[CP2K-user] [CP2K:20706] Incorrect Band gaps from simple calculations

[Thomas Kasel]

I will admit I am new to CP2K and used a lot of setting I found online in 
various powerpoints. 
I am trying to call the HSE06 functional.

Regards,
Tom
On Thursday, September 12, 2024 at 11:54:59 AM UTC-5 Lucas Lodeiro wrote:

> Hi
>
> there are many weird things from my point of view. 
> the main ones are: 
> *CUTOFF of 600 eV (44 Ry), which is less than the used RELCUTOFF of 60 
> Ry... you must use N times the RELCUTOFF for the CUTOFF.
> *small cell without kpoints... you must use supercell (4x4x4 for example) 
> or kpoint mesh to properly get the electronic structure.
> *your functional definition does not make sense to me... which functional 
> form are you pointing out?
> *why add all virtual orbitals? it is not useful at all, and very expensive.
>
> Regards - Lucas
>
>
> El jue, 12 sept 2024 a las 12:48, Thomas Kasel (<tomk... at gmail.com>) 
> escribió:
>
>> The original files are in the first posting. But I suppose those are no 
>> longer relevant. I have attached my input,  basis set, and pseudopotential 
>> for silicon. Thank you for all your help.
>>
>> Cheers,
>> Tom
>>
>> On Thursday, September 12, 2024 at 2:56:57 AM UTC-5 Jürg Hutter wrote:
>>
>>> Hi 
>>>
>>> Obviously, you have a serious problem in your (secrete) input. 
>>> Without further information it is impossible to help. 
>>>
>>> regards 
>>> JH 
>>>
>>> ________________________________________ 
>>> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
>>> Thomas Kasel <tomk... at gmail.com> 
>>> Sent: Wednesday, September 11, 2024 10:34 PM 
>>> To: cp2k 
>>> Subject: Re: [CP2K:20694] Incorrect Band gaps from simple calculations 
>>>
>>> I managed to find a way to print the HOMO - LUMO gap from the pdos. The 
>>> only problem now is that for some reason I get a band gap of 85 eV for 
>>> silicon when using a hybrid functional. 
>>>
>>> On Tuesday, September 10, 2024 at 1:54:25 PM UTC-5 Thomas Kasel wrote: 
>>> Thanks to your suggestions I managed to get the SCF to converge for PBE 
>>> based upon playing with the mixing. The only problem is now that CP2K is 
>>> not printing the HOMO-LUMO gap. Is there a setting I can specify to force 
>>> print the gap? 
>>>
>>> Regards, 
>>> Tom 
>>>
>>> On Tuesday, September 10, 2024 at 4:45:21 AM UTC-5 Jürg Hutter wrote: 
>>> Hi 
>>>
>>> For silicon: if you are using the unit cell (with 2 atoms) you need a 
>>> large number of k-points. 
>>> In this case SCF needs diagonalization and an appropriate mixing scheme. 
>>> I would also add smearing 
>>> of occupation numbers. If you have this working, you can start 
>>> investigating basis sets for convergence. 
>>>
>>> For graphene: The problem is the Dirac cone at the K special point. 
>>> Selecting a matching cell and k-point 
>>> sampling is mandatory to get correct results. There is ample literature 
>>> addressing this problem. 
>>>
>>> regards 
>>> JH 
>>>
>>> ________________________________________ 
>>> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of 
>>> Thomas Kasel <tomk... at gmail.com> 
>>> Sent: Monday, September 9, 2024 10:50 PM 
>>> To: cp2k 
>>> Subject: [CP2K:20677] Incorrect Band gaps from simple calculations 
>>>
>>> Hello All, 
>>>
>>> As a test I am trying to accurately (relatively) reproduce the band gaps 
>>> of silicon and graphene structures using PBE. I have however, run into an 
>>> issue where graphene gives a band gap of 1.2 eV while silicon gives a band 
>>> gap of 0.18 eV, the exact opposite of what one would expect. I would like 
>>> to ask what it is I am doing wrong in my calculations. Attached is a zip 
>>> file containing all my input files including basis set and 
>>> pseudopotentials. 
>>>
>>> Additionally, I cannot seem to get the SCF to converge unless I specify: 
>>>
>>> &OT 
>>> PRECONDITIONER FULL_ALL 
>>> MINIMIZER CG 
>>> &END OT 
>>>
>>> Why is this setting so critical to SCF convergence in these cases? 
>>>
>>> Cheers and thanks in advance, 
>>> Tom 
>>>
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