An equilibrium-molecular-dynamics study of diffusion of a heteronuclear diatomic fluid in random pore systems was reported. The pore space was generated by the use of a simple percolation technique on a tessellation of three-dimensional space with periodic boundary conditions. Simulations using the rattle algorithm at constant temperature were performed on the percolating cluster only where the substrate atoms were explicitly represented and the substrate-fluid and fluid-fluid interactions were modelled using Lennard-Jones potentials. Using this technique, results were presented for a heteronuclear diatomic molecule (CO-like) within a graphite-like system for porosities between the percolation threshold and φ=0.99, and at 100 to 1500K at atmospheric pressure. The results, which included mean-square-displacement and velocity-autocorrelation functions, indicated once again that mass diffusion within porous media was fundamentally different from that in the bulk phase. The degree of anomalous behavior tended to decrease with temperature and porosity. Although this was the case, the mean-square-displacement exponent in the long-time limit for the lower porosities (φ=0.312 and φ=0.4) increased with temperature to a limiting value much less than one in the vicinity of T=300K. Trends in the velocity-autocorrelation functions seen here were reported in past Lorentz gas simulation studies. Effective diffusion coefficients for the gas-in-pore system were calculated from the velocity-autocorrelation functions these appeared to vary exponentially with porosity and inverse temperature. This temperature variation was similar to that of a liquid in the bulk phase and hence brings into doubt the use of a temperature-independent tortuosity that related the diffusion coefficient of a gas in the bulk phase to that within porous media

Mass Diffusion of Diatomic Fluids in Random Micropore Spaces using Equilibrium Molecular Dynamics. Biggs, M., Agarwal, P.: Physical Review E, 1994, 49[1], 531-7