THE REPULSIVE WALL OF THE TANG-TOENNIES POTENTIAL FOR HE-2 REEXAMINED

In the case of He-2, Aziz et al. [Z. Phys. D 21,251 (1991)] proposed a modification to the original Tang-Toennies potential form (TT) [J. Chem. Phys. 80, 3726 (1984)] which allows for a more accurate repulsive wall. The total interaction energy E(int) can, in principle, be considered as the sum of uncorrelated and correlated energies, i.e. E(int) (r) = E(unc) (r) + E(c)(r). E(unc) is represented by the (SCF) Hartree-Fock interaction energy E(SCF) for the rare gas dimer. E(c), which is expressed in terms of ab initio dispersion coefficients and a suitable damping function to account for charge overlap effects, is dominated by the van der Waals attraction in the long range. While the other literature potentials reproduce some of the data, only the TT model as modified by Aziz et al. properly characterizes E(int) over the entire range and E(SCF) over its range of significance.