Potential model for the interaction of two like S state atoms involving spin symmetry

One of the problematic parts of the interaction of two atoms is the dispersion interaction resulting from interatomic electron correlation. Based on available variational and perturbational ab initio results for two like S state atoms with only s valence electrons, a model formula for the dispersion interaction is constructed in a way that different spin states of the system are considered. If the exchange dispersion component can be treated as a correction, then the formula contains two free parameters, one characterizing the orbital contraction and the other the exchange contribution. To this formula the Hartree–Fock energy with an intra-atomic correlation correction is added, thus giving a reliable two-parameter model for the full interaction. The two parameters can be fitted to experimental data of a system under consideration to get the potential.