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In this paper we review the first-principles theoretical framework of the Bethe–Salpeter equation which is nowadays the state-of-the-art approach for including self-energy, local fields and excitonic effects in the surface optical response. Two different approaches for calculating the dielectric screening will be described. In both cases a parallel and efficient iterative algorithm to find numerically the solution of the BSE equation has been implemented. In fact, if the surface states are not energetically separated from the bulk states and if one is interested in describing a large energy window, the traditional approach involving a full diagonalization of a very large excitonic Hamiltonian is prohibitive. The reflectance anisotropy spectrum of the monohydride Si(100) is considered and compared with experiments. A comparison of the results obtained within different treatments of the electron–hole screening is made. Convergence and numerical problems are discussed.

The relaxation dynamics of unaligned multi-walled carbon nanotubes decorated with metallic nanoparticles have been studied by using transient optical measurements. The fast dynamics due to the short-lived free-charge carriers excited by the pump are not affected by the presence of nanoparticles. Conversely, a second long dynamics, absent in bare carbon nanotubes, appears only in the decorated samples. A combination of experiment and theory allows us to ascribe this long dynamics to relaxation channels involving electronic states localized at the tube-nanoparticle interface.

We compute the optical conductivity of 2D honeycomb crystals beyond the usual Dirac-cone approximation. The calculations are mainly based on the independent-quasiparticle approximation of the complex dielectric function for optical interband transitions. The full band structures are taken into account. In the case of silicene, the influence of excitonic effects is also studied. Special care is taken to derive converged spectra with respect to the number of k points in the Brillouin zone and the number of bands. In this way both the real and imaginary parts of the optical conductivity are correctly described for small and large frequencies. The results are applied to predict the optical properties reflection, transmission and absorption in a wide range of photon energies. They are discussed in the light of the available experimental data.