  We study the performance of self-consistent mean-field and beyond-mean-field
approximations in shell-model valence spaces. In particular,
Hartree-Fock-Bogolyubov, particle-number variation after projection and
projected generator coordinate methods are applied to obtain ground-state and
excitation energies for even-even and odd-even Calcium isotopes in the
pf-shell. The standard (and non-trivial) KB3G nuclear effective interaction has
been used. The comparison with the exact solutions -- provided by the full
diagonalization of the Hamiltonian -- shows an outstanding agreement when
particle-number and angular-momentum restorations are performed and both
quadrupole and neutron-neutron pairing degrees of freedom are explicitly
explored as collective coordinates.
