UT theoretical chemistry code forum

Dear Sir,
I am currently learning to use the CI-NEB method, through which I simulated CO oxidation to CO2. I just interpolated only one image between the stable initial and final states with the "nebmake.pl" in my calculation. However, I found that the structure in the image may not be quite proper. For example, in the image, the C-O distance in CO molecule was too short(<1 angstrom) at first, and the calculation failed to converge. Then, I slightly modified the coordinates of C and O atoms in POSCAR of the image to prolong C-O distance and it converged at last. So, I would like to ask a few questions:
1. Am I right? Is the modification correct? If it is right, what's the guideline of the modification?
2. If I'm wrong, what should I do?
3. When I increased the number of images to continue, after interpolation with "nebmake.pl", the C-O distances in CO molecule were still very short in each image, and the force were also very large. To help the calculation converge, I modified the coordinates, but it did not work. Then, what should I do?

I'm looking forwards any comments. Thanks!

Best regards,
Leon

What ever number of images you choose, you should converge the band so that the forces are low (<0.1 eV/Ang). It doesn't make any sense to draw conclusions from un-converged images.

If you have a complex pathway, a single image may not converge. By this, I mean that the force stays high and the image geometry keeps changing. In this case, you may need to use 3 or even 5 images for a curved path. If you are using the climbing image, check that the highest energy image converges. At that point, you have a saddle and are done.

And let the optimizers relax the geometries instead of trying to do it by hand.

Dear Sir,

Thanks for your quick reply. It was really helpful to me. I will take your advice. At the present time, I may know how to proceed.
Thank you very much!