  Using the ground-state energy of 16-O obtained with the realistic V_UCOM
interaction as a test case, we present a comprehensive comparison of different
configuration interaction (CI) and coupled-cluster (CC) methods, analyzing the
intrinsic advantages and limitations of each of the approaches. In particular,
we use the importance-truncated (IT) CI and no-core shell model (NCSM) schemes
with up to 4-particle-4-hole (4p4h) excitations as well as the size extensive
CC methods with a complete treatment of one- and two-body clusters (CCSD) and a
non-iterative treatment of connected three-body clusters via the completely
renormalized correction to the CCSD energy defining the CR-CC(2,3) approach. We
discuss the impact of the center-of-mass contaminations, the choice of the
single-particle basis, and size-extensivity on the resulting energies. When the
IT-CI and IT-NCSM methods include the 4p4h excitations and when the CC
calculations include the 1p1h, 2p2h, and 3p3h clusters, as in the CR-CC(2,3)
approach, we observe an excellent agreement among the different methodologies.
This shows that despite their individual limitations, the IT-CI, IT-NCSM, and
CC methods can provide precise and consistent ab initio nuclear structure
predictions. Furthermore, the IT-CI, IT-NCSM, and CC ground-state energy values
obtained with 16-O are in good agreement with the experimental value, proving
that the V_UCOM two-body interaction allows for a realistic description of
binding energies for heavier nuclei and that all of the methods used in this
study account for most of the relevant particle correlation effects.
