Verifying That the Correct Geometry Was Obtained

The reaction coordinate is one specific path along the complete potential energy surface associated with the nuclear positions. It is possible to do a series of calculations representing a grid of points on the potential energy surface. The saddle point can then be found by inspection or more accurately by using mathematical techniques to interpolate between the grid points. 

This type of calculation does reliably find a transition structure. However, it requires far more computer time than any of the other techniques. As such, this is generally only done when the research requires obtaining a potential energy surface for reasons other than just finding the transition structure. 

The primary means of verifying a transition structure is to compute the vibrational frequencies. A saddle point should have one negative frequency. The vibrational motion associated with this negative frequency is the motion going 

It is also important to always examine the transition structure geometry to make sure that it is the reaction transition and not the transition in the middle of a ring flip or some other unintended process. If it is not clear from the geometry that the transition structure is correct, displaying an animation of the transition vibrational mode should clarify this. If still unclear, a reaction coordinate can be computed. 

Many techniques for finding transition structures are discussed above. The following is a listing of each of these starting with those that are easiest to use and most often successful. In other words, start with number 1 and continue down the list until you find one that works. 

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