First-principles optical spectra of low dimensional systems: single particle and many-body approaches

Low dimensional systems, such as organic molecules, nanotubes, nanowires, have attracted great interest in the last few years, due to their possible application in nanodevices. It is therefore important to describe accurately the electronic excitations, with highly reliable and efficient ab-initio approaches. A standard technique for studying the ground-state properties is the Density Functional Theory; however when electronic excited states are involved, the many-body Green's functions theory is used for obtaining quasi-particle excitation energies and optical spectra. In this paper we will present the current status of this theoretical and computational approach, showing results for a bulk semiconductor and for two different kinds of low dimensional systems