Author Topic: Symmetry detection problem: only the time reversal symemtry applies  (Read 59 times)

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Offline Dongzhe

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Dear ATK experts,

As a new user, I have a basic question concerning the symmetry operations for the nb of irreducible k-points.

I just runned the test example of Si bulk with 9x9x9 k-points (see the basic parameters below), however, the code only detects the time-reversal symmetry, thus Number of irreducible k-points: 365...

Can u explain why?

Thanks,
Dongzhe

PS: If I specify explicitly in MPgrid the symmetries by hand, I can reduce the k but this is rather impractical.

----------------------------
# Set up lattice
lattice = FaceCenteredCubic(5.4306*Angstrom)

# Define elements
elements = [Silicon, Silicon]

# Define coordinates
fractional_coordinates = [[ 0.  ,  0.  ,  0.  ],
                          [ 0.25,  0.25,  0.25]]

k_point_sampling = MonkhorstPackGrid(
    na=9,
    nb=9,
    nc=9,
    )
------------------------

Offline Anders Blom

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We have not yet implemented symmetry reduction for the main SCF loop in the LCAO code because it's technically a bit harder than with planewaves. We use solid harmonics, and the phase relationships when you apply the symmetry operations are not so trivial.

If you use the PlaneWave calculator in QuantumATK you will see that it does use symmetry reduction.