[Pw_forum] tpss: too many bands are not converged

[Yves Ferro]

Dear Davide,

Mete-GGA functional such as TPSS are known to have convergency problems and numerical instabilities during scf cycles, specifically when the unit-cell contains a lot of free volume, such as in your case probably.
You can try to decrease the size of the unit-cell in order to minimize the free space it contains. Of course, this will be at the expense of the inter-polyemer interaction you probably want to avoid.

Nevertheless, this will probably not cure your problem, which to my knowledge has no other solution than changing the meta-GGA functional to a GGA one.
Best regards,

Yves
 


Le 24 avr. 2014 à 13:36, Davide Tiana a écrit :

> 
> Dear all,
> I've been trying to calculate a polymer using tpss. I already fully  
> optimised it with different functional (pbesol, pw91, hse) and  
> pseudopotential (nc, paw). For some reason (apologise my ignorance if  
> it should be well known) when I try to calculate using tpss nc the  
> system simply does not converge crashing with this error:
> 
>      Error in routine c_bands (1):
>      too many bands are not converged
> 
> After some reaserch in old pw-forum mails, I tried decreasing  
> mixing_beta=0.2, increasing mixing_ndim=12, as well as mixing mode TF  
> and local-TF.
> everythings failed.
> 
> Does anyone have any tips or idea of why the system can't converge?
> 
> Thanks a lot,
> Davide
> 
> 
> 
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