ON THE IMPORTANCE OF THE FRAGMENT RELAXATION ENERGY TERMS IN THE ESTIMATION OF THE BASIS-SET SUPERPOSITION ERROR-CORRECTION TO THE INTERMOLECULAR INTERACTION ENERGY

The inclusion of the fragment relaxation energy terms in the estimatio n of the basis set superposition error (BSSE) correction to the intera ction energy is necessary in order to ensure formal convergence to the uncorrected result at the complete basis set (CBS) limit. The problem s associated with their omission are demonstrated for F-(H2O), Cl-(H2O ), and (H2O)(2) especially when very large basis sets are used. The fa mily of correlation consistent basis sets allows for a heuristic extra polation of both uncorrected and BSSE-corrected electronic energy diff erences of the three complexes to the MP2 CBS limits of -27.1, -15.1, and -4.9 kcal/mol respectively. (C) 1996 American Institute of Physics .