The Extended Hubbard Model at Large Interaction

Abstract

The half-filled Extended Hubbard model (i. e., the Hubbard model including nearest-neighbor interaction) is considered at strong coupling in fourth order perturbation theory (4thOPTh). The ground state energies in the spin- and charge-density-wave phases and the resulting phase diagram are calculated in one, two, three and higher dimensions. Quite generally one finds that second order perturbation theory alone is valid only at unrealistically large values of the interaction parameters U and V. In one dimension it is shown that, for U/t larger 6, 4thOPTh leads to excellent agreement with existing Monte Carlo data.