Search

We, at the ab initio level, simulated the rearrangement magnitudes of the adjacent neighboring ions, surrounding the (100) surface F-center in ABO3 perovskite matrixes. They are noticeably greater than the respective ionic shift magnitudes of the adjacent neighboring ions surrounding the bulk F-center. In ABO3 perovskites, the electron charge is noticeably better bounded on the inside of the bulk oxygen vacancy, as interior the respective (100) surface vacancy. The oxygen vacancy formation energy, located on the (100) surface of ABO3 perovskites, as a rule, is smaller as in the bulk. This slight energy distinction encourages the oxygen vacancy segregation from the ABO3 perovskite bulk to their (100) surfaces. The ABO3 complex oxide (100) surface F-center generated defect levels are positioned nearer to the (100) surface CB bottom than the bulk F-center generated respective defect levels. In contrary, the BaF2, SrF2 and CaF2, both, surface and bulk F-center charges are well localized inside the fluorine vacancy. The ionic rearrangement magnitudes of the adjacent neighboring ions, surrounding the surface and bulk F-centers in BaF2, SrF2 and CaF2 matrixes, are much smaller regarding the respective situation in ABO3 perovskites. [ABSTRACT FROM AUTHOR]

For rational design and improvement of electronic and optical properties of water-splitting photocatalysts, the ability to control the band edge positions relative to the water redox potentials and the photoresponse as a function of environmental conditions is essential. We combine ab initio molecular dynamics simulations with ab initio many-body theoretical calculations to predict the bandgap and band edge energies, as well as the absorption spectrum of pristine and N- and S-doped TiO2 nanotubes using the DFT+U and G0W0 approaches. Both levels of theory show similar trends, and N+S-codoping appears to be the optimal system for photocatalytic water splitting both in dry and humid conditions. However, the effect is rather moderate. Compared to DFT+U, the enhanced many-body effects in the G0W0 calculations push the absolute energies of the band edges to higher values and yield increased quasi-particle bandgaps in better agreement with experiment. In dry and humid conditions, the electronic bandgap for all systems is found to be in the range of 6.0–6.2 eV with a redshift from electronic gap to optical gap. The absorption spectra show an optical anisotropy and different absorption thresholds for different light polarizations. [ABSTRACT FROM AUTHOR]

In this research, density functional theory accompanied with linear combination of atomic orbitals (LCAO) method is applied to study the atomic and electronic structure of wurtzite and rocksalt ZnxMg1−xO pseudobinary compounds in their bulk phases. Calculated band gaps of ZnxMg1−xO solid solutions under study are further validated by means of spectroscopic ellipsometry and optical absorption. In agreement with an experiment, it is predicted that increase of Zn content in ZnxMg1−xO leads to narrowing of its band gap for both wurtzite and rocksalt phases. The calculated infra-red (IR) spectra show that the IR peaks are shifted towards larger frequencies along with decrease of Zn content. Presence of imaginary phonon frequencies in rocksalt ZnxMg1−xO of x > 0.625 allows us to suggest that it is necessary to use properly oriented substrates for epitaxial growth to overcome polycrystallinity inZnxMg1−xO thin films at concentration x = 0.4 – 0.6. [ABSTRACT FROM AUTHOR]