First principles study of electronic structure and optical properties of CaTiO3

Abstract

The electronic-energy band structure, site and angular momentum decomposed density of states (DOS) and charge-density contours of perovskite CaTiO3 are calculated by the first principles tight-binding linear muffin-tin orbitals method with atomic sphere approximation using density functional theory in its local density approximation. The calculated band structure shows an indirect (R-Γ) band gap of 1.5 eV. The total DOS as well as the partial density of states (PDOS) are compared with the experimental photoemission spectra. The calculated DOS are in reasonable agreement with the experimental energy spectra and the features in the spectra are interpreted by a comparison of the spectra with the PDOS. The origin of the various experimentally observed bands have been explained. From the DOS analysis, as well as charge-density studies, we conclude that the bonding between Ca and TiO3 is mainly ionic and that the TiO3 entities bond covalently. Using the projected DOS and band structure we have analyzed the interband contribution to the optical properties of CaTiO3. The real and imaginary parts of the dielectric function and hence the optical constants such as refractive index and extinction coefficient are calculated. The calculated spectra are compared with the experimental results for CaTiO3 and are found to be in good agreement with the experimental results. The effective number of electrons per unit cell participating in the interband transitions are calculated. The role of band structure calculation as regards the optical properties of CaTiO3 is discussed.