Band-structure and cluster-model calculations ofLaCoO3in the low-spin phase

We present band-structure and cluster-model calculations of ${\mathrm{LaCoO}}_3$ in the low-spin phase. The purpose of these calculations is to contrast and complement the results and conclusions of recent spectroscopic studies. The total density of states (DOS) is compared to the photoemission spectrum; the agreement is very good except for the many-body satellites which appear at higher binding energies. The unoccupied O p DOS reproduces fairly well the O 1s x-ray-absorption spectrum; the main discrepancy appears in the Co 3d region and is attributed to core-hole effects. The ground state predicted by the cluster-model calculation is highly covalent and contains mainly 62% of ${\mathit{t}}_{2\mathit{g}}^6$ ${(}^1$ ${\mathit{A}}_1$) and 36% of ${\mathit{t}}_{2\mathit{g}}^6$ ${\mathit{e}}_{\mathit{g}}$ ${(}^2$E)L. The first (one-electron) removal state has more 3${\mathit{d}}^6$L than 3${\mathit{d}}^5$ character whereas the first addition state is almost completely dominated by the 3${\mathit{d}}^7$ state. This means that low-spin ${\mathrm{LaCoO}}_3$ is in the charge-transfer regime and the optical band gap is of the p-d type. The Co 3d contribution to the photoemission spectrum calculated with the cluster-model reproduces not only the leading peaks but also the many-body satellites. The main drawback in this case is the absence of the spectral weight coming from the O 2p bands.