Cage-to-Cage Jumps of Xenon in Zeolite NaY: Transmission Coefficients from Molecular Dynamics Simulations

The diffusion of xenon in zeolite NaY at low temperatures is studied by molecular dynamics simulations of individual trajectories started at the cage-to-cage boundary. Transmission coefficients are obtained from the normalized reactive-flux correlation function. Recrossings of the cage-to-cage boundary by xenon atoms at very low temperatures are attributed to instantaneous shifts of the maximum of the potential energy along the diffusion path. At higher temperatures there are increasingly many recrossings due to the slow energy transfer from guest atoms to the zeolite lattice: The xenon atom can pass several energy barriers during one activation period. The individual jumps are investigated by introducing an absorbing barrier surrounding the two supercages on both sides of the central cage-to-cage boundary.