Potential energy surface of weakly bonded intermolecular complexes: does one need counterpoise corrections for a proper representation? A numerical test using near complete basis sets

Using as test systems the Ar ... HF and Ar ... H2O complexes, the validity of the counterpoise method when reproducing experimental potential energy surface shape, is evaluated. The MP2, MP3 and MP4 methods and various basis sets have been used, including some designed to saturate the s, p, d and f shells. It is found that the BSSE-corrected surfaces are parallel to the experimental one, getting closer to it as the basis set quality is increased. The BSSE-uncorrected surfaces strongly change their shapes with the basis, presenting large deviations from the experimental ones even with the largest basis sets. (C) 1998 Elsevier Science B.V.