Excitonic effects in the optical properties

A method for the inclusion of self-energy and excitonic effects in first-principles calculations of absorption spectra, within the state-of-the-art plane-wave pseudopotential approach, is presented. Self-energy effects are computed within GW, and the electron-hole interaction is treated solving an effective two-particles equation which is derived from the relevant Bethe-Salpeter equation. The link between the GW approach and the inclusion of excitonic effects is discussed. We illustrate the performance of the approach at the examples of the absorption spectrum of bulk silicon and the excited state charge density of Na-4.