Yambo Community Forum

Dear team Yambo,

How can I get the exciton wavefunctions for other states like 2s, 2p, or 3s?
In the input file the following settings are by default I think these three input lines are relevant for different excitonic states.
Can someone please explain a bit about them?

Thank you,
Pushpendra

Dear Pushpendra,

the keyword States indicated the index of the wfs you want to plot. They are ordered by increasing energies and you can look at them by sorting the BSE eigenvalues using ypp.
will plot the exc_wfs for the first 5 states.

Note that in presence of degenerate excitons yambo will merge them by default according to the degeneracy threshold (Degen_Step).
If you do not want to merge them you need to set it to 0 eV.

Best,
Daniele

Dear Daniele,

Thank you for the reply.

I get a single output file ( o.exc_qpt1_2d_1.xsf) of exciton wf if I take Degen_Step =0.0 for States= "1 - 1" and three output wfs if States= "1 - 3". For the second case (States= "1 - 3") does correspond to different excitonic peaks (like exciton A, exciton B, and exciton C respectively)?

Wishes,
Pushpendra

Dear Pushpendra,

I do not now what do you mean with exciton A,B,C.
Anyway they exciton indexes are ordered by increasing energy ad you can look at their energy by sorting them using ypp utility (ypp -s).
Best,
Daniele

Dear Daniele,

Sorry I'm not able to find the sorted eigen values of different excitons. Using ypp -s it gives

ypp: option requires an argument -- 's'

Use -h to list the options

but using just 'ypp s' it runs but gives 'r_electrons' file and it does not have any information about the exciton wf or eigen value.

Can you please explain that a bit more?
I want to identify which exciton wavefunction (o.exc_qpt1_2d_1.xsf, o.exc_qpt1_2d_2.xsf,o.exc_qpt1_2d_3.xsf) correspond to which exciton peak if I set

States= "1 - 3" # Index of the BS state(s)

Wishes,
Pushpendra

Dear Pushendra,

you can use ypp to sort the excitation energies: As appeared when you typed your command: use ypp -h to have the help of the utility listed.

Best,
Daniele

Dear Daniele,

Thanks a lot for your response. I got the sorted files.

Best,
Pushpendra

Dear Daniele，
When analyzing the exciton function, is the result reliable if the number of cell repeats in each direction is even rather than odd? What's the reason for odd numbers in this tutorial?
Thanks！

Dear Bu,

the reason if you want is merely aesthetic. You define the hole position in the unit cell and then the exciton is plotted in a supercell defined by the repetition units.
If the number of units is odd the hole will be placed in the central unit of the supercell. Actually if number of repeated of cell is even I do not know exactly where the hole will be placed, anyway it is indicated in the output file and you can check if it is in a reasonable position.
Best,
Daniele

Dear all,

For the same system, I would like to consult about several problems in understanding the exciton wave functions.
1、I use the PBE and HSE exchange-correlations respectively to perform the ground state and then solve the BSE directly. Can the first bright exciton wave function under the two exchange-correlations treated by ypp be directly compared? Does the distribution of a point in space refer to absolute or relative probability?
2、For the spatial character of the exciton YPP writes the exciton spatial distribution，can this be understood as fixing a hole at a given position, while the surrounding refers to the distribution of an electron in space? What is the unit of the electron distribution?

Thanks!

Xiangtian