I have searched the Pw_forum but was not able to find a response to a previous post. I am including the portion of the original post that I am curious about below. I have the same question. After running my electron-phonon calculations some of my q-points (G-M in graphene) have only a "-1" for each of the real x,y,z-components of one atom and zero everywhere else as written under "modes" in the electron-phonon output file. I assumed "modes" corresponded to the phonon eigenvectors, but this would imply 6 optical modes at some q values which is not correct (although along different symmetry lines it looks like the correct format for eigenvectors).
Thank you, Shela Part of original Post: Date: Thu, 14 May 2009 12:05:53 -0400 Subject: [Pw_forum] unitary matrix u Message-ID: <2C1C44865AA64068BE6465660B5DEA6E at ece.ncsu.edu> ".....there is always only one nonzero component. For instance, the first eigenvector is (-1,0,0,0,0,0). Obviously, all six eigenvectors are orthonormal, which is how it's supposed to be. But here is what bothers me. For acoustic phonon modes, the unit cell moves as a whole, i.e. both atoms must move with the same phase. So I expect to see something like (1/sqrt(2),0,0, 1/sqrt(2),0,0), instead of (-1,0,0,0,0,0). For optical branches on the other hand, two atoms have the opposite phase (the center of mass of the unit cell does not move), so I would expect to see something like (1/sqrt(2),0,0, -1/sqrt(2),0,0). My understanding is this: if every eigenvector has only one nonzero component, it means that in each mode, one atom is not moving at all! Maybe, I misunderstood the meaning of components of the matrix u? " -- Shela Aboud CEES Sr. Research Scientist 367 Panama St. GES 077A Stanford University Stanford, CA 94305-2220 shela.aboud at stanford.edu (650) 721-2276
