Electronic structures and optical properties of monoclinic ZrO2 studied by first-principles local density approximation plus U approach

The electronic structures and optical properties of the monoclinic ZrO2 (m-ZrO2) are investigated by means of first-principles local density approximation (LDA) + U approach. Without on-site Coulomb interactions, the band gap of m-ZrO2 is 3.60 eV, much lower than the experimental value (5.8 eV). By introducing the Coulomb interactions of 4d orbitals on Zr atom (U-d) and of 2p orbitals on O atom (U-p), we can reproduce the experimental value of the band gap. The calculated dielectric function of m-ZrO2 exhibits a small shoulder at the edge of the band gap in its imaginary part, while in the tetragonal ZrO2 and cubic ZrO2 it is absent, which is consistent with the experimental observations. The origin of the shoulder is attributed to the difference of electronic structures near the edge of the valence and conduction bands.