How to get optical band gap from absorption spectrum

[Bramhachari Khamari]

Dear Developers,
I have obtained GW+BSE spectrum for a material. I would like to know, how to get the optical band gap value from the absorption spectrum.

Regards
Bramhachari Khamari

[Palummo Maurizia]

Dear Bramhachari

if you used the diagonalization "d" option to solve the BSE and you have uncommented
the variable WRbsWF in your input you can simply use ypp to read the excitonic eigevalues from the database
doing ypp -e s 1

Look the tutorial here
http://www.yambo-code.org/wiki/index.ph ... e_excitons
section "Sorting the excitonic eigenvalues".

Best
Maurizia

[Daniele Varsano]

Dear Bramhachari,

the ypp -s command to sort the eigenvalues provides the excitation energies also without adding the WRbsWF variable in the input. This is needed to plot the excitonic wavefunction.
Moreover, for the optical bandgap maybe you want to look at the first "optically active" excitation, the strength of the excitation is also reported in the file generated by ypp.

Best,

Daniele