[CP2K-user] [CP2K:20716] Incorrect Band gaps from simple calculations

[Thomas Kasel]

Much appreciated!

Regards,
Tom

On Sunday, September 15, 2024 at 9:18:08 AM UTC-7 Lucas Lodeiro wrote:

> Here you can find detailed information on how to use a correct input for 
> hybrid functionals in CP2K, particularly there is a detailed input for 
> HSE06.
>
>
> https://www.cp2k.org/_media/events:2018_summer_school:cp2k-uk-stfc-june-2018-sanliang-ling.pdf
> https://github.com/cp2k/cp2k/tree/master/tests/QS/regtest-hfx-wfn-fitting
>
> Regards - Lucas
>
> El jue, 12 sept 2024 a las 14:33, Thomas Kasel (<tomk... at gmail.com>) 
> escribió:
>
>> 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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