Rare Events Sampling Methods for Quantum and Classical Ab Initio Molecular Dynamics.

Area of Science:

• Computational Chemistry
• Chemical Physics
• Molecular Dynamics

Background:

• Sampling rare events in molecular simulations is crucial for understanding chemical processes.
• Classical ab initio molecular dynamics (AIMD) and quantum wavepacket dynamics often struggle to efficiently sample rare events.
• Proton transfer reactions, like in the phenol-amine system, present significant sampling challenges.

Purpose of the Study:

• To develop a general approach for enhanced sampling of rare events in both classical AIMD and quantum wavepacket dynamics.
• To enable the exploration of energetically forbidden regions in potential energy surfaces.
• To improve the efficiency and accuracy of molecular dynamics simulations for complex chemical systems.

Main Methods:

• Introduction of fictitious degrees of freedom that harmonically interact with system dynamics.
• Steering dynamics towards energetically unfavorable regions in classical AIMD.
• Biasing wavepacket centroid trajectories towards difficult-to-sample potential energy surface regions in quantum dynamics.

Main Results:

• The proposed method successfully steers classical AIMD trajectories toward rare event regions.
• The approach effectively biases quantum wavepacket dynamics towards challenging areas of the potential energy surface.
• Demonstrated efficacy on a phenol-amine system (proton transfer) and model potentials.

Conclusions:

• The developed approach provides a robust and generalizable method for sampling rare events.
• Energy conservation is maintained throughout the simulations using this technique.
• This method significantly enhances the ability to study rare chemical events in molecular dynamics.