Correlations in Nuclei: Configuration Interaction, Coupled-Cluster and Beyond

Many-body correlations play a central role in the structure of nuclei. The mean-field methods, such as Skyrme Hartree-Fock and its extensions to Energy Density Functionals, induce correlations dynamically at the functional level, leaving the explicit wave functions uncorrelated. The Configuration Interaction (CI) method treats the many-body correlations exactly, but in a small configurations space. It is therefore desirable to include as many correlations as possible in larger model spaces. In this contribution I compare the results of Coupled Cluster techniques and of extrapolations methods, such as the Exponential Convergence Method, with the full CI results for nuclei around 56Ni