Electronic structure of bulk manganese oxide and nickel oxide from coupled cluster theory

TL;DR

This paper applies coupled cluster theory to study the electronic structure of bulk MnO and NiO, providing new insights into their insulating behavior and electronic excitations, and introduces a novel implementation of periodic ab initio EOM-CCSD.

Contribution

It presents the first implementation of unrestricted periodic ab initio EOM-CCSD and applies it to analyze the electronic structure of MnO and NiO.

Findings

Fundamental gaps of 3.46 eV (MnO) and 4.83 eV (NiO) slightly overestimated.

Both materials are in the intermediate Mott/charge-transfer insulator regime.

Near the Γ point, the lowest conduction quasiparticles are of s character.

Abstract

We describe the ground- and excited-state electronic structure of bulk MnO and NiO, two prototypical correlated electron materials, using coupled cluster theory with single and double excitations (CCSD). As a corollary, this work also reports the first implementation of unrestricted periodic ab initio equation-of motion CCSD. Starting from a Hartree-Fock reference, we find fundamental gaps of 3.46 eV and 4.83 eV for MnO and NiO respectively for the 16 unit supercell, slightly overestimated compared to experiment, although finite-size scaling suggests that the gap is more severely overestimated in the thermodynamic limit. From the character of the correlated electronic bands we find both MnO and NiO to lie in the intermediate Mott/charge-transfer insulator regime, although NiO appears as a charge transfer insulator when only the fundamental gap is considered. While the lowest quasiparticle excitations are of metal 3d and O 2p character in most of the Brillouin zone, near the {\Gamma} point, the lowest conduction band quasiparticles are of s character. Our study supports the potential of coupled cluster theory to provide high level many-body insights into correlated solids.