[Pw_forum] difference in output from dynmat.x and matdyn.x

[Sridhar Sadasivam]

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 <degironc at sissa.it>
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
>
>
>
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