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
![](/cms/asset/c70001ae-29b6-41f3-a72d-2c23f7d5c621/tmph_a_1504134_uf0001_c.jpg)
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