Comparisons between experimental argon and Lennard-Jones 12:6 shear viscosities

Abstract

A detailed description of the methodology for obtaining the shear viscosity of model liquids by non-equilibrium molecular dynamics computer simulation is made. This includes the choice of the algorithm for integrating the translational equations of motion. The method of virtual trajectories for obtaining the linear (“zero shear rate”) shear viscosity is outlined. There is good agreement with recent measurements of the experimental shear viscosity of argon and the corresponding Lennard-Jones equivalent fluid, at high density and temperature. This data is combined with the self-diffusion coefficients via the Stokes-Einstein relationship and it suggests an increasing effective flow unit diameter with decreasing density. Insights into the detailed microscopic origins for this are provided by velocity and force autocorrelation functions, radial distribution and fluctuation functions, and structure factors. The use of fluctuation expressions for the shear moduli and viscosities are shown to compare unfavourably in statistical accuracy with those furnished by non-equilibrium molecular dynamics.