Shear viscosity and thermal conductivity of the Lennard-Jones liquid computed using molecular dynamics and predicted by a memory function model for a large number of states

Abstract

For a large number of states, we have compared the thermal conductivity, λ, and the shear viscosity, η_s, of the Lennard-Jones fluid computed by equilibrium molecular dynamics (MD) and predicted by a memory function model. We used a simple gaussian model for the memory function and determined the parameters, i.e. the normalizing constant and the decay time, from the moments of the correlation function which were additionally computed by MD. For η_s the agreement between MD and the memory function results is within 10–20 per cent except for states near the ‘triple point’ of argon. The agreement between the results for λ is somewhat worse, particularly for lower densities. The reason for this is the remarkable negative part of the ‘exact’ memory function observable for all the states considered in this work. Comparison with the η_s and λ values calculated by Luckas and Lucas showed good agreement for the shear viscosity but significant discrepancies for the thermal conductivity. Accounting properly for the partial enthalpy in the heat current definition, which was neglected by those authors, we obtained λ-values in accordance with the present memory function results.