Locating transition structures by mode following: A comparison of six methods on the Ar8 Lennard‐Jones potential

Six different methods for walking from a minimum on a potential energy surface to a transition structure are tested on the Lennard‐Jones surface for a cluster of eight argon atoms. The six methods consist of two Newton–Raphson‐type algorithms using augmented Hessians, two methods for following gradient extremals, one following the intrinsic reaction coordinate on the image potential, and a constrained optimization technique. Only if the lowest mode of a given symmetry is followed can these methods locate transition structures in a stable manner. Optimizations along the higher modes display erratic or no convergence. The analysis shows that this is due to two factors: Hessian eigenvectors in general provide a poor direction for the uphill walk, and the presence of bifurcations along the path.

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