cNEB Diverges in specific images

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RonenKru
Posts: 2
Joined: Sat Jul 13, 2019 12:43 pm

cNEB Diverges in specific images

Post by RonenKru »

Hello Prof. Graeme,

I am trying to use cNEB for calculation of the energy barrier for catalysis of CO2 over MoS2 slab (On a specific side).
The reaction is as followed: MoS2 + H(ads) + CO2(g) ---> MoS2 + COOH (ads).
I am using IOPT=3 and 8 images, Attached cNEB files.
In this case it seems images 1-4 are diverging due to high forces on the X axis on CO2 molecule and maintains these high forces.
How would you suggest to approach this problem?

I am using these INCAR tags:
ISTART = 0
ICHARG = 2
SYSTEM = MoS2 slab
ENCUT = 500
ISMEAR = 0 ; SIGMA = 0.01
ALGO = Fast
EDIFF = 1E-6
EDIFFG = -0.1
NSW = 500
LREAL = A
ISIF = 2
PREC= Accurate
NPAR = 4
ISYM = 0

GGA = OR
LUSE_VDW = .TRUE.
AGGAC = 0.0000
LASPH = .TRUE.

LCHARG = FALSE
LWAVE = FALSE

ICHAIN = 0
LCLIMB = TRUE
IMAGES = 8
SPRING = -5
IBRION = 3
POTIM = 0

IOPT = 3
MAXMOVE = 0.2
TIMESTEP = 0.1
Attachments
CO2_COOH.zip
(11.9 MiB) Downloaded 273 times
graeme
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Posts: 1948
Joined: Tue Apr 26, 2005 4:25 am
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Re: cNEB Diverges in specific images

Post by graeme »

I used less computationally expensive settings and somewhat more conservative optimizer settings to reconverge both the endpoints and the neb. The primary barrier is 0.82 eV, but note that it looks like it will be a two-step process. The high spring constant for the CO2 molecule required a lower time step for the optimizer.
Attachments
neb.tar.gz
(47.82 MiB) Downloaded 384 times
RonenKru
Posts: 2
Joined: Sat Jul 13, 2019 12:43 pm

Re: cNEB Diverges in specific images

Post by RonenKru »

Thank you Professor!
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