[Pw_forum] Fwd: Phonon dispersion from using matdyn.x

[ankit jain]

Hello QE developers and users,

Recently, I am trying to calculate phonon dispersion of a 2D material using
pw.x, ph.x, q2r.x and matdyn.x but I am getting very strange results.

In my calculations the phonon frequencies reported by ph.x are all real for
all non-gamma phonon q-points. But, when I use matdyn.x to calculate phonon
frequencies at other points (other than the one for which ph.x calculated
frequencies), I get negative (imaginary) frequencies. And these negative
frequencies are present for non-gamma points as can be seen in attached
frequency file.

I am having difficulty in understanding these results and hoping someone
could help.

Thank You,
Ankit Jain
PhD Candidate
IIT India
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140831/de8d7368/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: pw.in
Type: application/octet-stream
Size: 602 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140831/de8d7368/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ph.in
Type: application/octet-stream
Size: 151 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140831/de8d7368/attachment-0001.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: q2r.in
Type: application/octet-stream
Size: 97 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140831/de8d7368/attachment-0002.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: matdyn.in
Type: application/octet-stream
Size: 375 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140831/de8d7368/attachment-0003.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: frequency
Type: application/octet-stream
Size: 1007 bytes
Desc: not available
URL: <http://lists.quantum-espresso.org/pipermail/users/attachments/20140831/de8d7368/attachment-0004.obj>