ZrO2 phonon frequencies at X and arbitrary q-point

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ilukacevic
Posts: 271
Joined: Sat Jan 16, 2010 12:05 pm
Location: Dept. of Physics, University J. J. Strossmayer, Osijek, Croatia
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ZrO2 phonon frequencies at X and arbitrary q-point

Post by ilukacevic » Wed Feb 24, 2010 9:28 am

Dear colleagues,

I'm trying to calculate phonon frequencies in cubic ZrO2. Previous attempt to find dispersions failed, for which I'm currently trying to find out what is happening when I go just a little from the Gamma point. For Gamma point I get a very good agreement with previous studies (even acoustic zeros without imposing asr), but as soon as I get away from it, results differ greatly. LO-TO splitting, dielectric constant and Born eff. charges are also reproduced correctly.

Since there is an instability at the X point, I tried to calculate these. Unfortunately, I get unstable transversal acoustic modes (both of them), instead of trans. optic one:

My
-3.672780E+02 -2.828415E+02 1.439990E+02 3.115149E+02 3.291936E+02 3.455205E+02 5.859111E+02 6.967360E+02 7.379747E+02

Previous theoretical study
-193 136 323 365 567 700

Similar thing happens when I try phonons at the q-point very close to Gamma. My acoustic modes immediately go imaginary, while they should be stable:

q-point 0.95000 0.95000 0.95000
Phonon frequencies in cm-1 :
- -1.750711E+02 -6.546669E+01 6.451006E+01 2.635530E+02 2.652804E+02
- 5.948007E+02 5.977425E+02 6.052206E+02 6.958626E+02


My input files for rf (at X) and anaddb (disp.) calc. are attached. I'm using abinit 5.8.4p on a linux cluster. All quantities are converged and I'm using the same psudos as in the previous study.

Could anyone help me with this problem?

Thank you in advance!

Yours,
Igor Lukacevic
Attachments
t11.in
(2.08 KiB) Downloaded 435 times
trf2_5.in
(6.83 KiB) Downloaded 409 times

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