The six-membered hydrogen ring has been studied extensively, in part because it is isoelectronic to the π system of an aromatic molecule such as benzene (although of course H 6 involves s-orbitals while the π system of benzene involves out-of-plane p orbitals). While the always-square S4 state of the 4-membered hydrogen ring is generally expected to have a strongly-correlated character across the board, the expected weakly-correlated regime that corresponds to aromaticity in the six-membered ring is well-reflected by the 2 ∆ and ⟨S 2 ⟩ UCCSD metrics in the singlet ground-state before and in the neighborhood of the equilibrium geometry of 1Å (Fig. The linear symmetric dissociation of HHeH functions as a simple model of superexchange with tunable biradical character, in which the paramagnetic hydrogens are coupled through a diamagnetic helium intermediate. The parallel or anti-parallel coupling of the spins localized on the H atoms results in two prominent low-lying states, 3 A + σu and 1 X + σg . While even UHF may recapture the singlet-triplet energy splitting (and thus the exchange coupling constant, J) at infinite distance, the wavefunction itself must include a large weight on the lowestlying doubly-excited configuration. The moderate to large biradicaloid character after 1.25Å results in the breakdown of CCSD and CCSD(T). Fig. shows that the coupling of the hydrogens mediated by the helium center leads to a similar trend as found in stretched H 2 , though in the singlet HHeH case 2 γ αα and 2 γ ββ arise from the additional electrons.