First-Principle Studies Of Some Different Structural Compounds

In this paper,we mainly study some spintronic materials.By using first principles theory,we calculate the electronic structure and magnetic properties of some materials.Our main goal is to investigate the half-metallic properties of some materials.Half-metallic magnets are very useful and important materials,because their band structure is metallic in one of the two spin channels and semiconducting or insulating in the other one,which makes electrons controlled in charge number and spinning.we investigate Rb Se and Cs Te compounds,double perovskite compound Ba2 Ce Co O6 and quaternary Heusler alloys Zr Co Fe Z(Z=Si,Ge)with different structures.The results show these kinds of materials are of the nice half-metallic properties,which may become very promising candidates for spintronics application.In the second chapter,we briefly introduce the theoretical basis of this paper.First,we introduce two commonly used methods of calculating energy band,the plane wave method and pseudopotential method.Then we introduce the Hartree-Fork approximation and deduce Hartree-Fork equation.Based on the Hartree-Fork equation,we introduce the density functional theory(DFT).DFT is widely used in condensed matter physics and computational materials,also it is the method that we use in this paper.In the third chapter,we investigate the electronic structure and magnetic properties of Rb Se and Cs Te compounds in Cs Cl,RS and ZB structures by using density functional theory calculation.It is shown that these two compounds exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 ?Bper formula unit in all the three structures.Total energy calculations indicate the Cs Cl phase is more stable than the other two phases.We investigate these two compounds with Cs Cl structure in detail.In the fourth chapter,the structural,electronic and magnetic properties of cubic double perovskite Ba2 Ce Co O6 were calculated using first-principles full-potential local-orbital minimumbasis method.This compound has a cubic crystal structure with space group Fm3 m.By analysing the band structure we found,at the equilibrium lattice constant,this compound is a half-metal.Moreover,the half-metallicity can be kept under a large range of pressure.Meanwhile,the thermodynamic characters are investigated using the quasi-harmonic Debye model.In the fifth chapter,we investigate the electronic structure and magnetic properties of two quaternary Heusler alloys Zr Co Fe Z(Z=Si,Ge)by using first-principle calculations.It is shown that Zr Co Fe Si is a half-metallic ferromagnet with considerable half-metallic gap of 0.22 e V.Zr Co Fe Ge is nearly half-metallic with a spin polarization of 98.99% at equilibrium lattice constant.Meanwhile,the changes of its properties under pressure are investigated.In the last chapter of the thesis,we summarize the whole paper and make a plan for the future work.