First Principles Study Of Transition Metal Compounds

In recent years, with continuous improvement and development of computer technology and methodof calculation, calculation of the physical much physics researchers of all ages with its incomparableadvantages. Among them, the first principle calculation （first-principles）, which is based on ab initiodensity functional theory （ab-initio calculation） theory has many applications in materials design, synthesis,simulation, etc., has become a computational materials science an important foundation and coretechnology. In this paper use the package BSTATE （Beijing Simulational Tool for Atom Technology） Firstprinciples calculation based on density functional theory （DFT） to study various characteristics of thetransition metal oxides.Recently, in strongly correlated electron interaction system caused the breadth of the researchcommunity attention. The transition metal oxides is a hot topic of research in this area recently, transitionmetal oxides began in the fifties and sixties. The revival of the system over the past decade, mainly due tothe discovery of high-temperature superconducting oxides and the CMR effect. More importantly, physics,basic research, these materials exhibit a rich physical content, such as by magnetic fields or light-inducedinsulator-metal transition, charge ordering, orbital ordering, phase separation, and inspire people toexploration, has become one of the hot current physics research. Transition metal d shell is not full ofelectronic elements, transition metal oxides are most strongly associated with the body has a commonfeature of the valence electron valence electrons （3d,4d） Comparison of local electron correlation effects isimportant. In this paper, we study the compounds of the perovskite structure, in order to explore some ofthe electronic structure of these materials, a variety of magnetic states and the charge ordering mechanism,the specific work includes:1，The electronic, magnetic, and orbital structures of KCrF3in its recently identified crystallographicphases （tetragonal and cubic）[S. Margadonna and G. Karotsis, J. Am. Chem. Soc.128,16436（2006）] arestudied by the first-principles method. In the tetragonal phase, both the generalized gradient approximation（GGA） and the generalized gradient approximation plus Hubbard parameter U （GGA+U） calculationsshow that the ground state is the A-type antiferromagnetic （A-AFM） configuration with G-type orbitalordering pattern. Our calculations show that the orbital structures and the magnetic configurations can bemeasured by the optical conductivity. In the cubic state, the GGA calculations show that the ground state is a ferromagnetic half-metaltate, while the GGA+U （Ueff=3.0eV） calculations show that the A-AFMinsulator phase is the ground state. Our calculations indicate that the electron-electron interactions ratherthan the electron-phonon interactions are he driving forces behind the orbital ordering.2, The electronic structure of recently discovered LaCo₂B₂was studied from first-principlescalculations. Our results indicate that the hybridization between Co-3d and B-2p is much stronger than thatbetween Fe-3d and As-4p in LaOFeAs and BaFe₂As₂, which removes the magnetic ordering of Co ions.Therefore, the ground state of LaCo₂B₂is nonmagnetic. At the Fermi level, the density of state of La-5d isvery high and here are four bands cutting across the Fermi level, which are mostly derived from dz2.