Elimination of unoccupied state summations in ab-initio self-energy   calculations for large supercells
  We present a new method for the computation of self-energy corrections in large supercells. It eliminates the explicit summation over unoccupied states, and uses an iterative scheme based on an expansion of the Green's function around a set of reference energies. This improves the scaling of the computational time from the fourth to the third power of the number of atoms for both the inverse dielectric matrix and the self-energy, yielding improved efficiency for 8 or more silicon atoms per unit cell. 
Lucia Reining (Ecole Polytechnique, Palaiseau, France) Giovanni Onida   (Univ. Rome ``Tor Vergata'', Rome, Italy) R.W. Godby...