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Molecular dynamic simulations of viscosity of argon at high pressures

A new formulation of the boundary conditions in Couette flow geometry was used to enforce a no-slip condition at the boundaries. This condition was used employing two counter-moving boundaries to enforce the symmetry of the flow. Molecular dynamics (MD) simulations employing Lenard–Jones potential were performed to derive shear force, the gradient of the velocity, and consequently, the shear velocity. MD simulations were preformed for high pressures, up to 1 GPa, and low temperatures, up to 500 K, i.e. for the region dominated by the interaction potential. The obtained results were compared with the existing experimental data [E.W. Lemmon and R.T. Jacobsen, Viscosity and thermal conductivity equations for nitrogen, oxygen, argon, and air, Int. J. Thermophys. 25(1) (2004), pp. 21–69]. It is shown that MD results are in very good agreement with the experiments, having a difference not higher than 4% for all the considered results. From the analysis of these results, it also follows that the dominant portion of the error is due to insufficiently precise determination of the velocity gradient in MD simulations.