Dear Dr. Giannozzi and Le, Thanks very much for your reply.
Actually, I also performed some test calculations using different q-mesh from 3x3x1 to 8x8x1. It is quite strange again that the calculation using odd q points i.e. 3x3x1, and 5x5x1 don?t include any negative phonon frequency. While the calculations with even q-mesh including 4x4x1, 6x6x1 and 8x8x1 give negative frequencies at q points near gamma. It should be pointed out that with increasing q-mesh i.e. from 4x4x1 to 8x8x1; the points with negative frequency become fewer and the frequency seems to be more close to zero. However, when I calculated the phonon frequency at point near Gamma directly, the negative frequency can be also found in acoustic mode ZA. I also tested the calculations using different version of QE (SVN, 4.3.2, 5.0.3 with May 6 patch), all version of codes give the same results. I am really confused about the results. The results using different q-mesh are enclosed. Can I trust the results produced by odd q-mesh like 5x5x1? Any suggestions will be appreciated. Thanks and best regards Wei-Bing Zhang > On 20/06/2013, Duy Le <ttduyle at gmail.com> wrote: >> 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 >> >> _______________________________________________ >> Pw_forum mailing list >> Pw_forum at pwscf.org >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > -- > ---------------------------------------------------------------------- > 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: zhangwb at csust.edu.cn, weibingzhangavh at gmail.com > ---------------------------------------------------------------------- > -- ---------------------------------------------------------------------- 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: zhangwb at csust.edu.cn, weibingzhangavh at gmail.com ----------------------------------------------------------------------