<div>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. </div>
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<div>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 ?<br><br></div>
<div class="gmail_quote">2009/4/8 Dal Corso Andrea <span dir="ltr"><<a href="mailto:dalcorso@sissa.it">dalcorso@sissa.it</a>></span><br>
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<div class="h5">On Wed, 2009-04-08 at 19:34 +0800, 程迎春 wrote:<br>> Dear PWscf users,<br>> In my recent calculation of 4H-AlN (ABCB stacking sequence),<br>> the band symmetry seems to be missed in bands.x calculation. The<br>
> output of bands.x is as following:<br>> **************************************************************************<br>> xk=( 0.00000, 0.00000, 0.00000 )<br>> double point group C_6v (6mm)<br>
> there are 9 classes and 3 irreducible representations<br>> the character table:<br>> E -E C2 2C3 -2C3 2C6 -2C6 3s_v 3s_d<br>> -C2 -3s_v -3s_d<br>
> G_7 2.00 -2.00 0.00 1.00 -1.00 1.73 -1.73 0.00 0.00<br>> G_8 2.00 -2.00 0.00 1.00 -1.00 -1.73 1.73 0.00 0.00<br>> G_9 2.00 -2.00 0.00 -2.00 2.00 0.00 0.00 0.00 0.00<br>> the symmetry operations in each class:<br>
> E 1<br>> C2 -C2 2 -2<br>> 2C6 3 4<br>> 2C3 5 6<br>> 3s_v-3s_v 7 -7 9 10 -10 -9<br>> 3s_d-3s_d 8 -8 12 -11 11 -12<br>
> -E -1<br>> -2C6 -3 -4<br>> -2C3 -5 -6<br>> Band symmetry, C_6v (6mm) double point group:<br>> e( 1 - 2) = -8.01764 eV 2 --> ?<br>> e( 3 - 4) = -7.17573 eV 2 --> ?<br>
> e( 5 - 6) = -7.13551 eV 2 --> ?<br>> e( 7 - 8) = -5.93881 eV 2 --> ?<br>> e( 9 - 10) = 1.12077 eV 2 --> G_7<br>> e( 9 - 10) = 1.12077 eV 2 --> 0 G_8<br>
> e( 11 - 12) = 3.70317 eV 2 --> 0 G_7<br>> e( 11 - 12) = 3.70317 eV 2 --> G_8<br>> e( 13 - 14) = 3.76782 eV 2 --> ?<br>> e( 15 - 16) = 6.34352 eV 2 --> ?<br>
> e( 17 - 18) = 6.35869 eV 2 --> G_9<br>> e( 19 - 20) = 6.58061 eV 2 --> ?<br>> e( 21 - 22) = 6.59473 eV 2 --> G_9<br>> e( 23 - 24) = 6.65103 eV 2 --> ?<br>
> e( 25 - 26) = 6.66500 eV 2 --> G_9<br>> e( 27 - 28) = 6.91040 eV 2 --> ?<br>> e( 29 - 30) = 6.92400 eV 2 --> G_9<br>> e( 31 - 32) = 7.00967 eV 2 --> G_7<br>
> e( 31 - 32) = 7.00967 eV 2 --> 0 G_8<br>> e( 33 - 34) = 11.19288 eV 2 --> ?<br>> e( 35 - 36) = 13.31415 eV 2 --> ?<br>> e( 37 - 38) = 13.59769 eV 2 --> ?<br>
> e( 39 - 40) = 14.02975 eV 2 --> ?<br>> e( 41 - 42) = 17.15974 eV 2 --> ?<br>> e( 43 - 44) = 17.32327 eV 2 --> ?<br>> e( 45 - 46) = 17.92003 eV 2 --> ?<br>
> **************************************************************************<br>> My question are :<br>> 1. what does "?" mean in " e( 1 - 2) = -8.01764 eV 2<br><br></div></div>It means that the symmetry finder is confused. The bands have not a<br>
symmetry that it recognizes.<br>There are several reasons for this:<br><br>1) The 'scf' and 'bands' calculations have been run with slightly<br>different parameters. (solution: recheck your input)<br><br>2) Your atomic positions are not sufficiently accurate: the number of<br>
digits is sufficient for pw.x to find the symmetries but the<br>wavefunctions are sufficiently inaccurate to confuse the symmetry<br>analyzer. (solution: correct your atomic positions)<br><br>3) If 1) and 2) do not work and you are sure about your coordinates,<br>
then probably there is a bug in the symmetry analyzer. (solution: report<br>to the forum. I will try to solve it if I can).<br><br>In your particular case: I am confused. On my PC the symmetry found with<br>your coordinates is C_3v and the symmetry analyzer seems to work. So<br>
please recheck your run. If you still find C_6v please recheck your<br>atomic positions.<br><br>Hope this helps.<br><br>Andrea<br>
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<div class="h5"><br><br><br>> --> ?" ?<br>> 2. what does "0" mean in " e( 9 - 10) = 1.12077 eV 2<br>> --> 0 G_8" ?<br>> 3. In 2H-AlN(AB stacking sequence), all the symmetries of bands are<br>
