The Helium Molecular Ion He

For small S, the three-electron bond energy in He should be not far from (better, a little less than) that of.  

The results of our model are seen to agree well with experiment, and were confirmed by ab initio calculations on the same systems (Magnasco, 2008). It was shown there that the single one-electron bond energy parameter (fi-aS) occurring in Equations (25-28) is just the model representation of the one-electron part of the exchange-overlap component of the interaction due to the exchange-overlap densities [a(r)b(r)— Sa2(r)] on A and [b(r)a(r)-Sb2(r)] on B. 

The naive extension of the model to the bonds of the second-row homonuclear diatomics (Li2 +, Li2, Be2 +, Be2), mostly involving overlap 

1 At the rather large internuclear distance of 5.63a0, the potential energy curve of the He(ls2)-He(ls2) interaction shows a shallow minimum of —33.4 x 10 corresponding to the formation of a so-called Van der Waals bond. This is possible since, at this large distance, the small Pauli repulsion between closed shells is overbalanced by a small London attraction (see Chapter 4). 

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