Divide-and-Conquer Method for Instanton Rate Theory.

Area of Science:

• Quantum chemistry
• Computational physics
• Chemical dynamics

Background:

• Ring-polymer instanton theory simulates quantum dynamics in molecular systems.
• Calculating reaction rates involves identifying tunneling pathways and analyzing fluctuations.
• Standard methods face computational challenges for large systems.

Purpose of the Study:

• To develop a computationally efficient method for calculating instanton fluctuations.
• To overcome the scaling limitations of traditional ring-polymer instanton methods.
• To enable accurate quantum dynamics simulations for larger molecular systems.

Main Methods:

• Developed a novel approach to compute instanton fluctuations.
• Reduced the computational scaling associated with matrix diagonalization.
• Applied the method to reactions with various potential-energy surfaces (fitted, analytic, ab initio).

Main Results:

• Achieved a significant reduction in computational scaling for fluctuation calculations.
• Demonstrated numerical stability of the new method.
• Successfully applied to diverse reaction systems.

Conclusions:

• The new method enhances the feasibility of ring-polymer instanton theory for large systems.
• Enables accurate calculation of thermal reaction rates at low temperatures.
• Provides a more efficient tool for studying quantum molecular dynamics.