We introduce a method that allows for the calculation of quasi-particle spectra in the GW approximation, yet avoiding any explicit reference to empty one-electron states. This is achieved by expressing the irreducible polarizability operator and the self-energy operator through a set of linear response equations, which are solved using a Lanczos-chain algorithm. We first validate our approach by calculating the vertical ionization energies of the benzene molecule and then show its potential by addressing the spectrum of a large molecule such as free-base tetraphenylporphyrin.
@article{arxiv.0910.0791,
title = {GW quasi-particle spectra from occupied states only},
author = {P. Umari and G. Stenuit and S. Baroni},
journal= {arXiv preprint arXiv:0910.0791},
year = {2015}
}