[Pw_forum] the high symmetry line of bcc phonon dispersion calculated by pw4.1.2

[Wei Zhou]

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                             |
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-- 
ZhouDawei
JiLin Universiyt ,ChangChun ,China
zdw2000 at gmail.com
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