Anharmonic phonons from minimal symmetrized basis

Anharmonic phonon methods of computing phonon quasiparticles and interatomic force constants (FCs) at a finite temperature, such as the effective potential methods [1], [2], rely on expensive direct supercell method of computing phonons and subsequent fit to finite-temperature ab-initio forces. We present a method that relies on a highly efficient reciprocal-space representation that fully exploits symmetries to minimize the number of degrees of freedom. The method overcomes the limitations of the harmonic and quasiharmonic approximations by allowing efficient prediction of the temperature dependence of phonons, and hence accurately the thermal properties of materials while retaining the familiar quasi-particle representation. For test cases, such as ferroelectric oxide SrTiO3, our method provides converged phonons that are in good agreement with the experiment.