Abstract
There are works of the Maeda-Morokuma group, which propose the artificial force induced reaction (AFIR) method (Maeda et al., J. Comput. Chem. 2014, 35, 166 and 2018, 39, 233). We study this important method from a theoretical point of view. The understanding of the proposers does not use the barrier breakdown point of the AFIR parameter, which usually is half of the reaction path between the minimum and the transition state which is searched for. Based on a comparison with the theory of Newton trajectories, we could better understand the method. It allows us to follow along some reaction pathways from minimum to saddle point, or vice versa. We discuss some well-known two-dimensional test surfaces where we calculate full AFIR pathways. If one has special AFIR curves at hand, one can also study the behavior of the ansatz. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.
Highlights
Considerable interest is attached to the search of reaction pathways in chemistry, especially the points which govern these ways: minimums and saddle points of index one (SP1) on the potential energy surface (PES) of a reaction system
We propose to use an increase of the parameter, α, up to the barrier breakdown point (BBP) at αmax of the artificial force induced reaction (AFIR) curve, and a decrease of the parameter, α, after the BBP
If a turning point emerges the corresponding curve should not serve for a model of a reaction path because the TP has usually a higher energy than the SP1. (iii) A problematic property of the AFIR method, at least in the example of Fig.2 ̇, as bad as in others, is that here an unsatisfactory behavior emerges into the inverse directions of the two global minimums
Summary
Considerable interest is attached to the search of reaction pathways in chemistry, especially the points which govern these ways: minimums and saddle points of index one (SP1) on the potential energy surface (PES) of a reaction system. Because of the nonlinearity of the AFIR ansatz, Eq (1), the resulting curves do 8 depend on the PES, they depend on the used coordinates We demonstrate it with a very simple test surface with one minimum and two SP of index 1, the KondaAvdoshenko-Makarov (KAM) surface.[12,13] It is a surface with two reaction pathways between a reactant and the exit. It is in contrast to the case of NTs.[23] At every stationary point we detect one AFIR curve which coarsely follows an eigenvector direction of the Hessian. At two minimums they follow the smaller eigenvalue direction, the ’reaction valley’, but at the third minimum the corresponding AFIR curve follows the larger eigenvalue direction. At the main SP1 near point (-0.8, 0.65) the AFIR curve here crosses along the ridge, not along the reaction path direction
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