[CP2K-user] [CP2K:22254] Re: Wavelet Poisson solver - Huge change in total energy when increasing the plane-wave cut-off energy from 1200 to 1260 Ry

[Mattia Perrone]

the issue seems solved:

https://github.com/cp2k/cp2k/issues/399

On Tuesday, May 5, 2026 at 3:25:03 PM UTC+2 Mattia Perrone wrote:

> Hi all 
>
> 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.
>
> I wanted to ask if a solution to the problem had been found in the meantime
>
> Thanks!
>
> mattia
>
>
> On Monday, December 29, 2025 at 10:50:33 AM UTC+1 Jürg Hutter wrote:
>
>> Hi 
>>
>> yes, I can reproduce your problem using a small molecule in a 30x30x30 
>> box with 
>> cutoffs 1200 and 1260. 
>>
>> These settings result in internal FFT grids of size 625 (works) and 648 
>> (fails). 
>> Some tests show that up to 640 (cutoff 1230) it works, everything larger 
>> fails. 
>>
>> This needs a deeper look into the wavelet poisson solver. Maybe we should 
>> open 
>> a bug report at the CP2K page on Github. 
>>
>> regards 
>> JH 
>>
>> ________________________________________ 
>> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
>> Torstein Fjermestad <tfjer... at gmail.com> 
>> Sent: Monday, December 29, 2025 10:18 AM 
>> To: cp2k 
>> 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 
>>
>> 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 <(509)%20234-6069> 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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>>
>

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