Finding transition states

An algorithm for locating transition states on a potential energy surface is described. The most important feature of the algorithm, which makes explicit use of the second derivative matrix of the potential surface, is that it is able to ''walk uphill'' from the minimum on a potential surface to the transition state essentially automatically. The method is illustrated by application to a two dimensional model problem, to the vinylidene--acetylene rearrangement (H2C = C:bold-arrow-left-rightHCequivalentCH), and to the dissociation and rearrangement of formaldehyde (H2CObold-arrow-left-rightH2+CO, HCOH). The algorithm is also seen to provide an improved way of following a reaction path from a transition state down to reactants or products