Dear Prof. Baroni Thanks for your reply. I wonder shouldn't the plot show the same frequency for a range of displacements? And the same freq. for the range to be the harmonic frequency? or the zero displacement limit, is the harmonic frequency? And when I test the displacements with the same amplitude, but different in sign (regarding the inward and outward atomic movements in the basis) I do not get the same results. Shouldn't the plot have symmetry vs. the vertical axis?
Thank You again Mohaddeseh On Mon, Aug 1, 2011 at 6:33 PM, Stefano Baroni <baroni at sissa.it> wrote: > 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 > > > > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://www.democritos.it/mailman/listinfo/pw_forum > > -- --------------------------------------------------------- Mohaddeseh Abbasnejad, Room No. 323, Department of Physics, University of Tehran, North Karegar Ave., Tehran, P.O. Box: 14395-547- IRAN Tel. No.: +98 21 6111 8634 & Fax No.: +98 21 8800 4781 Cellphone: +98 917 731 7514 E-Mail: m.abbasnejad at gmail.com Website: http://physics.ut.ac.ir --------------------------------------------------------- -------------- next part -------------- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110801/d123df66/attachment.htm
