<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>
<div>Â </div>
<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>> Â **************************************************************************<br>> Â Â Â Â Â Â Â Â Â Â xk=( Â 0.00000, Â 0.00000, Â 0.00000 Â )<br>> Â Â Â 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 Â Â 2.00 -2.00 Â 0.00 Â 1.00 -1.00 Â 1.73 -1.73 Â 0.00 Â 0.00<br>> G_8 Â Â 2.00 -2.00 Â 0.00 Â 1.00 -1.00 -1.73 Â 1.73 Â 0.00 Â 0.00<br>> G_9 Â Â 2.00 -2.00 Â 0.00 -2.00 Â 2.00 Â 0.00 Â 0.00 Â 0.00 Â 0.00<br>> Â Â Â 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>
> Â Â Â -E Â Â Â Â Â -1<br>> Â Â Â -2C6 Â Â Â Â -3 Â -4<br>> Â Â Â -2C3 Â Â Â Â -5 Â -6<br>> Â Â Â Band symmetry, C_6v (6mm) Â double point group:<br>> Â Â Â e( Â 1 - Â 2) = Â Â -8.01764 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( Â 3 - Â 4) = Â Â -7.17573 Â eV Â Â 2 Â --> Â ?<br>
> Â Â Â e( Â 5 - Â 6) = Â Â -7.13551 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( Â 7 - Â 8) = Â Â -5.93881 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( Â 9 - 10) = Â Â Â 1.12077 Â eV Â Â 2 Â --> G_7<br>> Â Â Â e( Â 9 - 10) = Â Â Â 1.12077 Â eV Â Â 2 Â --> Â 0 G_8<br>
> Â Â Â e( 11 - 12) = Â Â Â 3.70317 Â eV Â Â 2 Â --> Â 0 G_7<br>> Â Â Â e( 11 - 12) = Â Â Â 3.70317 Â eV Â Â 2 Â --> G_8<br>> Â Â Â e( 13 - 14) = Â Â Â 3.76782 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( 15 - 16) = Â Â Â 6.34352 Â eV Â Â 2 Â --> Â ?<br>
> Â Â Â e( 17 - 18) = Â Â Â 6.35869 Â eV Â Â 2 Â --> G_9<br>> Â Â Â e( 19 - 20) = Â Â Â 6.58061 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( 21 - 22) = Â Â Â 6.59473 Â eV Â Â 2 Â --> G_9<br>> Â Â Â e( 23 - 24) = Â Â Â 6.65103 Â eV Â Â 2 Â --> Â ?<br>
> Â Â Â e( 25 - 26) = Â Â Â 6.66500 Â eV Â Â 2 Â --> G_9<br>> Â Â Â e( 27 - 28) = Â Â Â 6.91040 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( 29 - 30) = Â Â Â 6.92400 Â eV Â Â 2 Â --> G_9<br>> Â Â Â e( 31 - 32) = Â Â Â 7.00967 Â eV Â Â 2 Â --> G_7<br>
> Â Â Â e( 31 - 32) = Â Â Â 7.00967 Â eV Â Â 2 Â --> Â 0 G_8<br>> Â Â Â e( 33 - 34) = Â Â 11.19288 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( 35 - 36) = Â Â 13.31415 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( 37 - 38) = Â Â 13.59769 Â eV Â Â 2 Â --> Â ?<br>
> Â Â Â e( 39 - 40) = Â Â 14.02975 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( 41 - 42) = Â Â 17.15974 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( 43 - 44) = Â Â 17.32327 Â eV Â Â 2 Â --> Â ?<br>> Â Â Â e( 45 - 46) = Â Â 17.92003 Â eV Â Â 2 Â --> Â ?<br>
