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Band gap - violation of principle of least energy?

  1. Feb 7, 2010 #1
    How does the band gap not violate the principle of least energy? Surely the most favourable states are those with minimum available energy - but there is a gap!
     
  2. jcsd
  3. Feb 7, 2010 #2

    ZapperZ

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    This is a bit puzzling. Why would the existence of a band gap violate principle of least energy? Even if there's no band gap, there are still electrons not in the "lowest" energy state, because those states are filled. That's why you have a Fermi level. So why would there be any problem when there's a band gap?

    Zz.
     
  4. Feb 7, 2010 #3
    But the states in the band gap aren't filled?
     
  5. Feb 7, 2010 #4

    ZapperZ

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    There are NO states in the gap!. That, by definition, is what is meant as a "band gap"! There are no states in the single-particle density of states there!

    Zz.
     
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