Metal-Insulator Transition in Ni Compounds
The metal-insulator transition in Ni compounds is discussed on the basis of two calculations which take account of electron correlation. The first calculation which assumes a linear model of a finite size simulating a compound NiX with X representing p-valence atom such as O and S determines rigorously the wave function of the ground state by use of the Lanczos method. The second one which adopts a realistic three dimensional model uses the Local Ansatz approach to take into account the correlation effect. It is concluded that a Ni atom in the metallic state near the transition keeps very likely a well developed magnetic moment. Correlation between neighboring Ni magnetic moments, however, will become much smaller than that in the insulating phase. The results are consistent with the photoemission experiment which observes quite a small change in the spectra across the transition.
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