First-principle Study Of The Electronic Spin-polarization Of Some Materials

With the development of theory, numerical algorithm and computing power, den-sity functional theory (DFT) calculation has become one of the most important methodsin condensed matter physics, quantum chemistry and material science. A great successhas been received in geometric configuration, electronic structure and magnetic prop-erties by DFT calculations. In this thesis, the adsorption of NO molecule on Ni(100)surface and the substitution effect of Heusler alloy are investigated by DFT method.The geometric structures, electronic properties, and the spin polarization around Fermilevel are discussed. The mechanisms about the variation of electronic and magneticproperties by molecular adsorption or element substitution are analyzed.The basic concept of DFT and its recent progress are reviewed in the first chap-ter. The DFT is based on the Hohenberg-Kohn theorems, the solution of Kohn-Shamequation and the finding of good approximation for exchange-correlation functional.Many calculation codes such like VASP, Gaussian, are developed accurately. DFT hasbecome one of the most routine and important calculating method at condensed matter,quantum chemistry and material science.The adsorption of NO molecule on Ni(100) is studied by DFT calculation in chap-ter 2. The adsorption geometry and spin-resolved electronic states of NO adsorbedNi(100) surface are discussed. The upright configuration is predicted at both low(0.125ML) and high (0.5ML) NO molecule coverage. The magnetic moment is sig-nificantly suppressed for surface Ni atom and almost quenched for NO molecule. Theback-donation process is proven to be dominant by spin-down electrons, which gives areasonable explanation for the significant variation of the magnetic properties.The substitution effect of Fe for Mn element in Hesler alloys ( ????2????1?????????????) is studied by DFT calculation in chapter 3. The electronic property and the spinpolarization around Fermi level are discussed at different ratio of Mn/Fe. The energylevel of the top/bottom of the spin-down valence/conduction band decreases with theincrease of the Fe. The Fermi level is found to be located at the gap of the spin-downelectronic states when x=0.5, resulting in the 100 % of the spin polarization at theFermi level and the really half metallicity.A summary is made in chapter 4.