The Formula of the dielectric functions

[Fredmei]

Dear developers,
Via Yambo, I can obtain the imaginary part of the dielectric functions from outfiles such as *.eps_q1_diago_bse. However, I am confused about the formula that the code used and if the formula still works when I choose a finite/non-zero q such as q35. Could you show the fomula of that directly or some reference papers?

Thanks a lot.
Fred Mei

[Daniele Varsano]

Dear Fred,
please sign your post including your affiliation, this is a rule of the forum and you can do once for all filling your user profile.
Form your message I assume you are doing a BSE calculation.

The expression is the one obtained from the solution of the BSE equation and it can be found in the yambo paper Marini et. al. Comp. Phys. Comm. 180, Pages 1392-1403 2009. Eq. 23. There, it is written for q=0, but the same expression is valid at finite q where you have vk-->ck-q transitions, so the excitonic matrix is constructed considering these transitions.
You can find the finite q expression in Eq. 8 of PHYSICAL REVIEW B 88, 155113 (2013)

Best,
Daniele