The ground state of a model simulating a compound NiX with X representing p -valence atom such as O and S is investigated by calculating rigorously the wave function for a linear cluster. The change from the state corresponding to the insulating phase with well developed magnetic moment of Ni to the state which may correspond to the metallic phase is investigated by decreasing the charge transfer energy of between Ni and X. It is found that in the state adjacent to the insulating state the spin correlation between neighboring Ni atoms decreases drastically, while the magnitude of the magnetic moment of each Ni atom remains large. It is found also that the photoemission spectra do not change appreciably across the transition. The implication of these results is discussed in connection to the observed insulator-metal transition in NiS and also to a similar calculation for CuX.