Analysis of the spectrum and Continuous part

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Analysis of the spectrum and Continuous part

Postby Flex » Thu Aug 04, 2016 12:09 am

Hello,

I have been using Yambo to calculate the absorption spectrum of monolayer MoTe2. I have satisfactory results, as you can see by comparing my results (image) to the fig 2 (a) in experimental article : "Optical Properties and Band Gap of Single- and Few-Layer MoTe2 Crystals" (DOI: 10.1021/nl502557g). Qualitatively, it seems to fit.

There is a 0.5 eV shift in the peak because I used DFT (which has a wrong band gap) as a base for the BSE calculation, so that is normal.

But I was wondering in what unit exactly was the BSE spectrum. Is it absorbance ? Is it normalized ?

Also, I only calculated some transitions around the gap, so I don't have all the transition peaks. But isn't there also a continuous part of the spectrum ? The actual spectrum isn't supposed to go to 0 after about 3 eV, here. Does BSE only calculate transitions ?

Thanks in advance
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Thierry Clette
Student at Université Libre de Bruxelles, Belgium
Flex
 
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Re: Analysis of the spectrum and Continuous part

Postby Daniele Varsano » Mon Aug 08, 2016 11:47 am

Dear Thierry,
I have been using Yambo to calculate the absorption spectrum of monolayer MoTe2. I have satisfactory results, as you can see by comparing my results (image) to the fig 2 (a) in experimental article : "Optical Properties and Band Gap of Single- and Few-Layer MoTe2 Crystals" (DOI: 10.1021/nl502557g).


Great!

But I was wondering in what unit exactly was the BSE spectrum. Is it absorbance ? Is it normalized ?


It is the imaginary part of the macroscopic dielectric matrix, this is the quantity needed to obtain absorption coefficients.

But isn't there also a continuous part of the spectrum ? The actual spectrum isn't supposed to go to 0 after about 3 eV, here. Does BSE only calculate transitions ?


The extension of the spectrum depends on how may bands you include in the calculation so in the range of energy covered on the possible transitions. The transition involved in the spectra can be either bound or unbound.

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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