The similarity-transformed Hamiltonian is defined as
$$ \begin{equation} \tag{13} \overline{H_N} \equiv e^{-T} H_N e^T . \end{equation} $$A more productive view on coupled-cluster theory thus emerges: This method seeks a similarity transformation such that the uncorrelated reference state (1) becomes an exact eigenstate of the similarity-transformed Hamiltonian (13).