[CP2K-user] [CP2K:21030] Re: Performance degregation for DCDFT starting with CP2K 2024.2

[Ralf Frischmann]

Thanks for the quick and comprehensive reply.

Is the density matrix-based derivative integral screening still in place 
for "standard" HFX calculations (i.e. non-response type), or is the 
screening also   
removed here? This should then have an effect on how to properly choose the 
EPS_SCHWARZ_FORCES threshold in relation to EPS_SCHWARZ?
 


On Wednesday, January 8, 2025 at 10:35:06 AM UTC+1 Augustin Bussy wrote:

> Hi Ralf,
>
> I believe this comes from a bug fix in HFX response forces: 
> https://github.com/cp2k/cp2k/commit/233cc0496608329821996a6a19a46b58c16292f1#diff-e05447976b45d06ff57c2ca772d89269da230e4970b6001c4ee2f25c70584cffR428-R430. 
> Before that, by default, the density matrix was used to screen the integral 
> derivative, also for response forces. This is not a safe assumption, and it 
> was therefore removed.
>
> To verify this hypothesis, you can try running CP2K v2024.1 with the added 
> keyword SCREEN_P_FORCES set to FALSE in the HFX%SCREENING section. This 
> should make the 2 runs equally slow.
>
> Best,
>
> Augustin
>
>
> On Wednesday, 8 January 2025 at 10:09:31 UTC+1 Ralf Frischmann wrote:
>
>> Dear all,
>>
>> when running a DCDFT calculation with pre-compiled CP2K binaries from 
>> GitHub, I do observe a significant reduction in overall runtime performance 
>> when moving from CP2K version 2024.1 to 2024.2 (and versions beyond). 
>>
>> The increase occurs in ENERGY_FORCE runs only. The crucial spot seems to 
>> be the execution part AFTER convergence of the gradient response solver 
>> "The linear solver converged in    7 iterations." 
>>
>> From the HFX_MEM_INFO output, it is apparent that version 2024.2 computes 
>> a somewhat larger number of "sph. DERIV's calculated on the fly" (see 
>> attached outputs for a 20 water PBC cell), but the difference in my opinion 
>> is too small to explain the increase in runtime of about 50% for that 
>> system size. 
>>
>> For larger system with 32 or 64 H2O molecules, the described runtime 
>> increase becomes more pronounced, reaching 250% for 64 H2O molecules.
>>
>> Is that expected/intended behavior?
>>
>> Any explanation, hint or advice would be greatly appreciated.
>>
>> Regards,
>>
>> Ralf
>>
>>
>>
>>
>>
>>
>>
>>  
>>
>>

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