Dear developers:
I have a problem related to the convergence test. Take bulk hBN as an example, I first generate the SAVE data with a kmesh 6 times 6 times 2, then based on this database I perform a series of convergence test related GW calculation (or BSE calculation). Then I obtained reasonable parameters to converge GW gap. Once these parameters I have got, the last convergence test should be done with different PW NSCF kmesh. My question is the new NSCF kmesh will affect previous converged variables?
convergence relation between PW NSCF kmesh and GW or BSE?
Moderators: Davide Sangalli, Daniele Varsano

 Posts: 34
 Joined: Tue May 07, 2019 9:53 am
convergence relation between PW NSCF kmesh and GW or BSE?
Dr. Longjun Xiang
School of Physical Science and Technology, ShanghaiTech University, China
School of Physical Science and Technology, ShanghaiTech University, China
 Daniele Varsano
 Posts: 3076
 Joined: Tue Mar 17, 2009 2:23 pm
 Contact:
Re: convergence relation between PW NSCF kmesh and GW or BS
Dear Longjun Xiang,
while the number of bands and dimension of the screening matrix are linked to each other, the k point dependency is rather independent of the other parameters, so you can maintain the convergence parameter found with the lower sampling.
Best,
Daniele
while the number of bands and dimension of the screening matrix are linked to each other, the k point dependency is rather independent of the other parameters, so you can maintain the convergence parameter found with the lower sampling.
Best,
Daniele
Dr. Daniele Varsano
S3CNR Institute of Nanoscience and MaX Center, Italy
MaX  Materials design at the Exascale
http://www.nano.cnr.it
http://www.maxcentre.eu/
S3CNR Institute of Nanoscience and MaX Center, Italy
MaX  Materials design at the Exascale
http://www.nano.cnr.it
http://www.maxcentre.eu/

 Posts: 34
 Joined: Tue May 07, 2019 9:53 am
Re: convergence relation between PW NSCF kmesh and GW or BS
OK, many thanks for your .
Rather than using your Yambopy module, I have written a series of python scripts to perform convergence tests. The following is my strategy (GW runlevel):
1.QE scf (keep converged at DFT level)
2.QE nscf with the lowest DFT converged kmesh and generate SAVE database.
3.GW_setup
a.initializing
b.find the Kpoint where the direct band gap is minimum. In the following, I will test the gap (LUMOHOMO) convergence at this KPOINT.
4.GW_SIGMAX
a.convergence test for variable EXXRLvcs
5.GW_SIGMAC
a.convergence test for variable NGsBlkXp and BndsRnXp with fixed EXXRLvcs
b.convergence test for variable GbndRange with fixed NGsBlkXp, BndsRnXp and EXXRLvcs
5.GW_KMESH
Based on previous converged tags, I will perform the convergence test for different nscf Kmesh. But now I cannot pick up the same Kpoint to do the test. Do I need to calculate all the Kpoints and then pick up the global minimum band gap for different nscf Kmesh as the parameter to identify convergence? Or is there any other method to reduce computational cost?
Rather than using your Yambopy module, I have written a series of python scripts to perform convergence tests. The following is my strategy (GW runlevel):
1.QE scf (keep converged at DFT level)
2.QE nscf with the lowest DFT converged kmesh and generate SAVE database.
3.GW_setup
a.initializing
b.find the Kpoint where the direct band gap is minimum. In the following, I will test the gap (LUMOHOMO) convergence at this KPOINT.
4.GW_SIGMAX
a.convergence test for variable EXXRLvcs
5.GW_SIGMAC
a.convergence test for variable NGsBlkXp and BndsRnXp with fixed EXXRLvcs
b.convergence test for variable GbndRange with fixed NGsBlkXp, BndsRnXp and EXXRLvcs
5.GW_KMESH
Based on previous converged tags, I will perform the convergence test for different nscf Kmesh. But now I cannot pick up the same Kpoint to do the test. Do I need to calculate all the Kpoints and then pick up the global minimum band gap for different nscf Kmesh as the parameter to identify convergence? Or is there any other method to reduce computational cost?
Dr. Longjun Xiang
School of Physical Science and Technology, ShanghaiTech University, China
School of Physical Science and Technology, ShanghaiTech University, China
 Daniele Varsano
 Posts: 3076
 Joined: Tue Mar 17, 2009 2:23 pm
 Contact:
Re: convergence relation between PW NSCF kmesh and GW or BS
Dear Dr. Longjun Xiang,
If you want instead to look directly to k points near the minimum, maybe you can check the convergence on the correction to the KS gap instead that on the QP energy gap itself.
Best,
Daniele
What you can do is to perform convergence tests on a point common to all the grid (e.g. gamma) and once the calculation is converged use that grid to calculate the minimum gap. Note that if the "real minimum" is not contained in the mesh, you can always interpolate your bands.But now I cannot pick up the same Kpoint to do the test. Do I need to calculate all the Kpoints and then pick up the global minimum band gap for different nscf Kmesh as the parameter to identify convergence? Or is there any other method to reduce computational cost?
If you want instead to look directly to k points near the minimum, maybe you can check the convergence on the correction to the KS gap instead that on the QP energy gap itself.
Best,
Daniele
Dr. Daniele Varsano
S3CNR Institute of Nanoscience and MaX Center, Italy
MaX  Materials design at the Exascale
http://www.nano.cnr.it
http://www.maxcentre.eu/
S3CNR Institute of Nanoscience and MaX Center, Italy
MaX  Materials design at the Exascale
http://www.nano.cnr.it
http://www.maxcentre.eu/

