Diffusion Model of Lennard-Jones Fluids Based on the Radial Distribution Function

In this paper, a theoretical model for diffusion in Lennard-Jones fluids over a larger density range is proposed. Instead of looking at molecular transport in real space, we treat molecular transport in radial distribution function space. Specifically, the radial distribution function, which reflects the static properties of the system, is used to calculate the mean free path of molecules, a key physical quantity for diffusion modeling. Then, on the basis of the rarefied hard sphere gas diffusion model, and with consideration of the correction of collision frequency and backscattering effect caused by the higher density, the expression of self-diffusion coefficient in Lennard-Jones fluid is obtained. Molecular dynamics was used to simulate the diffusion in Lennard-Jones fluids in a wide range of reduced densities from 0.298 to 1.19 and reduced temperatures from 0.833 to 1.67. Except for small deviations at very high densities, the simulation results agree with the model predictions when the temperature is not too low.