Table shows a comparison of the experimental BDEs and the computed values (B3LYP-D3BJ/6-311+G**, SDD/SDD ECP on Au and 6-311G** on I). The theoretical calculations overestimate the binding energies. In the exploratory calculations, we have found out that the overestimation is even larger if we use larger basis sets and if we (correctly) include the spin-orbit coupling and non-scalar relativity (X2C). We will investigate the origin of this peculiar effect in a large benchmarking study of the theoretical methods in future. For the purpose of this study, we will evaluate the relative trends (1 st vs 2 nd dissociation; Cl/Br/I ligands) that are reasonably reproduced irrespective of various methodological ingredients.