Interpolate exciton dispersion

[xjxiao]

Dear all,
When interpolating the exciton dispersion(https://wiki.yambo-code.eu/wiki/index.p ... Yambo_5.x)), can I calculate the BSE only for points along a specific path and then use interpolation to get the exciton dispersion curve for that path? Will this method produce accurate results?
I tried doing this. As shown in the screenshot of my input file,

1518196a-7e26-4d7c-8a31-c9ae1d873f26.png

I requested only the first state by setting States = "1 - 1". However, the output file contains three energy columns: e1, e2, and e3.

d4e8665e-f368-4541-910d-cf032205cef2.png

Are these degenerate excitons? Their interpolated energies are close but do not perfectly overlap.

exciton3.png

Is there any way to control the interpolation so that it only calculates the dispersion for the single lowest-energy exciton?

[Daniele Varsano]

Dear Xiangjun,

I suggest you to calculate the exciton energies on a regular grid before performing the interpolation. This will provide more accurate results.
It seems that your excitons are degenerate at gamma (q=0) but then they are not anymore. If you want to discard degeneracies
you can try to add in your input:
Degen_Step= 0.0 eV

this will select just the first exciton even if I'm not 100% sure that it will take effect in the interpolation procedure.

Best,
Daniele