ABSTRACTA method for the simultaneous determination of the thermal conductivity λ and the shearviscosity η of fluids by non-equilibrium molecular dynamics simulations is presented and testedusing the Lennard-Jones truncated and shifted fluid as example. The fluid is studied under thesimultaneous influence of a temperature gradient∂T/∂y and a velocity gradient ∂v/∂y and the resulting heat flux and momentum flux are measured todetermine λ and η. The influence of the magnitude of ∂T/∂y and ∂v/∂y on λ and η is investigated.The cross-effects are negligible, even for large gradients. The same holds for the influenceof ∂T/∂y on λ. However, there is a significant influence of ∂v/∂y on η, i.e.shear-thinning. The two-gradient method is applied in different ways: for small ∂T/∂ytemperature-averaged values of λ and η are obtained. As ∂T/∂y has no significant influenceon the results, simulations with large ∂T/∂y are evaluated using the local-equilibriumassumption, such that values are obtained at different temperatures in a single simulation. Inaddition to the results for λ and η, also results for the self-diffusion coefficient D aredeterminedared displacement. The new two-gradient method is d yields accurate results.
Simultaneous determination of thermal conductivity and shear viscosity using two-gradient non-equilibrium molecular dynamics simulations
