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

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 Γ 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.

Towards efficient and accurate ab initio solutions to periodic systems via transcorrelation and coupled cluster theory

“…The coupled cluster (CC) methodologies [1][2][3] at the level of singles and doubles (CCSD) and perturbative triples (CCSD(T)) [4] have become the de facto standard of single-reference ab initio quantum chemistry, and can be applied to systems consisting of hundreds of electrons [5][6][7][8]. In the past few years, these methods have also shown promise in applications to the solid state [9][10][11][12][13][14], although significant challenges remain before they can be routinely applied, as for example density functional theories are. On the one hand, because of quite steep computational scaling (O(N 6 ) and O(N 7 ) for CCSD and CCSD(T) respectively), it is desirable to keep the methods at the lowest possible CC level, namely CCSD, whilst maintaining accuracy.…”

Orbital-dependent photodynamics of strongly correlated nickel oxide clusters

“…13 Detailed calculations provide mounting support for the importance of such s character states, which are more delocalized. 14,15 This challenges conventional knowledge which considers only localized 3d (e g ) states in the conduction band edge and suggests that the photodynamics of NiO materials are influenced by the involvement of different electronic orbitals.…”

“…Here, femtosecond pump-probe spectroscopy coupled with theoretical calculations are used to show a unique reliance on the Ni orbital contributions to the photoexcited neutral nickel oxide cluster lifetimes, and by extension allow for a deeper understanding of the bulk-scale photoexcitation. Specifically, we show that the electron transfer from a O-2p orbital to a Ni-3d orbital, commonly referred to as ligand-to-metal charge transfer (LMCT) excitation, 7,15 undergoes rapid relaxation through e-e scattering. The introduction of O vacancies enables Ni-3d -Ni-4s transitions and Ni-3d -Ni-4p transitions that exhibit delocalized carriers and slower relaxation dynamics.…”

Ab initio modeling of excitons: from perfect crystals to biomaterials

“…Wang and Berkelback [31] have recently shown that Equation-of-Motion Coupled-Cluster Theory can yield promising results for optical excitation energies, exciton binding energies, exciton dispersion relations, and exciton-phonon interaction energies of simple crystalline solids like Si, C, SiC, MgO, or LiF. Other attempts are made in this direction for ground-state and excited-state methods that combine CC and perturbation theory based on a partitioning of excitations that are internal or external to an active space [32][33][34][35].…”