[CP2K-user] [CP2K:15615] Energy oscillations in vdW-DF calculations

[Krack Matthias (PSI)]

Hi Michael

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

HTH

Matthias

Von: cp... at googlegroups.com <cp... at googlegroups.com> Im Auftrag von Michael Fischer
Gesendet: Mittwoch, 23. Juni 2021 15:34
An: cp2k <cp... 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

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