Can exciton wavefunction plotted via ypp be periodic?

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Can exciton wavefunction plotted via ypp be periodic?

Postby xueshanxihua » Thu Apr 12, 2018 3:23 am

Dear all:

I'm using "ypp -e w" to plot the exciton wavefunction with a finished G0W0-BSE result. The hole position has been fixed by considering the orbital component of VBM. However, when setting the supercell to be extremely large, I find that the exciton wavefunction comes out to be periodic in real space, i.e., locally the wavefunction is still an envelope with finite size, but these "localized" envelopes repeat periodically in a larger scale.

So can anyone tell me how this happens? Have I done something wrong?

Many thanks~!
Zeyu Jiang
PhD Student
Department of Physics, Tsinghua University
Beijing, 100084
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Re: Can exciton wavefunction plotted via ypp be periodic?

Postby Daniele Varsano » Thu Apr 12, 2018 9:15 am

Dear Zeyu,
Nothing wrong, Yambo is a plane wave code.
if you look the expression of the excitonic wave function in real space as obtained by FFT, you realize that it is periodic after a distance given by 1/deltaK, where deltaK is the smaller K-K' available in your sampling. If you see that the exciton wave function touch the border of your build supercell given by Nk*Lside, it means that probably your calculation is not converged with respect your kpoint grid
and you need a larger k point grid.

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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