Effect of counterpoise correction on the geometries and vibrational frequencies of hydrogen bonded systems

The effect of the counterpoise correction on the geometries and vibrational frequencies of 15 H-bonded systems has been analyzed at the B3LYP and MP2 levels of theory, using the popular 6-31++G(d,p) basis set. The counterpois e correction increases the H-bond distance, decreases the intermolecular st retching frequency and decreases the red-shift of the donor H-X frequency. The observed changes are larger at the MP2 level of theory, for which the b asis set superposition error is significantly larger. At both levels of the ory, linear relationships between the percentage of BSSE, the relative chan ges of the H-bond distances and intermolecular stretching frequencies, offe r the possibility of estimating, from one single point counterpoise calcula tion, the geometry and frequencies that one would obtain from a counterpois e corrected potential energy surface.