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
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