[QE-users] Optical branches are not continuous at gamma point in phonon dispersion
Changpeng Lin
cplin.phys at gmail.com
Mon Nov 12 14:00:53 CET 2018
Dear all,
I calculated the phonon dispersion of polar materials by DFPT in ph.x and
set epsil = .true. and trans = .true. to determine the dielectric tensor
and Born effective charges.
I then get the phonon dispersion by matdyn.x and the input set as following,
&input
flfrc='TE.frc',
flfrq='TE.frq'
asr='simple',
q_in_band_form=.true.
q_in_cryst_coord=.true.
/
6
6
0.5 0.5 -0.5 100 !Z
0.0 0.0 0.0 100 !G
0.0 0.0 0.5 100 !X
0.25 0.25 0.25 100 !P
0.0 0.5 0.0 100 !N
0.0 0.0 0.0 1 !G
I found that optical branches are not continuous at gamma point. I guess
this is becasue the wrong LO-TO spiliting relation I got. How can I check
it?
More interestingly, I recently tested the phonon dispersion of PbTe by
supercell small displacement method and also determine the dielectric
tensor and Born effective charges by DFPT at gamma point only in ph.x. I
found that there was no LO-TO splitting at gamma point from the output of
dynmat.x. However, if I put the dielectric tensor and Born effective
charges by DFPT into Phonopy and combine the force constants obtained
from small displacement method, I get the correct LO-TO splitting from
Phonopy. So, where is wrong?
Thanks,
Changpeng
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20181112/5ca55cf8/attachment.html>
More information about the users
mailing list