The units of Dipoles obtained using yambopy

[Guo_BIT]

Dear Developers,

I have obtained the dipoles along different directions using Yambopy, following the website:
viewtopic.php?t=1889

The extracted data is as follows:

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0.12008734 - 0.18181457j
-0.36308822 - 0.017739873j
-2.1394248 - 0.07620608j
-4.828707 + 4.8151965j
20.601658 + 17.380335j
-7.0335217 - 4.9788766j
-1.5650864 - 0.9189489j
-0.08713954 - 0.15790565j
-0.058562797 - 0.31479385j

Furthermore, on the website mentioned above, it is stated that the unit of the dipoles obtained in this case is Bohr. According to my understanding, the square of the real part plus the square of the imaginary part of the dipole determines whether the exciton is bright or dark.

Therefore, is the unit of the exciton oscillator strengths obtained in the *_E_* file also be Bohr²?

[Daniele Varsano]

Dear Jingda,

sorry for the late reply, in the last month we had problem with the forum website and it is back only now.
Yes, the intensity should be Bohr^2, please note that in the output file they are normalized to their maximum.
Best,
Daniele

[Guo_BIT]

Dear Daniele,
Thank you very much for your kind reply. We are aware that the envelope function of the selected exciton can be obtained in graphical form (via Yambopy) as well as in percentage form (via ypp). We were wondering whether it would also be possible to extract the raw Avc, similar to the dipoles mentioned above.

Best regards,
Jingda Guo

[palful]

Dear Jingda,

You can easily obtain the BSE eigenvector in the format of numpy array by using yambopy. When you read the BSE database with `YamboExcitonDB`, you automatically have an array called `eigenvectors` containing the A_cvk coefficients.

You can follow this tutorial (section Exciton intro 1) to see how this can be done.

Cheers,
Fulvio

[Guo_BIT]

Dear Fulvio,

Thank you very much for your reply, and apologies for not being clear enough about our request earlier.

We have already obtained the contributions (or weights) of the selected exciton for the specified transitions (K, V, C) using Yambopy.
In my opinion, the data we obtained are still expressed in percentage form, similar to the results in the weights file produced by ypp. For example

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(0.9837849-0.056339588j)

This value indicates that the selected exciton essentially originates entirely from the specified transitions (K, V, C).

However, my supervisor would like to access more “raw” data — for example, the actual numerator and denominator values used in calculating the percentages. May I ask whether such data can be extracted, and whether they carry a clear physical meaning?

Best regards,
Jingda Guo

[Daniele Varsano]

Dear Jingda,

The A_cvk are not the weight expressed in percentage, they are the eigenvectors obtained by the BSE solution. Its square module is indeed the weight=|A_cvk|^2 and you can intepret as percentage as they obey the normalization: \sum_cvk |A_cvk|^2=1

Please note that if you are considering degenerate exciton, you'll have \sum_cvk |A_cvk|^2=N_deg

Best,

Daniele