Fig. 3: Towards “platinum standard” in E_int by benchmarking “gold standard” methods LNO-CCSD(T) and FN-DMC.

a Comparison of the interaction energies (E_int) computed using Fixed-Node Diffusion Monte Carlo, FN-DMC (0.015 or 0.025 time step) and Local Natural Orbitals - Coupled Cluster with Singles, Doubles, and perturbative triplets, LNO-CCSD(T) (extrapolated to Complete Basis Set (CBS) and Local Approximation-Free (LAF) limit) for the 42 equilibrium QUantum Interacting Dimer (QUID) dataset. For FN-DMC, error bars represent estimated one-σ statistical error for 4 × 10⁸ configurations. For LNO-CCSD(T), the error bars correspond to the estimated uncertainty from the best CBS and LAF extrapolations. Three cases are highlighted: L3I1 for which the methods are in perfect agreement, F2B1 for which the methods agree within their uncertainty estimates, and SF3I3 as the one case for which they are in slight disagreement. The NCI plots illustrating the non-covalent interactions in those molecular dimers are also shown⁵⁴. b Scatter plot of the absolute differences in the prediction of the interaction energies between LNO-CCSD(T) and FN-DMC, ΔE_int, versus the log of the ratio between the electrostatic (Elst) and dispersion (Disp) Symmetry Adapted Perturbation Theory (SAPT) components from sSAPT0⁵². The equilibrium QUID dimers are divided into three subsets: yellow (no H-bond in non-covalent interaction) and black (H-bond in non-covalent interaction) symbols indicate cases where the E_int predictions agree within their uncertainty estimates. Pink symbols denote dimers for which the predictions do not agree within uncertainty estimates, all of these feature an H-bond between the monomers.