Electronic structure and total energy calculations for oxide perovskites and superconductors

MgSiO3, BaTiO3, La2CuO4, and YBa2Cu3O7 are studied using the Linearized Augmented Plane Wave (LAPW) method and the Potential Induced Breathing (PIB) model. MgSiO3 is an important geophysical material and prototypical dense silicate, BaTiO3 is an important ferroelectric material, and La2CuO4 and YBa2Cu3O7 are examples of the new high-temperature superconductors. MgSiO3 is found to be quite ionic, whereas BaTiO3 has significant covalent character, and the high-temperature superconductors have an unusual combination of ionic, metallic, and covalent character. The equation-of-state of orthorhombic MgSiO3 is in good agreement with experiment, and the elastic constants, which were calculated and published before experimental data were available, are in close agreement with experiment. The ferroelectric phase transition in BaTiO3 from cubic to tetragonal is not found using highly accurate LAPW calculations. This lends support to order-disorder models for the phase transition. Also, contrary to many current models, the charge distortion in BaTiO3 centers around the Ti rather than the 0 ions. The PIB model gives the correct tetragonal to orthorhombic transition in La2CuO4. Lattice dynamics in the high-temperature superconductors shows numerous double-well type modes. A stable oxygen breathing mode is found using PIB, in agreement with experiment. A combination of elaborate LAPW and simple model calculations is shown to be a fruitful approach for understanding the bonding, total energies, lattice dynamics, and elasticity of oxide perovskites.

Duke Scholars

Author Michael J Mehl Thomas Lord Department of Mechanical Engineering and Materia ...