A local point of view of the Cu(100) → NiTPP charge transfer at the NiTPP/Cu(100) interface

A precise understanding, at the molecular level, of the massive substrate -> adsorbate charge transfer at the NiTPP/Cu(100) interface has been gained through the application of elementary symmetry arguments to the structural determination of the NiTPP adsorption site by photoelectron diffraction (PED) measurements and Amsterdam density functional calculations of the free D4h NiTPP electronic structure. In particular, the PED analysis precisely determines that, among the diverse NiTPP chemisorption sites herein considered (fourfold hollow, atop, and bridge), the fourfold hollow one is the most favorable, with the Ni atom located at 1.93 angstrom from the surface and at an internuclear distance of 2.66 angstrom from the nearest-neighbors of the substrate. The use of elementary symmetry considerations enabled us to provide a convincing modeling of the NiTPP-Cu(100) anchoring configuration and an atomistic view of the previously revealed interfacial charge transfer through the unambiguous identification of the adsorbate pi* and sigma* low-lying virtual orbitals, of the substrate surface atoms, and of the linear combinations of the Cu 4s atomic orbitals involved in the substrate -> adsorbate charge transfer. In addition, the same considerations revealed that the experimentally reported Ni(ii) -> Ni(i) reduction at the interface corresponds to the fingerprint of the chemisorption site of the NiTPP on Cu(100).The chemisorption site of NiTPP on Cu(100) has been determined by combining symmetry considerations with photoelectron diffraction. The Ni(ii)-> Ni(i) reduction at the interface rules the adsorption sites and the NiTPP orientation on the substrate.