New Scale Factors for Harmonic Vibrational Frequencies Using the B3LYP Density Functional Method with the Triple-ζ Basis Set 6-311+G(d,p)

Abstract

We have calculated optimal frequency scaling factors for the B3LYP/ 6-311+G(d,p) method for fundamental vibrational frequencies on the basis of a set of 125 molecules. Using the new scaling factor, the vibrational frequencies calculated with the triple-zeta basis set 6-311+G(d,p) give significantly better accuracy than those calculated with the double-zeta 6-31G(d) basis set. Scale factors were also determined for low-frequency vibrations using the molecular set of 125 molecules and for zero-point energies using a smaller set of 40 molecules. We have studied the effect on the calculated vibrational frequencies for various combinations of diffuse and polarization functions added to the triple-zeta 6-311G basis set. The 6-311+G(d,p) basis set is found to give almost converged frequencies for most molecules, and we conclude that our optimum scaling factors are valid for the basis sets 6-311G(d,p) to 6-311++G(3df,3pd). The new scale factors are 0.9679 for vibrational frequencies, 1.0100 for low-frequency vibrations, and 0.9877 for zero-point vibrational energies.

Consecutive Fragmentation Mechanisms of Protonated Ferulic Acid Probed by Infrared Multiple Photon Dissociation Spectroscopy and Electronic Structure Calculations

“…All geometry optimizations and associated frequency calculations have been performed at the B3LYP/6-311+G(d,p) level of theory, which has been shown to be a reliable protocol, with a good compromise between accuracy and cost, for smaller systems such as those described here [13,14,16,24,[33][34][35][36]. All harmonic frequencies obtained at this level of theory were scaled by 0.9679 [37] in order to compensate for errors arising from the use of a harmonic oscillator approximation in calculating the frequencies, as well as long range electron correlation effects.…”

Dispersion corrected DFT approaches for anharmonic vibrational frequency calculations: nucleobases and their dimers

“…In these calculations molecular conformations play a central role for determining the harmonic frequencies, and reliable structures are necessary starting points for further calculations, while accuracy requirements increase moving from simple confirmation of the nature of stationary points to the analysis of vibrational spectra through computed data (frequencies and intensities) which could be compared to experimental measurements. The common approach to correct frequencies for anharmonicity and improve their agreement with the experimental findings is obtained by using simple scaling factors [45][46][47][48][49] , or more sophisticated scaling methods [50][51][52] . Mode specific scaling improves the agreement between computed and experimental vibrational frequencies, but the uncertainty of the optimized scaling factors cannot be lower than 0.02 47 and the problem of transferibility is not trivial.…”

Ultrafast IR spectroscopy of the short-lived transients formed by UV excitation of cytosine derivatives

“…21,22 For these preliminary studies we undertook calculations on 1-methylcytosine (and its hydrate C?D 2 O) and determined the individual and difference spectra between the 1-methylcytosine and its tautomers (these are shown in the ESI). The calculations indicate that species I (or its hydrate I?D 2 O) should have a strong IR absorption band at higher frequency than dCyd in contrast with what is found experimentally.…”