??? 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 ? specify atomic coordinates with a larger number of (correct) digits..
Stefano de Gironcoli - SISSA and DEMOCRITOS > 2009/4/8 Dal Corso Andrea <dalcorso at sissa.it <mailto:dalcorso at sissa.it>> > > 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 <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 > Pw_forum at pwscf.org <mailto:Pw_forum at pwscf.org> > 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> > ------------------------------------------------------------------------ > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum >
