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<div class="moz-cite-prefix">dear Sridhar Sadasivam<br>
can you try to set zasr and asr to 'simple' in the
q2r+matdyn case and report the results ?<br>
thanks<br>
stefano<br>
<br>
<br>
On 11/15/2014 11:49 PM, Sridhar Sadasivam wrote:<br>
</div>
<blockquote
cite="mid:CANTo9TsakD9xV1AMZ2+sdKdRBGecrqinYpX5g3BgXWxaf4qWaQ@mail.gmail.com"
type="cite">
<div dir="ltr">Dear espresso users and developers,
<div><br>
</div>
<div>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. </div>
<div><br>
</div>
<div>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) </div>
<div><br>
</div>
<div>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)</div>
<div><br>
</div>
<div>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)? </div>
<div><br>
</div>
<div>Thanks,<br>
Sridhar</div>
<div>Purdue University</div>
<div><br>
</div>
</div>
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