[CP2K-user] [CP2K:14320] Re: Graphene problems with hybrid functional

[Lucas Lodeiro]

Hi Fabian,

I tried using a reduced cutoff of 4.0, and it works well with eps_schwarz
1e-6. The problem appears when the cutoff is higher than 6.0, in that case,
I reduced the  eps_schwarz until 1e-12, but the problem was the same, no
differences. I try reducing the eps_pgf_orb from 1e-6 to 1-e-8 and it work
without problem, and value of eps_schwarz did not change the result (a
difference of 1e-5 in energy or less). Thanks for your advice, it impulses
me to get insight of the eps keywords.

About the auxiliary basis set, I agree, cFIT3 is the smallest one and is
not the best choice, but I have to deal with very big systems where the RAM
is not enough, and I need to speed up the calculation using small basis
sets, as the DZVP-SR-MOLOPT... If tis calculations converges in a day or a
couple I will test with bigger basis sets.

Regards
Lucas Lodeiro

El lun, 30 nov 2020 a las 7:11, fa... at gmail.com (<fabia... at gmail.com>)
escribió:

> Hi Lucas,
>
> When I reduced the cutoff to 4.0 and eps_schwarz to 1e-8 it converged
> nicely. With a larger cutoff you probably have to decrease eps_schwarz even
> more. You should also check the impact of the aux basis, cFIT3 might not be
> the best choice.
>
> Cheers,
> Fabian
>
> On Sunday, 29 November 2020 at 00:59:40 UTC+1 Lucas Lodeiro wrote:
>
>> Hi all,
>>
>> I am trying to compute a hybrid functional calculation (PBE0-T_C_LR) over
>> a graphene structure, and at the second step the calculations go to very
>> bad "solutions".
>> I used the same approach and basis sets to compute the same hybrid
>> calculation over different systems without problems,
>> as: metallic aluminium, organic molecules, semiconductors like Cu2O, slabs
>> of semiconductors, and so on.
>> I do not know why the second step goes to a weird energy... I tried HSE,
>> HF, and other functional... all have the same problem. Only GGA-DFT behaves
>> well.
>> For hybrid calculations I used the GGA converged wfc, but the result is
>> similar if I start it using atomic density...
>>
>> I adjunct the input, output and coordinate file. I use a huge vacuum
>> space because I am trying to insert graphene into an interface, and I use
>> the same cell. But I tried using lower vacuum width, and changing the
>> periodicity and psolver, but nothing works...
>>
>> Some advice? Graphene is a problematic system for hybrid calculations as
>> diamond?
>>
>> Regards - Lucas Lodeiro
>>
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