Electronic Structure of the Perovskite Oxides:La1−xCaxMnO3

The electronic structures of the perovskite oxides, ${\mathrm{LaMnO}}_3$ and ${\mathrm{CaMnO}}_3$, are studied using density-functional methods. Antiferromagnetic insulating (AFI) solutions are obtained for both compounds within the local-density approximation (LDA). For ${\mathrm{LaMnO}}_3$ the Jahn-Teller distortion, found necessary for the AFI solution, produces occupied $\mathrm{Mn}(z^2-1\mathrm{})$ orbitals pointed along the long, basal-plane Mn-O bonds. The large on-site Coulomb $U$ and exchange $J$, obtained from “constrained” LDA calculations, $U\approx 8–10\mathrm{eV}$ and $J\approx 0.9\mathrm{eV}$, indicate important correlation effects and yield large redistribution of the spectral weight within the $\mathrm{LDA}+U$ approach.