[QE-users] Choosing convergence criteria for vc-relax

[Nicola Marzari]

Hi Robert,

this issue of optimal parameters is a bit of a neverending story, we are
preparing a short thing on this. But in a nutshell - yes, the electronic 
convergence should be tighter, especially for a follow-up phonon 
calculation. that number actually depends on the unit cell used, but for 
5 atoms, I would indeed try d-12 and d-14. For ecutwfc and ecutrho, 
well, my advise is to use the SSSP suggestions (google it); and say if 
you have 30 120, 40 160, 25 300, well, take the max of the ecutwfc 
suggested, for the gloval ecutwfc, and same for ecutrho.

			nic


On 17/05/2019 21:24, Appleton, Robert J wrote:
> Hello,
> 
> I am trying to study the phonons of the material BaZrS3 to determine if 
> it is stable for a given structure. I first use phonopy and vasp and 
> found negative frequency values for phoning band structure. My advisor 
> is concerned in the optimization of the structure and so we now want to 
> use quantum espresso. I have only used it a few times and mostly used 
> default or example inputs. The input I want to make sure is sufficient 
> is my criteria for convergence.
> 
> Under the &control:
> force convergence criteria right now is
> forc_conv_thr = .0001 <— this value seems to big but how do I choose a 
> value that is best for optimization but does not take to much computer time?
> 
> Under the &electrons:
> conv_thr = 1.d-9 <— I am considering changing to 1.d-12. Is this a good 
> idea?
> 
> Under &system:
> I am using ecutrho = 12 • ecutwfc
> 
> If you can give me some advice on how best to choose convergence 
> criteria for studying phonons that would be very good thanks.
> 
> Robert Appleton
> Cal State LA - MS Physics Student
> 
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-- 
----------------------------------------------------------------------
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