<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Dear Mayank,</div><div><br></div>have you plotted the electronic energy bands? are you sure that the the system is not (semi-) metallic, possibly because of some shortcomings of the XC functional you are using?<div><br></div><div>more generally, imaginary frequencies signal a mechanical instability of your system. if the instability occurs at a finite wave-vector, that means that he system may undergo a transition to a structure whose (larger) unit cell is commensurate with the instability wave-vector. If the instability occurs at q=0, then some distortions of atomic positions may occur, which in turn may determine a distortion of the cell shape. If it is a sound velocity that vanishes, this finally indicates an elastic instability of the shape of the unit cell.</div><div><br></div><div>in any case, more insight is needed, which in turn would probably require more work from you. </div><div>remember: no pain, no gain!</div><div><br></div><div>good luck,</div><div>SB</div><div> <br><div><div>On Aug 10, 2011, at 9:44 AM, mayank gupta wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div>Dear Sir<br><br>It's magnetic oxide SrFeO2. Kohn anomaloy occurs in metallic system.<br>Should I further increase k points or do something else.<br><br>Thanks<br><br><br><blockquote type="cite">it may depend on a Kohn anomaly (which are particularly sensitive to k-point sampling)<br></blockquote><blockquote type="cite">SB<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">On Aug 9, 2011, at 9:24 AM, mayank gupta wrote:<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite"><blockquote type="cite">Dear all<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">I am doing phonon calculation of a magnetic system, have not included<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">any magnetic interaction on it. I am calculating phonon at 2x2x2 mesh<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">(6 q points). I got the phonon frequency +ve at 5 q point while at<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">one q point it is negative. I have check this with 24 x24x24 k point<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">and with very high ecut and observed this particular phonon mode<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">doesn't converge with k point while rest is converged. is it because<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite">of not taking in to account the magnetic part or something else.<br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote><br>-- <br>Mayank<br><br>BHABHA ATOMIC RESEARCH CENTER<br>MUMBAI, INDIA<br>Office: 022-25595606<br>Home: 9920397437 / 9869834437<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></div></blockquote></div><br><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">---</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Stefano Baroni - SISSA</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">&</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">DEMOCRITOS National Simulation Center - Trieste</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "><a href="http://stefano.baroni.me/">http://stefano.baroni.me</a> [+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; font-size: 12px; "><br style="font-size: 12px; "></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font: normal normal normal 12px/normal Helvetica; min-height: 14px; font-size: 12px; "><span class="Apple-style-span" style="font-size: 14px; "><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; ">La morale est une logique de l'action comme la logique est une morale de la pensée - Jean Piaget</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; "><br></span></font></div></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Please, if possible, don't</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "> </span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">send me MS Word or PowerPoint attachments</span></font></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; font-size: 14px; "><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; ">Why? See:</span></font><font class="Apple-style-span" size="3"><span class="Apple-style-span" style="font-size: 12px; "> </span></font><font class="Apple-style-span" color="#0023E9" size="3"><span class="Apple-style-span" style="font-size: 12px; "><a href="http://www.gnu.org/philosophy/no-word-attachments.html">http://www.gnu.org/philosophy/no-word-attachments.html</a></span></font></div></div><div><font class="Apple-style-span" color="#0023E9" size="3"><br></font></div></span><br class="Apple-interchange-newline">
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