[CP2K-user] [CP2K:10799] Re: Problem in the preconditioner when using UKS

Krack Matthias (PSI) matthia... at psi.ch
Wed Oct 3 19:44:52 UTC 2018

Dear Daniele

You should take note of the electron count in the OT DIIS output and ask yourself, if the corresponding energy has any meaning.
The OT CG run converged to some state at least.



Von: cp... at googlegroups.com <cp... at googlegroups.com> Im Auftrag von Daniele Ongari
Gesendet: Mittwoch, 3. Oktober 2018 19:47
An: cp2k <cp... at googlegroups.com>
Betreff: [CP2K:10799] Re: Problem in the preconditioner when using UKS

[Screenshot from 2018-10-03 19-42-55.png]
here I come with a similar problem for Co-MOF-74 using different settings.
In the legend of the figure:
"diis" is using OT DIIS with 50 inner and 10 outer SCF cycles
"cg" is using OT CG with 2000 inner and no outer SCF cycles

I think the problem is related to the bandgap going close to zero and making the preconditioner to diverge, but this time the energy assumes even lower energies than the final ones.
Does it makes sense to have a lower energy being DFT not strictly variational, and this should be seen as a merely mathematical mess?

The calculation is converging when I run the OT CG minimization without outer steps: can I consider the final result of this calculation as reliable?



Il giorno mercoledì 19 settembre 2018 12:50:34 UTC+2, Daniele Ongari ha scritto:
Dear CP2K developers,
I want to report a serious problem with the preconditioner when computing the energy of Fe-MOF-74 with UKS settings.
Long story short the energy goes down, it is close to convergence but then, after recomputing the preconditioner in the outer step it starts to diverge: see the image.


Now, I attached the input and the output, but I already tried very different settings:
-diagonalization without smearing
-different BS
-UKS false (converged, but to a higher energy, forcing the closed shell)
- starting magnetization on metals
- CG minimizer
- lower multiplicity
- 2x and 3x replicated unit cell in the shortest dimension
- lowering ENERGY_GAP to 0.001
These calculation ALL failed (I made 16 attempts in total, changing settings!).

And at the end the only one working (the 17th attempt, ironically the unlucky number for Italians!) was to use CG minimizer with no outer SCF, hence not recomputing the preconditioner. It converged after ~600 inner steps, to:

 HOMO - LUMO gap [eV] :    1.917671
 HOMO - LUMO gap [eV] :    0.235602

 ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):            -1170.045288008604075

Please let me know what was the problem, if it is a known issue of the preconditioner and how to circumvent it: for the moment I'm using no outer steps to have a robust convergence, but I know that this may cause the convergence to a local miniimum!

Thanks a lot!

PhD candidate, LSMO, EPFL Sion

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