First-principles calculations of the electronic structure of open-shell   condensed matter systems
  We develop a Green's function approach to quasiparticle excitations of open-shell systems within the GW approximation. It is shown that accurate calculations of the characteristic multiplet structure require a precise knowledge of the self energy and, in particular, its poles. We achieve this by constructing the self energy from appropriately chosen mean-field theories on a fine frequency grid. We apply our method to a two-site Hubbard model, several molecules and the negatively charged nitrogen-vacancy defect in diamond, and obtain good agreement with experiment and other high-level theories. 
Johannes Lischner, Jack Deslippe, Manish Jain, Steven G. Louie
cond-mat.mtrl-sci