Improving the efficiency of the NEB reaction path finding algorithm

The nudged elastic band (NEB) method is a successful optimization method for obtaining minimum energy reaction paths if only the initial and final structures are known. However, the original implementation of the method had some limitations, which has meant that there has been considerable interest in proposing alternative NEB formulations, which show improved convergence behavior. In this work, we present two modifications to the standard NEB procedure. The first involves the use of a second-order quasi-Newton optimization technique applied separately to each of the images that form the path. The second consists of the use of an interpolating spline to represent the path. This ensures that the images along the path are evenly spaced and means that the arbitrary spring forces employed in the standard NEB method are no longer necessary. We tested these modifications on a set of small, but relatively complex, chemical systems and found that the computation time was reduced by as much as 90% compared with the standard method.