[CP2K-user] [CP2K:22218] Re: Converge EPS_SCHWARZ and CUTOFF_RADIUS for hybrid functionals

['Max H' via cp2k]

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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