Fundamental frequency from classical molecular dynamics.

Area of Science:

• Computational Chemistry
• Molecular Dynamics
• Quantum Mechanics

Background:

• Calculating molecular fundamental frequencies is crucial for understanding molecular behavior.
• Classical molecular dynamics (MD) offers a potential route for these calculations.
• Perturbation theory is a common method, but can be computationally intensive.

Purpose of the Study:

• To theoretically validate classical MD for fundamental frequency calculations.
• To determine appropriate initial conditions for MD simulations.
• To assess the accuracy and benefits of using ab initio MD.

Main Methods:

• Utilized classical and quantum normal form theories for analytical approaches.
• Performed two types of MD simulations: quartic force field and direct ab initio MD.
• Calculated frequencies for H2O, tetracene, and naphthalene using MP2/aug-cc-pVTZ.

Main Results:

• Established appropriate initial conditions for classical MD frequency calculations.
• Demonstrated that MD can achieve accuracy comparable to second-order perturbation theory.
• Showcased lower computational costs for large molecules compared to perturbation theory.

Conclusions:

• Classical MD is a viable and accurate method for calculating fundamental molecular frequencies.
• Ab initio MD provides benefits for frequency calculations, especially for complex systems.
• MD offers a computationally efficient alternative for molecular frequency analysis.