Transport properties in liquids from first principles: the case of liquid water and liquid Argon

TL;DR

This study uses first-principles molecular dynamics within DFT to evaluate shear and bulk viscosities of liquid water and Argon, providing new estimates for water and confirming the accuracy of the approach for both liquids.

Contribution

First-principles calculations of shear and bulk viscosities for liquid water and Argon, including the first estimates for water's bulk viscosity from such methods.

Findings

First-principles simulations describe water's dynamical properties at ~330 K.

The bulk-viscosity/shear-viscosity ratio for water is estimated for the first time.

Predicted thermal conductivity of liquid Argon matches experimental data.

Abstract

Shear and bulk viscosity of liquid water and Argon are evaluated from first principles in the Density Functional Theory (DFT) framework, by performing Molecular Dynamics simulations in the NVE ensemble and using the Kubo-Greenwood equilibrium approach. Standard DFT functional is corrected in such a way to allow for a reasonable description of van der Waals (vdW) effects. For liquid Argon the thermal conductivity has been also calculated. Concerning liquid water, to our knowledge this is the first estimate of the bulk viscosity and of the shear-viscosity/bulk-viscosity ratio from first principles. By analyzing our results we can conclude that our first-principles simulations, performed at a nominal average temperature of 366 K to guarantee that the systems is liquid-like, actually describe the basic dynamical properties of liquid water at about 330 K. In comparison with liquid water, the normal, monatomic liquid Ar is characterized by a much smaller bulk-viscosity/shear-viscosity ratio (close to unity) and this feature is well reproduced by our first-principles approach which predicts a value of the ratio in better agreement with experimental reference data than that obtained using the empirical Lennard-Jones potential. The computed thermal conductivity of liquid Argon is also in good agreement with the experimental value.