What are the wave vectors at which a standing wave is found for the diatomic chain? at the 1st BZ zone boundary for both acoustic and optical mode no standing waves are found for the diatomic chain (which is in contrast to the monatomic chain) O at the 1st BZ zone boundary, but only for the acoustic mode, in agreement with the solution of the monatomic chain O at the I point for the optical mode

What are the wave vectors at which a standing wave is found for the diatomic chain? at the 1st BZ zone boundary for both acoustic and optical mode no standing waves are found for the diatomic chain (which is in contrast to the monatomic chain) O at the 1st BZ zone boundary, but only for the acoustic mode, in agreement with the solution of the monatomic chain O at the I point for the optical mode