Ring-Polymer Molecular Dynamics and Kinetics for the H^– + C₂H₂ → H₂ + C₂H^– Reaction Using the Full-Dimensional Potential Energy Surface

Abstract

reaction is important in understanding the production mechanisms of anionic molecules in interstellar environments. Herein, the rate coefficients for the H − + C 2 H 2 → H 2 + C 2 H − reaction were calculated using ring-polymer molecular dynamics (RPMD), classical molecular dynamics (MD), and quasi-classical trajectory (QCT) approaches on a newly developed ab initio potential energy surface (PES) in full dimensions. PES was constructed by fitting a large number of ab initio energy points and their gradients using the permutationally invariant polynomial basis set method. There was no barrier in the reaction coordinates, which was a collinear-dominated reaction, and the reaction proceeded exothermically. It is found that the fitted PES provides the appropriate thermal rate coefficients based on all RPMD, classical MD, and QCT simulations at higher temperatures. The evaluation of the rate coefficients at lower temperatures should be conducted carefully because the fitting of the PES associated with the long-range interaction should be further improved. The spatial distribution of the nucleus allows a more effective attraction between the reactants.

Theoretical Calculations of the Thermal Rate Coefficients for the Interstellar NH3+ + H2 → NH4+ + H Reaction on a New Δ-Machine Learning Potential Energy Surface

“…This fitted PES was used to identify unphysical leaky holes on the PES. Previous studies reported that leaky holes frequently occur around nuclear configurations that have not been explored using GRRM or random sampling. , To identify such leaky holes, we performed extensive classical trajectory calculations starting from various structures. When an unphysical hole was found, additional sampling around the hole was performed to remove the unphysical hole.…”

Ring‐polymer Molecular Dynamics Simulation for the Adsorption of H2 on Ice Clusters (H2O)n (n=8, 10, and 12)

“…The method has been widely utilized and has successfully described chemical reactions such as collision processes in the gas phase and diffusion processes in the condensed phase. [12,[25][26][27][28][29][30][31][32][33][34][35] Our RPMD method employs the direct trajectory technique, which is similar to the dRPMD program [36] implemented in RPMDrate code. [37] For our RPMD approach, we performed thermalization and implemented real-time dynamics on the open-source PIMD Ver.…”

“…Further details of the collision procedure have been presented in our previous H 2 + (H 2 O) 8 , H 3 + + CO, and H À + C 2 H 2 studies. [12,34,35] Classical MD simulations were also performed in essentially the same way as the PIMD/RPMD calculations mentioned above. The classical Hamiltonian H p;r ð Þ has the conventional form for the n-atom system:…”

“…Nuclear quantum effects, such as zero‐point energy and tunneling [23,24] are represented by the RPMD method. The method has been widely utilized and has successfully described chemical reactions such as collision processes in the gas phase and diffusion processes in the condensed phase [12,25–35] . Our RPMD method employs the direct trajectory technique, which is similar to the dRPMD program [36] implemented in RPMDrate code [37] .…”

“…After the first impact between H 2 and (H 2 O) n , the EOM was integrated up to 3 ps. Further details of the collision procedure have been presented in our previous H 2 +(H 2 O) 8 , H 3 + +CO, and H − +C 2 H 2 studies [12,34,35] …”