ionic relaxation cannot converge
Dear VASP team,
I am trying to relax a heterostructure and encountered a similar question before in a similar system, but I'm not able to solve it with the method proposed (viewtopic.php?t=20432). Following the instruction there, my workflow is:
1. Run a dipole-off SCF calculation to generate WAVECAR.
2. Use that WAVECAR for a dipole-off relaxation with ISTART=1, MAXMIX=about 3* scf step, and one fixed atom.
3. If this step converges, later turn the dipole correction back on for the final relaxation.
The problem already occurs in step 2. The relaxation stops with:
ZBRENT: fatal error in bracketing
I then copied CONTCAR to POSCAR and continued, but the continuation stopped with the same ZBRENT bracketing failure. Doing this many times won't help, seems that force and energy are just oscillating.
As a diagnostic test, I changed to IBRION=1 and added NELMIN=4. This avoids the fatal ZBRENT error, but the relaxation reaches NSW=200 without “reached required accuracy”. The late-stage forces oscillate instead of converging; the final maximum force is still about 0.023 eV/Ang.
Could you advise what settings you would recommend for this kind of slab relaxation? The inputs/outputs are attached. I also tried to fix all in-plane components, since they won't change due to symmetry, and this also doesn't work.
Best,
Yujia