The ground-state electronic structures of ferromagnetic and antiferromagnetic CaMnO3 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 KMF(3) (M = Ni, Mn), that shows an exponential behaviour when the M-M distance is reduced. As regards the electronic structure, three unpaired electrons occupy very localized t(2g)-type d orbitals on Mn. About 1.8 electrons (according to a Mulliken partition scheme for the electronic charge) occupy Mn e(g)-type states (d(z2) and d(x2-y2) 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.
A QUANTUM MECHANICAL INVESTIGATION OF THE ELECTRONIC AND MAGNETIC PROPERTIES OF CaMnO3 PEROVSKITE
ORLANDO, Roberto;DOVESI, Roberto
1997-01-01
Abstract
The ground-state electronic structures of ferromagnetic and antiferromagnetic CaMnO3 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 KMF(3) (M = Ni, Mn), that shows an exponential behaviour when the M-M distance is reduced. As regards the electronic structure, three unpaired electrons occupy very localized t(2g)-type d orbitals on Mn. About 1.8 electrons (according to a Mulliken partition scheme for the electronic charge) occupy Mn e(g)-type states (d(z2) and d(x2-y2) 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.
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