Thermal transport coefficients for one-and two-component liquids from time correlation functions computed by molecular dynamics

Abstract

The determination of transport coefficients of liquids by molecular dynamics methods is described. Both non-equilibrium (NEMD) and equilibrium molecular dynamics (MD) are considered. However, while the MD is exhaustively treated, NEMD methods are reported only briefly. For the latter, we are only concerned with the so-called subtraction technique. One- and two-component systems are considered modelled by Lennard-Jones 1-centre pair potentials. In some cases also results virtually corresponding to the triple point of argo. However, for comparison with experimental data, we consider further thermodynamic states. For the two-component system, we frequently treat the Ar-Kr system at a liquid state to allow comparison with experimental data. In detail are discussed the time correlation functions for: the self-diffusion coefficient, the mutual diffusion coefficient, the bulk and shear viscosity, the thermal conductivity and the thermal diffusion coefficient (Soret/Dufour effect). The detailed molecular formulation of the various currents, e.g. the pressure tensor elements, are given. The partial contributions of these to the total correlation functions are separately analysed. Technical details of the computations are presented, and the accuracy of the calculated coefficients is thoroughly estimated. Relations to scattering correlation functions are outlined and some results for wave-vector dependent tranport coefficients are presented for comparison. We conclude the article with a limited comparison of computed and measured data for Ar and Ar-Kr.