Clarification on nebbarrier.pl vs. nebbarrierdist.pl and Distance Issues

[Trivanni Yadav]

Hello Dr. Henkelman,

I’ve just started my NEB calculations. Initially, when I used the nebmake.pl script to generate 5 images, I found that in two images, some ions were overlapping. I then used the nebavoid.pl script, and the issue was resolved.

Now, I have a question regarding the following:

1.What is the exact difference between the nebbarrier.pl and nebbarrierdist.pl scripts?

After finishing the VASP calculation, I used the nebbarrier.pl script, and it generated a neb.dat file. According to the instructions, the neb.dat file should contain information about the distances between images, the energy of each image, and the force along the band. However, when I used the script, I got the following values:

0 0.000000 0.000000 0.000000 0
1 0.000000 -12.324307 0.522118 1
2 0.000000 -10.626521 -2.124996 2
3 0.000000 1.283551 -4.298445 3
4 0.000000 -4.314786 -3.865482 4
5 0.000000 -3.956906 1.547100 5
6 0.000000 0.024674 0.000000 6

It seems the distances between the images are all zero, right? Also, I am unable to use nebspline.pl because I get this error:

Illegal division by zero at ./nebspline.pl line 70.

However, when I used the nebbarrierdist.pl script, I got the following values:

0 0.000000 0.000000 0.000000 0
1 19.846714 -12.324307 0.522118 1
2 39.643102 -10.626521 -2.124996 2
3 59.645364 1.283551 -4.298445 3
4 80.055967 -4.314786 -3.865482 4
5 100.896856 -3.956906 1.547100 5
6 120.487371 0.024674 0.000000 6


I am now confused about the difference between the two outputs. What could be causing the difference?

2. Also, what are the units for the distances and energy used in these scripts?

Thank you for your guidance!

[Trivanni Yadav]

Hello Dr. Henkelman,

Update:

When I first ran the nebresult.pl script, it generated various files, and this time I noticed that the neb.dat file was updated with the following data:

0 0.000000 0.000000 0.000000 0
1 19.846714 -12.324307 0.522118 1
2 39.643102 -10.626521 -2.124996 2
3 59.645364 1.283551 -4.298445 3
4 80.055967 -4.314786 -3.865482 4
5 100.896856 -3.956906 1.547100 5
6 120.487371 0.024674 0.000000 6

Now, I'm wondering what could have caused this update. Do you have any insights on why the neb.dat file was updated in this manner, especially after running nebresult.pl? Could this behavior be due to some issue with the initial script execution or the way the distances were calculated earlier?

Thank you for your time and guidance!

Best regards,
Trivanni