Dispersion contribution of two-atom interaction energy: Multipole interactions

Gives a theory of non-retarded dispersion interaction energy of molecules with charge distributions on them that readily allows inclusion of higher-order multipole interactions. The two-particle dispersion energy for a pair of harmonic oscillators is evaluated for dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions. It also is found that the dispersion energy remains finite for all separations between the oscillators, supporting the earlier result of Mahanty and Ninham (1975) for dipole-dipole interactions with distributed dipole moments.