[CP2K-user] [CP2K:19965] Ground state convergance issues with hybrid functional

[Ava Rajh]

Dear Augustin and others, 

I have followed your suggestions and the graphite convergence went 
wonderfully, and I obtained a good XAS spectra in the end. The calculations 
and further testing took a while so I am only now getting back to you. I 
have however stumbled on the same issue when trying to repeat the procedure 
with a similar system with one additional sodium atom between the graphitic 
layer. The structure was geometry optimized . well converged, and I am also 
starting from the well pre-converged GGA wavefunction file, but the SCF 
with any amout of HFX still won't converge and starts diverging wildly 
after only a few steps.  I have tried calculating with  up to EPS_SCHWARZ = 
1.0E-10, but it does not improve the situation. I have also tried 
increasing the cell size, to set the cutoff value up to 6A, but the issue 
persisted. 

If you or anyone else has any ideas what else I can try to get the wave 
function to converge I will be happy for any suggestions you can offer.
thank you for the time and all the help, 
Ava

On Friday, January 12, 2024 at 9:08:29 PM UTC+1 Ava Rajh wrote:

> Dear  Augustin, 
>
> Thank you very much for your input. My cell is quite small in z direction, 
> that's why I had to set the  cutoff radius to 2 (or 1.5). I will try to 
> increase the vertical size of the system and repeat the calculation. 
> I will also try other performance optimizations you suggested, and change 
> the basis set. 
>
> Thynk you for the suggestions, 
> kind regards, Ava
>
>
> V V pet., 12. jan. 2024 ob 17:33 je oseba Augustin Bussy <
> augusti... at chem.uzh.ch> napisala:
>
>> Dear Ava,
>>
>> you are correct, your issue most likely comes from your Hartree-Fock 
>> input. You are using a cutoff radius of 1.5 Ang for the truncated Coulomb 
>> potential. This is very small and might  lead to inaccuracies in the 
>> electronic structure. Typically, calculations are run with a truncation 
>> radius of 5-6 Ang. Note that the sphere with the same radius should fit in 
>> your simulation cell: you might need to increase the size of the system to 
>> fit such a large truncation radius.
>>
>> In terms of performance, you are using an extremely tight EPS_PGF_ORB 
>> value. This will lead to very slow calculations. The default of 1.0E-5 is 
>> usually enough, and 1.0E-6 is already considered very accurate. On the 
>> other hand, EPS_SCHWARZ = 1.0E-6 is fairly loose. Using 1.0E-8 might help 
>> with numerical stability. If you are going to run a larger system, you will 
>> probably need to tweak the HF%MEMORY%MAX_MEMORY value for optimal runtime.
>>
>> You can also try to use the more modern ADMM basis set defined in the 
>> BASIS_ADMM_UZH data file.
>>
>> Best,
>> Augustin
>> ------------------------------
>> *From:* cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Ava 
>> Rajh <ava.... at gmail.com>
>> *Sent:* Friday, January 12, 2024 11:34 AM
>> *To:* cp2k <cp... at googlegroups.com>
>> *Subject:* [CP2K:19733] Ground state convergance issues 
>>  
>> Hi all,
>>
>> I am trying to compare some ground state XAS and TDDFT XAS for a few 
>> systems and it was going great on other systems until I started on a 
>> relatively simple graphite cell. 
>> I performed cell optimization and used the resulting structure of 64 C 
>> atoms for XAS calculation but i am having issues with ground state 
>> calculation of a system which would be compatible with further TDDFT,. SCF 
>> does not seem to converge and either diverges wildly or oscillates around 
>> 0. 
>>
>> I have included a sample input file, I have tried also with the DIIS OT, 
>> denationalization, and with a PBE functional but the issue persist. I am 
>> hoping someone might have an idea if I missed something obvious. It seems 
>> that the problem might be in the HF part, as the convergence is slightly 
>> better if I change the HF fraction, but it ultimately always diverges. 
>>
>> I would be grateful f anyone has any comments on the issue I am facing 
>> and I apologize if I missed something obvious. 
>> kind regards, Ava
>>
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