Not sure I understand the problem: if k is a Bloch vector and G a
reciprocal-lattice vector, k+G is equivalent to k. This property can be
used to reduce the number of inequivalent k-points needed for the sum
over the (irreducible) Brillouin Zone
Paolo
On 10/02/2025 14:13, Lukas Cvitkovich wrote:
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Dear QE users and developers,
I am currently trying to reproduce the construction of an irreducible k-
point set as done by QE.
For this, I set "verbosity = high" to get the symmetry operations
printed in the output file.
I start from a uniform k-point mesh. Then, using the same symmetry
operations as QE, I transform every k-point and fold it back in the
first Brillouin zone.
If the resulting k-point falls on another k-point of the uniform grid,
it is NOT irreducible.
In this manner, as also described by Blöchl et al (Phys. Rev. B *49*,
16223, 1994) I find the set of irreducible kpoints.
My code agrees with QE for a simple structure (fcc crystal tested and
verified) but I have problems with a more complicated case (the 2D
magnet FGT).
In this example, 6 symmetry operations are found (see attached QE-output
file).
Starting from a 3x3x3 uniform grid, the irreducible set of kpoints -
according to QE - contains 7 points. However, I find 12 irreducible k-
points.
First, please note, that every point found by QE is also contained in my
set. But I find additional points which (according to QE) should be
related by some symmetry operation. By looking at the weights, I could
figure out which kpoints should belong together.
For instance: According to QE, the kpoints [1/3, 0, 0] and [2/3, 0, 0]
are equivalent, as well as [0, 0, 1/3] and [0, 0, 2/3] should be
equivalent too. I recognized that all the extra points could be
transformed into each other by translating the lattice. However,
applying all the symmetry operations from the QE output file (these are
exclusively rotations and not translations), I cannot transform these
points into each other. You might try for yourself.
So the question that I would like to ask is: Are there any "hidden"
symmetry operations which are not explicitly printed in the output file?
Could fractional translations be the reason? Is it maybe related to
differences between point group and space group? Any other hints to what
I am missing?
Thank you! Your help would be highly appreciated!
Best,
Lukas
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--
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 206, 33100 Udine Italy, +39-0432-558216
_______________________________________________________________________________
The Quantum ESPRESSO Foundation stands in solidarity with all civilians
worldwide who are victims of terrorism, military aggression, and indiscriminate
warfare.
--------------------------------------------------------------------------------
Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
users mailing list [email protected]
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