Supporting Information: Systematic discrepancies between reference methods for non-covalent interactions within the S66 dataset

In this supplemental material we provide: • a brief description of the three previous CCSD(T) estimates of the binding energy of the S66 dataset in Sec. S3, with the final estimates given in S4. • the total energy of each dimer and the corresponding monomers used to compute the binding energies reported in the main manuscript in Sec. S5; • an analysis on the mean relative differences between DMC and CCSD(T) on the S66 dataset in Sec. S6; • a quantitative analysis of the localization error on the binding energy for the case of acetic acid in Sec. S7; • the convergence of the DMC estimates with respect to the simulation time step for all the dimers in Sec. S8. • an energy decomposition analysis (into electrostatic, dispersive, induction and ex- change contributions) of the S66 dataset with the SAPT method in Sec. S9.