Vacuum spacing in 2D materials

Please post here any issue related to convergence parameters in linear response GW and BSE calculations.

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Laura Caputo
Posts: 49
Joined: Sun Apr 11, 2021 3:02 pm

Vacuum spacing in 2D materials

Post by Laura Caputo » Wed Sep 08, 2021 1:30 pm

Hello,

I'm going to calculate band gap corrections for 2D materials with GW. Since I need to converge the vacuum thickness, should it be enough to calculate the band gap taking into account small constant k point mesh for every vacuum thickness considered for the convergence to have feasible calculations?
Laura Caputo
Ph.D. Student
Université Catholique de Louvain
https://uclouvain.be/fr/repertoires/laura.caputo

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Daniele Varsano
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Re: Vacuum spacing in 2D materials

Post by Daniele Varsano » Wed Sep 08, 2021 1:57 pm

Dear Laura,

yes, you can perform tests out-of-convergence considering also that you do not have k points (and dispersion) in the direction orthogonal of the 2D plane.
Note that GW convergence with respect the vacuum is extremely slow, unless you use coulomb cutoff potentials (box, or ws in case you have an orthorhombic unit cell).
If you use the box, you should change the box_z value (slightly lower than your cell Lz size) for the different vacuum considered.

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/

Laura Caputo
Posts: 49
Joined: Sun Apr 11, 2021 3:02 pm

Re: Vacuum spacing in 2D materials

Post by Laura Caputo » Wed Sep 08, 2021 1:59 pm

Hello,

Thank you for the very fast reply. I am just checking the vacuum using the truncated Coulomb potential and using slightly smaller box to respect to the 'true' cell parameter used, as explained in the yambo tutorials.

Thank you again!
Laura Caputo
Ph.D. Student
Université Catholique de Louvain
https://uclouvain.be/fr/repertoires/laura.caputo

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