Relevance of DFT+U formalism to treat strongly correlated d electrons of Ta acting as an isolated impurity-probe in oxides. TDPAC and ab initio study

G.N. DARRIBA; R. FACCIO; P.D. EVERSHEIM; M. RENTERÍA

La Plata

Workshop; X Workshop on Novel Methods for Electronic Structure Calculations; 2023

To study the influence of doping impurities in condensed matter and the development of new functional materials, nowadays it is crucial to perform a combined experimental and theoretical study, with an accurate description of the electronic density rho(r) of the impurity-host system. Here we present an ab initio all-electron density functional theory (DFT) electronic structure calculations study, contributing to answer the general question of when it is relevant and necessary the inclusion of the Hubbard U parameter used in the DFT formalism (DFT+U) to correctly describe strongly correlated orbitals of diluted probe-atoms, in particular 5d orbitals of Ta doping semiconductors oxides. We selected for this purpose to study Ta-doped α-Al2O3, a semiconducting wide band-gap oxide with native cations that present the advantage of not having strongly correlated electrons. These calculations were compared with a precise experimental determination of the electric-field gradient (EFG) tensor at (181Hf)181Ta probe-atoms suitably localized at substitutional free of defects cation sites, essential for the above-mentioned purposes since enables to compare experimental results with theoretical predictions of the same physical situation. We studied theoretically the influence of the inclusion of the U parameter in the structural, electronic, and hyperfine properties of the impurity-host system, showing that the use of the DFT+U formalism does not introduce relevant structural changes with respect to DFT, evidencing that the anomalous large difference in the predictions of the EFG´s magnitude between both formalisms comes only from the modification of the electronic structure description.Based in the new insight gained in the present study, and the further comparison between DFT and the DFT+U predictions performed in 181Ta-doped rutile TiO2 and SnO2 we propose that the inclusion of the U parameter to treat the Ta-5d states when it behaves as a diluted impurity probe-atom would be only necessary when the donor level introduced is very localized in energy and space.