Ab-initio thermal properties of semiconductors with higher order anharmonicities

The thermal properties of semiconductors are affected by the anharmonicity of the interatomic crystal potential. In many semiconductors, inclusion of harmonic and the third-order anharmonic processes involving three phonons are sufficient in accurately reproducing measured thermal properties, such as specific heat and thermal conductivity. However, in highly anharmonic materials and in materials at high temperatures, higher-order anharmonicities and higher-order phonon processes can become important [1, 2]. In this talk, we describe an approach to calculate the ab-initio thermal properties of highly anharmonic semiconductor materials, in which up to fourth order anharmonicity in the crystal potential is included and different types of energy and momentum conserving three and four phonon processes correct to first and second orders in perturbation theory are considered. By evaluating higher order anharmonic contributions to free energy, phonon line shifts and line widths, our work will inform accurate prediction of crystal stability, neutron scattering cross-sections and thermal conductivity of several challenging anharmonic semiconductor crystals.


[1] O. Hellman et al., Phys. Rev. B 87, 104111 (2013)
[2] T. Feng et al., Phys. Rev. B 93, 045202 (2016)