Dear Lorenzo, I apologize for getting back so late on this. I had posted a reply but looks like the email bounced back due to some size restriction on the attachment. But to answer your question, I did not find a negative frequency anywhere else in the q-point grid. I am attaching my scf, ph, q2r and matdyn input files. I am facing the same problem with another crystal structure of SiO2 as well (cristobalite). I feel like I am making some mistake in the input files that is probably important for polar materials.
I would really appreciate it if someone could look into it. Thanks! Sridhar Purdue University On Mon, Nov 17, 2014 at 2:34 AM, Lorenzo Paulatto < [email protected]> wrote: > Dear Sridhar, > normally the sum rules imposed by matdyn are enough to set the acoustic > bands at gamma to exactly zero. If this is not the case, it normally means > that you have some negative frequency somewhere else in the q-point grid. > Please check the other matdyn files to see if this is the case: the > frequencies are at the end of the file. > > kind regards > > > > On 17/11/14 02:03, Sridhar Sadasivam wrote: > > Dear Stefano, > > Thanks for your reply. Here are the frequencies at gamma point when I > set zasr and asr to 'simple' > -12.8981 -12.8981 -4.5998 142.6073 168.0267 168.0267 > 249.0588 249.0588 340.4760 344.4668 379.2589 379.2589 > 417.0274 417.0274 429.6273 457.2113 657.8050 657.8050 > 746.0641 755.8553 755.8553 1032.5200 1032.5200 1037.0491 > 1048.5362 1136.7760 1136.7760 > > Thanks, > Sridhar > > On Sun, Nov 16, 2014 at 5:25 AM, stefano de gironcoli <[email protected]> > wrote: > >> dear Sridhar Sadasivam >> can you try to set zasr and asr to 'simple' in the q2r+matdyn case >> and report the results ? >> thanks >> stefano >> >> >> >> On 11/15/2014 11:49 PM, Sridhar Sadasivam wrote: >> >> Dear espresso users and developers, >> >> I am trying to obtain the phonon dispersion of alpha-quartz (SiO2) >> which has a 9 atom unit cell. I ran ph.x on a 3 x 3 x 3 q-point grid. I am >> seeing some strange behavior where there seems to be a difference in the >> frequencies output from dynmat.x and matdyn.x. I will explain my problem >> below. >> >> I diagonalized the dynamical matrix at the gamma point using dynmat.x >> with acoustic sum rule set to crsytal. Since SiO2 is a polar material, >> LO-TO splitting will need to be considered at the gamma point but I am >> ignoring it currently (I did not specify any direction for LO-TO splitting >> in the dynmat.x input). This gave me the following 27 frequencies (in >> cm^-1) at the gamma point: (0,0,0, 152.24, 175.57, 175.57, 256.32, 256.32, >> 341.09, 354.41, 376.86, 376.86, 419.01, 419.01, 435.37, 455.70, 659.12, >> 659.12, 744.54, 754.62, 1034.38, 1034.38, 1040.20, 1051.12, 1139.60, >> 1139.60) >> >> I also used q2r.x (with zasr = 'crystal') to obtain the force constants >> and then used matdyn.x (with asr = 'crystal') to obtain the frequencies at >> the gamma point. However with matdyn.x, I obtain the following frequencies >> at the gamma point: (-29.4088,-22.2535,-22.2535,152.2412,175.8141,175.8141, >> 256.3373, 256.3373, 341.0892, 355.4227, 376.0495 , 376.0495, 418.6344, >> 418.6344, 435.3710, 453.6862, 659.7607, 659.7607, 746.4843, 754.8867, >> 754.8867, 1034.1751, 1034.1751, 1039.7590, 1051.1207, 1139.8191, 1139.8191) >> >> Could someone please explain why I am getting imaginary frequencies >> from matdyn.x while dynmat.x gives real frequencies at the same q-point >> (gamma in this case)? >> >> Thanks, >> Sridhar >> Purdue University >> >> >> >> _______________________________________________ >> Pw_forum mailing >> [email protected]http://pwscf.org/mailman/listinfo/pw_forum >> >> >> >> _______________________________________________ >> Pw_forum mailing list >> [email protected] >> http://pwscf.org/mailman/listinfo/pw_forum >> > > > > _______________________________________________ > Pw_forum mailing > [email protected]http://pwscf.org/mailman/listinfo/pw_forum > > > -- > Dr. Lorenzo Paulatto > IdR @ IMPMC -- CNRS & Université Paris 6 > +33 (0)1 44 275 084 / skype: paulatzhttp://www-int.impmc.upmc.fr/~paulatto/ > 23-24/4é16 Boîte courrier 115, 4 place Jussieu 75252 Paris Cédex 05 > > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum >
SiO2.in
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matdyn.in.freq
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q2r.in
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ph_1.in
Description: Binary data
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