Spin-state transition and spin-polaron physics in cobalt oxide perovskites: ab initio approach based on quantum chemical methods

L Hozoi,H Stoll,U Birkenheuer,P Fulde

doi:10.1088/1367-2630/11/2/023023

Abstract

A fully ab initio scheme based on quantum chemical wavefunction methods is used to investigate the correlated multiorbital electronic structure of a 3d-metal compound, LaCoO3. The strong short-range electron correlations, involving both Co and O orbitals, are treated by multireference techniques. The use of effective parameters such as the Hubbard U and interorbital U′, J terms and the problems associated with their explicit calculation are avoided with this approach. We compute the ordering of the lowest N-particle states in the parent compound and provide new insight into the nature of charge carriers in the hole-doped material. Our results suggest that the transition to a magnetically active state at about 90 K in LaCoO3 involves a high-spin, t2g4eg2 configuration. Additionally, we explain the paramagnetic phase in the low-temperature lightly doped compound through the formation of Zhang–Rice-like oxygen hole states and ferromagnetic clusters.

Highlights

An accurate description of correlated electrons is one of the central problems of condensed-matter theory
A fully ab initio scheme based on quantum chemical wavefunction methods is used to investigate the correlated multiorbital electronic structure of a 3d-metal compound, LaCoO3
While recent x-ray absorption spectroscopy (XAS) [19] and inelastic neutron scattering (INS) [20] measurements indicate with increasing T a gradual transition into a S = 2 (t42ge2g) high-spin (HS) configuration of the Co 3d electrons, electron energy-loss spectroscopy data [21] and the observation of Co-O bondlength alternation [22] suggest the formation of a S = 1 (t52ge1g) intermediate-spin (IS) state for T > 90 K, susceptible to Jahn-Teller distortions

Summary

Introduction

An accurate description of correlated electrons is one of the central problems of condensed-matter theory. A fully ab initio scheme based on quantum chemical wavefunction methods is used to investigate the correlated multiorbital electronic structure of a 3d-metal compound, LaCoO3. On-site and intersite correlation effects are here investigated in direct space by multiconfiguration complete-active-space self-consistent-field (CASSCF) and multireference configuration-interaction (MRCI) calculations [6].

Results

Conclusion