[CP2K-user] [CP2K:22012] Re: Wavelet Poisson solver - Huge change in total energy when increasing the plane-wave cut-off energy from 1200 to 1260 Ry

[Torstein Fjermestad]

Dear Frederick, 

Thanks for the piece of advice.
I generated the input file by setting the name of the variable and its 
value like this:
@SET <name> <value>

In the QS section, I explicitly set the following variables:
@SET eps_def 1.0E-10
@SET extrapol PS
@SET precOM 1.0E-5
    &QS
      EPS_DEFAULT ${eps_def}
      EXTRAPOLATION ${extrapol}
      EPS_PGF_ORB ${precOM}
      EXTRAPOLATION_ORDER 3 
    &END QS
 
I followed your advice, and I decreased the value of  EPS_DEFAULT to  
1.0E-12 and the value of  EPS_PGF_ORB to 1.0E-6.
This did not have any notable effect on the results. 
(For the calculation with a cut-off of 1260 Ry, the energy after the first 
SCF iteration was -4394.5092346069 Hartree with the new settings 
and -4394.5090808424 Hartree with the previous settings. However, these 
values are already a few thousand Hartree below the converged value of the 
calculation with a cut-off of 1200 Ry (-1389.249071606565622 Hartree))

Should I decrease EPS_DEFAULT and EPS_PGF_ORB further, or are other 
variables I should change?

Thanks. 

Best regards,
Torstein

 

tirsdag 23. desember 2025 kl. 11:54:48 UTC+1 skrev Frederick Stein:

Dear Torstein,
You not only need to adjust the CUTOFF but also EPS_DEFAULT (and if set 
explicitly the other thresholds) in the QS section. How did you obtain the 
input file? I would never set all parameters. Especially EPS_DEFAULT sets a 
variety of other parameters if these are not set explicitly.
Best,
Frederick

Torstein Fjermestad schrieb am Montag, 22. Dezember 2025 um 20:09:02 UTC+1:

Dear all, 

As part of a basis set convergence test, I gradually increase the plane 
wave basis set cut-off energy. The atomic system is a cluster model of 
methanol adsorbed in a zeolite. I isolate the system from its neighboring 
unit cells by using the wavelet Poisson solver. 
I use a cubic box of 30 Å. The size of the system is about 21 Å in the 
longest direction. The atom-centered basis set is TZV2P. 
When I increase the cut-off from 900 Ry to 1200 Ry, the total energy varies 
in a range less than 5 kJ/mol. However, when I increase the cut-off from 
1200 Ry to 1260 Ry, the total energy is after  6 SCF iterations  1.38E+07 
kJ/mol lower! 
Because of the massively different total energy, I stopped the 
calculation.   

I have attached the output files of the two calculations. The complete 
input can be found at the start of the output files. 

What could be the cause of this behavior? 

Thank you very much for your help. 
Please tell me if you need more information to understand the problem 
better.

Best regards,
Torstein Fjermestad
 

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