COMPARISON OF MEAN-FIELD THEORIES OF AN EXTENDED HUBBARD-MODEL

Models of strongly interacting Fermi systems are sufficiently intractable that simple mean-field approximations (typically Hartree-Fock) are often employed to obtain qualitative insight into their properties, and also to set parameter values by comparing with band-structure calculations. However, if the correlations are accounted for with use of more sophisticated (but still mean-field-like) methods, qualitative changes in charge densities and magnetic properties can result. We compare four mean-field approximations for an extended Hubbard model and show that they yield quite different results. Implications for the choice of model for high-temperature superconductors are discussed. © 1990 The American Physical Society.