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> -- 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
