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<div class="moz-cite-prefix">Dear Umesh<br>
I'm not sure I understand your problem.<br>
if acoustic modes and optical ones have different symmetries
(LA and TO for instance in specific directins) they can overlap in
frequency but still be distinct objects that you can identify by
examining the eigenvectors. If they have the same symmetry
(typically no symmetry at all for a generic q direction in the BZ)
they interact and get mixed so there aren't purely acoustic or
purely optical modes any more.<br>
<br>
stefano<br>
<br>
<br>
On 01/08/2015 13:21, Umesh Roy wrote:<br>
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<div dir="ltr">Dear All,
<div> I have calculated modes of vibration of Iron in
different directions for a fix phonon wave vector q (in a
large number of directions). Since in Quantum espresso phonon
modes are printed in increasing order for a given q vector.
For a small group of q the acoustic and optical branches do
not overlap so, we can easily separate out the acoustic branch
from the optical branch. As we increase the magnitude of q the
acoustic branch and the optical branch get mixed up. So , how
to separate out the acoustic modes or is there any way of
filtering the optical modes?</div>
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<div>Thank you in advance</div>
<div><br>
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<div><span style="color:rgb(0,0,255)"><span
style="background-color:rgb(243,243,243)"><i><b>Umesh Chandra Roy</b><br>
Research Scholar, School of Physical
Sciences<br>
Jawaharlal Nehru University, New
Delhi-110067,<br>
</i></span></span></div>
<div><span style="color:rgb(0,0,255)"><span
style="background-color:rgb(243,243,243)"><i>India.<br>
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style="color:rgb(0,0,255)">Email</span>:</font><b>umesh24crp@gmail.com</b></a><br>
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