INVESTIGATION OF THE USE OF B3LYP ZERO-POINT ENERGIES AND GEOMETRIES IN THE CALCULATION OF ENTHALPIES OF FORMATION

The use of B3LYP/6-31G zero-point energies and geometries in the calc ulation of enthalpies of formation has been investigated for the enlar ged G2 test set of 148 molecules [J. Chem. Phys. 106 (1997) 1063]. A s cale factor of 0.96 for the B3LYP zero-point energies gives an average absolute deviation nearly the same as scaled HF/6-31G'' zero-point en ergies for G2, G2(MP2), and B3LYP/6-311 + G(3df,2p) enthalpies. A scal e factor of 0.98, which has been recommended in some studies, increase s the average absolute deviation by about 0.2 kcal/mol. Geometries fro m B3LYP/6-31G are found to do as well as MP2/6-31G* geometries in the calculation of the enthalpies of formation.