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<div class="moz-cite-prefix">On 03/08/2015 08:01, Umesh Roy wrote:<br>
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<div>Dear Stefano,</div>
Yes we can identify the type phonon modes by looking
at the eigen vectors whether it is LA or TO. To clarify my
question here in the following I attached the input file for
matdyn.x to compute the phonon frequencies from interatomic
force contant at any orbitrary q vectors. I have taken a fixed
q vector of magnitude |q|=0.4 in the units of (2*pi/a) and say
a number of directions of 196. I calculated phonon frequencies
along all these directions. For small group of q vectors we
know that first three modes are acoustic modes and the higher
modes are optical modes. As we increase magnitude of q vectors
we can have optical modes lower than the acoustic modes in
magnitude in a specific direction. As we see that the phonon
frequencies are written in the file <b>fe.freq</b> increasing
order. My question is if they are printed as increasing order
then how do we know which frequency belongs to acoustic branch
and which frequency belongs to optical branch? <br>
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you don't. <br>
or rather define what you mean by acoustic and apply the definition.
:)<br>
I can think of at least two definitions and they differ, so it's up
to you.<br>
It may be useful to ask yourself WHY you want to separate the
acoustic branches from the others.<br>
<br>
stefano<br>
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<div>Thank you.<br>
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