Sampling the proton transfer reaction coordinate in mixed quantum-classical molecular dynamics simulations.

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Chemical Physics

Background:

• Proton transfer (PT) reactions are fundamental in chemistry and biology.
• Exploring the reaction coordinate and transition states of PT reactions is computationally challenging.
• Traditional methods may not fully capture the quantum nature of the transferring proton.

Purpose of the Study:

• To introduce and validate a novel umbrella sampling approach for PT reactions.
• To utilize the vibrational energy gap as a reliable indicator for the transition state.
• To explore reaction free energy curves and nonadiabatic coupling in PT systems.

Main Methods:

• Developed an umbrella sampling technique based on the vibrational energy gap.
• Employed mixed quantum-classical simulations.
• Applied the method to a model phenol-amine proton transfer complex in a nanoconfined solvent.

Main Results:

• The vibrational energy gap method successfully identified transition state configurations.
• The approach accurately mapped the reaction free energy curve.
• Results were consistent with previous methods using collective solvent coordinates.
• Gained insights into vibrationally nonadiabatic coupling during proton transfer.

Conclusions:

• The vibrational energy gap umbrella sampling is an effective method for studying proton transfer reactions.
• This technique offers a new way to explore reaction dynamics and nonadiabatic effects.
• The method shows potential for simulating vibrational spectra of PT reaction complexes.