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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