[gpaw-users] Symmetry?

[Robert Warmbier]

Dear Jens,

I had to look up  what non-symmorphic is, well one always learns something new.

So, apparently, a-quartz has a non-symmorphic space group. So that seems to be the problem.

Thanks for the hint.

Best Robert


________________________________
Von: Jens Jørgen Mortensen [jensj at fysik.dtu.dk]
Gesendet: Dienstag, 5. November 2013 11:58
An: Robert Warmbier; gpaw-users at listserv.fysik.dtu.dk
Betreff: Re: [gpaw-users] Symmetry?

Den 31-10-2013 07:29, Robert Warmbier skrev:
Dear GPAW users and developers,

I was doing some calculations on a-quartz and was suprised to find, that the reduced k-point set of gpaw was rather large. Apparently gpaw found only 2 symmetries to exploit, while vasp found 6, for exactly the same geometry.

Is there a limitiation in gpaw or is my input wrong?

What kind of symmetries are missing?  Could it be that they are of the non-symmorphic type?  GPAW doesn't have those.

Jens Jørgen

Thanks Robert

here the input file:

from ase import Atoms
from gpaw import PW
from gpaw import GPAW, FermiDirac
import numpy as np

name = 'SiO2 a-quartz'

alat = 5.0324636616928924
clat = 5.5210687420867108

posSi1 = 0.4778762817077312

a1 = alat*np.array([1.0, 0.0, 0.0])
a2 = alat*np.array([-0.5, np.sqrt(3)/2, 0.0])
a3 = clat*np.array([0.0, 0.0, 1.0])

cell = np.array([a1,a2,a3])

symbols = ['Si', 'Si', 'Si', 'O','O', 'O', 'O', 'O', 'O']

crystal_positions = [(posSi1,0.0,1./3.),(0.0,posSi1,2./3.),(1-posSi1,1-posSi1,0.0),
                     (0.4153075517143993,  0.2531339614388382,  0.2029892890232297),
                     (0.7468660385611690,  0.1621735892755646,  0.5363226470232412),
                     (0.8378264107244283,  0.5846924482855935,  0.8696559600232383),
                     (0.2531339614388382,  0.4153075517143993,  0.7970107259767609),
                     (0.1621735892755646,  0.7468660385611690,  0.4636773829767684),
                     (0.5846924482855935,  0.8378264107244283,  0.1303440469767658),
                    ]
atoms = Atoms(symbols=symbols,
              scaled_positions=crystal_positions,
              cell=cell,
              pbc = True
              )

# first GS calc
calc = GPAW(mode=PW(ecut=700,cell=cell),
            xc='PBE',
            kpts=(5,5,5),
         #   txt='gs_e700_k5.out',
        #    occupations=FermiDirac(0.05)
            )

atoms.set_calculator(calc)
# Calculate the ground state
energy = atoms.get_potential_energy()
eigenvalues = calc.get_eigenvalues()
print eigenvalues

# Save the ground state
calc.write('gs_e700_k5.gpw', 'all')

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