It is again in this region that ph-AFQMC-G performs its best. As the atoms continue to separate, ph-AFQMC-G then begins to overcorrelate, while UCCSD(T) and ph-AFQMC-U curves nearly overlap. By 2.2Å all models except GCCSD(T) are within 1 mHa vs FCI. ph-AFQMC is consistently more accurate throughout the dissociation coordinate, with a maximum error of roughly 3 mHa. Its non-variational behavior beyond 2Å seems to be a recurring trend throughout the H n series. It also seems quite general that at long bond lengths CCSD(T) becomes exact more quickly than ph-AFQMC, though recall that the GHF energy becomes exact at infinite dissociation (and thus, the correlation energy vanishes). We also observe from most of the H n series that the bond length corresponding to the maximum ph-AFQMC-G error decreases with n, approaching the less-strongly-correlated equilibrium geometry. As FCI is also computationally infeasible for these systems we take as reference method ph-AFQMC with CASSCF trials; in CO 2 and O 2 we used active space sizes of 12e10o and 12e8o, respectively. Along their dissociation coordinates these systems exhibit unique GHF solutions that connect two different UHF solutions leading to large discontinuities in the GCCSD(T) curves -this has previously been attributed to abrupt changes of GHF state character. At larger separation these systems also exhibit state crossings (singlet to triplet in CO 2 and triplet to singlet in O 2 ) requiring us to dynamically choose the lowest energy state as the reference.