A QUANTUM-MECHANICAL INVESTIGATION OF THE ELECTRONIC AND MAGNETIC-PROPERTIES OF CAMNO3 PEROVSKITE

The ground-state electronic structures of ferromagnetic and antiferrom agnetic CaMnO3 perovskite in the ideal cubic phase have been investiga ted using the ab initio periodic Hartree-Fock approach. The system is a wide-gap insulator. The antiferromagnetic phase is correctly predict ed to be the more stable (0.07 eV per Mn atom at the equilibrium geome try), but the superexchange interaction is substantially overestimated . The energy difference between the two phases increases slowly and li nearly under compression, at variance with that for KMF(3) (M = Ni, Mn ), that shows an exponential behaviour when the M-M distance is reduce d. As regards the electronic structure, three unpaired electrons occup y very localized t(2g)-type d orbitals on Mn. About 1.8 electrons (acc ording to a Mulliken partition scheme for the electronic charge) occup y Mn e(g)-type states (d(z2) and d(x2-y2) Mn d orbitals), which howeve r overlap significantly with oxygen p orbitals; the degree of spin pol arization of these bond states is very low. The electronic structure o f the system is discussed in terms of the density of states and charge - and spin-density maps.