A new approach for finding a transition state connecting a reactant and a product without initial guess: applications of the scaled hypersphere search method to isomerization reactions of HCN, (H2O)2, and alanine dipeptide

A new method for finding a transition state (TS) between a reactant and a product on the potential energy surface has been proposed. The scaled hypersphere search (SHS) method, in which reaction pathways are found as minima on the hypersphere, has been applied to finding TS. Starting from a hypersphere centered at the product with a radius just including the reactant on its surface, successive contraction of the sphere radii gives a pathway leading to the TS region. Applications of this method to isomerization of HCN, (H2O)2, and alanine dipeptide demonstrated highly accurate estimation of TS without any initial guess.