Pivotal Role of Intersite Hubbard Interactions in Fe-Doped α-MnO₂

Abstract

We present a first-principles investigation of the structural, electronic, and magnetic properties of the pristine and Fe-doped α-MnO2 using density-functional theory with extended Hubbard functionals. The onsite U and intersite V Hubbard parameters are determined from first-principles and self-consistently using density-functional perturbation theory in the basis of Löwdin-orthogonalized atomic orbitals. For the pristine α-MnO2 we find that the so-called C2-AFM spin configuration is the most energetically favorable, in agreement with the experimentally observed antiferromagnetic ground state. For the Fe-doped α-MnO2 two types of doping are considered: Fe insertion in the 2 × 2 tunnels and partial substitution of Fe for Mn. We find that the interstitial doping preserves the C2-AFM spin configuration of the host lattice only when both onsite U and intersite V Hubbard corrections are included, while for the substitutional doping the onsite Hubbard U correction alone is able to preserve the C2-AFM spin configuration of the host lattice. The oxidation state of Fe is found to be +2 and +4 in the case of the interstitial and substitutional doping, respectively, while the oxidation state of Mn is +4 in both cases. This work paves the way for accurate studies of other MnO2 polymorphs and complex transition-metal compounds when the localization of 3d electrons occurs in the presence of strong covalent interactions with ligands.

Unraveling the effects of inter-site Hubbard interactions in spinel Li-ion cathode materials

“…[89] and in good agreement with the value of 1.1 eV computed using the PBE0r hybrid functional [34]. This agrees with the previous findings that PBEsol+U often improves the band gaps compared to PBEsol [77,78], while PBEsol+U +V outperforms PBEsol+U in terms of accuracy for band gaps [43,44]. For Mn 2 O 4 , PBEsol predicts the smallest band gap, PBEsol+U +V the largest, while PBEsol+U provides the band gap in between.…”

“…Adding the Hubbard U correction to the Mn-3d states allows them to localize and a clear energy separation between these Mn1-3d (Mn 3+ ) and Mn2-3d (Mn 4+ ) states can be seen, resulting in an insulating ground state. Adding the Hubbard V correction on top only leads to minor changes in the PDOS, consistently with the findings for other TM oxides [43,44]. Overall, the Hubbard U and V corrections lead to a PDOS where the valence band maximum (VBM) is dominated by O-2p states that are slightly hybridized with Mn 3+ -3d states, while the conduction band minimum (CBM) consists of strongly mixed O-2p and Mn 4+ -3d states.…”

“…LiMn 1.5 Ni 0.5 O 4 the on-site Hubbard U parameter has been chosen empirically such that some experimental properties of interest are well reproduced; this is different from a fully first-principles-based approach and likely contributed to the spread of the reported results. Most importantly, the effect of inter-site Hubbard V interactions [36][37][38] has never been investigated in the spinel cathode materials; these interactions have been shown to be very important in other transition-metal (TM) oxides due to strong metal-ligand hybridization [39][40][41][42][43][44][45][46][47][48][49].…”

Unraveling the effects of inter-site Hubbard interactions in spinel Li-ion cathode materials

“…Most importantly, the effect of inter-site Hubbard V interactions 36–38 has never been investigated in the spinel cathode materials; these interactions have been shown to be very important in other transition-metal (TM) oxides due to strong metal–ligand hybridization. 39–49…”

“…Most importantly, the effect of inter-site Hubbard V interactions [36][37][38] has never been investigated in the spinel cathode materials; these interactions have been shown to be very important in other transition-metal (TM) oxides due to strong metal-ligand hybridization. [39][40][41][42][43][44][45][46][47][48][49] Herein, we present a fully first-principles study of the structural, electronic, magnetic, and electrochemical properties of the spinel cathode materials Li x Mn 2 O 4 and Li x Mn 1.5 Ni 0.5 O 4 (x = 0 and 1) using DFT with extended Hubbard functionals (DFT+U+V), 36 where the on-site U and inter-site V Hubbard parameters are computed unbiasedly and fully from firstprinciples using density-functional perturbation theory (DFPT) 50,51 in a basis of Lo ¨wdin-orthogonalized atomic orbitals. This avoids any empiricism and possible ambiguities of Hubbard-corrected DFT studies.…”