Is Counterpoise Method a Proper Procedure for Evaluating the Dispersion Energy?

The counterpoise (CP) method, widely used to evaluate the basis set superposition error (BSSE) inherent in the supermolecular approach, is critically examined in the study of noncovalent interaction between rare gas atoms. Potential energy curves for the rare gas dimers (He₂, Ne₂, and Ar₂) are calculated with and without CP correction using the aug-cc-pVxZ basis sets (x = D, T, Q, 5) at multiple levels of theory (HF, MP2, MP4, and CCSD(T)). While CP correction effectively removes BSSE in the HF energy, which constitutes the major component of the total energies, in contrast, applying the CP correction energy to the electron correlation energy yields a positive BSSE, leading to systematically shallower potential energy curves, particularly when smaller basis sets are employed. We analyzed this contrasting behavior of the HF and electron correlation energy components in terms of the orbital basis inconsistency (OBI) and configuration basis inconsistency (CBI).