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

[Gabriele Sclauzero]

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

> 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>

-- 


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