[Pw_forum] Phonon dispersion with LO-TO splitting in teragonal system

[Kondaiah Samudrala]

---------- Forwarded message ----------
From: Kondaiah Samudrala <konda.physics at gmail.com>
Date: Tue, Dec 17, 2013 at 6:49 PM
Subject: Phonon dispersion with LO-TO splitting
To: pw_forum-owner at pwscf.org, pw_forum at pwscf.org, pw_forum-request at pwscf.org



Dear all,

I am phonon dispersion for teragonal system to check insulator to metal
transition. At gamma point frequencies,  I did not get any imaginary
frequencies in asr.out file, where as in complete phonon dispersion I got
imaginary frequencies and sudden shifts in high symmetry directions. I am
bit confused and croos check my i/p. Below I attached the i/p and o/p of
calculations

AB2.asr.out :
     Reading Dynamical Matrix from file AB2.dynG
     ...Force constants read
     ...epsilon and Z* read
     A direction for q was not specified:TO-LO splitting will be absent

     Polarizability (A^3 units)
     multiply by 0.273227 for Clausius-Mossotti correction
        21.410069    0.000000    0.000000
         0.000000   21.410069    0.000000
         0.000000    0.000000   18.627445

     IR activities are in (D/A)^2/amu units

# mode   [cm-1]    [THz]      IR
    1      0.00    0.0000    0.0000
    2      0.00    0.0000    0.0000
    3      0.00    0.0000    0.0000
    4    257.23    7.7116    2.1831
    5    257.23    7.7116    2.1831
    6    412.71   12.3727    0.0000
    7    412.71   12.3727    0.0000
    8    539.77   16.1819   24.4707
    9    620.07   18.5891    0.0000

     DYNMAT       :     0.00s CPU         0.03s WALL


   This run was terminated on:  22:47:55  16Dec2013

=------------------------------------------------------------------------------=
   JOB DONE.
=------------------------------------------------------------------------------=

AB2.ph.in

phonons at Full
 &inputph
   prefix='AB2',
   fildyn='AB2.dyn',
   tr2_ph=1.0d-16,
   outdir='./tmp'
   ldisp=.true.,
   nq1=4, nq2=4, nq3=4
 /


My lattice parameters are a= 3.4 and c=6.1 \AA . Pls correct me If I did
any wrong...

One more doubt is.. How to include LO-TO splitting in Complete phonon
dispersion???? I am doing Insulator to metal transition, and metal did not
contains LO-TO splitting. So, I  check LO-TO changes at transition pressure
and the same I want to compare with ambient pressure .

Looking for favorable reply and Thanks in advance...


with regards
S. Appalakondaiah
Research scholar
University of Hyderabad
Hyderabad
India
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