Efficient methods for finding transition states in chemical reactions:Comparison of improved dimer method and partitioned rational function optimization method

摘要

A combination of interpolation methods and local saddle-point search algorithms is probably the most efficient way of finding transition states in chemical reactions.Interpolation methods such as the growing-string method and the nudged-elastic band are able to find an approximation to the minimum-energy pathway and thereby provide a good initial guess for a transition state and imaginary mode connecting both reactant and product states.Since interpolation methods employ usually just a small number of configurations and converge slowly close to the minimum-energy pathway,local methods such as partitioned rational function optimization methods using either exact or approximate Hessians or minimum-mode-following methods such as the dimer or the Lanczos method have to be used to converge to the transition state.A modification to the original dimer method proposed by [Henkelman and Jonnson J.Chem.Phys.Ill,7010 (1999)] is presented,reducing the number of gradient calculations per cycle from six to four gradients or three gradients and one energy,and significantly improves the overall performance of the algorithm on quantum-chemical potential-energy surfaces,where forces are subject to numerical noise.A comparison is made between the dimer methods and the well-established partitioned rational function optimization methods for finding transition states after the use of interpolation methods.Results for 24 different small- to medium-sized chemical reactions covering a wide range of structural types demonstrate that the improved dimer method is an efficient alternative saddle-point search algorithm on medium-sized to large systems and is often even able to find transition states when partitioned rational function optimization methods fail to converge.