CONCERNING ZERO-POINT VIBRATIONAL-ENERGY CORRECTIONS TO ELECTRONIC ENERGIES

For comparison with experimentally obtained thermochemical data, zero-point vibrational energies (ZPVEs) are required to convert total electronic energies obtained from ab initio quantum mechanical studies into 0 K enthalpies. The currently accepted practice is to employ self-consistent-field (SCF) harmonic frequencies that have been scaled to reproduce experimentally observed fundamental frequencies. This procedure introduces systematic errors that result from a recognizable flaw in the method, namely that the correct ZPVE, G(0), is not one half the sum of the fundamental vibrational frequencies. Until better methods for accurately determining ZPVEs are presented, we recommend using different scaling factors for the determination of ZPVEs than those used to compare theoretically determined harmonic frequencies to observed fundamentals.