your phonon branches are really strange... with two atoms I would expect 6 modes per each q-point
stefano Viet Bac wrote: > Dear Pw_users, > > I am trying to do calculation phonon dispersion and EPC for 1D > Aluminum chain. I got the results which are strange phonon branches > appearing. In the case of 2 atom-cell, I got 4 phonon branches, two of > them are Optical and Acoustical phonon branches and two others, which > have zero and negative values, are unknown for me. In the case if I > have 1 atom-cell, that strange branch also appears. Could any body > explain for me what kind of frequencies here? > > I was surfing this forum and FAQ and I found many discussion about > negative frequencies, but I still cannot find the answers for me. > > Bac >
