The isotope effect in a binary Lennard-Jones liquid was studied by means of molecular dynamics simulations. Mass differences of 20 to 40% were used. At equilibrium density, with decreasing temperature, a strong reduction in the isotope effect was found for both species. This indicated 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 underlying the reduction in the isotope effect. Although the smaller minority atoms also exhibited a drop in isotope effect with increasing density, the relationship of the isotope effect to temperature and density differed for the 2 species.

Isotope Effect in the Diffusion of Binary Liquids. H.R.Schober: Solid State Communications, 2001, 119[1], 73-7