<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Dear Rakshit,</div><div><br></div><div>I'm just copy pasting from a previous answer in the forum to the same question: it might help, it might not.</div><div><br></div><div><span class="Apple-style-span" style="font-family: Times; "><pre>Hello,
Assuming that there are no problems of numerical inaccuracy or inadequate convergence
thresholds, negative frequencies at gamma point in a geometry-relaxed system usually mean that
(within the system and the calculation method used) there is some distortion (decreasing the
symmetry of the system) which leads to lower energy, i.e. you are at a saddle point in the energy
hypersurface. You must move some atom out of the initial symmetry and optimize geometry
again starting from that modified situation. If you can obtain the vector coordinates for the normal
mode of vibration corresponding to the negative frequency, a displacement of the involved atoms,
proportional to that normal mode, by e.g. a maximum of 0.2 angstrom will give to you a starting
displaced geometry closer to the true energy minimum. Sometimes you need to do this several
times if not all of the negative frequencies disappear after the first attempt.
If, after obtaining a new geometry with no negative frequencies at the gamma point, you still have
negative frequencies at other BZ points, this means that your system is unstable against some
atomic displacements that multiply some of the primitive cell vectors by e.g. 2 or 3, leading to a
supercell. Curing this situation may be more tedious.
Good luck,
Jose C. Conesa
Instituto de Catalisis y Petroleoquimica, CSIC
Campus de Cantoblanco
28049 Madrid - Spain
Phone Nr. 34-91-5854766
Fax Nr. 34-91-5854760
</pre><div><font class="Apple-style-span" face="monospace"><span class="Apple-style-span" style="white-space: pre;"><br></span></font></div></span><blockquote type="cite"><div><font class="Apple-style-span" color="#000000"><br></font><br>Message: 3<br>Date: Fri, 14 Aug 2009 11:25:23 +0530<br>From: Bipul Rakshit <<a href="mailto:bipulrr@gmail.com">bipulrr@gmail.com</a>><br>Subject: [Pw_forum] matdyn error<br>To: PWSCF Forum <<a href="mailto:pw_forum@pwscf.org">pw_forum@pwscf.org</a>><br>Message-ID:<br><span class="Apple-tab-span" style="white-space:pre"> </span><<a href="mailto:3a749910908132255x13311317j4eb55858c46affe0@mail.gmail.com">3a749910908132255x13311317j4eb55858c46affe0@mail.gmail.com</a>><br>Content-Type: text/plain; charset="iso-8859-1"<br><br>Dear pwscf users,<br><br>I am doing Gamma point phonon analysis for LaMnO3, after running matdyn.x i<br>am getting the following, error.<br><br>Norm of the difference between old and new effective charges:<br>0.00000000000000000000<br>Norm of the difference between old and new force-constants:<br>0.20461738165775616993<br> 0.833333333333333<br><br> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br> from frc_blk : error # 1<br> wrong total_weight<br> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br><br> stopping ...<br>2<br><br>Since at gamma point i am getting some -ve freq. the sum rule i want to<br>apply. And to see the final frequencies after applying sum rule.<br><br>Kindly guide me and suggest for the possible reason for this error.<br>-- <br>Dr. Bipul Rakshit<br>Research Associate,<br>S N Bose Centre for Basic Sciences,<br>Salt Lake,<br>Kolkata 700 098<br>India<br>-------------- next part --------------<br>An HTML attachment was scrubbed...<br>URL: <a href="http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0001.htm">http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0001.htm</a> <br>-------------- next part --------------<br>A non-text attachment was scrubbed...<br>Name: lamno3.ph.in<br>Type: application/octet-stream<br>Size: 316 bytes<br>Desc: not available<br>Url : <a href="http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0003.obj">http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0003.obj</a> <br>-------------- next part --------------<br>A non-text attachment was scrubbed...<br>Name: q2r.in<br>Type: application/octet-stream<br>Size: 71 bytes<br>Desc: not available<br>Url : <a href="http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0004.obj">http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0004.obj</a> <br>-------------- next part --------------<br>A non-text attachment was scrubbed...<br>Name: matdyn.in<br>Type: application/octet-stream<br>Size: 280 bytes<br>Desc: not available<br>Url : <a href="http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0005.obj">http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0005.obj</a> <br><br>------------------------------<br><br></div></blockquote></div><br></body></html>