Double hybrids improve the description of excimer binding considerably with absolute errors in the order of 21-27% and 3-5% for D e and r e , respectively. Further improvement on conventional DHDFAs results from the inclusion of range-separation with absolute errors in the order of 13-20% and 1-2% for D e and r e , respectively. Despite the closer resemblance of RS-DHDFAs curves with the reference curve (right panel in Fig. ) the binding strength is insufficiently described. The best method, ωB2GP-PLYP underestimates the dissociation energy by 3.65 kcal/mol, which is a larger error than for the benzene dimer in Section 4.2.1. Most likely, this error can be attributed to missing dispersion, as its importance increases with the number of electrons. This will be further discussed in Section 4.4.