Vibrational frequency scale factors for density functional theory and the polarization consistent basis sets

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Harmonic vibrational frequencies calculated using density functional theory (DFT) often show systematic deviations from experimental values.
• Accurate vibrational frequencies and zero-point vibrational energies (ZPVEs) are essential for understanding molecular properties and reaction energetics.

Purpose of the Study:

• To determine reliable scale factors for correcting calculated harmonic vibrational frequencies, vibrational contributions to enthalpy and entropy, and ZPVEs.
• To evaluate the performance of various density functionals (pure, hybrid, meta, double hybrid, dispersion-corrected) in combination with polarization-consistent basis sets.

Main Methods:

• Systematic calculation of harmonic vibrational frequencies, enthalpy, entropy, and ZPVEs for a range of density functionals and pc-n basis sets (n=0-4).
• Determination of scale factors by comparing calculated values to experimental vibrational frequencies from 41 organic molecules and ZPVEs from 24 small molecules.
• Analysis of the dependence of scale factors on functional choice and basis set level.

Main Results:

• Scale factors were successfully determined for different properties and computational methods.
• The choice of density functional was found to have a greater impact on scale factors than the basis set level for pc-n (n=1-4) sets.
• Distinct scale factors are recommended for the unpolarized pc-0 basis set compared to polarized sets.

Conclusions:

• The study provides recommended scale factors for various density functionals, enabling more accurate predictions of vibrational properties.
• These findings aid researchers in selecting appropriate computational parameters for reliable molecular simulations.
• The functional dependence highlights the importance of careful method selection in computational vibrational spectroscopy.