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

[Nicola Marzari]

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

> 
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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