[QE-users] differently complied QE

[Nicola Marzari]

Well, the numbers you get are not infinitely precise - there is
a threshold where you stop minimizing forces and cell geometry,
using forces and stresses that are not perfect because each SCF cycle is
not converged to infinite perfection.

Bottom line - try to tighten all the convergencies (scf convergence
at every cycle, and forces at every ionic relxations, and pressure...)

conv_thr for electrons
etot_conv_thr for ions
forc_conv_thr for ions
press_conv_thr for cell

are the variables to play with. I would make sure conv_thr is very tight
(10^-10 per atom, or even less) and then play with forc_ and press_

		nicola


On 07/01/2019 14:24, Aleksandra Oranskaia wrote:
> Hello dear users and developers of QE,
> 
> I have recently noticed that one and the same QE version that was 
> installed with different libraries, compilers, on different machines 
> (with very different hardware) not only gives different total energies 
> for the same inputs but also quite different optimized lattice constants 
> (say, 3.458 versus 3.453 that does not seem no be acceptable).
> 
> So the question is: how to know which installation accumulates some 
> small(?) numerical problems?
> In standard QE pw examples there is no example with variable-cell 
> relaxation done on “ideally” installed code, so there is no reference 
> point to reproduce.
> 
> 
> 
> Best,
> Alex.
> ___
> Aleksandra Oranskaia (M.Sc.)
> ChemS PhD student, KAUST
> Phone: +966 50 1335254
> 
> 
> 
> 
> 
> 
> 
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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