ABSTRACT
A method for the simultaneous determination of the thermal conductivity λ and the shear viscosity η 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 λ and η. The influence of the magnitude of and on λ and η is investigated. The cross-effects are negligible, even for large gradients. The same holds for the influence of on λ. However, there is a significant influence of on η, i.e. shear-thinning. The two-gradient method is applied in different ways: for small temperature-averaged values of λ and η 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 λ and η, also results for the self-diffusion coefficient D are determined from evaluating the mean squared displacement. The new two-gradient method is robust, efficient and yields accurate results.
GRAPHICAL ABSTRACT
Acknowledgments
The present research was conducted under the auspices of the Boltzmann-Zuse Society for Computational Molecular Engineering (BZS).
Disclosure statement
No potential conflict of interest was reported by the authors.
ORCID
Martin P. Lautenschlaeger http://orcid.org/0000-0003-3266-4218