Methods for the exploration of potential energy surfaces (PESs) are in many respects based on mathematical techniques for the optimization of multidimensional functions.^1–3  Optimization is a general term for the process of finding stationary points at which the first derivative is zero. Important geometrical structures on a PES that may be identified in this manner are minima (corresponding to equilibrium (EQ) structures (EQs)) and first-order saddle points (transition states (TSs)). Other targets include dissociation channels (DCs) and intrinsic reaction coordinates (IRCs), which are not stationary points but rather represent reaction channels or pathways. In some cases, only a local stationary point of a local reaction pathway can be found but, in principle, many EQs, TSs and DCs as well as IRCs will be located on a given PES.