HEAT-FLOW AND MASS DIFFUSION IN BINARY LENNARD-JONES MIXTURES

We have applied the Evans-Cummings (EC) nonequilibrium molecular-dynamics (NEMD) heat-flow algorithm for liquid mixtures to an equimolar Lennard-Jones (LJ) mixture where the potential parameters and the state point have been chosen to model an argon-krypton mixture at its triple point. We have calculated the thermal conductivity and the Soret coefficient for one 108-particle system and one 1024-particle system. In order to check the results we have used the color conductivity algorithm to obtain the mutual diffusion and the Dufour coefficients. According to the Onsager reciprocity relations the Dufour and the Soret coefficients should be equal, and this has also been found to be the case within the statistical uncertainty. The thermal conductivity and the diffusion coefficient increase slightly with the system size, but the statistical error makes it impossible to discern any size dependence of the cross-coupling coefficients. We also computed the Soret coefficient for three hypothetical types of LJ mixtures. A consistency control was done by evaluating the Green-Kubo (GK) relations for the different transport coefficients by performing an equilibrium molecular-dynamics simulation. The GK thermal conductivity and the diffusion coefficient agree very well with the NEMD results but GK cross-coupling coefficients are very noisy and the error is probably about 15%. The EC algorithm is a NEMD algorithm that violates adiabatic incompressibility of phase space, but this does not cause any difficulties.