Hi Mohaddesh. I do not understand why you say that the calculated frequency (which, I assume you define as 2 * Delta E / u^2 ???) does not converge as u->0. According to your plot, it does, and to a reasonable value. The finite slope of your plot around u=0 seems to me nothing but a manifestation of cubic anharmonicity ... What's wrong in this? SB
On Aug 1, 2011, at 3:01 PM, mohaddeseh abbasnejad wrote: > > Dear users, > > I have plotted the harmonic frequency (obtained within the frozen phonon > approach) of Diamond as a function of atomic displacements (small > displacements in the [1 1 1] direction, u(1)=?(u,u,u) and u(2)=?(-u,-u,-u) > are the displacements of two atoms in the basis). I expect to see a range of > displacements that tend to the similar frequency, but there is no convergence > in the plot. Also, the displacements with the same amplitude but different in > sign, do not tend to the same frequency, which is not what I expect, too. The > plot is attached. > I was wondering if anyone could help me to find the source of error. I should > expect the mentioned symmetry, right? Why there is no convergence? > > Thanks in advance. > > Yours, > Mohaddeseh > --------------------------------------------------------- > > Mohaddeseh Abbasnejad, > Room No. 323, Department of Physics, > University of Tehran, North Karegar Ave., > Tehran, P.O. Box: 14395-547- IRAN > E-Mail: m.abbasnejad at gmail.com > Website: http://physics.ut.ac.ir > > --------------------------------------------------------- > > <fig..pdf>_______________________________________________ > 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110801/ab3afc9c/attachment.htm
