Computational Thermochemistry: Scale Factor Databases and Scale Factors for Vibrational Frequencies Obtained from...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate prediction of molecular vibrational frequencies and zero-point energies is crucial for understanding chemical reactions and molecular properties.
• Existing computational methods often require significant empirical parameterization to achieve high accuracy.

Purpose of the Study:

• To determine optimized scale factors for 145 electronic model chemistries to improve calculations of vibrational harmonic and fundamental frequencies and zero-point energies.
• To develop a reduced model for scale factor optimization and derive universal scale factor ratios for interconversion.

Main Methods:

• Systematic optimization of scale factors for various electronic model chemistries, including density functional theory and wave function theory.
• Development and application of a reduced scale factor optimization model.
• Analysis of root-mean-square errors to quantify the impact of scaling on different vibrational properties.

Main Results:

• Optimized scale factors were determined for 145 electronic model chemistries.
• Scaling reduces errors in zero-point energies by a factor of 2.3 and fundamental vibrational frequencies by a factor of 3.0.
• Balanced multicoefficient correlation method based on coupled cluster theory with single and double excitations (BMC-CCSD) shows high accuracy for vibrational frequencies after scaling.

Conclusions:

• Scale factor optimization is an effective strategy to enhance the accuracy of vibrational frequency and zero-point energy calculations.
• The developed reduced model and universal scale factor ratios facilitate more efficient and accurate computational predictions.
• Specific density functionals like MPWLYP1M and B3LYP demonstrate high accuracy for zero-point energy calculations when using scale factors close to unity.