Abstract
Density-functional calculations using the linearized-augmented-plane-wave method were carried out for the scheelite materials and in order to determine their ground-state electronic properties. The results indicate that and have direct band gaps at the center of the Brillouin zone, while and have band extrema at wave vectors away from the zone center with possibly indirect band gaps. The magnitudes of the band gaps increase in the order The valence and conduction bands near the band gap are dominated by molecular orbitals associated with the and ions, where The valence-band widths are 5 and 5.5 eV for the Ca and Pb materials, respectively. In the Pb materials, the Pb states form narrow bands 1 eV below the bottom of the valence bands, and also hybridize with states throughout the valence bands, while the Pb states hybridize with states throughout the conduction bands. In the Ca materials, the Ca states contribute to a high density of states 3–4 eV above the bottom of the conduction bands.
- Received 6 January 1998
DOI:https://doi.org/10.1103/PhysRevB.57.12738
©1998 American Physical Society