Locating stationary points for clusters in cartesian coordinates

Abstract

Location of minima and transition states by eigenvector following using Cartesian coordinates and a projection operator is described. Comparisons with calculations employing standard internal coordinates are made for a wide variety of model clusters. The new method, suggested by Baker and Hehre, generally produces faster converagence and solves a number of problems that are inherent when using distance, bond angle, dihedral angle internal coordinates. In particiular, eigenvector-following calculations using analytic first and second energy derivatives should now be possible for much larger systems. Some example reaction paths are illustrated, including a new facetting rearrangement of 55- and 147-atom Mackay icosahedra. The basins of attraction of minima and transition states are also calculated, that is, the regions of the potential-energy surface for which stationary-point searches converge to a given structure. The superiority of the projection operator approach is again demonstrated, and the previous observation that initial geometrical contraction is helpful in transition-state searches is confirmed.