The diffusional isotope effect of a binary Lennard-Jones liquid was calculated using molecular dynamics simulations for mass differences of 20 to 40%. At equilibrium density, a strong reduction in the isotope effect was found with decreasing temperature, for both species. This reflected a marked increase in the collectivity of motion. Upon changing the density at a constant temperature the same effect was seen for the larger majority atoms. This showed that the density change was the main driving force behind the reduction of the isotope effect. Although the smaller minority atoms also exhibited a decrease in the isotope effect with increasing density, the relationship of the isotope effect to temperature and density differed for the two species.

Isotope Effect in the Diffusion of Binary Liquids. H.R.Schober: Solid State Communications, 2001, 119[2], 73-7