[DFTB-Plus-User] Copper geometry optimization convergence

[Bálint Aradi]

Dear Frank,

Welcome among the DFTB+ users! :-)

> I'm working on doing a simple geometry optimization of a copper unit 
> cell with GFN2-xTB and I find the SCC does not converge but the delta 
> energy is 1e-9 so it seems the energy is converged.

Please note, that the stanard GFN2-xTB parameterization does not really 
play well with periodic systems (as such systems were not taken into 
account during the parameterization). So, check very critically, whether 
the band structure you obtain for a given geometry is reasonable, and 
whether the optimization drives the atoms into a reasonable configuration.

> Are there other SCF convergence criteria besides the SCC?

Yes, we usually check the charges per default. If the energy is very 
small, but the SCC still does not stop, then probably charge sloshing 
occurs in your system.

> Can someone give me some pointers on dealing with metallic systems or 
> DFTB+ best practices?

Basically the same, as in all ab initio DFT-codes. High number of 
k-points, and possible also a high electronic temperature (higher than 
room temperature).

> If this is the wrong place to ask these questions, feel free to point me 
> in the right direction.

It was the right place to ask those questions.

Best regards,

Bálint



-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/

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