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Homework Help: Phonon vibrational modes

  1. Mar 20, 2015 #1
    1. The problem statement, all variables and given/known data
    2. Relevant equations

    3. The attempt at a solution
    Since it's 3D, I assume there's at least 3 acoustic modes and 3 optical modes? After all, the soundwaves/phonons must be able to travel in all directions.

    Further on, I know both longitudinal and transverse modes are possible, but I don't know how this affects the count..
  2. jcsd
  3. Mar 21, 2015 #2
    Nobody knows? Perhaps something in my question is unclear?
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