Coulomb cutoff and vacuum size

Concerns issues with computing quasiparticle corrections to the DFT eigenvalues - i.e., the self-energy within the GW approximation (-g n), or considering the Hartree-Fock exchange only (-x)

Moderators: Davide Sangalli, andrea.ferretti, myrta gruning, andrea marini, Daniele Varsano

DavidPolito93
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Re: Coulomb cutoff and vacuum size

Post by DavidPolito93 » Mon Mar 21, 2022 12:20 pm

Dear Daniele,

I am performing a computation on a large orthorhombic supercell for a 2D system which requires only the gamma point as k-point sampling.

I am concerned about using the ws cutoff as I recall that it works better as we increase the k-point sampling, while here we would have only 1 1 1 as k-point. Do you think it would be a problem or is it still better to use ws with respect to a box cut-off?

Best,

Davide Romanin
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Polytech - Paris-Saclay University
C2N, CNRS
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Daniele Varsano
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Re: Coulomb cutoff and vacuum size

Post by Daniele Varsano » Tue Mar 22, 2022 8:38 am

Dear Davide,

having k point sampling or large supercell should be equivalent if the supercell is large enough, so cutoff ws should work.
Of course, you will need to check if the supercell is large enough to guarantee the interaction in the relevant range (note that it would be the same using also the box cutoff).

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/

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