[Pw_forum] Question about the band symmetry analysis in space group P63/mmc

[Paolo Giannozzi]

This is what I get with your input:

     12 Sym. Ops., with inversion, found
          (note: 12 additional sym.ops. were found but ignored
           their fractional translations are incommensurate with FFT grid)

while with option "use_all_frac=.true.", or by setting the FFT grid to
nr1=50, nr2=50, nr3=80:

     24 Sym. Ops., with inversion, found (12 have fractional translation)

Paolo

On Wed, May 25, 2016 at 8:36 PM, Qihang Liu <qihang.liu85 at gmail.com> wrote:

> Dear all,
>
> I am struggling with the band symmetry analysis on a structure with a
> space group #194 P63/mmc (D_6h^4). I use the tag space_group to define it
> so I suppose the space group can be realized correctly by pwscf. As we
> know, the little group of Gamma point should follow the group of the
> crystal structure which is also D_6h. The the output of QE is D_3d. Please
> see the following input and outputs:
>
> scf.in
>  &control
>     prefix='bulk',
>     pseudo_dir='./'
>     outdir = './',
>     wf_collect = .true.,
>  /
>  &system
>     ibrav=  4,
>     celldm(1)=   8.568018,  celldm(3)=   1.660013, space_group = 194
>     nat=  3, ntyp= 3, nbnd = 48,
>     ecutwfc = 36.0, ecutrho = 320.0,
>     lspinorb = .true., noncolin = .true.,
>     occupations='smearing', smearing='gaussian', degauss=0.02,
>  /
>  &electrons
>   diagonalization='david',
>   conv_thr = 1.0e-8,
>   mixing_beta = 0.7,
>  /
> ATOMIC_SPECIES
>   Li 6.941 Li.rel-pbe-s-kjpaw_psl.0.2.1.UPF
>   Hg 200.5 Hg.rel-pbe-dn-kjpaw_psl.0.2.2.UPF
>   As 74.922 As.rel-pbe-n-kjpaw_psl.0.2.UPF
> ATOMIC_POSITIONS crystal_sg
> Li  0.0000000000000000  0.0000000000000000  0.0000000000000000
> Hg  0.3333333300000021  0.6666666699999979  0.2500000000000000
> As  0.6666666699999979  0.3333333300000021  0.2500000000000000
> K_POINTS automatic
>   9 9 6 0 0 0
>
> nscf.in
>  &control
>     calculation = 'nscf'
>     prefix='bulk',
>     pseudo_dir='./'
>     outdir = './',
>     wf_collect = .true.,
>  /
>  &system
>     ibrav=  4,
>     celldm(1)=   8.568018, celldm(3)=   1.660013, space_group = 194
>     nat=  3, ntyp= 3, nbnd = 48,
>     ecutwfc = 36.0, ecutrho = 320.0,
>     lspinorb = .true., noncolin = .true.,
>     occupations='smearing', smearing='gaussian', degauss=0.02,
>  /
>  &electrons
>   diagonalization='david',
>   conv_thr = 1.0e-8,
>   mixing_beta = 0.7,
>  /
> ATOMIC_SPECIES
>   Li 6.941 Li.rel-pbe-s-kjpaw_psl.0.2.1.UPF
>   Hg 200.5 Hg.rel-pbe-dn-kjpaw_psl.0.2.2.UPF
>   As 74.922 As.rel-pbe-n-kjpaw_psl.0.2.UPF
> ATOMIC_POSITIONS crystal_sg
> Li  0.0000000000000000  0.0000000000000000  0.0000000000000000
> Hg  0.3333333300000021  0.6666666699999979  0.2500000000000000
> As  0.6666666699999979  0.3333333300000021  0.2500000000000000
> K_POINTS crystal_b
>   3
>   0 0 0 30  ! Gamma
>   0 0 0.5 30 ! A
>   0.5 0 0.5 1 ! L
>
> bands.in
>  &bands
>     prefix  = 'bulk',
>     outdir='./',
>     filband = 'bands.dat',
>     lsym = .true.,
>  /
>
> Output:
>  **************************************************************************
>
>                     xk=(   0.00000,   0.00000,   0.00000  )
>
>      double point group D_3d (-3m)
>      there are 12 classes and  6 irreducible representations
>      the character table:
>
>        E     -E    2C3   -2C3  3C2'  -3C2' i     -i    2S6   -2S6  3s_v
>  -3s_v
>
> G_4+   2.00 -2.00  1.00 -1.00  0.00  0.00  2.00 -2.00  1.00 -1.00  0.00
>  0.00
> G_5+   1.00 -1.00 -1.00  1.00  0.00  0.00  1.00 -1.00 -1.00  1.00  0.00
>  0.00
> G_6+   1.00 -1.00 -1.00  1.00  0.00  0.00  1.00 -1.00 -1.00  1.00  0.00
>  0.00
> G_4-   2.00 -2.00  1.00 -1.00  0.00  0.00 -2.00  2.00 -1.00  1.00  0.00
>  0.00
> G_5-   1.00 -1.00 -1.00  1.00  0.00  0.00 -1.00  1.00  1.00 -1.00  0.00
>  0.00
> G_6-   1.00 -1.00 -1.00  1.00  0.00  0.00 -1.00  1.00  1.00 -1.00  0.00
>  0.00
>
> Can anyone help me to explain the inconsistency? Is is related to some
> non-symmophic symmetries that QE can not deal with? Thanks a lot.
>
> Best,
>
> Qihang Liu
>
> Research Associate
> Renewable and Sustainable Energy Institute (RASEI)
> University of Colorado Boulder
> Boulder, CO 80309-029 USA
> https://www.colorado.edu/zunger-materials-by-design/qihang-liu
>
>
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>



-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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