analyze the origin of the exciton peak

[damao4361556]

Hi Everyone

I am trying to analyze the origin of the spectrum peak in the tutorial of GaSb. (http://www.yambo-code.org/tutorials/GaSb/more.php)
As suggested, we need to sort the energy or intensity first, and then, generate the input for ypp and put the index #N of the exciton with higher strenght in the E_1 peak region.

I am afraid it is not clear to me about the latter sentence. We can get the number of the interested excitation or exciton by us.
What does it mean by " put the index #N of the exciton with higher strenght in the E_1 peak region"?

Since using this command (ypp -e a -F My_inputs/05_BSE_ypp.in -J 05_BSE) we will see:

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amplitude                    # [R] Amplitude
excitons                     # [R] Excitons
States= "1 - 1"              # Index of the BS state(s)
Degen_Step=   0.0100   eV    # Maximum energy separation of two degenerate states

What does the "1-1" refer to?

Also, how to analyze the origin of the exciton?

Using the o-05_BSE.exc_weights_at_17 file in the REFERENCE-OUTPUT directory, I can see that:

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#  Band_V     Band_C     K  ibz     Symm.      Weight     Energy
#  
   4.00000    5.00000   19.00000   27.00000    0.96271    1.64087
   4.00000    5.00000   19.00000    2.00000    0.96271    1.64087
   3.00000    5.00000   19.00000   26.00000    0.96268    1.64087
   4.00000    5.00000   19.00000    4.00000    0.96266    1.64087

It would be so kind if anyone can clarify the meaning of Column 4 (Symm.)

thanks

[Daniele Varsano]

Dear Eric,

What does the "1-1" refer to?

it is exactly the index of the exciton you want to analyze.
You need to sort the excitation first:

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ypp -e s

ypp will produce two file containing the excitations sorted by energy or intensity.
For each excitation you have the energy, strength and the corresponding index you need to insert in the ypp.in for analyzing the excitation.

Also, how to analyze the origin of the exciton?

Looking at the weights of the electron-hole KS transition forming the exciton.

It would be so kind if anyone can clarify the meaning of Column 4 (Symm.)

Yout system has symmetries and yambo use them. So you sample your Brillouin zone in the irreducible part only, the other point of the BZ are obtained by applying symmetry operation. So the transition are indicated by:
Valence Bands, Condution Bands, K point in the IBZ, Symmetry operation.
The symmetry operation associated by an index can be seen in the report file:

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  [02.02] Symmetries

Best,

Daniele

[damao4361556]

Hi Daniele

Thanks for your reply

Best

Eric