Comparison and evaluation of spectral energy methods for predicting phonon properties

Two frequency-domain methods for predicting phonon frequencies and lifetimes using the phonon spectral energy density are described. Both methods draw input from molecular dynamics simulations and lattice dynamics calculations, but differ in the form of the phonon spectral energy density. One phonon spectral energy density expression (referred to as Φ) can be formally derived from lattice dynamics theory. A similar approach in the time domain has been validated [Turney et al. Phys. Rev. B 79, 224305 (2009)]. The other phonon spectral energy density expression (referred to as Φ′) has been proposed [Thomas et al., Phys. Rev. B 81, 081411(R) (2010)] but not validated. The expressions for Φ and Φ′ are presented and then applied to predict the phonon properties and thermal conductivities of three systems: LennardJones argon, Stillinger-Weber silicon, and a carbon nanotube modeled using the Reactive Empirical Bond Order potential. Φ′ does not capture the total phonon spectral energy density predicted by Φ and therefore cannot correctly predict the phonon lifetimes or thermal conductivity. Its use in future work is discouraged and we recommend the use of Φ.