Searching for saddle points by using the nudged elastic band method:: An implementation for gas-phase systems

A new implementation of the Nudged Elastic Band (NEB) optimization method is presented. This approach uses a global procedure that yields the whole reaction path, and thus it provides an alternative to the sequential optimization of the transition state and consequent calculation of the minimum energy path. Furthermore the algorithm is very useful when one is not sure if a saddle point exists, because it can be used to eliminate the possibility of a saddle point when one does not exist. Three different versions of the NEB algorithm have been implemented. The influences of various parameters and methodological choices on the performance of the method have been studied, and the quality of the results is assessed by comparison with the saddle point and minimum energy path calculations sequential method. Recommendations are made for algorithmic choices and default parameters.