Spin state ofLaCoO3: Dependence onCoO6octahedra geometry

Abstract

The electronic structure of the rhombohedral $\mathrm{La}\mathrm{Co}{\mathrm{O}}_3$ perovskite is calculated for a number of structures with varying $\mathrm{Co}{\mathrm{O}}_6$ 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 $3d$ states, the $\mathrm{GGA}+\mathrm{U}$ method is employed. Depending on the $\mathrm{Co}-\mathrm{O}$ distance $d$ and the $\mathrm{Co}-\mathrm{O}-\mathrm{Co}$ bond angle $\beta$, 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 $(d,\beta )$ space is determined. The IS state is more stable than the LS state for structures with longer $\mathrm{Co}-\mathrm{O}$ distances and more open $\mathrm{Co}-\mathrm{O}-\mathrm{Co}$ angles. The $\mathrm{GGA}+\mathrm{U}$ results are in agreement with recently observed pressure-induced IS-LS transition.