Excitonic effects in the optical properties

A method for the inclusion of self-energy and excitonic effects in first-pr inciples calculations of absorption spectra, within the state-of-the-art pl ane-wave pseudopotential approach, is presented. Self-energy effects are co mputed within GW, and the electron-hole interaction is treated solving an e ffective two-particles equation which is derived from the relevant Bethe-Sa lpeter equation. The link between the GW approach and the inclusion of exci tonic effects is discussed. We illustrate the performance of the approach a t the examples of the absorption spectrum of bulk silicon and the excited s tate charge density of Na-4.