Did you perform the test for q-mesh? I would do 2x2x1, 3x3x1 and higher (if it is not that expensive) to see the evolution of phonon-dispersion. Usually, 4x4x1 q-mesh is enough for converged dispersion.
---------------------------------------------------- Duy Le Postdoctoral Associate Department of Physics University of Central Florida. Website: http://www.physics.ucf.edu/~dle On Wed, Jun 19, 2013 at 4:45 PM, Paolo Giannozzi <paolo.giannozzi at uniud.it> wrote: > You can make a calculation at a q point that has imaginary > frequencies, verify if you get the same result or if it is > an artifact of Fourier interpolation > > P. > > On Tue, 2013-06-18 at 09:38 +0800, Wei-Bing Zhang wrote: >> Dear all >> >> >> Recently, I am trying to calculate the phonon dispersion of 2D >> materials. I used 4x4x1 q-points in phonon calculation whereas a >> 16x16x1 k-points for self-consistent electronic calculation. The >> direct calculations indicate that all phonons frequencies are above >> zero on the grid of q-vectors including the Gamma point. However, when >> I transformed the dynamical matrices from G- to R-space and calculated >> phonon dispersions using ?matdyn.x?, some negative frequencies appear >> in acoustic mode ZA near Gamma point. Since I am really a new user >> for phonon calculation, I am not sure what happened. The input and >> output file are enclosed. Could you tell me what?s wrong with my >> calculations? Any suggestions will be appreciated. >> >> >> >> Thanks and best regards >> >> >> >> Wei-Bing Zhang >> >> >> >> >> ---------------------------------------------------------------------- >> Dr. Wei-Bing Zhang >> >> School of Physics and Electronic Sciences >> Changsha University of Science and Technology, >> Changsha, People?s Republic of China >> Phone : +86 186 73108538 >> E-mail: zwb256 at hotmail.com, weibingzhangavh at gmail.com >> ---------------------------------------------------------------------- >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum > > -- > Paolo Giannozzi, Dept. Chemistry&Physics&Environment, > Univ. Udine, via delle Scienze 208, 33100 Udine, Italy > Phone +39-0432-558216, fax +39-0432-558222 > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum
