  We present results from a new ab-initio method that uses the self-consistent
Gorkov Green's function theory to address truly open-shell systems. The
formalism has been recently worked out up to second order and is implemented
here in nuclei for the first time on the basis of realistic nuclear forces. We
find good convergence of the results with respect to the basis size in Ca44 and
Ni74 and discuss quantities of experimental interest including ground-state
energies, pairing gaps and particle addition/removal spectroscopy. These
results demonstrate that the Gorkov method is a valid alternative to
multireference approaches for tackling degenerate or near degenerate quantum
systems. In particular, it increases the number of mid-mass nuclei accessible
in an ab-initio fashion from a few tens to a few hundreds.
