[CP2K-user] [CP2K:15617] Energy oscillations in vdW-DF calculations

[Krack Matthias (PSI)]

Hello Michael

The OT convergence criterion is defined by the wavefunction gradient printed in the column “Convergence” which reached already 6.8E-10 and not by the energy change between two consecutive SCF iteration steps. You can also try an alternative OT minimizer like CG or restart using diagonalization with DIIS instead of OT. On the other hand, your system seems to be well converged already.

Best

Matthias

Von: cp... at googlegroups.com <cp... at googlegroups.com> Im Auftrag von Michael Fischer
Gesendet: Mittwoch, 23. Juni 2021 18:07
An: cp2k <cp... at googlegroups.com>
Betreff: Re: [CP2K:15617] Energy oscillations in vdW-DF calculations

Dear Matthias,

Thank you very much for the fast reply. Even when setting EPS_DEFAULT to 10-14, I get some of these oscillations, as shown below:
 Step     Update method      Time    Convergence         Total energy    Change
  ------------------------------------------------------------------------------
     1 OT DIIS     0.15E+00    5.1     0.00000073     -5301.9181906664 -5.30E+03
     2 OT DIIS     0.15E+00    2.5     0.00000029     -5301.9181922654 -1.60E-06
     3 OT DIIS     0.15E+00    2.5     0.00000005     -5301.9181886933  3.57E-06
     4 OT DIIS     0.15E+00    2.5     0.00000001     -5301.9181899089 -1.22E-06
     5 OT DIIS     0.15E+00    2.5     4.4595E-09     -5301.9181899089 -5.09E-11
     6 OT DIIS     0.15E+00    2.5     1.8983E-09     -5301.9181886941  1.21E-06
     7 OT DIIS     0.15E+00    2.5     6.8365E-10     -5301.9181899090 -1.21E-06

  *** SCF run converged in     7 steps ***

I am actually wondering why the SCF cycle converges at all, despite the change in total energy of 1.21E-06 Ha between the 6th and 7th iteration.

Best regards,
Michael

Matthias Krack schrieb am Mittwoch, 23. Juni 2021 um 16:59:17 UTC+2:
Hi Michael

you can also try to reduce EPS_DEFAULT to 1.0E-12 or less for a better numerical accuracy.

HTH

Matthias

Von: c... at googlegroups.com <c... at googlegroups.com> Im Auftrag von Michael Fischer
Gesendet: Mittwoch, 23. Juni 2021 15:34
An: cp2k <c... at googlegroups.com>
Betreff: [CP2K:15615] Energy oscillations in vdW-DF calculations

Dear CP2K community,

I am seeing a somewhat strange behaviour in CP2K calculations using vdW-DF functionals (version 7.1): Within one SCF cycle, the calculation sometimes reaches a point where it jumps back and forth between different energy values. Such behaviour is illustrated in a portion of a log file appended to this message. This calculation used the vdW-DF-b86r functional, but I have seen the same behaviour with other vdW-DF functionals.
I should add the following points:
1) The compound under consideration, a zeolite with an adsorbed molecule, contains only main group elements (Si, O, C, H, N).
2) Analogous calculations using DFT-D methods (like PBE-D3) show no convergence issues whatsoever.
3) A change of preconditioner (FULL_ALL/FULL_KINETIC) seems to affect the behaviour, but does not resolve the issue.

I should also note that I tested the "CUTOFF" parameter within &XC &vdW_POTENTIAL &NON_LOCAL part of the input and found that it should be increased with regard to the default setting to get converged adsorption energies (I use 400 Ry).

Any help or suggestions would be highly appreciated.
Best regards,
Michael

Portion of output - oscillations start in the 8th iteration
  Step     Update method      Time    Convergence         Total energy    Change
  ------------------------------------------------------------------------------
     1 OT DIIS     0.15E+00    5.0     0.00004571     -5301.9144127012 -5.30E+03
     2 OT DIIS     0.15E+00    2.4     0.00001858     -5301.9158989932 -1.49E-03
     3 OT DIIS     0.15E+00    2.4     0.00001214     -5301.9161596822 -2.61E-04
     4 OT DIIS     0.15E+00    2.5     0.00000142     -5301.9161913868 -3.17E-05
     5 OT DIIS     0.15E+00    2.4     0.00000043     -5301.9161930782 -1.69E-06
     6 OT DIIS     0.15E+00    2.4     0.00000011     -5301.9161943445 -1.27E-06
     7 OT DIIS     0.15E+00    2.4     0.00000005     -5301.9161967775 -2.43E-06
     8 OT DIIS     0.15E+00    2.4     0.00000001     -5301.9161955633  1.21E-06
     9 OT DIIS     0.15E+00    2.4     4.0079E-09     -5301.9161967782 -1.21E-06
    10 OT DIIS     0.15E+00    2.4     1.7554E-09     -5301.9161955634  1.21E-06
    11 OT DIIS     0.15E+00    2.4     6.2727E-10     -5301.9161967782 -1.21E-06

--
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp... at googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cp2k/45540fc6-9eb6-4a4b-91e0-037e3e918eaen%40googlegroups.com<https://groups.google.com/d/msgid/cp2k/45540fc6-9eb6-4a4b-91e0-037e3e918eaen%40googlegroups.com?utm_medium=email&utm_source=footer>.
--
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp... at googlegroups.com<mailto:cp... at googlegroups.com>.
To view this discussion on the web visit https://groups.google.com/d/msgid/cp2k/de44ca45-8343-440f-b8c5-e3996cd18c32n%40googlegroups.com<https://groups.google.com/d/msgid/cp2k/de44ca45-8343-440f-b8c5-e3996cd18c32n%40googlegroups.com?utm_medium=email&utm_source=footer>.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20210623/a22d8f4b/attachment.htm>