SCF convergence problem in vacancy defect modelling

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SCF convergence problem in vacancy defect modelling

Postby mmaeda » Thu Dec 08, 2016 1:26 pm

Dear Abinit users and developers,

I am modelling a spinel metal oxide system with O vacancy as a cubic supercell (55 atoms) by PAW and GGA+U; but struggling with SCF convergence. Any suggestion to fix the problem?

Some input parameters:
ecut 500 eV
pawecutdg 1600 eV
ixc 11
occopt 7
diemac 12.0
ionmov 2
optcell 1
dilatmx 1.05
ecutsm 0.5
tsmear 0.01
strprecon 0.1

Thanks,
Maki
mmaeda
 
Posts: 3
Joined: Wed Dec 07, 2016 5:49 am

Re: SCF convergence problem in vacancy defect modelling

Postby ebousquet » Mon Dec 12, 2016 12:46 pm

Dear Maki,
How bad is your convergence? Does it succeed to converge up to a given precision and then it is stuck at this precision or is it completely bad from the beginning or does it converge and then starts to diverge, do you have an error/wraning message, etc? An output file will be welcome or at least the "grep ETOT" of it to reply to you.
I would already advise you to first relax the internal coordinates by keeping the cell parameters unrelaxed and then relax them once the internal atomic coordinates will be relaxed, that might help the algorithm in finding the minimum.
Best wishes,
Eric
ebousquet
 
Posts: 303
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium

Re: SCF convergence problem in vacancy defect modelling

Postby mmaeda » Mon Dec 26, 2016 10:05 am

Hi Eric,

Thanks for your advice. I have tried to converge the system with ion position optimization (without cell parameter optimization). But the problem of SCF convergence has not been solved. The fisrt SCF cycle slowly converged, but remained the same order of magnitude in absolute energy change in the system and did not reach the convergence criteria. I tried to use several different iscf parameters to see if SCF converges. But none of them solved the problem, but in some cases SCF actually diverged instead. Any suggestion?

Thanks,
Maki
mmaeda
 
Posts: 3
Joined: Wed Dec 07, 2016 5:49 am

Re: SCF convergence problem in vacancy defect modelling

Postby ilukacevic » Tue Dec 27, 2016 10:56 am

Dear Maki,

Did you try increasing some of these variables: npulayit, nnsclo or nline in combination with iscf 7 or 17?

Best regards,

Igor
ilukacevic
 
Posts: 271
Joined: Sat Jan 16, 2010 1:05 pm
Location: Dept. of Physics, University J. J. Strossmayer, Osijek, Croatia

Re: SCF convergence problem in vacancy defect modelling

Postby ebousquet » Fri Jan 13, 2017 12:45 pm

Dear Maki,
Did you try to simply reduce the mixing parameter diemix?
All the best,
Eric
ebousquet
 
Posts: 303
Joined: Tue Apr 19, 2011 11:13 am
Location: University of Liege, Belgium


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