Dear Rakshit, I'm just copy pasting from a previous answer in the forum to the same question: it might help, it might not.
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 > > > Message: 3 > Date: Fri, 14 Aug 2009 11:25:23 +0530 > From: Bipul Rakshit <bipulrr at gmail.com> > Subject: [Pw_forum] matdyn error > To: PWSCF Forum <pw_forum at pwscf.org> > Message-ID: > <3a749910908132255x13311317j4eb55858c46affe0 at mail.gmail.com> > Content-Type: text/plain; charset="iso-8859-1" > > Dear pwscf users, > > I am doing Gamma point phonon analysis for LaMnO3, after running > matdyn.x i > am getting the following, error. > > Norm of the difference between old and new effective charges: > 0.00000000000000000000 > Norm of the difference between old and new force-constants: > 0.20461738165775616993 > 0.833333333333333 > > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% > %%%%%%%%% > from frc_blk : error # 1 > wrong total_weight > %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% > %%%%%%%%% > > stopping ... > 2 > > Since at gamma point i am getting some -ve freq. the sum rule i want > to > apply. And to see the final frequencies after applying sum rule. > > Kindly guide me and suggest for the possible reason for this error. > -- > Dr. Bipul Rakshit > Research Associate, > S N Bose Centre for Basic Sciences, > Salt Lake, > Kolkata 700 098 > India > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0001.htm > -------------- next part -------------- > A non-text attachment was scrubbed... > Name: lamno3.ph.in > Type: application/octet-stream > Size: 316 bytes > Desc: not available > Url : > http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0003.obj > -------------- next part -------------- > A non-text attachment was scrubbed... > Name: q2r.in > Type: application/octet-stream > Size: 71 bytes > Desc: not available > Url : > http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0004.obj > -------------- next part -------------- > A non-text attachment was scrubbed... > Name: matdyn.in > Type: application/octet-stream > Size: 280 bytes > Desc: not available > Url : > http://www.democritos.it/pipermail/pw_forum/attachments/20090814/9aeba1c4/attachment-0005.obj > > ------------------------------ > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20090814/0d9b7726/attachment.htm
