Role of finite-temperature dynamics and dispersion interactions on the phonon bandgap in thermoelectric SnSe

Portwin, KA; Galaviz, P; Stamper, CJ; Kutteh, R; Yu, DH; Cheng, ZX; Cortie, DL; Rule, KC

Role of finite-temperature dynamics and dispersion interactions on the phonon bandgap in thermoelectric SnSe

Date

2024-09-18

Authors

Publisher

American Physical Society

Abstract

The low lattice thermal conductivity in tin selenide is key to its excellent thermoelectric properties. The dominant mechanism for this phononic property, however, is debated. Past lattice-dynamic calculations for SnSe consistently predicted the existence of a phonon bandgap, which is puzzling as it has not been observed in spectroscopic experiments and is typically associated with low phonon-scattering rates in contrast to the observed physical properties. In this work, we accurately investigate the size of the phonon bandgap in SnSe using a direct comparison between experimental neutron spectroscopy, lattice-dynamic calculations, and 𝑎⁢𝑏𝑖⁢𝑛⁢𝑖⁢𝑡⁢𝑖⁢𝑜 molecular dynamics. We theoretically investigate the effects of van der Waals interactions in density functional theory calculations using the popular Grimme D2/D3 and semilocal methods and we also assess the effect of finite-temperature driven anharmonicity using Born-Oppenheimer 𝑎⁢𝑏𝑖⁢𝑛⁢𝑖⁢𝑡⁢𝑖⁢𝑜 molecular dynamics. The D2/D3 lattice dynamics calculations, which assume 0 K, predict a phonon bandgap, although the size and structure depends on the details of the van der Waals correction. In contrast, both the experiment and 𝑎⁢𝑏𝑖⁢𝑛⁢𝑖⁢𝑡⁢𝑖⁢𝑜 dynamics identify there is a valley in the density of states at finite temperature, ascribed to strong anharmonicity that shifts specific phonon modes. This finding highlights the need for great care when applying 0 K lattice dynamics and dispersion corrections to SnSe, with general implications for designing thermoelectric materials via computational methods. ©2025 American Physical Society.

Keywords

Temperature range, Phonons, Thermoelectricity, Selenium, Spectroscopy, Neutron spectroscopy, Molecular dynamics method, Crystal lattices, Thermoelectric properties, Density of states, Density functional method, Inelastic scattering, Time-of-flight spectrometers, Molecular dynamics method

Citation

Portwin, K. A., Galaviz, P., Stamper, C., Kutteh, R., Yu, D., Cheng, Z., Cortie, D. L., & Rule, K. C. (2024). Role of finite-temperature dynamics and dispersion interactions on the phonon bandgap in thermoelectric SnSe. Physical Review B, 110(9), 094311. doi:10.1103/PhysRevB.110.094311