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TT: Fachverband Tiefe Temperaturen
TT 7: Correlated Electrons: Electronic Structure Calculations
TT 7.2: Vortrag
Montag, 17. März 2025, 15:15–15:30, H31
LCAO fragment orbital projectors for DFT+U — •Christoph Freysoldt, Hao Chen, and Jörg Neugebauer — Max-Planck-Institut für Nachhaltige Materialien GmbH, Max-Planck-Str. 1, 40237 Düsseldorf
DFT+U is an efficient approach to describe correlated mixed-valence transition metal oxides such as Fe3O4=FeIIFe2IIIO4. The correlated orbitals are derived from, but not identical to the metal d-orbitals. Most DFT+U implementations employ local projectors with d-orbital symmetry centered on the transition metal atoms to extract the on-site occupation matrix of the correlated orbitals. Unfortunately, such projectors pick up not only intended occupations of localized orbitals, but also contributions from the extended metal-oxygen bonding states involving the O-2p orbitals. The spurious occupations are sensitive to the projector definition and the M-O bond length, and lead to artifacts in energies and structures. To arrive at a more reliable scheme, one must account for inter-atomic orbital overlap when defining the projectors. We propose using fragment orbitals from a linear combination of atomic orbitals (LCAO) that include the orbital mixing with the first ligand shell of each transition metal ion. To obtain analytic Pulay-like forces when atoms are displaced, the projectors are constructed from a simplified tight-binding model that reflects the atomic positions, but does not rely on the self-consistent electronic structure. We present preliminary results for iron oxides that exhibit improved occupations (closer to 0 and 1) and a reduced sensitivity to bonding distances.
Keywords: DFT+U; projector; correlated oxide