[gpaw-users] NEB convergence

[Marcin Dulak]

On 05/08/12 19:05, Hieu Doan wrote:
> Hi,
>
> I have recently had convergence issues with NEB calculations whenever a climbing image is turned on. Images are usually relaxed with fmax=0.5 and climbing=false before setting the final criteria to fmax = 0.05 and climbing=true.  Here are several things I have tried but did not help:
> - Change the eigensolver to davidson
eigensolver should not help for NEB (optimizer convergence),
but, intuitively, what may help is converging SCF better 
https://wiki.fysik.dtu.dk/gpaw/documentation/manual.html#manual-convergence
> - Lower dtmax from 0.3 to 0.1
> - Further relax images to fmax=0.2 before climbing image
>
> These calculations often reach the walltime limit while the force is still fluctuating nowhere around 0.05. I also notice that the climbing TS image either beaks and makes no sense.  My script is posted below. Any suggestion would be greatly appreciated!
how much properties depend on optimizer force stopping threshold?
What's the expected precision of NEB?
Maybe 0.05 is too strict to achieve?

Best regards,

Marcin
> ----------------------------------
> from ase import *
> from gpaw import GPAW, Mixer, FermiDirac
> from ase.visualize import view
> from ase.neb import NEB
> from ase.optimize import BFGS, FIRE
> from ase.parallel import rank, size
> from ase.io.trajectory import PickleTrajectory
> from ase.io import read, write
> import numpy as np
> import os
>
> token = 'image'
> nimages = 7      # number of images including initial and final
> parallel = True
> climbing = True
> maxforce = 0.05
>
> # Read initial and final states:
> initial = read(token+'_0.traj')
> final = read(token+'_'+str(nimages-1)+'.traj')
>
> # Make a band consisting of nimages images:
> interpolate = False
>
> n = size //(nimages-2)    # number of cpu's per image
> j = 1 + rank//n           # intermediate image number, start from 1
> assert (nimages-2) * n == size
> images = [initial]
>
> for i in range(1,nimages-1):
>     filename = token+'_'+str(i)
>     try:
>         atoms = read(filename+'.traj.bak')
>         print "Updated from traj file ",filename+'.traj.bak'
>     except:
>         atoms = initial.copy()
>         interpolate = True
>
>     ranks = np.arange((i-1)*n, i*n)
>
>     if rank in ranks:
>
>         calc = GPAW(h=0.18,
>                     xc='RPBE',
>                     kpts=(4,4,1),
>                     occupations=FermiDirac(0.1),
>                     eigensolver='dav',
>                     mixer=Mixer(beta=0.05, nmaxold=5, weight=50),
>                     maxiter=500,
>                     spinpol=False,
>                     txt=token+'_%d.txt' % j,
>                     communicator=ranks)
>         atoms.set_calculator(calc)
>
>     images += [atoms]
>
> images += [final]
>
> neb = NEB(images,parallel=parallel,climb=climbing)
>
> if interpolate:
>     neb.interpolate()
>
> # Optimize:
> qn = FIRE(neb,logfile='qn-'+token+'.log',dtmax=0.1)
> traj = PickleTrajectory(token+'_%d.traj' % j, 'w', images[j],
>                         master=(rank % n == 0))
> qn.attach(traj)
> qn.run(fmax=maxforce)
> ----------------------------------------
>
> Hieu A. Doan
> Graduate Research Assistant
> Department of Chemical and Biomolecular Engineering
> University of Houston
> _______________________________________________
> gpaw-users mailing list
> gpaw-users at listserv.fysik.dtu.dk
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>


-- 
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Marcin Dulak
Technical University of Denmark
Department of Physics
Building 307, Room 229
DK-2800 Kongens Lyngby
Denmark
Tel.: (+45) 4525 3157
Fax.: (+45) 4593 2399
email: Marcin.Dulak at fysik.dtu.dk

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