[Pw_forum] the missing symmetry of bands
Dal Corso Andrea
dalcorso at sissa.it
Thu Apr 9 10:23:38 CEST 2009
On Thu, 2009-04-09 at 15:53 +0800, 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 ?
If you want to classify the bands with C_6v symmetry you need
coordinates that have C_6v symmetry. Probably, you have to check your
coordinates by writing a small code and change the coordinates that
break the symmetry. Are you sure that you started vc-relax
with coordinates that had C_6v symmetry? I think that in this case you
should obtain final coordinates with the same symmetry. If it is
vc-relax that breaks the symmetry then, please, report the input of
vc-relax because this should not happen. However I am not an expert on
this part of QE, so maybe somebody else will look into this.
Andrea
>
>
> 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
> _______________________________________________
> 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
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