N methane molecules adsorbed in the interior of n alpha cages of the ZK4 zeolite, the all-silica analogue of zeolite A, is modeled by a modified hypergeometric distribution where the effects of mutual exclusion between particles are extracted from long molecular dynamics simulations. The trajectories are then analyzed in terms of time-correlation functions for the fluctuations in the occupation number of the alpha cages. The analysis digs out the correlations induced by the spatial distribution of the adsorbed molecules coupled with a migration mechanism where a molecule can pass from one alpha cage to another, one-by-one. These correlations lead to cooperative motion, which manifests itself as a nonexponential decay of the correlators. Our results suggest ways of developing improved lattice approaches that may be useful for studying diffusion in much larger systems and for a much longer observation time.
authors.affiliation: Universita di Sassari, Dipartimento di Chimica, Via Vienna 2, I-07100 Sassari, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Demontis
authors.forename: L A
authors.initials: LA
authors.lastname: Fenu
authors.forename: G B
authors.initials: GB
authors.lastname: Suffritti