Ab initio study of the Cu 2p and 3s core-level XPS spectra of copper phthalocyanine -: art. no. 045105

The x-ray photoelectron spectra (XPS) of copper tetraazaporphyrin (CuTAP), used as a model of copper phthalocyanine(CuPc) are studied by theoretical simulations. The nature of the main and satellite features observed in the XPS Cu 2p and Cu 3s photoelectron spectra are discussed based on the results of the charge-transfer (CT) model and of ab initio calculations in the sudden approximation limit. It is shown that the two descriptions of the core level final states can be derived from the two types of approaches. The final-state wave functions given by the CT model are described in a shakedown scenario. This process produces a "well-screened" final 2p(5)3d(10)(L) under bar configuration ((L) under bar denotes a ligand hole) on the Cu atom together with the core hole, resulting in the main spectral peak. On the other hand, the process where the outer electron stays on the ligand corresponds to the satellite with a poorly-screened 2p(5)3d(9) character. The ab initio calculations, performed on an isolated copper tetraazaporphyrin molecule at the Hartree-Fock (HF) level, the multi-configuration self-consistent field level, and the hybrid density-functional-theory levels show that the core hole final states (satellite/main peak) can be attributed to valence-valence transitions. We show that a correct intensity distribution of the different features, including the so-called white line and the satellite structures, can be obtained when the electronic relaxation and correlation and the overlap between the ground-state and final-state Slater determinants are explicitly taken into account. It is found that the nature of the main peak is strongly depending on the Ligand-to-Metal charge transfer, on the exchange interaction and on the core-hole-3d-hole interaction energies.