I have a 19-atom molecule (C,H,O only) in an 18 Angstrom cubic box and I'm trying to set up an NEB calculation. I did the following:
1) Relaxed the initial and final structures and called them POSCAR00 and POSCAR03
2) Made a parent directory containing the following files: KPOINTS, INCAR, POTCAR, POSCAR00, POSCAR03, and the vasp.sh script
3) Used the nebmake.pl script to generate 2 images so that I now have a POSCAR file in all of the following subdirectories: 00,01,02,03
My INCAR file for the NEB run with the B3LYP functional is:
SYSTEM = 2ACP
ISMEAR = 0 ! Gaussian smearing
NSW = 500 ! 500 ionic steps
LCLIMB = .TRUE.
LSCALAPACK= .FALSE.
IMAGES=2
SPRING = -5
ICHAIN=0
IBRION = 2 ! use the conjugate gradient algorithm
POTIM = 0.5
LHFCALC = .TRUE.
GGA = B3
AEXX = 0.2
AGGAX = 0.72
AGGAC = 0.81
ALDAC = 0.19
EDIFFG = -0.05
I'm wondering if this is set up correctly or if I am missing anything.
I've read that IBRION=2 usually fails to converge but it seems to be converging. I wasn't sure if I chose POTIM correctly or if it is necessary to include LSCALAPACK= .FALSE.
Thank you!
Nudged Elastic Band Set up with B3LYP
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Nudged Elastic Band Set up with B3LYP
Last edited by gg33 on Tue Feb 21, 2017 3:58 pm, edited 1 time in total.
Re: Nudged Elastic Band Set up with B3LYP
That could be ok but I would start with ~5 images to be safe and POTIM=0.1 with IBRION=3. You can switch to a different IBRION (e.g. 1) once the band has relaxed close to the minimum energy path.
SCALAPACK is optional and independent of the NEB calculation.
SCALAPACK is optional and independent of the NEB calculation.
Re: Nudged Elastic Band Set up with B3LYP
Could you please explain why I would want to start with more images? I thought less would make convergence easier.
Thanks for your reply!
Thanks for your reply!
Re: Nudged Elastic Band Set up with B3LYP
You need a sufficient number of images to resolve the reaction path. For a linear path, only one image is needed, but in general five is a pretty safe place to start.
Re: Nudged Elastic Band Set up with B3LYP
Thanks!
I also have one question in regards to convergence. My criteria for EDIFFG = -0.05 eV/A. If I understand correctly this is in reference to the CHAIN +TOTAL forces obtained by grep 'TOTAL' -A no.atoms OUTCAR
CHAIN + TOTAL (eV/Angst)
----------------------------------------------
0.02595 0.00667 -0.04955
-0.02838 0.00349 -0.03701
-0.02533 0.00341 -0.03680
-0.03096 0.00031 0.03256
-0.03429 0.00218 0.03985
0.04103 0.01190 -0.05209
-0.03306 0.00155 0.03835
0.02469 -0.00034 0.10074
0.02049 0.00458 0.09700
-0.04112 -0.00856 -0.05000
0.12643 -0.00365 -0.01414
-0.01342 0.00353 -0.02233
-0.01178 -0.00020 0.01944
0.05759 -0.00524 0.01095
0.02105 -0.00541 0.03180
0.02335 0.00397 -0.02538
0.00633 0.00047 0.06616
0.00548 -0.00609 -0.00162
If these forces do not drop to the convergence criteria within a reasonable amount of time would increasing POTIM to 0.5 and continuing to use IBRION=3 be a suitable approach to achieving convergence?
I also have one question in regards to convergence. My criteria for EDIFFG = -0.05 eV/A. If I understand correctly this is in reference to the CHAIN +TOTAL forces obtained by grep 'TOTAL' -A no.atoms OUTCAR
CHAIN + TOTAL (eV/Angst)
----------------------------------------------
0.02595 0.00667 -0.04955
-0.02838 0.00349 -0.03701
-0.02533 0.00341 -0.03680
-0.03096 0.00031 0.03256
-0.03429 0.00218 0.03985
0.04103 0.01190 -0.05209
-0.03306 0.00155 0.03835
0.02469 -0.00034 0.10074
0.02049 0.00458 0.09700
-0.04112 -0.00856 -0.05000
0.12643 -0.00365 -0.01414
-0.01342 0.00353 -0.02233
-0.01178 -0.00020 0.01944
0.05759 -0.00524 0.01095
0.02105 -0.00541 0.03180
0.02335 0.00397 -0.02538
0.00633 0.00047 0.06616
0.00548 -0.00609 -0.00162
If these forces do not drop to the convergence criteria within a reasonable amount of time would increasing POTIM to 0.5 and continuing to use IBRION=3 be a suitable approach to achieving convergence?