<br /><div>Hi all <br /></div><div><br /></div><div>I can confirm that also in my
case (different system and different setup) I observe the same
unexpected behavior, when the FFT grid size becomes larger than 640.</div><div><br /></div><div>I wanted ask know if a solution to the problem had been found in the meantime</div><div><br /></div><div>Thanks!</div><div><br /></div><div>mattia</div><br /><div class="gmail_quote"><div dir="auto" class="gmail_attr">On Monday, December 29, 2025 at 10:50:33 AM UTC+1 Jürg Hutter wrote:<br/></div><blockquote class="gmail_quote" style="margin: 0 0 0 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">Hi
<br>
<br>yes, I can reproduce your problem using a small molecule in a 30x30x30 box with
<br>cutoffs 1200 and 1260.
<br>
<br>These settings result in internal FFT grids of size 625 (works) and 648 (fails).
<br>Some tests show that up to 640 (cutoff 1230) it works, everything larger fails.
<br>
<br>This needs a deeper look into the wavelet poisson solver. Maybe we should open
<br>a bug report at the CP2K page on Github.
<br>
<br>regards
<br>JH
<br>
<br>________________________________________
<br>From: <a href data-email-masked rel="nofollow">cp...@googlegroups.com</a> <<a href data-email-masked rel="nofollow">cp...@googlegroups.com</a>> on behalf of Torstein Fjermestad <<a href data-email-masked rel="nofollow">tfjer...@gmail.com</a>>
<br>Sent: Monday, December 29, 2025 10:18 AM
<br>To: cp2k
<br>Subject: [CP2K:22012] Re: Wavelet Poisson solver - Huge change in total energy when increasing the plane-wave cut-off energy from 1200 to 1260 Ry
<br>
<br>Dear Frederick,
<br>
<br>Thanks for the piece of advice.
<br>I generated the input file by setting the name of the variable and its value like this:
<br>@SET <name> <value>
<br>
<br>In the QS section, I explicitly set the following variables:
<br>@SET eps_def 1.0E-10
<br>@SET extrapol PS
<br>@SET precOM 1.0E-5
<br> &QS
<br> EPS_DEFAULT ${eps_def}
<br> EXTRAPOLATION ${extrapol}
<br> EPS_PGF_ORB ${precOM}
<br> EXTRAPOLATION_ORDER 3
<br> &END QS
<br>
<br>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.
<br>This did not have any notable effect on the results.
<br>(For the calculation with a cut-off of 1260 Ry, the energy after the first SCF iteration was -4394.<a href="tel:(509)%20234-6069" value="+15092346069" target="_blank" rel="nofollow">5092346069</a> 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))
<br>
<br>Should I decrease EPS_DEFAULT and EPS_PGF_ORB further, or are other variables I should change?
<br>
<br>Thanks.
<br>
<br>Best regards,
<br>Torstein
<br>
<br>
<br>
<br>tirsdag 23. desember 2025 kl. 11:54:48 UTC+1 skrev Frederick Stein:
<br>Dear Torstein,
<br>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.
<br>Best,
<br>Frederick
<br>
<br>Torstein Fjermestad schrieb am Montag, 22. Dezember 2025 um 20:09:02 UTC+1:
<br>Dear all,
<br>
<br>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.
<br>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.
<br>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!
<br>Because of the massively different total energy, I stopped the calculation.
<br>
<br>I have attached the output files of the two calculations. The complete input can be found at the start of the output files.
<br>
<br>What could be the cause of this behavior?
<br>
<br>Thank you very much for your help.
<br>Please tell me if you need more information to understand the problem better.
<br>
<br>Best regards,
<br>Torstein Fjermestad
<br>
<br>
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