  Applying a variational multiparticle-multihole configuration mixing method
whose purpose is to include correlations beyond the mean field in a unified way
without particle number and Pauli principle violations, we investigate
pairing-like correlations in the ground states of $ ^{116}$Sn,$ ^{106}$Sn and $
^{100}$Sn. The same effective nucleon-nucleon interaction namely, the D1S
parameterization of the Gogny force is used to derive both the mean field and
correlation components of nuclear wave functions. Calculations are performed
using an axially symetric representation. The structure of correlated wave
functions, their convergence with respect to the number of particle-hole
excitations and the influence of correlations on single-particle level spectra
and occupation probabilities are analyzed and compared with results obtained
with the same two-body effective interaction from BCS, Hartree-Fock-Bogoliubov
and particle number projected after variation BCS approaches. Calculations of
nuclear radii and the first theoretical excited $0^+$ states are compared with
experimental data.
