DFT Investigations On The Double Perovskite Ba₂FeReO₆

First-principles calculations have made significant contributions to our understanding of condensed-matter systems and solid-state properties. We can do profound investigations to the physical properties of solid and surface, and predict many material qualities and their tendency of variations from microscopic structure by calculations. With the rapid development of theories and methods, first principle methods are also greatly improved in applicability and accuracy. But the first principles investigations for the complicated solids and surface systems, especially for the first-row elements or systems with d or f electrons, are still in initial stage and ideal results have not been obtained. Recently, more and more attention have been paid to the study of those systems. The main contents have been studied and important results in this research are presented as following:First principles density functional calculations are reported for double perovskite Ba2FeReO6 with two structures (fcc and 14/mmm) by using the FLAPW method and LSDA+U approach combined with spin-orbit coupling in this thesis. The results of band structure calculation of Ba2FeReO6 have been analyzed, which suggest that the band near Fermi surface is formed by d-d hybridization. The spin-up Fe 3d orbitals occupy the lower energy band and the band becomes narrower when screnned Coulomb U is considered. However, for the Re 5d orbitals, the band structure is almost unchanged due to its weak interaction between the electrons. At the same time, the magnetic moments of Fe, Re atoms are increased significantly at amplitudes of 0.45μB and 0.22μB for Iron and Re atoms, respectively. The half-metallic nature of Ba2FeReO6 disappears when the spin-orbital coupling is included in DFT computations and the material showes metallicity naturally. The spin-orbital coupling has different effects to the moment of Fe and Re atoms in the two different structures. For the fcc structure, the magnetic moments of Fe and Re decrease more or less, while for 14/mmm structured Ba2FeReO6, the situation is almost the same. We speculate that these observations might be caused by the differences in crystalline structures and the inclusion of screened Coloumb U between d elestrons.