> Â **************************************************************************<br>> My question are :<br>> 1. what does "?" mean in " Â e( Â 1 - Â 2) = Â Â -8.01764 Â eV Â Â 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>> Â --> Â ?" Â Â Â ?<br>> 2. what does "0" mean in " Â Â e( Â 9 - 10) = Â Â Â 1.12077 Â eV Â Â 2<br>> --> Â 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>
> Â Â Â Â Â Â Â Â Â Â title = 2h_aln,<br>> Â Â Â Â Â Â Â Â Â Â Â prefix = '4h_band',<br>> Â Â Â Â Â Â Â Â Â calculation = 'scf' ,<br>> Â Â Â Â Â Â Â Â restart_mode = 'from_scratch' ,<br>
> Â Â Â Â Â Â Â Â Â wf_collect = .false. ,<br>> Â Â Â Â Â Â Â Â Â Â Â outdir = './' ,<br>> Â Â Â Â Â Â Â Â Â Â Â wfcdir = './' ,<br>> Â Â Â Â Â Â Â Â Â pseudo_dir = './' ,<br>> Â Â Â Â Â Â Â Â Â Â Â tstress = .true. ,<br>
> Â Â Â Â Â Â Â Â Â Â Â tprnfor = .true. ,<br>> Â Â Â Â Â Â Â Â Â Â wf_collect = .true. ,<br>> Â /<br>> Â &SYSTEM<br>> Â Â Â Â Â Â Â Â Â Â Â Â ibrav = 4,<br>> Â Â Â Â Â Â Â Â Â Â celldm(1) = 5.866002785691,<br>
>           celldm(3) = 3.238615289089,<br>>              nat = 8,<br>>             ntyp = 2,<br>>            ecutwfc = 80,<br>>             nbnd  = 46,<br>
> Â Â Â Â Â Â Â Â Â Â Â Â nosym = .false. ,<br>> Â Â Â Â Â Â Â Â Â Â Â lspinorb = .true.,<br>> Â Â Â Â Â Â Â Â Â Â Â noncolin= .true.,<br>> Â Â Â Â Â Â Â Â Â Â starting_magnetization=0.00,<br>> Â /<br>> Â &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 Â Â Â Â 0.000000000 Â 0.000000000 Â -0.000722968<br>> N Â Â Â Â 0.000000000 Â 0.000000000 Â 0.499277032<br>> N Â Â Â Â 0.333333333 Â 0.666666667 Â 0.249293699<br>> N Â Â Â Â 0.666666667 Â 0.333333333 Â 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>> Â 8 8 8 1 1 1<br>><br>> <a href="http://band.in/" target="_blank">band.in</a><br>> &control<br>> Â Â Â Â Â Â Â Â Â Â Â title = 2h_aln,<br>> Â Â Â Â Â Â Â Â Â Â Â prefix = '4h_band',<br>
> Â Â Â Â Â Â Â Â Â calculation = 'bands' ,<br>> Â Â Â Â Â Â Â Â restart_mode = 'from_scratch' ,<br>> Â Â Â Â Â Â Â Â Â wf_collect = .false. ,<br>> Â Â Â Â Â Â Â Â Â Â Â outdir = './' ,<br>
> Â Â Â Â Â Â Â Â Â Â Â wfcdir = './' ,<br>> Â Â Â Â Â Â Â Â Â pseudo_dir = './' ,<br>> Â /<br>> Â &SYSTEM<br>> Â Â Â Â Â Â Â Â Â Â Â Â ibrav = 4,<br>> Â Â Â Â Â Â Â Â Â Â celldm(1) = 5.866002785691,<br>
> Â Â Â Â Â Â Â Â Â Â celldm(3) = 3.238615289089,<br>> Â Â Â Â Â Â Â Â Â Â Â Â Â nat = 8,<br>> Â Â Â Â Â Â Â Â Â Â Â Â ntyp = 2,<br>> Â Â Â Â Â Â Â Â Â Â Â ecutwfc = 80,<br>> Â Â Â Â Â Â Â Â Â Â Â nbnd=46,<br>> Â Â Â Â Â Â Â Â Â Â Â Â Â lspinorb = .true.,<br>
> Â Â Â Â Â Â Â Â Â Â Â noncolin= .true.,<br>> Â Â Â Â Â Â Â Â Â Â starting_magnetization=0.0,<br>> Â /<br>> Â &ELECTRONS<br>> Â Â Â Â Â Â electron_maxstep = 100,<br>> Â Â Â Â Â Â Â Â Â Â 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) Â Â Â Â Â Â Â 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>