To run reaction dynamics or compute reaction rate constants ab-initio, one needs a potential energy surface. In the case of transition state theory the minimum energy path needs to be identified and computed and subsequently the transition state needs to be determined. If the transition state is known then the full path need not be determined to implement TST.

The computation of a full potential energy surface is generally time-consuming and complex. Therefore, methods have been developed to try to interpolate between known fixed geometries to compute an energy pathway while avoiding to compute the full potential energy surface. These include the Nudge Elastic Band method (NEB) [1], the String Method [2], the Growing String Method (GSM), the Freezing String Method (FSM) [4].

In the next post I will describe how to implement the NEB method for a reaction.

[1] G. Henkelman and H. Jónsson, *J. Chem. Phys.* **113**, 9901-9904 (2000).

[2] E. Weinan, W. Ren, and E. Vanden-Eijnden, *Phys. Rev. B* **66**, 052301 (2002).

[3] B. Peters, A. Heyden, A. T. Bell, and A. Chakraborty, *J. Chem. Phys.* **120**, 7877 (2004).

[4] A. Behn, P. M. Zimmerman, A. T. Bell, and M. Head-Gordon, *J. Chem. Phys.* **135**, 224108 (2011)

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