Electronic, structural, and optical properties of crystalline yttria

The electronic structure of crystalline ${\mathrm{Y}}_2{\mathrm{O}}_3$ is investigated by first-principles calculations within the local-density approximation (LDA) of the density-functional theory. Results are presented for the band structure, the total density of states (DOS), the atom- and orbital-resolved partial DOS, effective charges, bond order, and charge-density distributions. Partial covalent character in the Y-O bonding is shown, and the nonequivalency of the two Y sites is demonstrated. The calculated electronic structure is compared with a variety of available experimental data. The total energy of the crystal is calculated as a function of crystal volume. A bulk modulus $B$ of 183 Gpa and a pressure coefficient $B^{\prime }$ of 4.01 are obtained, which are in good agreement with compression data. An LDA band gap of 4.54 eV at Γ is obtained which increases with pressure at a rate of ${\mathrm{dE}}_g/dP=0.012\mathrm{}\mathrm{e}\mathrm{V}/\mathrm{G}\mathrm{p}\mathrm{a}$ at the equilibrium volume. Also investigated are the optical properties of ${\mathrm{Y}}_2{\mathrm{O}}_3$ up to a photon energy of 20 eV. The calculated complex dielectric function and electron-energy-loss function are in good agreement with experimental data. A static dielectric constant of $\varepsilon \mathrm{}\left(0\right)=3.20\mathrm{}$ is obtained. It is also found that the bottom of the conduction band consists of a single band, and direct optical transition at Γ between the top of the valence band and the bottom of the conduction band may be symmetry forbidden.