Improving bulk thermoelectric materials using heat conduction calculations based on first principles

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We developed a multiscale phonon transport calculation tool by seamlessly combining density functional theory, lattice dynamics, molecular dynamics, and Monte-Carlo methods to analyze phonon-mode dependent thermal transport in single crystal, substitutional alloy, and nanostructured bulk thermoelectric materials. We have targeted half-Heusler compounds, lead chalcogenides, and magnesium silicide as the base materials. After validating the calculation in comparison with experiments, extended calculations were performed for alloyed crystals to clarify the dependence of the thermal conductivity reduction on the composition ratio. Furthermore, through calculations of cumulative thermal conductivity and thermal conductivity spectra, we have identified the appropriate class of nanostructure for each base materials.