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

[michele de angelis]

[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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