Explain what is meant by the electron-phonon interaction. Taking the one-dimensional diatomic chain treated in Chap. 6 as an example, illustrate with a simple diagram the difference between the coupling of an electron to an acoustic and an optic vibration of the chain. It is helpful to think of the electronic bands as overlapping atomic wavefunctions, i.e., to think with the “tight-binding model” of the electronic band structure.