A quantum mechanical investigation of the electronic and magnetic properties of perovskite

Abstract

The ground-state electronic structures of ferromagnetic and antiferromagnetic perovskite in the ideal cubic phase have been investigated using the ab initio periodic Hartree - Fock approach. The system is a wide-gap insulator. The antiferromagnetic phase is correctly predicted to be the more stable (0.07 eV per Mn atom at the equilibrium geometry), but the superexchange interaction is substantially overestimated. The energy difference between the two phases increases slowly and linearly under compression, at variance with that for , that shows an exponential behaviour when the M - M distance is reduced. As regards the electronic structure, three unpaired electrons occupy very localized -type d orbitals on Mn. About 1.8 electrons (according to a Mulliken partition scheme for the electronic charge) occupy Mn -type states ( and Mn d orbitals), which however overlap significantly with oxygen p orbitals; the degree of spin polarization of these bond states is very low. The electronic structure of the system is discussed in terms of the density of states and charge- and spin-density maps.