Theory Meets Experiment in Low-Dimensional Structures with Correlated Electrons

By means of density functional theory calculations, we explain the anomalous thermally induced peaks in the XPS spectra of the core electrons previously reported for a metalloporphyrin molecule adsorbed on TiO₂ surface [JCP 146, 184704 (2017)]. The shift of such levels is routinely interpreted as a signature of charge exchange with the substrate. However, in this case we show that some atoms with no chemical bonding to the surface also experience significant core level shifts. Our interpretation based by simulations is that the electronic structure of this dye synthesizer-semiconductor complex is partly originated from its core geometry deformation. In particular, the next neighbors are also affected. One should therefore use the valuable photoelectron spectroscopy outputs with caring such effects. Our theoretical prediction is in fair agreement with experiment, based on which we are able to disclose the mechanism of the splitting the degenerate core states in terms of the symmetry breaking rather than the dye-substrate chemical bonding. This, additionally, shows that how one can facilitate the high sensitivity of photoelectron spectroscopy to help identification the adsorption site and orientation of molecules on atomic surfaces.