Novel Properties Of NiO And The Related Systems

Because of the strong correlations between d (f) electrons, transition metal oxides exhibit very rich and intriguing physical and chemical properties. The studies of strongly correlated electronic system have thus attracted a lot of attention over the last decades. Due to localized d (f) electrons in strongly correlated materials, Density Functional Theory (DFT) based on a one-electron method cannot give an accurate description of strongly correlated system. On the other side, although the separate elementary processes of normal system can be addressed in detail based on DFT calculations, the system functionalities are determined by the statistical interplay of many elementary processes. In order to obtain an atomic-scale understanding of the real materials, new multi-scale modeling methodologies have to be developed, in which DFT should be combined with other theories such as thermodynamics.The present dissertation has investigated various physical and chemical properties of a typically strongly correlated materials NiO including high pressure behavior, defect physics, and surface physics using GGA+U method in combination with Heisenberg spin Hamiltonian and thermodynamic formalism. The strong electronic correlations have also been taken into account in GGA+U method. In order to clarify the underlying mechanism from nickel surface to nickel oxide, we also perform a multi-scale modeling for oxidation of nickel surface based on the DFT and thermodynamics. Present results are in excellent agreement with experiments and the related mechanisms are also discussed.The main contents of this dissertation are as following:1. The structural distortion and electronic properties of NiO under high pressure have been investigated using generalized gradient approximation (GGA) and GGA+U method. The present results show that GGA calculation and earlier LDA calculation do not give a proper description of structural distortion under high pressure. When strong correlations are included in GGA+U method, the calculation results are in good agreement with the experimental measurements. Meanwhile, we also investigate the structural distortion of MnO and FeO under high pressure. The results indicate that the strong electronic correlation plays a very important role in structural distortion of transition metal monoxide under high pressure.2. The magnetic exchange interactions and the related properties of NiO under high pressure has been investigated systematically based on GGA+U method and Heisenberg spin Hamiltonian. The Néel temperature under high pressure of NiO is also evaluated. Present results give theoretical evidence that the Bloch's law is valid under high pressure. These results are consistent with experiments and the related mechanisms are also discussed.3. The stability of native vacancy defects in NiO have been investigated using the GGA+U method. The results indicate that both the oxygen chemical potential and Fermi level play a very important role in stability of defect. The native p-type conductivity is found to be originated from the nickel vacancy. In addition, it can be found that introducing different ionization state of Ni vacancy in NiO, a half-metallic anti-ferromagnetic or half-metallic ferromagnetic behavior can be found. This phenomenon can be understood based on the spin-triplet ground state of nickel vacancy.4. The stability of polar NiO(111) and MgO(111) surface has been investigated using density functional theory in combination with a thermodynamic formalism. The most stable phases under different temperature and pressure conditions have been determined, which are consistent with recent experiments. The results indicate that surface reconstruction will cancel the polarity and oxygen chemical potential which is determined by temperature and oxygen pressure plays a very important role in the stability of polar surface.5. In order to obtain an atomic-scale understanding for the oxidation of nickel surface, we have studied the adsorption process of oxygen on Ni (110) surface firstly. The most stable adsorption structures at different substrates including the reconstructed and unreconstructed surface have been determined. The surface structure, electronic and magnetic structure, and their change induced by oxygen absorption are focused. Furthermore, we also perform a multi-scale modeling to analyze the oxidation of Ni(110) surface. The surface adsorption diagram of O/Ni (110) system over a wide range of temperature and pressure condition has also been determined. These results could effectively solve the debates in different experiments.6. Finally, we have investigated electronic structure and Fermi surface character of a novel superconductor LaNiPO based on First-principles calculation. The quantificational binding properties of LaNiPO are obtained based on Bader analysis of the charge density. In addition, we also discuss the superconductivity mechanism through density of sates, band decomposed charge density and orbital components of Fermi surfaces.