Bandgap Underestimation

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ankitsha
Posts: 3
Joined: Fri Nov 05, 2021 11:22 pm

Bandgap Underestimation

Post by ankitsha » Tue Nov 23, 2021 6:42 pm

Hi Yambo Community,
I am trying to obtain the electronic dispersion for Gallium oxide and I expect the bandgap to be around 4.9eV, but according to the calculation, I get a bandgap of around 2eV.
Attached is the yambo input file and the scf file used to generate the database.
Any help in this regard will be greatly appreciated.

Thank You,
Ankit Sharma
University at Buffalo
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Daniele Varsano
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Re: Bandgap Underestimation

Post by Daniele Varsano » Wed Nov 24, 2021 9:52 am

Dear Ankit,
can you post the report file of your calculation?

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

ankitsha
Posts: 3
Joined: Fri Nov 05, 2021 11:22 pm

Re: Bandgap Underestimation

Post by ankitsha » Wed Nov 24, 2021 6:52 pm

Hi Daniele,
Attached is the output files as a zip generated as part of the run.
Please let me know if you need more information.

I am using ypp for band interpolation.


Thank You,
Ankit Sharma
University at Buffalo
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Daniele Varsano
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Re: Bandgap Underestimation

Post by Daniele Varsano » Thu Nov 25, 2021 11:20 am

Dear Ankit,
from what I can see in the report your gap e.g. at gamma goes from 1.89eV (KS) to 2.95eV (GW)

Code: Select all

B=44 Eo= -0.01 E= -0.25 E-Eo= -0.24 Re(Z)=0.78 Im(Z)=-.1266E-2 nlXC=-25.99 lXC=-20.50 So= 5.192
 B=45 Eo=  1.88 E=  2.70 E-Eo=  0.82 Re(Z)=0.83 Im(Z)=-.9087E-3 nlXC=-11.13 lXC=-14.79 So=-2.670
Of course you need to check if the value it is converged with respect all the parameters. Note also, in case you used a psp with non linear core correction they are by default discarder but you can include by using the variable:

Code: Select all

UseNLCC 
This I cannot verify as the Vxc part is not reported in the report file as it is not calculated in the present run but it is read from a previous one.

Note that you did an interpolation on the DFT band structure and not the GW one, in order to interpolate the GW structure you need to include in the ypp input file the keyword GFbQPdb pointing to the QP database as:

Code: Select all

GfnQPdb= "E < ./gao_gw_ppa_r01/ndb.QP"
as explained in this tutorial:
http://www.yambo-code.org/wiki/index.ph ... Structures

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

ankitsha
Posts: 3
Joined: Fri Nov 05, 2021 11:22 pm

Re: Bandgap Underestimation

Post by ankitsha » Mon Nov 29, 2021 5:44 pm

Hi Daniele,
Thank you very much for your response. I checked for convergence in the HF gap but will running the main calculation I set the cutoff as 80 Ry to be consistent with the planewave cutoff used for the SCF calculation.
I will reassess the calculation again and get back to you on this.

Thank you very much for your help.

Thank You,
Ankit Sharma
University at Buffalo

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