Hello everyone, I am making a phonon calculation using ph.x. I have a 2D structure with 5 atoms in the unitcell. I use perodic bounday conditions. My phonon results are all perfectly fine except for one (almost) horizontal band apperaing in the negative region.
In the quantum espresso web site I read a notice saying that negative frequencies can arrive for rotational modes of a molecule. When I look at the details of the negative band, it is at the irreducible representation corresponding to A mode, which suggests that it is a rotational mode (I think?) My question is, what is the reason of such an artifact? My structure is not a single molecule but a supercell, so does it also apply to my calculation? Or should I look for something else? Any kind of help is appreciated. Veli -------------- next part -------------- An HTML attachment was scrubbed... URL: http://pwscf.org/pipermail/pw_forum/attachments/20130313/2bcda8ba/attachment.html
