THE VALIDITY OF THE HARTREE-FOCK APPROXIMATION FOR STUDYING THE FERMISURFACES OF DOPED CUPRATES

It is shown here that the band structure and Fermi surface of Bi2Sr2Ca Cu2O8+delta, recently measured by angle-resolved photoemission spectro scopy, can be obtained via an extended three-band Hubbard model, withi n the unrestricted Hartree-Fock approximation, provided oxygen-oxygen hopping is included and the oxygen-copper hopping is reduced below a c ritical value. This applies to other copper oxides provided that the a ppropriate parameters are considered for each compound. The results ag ree remarkably well with earlier local density calculations and spectr oscopic measurements.