The electronic structure of Ba2Cu3O4Cl2

Band structure calculations for Ba2Cu3O4Cl2 within the local density approximation (LDA) have been carried out and the total as well as partial densities of states have been calculated. The investigated compound is similar to the antiferromagnetic parent compounds of cuprate superconductors but contains additional Cu(B) atoms in the planes. Within the LDA metallic behaviour is found with two bands crossing the Fermi level. The result is in disagreement with the experimentally observed antiferromagnetic insulating state, showing the necessity to deal with the electron correlations in a more detailed way. To decide which orbitals should be correlated, a model with Cu-3d and O-2p orbitals was constructed. It is shown that the coupling between the Cu(A) and the additional Cu(B) subsystem is small.