  This thesis is devoted to ab initio calculations of ground and excited state
properties of different systems within density functional theory and time
dependent density functional theory. From the numerical point of view we
implemented an original method in the DP code to calculate the independent
particle response function. Moreover, we generalized the DP code to the spin
degree of freedom in order to study the magnetic properties of realistic
condensed matter systems. We studied reflectance anisotropy and energy loss
spectra of a clean and oxidized surface, and we performed an analysis of the
origin of the main spectral features. Thanks to the comparison between
experimental and theoretical energy loss spectra, we roule out the p(2x1)
reconstruction for the Si(100) surface. Moreover, in the case of a simple BeH
molecule we evidenced the problem of correctly describing the excitation
spectra for open shell systems within the TDDFT framework. In the second part
of the thesis, we presented the study of the optical properties of magnetic
systems such as FeS2, CoS2 or NiS2, interesting materials for possible
technological applications in the growing field of spintronics. Within this
context we calculated ground state properties and optical condictivity of BCC
bulk iron, for which we found a nice agreement with available experimental
data.

Materials Science