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

[Giovanni Cantele]

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 <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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