Weight at q-point other than gamma

[subhayan]

Dear developer,

I am trying to calculate the contribution of individual e-h pairs in the excited state. The test system is bulk hBN (as given here : http://www.yambo-code.org/wiki/index.ph ... ter_kernel). I am using more-or-less the same input files with minor changes. However, while calculating the weights with ypp, I seem to be able to access only the q=0 components. If, in the input file for ypp, I change the variable "Qpts" to any value other than "1", I get an error message saying "[ERROR] ndb.BSS_diago not found". Indeed, in the SAVE directory, all the ndb.BS files correspond to Q1. Does this mean te excitonic Hamiltonian is constructed and solved only at q=0? Please note that, in the yambo input file the value for "% QpntsRXs" is "1 | 14 |". Could you please suggest a way to get the weights at other q-points?

Best regards,
Subhayan

[Daniele Varsano]

Dear Subhayan,
finite q Bethe Salpeter equation is present yambo, but not yet released in the GPL version, hopefully it will be released soon.
You access q=0 components because you calculated excitations for q=0.
If you are interested in optics anyway, absorption spectra have to be calculated for q=0. Finite q is needed when calculating electron-energy loss spectra.

Please note that in the yambo input file the value for "% QpntsRXs" is "1 | 14 |"

This is because you need the screening at all q in order to build the kernel of the excitonic Hamiltonian also at q=0, this is not the "q" of the excitation, you can realize it by looking at the expressions in the tutorial you are indicating. There cv belong to the same k (q=0) and are coupled with c'v' at another k' (q=0).

Best,
Daniele

[subhayan]

Dear Daniele,

Perfect. This answers my question.
Thank you very much.

Best regards,
Subhayan