Scaling factors for fundamental vibrational frequencies and zero-point energies obtained from HF, MP2, and DFT/DZP and TZP harmonic frequencies

Abstract

Recently, segmented contracted basis sets of double, triple, and quadruple zeta valence quality plus polarization functions (XZP, X = D, T, and Q) for the atoms from H to Ar were presented by Jorge et al. Scaling factors for the fundamental vibrational frequencies, low-frequency vibrations, and zero-point vibrational energies (ZPVEs) evaluated at 14 levels of theory are reported. The ab initio Hartree–Fock (HF) and second-order Møller–Plesset perturbation theory (MP2) methods, and several variants of density functional theory (DFT: B1LYP, B3LYP, B3P86, B3PW91, and BP86) have been examined in conjunction with the DZP and TZP basis sets. The experimental fundamental vibrational frequencies of 63 small molecules and the ZPVEs of 24 small molecules are used to determine the scaling factors through the least-square fitting procedure. Scaling factors suitable for low-frequency vibrations were obtained from least-squares fits of inverse frequencies. For each model used in this work, a recommended scale factor is presented. Overall, the most successful method to estimate fundamental frequencies and ZPVEs is B3LYP along with the TZP and DZP sets, respectively.