Variational bounds for lattice fermion models II. Extended Hubbard model in the atomic limit

Abstract

The authors derive a mean-field expression for the Helmholtz free energy of the extended Hubbard model with on-site repulsion and longer range attraction in the atomic limit. The mean-field free energy is exact in the infinite-dimensional and long-range limits and reduces to the exact ground state energy at T=0. Implications for the phase diagram of the extended Hubbard model are discussed.