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SOC-induced exciton weight change
Posted: Thu Dec 12, 2024 5:21 am
by Guo_BIT
Dear Developers,
I used YPP to calculate the contribution of excitons. When symmetry is turned off and SOC is not considered, the lowest energy state and the second-lowest energy state are independently contributed by (0.5, 0, 0) and (0, 0.5, 0), respectively.
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# Band_V Band_C Kv-q ibz Symm_kv Kc q ibz Symm_kc Weight
]#
36 37 649 1 649 1 0.876284
However, when taking SOC into account, the exciton of the ground state is contributed by both of these k-points together
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# K-point [iku] Weight
# : 0.00000000 -0.500000000 0.00000000 0.554620981
# : -0.500000000 0.00000000 0.00000000 1.00000000
Considering the distribution of these k-points in reciprocal space, I am wondering whether this result is physical significance or is simply a computational artifact.
This is important for our current research, and I look forward to your response.
Best wishes
Jingda Guo
Re: SOC-induced exciton weight change
Posted: Thu Dec 12, 2024 12:17 pm
by Daniele Varsano
Dear Jingda,
are you sure that you are not considering degenerate excitons all together? To avoid this, you should set Degen_Step=0.0 eV in your ypp input file.
Can you please post the output file of your calculations?
Best,
Daniele
Re: SOC-induced exciton weight change
Posted: Thu Dec 12, 2024 1:14 pm
by Guo_BIT
Dear Daniele:
To avoid degeneracy, I set the following in the ypp.in file:
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excitons # [R] Excitonic properties
amplitude # [R] Amplitude
States= "1 - 8" # Index of the BS state(s)
BSQindex= 1 # Q-Index of the BS state(s)
Degen_Step= 0.00000 eV # Maximum energy separation of two degenerate states
then I calculated the weight of the first exciton
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# Maximum Residual Value = 0.35041E+00
#
# E [ev] Strength Index
#
0.338274464E-1 0.352137751E-3 1.00000000
0.338313021E-1 0.886224792E-3 2.00000000
0.338357650E-1 0.186500802E-4 3.00000000
0.338525586E-1 0.333322123E-5 4.00000000
0.338968784E-1 0.917177204E-5 5.00000000
0.340177938E-1 1.00000000 6.00000000
0.340196043E-1 0.281616807 7.00000000
0.344031453E-1 0.252245002E-6 8.00000000
The specific weights are as follows, where 72 and 73 represent the valence and conduction bands
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# Electron-Hole pairs that contribute to Excitonic State 1 for iq=1 more than 5.000000%
# K-point [iku] Weight
# : 0.00000000 -0.500000000 0.00000000 0.554620981
# : -0.500000000 0.00000000 0.00000000 1.00000000
#
#
# Band_V Band_C Kv-q ibz Symm_kv Kc q ibz Symm_kc Weight Energy [eV]
#
71 74 289 1 289 1 0.298324 0.079534
71 73 289 1 289 1 0.250963 0.079534
72 74 13 1 13 1 0.174108 0.079536
71 73 13 1 13 1 0.095660 0.079536
72 73 289 1 289 1 0.075195 0.079534
71 74 13 1 13 1 0.050809 0.079536
Re: SOC-induced exciton weight change
Posted: Thu Dec 12, 2024 2:15 pm
by Daniele Varsano
Dear Jingda,
please note that the weight reported at the beginning of the files on the relevant k points are normalized to the largest weight, and this can be misleading when comparing two different calculations.
I suggest you to plot weight to the whole BZ, or along a band structure, to inspect differences in the two calculations.
This can be done using the yambo-py utility, as explained in this tutorial:
https://wiki.yambo-code.eu/wiki/index.p ... _databases
In any case, from the sort file you posted, it is evident that you have many degenerate excitons. As they are degenerate, you can have different separate contributions or a linear combination of them. In order to recover the entire picture, probably you need to consider a linear combination of them, or analyze them one by one at the same foot, i.e. not considering the tiny energy difference they display.
Best,
Daniele