Structural and Electronic Properties of MgO/TiO2 Interfaces: A First-Principles Molecular-Simulation Study

Owing to their importance in solar energy applications, we investigate here the MgO/TiO2 interface based on first-principles density functional theory (DFT) calculations, focusing on elucidating the underlying geometric structure and electronic properties. For the MgO and TiO2 surfaces as well as the TiO2/MgO(001) heterojunction, DFT+U calculations were performed to explore the densities of states, charge-density differences, local potentials, and the band offset. These studies reveal that the MgO/TiO2(001) heterostructure is of type I, that is, of straddling-gap type rather than staggered type. In the case of the MgO/TiO2 interface, we have explored the band structures and valence band and conduction band offsets in addition to performing Bader charge analysis. The thermodynamic stability of these heterostructures was scrutinized. Furthermore, we explored the TiO2 convergence of predicted properties by increasing the thickness of TiO2 at the MgO/TiO2 interface, revealing that increasing the thickness of the TiO2 surface beyond that originally considered does not change the electronic properties, such as the valence band maximum and conduction band minimum. The optical absorption study reveals boosts therein for the constructed heterostructures, which were significantly enhanced with a detectable red shift compared with those of individual slabs.