The determination of transition state (TS) on potential energy surface (PES) is a critical step in the theoretical study of chemical reactions. To reduce the computational cost without losing the accuracy in TS searching, we have developed an elastic image pair (EIP) method to locate TS. In this method, only two images are generated and optimized in TS searching, which is much less than nudged elastic band (NEB) method (usually need 4~20 images). Additional spring forces are added to the images to control the distance and relative energies between the images. This method was tested with 45 reactions including Baker system and was compared with the NEB method. The testing result shows its efficiency in the transition state searching. The average total force evaluation steps in searching transition states using the EIP method (58 steps) was reduced by 78% compared to those using the NEB method (269 steps). The TSs found by the EIP method own less root mean square forces (RMSF) than those found by the NEB method, the average RMSF value of the located TS structures are 0.0014 and 0.0068 Hartree/Bohr, respectively. This new method is more stable and reliable in finding transition states with much less computationally demanding. As the EIP method is largely intuition free, it could be useful in the automatic reaction pathway searching on complex PES.

Searching transition states on potential energy surfaces with elastic image pair method

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