Dielectric constants and Born effective charges of TiO2 rutile.

Abstract

The high-frequency dielectric-constant tensor and the Born effective charge of ${\mathrm{TiO}}_{2}$ rutile are calculated using variational density-functional perturbation theory. The calculated structural properties and high-frequency dielectric constant show agreement with experiments at the level of a few percent. The Born effective charges of ${\mathrm{TiO}}_{2}$ rutile are found to be much larger than the charges corresponding to ${\mathrm{Ti}}^{4+}$ or ${\mathrm{O}}^{2\mathrm{\ensuremath{-}}}$ ions. We compare these results with those obtained for ${\mathrm{SiO}}_{2}$ stishovite, for which the value of the Born effective charges is closer to an ionic picture.