[QE-users] Regarding the optimization of SCF calculations in supercells

[Mateus Corradini Lopes]

Hello Giovanni,

thank you very much for the quick reply and the tips. As requested, here 
is my execution line:

export OMP_NUM_THREADS=48.
mpirun -np 10 pw.x -in input/“$INPUT” -nb 1 -nt 2 > output/"$OUTPUT”


I'm trying to run MPI+openMP in a hybrid way, since using pure MPI has 
prohibitively increased the use of RAM.  Regarding the second point, I 
used K_POINTS gamma for the supercell calculations, I don't know if 
that's exactly your question. As for ecutwfc and ecutrho, I used 50 Ry 
and 400 Ry respectively. Regarding the fourth point, as these are steps 
in a finite displacement process, at least one coordinate will be subtly 
disturbed, referring to the displacement of the atom of the method 
itself, but in fact as you mentioned, there were other coordinates that 
were a little disturbed due to the relaxation I did with vc-relax before 
generating the supercell, which changed the atomic positions a little 
for these strange coordinates. I'm already testing the calculation 
without this relaxation to see if it improves. I'm still looking for 
more suggestions to improve the calculation.

Sincerely,

M.Sc. Mateus Corradini Lopes
PhD. student
Gleb Wataghin Institute of Physics - Unicamp


Em 22/05/2025 16:34, Giovanni Cantele escreveu:
> Hi,
>
> first of all it would be nice also to have the command you use to run 
> pw.x (because if you for example use pools, this replicates the memory 
> requirements).
>
> Second: which k-point grid do you use to sample the Brillouin zone? In 
> the case of a 1x1x1 grid, do you use gamma-only algorithms?
>
> Third: which ecutwfc and ecutrho do you use?
>
> Fourth: I understand you need a "perfect" supercell as derived from 
> replicating a bulk cubic cell. Coordinates like 0.0013807042891237 
> or 0.1874999906250000 are harmful (unless you need to break symmetry 
> or they are exactly what you want), in that they prevent pw.x from 
> finding symmetries. The latter might be quite helpful in (sometimes 
> even significantly) reducing the calculation load (in terms of 
> k-points but not only!). So, I would round all coordinates so as to 
> obtain exactly the number you expect.
>
> Hope this helps.
> Giovanni
>
> -- 
>
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it <mailto:giovanni.cantele at spin.cnr.it>
> Phone: +39 081 676910
> Skype contact: giocan74
>
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> Web page: https://sites.google.com/view/giovanni-cantele/home
>
>
> Il giorno gio 22 mag 2025 alle ore 20:03 Mateus Corradini Lopes 
> <mclopes at ifi.unicamp.br> ha scritto:
>
>     Dear all,
>
>     I have recently been working on obtaining transport properties for
>     certain types of materials. One of the parts of the work is to obtain
>     the lattice thermal conductivity (\kappa_latt), so I'm trying to use
>     phono3py+Quantum Espresso to calculate the supercell and obtain the
>     force constants.
>
>     At the moment I'm trying to calculate the \kappa_latt of GaAs as a
>     test,
>     I've already managed to generate the supercells (4x4x4 and 3x3x3
>     based
>     on the conventional GaAs cell, which gives 512 and 216 atoms
>     respectively) and I've used phono3py's --cutoff-pair to reduce the
>     number of inputs, but even though I've tried various ways of
>     running the
>     calculation I haven't found a way to make it feasible in terms of
>     computational time and RAM (the lowest I could get was “Estimated
>     total
>     dynamical RAM > 115.43 GB”). I have access to a cluster with 480
>     processors (10 nodes with 48 processors each) and I would like to
>     know
>     what is the best way to run this system, in terms of optimizing the
>     input and the parallelism used, balancing precision and
>     computational time.
>
>     Ps. I'm attaching an example of the input I'm currently using.
>
>     Thank you in advance,
>
>     M.Sc. Mateus Corradini Lopes
>     PhD. student
>     Gleb Wataghin Institute of Physics - Unicamp
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