Abstract EN:

My thesis fits into the domain of theoretical spectroscopy. This term describes a set of theoretical approaches that go hand-in-hand with several experimental techniques such as optical absorption and reflectivity, inelastic X-ray scattering (IXS), electron energy-loss spectroscopy (EELS) and photoelectron (or photoemission) spectroscopy. This set of ab-initio theories is used to simulate, study, predict and understand what is and will be seen in experiment. These spectroscopies are all connected to the dielectric function ε(ω ) of an electronic system which is, in fact, a fundamental quantity in many modern electronic structure theories. In particular I focused my research on photoemission spectroscopy, where the dielectric function enters as the screening of the hole due to the system. During my thesis I have worked on the development of new theoretical approaches, the aim of my project being to go beyond state-of-the-art methods used in electronic structure calculations. These methods stem mainly from two larger theoretical frameworks: Time-Dependent Density-functional Theory (TDDFT) and Green's function theory -- also known as Many-Body Perturbation Theory (MBPT). I carried on the theoretical development in parallel with numerical simulations on real materials and with experimental measurements, performed to verify the reliability of theory.