En las fronteras de la Materia Condensada

The GW approximation based on an all-electron Projector Augmented-Wave (PAW) method has been developed to compute the quasiparticle properties of materials. Within this approach, the self-energy is a product of the one-particle Greens function G and the dynamically screened interaction W computed within the random phase approximation (RPA). Starting from the calculated local density approximation (LDA) ground state, the LDA eigenvalues are corrected by treating the difference between the self-energy and the exchange-correlation potential as a perturbation. The calculated quasiparticle energies obtained by means of this procedure are, generally, in good agreement with experiment. It is surprizing, however, that the quasiparticle energies are found to be neither sensitive to the scheme used for decoupling core and valence electrons nor to the different type of plasmon-pole models used to produce the dynamically screened interaction W. The quasiparticle energies are then used to compute the macroscopic dielectric function including both local-field and excitonic (electron-hole interaction) effects. The standard procedure for including these effects in the calculation of the dielectric function consists in solving the so called Bethe-Salpeter equation. This approach has been applied to different semiconductors and insulators, and it has been shown that the inclusion of electron-hole attraction is necessary for a detailed comparison of the theoretical and experimental optical spectra.