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

[michele de angelis]

Dear Giovanni,
Thanks for the answer, I wanted to ask you what are the best options and combinations for this type of calculation, in terms of: smearing (type and value),  mixing_mode type and the type of diagonalization. Also the value I’m using for ecutrho is larger than the convergence value which is 200 Ry, I increased the number of bands by 40% and I left the convergence value for Ecutwfc and K-grid (obviously being a slab I’m using 6x6x1). These values seem to make sense but if you have advice I gladly accept them also in considering other command lines to activate on QE.
Thanks again and sorry for the trouble.
Have a good day,
Michele

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Da: users <users-bounces at lists.quantum-espresso.org> per conto di Giovanni Cantele <giovanni.cantele at spin.cnr.it>
Inviato: mercoledì, maggio 28, 2025 12:19:10 PM
A: Quantum ESPRESSO users Forum <users at lists.quantum-espresso.org>
Oggetto: Re: [QE-users] YBCO (001) slabs: "convergence" problem

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<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 mer 28 mag 2025 alle ore 11:23 michele de angelis <michele.deangelis.01 at alumni.uniroma2.eu<mailto:michele.deangelis.01 at alumni.uniroma2.eu>> ha scritto:
[https://res-1.cdn.office.net/assets/mail/file-icon/png/generic_16x16.png]YBCO_001_CuO2_2layers.in<https://uniroma2-my.sharepoint.com/:u:/g/personal/michele_deangelis_01_alumni_uniroma2_eu/EdqwsiZzdStJhJGXaYDSIOsB0WUkus6riva9xFNK4dvGrw>
[https://res-1.cdn.office.net/assets/mail/file-icon/png/generic_16x16.png]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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