Theoretical spectroscopy of realistic condensed matter systems

This thesis is devoted to the ab initio calculation of ground state and excited state properties of different systems within the density functional theory and the time dependent density functional theory.From the numerical point of view we implemented an original method in a plane waves code devoted to calculate the independent particle response function.Moreover, we generalized the same code to the spin degree of freedom in order to study the magnetic properties of realistic condensed matter systems.We studied the reflectance anisotropy spectra and the energy loss spectraof the clean and oxidized surface, and we performed the analysis of the originof the main spectral features.Thanks to the comparison between experimental and theoretical REEL spectra,we could roule out the p(2x1) reconstruction for this surfcace.Moreover, we evidenced the problem of the correct description of the excitation spectra for open shell systems within the TDDFT framework, in thecase of the simple BeH molecule.In the second part of the thesis, we presented the study of the opticalproperties of magnetic systems such as FeS2, CoS2 or NiS2, interesting materialsfor possible technological applications in the growing field of spintronics.Within this context we calculated the ground state properties and the opticalcondictivity of BCC bulk iron, for which we found a nice agreement withavailable experimental data.