[Pw_forum] the missing symmetry of bands

Thu Apr 9 11:22:39 CEST 2009

```Thank you for your kindly help!

It is indeed the problem about sufficiency of digital number for pw.x to
find the symmetries.  After changing the atom position to satisfy  the
fractional translation of (0,0,0.5) , pw.x can find all the operation.
2009/4/9 Gabriele Sclauzero <sclauzer at sissa.it>

> Actually the solution was in point (2) of the reply you got by Andrea:
>
>  >     2) Your atomic positions are not sufficiently accurate: the number
> of
>  >     digits is sufficient for pw.x to find the symmetries but the
>  >     wavefunctions are sufficiently inaccurate to confuse the symmetry
>  >     analyzer. (solution: correct your atomic positions)
>
> If you get your position from a relax calculation, most probably it means
> that the
> symmetry of the starting atomic configuration was already C_3v, since
> during the
> relaxations steps the symmetry should be conserved (unless exceptional
> cases).
> So please check the initial symmetry in your relax calculation and
> eventually change the
> starting configuration.
> If you don't want to repeat the calculations you can try to fix the atomic
> positions by
> hand. I think that what you are missing to recover the full symmetry is a
> fractional
> translation of (0,0,0.5) in crystal axis. For instance, the last two Al are
> 0.5002 apart
> along the z direction, instead of 0.500000.
>
> HTH
>
> GS
>
> 程迎春 wrote:
> > Actually the symmetry of 4H-AlN is C_6v, but the pw.x can not find all
> > the 12 operations. So I followed the user's guide Page 60, I changed
> > PW/eqvect.f90. The value of accep is changed to be 10^-3.  The changed
> > pw.x can find all 12 operations.  This change is the reason why you got
> > C_3v symmetry.
> >
> > After I rechanged the value of accep to be 10^-5, pw.x only can find 6
> > operations.  Can you give some additional advices to find other
> operations ?
> >
> > 2009/4/8 Dal Corso Andrea <dalcorso at sissa.it <mailto:dalcorso at sissa.it>>
>  >
> >     On Wed, 2009-04-08 at 19:34 +0800, 程迎春 wrote:
> >      > Dear PWscf users,
> >      >         In my recent calculation of 4H-AlN (ABCB stacking
> sequence),
> >      > the band symmetry seems to be missed in bands.x calculation.  The
> >      > output of bands.x is as following:
> >      >
> >
>  **************************************************************************
> >      >                     xk=(   0.00000,   0.00000,   0.00000  )
> >      >      double point group C_6v (6mm)
> >      >      there are  9 classes and  3 irreducible representations
> >      >      the character table:
> >      >        E     -E     C2    2C3  -2C3   2C6  -2C6   3s_v  3s_d
> >      >                    -C2                           -3s_v -3s_d
> >      > G_7    2.00 -2.00  0.00  1.00 -1.00  1.73 -1.73  0.00  0.00
> >      > G_8    2.00 -2.00  0.00  1.00 -1.00 -1.73  1.73  0.00  0.00
> >      > G_9    2.00 -2.00  0.00 -2.00  2.00  0.00  0.00  0.00  0.00
> >      >      the symmetry operations in each class:
> >      >      E             1
> >      >       C2  -C2      2   -2
> >      >       2C6          3    4
> >      >       2C3          5    6
> >      >       3s_v-3s_v    7   -7    9   10  -10   -9
> >      >       3s_d-3s_d    8   -8   12  -11   11  -12
> >      >      -E           -1
> >      >      -2C6         -3   -4
> >      >      -2C3         -5   -6
> >      >      Band symmetry, C_6v (6mm)  double point group:
> >      >      e(  1 -  2) =     -8.01764  eV     2   -->   ?
> >      >      e(  3 -  4) =     -7.17573  eV     2   -->   ?
> >      >      e(  5 -  6) =     -7.13551  eV     2   -->   ?
> >      >      e(  7 -  8) =     -5.93881  eV     2   -->   ?
> >      >      e(  9 - 10) =      1.12077  eV     2   --> G_7
> >      >      e(  9 - 10) =      1.12077  eV     2   -->   0 G_8
> >      >      e( 11 - 12) =      3.70317  eV     2   -->   0 G_7
> >      >      e( 11 - 12) =      3.70317  eV     2   --> G_8
> >      >      e( 13 - 14) =      3.76782  eV     2   -->   ?
> >      >      e( 15 - 16) =      6.34352  eV     2   -->   ?
> >      >      e( 17 - 18) =      6.35869  eV     2   --> G_9
> >      >      e( 19 - 20) =      6.58061  eV     2   -->   ?
