[Pw_forum] the missing symmetry of bands
Dal Corso Andrea
dalcorso at sissa.it
Wed Apr 8 14:49:58 CEST 2009
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
>
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--
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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