Biasing a transition state search to locate multiple reaction pathways

Abstract

Articles you may be interested inAb initio reaction pathways for photodissociation and isomerization of nitromethane on four singlet potential energy surfaces with three roaming paths Development and application of a hybrid method involving interpolation and ab initio calculations for the determination of transition states A variety of chemical systems exhibit multiple reaction pathways that adjoin to a common reactant state. In fact, any reaction producing side products or proceeding via a stable intermediate involves a species possessing at least two reaction pathways. Despite improvements in ab initio transition-state search algorithms it remains difficult to detect multiple reaction pathways. Typically, multiple reaction pathways can only be detected by intuitively varying the initial point in the transition-state search trajectory. This reliance on intuition limits the ability to discover new and unexpected chemistry using ab initio methods. This paper proposes a systematic and intuition-free method for biasing a transition-state search to identify multiple reaction pathways originating from a common reactant state. The method allows the successive location of transition states, with each successful search contributing to a cumulative bias potential for the following search. The method is applicable to all psuedo-Newton-Raphson-type transition-state searches. The procedure was tested for a model potential energy surface and for the thermal rearrangement of trans-1,4-dimethylcyclobutene. In the latter case, four reaction pathways were discovered: two exothermic conrotatory ring openings leading to hexadienes, an endothermic methyl migration pathway leading to a carbene, and an exothermic rearrangement leading to 3-methyl-1,4-pentadiene. In accordance with experiment, the calculations predict that the conrotatory pathway leading to trans,trans-2,4-hexadiene is the kinetically dominant pathway. The methodology was also used to compute selectivities for competitive pathways producing trans and cis triflouropentadiene products in the thermal rearrangement of 3-triflouromethyl-cyclobutene. Again, results were in accord with experimental observations.

A Career in Catalysis: Alexis T. Bell

“…186,187 (3) Efficient, automated methods for discovering reaction pathways and intermediates. In collaboration with Arup Chakraborty and Frerich Keil, Alex developed new transition state search algorithms with improved efficiency, [188][189][190][191][192][193][194] improved fault tolerance, 195 biases to avoid rediscovery, 196 and automated path generation capabilities 197 and NO decomposition by Fe-ZSM-5. The works by Heyden et al 198,199 and Hansen et al 200 expanded the NO x reduction mechanisms to include hundreds of elementary reactions at monoand bi-nuclear Fe sites.…”

Automated discovery of chemically reasonable elementary reaction steps

“…Although methods that explore reactive paths through coordinate biases in principle could be very useful, designating these coordinates is usually a system‐dependent task. Methods in category (2) often follow shallowest ascent coordinates to TSs, and can even allow multiple TSs to be found from the same intermediate . Shallowest ascent methods give no guarantee that the most important TSs are located for a given system (these tend to repeatedly locate the same TS over multiple runs), in contrast to type (1) methods that are likely to find the important TSs when the appropriate bias coordinate is chosen.…”

Development and application of a hybrid method involving interpolation and ab initio calculations for the determination of transition states

“…39͒ is commonly used to benchmark the performance of new TS-finding methods. 7,17,[39][40][41] The MEP on this PES differs significantly from the linearly interpolated path and, as seen in Fig. 3, there are two saddle points ͑TS1, TS2͒ located between three local minima ͑A, B, C͒ on the MEP.…”