Abstract
The variational cluster approximation (VCA) is applied to the calculation of thermodynamical quantities and single-particle spectra of . Trial self-energies and the numerical value of the Luttinger-Ward functional are obtained by exact diagonalization of a cluster. The VCA correctly predicts as a paramagnetic insulator, and a gradual and relatively smooth increase in the occupation of high-spin 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.
3 More- Received 2 October 2009
DOI:https://doi.org/10.1103/PhysRevB.81.035101
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