[QE-users] YBCO (001) slabs: "convergence" problem

[Giovanni Cantele]

Dear Michele,

I have had the time for just a quick inspection to your files, and
unfortunately I did not find possible mistakes.
Maybe someone else will be more helpful in this regard.
Both the total energy and the total force in the output are
monotonically decreasing, with the exception of the
4th relaxation step.
The only thing that might be odd (but it could be correct for the system
you're studying) is that the
comparison of the initial and the latest structure shows only an outwards
relaxation of the topmost and lowest atomic
layers.

I can just suggest at the moment to restart from scratch a calculation in
which you use as initial
positions the latest (or the ones before the latest) printed by the code.
It shouldn't change anything in principle, but
there have been several cases in my experience in which that properly
worked, as if at some point of the structural optimization the
starting charge density were for some reason "wrong" or "inappropriate"
(even if coming from the previous steps), and
restarting from atomic/random wave functions prevents the code from
remaining stuck. However, I don't have a clear explanation for that
if not that this recipe has worked for me!

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 mer 28 mag 2025 alle ore 11:23 michele de angelis <
michele.deangelis.01 at alumni.uniroma2.eu> ha scritto:

> YBCO_001_CuO2_2layers.in
> <https://uniroma2-my.sharepoint.com/:u:/g/personal/michele_deangelis_01_alumni_uniroma2_eu/EdqwsiZzdStJhJGXaYDSIOsB0WUkus6riva9xFNK4dvGrw>
> YBCO_001_CuO2_2layers.out
> <https://uniroma2-my.sharepoint.com/:u:/g/personal/michele_deangelis_01_alumni_uniroma2_eu/EWwLUiRWxFxLiOe-okzTGBkBJ5sQt7QCPbjEqCaKYWBDQA>
> Dear all,
> I am trying to relax YBCO (001) slabs with symmetric terminations (same on
> both sides) and a vacuum spacing of 7.5 Å on each side (7.5 Å – slab – 7.5
> Å). I have tested all four possible surface terminations of YBCO, but none
> of the relaxations converge properly. After m SCF cycles and n BFGS cycles,
> the SCF calculation starts to exceed 100 iterations.
> Moreover, the total energy values reported in the output file do not show
> a monotonic trend but oscillate instead. In contrast, the total force does
> decrease, from 0.9 down to about 0.09. I am using PBE-PAW pseudopotentials
> with the GGA approximation. The initial geometry has been carefully
> verified.
> Spin and polarization effects are not included, as the slabs are
> symmetric. I have attempted several adjustments to improve convergence,
> including:
> - Reducing mixing_beta to 0.1
> - Increasing degauss to 0.05 and changing the smearing type
> - Setting mixing_mode = 'local-TF'
> - Switching the diagonalization method to cg
>
> However, the problem persists.
> Could you kindly help me understand what might be going wrong? My input
> and output files are attached below for reference.
> Thank you in advance for your support.
>  Best regards,
>
> Michele De Angelis
> PhD student, Dept. of Chemical Sciences and Technologies, Univesity of
> Rome Tor Vergata (Italy)
>
>
>
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