> >      >      e( 21 - 22) =      6.59473  eV     2   --> G_9
> >      >      e( 23 - 24) =      6.65103  eV     2   -->   ?
> >      >      e( 25 - 26) =      6.66500  eV     2   --> G_9
> >      >      e( 27 - 28) =      6.91040  eV     2   -->   ?
> >      >      e( 29 - 30) =      6.92400  eV     2   --> G_9
> >      >      e( 31 - 32) =      7.00967  eV     2   --> G_7
> >      >      e( 31 - 32) =      7.00967  eV     2   -->   0 G_8
> >      >      e( 33 - 34) =     11.19288  eV     2   -->   ?
> >      >      e( 35 - 36) =     13.31415  eV     2   -->   ?
> >      >      e( 37 - 38) =     13.59769  eV     2   -->   ?
> >      >      e( 39 - 40) =     14.02975  eV     2   -->   ?
> >      >      e( 41 - 42) =     17.15974  eV     2   -->   ?
> >      >      e( 43 - 44) =     17.32327  eV     2   -->   ?
> >      >      e( 45 - 46) =     17.92003  eV     2   -->   ?
> >      >
> >
>  **************************************************************************
> >      > My question are :
> >      > 1. what does "?" mean in "  e(  1 -  2) =     -8.01764  eV     2
> >
> >     It means that the symmetry finder is confused. The bands have not a
> >     symmetry that it recognizes.
> >     There are several reasons for this:
> >
> >     1) The 'scf' and 'bands' calculations have been run with slightly
> >     different parameters. (solution: recheck your input)
> >
> >     2) Your atomic positions are not sufficiently accurate: the number of
> >     digits is sufficient for pw.x to find the symmetries but the
> >     wavefunctions are sufficiently inaccurate to confuse the symmetry
> >     analyzer. (solution: correct your atomic positions)
> >
> >     3) If 1) and 2) do not work and you are sure about your coordinates,
> >     then probably there is a bug in the symmetry analyzer. (solution:
> report
> >     to the forum. I will try to solve it if I can).
> >
> >     In your particular case: I am confused. On my PC the symmetry found
> with
> >     your coordinates is C_3v and the symmetry analyzer seems to work. So
> >     atomic positions.
> >
> >     Hope this helps.
> >
> >     Andrea
> >
> >
> >
> >      >  -->   ?"      ?
> >      > 2. what does "0" mean in "     e(  9 - 10) =      1.12077  eV
> 2
> >      > -->   0 G_8" ?
> >      > 3. In 2H-AlN(AB stacking sequence), all the symmetries of bands
> are
> >      > shown. Why in 4H-AlN, it seems much more complicated.
> >      >
> >      > The input files about 4H-AlN for pw.x and bands.x are as
> following:
> >      > scf.in <http://scf.in/>
>  >      > &control
> >      >                     title = 2h_aln,
> >      >                       prefix = '4h_band',
> >      >                  calculation = 'scf' ,
> >      >                 restart_mode = 'from_scratch' ,
> >      >                   wf_collect = .false. ,
> >      >                       outdir = './' ,
> >      >                       wfcdir = './' ,
> >      >                   pseudo_dir = './' ,
> >      >                      tstress = .true. ,
> >      >                      tprnfor = .true. ,
> >      >                    wf_collect = .true. ,
> >      >  /
> >      >  &SYSTEM
> >      >                        ibrav = 4,
> >      >                    celldm(1) = 5.866002785691,
> >      >                    celldm(3) = 3.238615289089,
> >      >                          nat = 8,
> >      >                         ntyp = 2,
> >      >                      ecutwfc = 80,
> >      >                        nbnd  = 46,
> >      >                        nosym = .false. ,
> >      >                      lspinorb = .true.,
> >      >                      noncolin= .true.,
> >      >                    starting_magnetization=0.00,
> >      >  /
> >      >  &ELECTRONS
> >      >             electron_maxstep = 100,
> >      >                     conv_thr = 1.D-10,
> >      >  /
> >      > ATOMIC_SPECIES
> >      >     N   14.00700  N.rel-pbe-rrkjus.UPF
> >      >    Al   26.98200  Al.rel-pbe-rrkj.UPF
> >      > ATOMIC_POSITIONS (crystal)
> >      > N        0.000000000   0.000000000  -0.000722968
> >      > N        0.000000000   0.000000000   0.499277032
> >      > N        0.333333333   0.666666667   0.249293699
> >      > N        0.666666667   0.333333333   0.749293699
> >      > Al       0.000000000   0.000000000   0.188800277
> >      > Al       0.000000000   0.000000000   0.688800277
> >      > Al       0.333333333   0.666666667   0.437593675
