Structure-dependent electronic properties of oxides from first principles

This thesis contains several investigations on the structure dependent electronic properties of oxides, studied via first-principle calculations or tight-binding models. We start by reviewing the background of structure correlated properties and functionalities in transition metal oxides, followed by the introduction of the density functional theory which will be used throughout this thesis. We next consider the spin-phonon coupling effect for SrMnO3/LaMnO3 superlattice with epitaxial strain. We explain the origin of the intriguing emergence of the large spin-phonon coupling effect for tensile strain. As the study of superlattice goes on, we realize the emergent need of a systematic way to determine the ground state structure for superlattices. Thus we develop the “stacking method” to solve this problem, and test it using PbTiO3/SrTiO3 whose structure is known to be complicated. We then use the stacking method for the further study on epitaxially strained SrCrO3/SrTiO3 superlattice, and find a nonpolar-polar structural transition along with a metal-insulator transition. We conclude that the polar structure induces an orbital ordering, leading to the insulating state. We also study the interband transition effect in the epitaxially strained SrVO3, and show that the suppressed interband transitions lead to the significant transmittance for SrVO3 thin films. Finally we define the surface polarization effect for those surfaces where in-plane inversion symmetry is broken. We extend the Berry-phase theory of the bulk polarization to the case of surface polarization by formulating the problem in the hybrid Wannier representation. The surface polarization is in agree with the accumulating charge at the common edge of two facets as expected.Ph.D.Includes bibliographical referencesby Yuanjun Zho