Predicting Accurate Phonon Spectra: An Improved Description of Lattice Dynamics in Thermoelectric Clathrates Based on the SCAN Meta-GGA Functional

Abstract

Due to their thermoelectric properties, intermetallic clathrates are technologically highly interesting materials. Especially their strongly reduced lattice thermal conductivity has been largely investigated and strongly debated. Although density-functional-theory-based lattice dynamics calculations have helped clarify the thermal transport in clathrates, significant discrepancies remain between experiment and theory, especially in Ge-based clathrates. In this work, we show that the recently released meta-generalized-gradient approximation functional SCAN (strongly constrained and appropriately normed) is able to overcome these issues and provide a much improved agreement between the experimental and the theoretical phonon spectra, thus enabling quantitative predictions of the clathrate phases with a high potential for thermoelectric applications.