Phonon anharmonicity via harmonic ensemble lattice dynamics (HELD)

The vibrations of atoms about their equilibrium positions critically influence the thermal properties of the material, and the vibrations themselves are affected by volume and temperature. The effects of volume (quasiharmonicity) can be handled accurately and efficiently by modern techniques, but the effects of temperature (anharmonicity) are more challenging to compute and much more computationally expensive. We present a method that calculates ‘instantaneous’ phonon dispersion curves in the harmonic approximation from structures with thermal disorder that are then aggregated into intensity maps to produce finite phonon linewidths that approximate anharmonic phonon broadening. The severity of the approximations and the advantages of this technique will be discussed, and the results for several BCC elements and BCC-based alloys will be shared.