Improved Method for the Self-Diffusion Coefficient in the Modified Free Volume Theory: Simple Fluids

In this paper, we further examine the modified free volume (MFV) theory of diffusion in an effort to improve the accuracy of self-diffusion coefficients calculated with the help of the generic van der Waals equation of state. It is shown that the self-diffusion coefficient of the Lennard-Jones (LJ) fluid can be improved significantly over the results obtained by the previously employed method. In the previous method, we have used the hard sphere self-diffusion coefficient for the pre-exponential factor in the MFV theory formula for the self-diffusion coefficient. We show in this paper that if the hard sphere self-diffusion coefficient used for the pre-exponential factor is replaced with the Chapman-Enskog formula for the LJ fluid the accuracy of the self-diffusion coefficient improves impressively in the liquid density for a wide range of temperature.