Multiband d-p model and self-doping in the electronic structure of Ba sub(2) IrO sub(4)

We introduce and investigate the multiband d-p model describing a IrO sub(4) layer (such as realized in Ba sub(2) IrO sub(4)) where all 34 orbitals per unit cell are partly occupied, i.e., t sub(2g) and e sub(g) orbitals at iridium and 2p orbitals at oxygen ions. The model takes into account anisotropic iridium-oxygen d-p and oxygen-oxygen p-p hopping processes, crystal-field splittings, spin-orbit coupling, and the on-site Coulomb interactions, both at iridium and at oxygen ions. We show that the predictions based on assumed idealized ionic configuration (with n sub(0)= 5 + 4 x 6 = 29 electrons per IrO sub(4) unit) do not explain well the independent ab initio data and the experimental data for Ba sub(2) IrO sub(4). Instead we find that the total electron density in the d-p states is smaller, n= 29 -x< n sub(0)(x > 0). When we fix x= 1, the predictions for the d-p model become more realistic and weakly insulating antiferromagnetic ground state with the moments lying within IrO sub(2) planes along (110) direction is found, in agreement with experiment and ab initio data. We also show that (i) holes delocalize over the oxygen orbitals and the electron density at iridium ions is enhanced; hence (ii) their e sub(g) orbitals are occupied by more than one electron and have to be included in the multiband d-p model describing iridates.