The electronic structure of the LaMnO3 orthorhombic crystal of a stoichiometric composition and of La0.75MnO3 crystals with a La vacancy in the unit cell is calculated in the LSDA+U approximation of density functional theory. The calculations showed that LaMnO3 is an insulator with a forbidden gap of 0.5 eV and with antiferromagnetic ordering of magnetic moments. The magnetic moment on the manganese ions is 3.78 BM. The La atom has ionic bonds in the lattice, while the bond between oxygen and manganese is covalent. After lanthanum has been removed, geometry optimization of the unit cell leads to La0.75MnO3 stable structures. In one of the structures, which is lower in energy, the states of manganese may be attributed to Mn4+ ions. In both structures with removed lanthanum, the oxygen ions have reduced effective charge, so that one can speak about O− ions appearing along with O2− in the structure. The oxygen, as well as lanthanum and manganese, ions are nonequivalent in these structures; their nonequivalence is primarily reflected by the local densities of states. This leads to charge and magnetic nonequivalence of ions. In La0.75MnO3 crystals, the degree of bond covalence between manganese and oxygen decreases.
lanthanum manganites chemical bond density of states magnetic moment
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