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

[Michael Fischer]

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
>
>  
>
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