Kpoint indexes in Coulomb matrix elements

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

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Nhat Minh Pham
Posts: 14
Joined: Tue Feb 15, 2022 12:07 am
Location: 01 Mac Dinh Chi, Ben Nghe, District 1, Ho Chi Minh City, Viet Nam

Kpoint indexes in Coulomb matrix elements

Post by Nhat Minh Pham » Fri Mar 11, 2022 7:51 am

Dear developers,

K-points used in Coulomb matrix elements are in full Brillouin zone, I'm wondering if its indexes and values are the same as kmesh.pl (Wannier90 utility)?
As I see in k_expand.f90 and k_build_up_BZ_tables.f90, Yambo uses k-points in ibz and opens it to bz by multiplying k-points in ibz with some symmetry matrices.
With k-points in ibz having - sign and multiplying procedure to expand, I doubt that k-points' indexes and values are equal to the results of kmesh.pl.
If it's not the same can you help me output kpoints' values?

Best,
Minh
Pham Nhat Minh
MS student, Ho Chi Minh University of Science,
Ho Chi Minh City Institute of Physics
https://www.hcmus.edu.vn/

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Daniele Varsano
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Joined: Tue Mar 17, 2009 2:23 pm
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Re: Kpoint indexes in Coulomb matrix elements

Post by Daniele Varsano » Tue Mar 15, 2022 8:39 am

Dear Nhat Minh Pham
here is the answer sent to me by Matteo Zanfrognini (a PhD student at CNR Nano in Modena):

kmesh.pl creates a k grid sampling the full BZ, without considering symmetries of the systems.
Therefore, if you generate a k grid (say nk1,nk2,nk3) with kmesh.pl, this will be different from the k grid used by Yambo, if it is launched on top of an nscf calculation performed over a (nk1,nk2,nk3) "automatic" grid in Quantum Espresso.
Further, also in the case in which you run Quantum Espresso without symmetries (i.e. setting nosym=.true. and noinv = .true. in the nscf input) the k grid generated by QE and then used by Yambo will be different from the grid one can produce with kmesh.pl.
There are two possible ways to read the coordinates of the k points used by Yambo:
1) run the initialization step with the -fatlog option: in this way, the coordinates of all the k and q points used by Yambo will be directly written in the Report file (r_setup);
2) you can use the yambopy routines: if you look inside the class YamboLatticeDB (defined into latticedb.py), the method from_db_file reads the k points from the ns.db1 file written in the SAVE directory.

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/

Nhat Minh Pham
Posts: 14
Joined: Tue Feb 15, 2022 12:07 am
Location: 01 Mac Dinh Chi, Ben Nghe, District 1, Ho Chi Minh City, Viet Nam

Re: Kpoint indexes in Coulomb matrix elements

Post by Nhat Minh Pham » Wed Mar 16, 2022 2:16 am

Dear Daniele,

Thank you very much.
I think K point coordinates in r_setup are in the irreducible Brillouin zone, what I want is K point coordinates which are connected to K point indexes used in Coulomb matrixes.
I think those K points are in the full first Brillouin zone produced by expanding the irreducible Brillouin zone.

Best,
Minh
Pham Nhat Minh
MS student, Ho Chi Minh University of Science,
Ho Chi Minh City Institute of Physics
https://www.hcmus.edu.vn/

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