good. can you take one more test to change the pseudo and see. May be I am wrong but see.
On Sun, Apr 13, 2014 at 11:02 PM, ankit jain <ankitjain.me.iitk at gmail.com>wrote: > I have tried acoustic sum rule and it does not change negative > frequencies. > I have rerun calculations with several different parameters and seems to > have modified my vc-relax output file. I am re-running it and will send it > as soon as it is done. > > > On Mon, Apr 14, 2014 at 1:51 AM, Prasenjit Ghosh <prasenjit.jnc at > gmail.com>wrote: > >> Did you try using the acoustic sum rule and see whether the imaginary >> frequencies are still there? Also can I have a look at the vc-relax output >> file? >> >> Prasenjit >> >> >> On 14 April 2014 11:10, ankit jain <ankitjain.me.iitk at gmail.com> wrote: >> >>> Hello Prasenjit, >>> >>> I am getting negative phonon frequencies for non-gamma points also. >>> After structure optimization, the total force is 0.000020 Ry/au and >>> pressure is -0.24 kbar. >>> >>> I am using ecutwfc of 100 Ry, which is converged with respect to the >>> total energy of the system. I am not able to do convergence with respect to >>> phonon modes as some modes have negative frequencies. Is there a way to do >>> ecutwfc convergence for phonon modes without calculating phonon frequencies? >>> >>> I am atatching my pw.in, ph.in pw.out and ph.out files (which I forgot >>> to attch in my original mail) here. >>> >>> Thanks, >>> ANkit Jain >>> >>> >>> On Mon, Apr 14, 2014 at 1:29 AM, Prasenjit Ghosh < >>> prasenjit.jnc at gmail.com> wrote: >>> >>>> For which q-point are you getting the imaginary modes? If it is at >>>> gamma, then it may be related to the instability in the structure, if it is >>>> at other q-points, may be lattice parameter is not properly optimized. How >>>> large is the stress you are getting at the end of the vc-relax calculation >>>> (when the code recalculates the total energy, stress and forces with the >>>> optimized lattice parameters & atomic positions). Also have you checked the >>>> convergence of the phonon modes with ecutwfc because typically the phonons >>>> converge much slowly with the size of the basis set than other parameters? >>>> >>>> With regards, >>>> >>>> Prasenjit >>>> >>>> >>>> On 13 April 2014 21:55, Ankit <ankitjain.me.iitk at gmail.com> wrote: >>>> >>>>> Hello QE developers and users, >>>>> >>>>> I am trying to calculate phonon dispersion using ph.x and matdyn.x >>>>> routines of QE and I am stuck woth negative frequencies for a while >>>>> now. >>>>> >>>>> I have a 1-D chain of polyethylene which has 6 atoms in the unit-cell. >>>>> The polymer chain is aligned in z-direction and I have added vacuum on >>>>> x- and y- direction. I did the structure relaxation and I am getting >>>>> total force after relaxtion as 0.000020, which I guess is sufficiently >>>>> small. >>>>> >>>>> After relaxation, when I am trying to calculate phonon dispersion using >>>>> ph.x and matdyn.x I am getting netting frequencies for some of the >>>>> phonon modes. I searched online and on QE mailing list and tried >>>>> couple >>>>> of different things: >>>>> >>>>> 1. The negative frequencies are appearing for non-gamma point as well, >>>>> so I guess its not a ASR issue. Anyway, I am using ASR but even after >>>>> this I am getting negative frequencies. >>>>> 2. I reduced my tr2_ph and conv_thr to 1.0d-14 and 1.0d-15 which I >>>>> guess >>>>> are very small as suggested on QE FAQs. >>>>> 3. I checked phonon mode shapes for modes with negative frequencies and >>>>> they do not look like rotational mode. >>>>> 4. I tried changing number of k points from 6 to 12 in z direction but >>>>> this is also not the cause. >>>>> >>>>> I am really stuck here and not sure about the cause of negative >>>>> frequencies. With vc-relax, my structure is getting relaxed which I >>>>> guess means my structure is stable. But then I am not sure why I am >>>>> getting negative frequencies. >>>>> >>>>> I really appreciate any help or suggestions. >>>>> >>>>> Thanks, >>>>> >>>>> Ankit Jain >>>>> IIT Indore, >>>>> Indore, >>>>> India >>>>> >>>>> >>>>> _______________________________________________ >>>>> Pw_forum mailing list >>>>> Pw_forum at pwscf.org >>>>> http://pwscf.org/mailman/listinfo/pw_forum >>>>> >>>> >>>> >>>> >>>> -- >>>> PRASENJIT GHOSH, >>>> IISER Pune, >>>> Dr. Homi Bhabha Road, Pashan >>>> Pune, Maharashtra 411008, India >>>> >>>> Phone: +91 (20) 2590 8203 >>>> Fax: +91 (20) 2589 9790 >>>> >>>> _______________________________________________ >>>> 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 >>> >> >> >> >> -- >> PRASENJIT GHOSH, >> IISER Pune, >> Dr. Homi Bhabha Road, Pashan >> Pune, Maharashtra 411008, India >> >> Phone: +91 (20) 2590 8203 >> Fax: +91 (20) 2589 9790 >> >> _______________________________________________ >> 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 > -- With Best Regards, ------------------------------------ Dr. Sanjeev Kumar Gupta Fulbright Post-Doctoral Scholar Dept. of Physics Michigan Technological University 1400 Townsend Drive, Houghton MI 49931, USA ------------------------------------ -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20140413/ac4a61eb/attachment.html
