Multi-reference Brillouin-Wigner double-excitations approximation

Single-root multi-reference Brillouin-Wigner coupled cluster single- and double-excitations approximation... 

In Section 4.2.3.2, we presented the basic equations of single-root (state-specific) multi-reference Brillouin-Wigner coupled cluster theory. We derived these equations from the single-root (state-specific) multi-reference Brillouin-Wigner perturbation theory presented in Section 4.2.3.1. In this section, we turn our attention to the coupled cluster single- and double-excitations approximation, ccsd. We present... 

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