Short- and Intermediate-range Forces

At long range, a perturbation method is the obvious choice for the calculation of intermolecular interactions. At short ranges the standard methods of valence calculation are an equally obvious choice, and quite a lot of work of this kind is being reported. This type of calculation is also being carried out at intermediate distances at which perturbation theories of the type mentioned in Section 2 are also appropriate. 

Straight self-consistent field calculations have been carried out on the interaction of water with neon and argon.30 Here it is possible to obtain some of the attractive contribution to the intermolecular force since there will be an inductive second-order interaction caused by the large dipole of the water molecule. Such interactions appear at the SCF level and the authors find a minimum in the potential at an O -Ne distance of 3.63 A, with a binding energy of 0.71 kJ mol-1. There is a shallower minimum in the case of argon. Calculations at a similar level of sophistication have been carried out on the H2----He system,31 primarily, however, from the 

He-----Bea+ system. The repulsive potential agrees quite well with scattering data 

All the data on the H2----Ha potential at short range obtained by ab initio calcula- 

SCF-CI calculations have also been carried out for Ne-----Ne 39 in much the same 

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