Ciao Stefano, Thanks for a clear explanation.
Prasenjit On 10 August 2011 18:00, Stefano Baroni <baroni at sissa.it> wrote: > Dear Mayank, > 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? > 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. > in any case, more insight is needed, which in turn would probably require > more work from you. > remember: no pain, no gain! > good luck, > SB > > On Aug 10, 2011, at 9:44 AM, mayank gupta wrote: > > Dear Sir > > It's magnetic oxide SrFeO2. Kohn anomaloy occurs in metallic system. > Should I further increase k points or do something else. > > Thanks > > > it may depend on a Kohn anomaly (which are particularly sensitive to k-point > sampling) > > SB > > On Aug 9, 2011, at 9:24 AM, mayank gupta wrote: > > Dear all > > > I am doing phonon calculation of a magnetic system, ?have not included > > any magnetic interaction on it. I am calculating phonon at ?2x2x2 mesh > > (6 q points). I got the phonon frequency +ve at 5 q point ?while at > > one q point it is negative. I have check this with 24 x24x24 k point > > and with very high ecut and observed ?this particular phonon mode > > doesn't converge with k point while rest is converged. is it because > > of not taking in to account the magnetic part or something else. > > > > > -- > Mayank > > BHABHA ATOMIC RESEARCH CENTER > MUMBAI, INDIA > Office: ?022-25595606 > Home: 9920397437 / 9869834437 > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > --- > Stefano Baroni - SISSA??&??DEMOCRITOS National Simulation Center - Trieste > http://stefano.baroni.me?[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni > (skype) > La morale est une logique de l'action comme la logique est une morale de la > pens?e - Jean Piaget > Please, if possible, don't??send me MS Word or PowerPoint attachments > Why? See:??http://www.gnu.org/philosophy/no-word-attachments.html > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > -- PRASENJIT GHOSH, Assistant Professor, IISER Pune, First floor, Central Tower, Sai Trinity Building Garware Circle, Sutarwadi, Pashan Pune, Maharashtra 411021, India Phone: +91 (20) 2590 8203 Fax: +91 (20) 2589 9790
