[QE-users] question about last steps of vc-relax

[Nicola Marzari]

Thanks Paolo!


This is a chance to remind everyone that there are sets of carefully 
tested pseudopotentials (PBE and PBEsol) with suggested cutoffs on
https://materialscloud.org/sssp ; these cover the entire periodic table. 
There are two choices - efficiency or precision. They have been verified 
again all electron calculations in https://arxiv.org/abs/2305.17274 - so 
consider these result scarefully - if your pseudopotential are not 
accueate, or cutoffs or samplings, your results will be incorrect.

The QE input generator (not yet updated to the last SSSP 1.3) gives also 
some reasonable input parameters you can always use as a sanity check 
https://www.materialscloud.org/work/tools/qeinputgenerator

			nicola



On 04/09/2023 11:42, Paolo Giannozzi wrote:
> On 9/4/23 11:09, Konstantin Glazyrin wrote:
> 
>> An example - target relaxation pressure 600 kbar:
>> 1 - total   stress  (Ry/bohr**3)                   (kbar)     P= 
>>   600.65 - last run of structure relaxation
>> 2 - total   stress  (Ry/bohr**3)                   (kbar)     P= 
>>   484.28 - final scf run
>> May I ask - what does it indicate
> 
> it indicates that your kinetic cutoff is too low for a good description 
> of the pressure
> 
>> which value I should trust more and how should I proceed?
> 
> the former is the pressure, computed for the plane-wave basis set of the 
> INITIAL unit cell.
> The latter is the pressure, computed for the plane-wave basis set of the 
> FINAL unit cell.
> They should converge to the same value at sufficiently high cutoff.
> 
>> Is it because of this?
>> SCF correction compared to forces is large: reduce conv_thr to get 
>> better values
>> For me it is conv_thr =   6.4000000000d-06
> 
> it is a bit too large, but it is hardly related to the original problem
> 
> Paolo
> 
>> Thank you!
>> best wishes,
>>              Konstantin
>>
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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