Spin-forbidden and momentum-forbidden dark excitons

Run-time issues concerning Yambo that are not covered in the above forums.

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Sumit
Posts: 20
Joined: Wed Jun 09, 2021 12:10 pm

Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Sumit » Tue May 24, 2022 1:20 pm

Dear Daniele sir,

Okay fine if we leave that paper. Then can you please suggest to me how can I proceed to know the better results and determine whether my 2D system consists EI phase or not? Because I already told you that there is a small scissor correction ~ 100meV. And I am using average parameters for exchange and correlation cutoff.
What else can be wrong as shown in the BSE input file in the previous post. And I have used
% LongDrXs
1.000000 | 0.000000 | 0.000000
Should I use 1.000000 | 1.000000 | 0000000 electric field direction?

Suggest me the way to get fine BSE spectra!

Thank you

Regards
Sumit Kukreti
Ph.D. scholar
IIT Jodhpur INDIA

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Daniele Varsano
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Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Daniele Varsano » Tue May 24, 2022 3:05 pm

Dear Sumit,
can you please your report file? (GW and BSE).

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Sumit
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Joined: Wed Jun 09, 2021 12:10 pm

Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Sumit » Wed May 25, 2022 5:18 am

Dear Daniele sir,

I have attached my yambo BSE input file
file.tar.gz
. And the GW calculation were done using Vasp code and found 0.2327 eV indirect gap value. I am using scissor correction in BSE because I found only increased gap in GW and the remaining pattern of band is same as in PBE.

Thank you!

Regards
Sumit Kukreti
Ph.D. Scholar
IIT Jodhpur INDIA
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Daniele Varsano
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Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Daniele Varsano » Wed May 25, 2022 8:57 am

Dear Sumit,
the GW calculation were done using Vasp code
1) OK, note that this could be inaccurate as Vasp probably use different pseudopotential and as far as I know there is no Coulomb truncation technique applied: this reflects in a volume-dependent gap which generally increases wrt the size of the supercell. You should carefully check if the gap found with VASP is converged wrt the vacuum size.

Next about convergences:

Code: Select all

 K-points                                         :  27
2) This should be carefully checked, BSE convergence wrt k point can be slow, and 27 points seems to me a very small number for a 2D material.

Code: Select all

% BSEBands
   27 | 33 |                         # [BSK] Bands range
%
3) Check if 3 conduction bands only are enough to get converged results.

Code: Select all

% BndsRnXs
   1 | 100 |                         # [Xs] Polarization function bands
%
4) Check also if 100 bands are enough for the screening, having 30 occupied bands it is possible you need more empty bands.

Code: Select all

% BSEQptR
 1 | 27 |                             # [BSK] Transferred momenta range
%
5) To check convergences it is no need to calculate the BSE for all the Q points, you can do it just for the optical limit or for the q point corresponding to the indirect gap.

In my opinion points 1,2 are the ones deserving more attention.
Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Sumit
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Joined: Wed Jun 09, 2021 12:10 pm

Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Sumit » Wed May 25, 2022 11:22 am

Dear Daniele sir,

Okay, I will check GW with Yambo. However, I tried it but was taking time and I am unable to run this parallel to our machine.

And as per your suggestion in the point (2) K points: 27 should be increased. So I would like to clarify one thing I have used 15 15 1 mesh and 150 bands but the number 27 kpoints in the irreducible Brillouin zone. So how can I increase this number from 27 ? This is fixed with respect to kmesh.

Thank You

Regards
Sumit Kukreti
Ph.D. scholar
IIT Jodhpur INDIA

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Daniele Varsano
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Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Daniele Varsano » Wed May 25, 2022 1:17 pm

Dear Sumit,
And as per your suggestion in the point (2) K points: 27 should be increased. So I would like to clarify one thing I have used 15 15 1 mesh and 150 bands but the number 27 kpoints in the irreducible Brillouin zone. So how can I increase this number from 27 ? This is fixed with respect to kmesh.
You need to perform a new ground state calculation with a larger grid.
*For GW calculation you can benefit from a new algorithm accelerating k point convergence in 2D material:
http://arxiv.org/abs/2205.11946
Relevant variables are listed in this thread:
viewtopic.php?p=11886#p11886

*What is your problem in running in parallel? I fear that for the system you are studying, to reach convergence parallel calculations are mandatory.

