FUNCTIONAL COUNTERPOISE CORRECTIONS FOR THE NMR CHEMICAL-SHIFT IN A MODEL DIMERIC WATER-SYSTEM

Perturbed Hartree-Fock calculations in the gauge including atomic orbital approach (GIAO) with the 6-311G (d, p) basis have been carried out on a model dimeric water system to assess the importance of functional counterpoise corrections to the theoretically calculated chemical shift and shift anisotropy changes upon association. The basis set superposition error (bsse) found for the shift properties is found to be theoretically significant in this system for only the anisotropies of the oxygen and hydrogen atoms of those water molecules acting as proton acceptors, a result that can be understood in terms of the effect on the water lone pair orbitals by the donor water ghost orbitals. The results suggest that counterpoise corrections may be necessary when treating hydrogen bonded species with medium size basis sets. © 1990.