Accurate calculations of phonon dispersion in CaF2 and CeO2

We report the lattice dynamic properties of CaF2 and CeO2 obtained using a direct method in combination of a mixed-space approach accounting for the vibration-induced dipole-dipole interactions. We overcame the overestimation of T-1u TO mode shown in prior calculations using the linear response theory. For CaF2, we employed the Perdew-Burke-Ernzerhof functional and achieved a significant improvement over previous linear response calculations by comparing the results with experimentally measured phonon dispersion curves. For CeO2, we adopted the Heyd-Scuseria-Ernzerhof hybrid functional and an elongated supercell and obtained results in excellent agreement with experimental measurements. We attributed the improved calculation results to the convenience of the direct method in implementing new exchange-correlation functionals and use of the mixed-space approach for treating the long-range dipole-dipole interactions.