 Posts: 34
 Joined: Tue May 07, 2019 9:53 am
Re: convergence relation between PW NSCF kmesh and GW or BS
Thanks for your quick reply. I found the first point always be Gamma point according to the NSCF output file.
Dr. Longjun Xiang
School of Physical Science and Technology, ShanghaiTech University, China
School of Physical Science and Technology, ShanghaiTech University, China

 Posts: 169
 Joined: Sat Aug 17, 2019 2:48 pm
Re: convergence relation between PW NSCF kmesh and GW or BSE?
Dear developers, I hope all of you are doing well!
I want to ask about a parameter used in BSE convergence used the Yambopy convergence tutorial, "BSEEhEny"
Q1: Does it have to be mentioned in the input file explicitly? In the tutorial, it is mentioned that it is similar to BSEBands? So, if I have done convergence w.r.t. BSEBands then I don't need BSEEhEny anymore? Right?
Q2: BSEEhEny is in the unit of energy and its syntax is in pair as,
So, even if I opt to go with BSEEhEny, then how should I provide the energy range (since it is not the spectrum energy range)? It must be some sort of cutoff?
Thanks,
I want to ask about a parameter used in BSE convergence used the Yambopy convergence tutorial, "BSEEhEny"
Q1: Does it have to be mentioned in the input file explicitly? In the tutorial, it is mentioned that it is similar to BSEBands? So, if I have done convergence w.r.t. BSEBands then I don't need BSEEhEny anymore? Right?
Q2: BSEEhEny is in the unit of energy and its syntax is in pair as,
Code: Select all
% BSEEhEny
0.000000 0.000000  eV # [BSK] Electronhole energy range
%
Thanks,
Haseeb Ahmad
MS  Physics,
LUMS  Pakistan
MS  Physics,
LUMS  Pakistan
 Daniele Varsano
 Posts: 3076
 Joined: Tue Mar 17, 2009 2:23 pm
 Contact:
Re: convergence relation between PW NSCF kmesh and GW or BSE?
Dear Haseeb,
BSEBands and BSEEhEny are alternative.
I suggest you use BSEBands.
When using BSEEhEny you provide and energy windows (Emin and Emax) and all the bands such that Emin < EcEv < Emax are included in the BSE matrix building.
Best,
Daniele
BSEBands and BSEEhEny are alternative.
I suggest you use BSEBands.
When using BSEEhEny you provide and energy windows (Emin and Emax) and all the bands such that Emin < EcEv < Emax are included in the BSE matrix building.
Best,
Daniele
Dr. Daniele Varsano
S3CNR Institute of Nanoscience and MaX Center, Italy
MaX  Materials design at the Exascale
http://www.nano.cnr.it
http://www.maxcentre.eu/
S3CNR Institute of Nanoscience and MaX Center, Italy
MaX  Materials design at the Exascale
http://www.nano.cnr.it
http://www.maxcentre.eu/