The first system is H 2 at the dissociation limit in a minimal basis. Each hydrogen atom supplies two spin orbitals, which we will label as |0⟩, 0 , |1⟩ and 1 respectively. The meanfield ground state is given by |Φ 0 ⟩ = 00 . Additionally, there is only one double excitation given by Φ 11 00 = 11 . In this specific example, the singles-doubles Hamiltonian coupling element vanishes by symmetry. Assuming spin-independent values for the orbital energies and ERIs, the Hamiltonian can be written as: