Evidence of fifth- and higher-order phonon scattering entropy of zone-center optical phonons

Authors of recent studies have established the significance of fourth-order anharmonicity in the linewidth of zone-center optical phonons, while it is unknown whether the fifth- and even higher-order phonon scattering is important. In this paper, we estimate the convergence of phonon scattering entropy with respect to perturbation orders. Using density functional perturbation theory, we calculate the three- and four-phonon linewidths for zone-center optical phonons in a series of zinc-blende III--V compounds including InP, c-GaN, BN, AlSb, GaP, InSb, AlAs, InAs, GaSb, and AlP. Our results show that, although the agreement between theory and experiment is greatly improved by incorporating four-phonon scattering, considerable discrepancies still exist, especially at high temperatures. We reveal that, on average, the phonon scattering entropy converges well at the eighth order, and the fifth- and higher-order phonon scattering entropy is about 37% of that of four-phonon scattering at Debye temperature and increases with temperature. With four-, five-, and higher-order phonon scattering included, the linewidth deviates largely from the linear scaling with temperature. In this paper, we provide evidence of the higher-than-fourth-order lattice anharmonicity in zone-center optical phonon linewidths as well as Raman and infrared spectra.