GW calculations of large model structures

We introduce a novel approach for performing first-principles GW calculations of large model structures. A description of the valence and conduction manifolds in terms of non-orthogonal generalized Wannier functions permits to minimize the dimension of the basis set required for describing the space of single electron transitions. This dimension scales linearly with the size of the system. Then a space-time approach is used to calculate the self-energy operator in the space of Kohn-Sham eigenstates. Ultrasoft pseudopotentials are straightforwardly implemented within this scheme.We validate our approach by calculating the vertical ionization energies of small molecules and find excellent agreement with the experiment. Then we shows its potentiality by addressing a model structure of vitreous silica.