Electronic properties and dielectric response of surfaces and nanowires of silicon from ab-initio approaches

We present here an ab-initio study, within the Density Functional Theory (DFT), of the formation energy of doped Silicon Nanowires (Si-NWs). While this theoretical approach is appropriate to calculate the ground-state properties of materials, other methods, like Many-Body Perturbation Theory (MPBT) or Time Dependent Density Functional Theory (TDDFT), formally provide a correct description of the electronic excited states. Then, in the second part of this paper, we show how the many-body effects, introduced using the MBPT, modify the optical properties of the Si(100) surface.