Phonons and static dielectric constant inCaTiO3from first principles

Abstract

${\mathrm{CaTiO}}_{3}$ has a static dielectric constant that extrapolates to a value greater than 300 at zero temperature. We investigate the origin of this large dielectric response on a microscopic level, using first-principles plane-wave pseudopotential density functional theory calculations. The electronic dielectric tensor and the complete set of zone center phonons and ionic Born effective charges are determined for ${\mathrm{CaTiO}}_{3}$ in its low temperature 20-atom per cell orthorhombic phase via frozen phonon electronic structure, polarization, and force constant calculations. Dispersion theory is then used to obtain the dielectric tensor. The dielectric response is dominated by low frequency $(\ensuremath{\nu}\ensuremath{\approx}90{\mathrm{cm}}^{\ensuremath{-}1})$ polar optical modes in which cation motion opposes oxygen motion. The frequencies of these phonons, and thus the dielectric constant, are predicted to be pressure sensitive.