Thermal diffusion factors for the Lennard-Jones/spline system

A steady-state, molecular-dynamics method is used to calculate the thermal diffusion factor α for binary isotopic mixtures at a single, supercritical temperature. The variation of α with density, composition, and the isotope mass ratio is examined for a system of particles having a Lennard-Jones/spline interparticle pair potential. The Lennard-Jones/spline potential is a finite-ranged modification of the Lennard-Jones potential. We compare the calculated values of α with those from revised Enskog theory, modified Enskog theory, and an approximation suggested by Haase. None of these theories compares well with the molecular dynamics calculations, although modified Enskog theory and a scaled version of revised Enskog theory provide reasonable estimates of α over a limited range of low densities.