A method to calculate the thermal diffusivity ${\mathit{D}}_{\mathit{T}}$ from spontaneous fluctuations in the local heat energy density is presented. Calculations of the thermal diffusivity are performed for the Lennard-Jones fluid, carbon dioxide, and water. The results for the Lennard-Jones fluid are in agreement with calculations of the thermal conductivity using Green-Kubo relations and nonequilibrium molecular-dynamics techniques. The results for carbon dioxide and water give thermal diffusivities within a factor of 2 of the experimental values.

• Received 4 October 1993

DOI:https://doi.org/10.1103/PhysRevE.49.2049