Thermal conductivity of half-Heusler compounds from first-principles calculations

We demonstrate successful application of first-principles-based thermal conductivity calculation on half-Heusler compounds that are promising, environmentally friendly thermoelectric materials. Taking the case of a p-type half-Heusler structure, the harmonic and anharmonic interatomic force constants were obtained from a set of force-displacement data calculated by the density functional theory. Thermal conductivity was obtained by two different methods: (1) Boltzmann-Peierls formula with phonon relaxation times calculated by either Fermi's golden rule of three-phonon scattering processes or spectral analysis of molecular dynamics phase space trajectories and (2) Green-Kubo formula for heat current obtained by equilibrium molecular dynamics simulations. The calculated temperature dependence of thermal conductivity is in reasonable agreement with experiments. The method was extended to alloy crystals assuming the transferability of interatomic force constants. By having access to accurate phonon-dependent transport properties, the contribution from an arbitral subset of phonon modes can be quantified. This helps understanding the influence of nanostructures on thermal conductivity.