  The ground state pairing correlations in finite fermionic systems are
described with a high degree of accuracy within a variational approach based on
a combined coupled-cluster and particle-number-projected BCS ansatz. The
flexibility of this symmetry-preserving wavefunction enables a unified picture
valid from weak to strong coupling, both in small and large systems. The
present variational approach consistently yields an energy upper bound while
operating at the same level of precision of the non-variational particle-number
projected Bogoliubov-coupled-cluster theory [Phys. Rev. C 99, 044301 (2019)].
