Potential curve of the Li-2 ground state for large internuclear distances. A contribution to the understanding of interatomic forces

Variational calculations based on a special multi-configuration approach are performed for the Li-2 ground state in the region between 5 and 30 au. The two-configuration energy E-2 reaches its asymptotic limit at 17 au. The difference E-D = E-12 -E-2 called the (r)dispersion contribution(n) to the binding energy turns out to be practically equal to the London energy E-L = - epsilon R-6(-6) for R >= 10 au. The wave function of the valence pair in its natural expansion form is compared with its asymptotic counterpart (valid for large R). In the region where the London formula holds the structure of the natural expansion is essentially the same as for R -> infinity, but the coefficients of the natural expansion deviate much more from their asymptotic formula as the energy does.