Simultaneous determination of thermal conductivity and shear viscosity using two-gradient non-equilibrium molecular dynamics simulations

<p>A method for the simultaneous determination of the thermal conductivity <i>λ</i> and the shear viscosity <i>η</i> of fluids by non-equilibrium molecular dynamics simulations is presented and tested using the Lennard-Jones truncated and shifted fluid as example. The fluid is studied under the simultaneous influence of a temperature gradient and a velocity gradient and the resulting heat flux and momentum flux are measured to determine <i>λ</i> and <i>η</i>. The influence of the magnitude of and on <i>λ</i> and <i>η</i> is investigated. The cross-effects are negligible, even for large gradients. The same holds for the influence of on <i>λ</i>. However, there is a significant influence of on <i>η</i>, i.e. shear-thinning. The two-gradient method is applied in different ways: for small temperature-averaged values of <i>λ</i> and <i>η</i> are obtained. As has no significant influence on the results, simulations with large are evaluated using the local-equilibrium assumption, such that values are obtained at different temperatures in a single simulation. In addition to the results for <i>λ</i> and <i>η</i>, also results for the self-diffusion coefficient <i>D</i> are determined from evaluating the mean squared displacement. The new two-gradient method is robust, efficient and yields accurate results.</p