1. The problem statement, all variables and given/known data Good morning. I am currently doing an solid state problem; in this part, I have to tell if these vibration modes are odd or even. I am working at the lattice centre. The modes are these http://postimg.org/image/8nmv7ickz/. 2. Relevant equations None 3. The attempt at a solution The centre of inversion is the blue cross; I have studied only two dimensional modes, so I don't have very clear how the three dimensional translations have to be done; I think it that this is what happens: http://postimg.org/image/xd01nfxr1/ which would make both modes odd. Can someone please confirm this? Thanks for reading.