[Pw_forum] Separation between acoustic modes and optical modes

[Umesh Roy]

Dear Stefano,
         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 *fe.freq* 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?



Thank you.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150803/dbff9619/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: matdyn.in
Type: application/octet-stream
Size: 9100 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150803/dbff9619/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: fe.freq
Type: application/octet-stream
Size: 11985 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20150803/dbff9619/attachment-0001.obj>