Importance of static correlation in the band structure of high-temperature superconductors

Recently the authors presented a new band structure for La{sub 2{minus}x}Sr{sub x}CuO{sub 4} and other high-temperature superconductors in which a second narrow band was seen to cross the primary band at the Fermi level. The existence of this second Fermi level band is in complete disagreement with the commonly accepted LDA band structure. Yet it provided a crucial piece of physics which led to an explanation for superconductivity and other unusual phenomena in these materials. In this work, details as to the nature of the failure of conventional methods in deriving the band structure of the cuprates are presented. In particular, a number of chemical analogues describe the problem of static correlation in the band structure calculations and show how this can be corrected with the predictable outcome of a Fermi level band crossing.