Spin state of $\mathrm{La}\mathrm{Co}{\mathrm{O}}_{3}$: Dependence on $\mathrm{Co}{\mathrm{O}}_{6}$ octahedra geometry

Spin state of $La Co O_{3}$ : Dependence on $Co O_{6}$ octahedra geometry

K. Knížek, P. Novák, and Z. Jirák

Phys. Rev. B 71, 054420 – Published 28 February 2005

Abstract

The electronic structure of the rhombohedral $La Co O_{3}$ perovskite is calculated for a number of structures with varying $Co O_{6}$ octahedra geometry. The calculations are based on the generalized gradient approximation (GGA) to the density functional theory and, in order to describe better the strong electron-electron correlation in Co $3 d$ states, the $GGA + U$ method is employed. Depending on the $Co - O$ distance $d$ and the $Co - O - Co$ bond angle $β$ , the spin $S$ of the cobalt ion is found to correspond either to the intermediate spin state [(IS), $S = 1$ ] or to the low spin state [(LS), $S = 0$ ]. The border line dividing the IS and LS states in the $(d, β)$ space is determined. The IS state is more stable than the LS state for structures with longer $Co - O$ distances and more open $Co - O - Co$ angles. The $GGA + U$ results are in agreement with recently observed pressure-induced IS-LS transition.