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<div class="gmail_quote">2010/2/24 Gabriele Sclauzero <span dir="ltr"><<a href="mailto:sclauzer@sissa.it">sclauzer@sissa.it</a>></span><br>
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<div class="im">Wei Zhou wrote:<br>> hello all, recently I calculated the phonon of bcc sodium using<br>> pw4.1.2, when I plot the phonon dispersion along high symmtry ,I meet a<br>> problem;<br>> for bcc structure ,there are four high symmetry points in crystall<br>
> coordinations :<br></div>> *G:(0,0,0) H**(1/2,-1/2,1/2 ) P:(1/4,1/4,1/4) N: (0,0,1/2 )*<br>
<div class="im">> I plot the phonon dispersion along the high symmetry *H-P-G-H-N-P-N-G,<br>> *the results is obivously wrong, which differ the results from others ,I<br>> am sure the phonon calculations does not have problem , the problem is<br>
> to how to get the correct the symmetry lines.<br>> and I also found if I use the following high symmetry points<br>> directly ,then the results is OK<br></div>> * 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)*<br>
<br>How did you get this points? Have you tried all the possible permutations? :)<br>You get the correct result because these are the correct coordinates in the convention<br>followed by the PH code (which is however quite standard when specifying k or q points for<br>
the cubic systems).<br>The q-points should be given in Cartesian coordinates and units of 2\pi/a. If you draw the<br>BZ of the BCC lattice (which corresponds to the Wigner-Seitz cell of the FCC) with the<br>axis of the conventional cell (a SC cell containing 4 atoms) along the x, y, and z<br>
Cartesian axis you will realize it.<br><br>HTH<br><br>GS<br>
<div class="im"><br></div></blockquote>
<div>in fact, I just get the coordination from the web :<a href="http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-kv-list">http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-kv-list</a></div>
<div>k-vector label Wyckoff position Parameters <br>CDML ITA ITA <br>GM 0,0,0 4 a m -3 m 0,0,0 <br>H 1/2,-1/2,1/2 4 b m -3 m 0,1/2,0 <br>P 1/4,1/4,1/4 8 c -4 3m 1/4,1/4,1/4 <br>N 0,0,1/2 24 d <a href="http://m.mm">m.mm</a> 1/4,1/4,0 <br>
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.</div>
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<div class="im">> then I feel puzzled, would some one give some idea about this?<br>> any help will be appreciated<br>><br>> --<br>> ZhouDawei<br>> JiLin Universiyt ,ChangChun ,China<br></div>> <a href="mailto:zdw2000@gmail.com">zdw2000@gmail.com</a> <mailto:<a href="mailto:zdw2000@gmail.com">zdw2000@gmail.com</a>><br>
<br>--<br><br><br>o ------------------------------------------------ o<br><font color="#888888">| Gabriele Sclauzero, PhD Student |<br>| c/o: SISSA & CNR-INFM Democritos, |<br>| via Beirut 2-4, 34014 Trieste (Italy) |<br>
| email: <a href="mailto:sclauzer@sissa.it">sclauzer@sissa.it</a> |<br>| phone: +39 040 3787 511 |<br>| skype: gurlonotturno |<br>o ------------------------------------------------ o<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>ZhouDawei<br>JiLin Universiyt ,ChangChun ,China<br><a href="mailto:zdw2000@gmail.com">zdw2000@gmail.com</a><br>