(248b) Variable Reaction Coordinate Transition State Theory for Computing the Rate Constant of Barrierless Reactions on Catalytic Surfaces
AIChE Annual Meeting
2024
2024 AIChE Annual Meeting
Computational Molecular Science and Engineering Forum
Recent Advances in Molecular Simulation Methods
Tuesday, October 29, 2024 - 8:12am to 8:24am
Harmonic Transition State Theory (HTST) has been a cornerstone in predicting rate constants for chemical reactions with first-order saddle points. Despite its widespread application and efficiency, it encounters limitations in accurately determining reaction rates for reactions without the first-order saddle point (also known as barrierless reaction), such as homolysis in the gas phase. To address these constraints, Variational Transition State Theory (VTST) was developed. VTST significantly enhances our understanding of chemical reaction mechanisms and improves our ability to predict reaction rates of those reactions without the saddle point. Distinguished by its various forms, each offering unique benefits, VTST encompasses a range of methodologies. This research primarily examines the Variable Reaction Coordinate Transition State Theory (VRC-TST), a method that excels in the evaluation of multi-dimensional partition functions for the transition state. We can use VRC-TST to analyze the kinetics of barrierless reactions accurately. Here, we delve into the core principles of VRC-TST and introduce the open-source software, ROTDpy. This software represents a significant advancement, facilitating the precise calculation of rate constants for a wide range of reactions. Although the method was developed originally for radical-radical recombination in the gas phase, we have now extended this methodology to include barrierless adsorption desorption reactions. In this study, we have employed ROTDpy to compute the rate constants for some systems, including the barrierless desorption of carbon monoxide and nitrogen monoxide from various transition metal surfaces. The results from these computations are compared with the Potential of Mean Force approach of Doren and Tully, thereby providing a robust validation of our computational findings. [1,2]
[1] Doren D. J., Tully J. C., Dynamics of precursor-mediated chemisorption. J. Chem. Phys. 94, 8428 (1991).
[2] Doren D. J., Tully J. C., Precursor-mediated adsorption and desorption: A theoretical analysis. Langmuir 4, 256 (1988).