[DFTB-Plus-User] SCC Never converged inn DFTB MD

[Bálint Aradi]

Dear Achyut Subedi,

I would probably first test, whether the geometry, for which the SCC 
fails to converge, is a physically sound one at all. Especially, since 
your system is periodic, repeat the geometry (e.g. with repeatgen) and 
investigate it with a molecular viewer, whether the images have the 
right distances from each other.

Then, you could also set AdaptFillingTemp = No and set the temperature 
for the electronic filling in Filling = Fermi { Temperature [K] = ... }
independently from the inonic temperature and so also considerably 
higher, if needed.

And last, you might try ConvergentSccOnly = No, so that MD proceeds, 
even if the charges are not convergent. However, it might result in 
absolutely unphysical MD steps (especially if the SCC error is high), so 
be careful about it.

Best regards,

Bálint



On 9/15/25 9:50 PM, ACHYUT SUBEDI wrote:
> Hello everyone,
> 
> I was trying to DFTB MD for my structure which contains a metal and a 
> few organic elements.
> 
> I first tried to relax the structure and take the relaxed structure to 
> perform DFTB MD.
> 
> Initially I was facing the SCC Convergence issue even after 10000 
> iterations. So I searched in the DFTB Discussion to solve this issue.
> 
> It was suggested that if I use a very high electronic temperature, the 
> SCC Converges and then I can use that converged charge to 
> perform further calculations.
> 
> 
> But in my case, even if I used converged charges, the SCC didn't 
> converge and no forces and energy outputs were written.
> 
> NOTE: I tried using maximum iteration cycles to be 20000 as well but 
> the SCC error instead of decreasing, always increased!
> 
> 
> Is there a specific parameter that I can tweak to make this SCC Converge?
> 
> 
> I look forward to hearing from you all soon.
> 
> I have attached my input file and slurm file for your reference.
> 
> Best regards
> Achyut Subedi
> 
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-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.uni-bremen.de/en/lmcqm/b-aradi

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