INDUCTION AND DISPERSION DAMPING FUNCTIONS, AND THEIR RELATIVE SCALE WITH INTERSPECIES DISTANCE, FOR (H-(H,HE,LI) INTERACTIONS(,HE+,LI+))

Accurate calculations of the non-expanded induction and dispersion ene rgies and the related damping functions, associated with the R(-n) mul tipolar expanded induction and dispersion energies through n=8 and 10 respectively, are carried out for the nine pair interactions (H+, He+, Li+)-(H, He, Li). Highly correlated monomer wavefunctions, for both t he relevant ground states and excited pseudostates, are employed in th e calculations and the results are used to discuss the relative scale of the damping functions with interspecies separation. The results for the dispersion damping functions are used to test the usefulness of v arious choices for empirical scaling parameters that connect the dampi ng functions for a given ion-atom interaction to those for H (1s)-H(1s ) as a standard interaction. The discussion contains a rationalization of the trends in the scaling parameters, as a function of R, based on the extent to which the lowest S-->L not equal 0 transitions contribu te to the dispersion energy coefficients together with a ''size effect ''. Considerable attention is given to the difference in the behaviour of induction versus dispersion damping functions, as a function of R. These differences are explained by examining the effects of the types of terms in the interspecies perturbation that contribute to inductio n versus dispersion energies. The possibility of obtaining induction d amping functions by scaling the results for a standard interaction is discussed with the conclusion that this will generally be more difficu lt for induction energies than for dispersion energies. Relative to th e H+-H(ls) interaction studied previously, the other interactions cons idered in this paper furnish a wider choice of ''standard'' systems fo r this purpose.