Abstract
The electronic-energy band structure, site, and angular-momentum decomposed density of states (DOS) and charge-density contours of perovskite in the paraelectric phase are calculated by the first-principles tight-binding linear muffin-tin orbitals method with the atomic-sphere approximation using density-functional theory in its local-density approximation. The calculated band structure shows a direct band gap of 1.2 eV at the Γ point in the Brillouin zone. The total DOS is compared to the experimental x-ray photoemission spectrum. From the DOS analysis, as well as charge-density studies, we conclude that the bonding between Ba and is mainly ionic and that the entities bond covalently. Using the projected DOS and band structure we have analyzed the interband contribution to the optical properties of The real and imaginary parts of the dielectric function and hence the optical constants (such as the reflectivity, refractive index, extinction coefficient, absorption coefficient, and the electron energy-loss spectrum) are calculated. The calculated spectra are compared with the experimental results for at room temperature in the ferroelectric phase and are found to be in good agreement with the experimental data in the low-energy regions. The role of band-structure calculation as regards the optical properties of is discussed.
- Received 22 November 1999
DOI:https://doi.org/10.1103/PhysRevB.62.8828
©2000 American Physical Society