Transport Anomalies in the Gaussian Core Model Fluid

Abstract

In this study, we investigate the self-diffusion coefficient, the shear viscosity and the thermal conductivity of a single-component system interacting via a Gaussian core (GC) potential. The transport properties are studied by means of the Green-Kubo formulas calculated from molecular dynamics simulation. We show that, for certain state conditions, anomalous behaviour occurs for the diffusivity and the shear viscosity. Therefore, the Stokes-Einstein relation is violated for the GC fluid. We do not find anomalous behaviour for the thermal conductivity. We develop an equation of state for the deviation of the ideal gas pressure and we derive the excess entropy from this equation. Depending on the phase space region, the excess entropy also shows anomalous behaviour. We discuss recently developed scaling relationships between excess entropy and transport properties. Because the GC potential is bounded, these relationships do not work properly for the GC fluid. Using new empirical scaling relations we are able to fit the diffusion coefficient within one single master curve for the whole density and temperature range we have simulated. We were also able to find a single master curve for the viscosity, but only for state conditions where the classical Stokes-Einstein relation is valid.