Systematic study of vibrational frequencies calculated with the self-consistent charge density functional...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Accurate prediction of molecular vibrational frequencies is crucial for understanding chemical reactions and material properties.
• Traditional ab initio methods provide high accuracy but are computationally expensive.
• Semiempirical methods offer a balance between speed and accuracy, but their performance varies.

Purpose of the Study:

• To evaluate the accuracy of the self-consistent charge density functional tight-binding (SCC-DFTB) method for calculating harmonic vibrational frequencies.
• To determine an optimal scaling factor for SCC-DFTB frequencies.
• To compare the performance of SCC-DFTB with experimental data and other theoretical methods.

Main Methods:

• Calculation of harmonic vibrational frequencies using an efficient analytical algorithm for the SCC-DFTB method.
• Testing on a dataset of 66 molecules and 1304 vibrational modes.
• Comparison of SCC-DFTB results with experimental values and other quantum chemistry methods (HF, BLYP, B3LYP).

Main Results:

• An optimal scaling factor of 0.9933 was determined for SCC-DFTB frequencies.
• Scaled SCC-DFTB frequencies showed improved accuracy compared to other semiempirical methods.
• The mean absolute deviation for scaled SCC-DFTB frequencies was 56 cm⁻¹, with a standard deviation of 82 cm⁻¹.
• SCC-DFTB demonstrated substantial computational time savings, reducing calculations from hours to seconds.

Conclusions:

• SCC-DFTB is a computationally efficient method for predicting harmonic vibrational frequencies with good accuracy.
• The method offers a viable alternative to more computationally demanding ab initio techniques for certain applications.
• Further validation against a wider range of molecular systems is warranted.