AUTHOR=Kim Won June , Han Myung Hoon , Lebègue Sébastien , Lee Eok Kyun , Kim Hyungjun 

TITLE=Electronic Structure and Band Alignments of Various Phases of Titania Using the Self-Consistent Hybrid Density Functional and DFT+U Methods

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 7 - 2019

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00047

DOI=10.3389/fchem.2019.00047

ISSN=2296-2646

ABSTRACT=To understand, and thereby rationally optimize photoactive interfaces, it is of prime importance to elucidate the electronic structures and band alignments of the interfaces. For the first-principles investigation of these properties, conventional density functional theory (DFT) needs a remedy to mitigate its well-known bandgap underestimation problem. Hybrid functional and Hubbard U correction are computationally efficient methods to overcome this limitation; however, the results are largely dependent on the choice of parameters. In this study, we employ recently developed self-consistent approaches, which enable non-empirical determination of the parameters, to investigate TiO2 interfacial systems – the most prototypical photocatalytic systems. We investigate the structural, electronic, and optical properties of rutile and anatase phases of TiO2. We find that the self-consistent hybrid functional predicts the most reliable structural and electronic properties that are comparable to the experimental and high-level GW results. Using the validated self-consistent hybrid functional method, we further investigate the band edge positions between rutile and anatase surfaces in vacuum and in an electrolyte medium by coupling with the Poisson-Boltzmann theory. This suggests the possibility of a transition from the straddling-type to the staggered-type band alignment between rutile and anatase phases in the electrolyte medium, which is manifested by the formation of a Stern-like layer at the interfaces. Our study not only confirms the efficacy of the self-consistent hybrid functional method in reliably predicting the electronic structure of photoactive interfaces, but also elucidates a potentially dramatic change in the band edge positions of TiO2 in aqueous electrolyte medium which can extensively affect its photophysical properties.