Reaction Coordinates and Mechanistic Hypothesis Tests.

Area of Science:

• Chemical kinetics
• Computational chemistry
• Statistical mechanics

Background:

• Reaction coordinates are fundamental to classic rate theories, enabling prediction of kinetic trends and extraction of activation parameters.
• Trajectory-based methods offer direct rate calculations but yield abstract coordinates lacking generalizability.
• Abstract coordinates from trajectory methods limit mechanistic insights across conditions and reaction families.

Purpose of the Study:

• To discuss methods for identifying physically meaningful reaction coordinates.
• To address the limitations of abstract coordinates generated by trajectory-based methods.
• To highlight advanced techniques for optimizing reaction coordinate selection.

Main Methods:

• Committor analysis
• Variational transition state theory
• Kramers-Langer-Berezhkovskii-Szabo theory
• Statistical inference using path sampling data
• Likelihood maximization and inertial likelihood maximization

Main Results:

• Methods for identifying physically meaningful reaction coordinates are presented.
• Statistical inference can screen, mix, and optimize thousands of trial coordinates.
• Likelihood maximization approaches are emphasized for coordinate optimization.

Conclusions:

• Physically meaningful reaction coordinates are essential for robust kinetic predictions and mechanistic understanding.
• Advanced computational methods can significantly improve the identification and optimization of reaction coordinates.
• The discussed methods offer a pathway to generalize insights from trajectory-based simulations across diverse chemical systems.