Thank you so much dear Caterina

Yes, You are right. The EXCITON_BSE###_.OUT is included quantities that you pointed.
To our knowledge, for example, the binding energy determines which exciton is bound or not.

I want to know with these three quantities, the energy of the excitons in the spectrum, their binding energies and the oscillator strengths, how I can interpret: 1.origin of excitons 2.be a dark exciton or bright

Can you guide me please?
Or is there a reference included this information for introducing to me?

Dear Hajar,

the oscillator strength (OS) of the exciton tells you about its intensity. Therefore, bright excitons have strong OS, while dark excitons have zero or negligible OS.
However, from the files EXCITON_###.OUT you cannot extract any information about the origin of the exciton in terms of single-particle transitions.

Best regards,
Caterina Cocchi
(exciting team)

Thank you so so much dear Caterina

An other question, please:

How can I determine the origin of an excitonic feature? i.e. how can I find which band to band transition leads to the excitonic feature? Is there an output file in exciting-code showing that? If no, based on what information or data this interpretation can be possible?

The best for you.

Dear Hajar,

the information you are looking for is not directly printed in any output file of the current release of exciting.

Nevertheless, a thorough analysis of your system, already at the ground-state level (band-structure, single-particle wave functions, crystal symmetries etc.), can definitely help you to better understand also the excited-state properties.

Best regards,
Caterina Cocchi
(exciting team)

Than you very very much dear Caterina
Best whishes