the total number of k point in the full BZ

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the total number of k point in the full BZ

Postby sky-zhou » Mon Feb 19, 2018 4:36 pm

I am new to quantum espresso and yambo, but has some experience with abinit and DP codes. Recently, I find something that is wired to me:

I start from LDA+U, giving the k point grid as 4 4 4 0 0 0 (Gamma centered 4x4x4 grid) in QE that should give 64 k points in the full BZ (12 k points in the Irreducible part BZ), however, yambo finds only 58 k points in the FBZ. When I changed to LDA calculation of Si, giving the same k grid, yambo finds the correct number 64 for the FBZ....

I attached " r_setup" file from the LDA+U calculation to make my question clear.


Can someone tell me the reason? Maybe it is better to tell me how does yambo find the kpoints in FBZ from the k points in IBZ using the symmetry, e.g., tell me the routine where this is done.

Many thanks!

Cheers,

Sky
Jianqiang Sky ZHOU
Institut des NanoSciences de Paris (INSP)
European Theoretical Spectroscopy Facility
sky-zhou
 
Posts: 8
Joined: Mon Feb 19, 2018 12:32 pm

Re: the total number of k point in the full BZ

Postby Daniele Varsano » Thu Feb 22, 2018 3:38 pm

Dear Sky,
-please note the r_setup is not attached.
-yambo at the moment does not support DFT+U calculation as starting point: we are working on that but at the moment it is not supported
-yambo reads the K points in the IBZ and symmetries from QE, from that reconstruct the points in the BZ. Please note that non-symmorphic symmetries are not supported.

You can compare if all the symmetries of PW are correctly reported in the yambo report.

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/
User avatar
Daniele Varsano
 
Posts: 2027
Joined: Tue Mar 17, 2009 2:23 pm

Re: the total number of k point in the full BZ

Postby sky-zhou » Thu Feb 22, 2018 5:02 pm

Dear Daniele,

1. I am sorry for the missing file, but now I realize that the problem is in QE instead of yambo... So it does not matter anymore...

2. I understand your concern about DFT+U but as far as I know, it only matters at q=0 limit because yamboo needs the commutator to the Hamiltonian which contains U. All the rest q values should be safe, right? I hope you can confirm that so I will be able to calculate some chi at q!= 0 .

3. The problem now is that the symmetries report by QE is not complete.... I am working on that these days, and find that QE report 12 symmetries but what it actually uses to get the inequivalent k poitns are 23 symmetries....maybe because of +k and -k problem.... I do not know the reason yet but trying to figure out this point.

4. I put force_symmorphic in QE calculation so that the non-symmorphic symmetries are not taken into account in QE.

Many thanks!

Sky




Daniele Varsano wrote:Dear Sky,
-please note the r_setup is not attached.
-yambo at the moment does not support DFT+U calculation as starting point: we are working on that but at the moment it is not supported
-yambo reads the K points in the IBZ and symmetries from QE, from that reconstruct the points in the BZ. Please note that non-symmorphic symmetries are not supported.

You can compare if all the symmetries of PW are correctly reported in the yambo report.

Best,

Daniele
Jianqiang Sky ZHOU
Institut des NanoSciences de Paris (INSP)
European Theoretical Spectroscopy Facility
sky-zhou
 
Posts: 8
Joined: Mon Feb 19, 2018 12:32 pm

Re: the total number of k point in the full BZ

Postby Daniele Varsano » Thu Feb 22, 2018 6:06 pm

Dear Sky,

Code: Select all
2. I understand your concern about DFT+U but as far as I know, it only matters at q=0 limit because yamboo needs the commutator to the Hamiltonian which contains U. All the rest q values should be safe, right? I hope you can confirm that so I will be able to calculate some chi at q!= 0 .

It depends on what you need to calculate. If you are interested in linear response it should be sage, but if you need to do a GW calculation then you need to subctract from the self energy the U contribution to each KS state and this part needs coding we are planning to do in the next days/months.

About symmetry problem you can check in the r_setup if yambo recognize that there is the time reversal symmetry.

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/
User avatar
Daniele Varsano
 
Posts: 2027
Joined: Tue Mar 17, 2009 2:23 pm

Re: the total number of k point in the full BZ

Postby sky-zhou » Fri Feb 23, 2018 9:53 am

Dear Daniele,

Thank you very much for your explanation. At this moment I think I will only do a linear response RPA calculation. If I want to do GW, I will start from LDA but not LDA+U...

I have checked carefully the time reversal symmetry in QE code, it does not make any difference on this problem.... Actually, I will use shifted grid or double grid such that symmetry will not be used, so at this moment, it is fine to run calculations. But I will also try to figure out what is happening when a non-shifted grid is used.

Cheers,

Sky


Daniele Varsano wrote:Dear Sky,

Code: Select all
2. I understand your concern about DFT+U but as far as I know, it only matters at q=0 limit because yamboo needs the commutator to the Hamiltonian which contains U. All the rest q values should be safe, right? I hope you can confirm that so I will be able to calculate some chi at q!= 0 .

It depends on what you need to calculate. If you are interested in linear response it should be sage, but if you need to do a GW calculation then you need to subctract from the self energy the U contribution to each KS state and this part needs coding we are planning to do in the next days/months.

About symmetry problem you can check in the r_setup if yambo recognize that there is the time reversal symmetry.

Best,

Daniele
Jianqiang Sky ZHOU
Institut des NanoSciences de Paris (INSP)
European Theoretical Spectroscopy Facility
sky-zhou
 
Posts: 8
Joined: Mon Feb 19, 2018 12:32 pm


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