Unified ring polymer molecular dynamics rate calculations for reactions with separable and non-separable reactants

Area of Science:

• Chemical Physics
• Computational Chemistry
• Reaction Dynamics

Background:

• Ring polymer molecular dynamics (RPMD) rate theory accurately estimates reaction rate coefficients, including nuclear quantum effects.
• Standard RPMD methods for gas-phase reactions use two dividing surfaces, which are difficult to apply to surface or solution chemistry due to reactant-medium coupling.
• Existing single dividing surface (SDS) RPMD implementations often use Cartesian coordinates, limiting their applicability to complex reactions.

Purpose of the Study:

• To present a novel SDS-based RPMD implementation designed to overcome limitations in calculating reaction rates for complex chemical processes.
• To provide a unified computational framework for both gas-phase and surface reaction rate calculations.

Main Methods:

• Developed an SDS-based RPMD implementation capable of handling non-separable systems and complex reaction coordinates.
• Applied the new implementation to four representative reactions: gas-phase H + H2 exchange, gas-phase CH3NC isomerization, H recombinative desorption from Pt(111), and NO desorption from Pd(111).

Main Results:

• The new SDS-RPMD implementation successfully calculates rate coefficients for diverse reactions, including those involving surfaces.
• Demonstrated the method's applicability to both unimolecular and bimolecular reactions.
• Showcased a unified approach for treating gas-phase and surface reactions computationally.

Conclusions:

• The presented SDS-based RPMD method offers a versatile and accurate tool for studying chemical reaction dynamics across different environments.
• This implementation facilitates a consistent and rigorous treatment of quantum effects in chemical reactions, from gas-phase to surface phenomena.