Premium
Multiband model for the electronic structure of Sr 2 TiO 4
Author(s) -
RoŚciszewski Krzysztof,
Piekarz Przemysław,
OleŚ Andrzej M.
Publication year - 2017
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201700022
Subject(s) - atomic orbital , ion , atomic physics , electron , ionic bonding , coulomb , charge density , ionization , density functional theory , electronic structure , physics , chemistry , materials science , condensed matter physics , computational chemistry , quantum mechanics
We introduce and investigate the multiband d – p model for a TiO4 layer, such as realized in Sr2 TiO4 , with all t 2 gand e g orbitals (at titanium ions) and 2 p orbitals (at oxygen ions). Complementary density functional theory ab initio computations are employed to determine the actual electron number per TiO4 unit and one finds perfect Sr ionization with Sr+ 2ions and charged (TiO4 )− 2layer. This system is predicted to be a robust nonmagnetic insulator, in agreement with experiment. The above charge distribution is crucial and when we deviate from it, even by a small amount, the system becomes conducting or very close to conducting and various magnetic structures compete with one another. This finding is generic, that is, it holds in a broad range of d – p Hamiltonian parameters. As expected, d – p hybridization strongly redistributes electrons and leads to titanium ions between d 1 and d 2 ionic configurations. Surprisingly, Sr2 2 + ( TiO4 ) 2 −is not a simpleminded t 2 gsystem but instead electron densities are finite and roughly the same in all different 3 d orbitals (of t 2 gand e g symmetry) and the electron densities within O( 2 p ) orbitals are within the range 5.4–5.9. By selecting the charge‐transfer energy, Δ = ϵ d − ϵ p , we reproduce the experimental band gap of 3.8 eV. We emphasize that a realistic treatment of electronic distribution requires local Coulomb interactions at 2 p oxygen orbitals and we show that the Coulomb interactions at titanium ions are strongly renormalized when the Coulomb interactions at oxygen ions are neglected.