Rare events via multiple reaction channels sampled by path replica exchange

Area of Science:

• Computational Chemistry
• Statistical Mechanics
• Chemical Dynamics

Background:

• Transition path sampling (TPS) and transition interface sampling (TIS) are methods for studying activated processes.
• Standard TPS and TIS struggle with systems having multiple high-barrier reaction channels.
• Efficiently sampling multiple reaction pathways is crucial for accurate rate constant determination.

Purpose of the Study:

• To develop a robust method for sampling multiple reaction channels in complex systems.
• To compute rate constants and free energy barriers in a single simulation for systems with multiple pathways.
• To bridge the gap between transition interface sampling and forward flux sampling methods.

Main Methods:

• Combined replica exchange with transition interface sampling (TIS) to overcome limitations of standard TIS.
• Included both forward and backward reactions within a single simulation framework.
• Illustrated the method using Langevin dynamics on a two-dimensional potential; proposed a simpler forward-shooting algorithm.

Main Results:

• The combined replica exchange and TIS method successfully samples multiple reaction channels.
• Rate constants and free energy barriers were computed accurately in a single simulation.
• A simpler forward-shooting algorithm yielded equally accurate results, bridging TIS and forward flux sampling.

Conclusions:

• Replica exchange combined with TIS provides an effective solution for sampling complex activated processes with multiple pathways.
• The method allows for simultaneous computation of rate constants and free energy barriers.
• Replicas' diffusive behavior can inform the selection of order parameters for interface definition.