Electronic band gap vs optical band gap

Run-time issues concerning Yambo that are not covered in the above forums.

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Electronic band gap vs optical band gap

Post by burkzdemir » Sat Jul 27, 2019 2:12 pm

Dear Yambo Developers,

I am running GW+BSE calculations and obtaining dielectric functions. However, when I look at the absorbance, I see that the optical band gap (1 eV) is smaller than the electronic band gap (2 eV). How is this possible?

Burak Ozdemir
University of Ostrava, Ostrava, Czech Republic

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Daniele Varsano
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Re: Electronic band gap vs optical band gap

Post by Daniele Varsano » Mon Jul 29, 2019 7:58 am

Dear Burak,
this is always the case when you are in the presence of bound excitons. The difference between the electronic bandgap and the optical gap is indeed the binding energy of the exciton due to the electron-hole attraction, i.e. the energy needed to separate the electron-hole pair in two independent electrons and holes.

Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale

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