Viscosity calculations of n -alkanes by equilibrium molecular dynamics

Abstract

We report shear viscosity results obtained using extensive equilibrium molecular dynamics simulations. By direct numerical comparison, we show the equivalence of the Green-Kubo and Einstein approach to the calculation of viscosity in both the atomic and molecular representations. Comparing the results for two models of linear alkanes, we discuss the molecular factors determining their low-temperature liquid-state transport properties. In the mass range considered here $\mathrm{(⩽}{\mathrm{C}}_{16}\mathrm{),}$ large corrections to Rouse-dynamics scaling are observed, as expected. We indicate, however, how the scaling relation between rotational-diffusion-time and shear-viscosity still provides a semi-quantitative way of estimating the latter, using simulations which are at least one order of magnitude shorter than required for direct determination of viscosity for n-alkanes.