Spin state transition in LaCoO3 by variational cluster approximation

TL;DR

This paper uses the variational cluster approximation to study the spin state transition in LaCoO3, successfully predicting its paramagnetic insulating state and reproducing temperature-dependent spectral features, while noting the importance of additional effects.

Contribution

It applies the variational cluster approximation to LaCoO3, providing detailed thermodynamical and spectral predictions that align with experiments and highlight the roles of spin states and correlations.

Findings

LaCoO3 is correctly predicted as a paramagnetic insulator.

The model reproduces the temperature dependence of photoelectron spectra.

Discrepancies suggest the need to include spin orbit coupling and lattice effects.

Abstract

The variational cluster approximation is applied to the calculation of thermodynamical quantities and single-particle spectra of LaCoO3. Trial self-energies and the numerical value of the Luttinger-Ward functional are obtained by exact diagonalization of a CoO6 cluster. The VCA correctly predicts LaCoO3 as a paramagnetic insulator and a gradual and relatively smooth increase of the occupation of high-spin Co3+ ions causes the temperature dependence of entropy and magnetic susceptibility. The single particle spectral function agrees well with experiment, the experimentally observed temperature dependence of photoelectron spectra is reproduced satisfactorily. Remaining discrepancies with experiment highlight the importance of spin orbit coupling and local lattice relaxation.