Noncovalent Interaction Energies with Phaseless Auxiliary-Field Quantum Monte Carlo

) reference values, we find accuracy consistently better than CCSD, and sometimes dramatically better than MP2. In addition, we use the water dimer (with available CCSDTQ reference energies) to demonstrate that noncovalent interaction energies calculated with ph-AFQMC-RHF benefit significantly from error cancellation. In this spirit, we further show how a branching correlated sampling scheme can be used to reduce the computational cost of noncovalent interaction energy calculations, paving the way for more tractable ph-AFQMC studies of larger molecules.