Yambo Community Forum

Dear Khaled,

1) When you solve the BSE, the meaningful part of the exciton energy is the real part. If you are interested in exciton lifetime you need to do a model for it first.
2) If you want to extract the transition dipole matrix you can write them either looking into ./src/bse/K_diag_compute_epsilon.F, when the epsilon is built after the diagonalization of the dielectric matrix.
Otherwise with the postprocessing ypp, when excitons are sorted out (have a look in ./ypp/exciton_sort_and_report.F), the BS_R are read, normalized and printed out.

Best,

Daniele

Dear Dr. Daniele Varsano,

Thanks a lot Dr. Daniele for your great help. I was able to extract the transition dipole matrix, but I am not sure a bout the units of the transition dipole matrix $ | \sum_{vck} \langle vq-k | e^{-iqr} | ck \rangle A_{\lambda} |^{2} $
because I extracted this term alone (even I couldn't figure out if you used the electric dipole approimation for this term or not). Please, Can you help me for getting this information. Thank you in advance.

Best regards,

Khaled.

Dear Khaled,
the internal unit in the code is the atomic unit (bohr for length, Hartree for energy etc..).
The electric dipole approximation it is used for the q=0 term.

Best,

Daniele

What is exactly the unit of the matrix elements ?

A transition dipole has SI units of Coulomb.meters, so here, should it be electron charge.bohr ?

Dear Thierry,
yes, it should be as you wrote.

Daniele

Dear Yambors,

I have a pretty simple question.

In the BSE input file, one of the important parameter is BSSmod:

BSSmod= "d" # [BSS] (h)aydock/(d)iagonalization/(i)nversion/(t)ddft`

I was curious about the last option (t), here t represetns TDDFT? since it is just the method to solve BSE equation, so what does TDDFT means here. I have done TDDFT using LRCs approx. already.


Thanks,

Dear Haseeb,
this variable was meant for a tddft kernel derived from the BSE equation: see e.g. Phys. Rev. Lett. 91, 256402 (2003). This feature is not present anymore in the code.
Best,
Daniele