Estimation of correlation energy and the exchange constant in yttrium barium copper oxides

Abstract

The Hubbard on-site correlation energy U and the transfer energy t for the electron hop between the copper d_x²-y² and the overlapping p orbital of the nearest-neighbour oxygen atom are estimated based on the XPS results on these compounds. Using these parameters, it is predicted that the BIS spectra should show a peak around 2 eV. The strength of the exchange interaction between the copper atoms is estimated to be 0.14 eV in the planes and 0.07 eV in the chains, correct to fourth order in perturbation theory for a half-filled d_x²-y² band.