<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Dec 9, 2007, at 2:27 PM, Guoying Gao wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">On Dec 9, 2007 9:06 PM, Stefano Baroni <<a href="mailto:baroni@sissa.it">baroni@sissa.it</a>> wrote:<br><blockquote type="cite">Imaginary frequencies are usually a sign of a mechanical instability, as<br></blockquote><blockquote type="cite">discussed many times in this forum as well as in many condensed-matter<br></blockquote><blockquote type="cite">textbooks. I think the answer is yours: if you want to calculate the<br></blockquote><blockquote type="cite">electron-phonon interaction of an instable (possibly metastable) phase of a<br></blockquote><blockquote type="cite">material, please do. If instead instability is soemething that troubles you,<br></blockquote><blockquote type="cite">then you better settle your troubles first. Cheers - SB<br></blockquote>Hi Stefano,<br> Thanks for your reply.<br> I know the imaginary frequencies signifying a mechanical<br>instability, but I want to know whether we can calculate it or not and<br>is it meanful to do this?</blockquote><div><br class="webkit-block-placeholder"></div>as said, I think that only you can be the judge</div><div>S.</div><div><br><blockquote type="cite"> We just want to estimate the values of Tc.<br>Guoying<br>_______________________________________________<br>Pw_forum mailing list<br><a href="mailto:Pw_forum@pwscf.org">Pw_forum@pwscf.org</a><br>http://www.democritos.it/mailman/listinfo/pw_forum<br></blockquote></div><br><div> <span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 14px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; 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"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">---</span></span></span></span></span></span></span></span></span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px;"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">Stefano Baroni - SISSA</span></span></span></span></span></span></span></span></span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px;"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "> </span></span></span></span></span></span></span></span></span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px;"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; 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"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">Please, if possible, don't</span></span></span></span></span></span></span></span></span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px;"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "> </span></span></span></span></span></span></span></span></span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px;"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">send me MS Word or PowerPoint attachments</span></span></span></span></span></span></span></span></span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px;"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; ">Why? See:</span></span></span></span></span></span></span></span></span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px;"><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "><span class="Apple-style-span" style="font-size: 12px; "> </span></span></span></span></span></span></span></span></span></font><a href="http://www.gnu.org/philosophy/no-word-attachments.html"><font class="Apple-style-span" color="#0023E9" size="3"><span class="Apple-style-span" style="font-size: 12px;; color: rgb(0, 35, 233); -khtml-text-decorations-in-effect: underline; "><span class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><span class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><span class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><span class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><span class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><span class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><span class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; "><span class="Apple-style-span" style="color: rgb(0, 35, 233); font-size: 12px; -khtml-text-decorations-in-effect: underline; ">http://www.gnu.org/philosophy/no-word-attachments.html</span></span></span></span></span></span></span></span></span></font></a></div><div><br class="khtml-block-placeholder"></div><br class="Apple-interchange-newline"></span></span></span></span></span></span></span></span></div></span> </div><br></body></html>