[CP2K-user] [CP2K:20698] Incorrect Band gaps from simple calculations

[Jürg Hutter]

Hi

Obviously, you have a serious problem in your (secrete) input.
Without further information it is impossible to help.

regards
JH

________________________________________
From: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Thomas Kasel <tomkasel 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

--
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<mailto: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<https://groups.google.com/d/msgid/cp2k/519f408c-fb0c-4c48-9a70-a36fbdc02f23n%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/ZR0P278MB0759254DD919E0063FA18BB89F642%40ZR0P278MB0759.CHEP278.PROD.OUTLOOK.COM.