The results for CO 2 are shown in Figure , with energy differences from FCI shown in ). We thus expect ph-AFQMC-G to be applicable to system sizes that are out of reach for loworder Coupled Cluster models, while preserving desirable properties of an approximate model chemistry including size-consistency, size-extensivity, orbital invariance, and a black-box nature. In addition, we find that ph-AFQMC-G produces smooth potential energy surfaces (insofar as is possible with a stochastic method) even for the double dissociation of CO 2 and the dissociation of O 2 . These are notoriously challenging systems with UHF to GHF instabilities and regions in which the ground-state spin multiplicity switches; indeed, GCCSD(T)