First Principles Study Of The Transition Metal Oxides Materials

With the rapid development of computer technology, computational physics has made a big progress and plays an important role in the study of natural science. It can be a very useful method to explore the law of nature. Especially, it can analogy and predict the complicated physical phenomenon. The first-principles calculation based on density function theory has many applications in many aspects, such as simulating computation and materials design. This has made it to be a frontier approach in physical of calculation. In this thesis, I mainly used the BSTATE (Beijing Simulational Tool for Atom Technology) package which is based on density functional theory (DFT) to calculate the physical properties of the two types of transition metal oxides.Transition metal oxide is mainly composed of transition metals and oxygens. Among them, d orbital of the transition metals is not full. It has attracted great attention because of its various physical properties. Transition metal oxides has expanded new areas of physics research, especially after the high-temperature superconductivity and colossal magnetoresistance materials are found, people are more aware of its large prospect of applications as well as its theoretical value to the underlying science. A significant feature of transition metal oxides is that the d orbital electrons have a localized distribution and the interactions between the electrons can not be ignored. In this thesis, I analyzed some properties of these materials containing the electronic structures, magnetism and orbital ordering, etc. This thesis contains the following studies:1、This paper shortly introduces several important research directions of transition metal oxide, then summarizes the basic theory and method about the first-principles calculation based on density functional theory. We use the BSTATE package to do a lot of calculations, and show the physical significances of the density of state and band structure.2、We use first-principles methods to study the density of states, band structure and Fermi surface nesting effect of the newly discovered BaTi2A2O (A=As, Sb, Bi) compounds. Total density of state and partial density of states diagram show that the Fermi surface of these three materials all consist of electrons from the dxy、dx2-y2、dz2orbitals. Its Fermi surface consist of three parts and the nesting vector is q1�'=(π/a,0,0) and q2�'=(π/a,0,0). Making a comparison of the three materials, we found that in the same doping case BaTi2Bi20has a stronger nesting effect than BaTi2Sb20. From the calculation results of different magnetic susceptibilitys (one-dimensional magnetic susceptibility and two-dimensional magnetic susceptibility) under different types of doping (electron doping and hole doping). We know that superconductor can be only found in the hole-doped compounds. By calculating the lowest energy of the material, we can see that the magnetic ground state of BaTi2Bi20is the two-fold degenerate states of bi-collinear antiferromagnetism (AF3) and blocked checkerboard antiferromagnetism (AF4) of second degree degenerate states. As to BaTi2As20, site-elective AF may also be its magnetic ground state.3、 based on first principles, we study the Sr7Mn4O15material, in which the lattice constant and atomiccoordinates data are from the neutron powder diffraction experiments. In order to find the moststable configuration, we used the method of adding U and in the end we found the magnetic groundstate of this material may be AF1and AF2these two degenerate states.