Best,

Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Sumit
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Joined: Wed Jun 09, 2021 12:10 pm

Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Sumit » Wed May 25, 2022 3:20 pm

Dear Daniele sir,

(1) I tried calculation using 11 11 1 and 15 15 1 kesh. In these cases, total k points are 121 and 225 respectively while irreducible kpoint remain 27.
This number is not increasing with increasing mesh.

(2) And as you mentioned in the shared link of the new 2D Coulomb truncation method: in the GW input file the tag for parallelization:

PAR_def_mode= "balanced" # [PARALLEL] Default distribution mode ("balanced"/"memory"/"workload")
X_and_IO_CPU= "1 1 1 16 1" # [PARALLEL] CPUs for each role
X_and_IO_ROLEs= "q g k c v" # [PARALLEL] CPUs roles (q,g,k,c,v)
X_and_IO_nCPU_LinAlg_INV=-1 # [PARALLEL] CPUs for Linear Algebra (if -1 it is automatically set)
X_Threads=0 # [OPENMP/X] Number of threads for response functions
DIP_CPU= "1 16 1" # [PARALLEL] CPUs for each role
DIP_ROLEs= "k c v" # [PARALLEL] CPUs roles (k,c,v)
DIP_Threads=0 # [OPENMP/X] Number of threads for dipoles
SE_CPU= "1 1 16" # [PARALLEL] CPUs for each role
SE_ROLEs= "q qp b" # [PARALLEL] CPUs roles (q,qp,b)
SE_Threads=0

I am unable to specify and understand these tags and that's why I am struggling to run the G0W0 calculation on 32 cores.

Thank you

Regards
Sumit Kukreti
PhD scholar
IIT Jodhpur INDIA

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Daniele Varsano
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Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Daniele Varsano » Thu May 26, 2022 9:41 am

Dear Sumit,

1) This is strange, can you post the QE output file? Note that the kmesh should be changed in the nscf calculation.
2) The input I posted is just an example for a run with 16 mpi, you need to adapt to the resources of your run. The product of the CPU assigned for each role needs to match the number of MPI tasks. Note that this is general for yambo and not related at all to the new cutoff and rimW scheme.

e,g for 32 CPU:

Code: Select all

X_and_IO_CPU= "1 1 1 16 2" # [PARALLEL] CPUs for each role
X_and_IO_ROLEs= "q g k c v" # [PARALLEL] CPUs roles (q,g,k,c,v)
DIP_CPU= "1 16 2" # [PARALLEL] CPUs for each role
DIP_ROLEs= "k c v" # [PARALLEL] CPUs roles (k,c,v)
SE_CPU= "1 1 32" # [PARALLEL] CPUs for each role
SE_ROLEs= "q qp b" # [PARALLEL] CPUs roles (q,qp,b)
Here you can find a tutorial on yambo parallel strategies: http://www.yambo-code.org/wiki/index.ph ... strategies

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Sumit
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Joined: Wed Jun 09, 2021 12:10 pm

Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Sumit » Thu May 26, 2022 1:45 pm

Dear Daniele sir,

I have attached my QE output files.
send.tar.gz
Thank You

Regards
Sumit Kukreti
Ph.D. scholar
IIT Jodhpur
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Daniele Varsano
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Re: Spin-forbidden and momentum-forbidden dark excitons

Post by Daniele Varsano » Thu May 26, 2022 3:22 pm

Dear Sumit,

I was meaning the two different nscf qe output (an input) from the two different grids.
In any case please pay attention to the warning messages from QE:

Code: Select all

     Message from routine setup:
     no reason to have ecutrho>4*ecutwfc
     Message from routine setup:
     using ibrav=0 with symmetry is DISCOURAGED, use correct ibrav instead
Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

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