For the planar dissociation of H 4 , and in fact for any even n H ring, there is no external instability from UHF to GHF throughout the curve; therefore one expects equivalent results from unrestricted and generalized correlation methods. The U=G CCSD and CCSD(T) curves are much improved over the restricted CC variants, but relatively large errors remain in the region between 2 and 3Å. As shown in Figure , ph-AFQMC with UHF=GHF trials reduces the maximum energy error of U/GCCSD(T) by ∼2 mHa. For some perspective on the energy scale, we note that at the 2Å bond length corresponding to the maximum error for ph-AFQMC, the total correlation energy of the system is 31.4 mHa.