Communications: A systematic method for locating transition structures of A+B-->X type reactions.

Search for transition structures (TSs) as first-order saddles is one of the most important tasks in theoretical study of chemical reaction. Although automated search has been established either by starting from a local minimum (MIN) or by connecting two MINs, there is no systematic method which can locate TSs of A+B-->X(+Y) type reactions starting from separated reactants. We propose such an approach for the first time; it was demonstrated to work very well in the SN2, Diels-Alder, and Wittig reactions.