We note that \( H = E_{HF} + H_N \), where
$$ \begin{align} E_{HF} &\equiv \langle\Phi_0\vert H\vert \Phi_0\rangle = \sum_{i} \varepsilon^i_i +\frac{1}{2}\sum_{ij}\langle ij\vert V\vert ij\rangle \tag{10} \end{align} $$is the Hartree-Fock energy. The coupled-cluster method is a very efficient tool to compute nuclei when a "good" reference state is available. Let us assume that the reference state results from a Hartree-Fock calculation.