[CP2K-user] [CP2K:22227] Re: Converge EPS_SCHWARZ and CUTOFF_RADIUS for hybrid functionals

['Max H' via cp2k]

Dear Frederick,

I apologize for the confusion. (I tested both options, restarting from the 
PBE converged guess and the ATOMIC guess, although both fail.)

I removed the *_CUTOFF and XC_GRID options in recent tests, but this does 
not improve the outcome. I have attached a recent input file and parts of 
the output file, which include information on the SCF. I would appreciate 
it if you could take a look at it and perhaps point out the error for me.

A test with EPS_SCHWARZ 1E-9 instead of 1E-8 yields somewhat more 
consistently negative energies in the SCF. Could it be necessary to test 
yet smaller EPS_SCHWARZ values?

All the best,
Max

On Tuesday, May 5, 2026 at 1:02:26 PM UTC+2 Frederick Stein wrote:

> Dear Max,
> a larger cell should not be necessary. I have just seen that you set 
> SCF_GUESS ATOMIC instead of RESTART. Thus, you start from an atomic guess 
> instead of your restart file. I also would not use XC_GRID and I would not 
> touch the *_CUTOFF parameters in the XC section.
> Best,
> Frederick
>
> Max H schrieb am Dienstag, 5. Mai 2026 um 12:22:19 UTC+2:
>
>> Dear Frederick,
>>
>> thank you for your kind explanation.
>> I have been doing a few tests with CUTOFF_RADIUS 8.2 (slightly smaller 
>> than half the smallest cell dimension) and various values of EPS_SCHWARZ 
>> (from 1E-6 to 1E-8).
>> Unfortunately, the SCF does not converge at all. The first iteration 
>> yields a negative energy, but the energies become positive after the second.
>> I am restarting the SCF from a previously converged calculation at the 
>> PBE level of theory (convergence with fewer than 50 iterations) and employ 
>> the "MIN_PAIR_LIST_RADIUS -1" setting in the QS block of the input 
>> (attached).
>>
>> Is it possible to conclude from the SCF behaviour that calculations on 
>> multiple unit cells with a yet larger CUTOFF_RADIUS are required?
>>
>> Kind regards,
>> Max
>>
>>
>> On Friday, April 24, 2026 at 6:24:33 PM UTC+2 Frederick Stein wrote:
>>
>>> Dear Max,
>>> Both parameters are determined differently.
>>> CUTOFF_RADIUS needs to be less than half of the distance of an atom to 
>>> its nearest image. For sufficiently large cells, you may even reduce it to 
>>> values at the order of 5-7 A (please check convergence of your results in 
>>> that case). If this parameter is not yet converged, you employ the 
>>> MULTIPLE_UNIT_CELL as you suggested. Convergence is expected if 
>>> CUTOFF_RADIUS can be set to values of at least 5 A.
>>> EPS_SCHWARZ is determined by checking convergence of total energies. A 
>>> good starting point is 1E-6 but larger values may be necessary, especially 
>>> if you set "SCREEN_ON_INITIAL_P T" or with ADMM (ADMM is recommended).
>>> Best,
>>> Frederick
>>>
>>> Max H schrieb am Freitag, 24. April 2026 um 17:05:35 UTC+2:
>>>
>>>> Dear all,
>>>>
>>>> I plan on doing some single point calculations with the PBE0 functional 
>>>> and a ccGRB basis and would appreciate advice on the selection of 
>>>> appropriate parameters, because I have not found information of sufficient 
>>>> detail.
>>>>
>>>> I read in the recent review (JPhysChemB, "The CP2K Program Package 
>>>> Made Simple") and in various other sources that the EPS_SCHWARZ and 
>>>> CUTOFF_RADIUS parameters are crucial for accuracy and computational 
>>>> efficiency.
>>>>
>>>> What is the typical approach to converge these values? Are single-point 
>>>> calculations with one SCF cycle sufficient as soon as energy convergence is 
>>>> observed (comparable to the convergence protocols for CUTOFF and 
>>>> REL_CUTOFF)?
>>>>
>>>> When studying metallic systems, which values of CUTOFF_RADIUS can be 
>>>> expected?
>>>> Supposing that the CUTOFF_RADIUS did not converge at half the smallest 
>>>> cell dimension, is the best approach then to set MULTIPLE_UNIT_CELL 2 2 1 
>>>> (xy periodic system) in the &CELL block or do special restrictions arise?
>>>>
>>>> I appreciate your kind advice.
>>>>
>>>> Best,
>>>> Max
>>>>
>>>>
>>>>
>>>>

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