## Several maxima and minima with CI-NEB

Vasp transition state theory tools

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bhinnema
Posts: 8
Joined: Wed May 17, 2006 5:03 pm

### Several maxima and minima with CI-NEB

Dear all,

I would like to ask a question about the CI-NEB code. If there are several maxima and minima in the pathway, how does the CI method work? Will it move the closest image to the extremum for all extrema, or only for the one highest in energy, or how is this choice made?

Thanks a lot, Berit
andri
Posts: 117
Joined: Tue Apr 26, 2005 6:20 am
The CI-NEB will converge one image to the overall maximum of the MEP. If you need to isolate the other maxima better then you can either run a separate CI-NEB around a given maximum or launch a min-mode (dimer or lanczos) search from one of the images in the original CI-NEB.
graeme
Posts: 1998
Joined: Tue Apr 26, 2005 4:25 am
Contact:
The climbing image is only used for the highest energy image along the path. In principle, the algorithm could be applied to any local maximum (and/or minimum) along the path, but we have done this with the implementation in vasp. Usually when an intermediate minimum is found, it's easier to minimize the geometry as a separate calculation, and construct a new neb for the second reaction barrier.

However, if it would help to rigorously converge to all extrema along the minimum energy path, we would be happy to add a flag for it.
bhinnema
Posts: 8
Joined: Wed May 17, 2006 5:03 pm
Dear Andri and Graeme,

thanks for your answers. I had already thought about splitting up the NEB pathway and do each piece separately and this is probably the best solution. I was just curious about how the implementation is in VASP.
So do I understand it correctly that the extrema with the highest energy is determined and then the image closest to it in reaction coordinate is moved there?

You are probably right that if there are local minima, one should look at the path more closely instead of generically converge to all extrema, but I am not sure.

Another question, if one wants to refine a particular piece of the NEB path (around the saddle point), does it make sense to do a NEB calculation only between two points which are not local minima? I am not sure.

Thanks a lot, Berit
graeme