Improved stability regions for ground states of the extended Hubbard model

The ground-state phase diagram of the extended Hubbard model containing nearest- and next-to-nearest-neighbor interactions is investigated in the thermodynamic limit using an exact method. It is found that taking into account local correlations and adding next-to-nearest-neighbor interactions both have significant effects on the position of the phase boundaries. Improved stability domains for the eta-pairing state and for the fully saturated ferromagnetic state at half-filling have been constructed. The results show that these states are the ground states for model Hamiltonians with realistic values of the interaction parameters. [S0163-1829(99)12015-0].