Another common approach to infer a vdW radius is the use of noble gas atoms as atomic probes, since the latter form non-covalent interactions with other atoms and molecules. Here, the vdW radius simply corresponds to the difference between the equilibrium distance of the complex and the vdW radius of the atomic probe. For this work, we focused on systems with neutral hydrogen atoms, and for the probe, we selected helium and neon atoms to estimate the vdW radius in the complexes Rg-H 2 (with a fixed H-H length of 0.74 Å) and Rg-H, see Table . By analyzing the contribution of each SAPT force with respect to the total attractive forces, the dispersion term is, in fact, the major contributor. However, in the case of neon probes, the electrostatic force is considerably high, as previously observed by Mantina. Therefore, the helium probe seems to be a more suitable atom than neon for effective vdW radii, with a value of 2.92 and 3.86 Bohr for closed-shell and open-shell hydrogen atom, respectively. This corresponds to an estimated free vdW radius of 3.15 and 3.86 Bohr, respectively.