I want to calculate the path of diffusion of surface vacancies in ZnO. I was able to get converged results for a 2x2 3 layered cell using 5 images, but the same calculation didn't converge with 3 images. Now I want to do the same calculations, but with a bigger cell ( 3 layered 3x3 cell). I have tried using 5 and 7 images, but the calculations just won't converge. I preconverged all the images using IBRION = 3 and I converged the end points using IBRION =1 and I am using IBRION =1 for the NEB run. I am attaching the input files.
Any pointers?
Hi,
In general, increasing the number of images improves the NEB convergence. Did you try launching the NEB with the larger cell starting from the converged path that you obtained for the smaller cell? It might help.
In my opinion, the best would be to try using 9 images starting from the path that you obtained with the small cell with 5 images (you can linearly interpolate the position of every other image to get to 9 images).
Best of luck.
Actually the more images you used will get the better transition state. You can do it via two ways. Either you use 9-10 images, run for a while (50-70 steps) and make sure you check the force on the relaxed atom during the NEB, then choose the highest point and re-optimize with tight energy and force convergence criterion. The second way is to use the "Climbing NEB" implemented by Henkelman in UT Tax group (http://theory.cm.utexas.edu/vtsttools/neb.html#neb).
Thanks for the help
I was able to get converged results for 7 images by freezing the bottom layer, though it took 941 steps. I did not use the converged path though. I gave 9 images a shot too, but i was surprised that the calculations did not converge. I will try doing the calculations using the converged path now and next I will try the climbing image method. Thanks again
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