Some questions about the absorption coefficient of bulk silicon calculated in YAMBO

[tom]

Dear developers,

I have some questions about how to get the meaningful absorption coefficient when using YAMBO to do the GW-BSE calculation for bulk silicon materials.  I have already known how to use RIM and CUT settings to treat low-dimensional systems, and have successfully got the bulk silicon alpha. Below are my questions:

1.Is the output file o-GW.eps_q1_diago_bse of GW-BSE calculation containing the bulk silicon Energy range\E/ev[1],dielectric functions \epsilon?Does this file is produced by using the formula Absorb = \sqrt（2） * \omega /c * \sqrt （\sqrt （Im^2 + Re^2） - Re））?If not this case, what is this file?

2.When I use the formula Absorb = \sqrt（2） * \omega /c * \sqrt （\sqrt （Im^2 + Re^2） - Re）），the resulting absorption coefficient （figure a）does not match the literature（figure b）. In the literature, absorption starts at the band gap energy, but the data I obtained starts absorbing from 0 energy, which is clearly incorrect. I haven't been able to identify where the issue lies.

So I get not the epsilon？Therefore, it cannot be used to determine absorption coefficient？

figure a.png

figure b.png

Please give me some advice. Thanks in advance.

[Daniele Varsano]

Dear Tom,
please sign your post with your full name and affiliation, this is a rule of the forum. You can do once all by filling your signature in the user profile.
Next, please post your question in the right subforum, this is another rule of the forum to make it useful to all the users. Your question is not related with compilation issues.

It is not clear from your question if you are dealing with a bulk or a reduced dimensional system. In case you used a cutoff you need to look at the alpha function and not the epsilon.

What is contained in the o.eps_q1_diago_bse file is indeed the dielectric function defined as Eq.11 in the Yambo cheatsheet: https://wiki.yambo-code.eu/wiki/images/ ... et-5.0.pdf

If you get non-zero absorption at zero edge, it could be related to the smearing value you used in the input file, you can try to reduce it. If this is not the case, have a look at the dielectric function and see if it does make sense. If not, you can post here your input/report/output file, and we will have a look.

Best,
Daniele

[tom]

Hi,
I am so sorry,i come from China, Beijing university.I followed your advice and the problem was solved well, but now there is a problem in the electronic child coupling problem. I use yambo version 5.2.4, and I strictly follow the operation steps of YAMbo official website, and this error occurs here after calculation, and the error is still the same after replacing a server,I tried with QE 7.0 with npool 2. It generates elph_dir and all the s.dbph files, but fails to generate gkkp matrices when ypp_ph is executed (note force_symmorphic=.true. warning is a bug in this case):

Code: Select all

<---> [06] == Electron-Phonon Databases ==
<---> Inspecting databases ...
<---> ELPH databases: phonon frequencies and eigenvectors | | [000%] --(E) --(X)
<---> ELPH databases: phonon frequencies and eigenvectors |########################################| [100%] --(E) --(X)
<---> ELPH databases: K+Q-grid check | | [000%] --(E) --(X)
<---> ELPH databases: K+Q-grid check |########################################| [100%] --(E) --(X)
<---> [07] == Q-points list in the DBS (iku units) ==
<---> :: Code generator :PWscf
<---> :: DB Kind :dressed
<---> :: Expanded :no
<---> :: Q-points(read) : 7
<---> :: Q-points(written) : 7
<---> :: K-points : 4
<---> :: Bands (all) : 40
<---> :: Bands (loading) : 1 40
<---> :: Branches : 6
<---> :: Uniform sampling :yes
<---> :: Symmetry expanded :no
<---> :: Debye Energy : 193.5768 [meV]
<---> [08] == Q-points list in Yambo (iku units) ==


<---> ELPH databases: transfer and I/O | | [000%] --(E) --(X)
[ERROR] STOP signal received while in[08] == Q-points list in Yambo (iku units) ==
[ERROR] Error expanding GKKP: please set force_symmorphic=.true. in NSCF and nk=1 in DVSCF calculation

Regards,
Sitangshu

[claudio]

Dear Sitangshu

may you put all input file you used in your calculations in the forum.
Another thing, did you parallelized on k-points in the DVSCF calculation?
ph.x -nk 3
if it is this the case please do not use this parallelization

let me know
best
Claudio

[tom]

Thank you very much for your reply. I didn't understand what you meant by parallelization. I will put the script I submitted on it. In addition, I encountered parallel problems when calculating the electron phonon coupling, but I did not know how to set parallel, because I did not generate yambo input file in the step of electron phonon coupling, so I used yambo version 5.0.4, but this error occurred when calculating BSE, and then the calculation stopped. Here I have a few questions to ask you, 1. When will parallel computing be set? Is it added in the input file.in or in the script? How do I add these parallel parameters? I didn't see it in the tutorial, does my current version 5.0.4 work with parallel computing?

#!/bin/bash
#SBATCH -n 64 # Number of tasks to be launched
#SBATCH -N 1 #Node count required for the job
#SBATCH -p standard # Queue

# 执行任务
## 载入QuantumEspresso
module load QuantumEspresso
mpirun ph.x < dvscf.in > dvscf.out

# 任务结束
echo "Job $SLURM_JOB_ID done at " `date`


#!/bin/bash
#SBATCH -n 64 # Number of tasks to be launched
#SBATCH -N 1 #Node count required for the job
#SBATCH -p standard # Queue

# 执行任务
## 载入QuantumEspresso
module load intel impi
mpirun -np 64 yambo_ph -F yambo.in_BSE -J T300_BSE

# 任务结束
echo "Job $SLURM_JOB_ID done at " `date`

Looking forward to your reply, thank you