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We show that the centroid molecular dynamics (CMD) method provides arealistic way to calculate the thermal diffusivity $a=\lambda/\rho c_{\rm V}$of a quantum mechanical liquid such as para-hydrogen. Once $a$ has beencalculated, the thermal conductivity can be obtained from $\lambda=\rho c_{\rmV}a$, where $\rho$ is the density of the liquid and $c_{\rm V}$ is theconstant-volume heat capacity. The use of this formula requires an accuratequantum mechanical heat capacity $c_{\rm V}$, which can be obtained from a pathintegral molecular dynamics simulation. The thermal diffusivity can becalculated either from the decay of the equilibrium density fluctuations in theliquid or by using the Green-Kubo relation to calculate the CMD approximationto $\lambda$ and then dividing this by the corresponding approximation to $\rhoc_{\rm V}$. We show that both approaches give the same results for liquidpara-hydrogen and that these results are in good agreement with experimentalmeasurements of the thermal conductivity over a wide temperature range. Inparticular, they correctly predict a decrease in the thermal conductivity atlow temperatures -- an effect that stems from the decrease in the quantummechanical heat capacity and has eluded previous para-hydrogen simulations. Wealso show that the method gives equally good agreement with experimentalmeasurements for the thermal conductivity of normal liquid helium.

Nuclear quantum effects in thermal conductivity from centroid molecular dynamics