Biological and Chemical Physics
Because of the extremely small binding energy of the helium dimer, the nuclear wave function is delocalized over an extremely large range of separations. One might therefore expect the properties of this extraordinary species to be sensitive to the potential at very large internuclear distances, r, where relativistic corrections to the usual van der Waals interaction may be important. We have estimated the effect of retardation, which changes the r-6 dependence of the potential to r-7 in the limit of large r, and have found that the binding energy and expectation value (r) are indeed significantly affected by its inclusion.
Luo, Fei; Kim, Geunsik; McBane, George C.; Giese, Clayton F.; and Gentry, W. Ronald, "Influence of Retardation on the Vibrational Wave Function and Binding Energy of the Helium Dimer" (1993). Peer Reviewed Articles. 7.