Abstract
We present a method for the automatic determination of transition states (TSs) that is based on Grimme’s RMSD-PP semiempirical tight binding reaction path method (J. Chem. Theory Comput. 2019, 15, 2847–2862), where the maximum energy structure along the path serves as an initial guess for DFT TS searches. The method is tested on 100 elementary reactions and located a total of 89 TSs correctly. Of the 11 remaining reactions, nine are shown not to be elementary reactions after all and for one of the two true failures the problem is shown to be the semiempirical tight binding model itself. Furthermore, we show that the GFN2-xTB RMSD-PP barrier is a good approximation for the corresponding DFT barrier for reactions with DFT barrier heights up to about 30 kcal/mol. Thus, GFN2-xTB RMSD-PP barrier heights, which can be estimated at the cost of a single energy minimisation, can be used to quickly identify reactions with low barriers, although it will also produce some false positives.
Highlights
The computational determination of chemical reaction networks (Maeda, Ohno & Morokuma, 2013; Bhoorasingh et al, 2017; Kim et al, 2018; Unsleber & Reiher, 2020; Robertson, Ismail & Habershon, 2019; Suleimanov & Green, 2015) requires that the estimation of barrier heights and/or location of transition states (TSs) be automated
The reason for running three times per parameter set is that the root mean square deviation (RMSD)-PP procedure includes a random ‘‘initial distortion parameter’’ which can lead to slightly different reaction paths for each run
We present a method for the automatic determination of transition states (TSs) that is based on Grimme’s RMSD-PP method (Grimme, 2019) for the rapid estimation of reaction paths using the GFN2-xTB semiempirical tight binding model (Fig. 1)
Summary
The computational determination of chemical reaction networks (Maeda, Ohno & Morokuma, 2013; Bhoorasingh et al, 2017; Kim et al, 2018; Unsleber & Reiher, 2020; Robertson, Ismail & Habershon, 2019; Suleimanov & Green, 2015) requires that the estimation of barrier heights and/or location of transition states (TSs) be automated. Many methods for automated barrier height estimation and TS location have been proposed (Mills & Jónsson, 1994; Jónsson, Mills & Schenter, 1995; Henkelman, Uberuaga & Jónsson, 2000; Weinan, Ren & Vanden-Eijnden, 2002; Weinan, Ren & Vanden-Eijnden, 2005; Peters et al, 2004; Zimmerman, 2013a; Bhoorasingh et al, 2017; Schlegel, 2011). This method is attractive to use when screening large amounts of reactions, as
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