A Multi-Configuration Mixing Approach with Symmetry-Projected Complex Hartree-Fock-Bogoliubov Determinants

A multi-configuration mixing approach built on essentially complex, symmetryprojected Hartree-Fock-Bogoliubov (HFB) mean fields is introduced. The mean fields are obtained by variation after projection. The configuration space consists out of the symmetry-projected HFB vacuum and the symmetry-projected twoquasiparticle excitations for even, and the symmetry-projected one-quasiparticle excitations for odd A systems. The underlying complex HFB transformations are assumed to be time-reversal invariant and axially symmetric. The model allows nuclear structure calculations in large model spaces with arbitrary two-body interactions. The approach has been applied to Ne and Ne. Good agreement with the exact shell model results and considerable improvement with respect to older calculations, in which only real HFB transformations were admitted, is obtained.