2010/2/24 Gabriele Sclauzero <sclauzer at sissa.it> > Wei Zhou wrote: > > hello all, recently I calculated the phonon of bcc sodium using > > pw4.1.2, when I plot the phonon dispersion along high symmtry ,I meet a > > problem; > > for bcc structure ,there are four high symmetry points in crystall > > coordinations : > > *G:(0,0,0) H**(1/2,-1/2,1/2 ) P:(1/4,1/4,1/4) N: (0,0,1/2 )* > > I plot the phonon dispersion along the high symmetry *H-P-G-H-N-P-N-G, > > *the results is obivously wrong, which differ the results from others ,I > > am sure the phonon calculations does not have problem , the problem is > > to how to get the correct the symmetry lines. > > and I also found if I use the following high symmetry points > > directly ,then the results is OK > > * G :(0,0,0) ,H* *( 0.00 1.00,0.00), P(0.5,0.5, 0.50),N(0.5, 0.5, 0.00)* > > How did you get this points? Have you tried all the possible permutations? > :) > You get the correct result because these are the correct coordinates in the > convention > followed by the PH code (which is however quite standard when specifying k > or q points for > the cubic systems). > The q-points should be given in Cartesian coordinates and units of 2\pi/a. > If you draw the > BZ of the BCC lattice (which corresponds to the Wigner-Seitz cell of the > FCC) with the > axis of the conventional cell (a SC cell containing 4 atoms) along the x, > y, and z > Cartesian axis you will realize it. > > HTH > > GS > > in fact, I just get the coordination from the web : http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-kv-list k-vector label Wyckoff position Parameters CDML ITA ITA GM 0,0,0 4 a m -3 m 0,0,0 H 1/2,-1/2,1/2 4 b m -3 m 0,1/2,0 P 1/4,1/4,1/4 8 c -4 3m 1/4,1/4,1/4 N 0,0,1/2 24 d m.mm 1/4,1/4,0 and I turn them into Cartesian coordinates and units of 2\pi/a, then I plot the phonon dispersion curve , the results is wrong ,it seems the coordination dos not correct,then I feel puzzled.
> > then I feel puzzled, would some one give some idea about this? > > any help will be appreciated > > > > -- > > ZhouDawei > > JiLin Universiyt ,ChangChun ,China > > zdw2000 at gmail.com <mailto:zdw2000 at gmail.com> > > -- > > > o ------------------------------------------------ o > | Gabriele Sclauzero, PhD Student | > | c/o: SISSA & CNR-INFM Democritos, | > | via Beirut 2-4, 34014 Trieste (Italy) | > | email: sclauzer at sissa.it | > | phone: +39 040 3787 511 | > | skype: gurlonotturno | > o ------------------------------------------------ o > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > -- ZhouDawei JiLin Universiyt ,ChangChun ,China zdw2000 at gmail.com -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20100224/9cb58ba3/attachment-0001.htm
