Computing the Heat Conductivity of Fluids from Density Fluctuations.

Area of Science:

• Computational physics
• Materials science
• Chemical engineering

Background:

• Equilibrium molecular dynamics (EMD) with the Green-Kubo (GK) method is standard for liquid thermal conductivity.
• The GK method's reliance on a heat flux definition complicates its use for systems with nonpairwise interactions.

Purpose of the Study:

• To develop an unambiguous method for calculating thermal conductivity in bulk fluids.
• To overcome the limitations of the Green-Kubo method for complex interaction potentials.

Main Methods:

• Utilizing a hydrodynamic description of thermally driven density fluctuations.
• Validating the new method against the Green-Kubo approach for pairwise interacting systems.

Main Results:

• The hydrodynamic method provides unambiguous thermal conductivity calculations, independent of heat flux definitions.
• Consistent results were obtained when comparing with the Green-Kubo method for simple fluids.
• Successfully computed thermal conductivity for supercritical water and high-pressure liquid hydrogen.

Conclusions:

• The hydrodynamic approach offers a robust and unambiguous alternative for thermal conductivity calculations.
• This method is particularly valuable for systems with nonpairwise interactions and complex potentials, such as machine-learned interatomic potentials.