The dissociation energies of He2, HeH, and ArH:: a bond function study

The bond energies and bond lengths are determined for He-2, HeH, and ArH at the CCSD(T) level using both atom-centred basis sets and those that include bond functions. The addition of bond functions dramatically improves that rate of convergence of the results with respect to the size of the atom-centred basis set; with bond functions, triple-zeta atom-centred basis sets outperform quintuple-zeta basis sets without bond functions. The addition of bond functions also reduces the number of diffuse functions that must be added to the atom-centred sets. Employing bond functions appears to offer a cost-effective method for computing the interaction energy between weakly bound systems, especially for He.