Some Practical Suggestions for Optimizing Geometries and Locating Transition States

Abstract

ABSTRACf The optimization of equilibrium geometries and transition states by molecular orbital methods is discussed from a practical point of view. Most of the efficient geometry optimization J;rlethods rely on analytical energy gradients and quasi-Newton algorithms. For ar1y optimization method, there are three areas of input that directly affect the behavior of the optimization: (a) the choice of internal coordinates, (b) the starting geometry and (c) the initial estimate of the Hessian. A number of topics related to these three areas are discussed with the aim of improving the performance of optimizations; these include symmetry, dummy atoms, avoiding coordinate redundancy, overcoming strong coupling among coordinates, conversion between coordinate systems, testing stationary points and what to do when optimizations fail.