General model for explicitly hole-doped superconductor parent compounds: Electronic structure of Ca2-xNaxCuO2Cl2 as a case study

Periodic density functional theory (DFT) + U calculations using sufficiently large supercells to explicitly account for dopant disorder are reported for undoped Ca2CuO2Cl2 and for the doped Ca2-xNaxCuO2Cl2 (x = 0.125 and x = 0.250). For the undoped material, the charge-transfer antiferromagnetic character is properly reproduced. For the doped systems, a metallic character is predicted with the conduction band dominated by the O(2p) states, with doping having a small effect on the antiferromagnetic order of the Cu2+ cations within the CuO2 planes while maintaining the diamagnetic character in the rest of centers. The analysis of the spin density plots for the doped material evidences the appearance of a new feature reminiscent of the so-called Zhang-Rice singlet, thus providing unbiased independent support to the corresponding model Hamiltonian. However, it is also worth pointing out that the present DFT picture provides only an average static representation of what is expected to be a dynamic electronic structure.