Hello Prasenjit, Please find the output file for vc-relax attached. I had rerun my calculations so this file has slightly different coordinate from what is reported in pw.in.
Thanks, Ankit Jain On Mon, Apr 14, 2014 at 2:12 AM, Sanjeev Gupta <physics.skgupta at gmail.com>wrote: > 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 > ------------------------------------ > > _______________________________________________ > Pw_forum mailing list > Pw_forum at pwscf.org > http://pwscf.org/mailman/listinfo/pw_forum > -------------- next part -------------- An HTML attachment was scrubbed... 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