Variable of ex-ph matrix element

[pangrt]

Dear all,
I am trying the ex-ph module, and my result seems to be that the ndb.excph_gkkp_fragment_1 EXCITON_PH_GKKP_SQUARED_Q1 matrix is generated by incident excitons, phonons and virtual excitons |g|. May I ask how or where the exciton Q and phonon q are set?

Thanks!
Pangrt

[claudio]

Dear Pangrt

may you tell exactly which example are you following for the exicton-phonon?

In general Yambo automatically takes care of momentum conservation as Q' = Q-q or Q'=Q+q

But if you give me more information I can give you a better answer

best
Claudio

[pangrt]

Dear claudio,
I used a k-grid of 12 12 1 in nscf and did not use a double grid, which generated 144 ndb.excph_gkkp_fragment files. Taking ndb.excph_gkkp_fragment_3 as an example, does the point q=3 correspond to an exciton or a phonon?
Also, when the in and out of the exciton are both 1, why is the excph matrix 144*mode, instead of 144(exciton)*144(phonon)*mode?
Thanks!
Pangrt

[claudio]

Dear Thanks

the database ndb.excph_gkkp_fragment correspond to the exciton phonon scattering of the exciton at Q=0
with a phonon at finite q, namly the matrix elements G(Q=0,q).
For the moment yambo calculate only the scatteting for the excitons at Q=0.
In principle it is possible to calculate also other scattering but are not implemented yet

best
Claudio