[Pw_forum] SCF correction compared to forces is too large, reduce conv_thr

[Stefano de Gironcoli]

dear artee sharma,

conv_thr=1.0e-5 is a rather large value, acceptable if you just want  
the energy but not if you want forces. 1.0e-6 is the default and for  
relaxations one rather tends to reduce it...

Convergence for large systems (especially inhomogeneous metallic ones)  
may be slow. mixing_mode='local-TF' usually helps in these cases. are  
you using it ?

Even when the first scf convergence is painfully slow the subsequent  
ones should be better as potential and wfcs are extapolated from  
previous steps. check that you are indeed using these extrapolations  
(should however be the default for relaxation, so probably you do).

Sometime when a system does not want to converge it's trying to tell  
you something ... Is it a magnetic or metallic system ? are you using  
smearing ? are you sure the number of bands and your k-point sampling  
is accurate enough ?

hope this helps,
  stefano

Stefano de Gironcoli - SISSA and DEMOCRITOS

Quoting artee sharma <mailtoartee at gmail.com>:

> Dear Stefano.
>    thanks for reply. my conv_thr in input file is 1.0e-5? i have a large
> system, takes too much time to convarage, so kept it low. Shall i decrease
> it by further one order?
>   latest output is showing:
>   Total force =     0.023049     Total SCF correction =     0.002483
> so i think my system has not converged yet, force is high.
> regards
> artee sharma
> Department of physics
> Bhavnagar University
> India
>
>
>
>
> On Sat, Mar 21, 2009 at 11:46 AM, Stefano de Gironcoli   
> <degironc at sissa.it>wrote:
>
>> I think it might be better to stop it. According to the message the forces
>> you are calculating may be not accurate and any further relaxation based on
>> them is not likely to improve your geometry.
>>
>> However, are you sure your system is not yet relaxed enough ?
>> What is your conv_thr and your force threshold ?
>>
>> stefano de Gironcoli - SISSA & DEMOCRITOS
>>
>> PS: don't forget to  provide your affiliation
>>
>>
>>
>>
>>
>> Quoting artee sharma <mailtoartee at gmail.com>:
>> **
>>
>>
>> ----------------------------------------------------------------
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>



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