[QE-users] Optimal pw command line for large systems and only Gamma point

[Giuseppe Mattioli]

Ciao Nicola
You're right, I've mixed two different things too much with a  
misleading result. The first information was "use Gaussian smearing  
because in my experience makes scf more stable". The second was "if  
you use Gaussian smearing and scf_must_converge=.false., then you may  
reduce smearing to lower values that avoid the smearing of too much  
charge density across the semiconductor band gap (if there is any in  
such nanoclusters...), with a partial occupation of orbitals that  
should be empty".
Thanks for the clarification, I think it will be useful to Antonio.
Best
Giuseppe

Quoting Nicola Marzari <nicola.marzari at epfl.ch>:

> On 13/05/2024 17:26, Giuseppe Mattioli wrote:
>
>>>     occupations= 'smearing'
>>>     smearing= 'cold'
>>>     degauss= 0.05 ! I know it's quite large, but necessary to  
>>> stabilize the SCF at this preliminary stage (no geometry step done  
>>> yet)
>>>     mixing_beta= 0.4
>>
>> If you want to stabilize the scf it is better to use a Gaussian  
>> smearing and to reduce degauss (to 0.01) and mixing beta (to 0.1 or  
>> even 0.05~0.01). In the case of a relax calculation with a  
>> difficult first step, try to use scf_must_converge=.false. and a  
>> reasonable electron_maxstep (30~50). It often helps when the scf is  
>> not completely going astray.
>
>
> Ciao Giuseppe, I would agree that in a semiconductor it might be  
> more natural to use Gaussian (although even for cold things are now  
> sorted out -  
> https://journals.aps.org/prb/abstract/10.1103/PhysRevB.107.195122);  
> but I wonder why reducing the smearing would help convergence.
>
> To me, the smaller the smearing the more you can be affected by  
> level-crossing instabiities?
>
> 			nicola
>
>>
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, SNSF
> Head, Laboratory for Materials Simulations, Paul Scherrer Institut
> Contact info and websites at http://theossrv1.epfl.ch/Main/Contact



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>