Interestingly, there is a split in the vdW force directions between 'heavier' atoms in the QUID dimers, i.e. O, F, Cl, S, and P and the 'lighter' ones i.e. H, C, and N. The 'lighter' atoms represented more in organic molecules demonstrate a larger spread of angle difference between the forces up to 120 • -180 • . By construction, for the pairwise D4 and XDM methods, the vdW force is a simple vector sum where all force vectors are aligned along the vector connecting pairs of atoms. In contrast, many-body effects that are treated to infinite order in MBD can thus substantially alter the force directions, and this difference is much more pronounced than for force magnitudes. This could have a visible effect on MD trajectories, although these implications remain to be assessed in a future study.