First-principles study on electronic structure and absorption spectra for the CaWO4 crystal with oxygen vacancy

The electronic structure and absorption spectra for the perfect CaWO4 and the CaWO4 containing oxygen vacancy VO2+ have been calculated using density functional theory code CASTEP with the lattice structure being optimized. The results indicate that the CaWO4 crystal containing VO2+, an additional absorption spectrum in the region of visible light. And the absorption spectrum can be fit into two Gaussian-shape absorption spectra with peaks at 360 and 415 nm. These peaks are located at the experimentally observed position. It is predicted that the 340 and the 420 nm absorption spectra are related to the existence of VO2+ in the CaWO4 crystal.