TIGHT-BINDING PARAMETERS AND EXCHANGE INTEGRALS OF BA2CU3O4CL2

Band-structure calculations of Ba2Cu3O4Cl2, within the local-density a pproximation (LDA) are presented. The investigated compound is similar to the antiferromagnetic parent compounds of the cuprate superconduct ors but contains additional Cu-B atoms in the Cu-O planes. Within the LDA, metallic behavior is found with two bands crossing the Fermi surf ace. These bands are built mainly from Cu 3d(x2-y2) and O 2p(x,y) orbi tals, and a corresponding tight-binding (TB) model for these bands has been parameterized. Ail orbitals can be subdi vided in two sets corre sponding to the A and B subsystems, respectively, the coupling between which is found to be small. To describe the experimentally observed a ntiferromagnetic insulating stale, we propose an extended Hubbard mode l using the parameters derived from the TB fil and local correlation t erms characteristic for cuprates. Using this parameter set we calculat e the exchange integrals for the Cu3O4 plane, the results being in qui te reasonable agreement with the experimental values for the isostruct ural compound Sr2Cu3O4Cl2.