High Migration Energy Barrier

[musanna]

Dear Prof. Henkelman,

I am confused with the high energy barrier (5 eV). Is it physically possible or i am missing something? Please give your suggestion on it. I am adding the files here.

Thank you very much.
Musanna

[graeme]

I can not see the final geometries in your calculation, but I can see from your plot that this calculation is not converged and basically the calculation has gone bad. Try an initial run with TIMESTEP=0.01 until the forces drop below 1 eV/Ang. Check that things are reasonable and then continue with whatever optimizer you prefer.

[musanna]

Hello Prof. Henkelman,

I added all the files this time. Images 0 to 4 seems converging but image 5 is diverging for some reason. Can you please give your suggestions on this?

My input file is :


SYSTEM = NEB-Calc
ISYM = 0 # switch on symmetry
ISTART = 0
ICHARG = 2
IALGO = 38
#PREC = ACCURATE # Advised to do so
ALGO = VeryFast #for checking only
PREC = normal #for checking only
LWAVE = .FALSE.
LCHARG = .FALSE
#LREAL = A
NCORE = 4

Electronic Relaxation:

ENCUT = 400
EDIFF = 1.0E-4
NELMIN = 5

Ionic Relaxation:

EDIFFG = -0.1
NSW = 500

DOS related values:
ISMEAR = 0
SIGMA = 0.026
ISIF = 2


NEB Related:

IMAGES = 5 # Number of NEB images between the fixed endpoints
SPRING = -5.0 # The spring constant, in eV/Ang^2 between the images; negative value turns on nudging
ICHAIN = 0 # Indicates which method to run. NEB (ICHAIN=0) is the default
LCLIMB = .TRUE. # Flag to turn on the climbing image algorithm
#LNEBCELL = .TRUE. # Flag to turn on SS-NEB. Used with ISIF=3 and IOPT=3
# Must set IOPT = 3 or 7 when using LNEBCELL=.TRUE.
IOPT = 3 # QM (Quick-Min) force based optimizers is used and good for high force far from minmum
# O(default vasp),1(LBFGS),2(CG),4(SD),7(FIRE)
IBRION = 3 # Disbale VASP default optimizers which are basesd on Energy
POTIM = 0 # Disbale VASP default optimizers which are basesd on Energy
MAXMOVE = 0.2 # Maximum allowed step size for translation(Default comes with IOPT=3)
TIMESTEP = 0.01 # Dynamical time step (Default comes with IOPT=3)
LSCALAPACK = .FALSE.
NPAR = 4

Thanks,
Musanna

[graeme]

My biggest concern is that you have relaxed the endpoints with ISIF=3 and the band with ISIF=2; the band has different lattice constants from the endpoints. Make sure you use the same settings and ideally the same code (they are with different versions of vasp) for the end point relaxation and the NEB.

[musanna]

Hello Professor,

I relaxed the end point using the same setting. However, still the energy barrier seems wrong. Also, the fifth images force and energy are not converging for some reason which is not related to end point relaxation , i think. I am a bit confused now! Can you please a take a look? I would be really grateful. I am adding the files here.

Musanna

[musanna]

Hello Professor,

Any suggestions? I couldn't be able to solve this problem.

Musanna

[graeme]

Well, it's not really the barrier; your final state is 3 eV above your initial state. It's also not clear to me that your final state is fully relaxed, but again, if you have a final state that is 3 eV above your initial state, the barrier will be at least that high.