QuantumATK Forum

QuantumATK => General Questions and Answers => Topic started by: Dongzhe on June 10, 2021, 19:19

Title: Symmetry detection problem: only the time reversal symemtry applies
Post by: Dongzhe on June 10, 2021, 19:19

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,
    )
------------------------

Title: Re: Symmetry detection problem: only the time reversal symemtry applies
Post by: Anders Blom on June 16, 2021, 23:05

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.