Heat flow and mass diffusion in binary Lennard-Jones mixtures. II.

Abstract

We have used the Evans-Cummings (EC) nonequilibrium-molecular-dynamics (NEMD) heat-flow algorithm for liquid mixtures to calculate the thermal conductivity and the Dufour coefficient of a binary Lennard-Jones mixture. A consistency check has been carried out by applying the NEMD color-conductivity algorithm to evaluate the mutual diffusion and the Soret coefficients, which, according to the Onsager reciprocal relations, are equal. Further checking was carried out by comparing these NEMD results with equilibrium Green-Kubo calculations. This work extends that recently carried out by us [S. Sarman and D. J. Evans, Phys. Rev. A 45, 2370 (1992), hereafter referred to as I] to a much lower density and higher temperature than that studied in I. At this state point the Soret and Dufour coefficients are much larger than their corresponding triple-point values in I. This enables considerably more accurate checks of algorithm validity. The NEMD and the Green-Kubo estimates for the thermal conductivity and the mutual diffusion coefficients agree within statistical uncertainties of about 2%. The difference between the cross-coupling coefficients obtained by the various methods is more than twice as accurate as in I, namely, 6% compared to 15%. This provides a convincing check of the correctness of the EC algorithm. We have also developed a way of applying the EC algorithm that increases the accuracy of estimates of the Dufour coefficient. When this method was applied to the triple-point fluid, the results agreed with those in I; however, the errors were reduced by a factor of 3.