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questions about the results of BSE calculations?
Posted: Thu Sep 10, 2020 8:36 am
by Dean
Dear developers,
1. After doing BSE calculations with Diago solver, I want to analyze the exciton oscillator strenght and amplitude and got the file o-2D.exc_weights_at_1, which shows :
# Electron-Hole pairs that contributes to Excitonic State 1 more than 5%
#
# K-point [iku] Weight
# 0.26667 0.46667 0.00000 0.09283
# 0.333333 0.500000 0.000000 1.000000
#
# Band_V Band_C K ibz Symm. Weight Energy
#
21.00000 22.00000 27.00000 2.00000 0.90921 2.06548
21.00000 22.00000 27.00000 1.00000 0.90919 2.06548
My question is why it show two same kpoints (ibz: 27) contributing to this Excitonic State? but two different k-points in iku Points coordinates?
2. After doing BSE calculations with Inversion solver, the file o-2D-.eps_q1_inv_bse shows 7 columns. What does each column stand for?
With regards,
Thanks.
Re: questions about the results of BSE calculations?
Posted: Thu Sep 10, 2020 9:11 am
by Daniele Varsano
Dear Yimin,
My question is why it show two same kpoints (ibz: 27) contributing to this Excitonic State?
These are not the *same* k point in the BZ, but two k points related by symmetry (4th column)!
The matrix relating the two k points is listed in the report file where the symmetries are indexed (here 1 is the identity, the index 2 is listed in the report).
but two different k-points in iku Points coordinates?
This is a different list, as in the K-point analysis all the v-> c transitions our a given k points are summed up.
o-2D-.eps_q1_inv_bse shows 7 columns. What does each column stand for?
# E/ev[1] EPS-Im[2] EPS-Re[3] EPSo-Im[4] EPSo-Re[5] EPS`-Im[6] EPS`-Re[7]
energy, imaging/real part of eps , imag/real part of non interacting eps , imag/real part of eps for the iteration before convergence
Best,
Daniele
Re: questions about the results of BSE calculations?
Posted: Fri Sep 11, 2020 2:02 am
by Dean
Dear Daniele,
Thanks very much.
Re: questions about the results of BSE calculations?
Posted: Thu Mar 10, 2022 4:07 pm
by pyadav
Dear team Yambo,
I have done a BSE calculation and sorted the exciton eigenvalues. I have also produced the 'amplitudes' and 'weights' files'. From the absorption plot and the sorted eigenvalues, I have my first exciton peak at 2.35 eV but from the weight file, the last column shows the transition energy =1.99 eV for the same exciton.
I seek someone's response to clarify the difference in these energies here. Why the last column of the weight file has a different energy than the exciton resonance energy.
Please see the attachment for more details.
It will be also very helpful if I may know how can I plot the exciton WF in the momentum space using the weight file.
Thank you,
Pushpendra
Re: questions about the results of BSE calculations?
Posted: Mon Mar 14, 2022 2:25 pm
by Daniele Varsano
Dear Pushpendra,
the weight file provides you the Kohn-Sham transition involved in a given exciton and the last column it is its KS transition energy (Ec-Ev). Note it is the KS and not the QP energy and it is its independent particle contribution so it should not be equal to the exciton energy.
About excitons in K space you can have a look to this thread:
viewtopic.php?t=1656
Best,
Daniele
Re: questions about the results of BSE calculations?
Posted: Mon Mar 14, 2022 7:00 pm
by pyadav
Dear Daniele,
Thank you so much for the reply and the clarifications.
I have another query about the same file-
Code: Select all
Electron-Hole pairs that contribute to Excitonic State 56 for iq=1 more than 5.000000%
#
# K-point [iku] Weight
# : 0.00000000 0.00000000 0.00000000 0.176415621
# : 0.00000000 0.833333333E-1 0.00000000 0.595666140
# : 0.833333333E-1 0.125000000 0.00000000 0.894073849E-1
# : 0.250000000 0.458333333 0.00000000 1.00000000
#
# Band_V Band_C Kv-q ibz Symm_kv Kc ibz Symm_kc Weight Energy
#
41.0000000 44.0000000 18.0000000 7.00000000 18.0000000 7.00000000 0.161323024 2.65908217
.
