An error occurred when analyzing excitons using BSE spectroscopy

[202321070091]

Dear all,
After calculating the characteristics of excitons according to the tutorial and preparing to calculate the exciton oscillator strength and example, when executing the command " ypp -F ypp_AMPL.in -J 2D_WR_WC -e a 1
", an error "[ERROR] STOP signal received while in[06] Excitonic Properties @ Q-index #1,[ERROR] Diagonalization database does not contain excitonic eigenstates. Re-run yambo using the WRbsWF flag in the input file." appeared.
Similarly, during step "ypp -F ypp_WF.in -J 2D_WR_WC -e w 1", the same error occurred. I tried to change the value of BSQIndex to 200 (I'm not sure if this is correct) and added the WRbsWF parameter to the input file. Although there were no errors, unable to generate output file for tutorial (o-2D_WR_WC.exc_2d_1.xsf, o-2D_WR_WC.exc_qpt1_amplitude_at_1 o-2D_WR_WC.exc_qpt1_weights_at_1 ...). How can I solve this problem? (The parameter WRbsWF in the input file "ypp_WF. in" was manually added by me. The input file generated based on the commands in the tutorial does not include this parameter, but unless I change the parameter BSQIndex at the same time, those two errors will still appear)

Yours sincerely, WangQi

[Daniele Varsano]

Dear WangQi,
in order to analyze and plot excitonic wavefunctions you need to print the BSE eigenvectors. This is done adding the WRbsWF in yambo input file when
diagonalizing the BSE matrix and not in the ypp.in file.
This is explained in this tutorial:
https://www.yambo-code.eu/wiki/index.ph ... ter_kernel

So you need to diagonalize again the BSE adding that flag before using ypp to analyze the excitons.

Best,
Daniele

[202321070091]

Dear Daniele,
Thank you for your answer. As a beginner, I apologize for encountering many problems. When I followed the tutorial "Calculating optical spectra including excitonic effects: a step-by-step guide" for calculation, as the example provided was a bulk material and I wanted to process two-dimensional materials, I only modified the first two values of the parameter LongDrXs in the "Static screening" section. That is, I only added a perturbation electric field in the xy direction. When I reached step "Bethe-Salpeter kernel runlevel", I encountered an error "[ERROR] STOP signal received while in[05.01.01] Transition pre-analysis @q1, [ERROR] The whole BSE has zero dimension!" when executing the command "yambo -F 02_2D_BSE_kernel.in -J 2D_BSE". What should I pay attention to when using the tutorial on processing three-dimensional materials for two-dimensional materials?
Yours sincerely, WangQi

[Daniele Varsano]

Dear WangQi,
I suggest you to go step by step and follow the tutorials carefully, trying to understand the meaning of the variables.
As a first suggestion, it is recommended to generate input file using the command line and not modifying previous input file, in particular when dealing with different systems, in this way most of the default variable are set correctly. When dealing with 2D systems you need to isolate the system from its replica and the use of a truncated potential is recommended (see e.g. https://www.yambo-code.eu/wiki/index.ph ... al_systems).

The problem you are facing is related with the bands you are using to build the BSE kernel:

Code: Select all

% BSEBands
   6 |  10 |                         # [BSK] Bands range
%

insepcting the report file you can recognize that:

Code: Select all

 [X] Filled Bands                                  :   4
  [X] Empty Bands                                   :    5   60
 

so in your input you are considering only empty states, so that any v->c transition is included and that's the reason why the whole BSE has zero dimension. You need to include at least one occupied and pne empty band, and of course next you will need to increase the number of bands up to convergence.

Best,
Daniele

[202321070091]

Dear Daniele,
I would like to ask for my advice on visualizing excitons. When I reached step "Plot the exciton spatial distribution", I successfully generated o-2D-WR_WC. exc_qpt1_2d_1. xsf and o-2D-WR_WC. exc_qpt1_2d_2. xsf files. However, when I imported them into VESTA, the atoms were not displayed and there were no images. May I ask if this is my calculation error?
Yours sincerely, WangQi

[Daniele Varsano]

Dear WangQi,

this seems a bug of VESTA, see here:
viewtopic.php?p=6986#p6986

I was not able to visualise your file neither but the structure appears for example setting the origin to zero (line 109 set to 0,0,0) but of course this is not what you want.
Anyway, I'm not sure VESTA can display 2D grids as you are requesting. I suggest you either to switch to a 3D plot and then plotting an isosurface, or
to use the XcrysDen visualisation software.

Best,
Daniele