  We calculate the ground-state properties of well deformed, even-even N=Z
nuclei in the region between Ni-56 and Sn-100 within two different approaches,
focusing on the binding energy and deformation and pairing properties. First,
we employ the Hartree-Fock-BCS (HFBCS) approximation with the Skyrme effective
nucleon-nucleon interaction and discuss how the results depend on the
parameterization of the interaction and on the pairing force parameters
adjusted in various schemes to reproduce the experimental odd-even mass
differences. Then, within the Higher Tamm-Dancoff Approximation (HTDA), which
explicitly conserves the particle number, we calculate the same properties
starting from the HFBCS solutions. The HTDA treatment of the ground-state
correlations is converged within a n-particle-n-hole expansion using up to n=4
particle-hole excitations of the pair type (in the sense of Cooper pairs). We
compare the ground-state properties calculated in these two descriptions of
pairing correlations and deduce the importance of the particle-number
conservation in weak pairing regimes. Finally, we extend the HTDA calculations
so as to include the proton-neutron residual interaction and investigate the
role of proton-neutron pairing on the above ground-state properties.
