Band-structure calculations for the 3dtransition metal oxides inGW

Abstract

Many-body GW calculations have emerged as a standard for the prediction of band-gaps, bandstructures, and optical properties for main-group semiconductors and insulators, but it is not well established how predictive the GW method is in general for transition metal (TM) compounds. Surveying the series of 3d oxides within a typical GW approach using the random phase approximation reveals mixed results, including cases where the calculated band gap is either too small or too large, depending on the oxidation states of the TM (e.g., FeO/Fe 2 O 3 , Cu 2 O/CuO). The problem appears to originate mostly from a too high average d-orbital energy, whereas the splitting between occupied and unoccupied dsymmetries seems to be reasonably accurate. It is shown that augmenting the GW self-energy by an attractive (negative) and occupation-independent on-site potential for the TM d-orbitals with a single parameter per TM cation can reconcile the band gaps for different oxide stoichiometries and TM oxidations states. In Cu 2 O, which is considered here in more detail, standard GW based on wavefunctions from initial density or hybrid functional calculations yields an unphysical prediction with an incorrect ordering of the conduction bands, even when the magnitude of the band gap is in apparent agreement with experiment. The correct band ordering is restored either by applying the d-state potential or by iterating the wave functions to self-consistency, which both have the effect of lowering the Cu-d orbital energy. While it remains to be determined which improvements over standard GW implementations are needed to achieve an accurate ab initio description for a wide range of transition metal compounds, the application of the empirical on-site potential serves to mitigate the problems specifically related to d-states in GW calculations.2

Sodium Charge Storage in Thin Films of MnO2Derived by Electrochemical Oxidation of MnO Atomic Layer Deposition Films

“…This bandgap agrees well with values of 3.5-3.8 eV reported for crystalline MnO. 37,38 The refractive index from SE analysis shown in Figure 2 also indicates crystalline MnO. The refractive index from SE was 2.16 at 589 nm.…”

Automation methodologies and large-scale validation for GW : Towards high-throughput GW calculations

“…The trends observed here agree well with Lany's observations on 3d-transition metal oxides. 74 For the transition metal containing compounds we observe a mean absolute deviation of 0.64 eV from the experimental gaps. For the compounds without transition metals this reduces to 0.38 eV.…”

Polymorphous band structure model of gapping in the antiferromagnetic and paramagnetic phases of the Mott insulators MnO, FeO, CoO, and NiO

“…The following are the sources for the experimental values: Ref. 10 for the band gaps of the AFM phases; Ref. 11 for the band gaps of the PM phases; Ref.…”

“…As is generally taught 8,9 , the ensuing electronic structure of compounds having partially occupied energy bands described in a structure where all atoms are equivalent would be metallic 2,3 with the Fermi level intersecting a band. Yet, experimentally MnO, FeO, CoO and NiO are local-moment large band gap insulators, both in the AFM and PM phase [10][11][12] (see Table I). The fundamental disagreement between such band structure theory and experiment set the historical stage for modeling the electronic structure of the PM phases of MnO, FeO, CoO and NiO by many-body, correlated electron descriptions, such as the description based on the Hubbard Hamiltonian 13,14 , or, more recently, dynamical mean field theory (DMFT) 15,16 .…”