## Phonon waves

Dear hokhani,
Remember we used the periodic boundary condition, just because we have decided to ignorate the effect of the boundary, so you of course can not get any results about "travelling beyond end points". Anyway, in most semiconductor textbook when we consider interaction btw. phonon with electron, photon etc. we never consider the end point case.

And you said "it is in it's second exited state", "it has two phonons", could you tell me who is the "it"??

 Quote by zhanghe Dear hokhani, Remember we used the periodic boundary condition, just because we have decided to ignorate the effect of the boundary, so you of course can not get any results about "travelling beyond end points". Anyway, in most semiconductor textbook when we consider interaction btw. phonon with electron, photon etc. we never consider the end point case. And you said "it is in it's second exited state", "it has two phonons", could you tell me who is the "it"??
We were talking about the vibrational wave. Of course, the same logic applies to a harmonic oscillator consisting of a single atom attached to one very heavy-atom.

The single-atom harmonic oscillator is what is called a "limiting case" for the extended wave. The extended wave comes about because the atoms are coupled to each other by elastic forces. If the two atoms are connected by an elastic force, one atom being much more massive than the other, then the light atom can be considered a harmonic oscillator by its.

 Quote by zhanghe Dear hokhani, Remember we used the periodic boundary condition, just because we have decided to ignorate the effect of the boundary, so you of course can not get any results about "travelling beyond end points". Anyway, in most semiconductor textbook when we consider interaction btw. phonon with electron, photon etc. we never consider the end point case. And you said "it is in it's second exited state", "it has two phonons", could you tell me who is the "it"??
By "it" I mean 1D-harmonic oscillator which has only one oscillation mode and has for example two phonons in that mode.