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An evaluation of harmonic vibrational frequency scale factors
Jeffrey P Merrick1, Damian Moran, Leo Radom
1School of Chemistry and Centre of Excellence in Free Radical Chemistry and Biotechnology, University of Sydney, Sydney, New South Wales 2006, Australia.
The Journal of Physical Chemistry. A
|October 24, 2007
Summary
Accurate vibrational frequencies and energies are crucial for computational chemistry. This study derives scale factors for various computational methods, improving the reliability of theoretical calculations for molecular vibrations and thermal properties.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Spectroscopy
Background:
- Accurate prediction of molecular vibrational frequencies and energies is essential for understanding chemical systems.
- Theoretical calculations often require scale factors to correct for approximations in methods and basis sets.
- Existing scale factors may not cover the wide range of modern computational approaches.
Purpose of the Study:
- To derive and evaluate scale factors for fundamental vibrational frequencies, zero-point vibrational energies (ZPVEs), and thermal contributions.
- To assess the performance of numerous wave function and density functional theory (DFT) methods with various basis sets.
- To investigate the impact of exact exchange percentage and basis set size on scale factor accuracy.
Main Methods:
- A least-squares approach was used to derive scale factors by comparing theoretical harmonic frequencies with experimental data.
- Over 100 levels of theory, including wave function methods (HF, MP2, CCSD(T)) and DFT functionals (B3-LYP, PBE), were examined.
- Multiple basis sets (e.g., 6-31G(d), cc-pVnZ) were employed, and the effect of varying exact exchange in DFT was analyzed.
Main Results:
- Scale factors were determined for vibrational frequencies using 1066 experimental vibrations and for ZPVEs using 39-48 molecules.
- A near-linear relationship was observed between scale factor magnitude and the percentage of exact exchange in hybrid DFT.
- The study provides a comprehensive evaluation of scale factors across a broad spectrum of computational chemistry methods and basis sets.
Conclusions:
- The derived scale factors enhance the accuracy of computed vibrational frequencies, ZPVEs, and thermal properties.
- This work offers valuable guidance for selecting appropriate computational methods and basis sets for vibrational analysis.
- The findings contribute to more reliable theoretical predictions in computational chemistry and related fields.
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