Intermolecular bond lengths: Extrapolation to the basis set limit on uncorrected and BSSE-corrected potential energy hypersurfaces

Geometry optimizations were carried out for the (HF)(2), (H2O)(2), and HF-H 2O intermolecular complexes using the MP2/aug-cc-pVXZ (X = 2, 3, 4, and 5) theoretical models on both the uncorrected and counterpoise (Cr) corrected potential energy hypersurfaces (PES). Our results and the available literat ure data clearly show that extrapolation of intermolecular distances to the complete basis set (CBS) limit is satisfactory on PESs corrected for BSSE. On the other hand, one should avoid such extrapolations using data obtaine d from uncorrected PESs. Also, fixing intramolecular parameters at their ex perimental values could cause difficulties during the extrapolation. As the available literature data and our results clearly show, the Mr2/aug-cc-pVX Z (X = 2, 3, 4} data series of intermolecular distances obtained from the C T-corrected surfaces can be safely used for the purpose of CBS extrapolatio ns. (C) 2000 John Wiley & Sons, Inc.