<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">Emine: (001) and (011) are *NOT* two "X" points in the FCC Brillouin zone. The difference between the second and the first (010) is *NOT* a reciprocal-space vector. If it was, X would also be, which you will agree it is not. As a matter of fact, (011) has its own nickname (it is called "K"). No surprise, therefore, that frequencies @K are different from frequencies @X. Are these arguments clear and convincing enough? Stefano<DIV><BR class="khtml-block-placeholder"><DIV><BR><DIV><DIV>On Dec 9, 2006, at 11:10 PM, e kb wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"><DIV>Dear QE users,</DIV> <DIV>I am performing phonon calculations for a zinc blende structure,</DIV> <DIV>I calculated the frequencies at high symmetry points, evaluating a single point at each time.</DIV> <DIV>So I followed the procedure of scf, nscf and ph.x calculation one by one for L(0.5 0.5 0.5) - Gamma - X(0,0,1) - X(0,1,1) points.</DIV> <DIV>In these calculations every parameter (else than q-vector in &phonon list in nscf calculation and phonon card for ph.x input of course) is kept fixed. </DIV> <DIV> </DIV> <DIV>Although I expect the frequencies at two X points - (0,0,1) and (0,1,1) - to be the same,</DIV> <DIV>the difference in TA modes' frequencies are around 30 cm-1, </DIV> <DIV>in the other ones, around 5 cm-1.</DIV> <DIV> </DIV> <DIV>I would like to attribute this to unconverged lattice parameters, cut off energies or thresholds etc. but what I do not understand is why the program treats these two points differently, although they should be equivalent. So I expect to see the same value for frequency at these points, even if it is wrong, highly negative, or sth else that it should not be.</DIV> <DIV> </DIV> <DIV>I will appreciate any answers.</DIV> <DIV>Thank you.</DIV> <DIV> </DIV> <DIV>Emine Kucukbenli</DIV> <DIV> </DIV> <DIV> </DIV><DIV> <BR class="khtml-block-placeholder"></DIV><HR size="1">Everyone is raving about <A href="http://us.rd.yahoo.com/evt=42297/*http://advision.webevents.yahoo.com/mailbeta">the all-new Yahoo! 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