[QE-users] convergence criterion?

[Nicola Marzari]

Dear all,


also, as mentioned several times in this mailing list:

1) extensive tests for the pseudopotentials have been done, and
are reported here:
https://www.materialscloud.org/discover/sssp/table/efficiency

2) same for kpoints and convergence tolerance
https://www.materialscloud.org/work/tools/qeinputgenerator

These two tools should not remove the need to test and understand, but
would be a solid starting point to understand if you need a higher 
cutoff, more k-points, etc...

				nicola


On 15/01/2020 10:25, Matic wrote:
> Hi Matthew,
>> I've often heard it said that 1meV/atom is a good criterion for 
>> convergence tests to set ecutwfc, ecutrho and K-point sampling.  I 
>> wonder if that makes
>> sense in if the structure has very light and heavy atoms.  One I'm 
>> working on now contains Ca, Si, O and H.  Since each H contributes 
>> only one electron, should
>> it count equally in the tally of 104 atoms?  Should the criterion be a 
>> certain energy/total electron?  Energy/valence electron (defined in 
>> the pseudo)?
> 
> Convergence of ecutwfc/ecutrho is a property of the pseudpotential used, 
> so you should converge ecutwfc/ecutrho for the each new atom type 
> (pseudopotential) in your system and then used the maximum value 
> obtained for all calculations. A hint for appropriate values is 
> typically listed in the pseudopotential file. The easiest way to do this 
> is just to make a small box containing the atom and increase ecutwfc 
> (using lets say ecutrho=8*ecutwfc_max) until the energy stays within 
> approx ~1 mRy. Once you obtain the converged ecutwfc then you can 
> decrease ecutrho to a more appropriate value.
> 
> Here is a hands-on presentation from a workshop where this is described: 
> http://indico.ictp.it/event/7921/session/320/contribution/1261/material/0/
> 
> Best Regards,
> 
> Matic
> 


-- 
----------------------------------------------------------------------
Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
Director, National Centre for Competence in Research NCCR MARVEL, EPFL
http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project