Viscosity and self-diffusion of simple liquids. Hard-sphere treatment of molecular dynamics data

Abstract

Non-equilibrium molecular dynamics computer simulations performed on the Lennard-Jones, LJ, fluid along the kT/Iµ= 1.46 isotherm give values for the Newtonian shear viscosity, η, that are, upon conversion to real units, in excellent agreement with recent experimental viscosity values for argon. These data are combined with literature LJ η and self-diffusion coefficients, D, to prove the usefulness of an MD-corrected Chapman–Enskog theory for hard-sphere fluid-transport coefficients applied to LJ fluids. The simulation LJ η and D are predicted over the fluid range up to the solid–fluid phase boundary by attaching a temperature-dependent effective hard-sphere diameter to the LJ molecule. This theory is extended to derive expressions for the constant-volume and constant-pressure activation energies, and pressure transport coefficients in terms of the isobaric thermal expansivity and isothermal compressibility of the LJ fluid. The behaviour of these “second-order transport coefficients” along isotherms is discussed, emphasising the relationship between the transport coefficients and thermodynamic properties of the LJ fluid.