Inter-atomic and Inter-ionic Potentials

Abstract

The interatomic potential that is responsible for forming chemical bound was discussed in Chap. 6. The simplest prototype is the singlet ground state of the H₂ molecule. As we have seen, the stabilization of the bond is provided mainly by the exchange integral. For the triplet state of the H₂ molecule, the exchange integral becomes the repulsive part of the potential. However, at large inter-atomic separations, there is always an attraction between any pair of atoms regardless of which state they are in. This is known as the dispersion energy as discussed in Chap. 4. It is due to the interaction of a dipole with an instantaneous induced dipole. Therefore even for the triplet state of H₂, there is a shallow well at about 7.8 a.u. due to the interplay between the exchange repulsion and the long range attraction. This is to be contrasted with the chemical potential with a deep well at 1.4 a.u. This shallow well potential is the simplest prototype of all van der Waals potentials which are responsible for many physical processes.