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absorption spectrum
Posted: Thu May 01, 2025 4:11 pm
by xjxiao
Dear all,
The absorption spectrum calculated by BSE does not rise slowly from zero. Is this an issue? What could be the possible cause of this problem?
absorption.png
Looking forward to your reply.
Re: absorption spectrum
Posted: Fri May 02, 2025 8:49 am
by Daniele Varsano
Dear Xiangjun,
this is due to a tail of the Lorentzian broadening. This is not an issue, and you can avoid this by lowering the damping (BDmRange) in the input file.
Best,
Daniele
Re: absorption spectrum
Posted: Wed May 07, 2025 3:26 pm
by xjxiao
Dear Daniele,
Thanks a lot for your help!
I kept reducing the BDmRange, but it still seems impossible to make the imaginary part of the dielectric function zero at zero energy (the system has no excitons at zero energy). Why does this happen?
o-bse_44_qp.alpha_q1_diago_bse
Code: Select all
% BEnRange
0.000000 | 4.000000 | eV # [BSS] Energy range
%
% BDmRange
0.100000 | 0.100000 | eV # [BSS] Damping range
%
BEnSteps= 300 # [BSS] Energy steps
o-bse_44_qp.alpha_q1_diago_bse_01
Code: Select all
% BEnRange
0.000000 | 4.000000 | eV # [BSS] Energy range
%
% BDmRange
0.014000 | 0.014000 | eV # [BSS] Damping range
%
BEnSteps= 300 # [BSS] Energy ste
o-bse_44_qp.alpha_q1_diago_bse_02
Code: Select all
% BEnRange
0.000000 | 4.000000 | eV # [BSS] Energy range
%
% BDmRange
0.005000 | 0.005000 | eV # [BSS] Damping range
%
BEnSteps= 300 # [BSS] Energy ste
BDmRange_contrast.png
Re: absorption spectrum
Posted: Fri May 09, 2025 8:18 am
by Daniele Varsano
Dear Xiangjun,
as you can see from your plot this is just a tail of the Lorentzian broadening.
You have an excitation at very low energy, so it is hard to have the absorption exactly zero at zero energy.
Anyway, this is just aesthetic. For clarity, you can superimpose a vertical line at the excitation energies. You can use ypp to print the excitations:
ypp -e s -b 1
and plot the resulting o*_E_sorted file as:
>gnuplot
p "o*_E_sorted" u 1:2 w i
Best,
Daniele