.
42.0000000 45.0000000 1.00000000 1.00000000 1.00000000 1.00000000 0.720630997E-1 2.82974004
41.0000000 46.0000000 1.00000000 1.00000000 1.00000000 1.00000000 0.720630310E-1 2.82974004
41.0000000 45.0000000 1.00000000 1.00000000 1.00000000 1.00000000 0.713252177E-1 2.82974004
42.0000000 46.0000000 1.00000000 1.00000000 1.00000000 1.00000000 0.713251544E-1 2.82974004
In this output section, I understand that the exciton is appearing between the
: 41-44, at K [18]: 0.25 0.33 0.00 [rlu],
: 42-45, at K [18]: 0.00 0.00 0.00 [rlu],
and so on, via direct transitions. I want to know what does the following lines say?
Code: Select all
# K-point [iku] Weight
# : 0.00000000 0.00000000 0.00000000 0.176415621
# : 0.00000000 0.833333333E-1 0.00000000 0.595666140
# : 0.833333333E-1 0.125000000 0.00000000 0.894073849E-1
# : 0.250000000 0.458333333 0.00000000 1.00000000
Best,
Pushpendra
Re: questions about the results of BSE calculations?
Posted: Tue Mar 15, 2022 11:31 am
by Daniele Varsano
These provide the same information integrated on bands. So it is the weight of the vertical transition at a given k point where the contribution on different bands has been summed up.
Best,
Daniele
Re: questions about the results of BSE calculations?
Posted: Tue Mar 15, 2022 12:22 pm
by pyadav
Dear Daniele,
Thank you for the response.
A small confusion here for me is as follow-
Since from the different band transitions, we see that there are only two irreducible k-points (18 and 1) are involved which correspond to (0.25, 0.33, 0.00 and 0.00, 0.00, 0.00) respectively. I'm unable to understand why there are four k-points
Code: Select all
# K-point [iku] Weight
# : 0.00000000 0.00000000 0.00000000 0.176415621
# : 0.00000000 0.833333333E-1 0.00000000 0.595666140
# : 0.833333333E-1 0.125000000 0.00000000 0.894073849E-1
# : 0.250000000 0.458333333 0.00000000 1.00000000
and only $\Gamma$ point is consistent but not the other three k-points with the irreducible rep. k-points.
This may be trivial for you but I'm just not able to catch the correspondence between the commented and uncommented k-points.
Apart from this, what is the difference between strength and weight? does strength mean oscillator strength?
Any help would be much appreciated.
Thank you,
Pushpendra.
Re: questions about the results of BSE calculations?
Posted: Wed Mar 16, 2022 4:10 pm
by Daniele Varsano
Dear Pushpendra,
the weights are the modulus square of the BSE eigenstate |A^i_kcv|^2, while the strengths involve the dipole moments and tells you if the exciton is bright or not.
Note that \sum_|A^ikcv|^=1 and it happens it is not your case. This means you have degenerate exciotns that have been merged. Moreover in the output are reported only the weight > threshold (5%).
In order to avoid confusion you can set the following variables in the ypp input file:
e.g to have the transition larger than 1% or 0eV to have all the transition.
and:
Code: Select all
Degen_Step= 0.0 eV # Maximum energy separation of two degenerate states
to consider just one single exciton.
Please note also that to each k point in the IBZ is associated a symmetry to bring it in the BZ, in your case is the symm number 7, in the report you can find the associated rotation matrix.
Best,
Daniele
Re: questions about the results of BSE calculations?
Posted: Thu Mar 17, 2022 6:27 pm
by pyadav
Dear Prof. Daniele,
Thank you so much for your response and the clarifications. I'm really thankful to you for your kind help.
Best wishes,
Pushpendra.