[Pw_forum] the missing symmetry of bands

程迎春 yccheng.nju at gmail.com
Thu Apr 9 09:53:51 CEST 2009


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>

>  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
> please recheck your run. If you still find C_6v please recheck your
> 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
> > &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
> > &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
> > &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
> >
> > _______________________________________________
> > Pw_forum mailing list
> > 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
>
>
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
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>



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