LOCATING STATIONARY-POINTS FOR CLUSTERS IN CARTESIAN COORDINATES

Location of minima and transition states by eigenvector following usin g Cartesian coordinates and a projection operator is described. Compar isons with calculations employing standard internal coordinates are ma de for a wide variety of model clusters. The new method, suggested by Baker and Hehre, generally produces faster convergence and solves a nu mber of problems that are inherent when using distance, bond angle, di hedral angle internal coordinates. In particular, eigenvector-followin g calculations using analytic first and second energy derivatives shou ld now be possible for much larger systems. Some example reaction path s are illustrated, including a new facetting rearrangement of 55- and 147-atom Mackay icosahedra. The basins of attraction of minima and tra nsition states are also calculated, that is, the regions of the potent ial-energy surface for which stationary-point searches converge to a g iven structure. The superiority of the projection operator approach is again demonstrated, and the previous observation that initial geometr ical contraction is helpful in transition-state searches is confirmed.