NiO: Correlated Band Structure of a Charge-Transfer Insulator

Abstract

The bandstructure of the prototypical charge-transfer insulator NiO is computed by using a combination of an ab initio bandstructure method and the dynamical mean-field theory with a quantum Monte-Carlo impurity solver. Employing a Hamiltonian which includes both Ni-d and O-p orbitals we find excellent agreement with the energy bands determined from angle-resolved photoemission spectroscopy. This solves a long-standing problem in solid state theory. Most notably we obtain the low-energy Zhang-Rice bands with strongly k-dependent orbital character discussed previously in the context of low-energy model theories.PACS numbers: 71.27.+a, 71.10.-w, 79.60.-i The quantitative explanation of the electronic structure of transition metal oxides (TMOs) and other materials with correlated electrons has been a long-standing challenge in condensed matter physics. While the basic concept explaining why materials such as NiO are insulators was formulated by Mott already a long time ago [1], the development of an appropriate, material-specific computational scheme proved to be a formidable task. The electronic structure of the late TMOs, including the cuprate superconductors, is not only affected by the electronic correlations, it is further complicated by the hybridization between the transition metal d-states and O p-bands located between the lower and upper Hubbard bands formed by the transition metal d orbitals. For such materials Zaanen, Sawatzky and Allen [2] introduced the term "charge transfer insulator", a prototypical example of which is NiO. In principle the simple crystal structure of NiO allows for a straightforward comparison between theory and experiment. However, a theoretical description of the NiO bandstructure is made difficult by the competition between the local many-body effects, due to strong Coulomb interaction between Ni d electrons, and the band dispersion, due to the lattice periodicity, both observed with the angle-resolved photoemission spectroscopy (ARPES) [3,4].In this Letter we use a combination of a conventional bandstructure approach, based on the local density approximation (LDA), and the dynamical mean-field theory (DMFT) [5,6,7] to investigate the bandstructure of NiO. No adjustable parameters enter. While the application of the LDA+DMFT [8, 9, 10] framework has proven successful for the early TMOs, the charge-transfer materials were routinely avoided due to the additional complexity arising from the presence of p-bands. In the present work the O p-orbitals and their hybridization with Ni d-orbitals are explicitly included, thus allowing for a unified description of the full spectrum. Our results reveal a non-trivial effect of the p − d hybridization in strongly correlated system studied so far only in terms of simple models [11,12,13].The application of the standard bandstructure theory to NiO is marked by a failure of LDA to produce an insulating groundstate [14]. The antiferromagnetic order within LDA [15], despite rendering NiO an insulator, does not present much of an improvement sinc...

First-principles modeling of localizeddstates with theGW@LDA+Uapproach

“…10,15,21,25,43,83,96,[112][113][114][115][116] The four compounds roughly fall into two classes: ͑1͒ MnO and NiO, for which standard band theory within LDA or GGA still predicts an insulating ground state when applied in the AFM-II phase but with significantly underestimated band gaps; ͑2͒ FeO and CoO, for which LDA and GGA give metallic ground states even in the AFM-II phase. 7 In this work we consider only the AFM-II phase.…”

Exchange interactions in transition metal oxides: the role of oxygen spin polarization

“…The simple rock-salt structure along with the inability of regular DFT functionals to correctly describe these materials, make NiO and MnO typical benchmark systems to test methods for the calculation of exchange interactions in strongly correlated systems. Beyond the DFT methods such as LDA+U, [34,44,45] hybrid functionals, [46,47] the self-interaction correction, [41,48] GW approximation [49] and dynamical mean-field theory [42,50] have been used successfully to improve the correspondence between calculations and experiments in these materials. [34,42,46,47] In contrast, LSIC overestimates the electron localization, leading to a slight underestimation of the exchange interactions.…”

Correlated band structure of NiO, CoO, and MnO by variational cluster approximation

“…This is also in contradition to LDA calculations which predicts band widths of around 2eV for the TM3d-derived bands. Starting with the work of Hubbard [11] a variety of theoretical methods have been invented to deal with this problem [12,13,14,15,16,17,18,19,20,21,22]. Major progress towards a quantitative description of 3d TM oxides has been made by the cluster method initiated by Fujimori and Minami [23,24,25,26,27] This takes the opposite point of view as compared to band theory, namely to abandon translational invariance and instead treat exactly -by means of atomic multiplet theory [28,29] -the Coulomb interaction in the 3d-shell of a TM-ion in an octahedral 'cage' of nearest-neighbor oxygen atoms.…”