The phD thesis entitled “Simulation of core-electron spectroscopies of gas-phase molecules and adsorbates by DFT and TDDFT methods” deals with the simulation and interpretation of data obtained from X-ray Photoelectron Spectroscopy (XPS) and Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS) of molecules in the gas phase and adsorbed on metal surfaces. In particular, studies in the gas-phase have focused on the elucidation of the electronic structure of molecular building blocks that can be exploited for the design of novel high-performance electronic and optoelectronic devices, while investigations on surface chemistry put a special emphasis on the characterization of the electronic structure of boron-containing adsorbates that can be used for surface functionalization. The main collaborations implicated in these studies have involved experimentalists afferent to the Gas Phase Photoemission and ALOISA beam lines of the Elettra Synchrotron in Trieste, the Department of Physics and Astronomy, Molecular and Condensed Matter Physics of Uppsala University (Sweden), and the Molecular Solids Group of the Philipps University of Marburg (Germany). To establish and quantify the relationship between the measured spectral features and the electronic structure information, theoretical calculations by means of density functional theory (DFT) and its time-dependent generalization (TDDFT) in the linear response regime have been performed, thus supporting XPS and NEXAFS experimental measurements. In many instances, the agreement between theory and experiment has proven to be remarkable, allowing a reliable assignment of the main spectral features, and their association with the different atomic contributions. Furthermore, the employed computational methods have provided valuable and original outcomes, with new insights on the nature of the virtual states implicated in the X-ray absorption process.
