Studies in Molecular Dynamics. VIII. The Transport Coefficients for a Hard-Sphere Fluid

Abstract

The diffusion coefficient, the shear and bulk viscosity, and the thermal conductivity have been evaluated by means of their Einstein expressions by molecular dynamics computation over the entire fluid region. The autocorrelation functions for the different transport coefficients as well as their various components (such as kinetic and potential) have been obtained also. The results are compared to the predictions of the Enskog theory which involves a nearly exponential autocorrelation function. The observed deviations from an exponentially decaying autocorrelation function persist for many mean collision times, indicating that highly collective effects must be involved. The largest deviations for the transport coefficients occur near solid densities for the viscosity which is about twice as large as the Enskog prediction and for the diffusion coefficient which is about a factor of 2 smaller. In conformity with the Stokes relation, the product of diffusion and viscosity is found to be nearly constant over the entire fluid density range and in nearly quantitative agreement with the theoretically predicted constant using slipping boundary conditions. The deviations from the Enskog theory for the thermal conductivity are barely perceptible within the few percent accuracy of the data. The same is true for the bulk viscosity with its larger inaccuracies.