DISPERSION ENERGY DAMPING FUNCTIONS, AND THEIR RELATIVE SCALE WITH INTERATOMIC SEPARATION, FOR (H,HE,LI)-(H,HE,LI) INTERACTIONS

Accurate calculations of the non-expanded dispersion energies and damping functions, associated with the R(-n) multipolar dispersion energies for n less-than-or-equal-to 10, are carried out for the six pair interactions arising from ground state H, He and Li. Highly correlated monomer wavefunctions, for both the relevant ground and excited states, are employed in the computations and the results are used to discuss the relative scale of the damping functions with interatomic separation. The results for the damping functions are also used to help assess the validity of various choices, in the literature, for empirical scaling parameter's that connect the damping functions for a given interaction to those for H(1s)-H(1s) as a standard interaction and a new, effective, scaling procedure for heteronuclear dimers is proposed. The discussion also contains a rationalization of the trends in the scaling parameters, as a function of R, which is based on the extent to which the lowest S --> L not-equal 0 transitions contribute to the dispersion energy coefficients for a given interaction relative to the H-H interaction.