bright and dark exciton

[sunxl]

Dear all,

When I edit copy and submit posts, I always get blocked, so I present my questions in the form of images.
I appreciate any guidance and tutorial on that!
Best,
sunxl

q.pdf

[Daniele Varsano]

Dear Sunxl,

1) The weights iare defined as |Acvk|^2 where Acvk are the eigenvectors components of the exciton. They provide the weight of the single particle transitions participating in the excitons. \Psi_exc (r_e,r_h)=\Sum Acvk \psi_vk(r_h) \psi_ck(r_e)

If the exciton with the highest intensity has a weight of only 0.001, does such a small weight affect my analysis of exciton optical absorption spectra and similar analyses.

It is not clear what do you mean with "has a weight of only 0.001", given an exciton, there is a weight for each transition. The largest the weight, the more this transition is participating in the building up of the exciton. In some case you have few transitions with large weights, in other cases you can have an exciton formed by many transition with small weights.

2) These are not the exciton position, but the energy difference Ec-Ev (Kohn-Sham) of the transition participating in the exciton.

3) There is not a real threshold value. Properly, dark exciton (light forbidden excitation) have zero oscillator strength, but then you have the numerical precision to take into account. Exciton with very small oscillator strength can anyway be considered as dark.

Best,
Daniele