Accuracy of counterpoise corrections in second-order intermolecular potential calculations. 1. Helium dimer

With use of a localized orbital approach to second-order correlation energy, the specific terms relating to overcompensation of the couterpoise correction for basis set superposition errors can be explicitly defined and evaluated for a given basis set. The method is described and applied to helium interaction energies. It is found that the couterpoise correction does not seriously overestimate the correction if the basis set is good. The error is much less than 1% in most cases.