> shown. Why in 4H-AlN, it seems much more complicated.<br>><br>> The input files about 4H-AlN for pw.x and bands.x are as following:<br>> <a href="http://scf.in/" target="_blank">scf.in</a><br>> &control<br>
> title = 2h_aln,<br>> prefix = '4h_band',<br>> calculation = 'scf' ,<br>> restart_mode = 'from_scratch' ,<br>
> wf_collect = .false. ,<br>> outdir = './' ,<br>> wfcdir = './' ,<br>> pseudo_dir = './' ,<br>> tstress = .true. ,<br>
> tprnfor = .true. ,<br>> wf_collect = .true. ,<br>> /<br>> &SYSTEM<br>> ibrav = 4,<br>> celldm(1) = 5.866002785691,<br>
> celldm(3) = 3.238615289089,<br>> nat = 8,<br>> ntyp = 2,<br>> ecutwfc = 80,<br>> nbnd = 46,<br>
> nosym = .false. ,<br>> lspinorb = .true.,<br>> noncolin= .true.,<br>> starting_magnetization=0.00,<br>> /<br>> &ELECTRONS<br>
> electron_maxstep = 100,<br>> conv_thr = 1.D-10,<br>> /<br>> ATOMIC_SPECIES<br>> N 14.00700 N.rel-pbe-rrkjus.UPF<br>> Al 26.98200 Al.rel-pbe-rrkj.UPF<br>> ATOMIC_POSITIONS (crystal)<br>
> N 0.000000000 0.000000000 -0.000722968<br>> N 0.000000000 0.000000000 0.499277032<br>> N 0.333333333 0.666666667 0.249293699<br>> N 0.666666667 0.333333333 0.749293699<br>
> Al 0.000000000 0.000000000 0.188800277<br>> Al 0.000000000 0.000000000 0.688800277<br>> Al 0.333333333 0.666666667 0.437593675<br>> Al 0.666666667 0.333333333 0.937793675<br>
> K_POINTS automatic<br>> 8 8 8 1 1 1<br>><br>> <a href="http://band.in/" target="_blank">band.in</a><br>> &control<br>> title = 2h_aln,<br>> prefix = '4h_band',<br>
> calculation = 'bands' ,<br>> restart_mode = 'from_scratch' ,<br>> wf_collect = .false. ,<br>> outdir = './' ,<br>
> wfcdir = './' ,<br>> pseudo_dir = './' ,<br>> /<br>> &SYSTEM<br>> ibrav = 4,<br>> celldm(1) = 5.866002785691,<br>
> celldm(3) = 3.238615289089,<br>> nat = 8,<br>> ntyp = 2,<br>> ecutwfc = 80,<br>> nbnd=46,<br>> lspinorb = .true.,<br>
> noncolin= .true.,<br>> starting_magnetization=0.0,<br>> /<br>> &ELECTRONS<br>> electron_maxstep = 100,<br>> conv_thr = 1.D-10,<br>
> /<br>> ATOMIC_SPECIES<br>> N 14.00700 N.rel-pbe-rrkjus.UPF<br>> Al 26.98200 Al.rel-pbe-rrkj.UPF<br>> ATOMIC_POSITIONS (crystal)<br>> N 0.000000000 0.000000000 -0.000722968<br>> N 0.000000000 0.000000000 0.499277032<br>
> N 0.333333333 0.666666667 0.249293699<br>> N 0.666666667 0.333333333 0.749293699<br>> Al 0.000000000 0.000000000 0.188800277<br>> Al 0.000000000 0.000000000 0.688800277<br>
> Al 0.333333333 0.666666667 0.437593675<br>> Al 0.666666667 0.333333333 0.937793675<br>> K_POINTS<br>> 2<br>> 0.000000 0.000000 0.000000 1.00<br>> 0.000000 0.000000 0.083333 1.00<br>
><br>><br>> <a href="http://bands.in/" target="_blank">bands.in</a><br>> &inputpp<br>> prefix='4h_band'<br>> outdir='./'<br>> filband='spin.dat'<br>> lsigma(3)=.true.<br>
> lsym=.true.<br>> /<br>><br>> Thank you in advance!<br>><br>><br>> --<br>> Y. C. Cheng<br>> Department of Phyics<br>> Nanjing University<br>> Nanjing 210093<br>> P. R. China<br>> Tel: 86-25-83592907<br>
> Email: <a href="mailto:yccheng.nju@gmail.com">yccheng.nju@gmail.com</a><br>><br></div></div>> _______________________________________________<br>> Pw_forum mailing list<br>> <a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
> <a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br>--<br>Andrea Dal Corso Tel. 0039-040-3787428<br>SISSA, Via Beirut 2/4 Fax. 0039-040-3787528<br>
34014 Trieste (Italy) e-mail: <a href="mailto:dalcorso@sissa.it">dalcorso@sissa.it</a><br><br><br>_______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>
<a href="http://www.democritos.it/mailman/listinfo/pw_forum" target="_blank">http://www.democritos.it/mailman/listinfo/pw_forum</a><br></blockquote></div><br><br clear="all"><br>-- <br>Y. C. Cheng<br>Department of Phyics<br>
Nanjing University<br>Nanjing 210093<br>P. R. China<br>Tel: 86-25-83592907<br>Email: <a href="mailto:yccheng.nju@gmail.com">yccheng.nju@gmail.com</a><br>