[CP2K-user] [CP2K:20694] Incorrect Band gaps from simple calculations

[Thomas Kasel]

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 
>>
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "cp2k" group. 
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to cp2k+uns... at googlegroups.com<mailto:cp2k+uns... at googlegroups.com>. 
>>
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/cp2k/cf2a1d8d-c40c-4da4-9857-38cd2b7e7e91n%40googlegroups.com
>> <
>> https://groups.google.com/d/msgid/cp2k/cf2a1d8d-c40c-4da4-9857-38cd2b7e7e91n%40googlegroups.com?utm_medium=email&utm_source=footer>. 
>>
>>
>

-- 
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp2k+unsubscribe at googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cp2k/519f408c-fb0c-4c48-9a70-a36fbdc02f23n%40googlegroups.com.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20240911/7d1a2729/attachment.htm>