Nuclear-electronic orbital quasiclassical trajectory method for vibrational spectroscopy.

Area of Science:

• Computational Chemistry
• Molecular Dynamics
• Spectroscopy

Background:

• Simulations of vibrational spectra are crucial for interpreting experimental data and understanding molecular behavior.
• Accurately incorporating anharmonicity, especially for quantum protons, remains a challenge in molecular simulations.

Purpose of the Study:

• To present an efficient and accurate computational approach for simulating vibrational spectra, explicitly including anharmonicity.
• To enable the study of molecular systems with significant anharmonic effects and coupled vibrational modes.

Main Methods:

• The study introduces the nuclear-electronic orbital-quasiclassical trajectory (NEO-QCT) method.
• This approach combines real-time nuclear-electronic orbital (NEO) time-dependent density functional theory with Ehrenfest dynamics for quantum protons and quasiclassical trajectories (QCT) for classical nuclei.
• NEO-QCT incorporates zero-point energy for classical nuclei and naturally handles anharmonicity of quantum protons.

Main Results:

• The NEO-QCT method successfully captures anharmonic heavy nuclear motion and quantum proton anharmonicity in various molecular systems (HCN, HNC, FHF-, CH2O, HCOOH).
• It accurately reproduces distinct spectral features of the formate-water complex, including redshifted and broadened OH stretch bands due to hydrogen bonding.
• The simulations demonstrate the method's ability to handle strong anharmonicity and coupling between vibrational modes.

Conclusions:

• The NEO-QCT approach provides a computationally practical tool for simulating vibrational spectra of molecules with significant anharmonicity.
• This method enhances the interpretation of experimental data and deepens the understanding of molecular structure and dynamics in complex systems.