  The calculation of quasi-particle spectra based on the GW approximation is
extended to systems of hundreds of atoms, thus expanding the size range of
current approaches by more than one order of magnitude. This is achieved
through an optimal strategy, based on the use of Wannier-like orbitals, for
evaluating the polarization propagator. Our method is validated by calculating
the vertical ionization energies of the benzene molecule and the band structure
of crystalline silicon. Its potentials are then demonstrated by addressing the
quasi-particle spectrum of a model structure of vitreous silica, as well as of
the tetraphenylporphyrin molecule.
