UT theoretical chemistry code forum

[attachment=0]CNEB.png[/attachment]

I am running a Cl-NEB run and now the nebef.pl results read like above. We can find two extrema in energy: the local minimum of image 2 at -0.0675 and the maximum of image 4 at -0.0299 ref to initial image 00.

When I check the OUTCAR of all the images, I am puzzled:

for 01/OUTCAR:
NEB: the previous image is higher in energy: F
NEB: the next image is higher in energy : F
NEB: image is at an extrema

for 02/OUTCAR:
NEB: the previous image is higher in energy: T
NEB: the next image is higher in energy : T
NEB: image is at an extrema

for 04/OUTCAR:
NEB: the previous image is higher in energy: F
NEB: the next image is higher in energy : F
NEB: image is at an extrema

My question is: for 01/OUTCAR, why "NEB: the previous image is higher in energy: F" ? It should be TRUE! And the image 01 is not an extrema!

The next two extrema are right. And, the MEP will be divided in to three areas: 00-02, 02-04 and 04-07. And the distance bwtween neighbor images will be pushed to be equal for each of the three areas, respectively?

This is a good point; and something that we know about. The logic for this is as follows:

VASP does not read the energy of the first (00) and final (07, in your case); it only reads those geometries.

You can set the energy of the endpoints through the INCAR file using:

EFIRST = -661.829567 (or whatever the initial energy happens to be)
ELAST = -665.160154

and everything should work as you expect. But when there is no information about the energy of the endpoints, we assume that they are minimized and therefore have a lower energy than the next-neighbor images (01 and 06 in your case). If this is not true, we suspect that you are doing something unusual such as finding a path that is not between local minima. If this is the case, we recommend that you turn off the climbing image.

Dear Graeme, you are so helpful! I love you! ~

I put a small molecule in the slab vacuum 4 Angstrom from the surface. The molecule will be adsorbed to the surface and react with pre-adsorbed surface species. In this process, there is a energy barrier.

So the initial geometry is true acting as a guess beginning. But, I think the climbing tage (= TRUE)is still needed. Do you agree my opinion?

When I have set EFIRST and ELAST as you suggested, a new line was added to all the 01-06/OUTCAR :

NEB: no climbing image found.

What does this mean to 04 image which is supposed to be the TS with a local maximum energy? For another CNEB run with two fully optimized endpoints, the same INCAR (except images number) did not make this line. Should I set the EFIRST to a value lower than the 04 image energy but higher than 01 image to make the CLIMBING functional work?

Why did you suggest in my case to turn off climbing tag?

Graeme, the line (NEB: no climbing image found) disappeared when I set the EFIRST to a value between the energy 01 image and 04.

I think I have got your points in EFIRST and ELAST in INCAR.

Cheers ~