follow up. Now I see I forgot about the hbar=1.05457182e-34 # in (J s).
The revised formula for the Van der Waals energy of 2 atoms spaced by 6 um would be now
5.24e-24/(6e-6)^61e-341e12= 1.1e-14(pJ) (pico-Joule)
is this value reasonable to you?