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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2764

Advisors: Dr. S. K. Ghoshal
Copyright: Mar-2010
Date Added: 7-May-2012
Abstract: Abstract In this thesis, we have investigated the structural, electronic, and magnetic properties of pure LaMnO3 from first-principles using the quantum-ESPRESSO open-source code. Unlike previous theoretical works, most of which implemented experimental structure, we have performed full structural relaxations for both the cubic and orthorhombic structures within the GGA and LDA+U approaches. Our simulated structural parameters are in very good agreement with experimental values. We have used these theoretical geometries in all the calculations. Consistent with the general theory of the CMR manganites but not reported in earlier theoretical works, the band structure and DOS calculations for the cubic ferroelectric phase predict half-metallicity. We have also examined the phonon-dispersion and the corresponding density of states for the theoretically optimized cubic ferromagnetic LaMnO3 from which we are able to observe two strong crystal instabilities. The phonon dispersion is calculated along the high-symmetry axes throughout the Brillouin zone. The densities of states calculated for the orthorhombic structure with different magnetic orderings strongly suggest the need for structural relaxation in order to get the experimentally observed insulating ground state for LaMnO3. Both GGA and LDA+U calculations for the fully relaxed orthorhombic A-type antiferromagnetic structure reproduce the insulating character. However, the value of the insulating gap obtained within the LDA+U case is much closer to experiment than that of GGA, which in turn means that a better description of LaMnO3 is possible with the inclusion of the on-site coulomb interaction.
URI: http://hdl.handle.net/123456789/2764
Appears in:Thesis - Material Science

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