The self-diffusion coefficient in the gas phase at moderate densities,obtained by computer simulations

The self-diffusion coefficient for Lennard-Jones molecules has been determined by molecular dynamics for densities up to the critical one and for temperatures ranging from T = 1.3∈/k to T = 5.56∈/k. At low density, the results are in a good agreement with the theoretical predictions; at elevated densities agreement with the available experimental results is found, although the scarcity of experimental data prevents a general comparison between real systems and the molecular dynamical calculations.Additional computations with different pair-potentials lead to results which throw some doubts on the reliability of the so-called Modified Enskog Theory.