Electronic structures and optical properties of defective V2O5 unveiled by many-body Green's function theory

We explore the impact of typical point defects, including oxygen vacancies (Ov) and hydroxyl groups (Hy), on the electronic and optical properties of bulk V2O5 by the many-body Green's function theory. The electronic bandgap of the pristine V2O5 predicted by the QPGW method is wider than that of the experimental sample by ∼1 eV. We find that the defect effect should be an important factor accounting for this big disparity. According to QPGW, Ov and Hy may cause the bandgap of V2O5 to be narrowed by 0.5 and 0.8 eV, respectively. The DFT+U and HSE06 approaches do not exhibit this phenomenon, as they produce an overly localized distribution of the unoccupied orbitals near the conduction band edge. These orbitals are predicted to be rather delocalized in QPGW, owing to the off-diagonal elements of the self-energy matrix. If choosing a low-cost approach to replace the expensive QPGW, evGW is ideal for determining the position of the Fermi level with respect to the valence band edge, while G0W0 is the best for estimating the gaps between occupied states (including valence bands and the in-gap defect states) and the unoccupied ones. The performance of HSE06 is irregular and not good for the defective systems. Optical absorption spectra of the defective V2O5 evaluated by the Bethe-Salpeter equation based on the G0W0 single-particle levels well reproduce peaks in the infrared region of the experimental spectrum.