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Posted: **Mon Dec 09, 2024 2:53 pm**

Hello,

I am trying to run NEB calcs for 5 images for water on defective graphene surface. The first calcs, ran well without issues, but reruning the unfinished calculation after clearing my run directory with vfin.pl started giving this bug error.

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|                     _     ____    _    _    _____     _                     |
|                    | |   |  _ \  | |  | |  / ____|   | |                    |
|                    | |   | |_) | | |  | | | |  __    | |                    |
|                    |_|   |  _ <  | |  | | | | |_ |   |_|                    |
|                     _    | |_) | | |__| | | |__| |    _                     |
|                    (_)   |____/   \____/   \_____|   (_)                    |
|                                                                             |
|     internal error in: nonlr.F  at line: 596                                |
|                                                                             |
|     REAL_OPTLAY: internal error (1) 483402 492794                           |
|                                                                             |
|     If you are not a developer, you should not encounter this problem.      |
|     Please submit a bug report.                                             |
|                                                                             |
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I have tried to increase NCORE in my incar and delete the vaspout.h5 in the folders before rerunning but it doesn't help.

Any advise on how to solve this bug will be appreciated. Thanks.

Posted: **Wed Dec 11, 2024 1:23 pm**

Dear inioluwa_afolabi,

it seems the reason for the failure is that one or more images have ions that are way too close to each other.
VASP is actually reporting this, for instance looking at the out.log file, I see following line:

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...
 06/POSCAR found :  3 types and      52 ions
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|                                                                             |
|           W    W    AA    RRRRR   N    N  II  N    N   GGGG   !!!           |
|           W    W   A  A   R    R  NN   N  II  NN   N  G    G  !!!           |
|           W    W  A    A  R    R  N N  N  II  N N  N  G       !!!           |
|           W WW W  AAAAAA  RRRRR   N  N N  II  N  N N  G  GGG   !            |
|           WW  WW  A    A  R   R   N   NN  II  N   NN  G    G                |
|           W    W  A    A  R    R  N    N  II  N    N   GGGG   !!!           |
|                                                                             |
|     The distance between some ions is very small. Please check the          |
|     nearest-neighbor list in the OUTCAR file.                               |
|     I HOPE YOU KNOW WHAT YOU ARE DOING!                                     |
|                                                                             |
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 POSCAR, INCAR and KPOINTS ok, starting setup
...

I have looked at 01/POSCAR using vesta and found that the distance between the C-ion 32 and 35 is less than 0.42 A. Other ions seem also seem to be very close to each other. This is most likely the reason why your second NEB crashes.

Also, I am not convinced your first NEB calculation finished successfully.
For instance, inspecting the 01/OUTCAR of your first NEB shows already increasing forces after each ionic step.
The same holds true for other images.

I am not entirely sure what's the cause of this problem, though.

Maybe IVDW causes it? Maybe, you need to use an alternative ionic minimizer, such as IBRION=3 as described on SPRING wiki entry.
In any case, I would first try to converge with an simpler DFT functional, for instance plain PBE or Opt-PBE, and continue with the preconverged images using the preferred IVDW settings.

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