Single particle dynamics of molecular hydrogen in carbon nanotubes

We present the results of classical molecular dynamics simulations of hydrogen in an array of carbon nanotubes at T = 293 K and various densities. The self-diffusion coefficient is found to be higher for molecules inside the carbon tubes. The microscopic mechanism of self-diffusion is studied through the velocity autocorrelation function using the memory function approach. A simple phenomenological model is able to reproduce all the characteristic of single particle motion for molecules confined inside and outside the nanotube array in the whole range of densities. We discuss the physical meaning of the parameters of our model and the origin of the enhanced diffusion for molecules inside the tube with respect to the interstitial ones. (C) 2003 Elsevier B.V. All rights reserved.