Improved Geometries and Frequencies with the PFD-3B DFT Method.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate prediction of molecular properties is crucial in chemistry.
• Density-Functional Theory (DFT) methods are widely used but vary in accuracy.
• Evaluating new functionals like PFD-3B against experimental data is essential.

Purpose of the Study:

• To assess the performance of the PFD-3B functional for calculating bond lengths and vibrational properties.
• To compare PFD-3B against other DFT methods using a diverse test set.
• To determine the accuracy of PFD-3B for various molecular parameters.

Main Methods:

• Calculation of bond lengths for 120 diatomic species using the PFD-3B functional.
• Utilized moderate (3Za1Pa + f) and small (2ZP0H) basis sets.
• Comparison of calculated properties (bond lengths, vibrational constants, rotational constants, ZPE) with experimental data.

Main Results:

• PFD-3B significantly outperforms competitive DFT methods.
• Achieved high accuracy for bond lengths (0.01 Å rms error) and harmonic vibrational constants (38 cm^-1 rms error).
• Accurate prediction of anharmonic constants (±4 cm^-1), rotational constants (±2%), and zero-point energy (±0.06 kcal mol^-1).

Conclusions:

• PFD-3B demonstrates superior accuracy for predicting molecular properties of diatomic species.
• The functional shows reliability even for atypical structures, as shown with the ethylene cation.
• PFD-3B offers a robust and accurate computational tool for chemical research.