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Number of modes for a 2d crystal

  1. Apr 4, 2014 #1
    Hi, I have problems with the following:

    Number of modes for a 2d crystal with one atom per primittive unit cell.

    1. Number of discrete vibrational modes?
    Should there be 2N of them? That is what I come up with if I think of one transverse and one longitudinal mode for each k. But I am unsure.

    2. So am I able to obtain two branches from this crystal?
    Both of them are acoustical?

    Thank you :D
  2. jcsd
  3. Apr 5, 2014 #2


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    Science Advisor

    Yes, both conclusions seem to be correct to me.
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