First-principles study of optical properties of barium titanate

The optical properties of perovskite barium titanate in the core-level spectra are investigated by the first principles under scissor approximation. There are nine peaks at the curve of the imaginary part of dielectric function. The optical spectra are assigned to interband contribution from O 2p valence bands to Ti 3d conduction bands in the low-energy region and outer core electron excitation (core level excitation) from near valence band semicore levels Ba 5p and O 2s to conduction band in the high-energy region. In contrast to the calculated results by the tight-binding linear muffin-tin orbitals method, our results are in better agreement with the experimental results.