How to relate k point index to coordinates

[yhypku]

Dear all,
I ran a 36x36 BSE of 2D BN on yambo and follow the advice of Daniele in poster: viewtopic.php?f=9&t=1742&p=9073&hilit=weight#p9073
to print the real and imaginary part of A(cv)_lamda. However, I only get the index of the k points('ik' in the code), not the exact coordinates. For my case, the maximum index is 1296(36x36), and I would like to know how to deal with them properly.
Thanks in advance for your hard work for the community of Yambo.
Best,
Huaiyuan

[Daniele Varsano]

Dear Huaiyuan,
in each report, you have the k points coordinate corresponding to the indexes (check for Energies [ev] & Occupations section):
you find something like:

Code: Select all

*X* K [1] : 0.000000  0.000000  0.000000 ( cc) * Comp.s 160123 * weight   0.05556
              0.000000  0.000000  0.000000 (rlu)
  E -44.84562 -44.82319 -44.79297 -44.78954 -44.77050 -44.76947 -44.71061 -44.70914
....
*X* K [9] :-0.275149  -0.05404  0.000000 ( cc) * Comp.s 160264 * weight   0.05556
             -0.500000 -.4470E-7  0.000000 (rlu)
  E -44.84553 -44.82310 -44.79297 -44.78954 -44.77050 -44.76946 -44.71061 -44.70914
....

Between [ik] is the index, next there are the coordinates:
cc : cartesian coordinates
rlu : reciprocal lattice units

Best,
Daniele

[yhypku]

Dear Daniele:
Thanks for your reply. I'm sorry that I didn't explain my question clearly. The k points in your reply is the IBZ kpoints, but I would like to know all the kpoints information, cause in the output 'ik' could get 1296(36x36). Is there a convenient way to do that?
Best,
Huaiyuan

[Daniele Varsano]

Dear Huaiyuan,
sorry, I didn't understand,
Anyway, if I have understood now if you want information on k points in the whole BZ, you can add these two lines (see e.g. lines from 158 and beyond) after the line 84 indicated in the post you mentioned:

Code: Select all

ikibz = Xk%sstar(ikbz,1)
 is = Xk%sstar(ikbz,2)

and print ikibz and is.

In this way, for each k points in the whole BZ, you have the corresponding k point in the IBZ and the related symmetry operation.
Symmetry operations are indexed and reported in the report file.

Hope this answer to your question,
Best,
Daniele

[yhypku]

Thanks, it helps me a lot.

[yhypku]

Dear Daniele:
I followed your suggestion and print out the Acv_lamda in the whole BZ. The system is 2D BN, using 36*36 kgrid to run the BSE. What confuses me is that the exciton of index 1 and index 2 have the same Acv_lamda in the whole BZ, but they have different oscillating strength. Could you please tell me what's the reason for that?
Here are my E_sorted file.
# Maximum Residual Value = .49576E+00
# E [ev] Strength Index
#
5.473043918610 1.000000000000 1.000000000000
5.473090171814 0.910880088806 2.000000000000
(Acv_lamda for 1 and 2 are too large to add into attachments. They are just the same.)
Best,
Huaiyuan

[Daniele Varsano]

Dear Huaiyuan,
you have two degenerate excitons, most probably coming from degenerate transitions.
Note that the strength is normalized to its maximum reported in the output ( 0.49576), so the two strength differs for about 1%.
When you say they have the same A_cv_lambda you refer to their modulus? I would say that A_cv_lambda for two eigenvalues cannot be the same.

Important: when analyzing excitons, it is recommended to see to zero the degeneracy threshold, otherwise, two degenerate states are merged together. In order to do that you need to set: Degen_Step=0.0 eV in your ypp input file, as by default it is set to 10^-3 eV. This could be the reason why you have two identical eigenvectors.

Best,
Daniele

[yhypku]

Dear Daniele:
I'm afraid that their Acv_lamdas are the same too. The whole file is too large to add into attachment so I just post part of it. The outputs represent i_lamda, ikbz, ikibz, is, iv, ic, ReA, ImA in order. File A1 is the part of the Acv_lamda of the first exciton and A2 is that of the second exciton. I really don't know the reason.
Best,
Huaiyuan

[Daniele Varsano]

Dear Huaiyuan,
have you seen my comment above about degeneracy step?
Can you check the normalization of each lambda \sum_cv |A_cv|^2

Best,
Daniele

[yhypku]

Dear Daniele:
I set degen_step = 0 and the eigenvectors become different. Thanks for your help.
Best,
Huaiyuan