An automated transition state search using classical trajectories initialized at multiple minima

Abstract

Very recently, we proposed an automated method for finding transition states of chemical reactions using dynamics simulations; the method has been termed Transition State Search using Chemical Dynamics Simulations (TSSCDS) (E. Martínez-Núñez, J. Comput. Chem., 2015, 36, 222-234). In the present work, an improved automated search procedure is developed, which consists of iteratively running different ensembles of trajectories initialized at different minima. The iterative TSSCDS method is applied to the complex C3H4O system, obtaining a total of 66 different minima and 276 transition states. With the obtained transition states and paths, statistical RRKM calculations and Kinetic Monte Carlo simulations are carried out to study the fragmentation dynamics of propenal, which is the global minimum of the system. The kinetic simulations provide a (three-body dissociation)/(CO elimination) ratio of 1.49 for an excitation energy of 148 kcal mol(-1), which agrees well with the corresponding value obtained in the photolysis of propenal at 193 nm (1.1), suggesting that at least these two channels: three-body dissociation (to give H2 + CO + C2H2) and CO elimination occur on the ground electronic state.

A model of tetrahydrofuran low-temperature oxidation based on theoretically calculated rate constants

“…On the other hand, radical intermediate structures were then obtained by substraction of one H atom from several positions of the structure. Finally, we used the Transition State Search using Chemical Dynamics Simulations with the TSSCDS software [16,17] to obtain the transition state structures associated with the studied reactions. Intrinsic reaction coordinate (IRC) calculations were also carried out to confirm that the transition states linked the expected reactants, intermediates and products.…”

Automated reaction path searches for spin‐forbidden reactions

“…From these potential energy surface characterizations, one can qualitatively understand the mechanisms of a chemical reaction . Recently, automated reaction path searches using various computational algorithms are becoming useful tools, which enable identification of energetically important reaction pathways on the potential energy surface directly obtained from quantum chemistry calculations . For example, Maeda and Ohno have developed a powerful and automated scaled hypersphere search algorithm implemented in the GRRM (Global Reaction Route Mapping) computer code, which has been interfaced with various quantum chemistry software packages.…”

“…More recently, it should be mentioned that efficient reaction path search algorithms on the basis of string method, including the single‐ended growing string method and freezing string method, have also been developed . These newly developed algorithms have been benchmarked and applied to a large number of chemical reaction systems to understand the detailed mechanisms, kinetics and dynamics . According to the most recent computational work, the string methods are found to be more efficient than AFIR for atmospheric and combustion reaction systems …”

vdW‐TSSCDS—An automated and global procedure for the computation of stationary points on intermolecular potential energy surfaces

“…Most of the aforementioned methods focus on chemical reactivity, in other words, the breaking and formation of covalent bonds . In other words, they are either not able to or, in their present form, not adequate to treat non‐covalently bound systems.…”