Density-functional studies of the electronic structure of the perovskite oxides: La1−xCaxMnO3

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Abstract
Using density‐functional methods, we study the electronic structures of the lanthanum‐based ‘‘double‐exchange’’ perovskite magnets. Antiferromagnetic insulating solutions are obtained for both the end members, LaMnO3 and CaMnO3, within the local density approximation (LDA), with the Jahn‐Teller (JT) distortion of the oxygen octrahedron taken into account. The JT distortion splits off the Mn(3d)eg bands producing an energy gap within the LDA, with the bands derived from the (z2−1) orbital, pointed along the long basal‐plane Mn—O bond, occupied and the (x2−y2) bands empty. The on‐site Coulomb repulsion and the intra‐site exchange terms are found to be, respectively, U≂8–10 eV and J≂0.9 eV, from the ‘‘constrained’’ density‐functional theory. The large value of U as compared to the bandwidth indicates that the manganese perovskite oxides are strongly correlated systems.