• For finite molecules, spin is a well-defined quantum number, and yet spin-symmetry breaking in a single-determinant wavefunction can recover more accurate energies in certain cases than the spin-pure counterpart. Let us consider again the case of stretched H 2 (which is isoelectronic to chemically relevant organic diradicaloids as well as many di-Cu(II) active sites). Here, ⟨S 2 ⟩ UHF goes from zero before the Coulson-Fischer point to one at complete dissociation; in the latter regime the UHF wavefunction can be expanded as an equal mixture of pure singlet and triplet states. The triplet state in fact has a more accurate electron density distribution than that of the closed-shell spin-pure determinant (although the spin-density distribution is also qualitatively wrong). Thus, the spin-contamination enables a single-determinant to capture (to some extent) an open-shell singlet electronic structure that is required of biradicals, and can be viewed as physically motivated, or "essential" according to Head-Gordon and coworkers.