Such variations in the vdW radius could lead to drastic effects. For example, in Figure , we show how a variation of the hydrogen vdW radius could affect the hydrogen-hydrogen vdW interaction energy E vdW as estimated from a Lennard-Jones potential for a local minima structure of a water cluster (H 2 O) 30 . In that model, the vdW radii are also employed as a cutoff value to calculate E vdW if the internuclear distance is larger than their respective sum of vdW radii. Therefore, increments of vdW radii also reduce the number of vdW interacting atoms, n vdW , counteracting the reduction in the interaction energy. This effect is evidenced by the exchange between flat and descending regions of both quantities in Figure . The variation of E vdW and n vdW are directly linked to the geometrical distribution of the water cluster. Evidently, even small changes in the vdW radii can yield large differences in vdW interactions, emphasizing the importance of revealing physically-motivated and reliable values for atomic vdW radii.