Ground state and excited state properties of LaMnO$_3$ from full-potential calculation

Abstract

The ground state and excited state properties of the perovskite LaMnO$_3$ are calculated based on the generalized-gradient-corrected relativistic full-potential method. The electronic structure, magnetism and energetics of various spin configurations for LaMnO$_3$ in the ideal cubic perovskite structure and the experimentally observed distorted orthorhombic structure are obtained. The excited state properties such as the optical, magneto-optical, x-ray photoemission (XPS), bremsstrahlung isochromat (BIS), x-ray absorption near edge structure (XANES) spectra are calculated and found to be in excellent agreement with available experimental results. The present results suggest that the correlation effect is not significant in LaMnO$_3$ and the presence of ferromagnetic coupling within the $ab$ plane as well as the antiferromagnetic coupling perpendicular to this plane can be explained through the itinerant band picture. As against earlier expectations, our calculations show that the Mn 3$d$ $t_{2g}$ as well as the $e_{g}$ electrons are present in the whole valence band region. In particular significantly large amounts of $t_{2g}$ electrons are present in combination with the $e_{g}$ electrons at the top of the valence band against the common expectation of presence of only pure $e_{g}$ electrons. We have calculated the hyperfine field parameters for the A-type antiferromagnetic and the ferromagnetic phases of LaMnO$_3$ and compared the findings with the available experimental results. The role of the orthorhombic distortion on electronic structure, magnetism and optical anisotropy are analyzed.