> >      > Al       0.666666667   0.333333333   0.937793675
> >      > K_POINTS automatic
> >      >   8 8 8 1 1 1
> >      >
> >      > band.in <http://band.in/>
>  >      > &control
> >      >                       title = 2h_aln,
> >      >                       prefix = '4h_band',
> >      >                  calculation = 'bands' ,
> >      >                 restart_mode = 'from_scratch' ,
> >      >                   wf_collect = .false. ,
> >      >                       outdir = './' ,
> >      >                       wfcdir = './' ,
> >      >                   pseudo_dir = './' ,
> >      >  /
> >      >  &SYSTEM
> >      >                        ibrav = 4,
> >      >                    celldm(1) = 5.866002785691,
> >      >                    celldm(3) = 3.238615289089,
> >      >                          nat = 8,
> >      >                         ntyp = 2,
> >      >                      ecutwfc = 80,
> >      >                      nbnd=46,
> >      >                          lspinorb = .true.,
> >      >                      noncolin= .true.,
> >      >                    starting_magnetization=0.0,
> >      >  /
> >      >  &ELECTRONS
> >      >             electron_maxstep = 100,
> >      >                     conv_thr = 1.D-10,
> >      >  /
> >      > ATOMIC_SPECIES
> >      >     N   14.00700  N.rel-pbe-rrkjus.UPF
> >      >    Al   26.98200  Al.rel-pbe-rrkj.UPF
> >      > ATOMIC_POSITIONS (crystal)
> >      > N        0.000000000   0.000000000  -0.000722968
> >      > N        0.000000000   0.000000000   0.499277032
> >      > N        0.333333333   0.666666667   0.249293699
> >      > N        0.666666667   0.333333333   0.749293699
> >      > Al       0.000000000   0.000000000   0.188800277
> >      > Al       0.000000000   0.000000000   0.688800277
> >      > Al       0.333333333   0.666666667   0.437593675
> >      > Al       0.666666667   0.333333333   0.937793675
> >      > K_POINTS
> >      >          2
> >      >   0.000000  0.000000  0.000000  1.00
> >      >   0.000000  0.000000  0.083333  1.00
> >      >
> >      >
> >      > bands.in <http://bands.in/>
> >      > &inputpp
> >      > prefix='4h_band'
> >      > outdir='./'
> >      > filband='spin.dat'
> >      > lsigma(3)=.true.
> >      > lsym=.true.
> >      > /
> >      >
> >      > Thank you in advance!
> >      >
> >      >
> >      > --
> >      > Y. C. Cheng
> >      > Department of Phyics
> >      > Nanjing University
> >      > Nanjing 210093
> >      > P. R. China
> >      > Tel: 86-25-83592907
> >      > Email: yccheng.nju at gmail.com <mailto:yccheng.nju at gmail.com>
> >      >
> >      > _______________________________________________
> >      > Pw_forum mailing list
> >      > Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org>
> >      > http://www.democritos.it/mailman/listinfo/pw_forum
> >     --
> >     Andrea Dal Corso                    Tel. 0039-040-3787428
> >     SISSA, Via Beirut 2/4               Fax. 0039-040-3787528
> >     34014 Trieste (Italy)               e-mail: dalcorso at sissa.it
> >     <mailto:dalcorso at sissa.it>
> >
> >
> >     _______________________________________________
> >     Pw_forum mailing list
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> >     http://www.democritos.it/mailman/listinfo/pw_forum
> >
> >
> >
> >
> > --
> > Y. C. Cheng
> > Department of Phyics
> > Nanjing University
> > Nanjing 210093
> > P. R. China
> > Tel: 86-25-83592907
> > Email: yccheng.nju at gmail.com <mailto:yccheng.nju at gmail.com>
> >
> >
> > ------------------------------------------------------------------------
> >
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> > http://www.democritos.it/mailman/listinfo/pw_forum
>
> --
>
>
> o ------------------------------------------------ o
> | Gabriele Sclauzero, PhD Student                  |
> | c/o:   SISSA & CNR-INFM Democritos,              |
> |        via Beirut 2-4, 34014 Trieste (Italy)     |
> | email: sclauzer at sissa.it                         |
> | phone: +39 040 3787 511                          |
> | skype: gurlonotturno                             |
> o ------------------------------------------------ o
>  _______________________________________________
> Pw_forum mailing list
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>

--
Y. C. Cheng
Department of Physics
Nanjing University
Nanjing 210093
P. R. China
Tel: 86-25-83592907
Email: yccheng.nju at gmail.com
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