On Wed, 2009-04-08 at 19:34 +0800, ??? 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