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Canonical Bose-Einstein statistics

  1. Feb 9, 2007 #1
    I've been curious as to why Bose-Einstein statistics are always derived using the grand canonical partition function. Yes, I know it is easier, but there must also be an expression for the canonical ensemble. However, I was suprised that I have been unable to find it in the standard sources - so here is my own (troubled) derivation.

    I start with the grand canonical partition function:

    [tex]\sum^{0,1,..,M}_{\{n_k\}} \prod^{\infinty}_{k=1} e^{-\beta\left(\epsilon_k - \mu\right) n_k[/tex]

    where M is 1 for FD and M is infinity for BE stats.

    I now impose the constraint of [tex]N=\sum_k n_k[/tex] and wind up with:

    [tex]\lambda^{N} \prod_{k=1}^{\infinty} \left(1 - e^{-\beta \epsilon_k} \right)^{\pm} = Z_{BE}^{FD}[/tex]

    why didn't the chemical potential go away? I was expecting to get the same expression, but without any lambda term out in front.

    Any ideas? Anyone at least KNOW what the canonical expression IS (so that I can compare my answer)?
    Last edited: Feb 9, 2007
  2. jcsd
  3. Feb 11, 2007 #2
    everyone and his brother seem to be researching BE condensates these days, and yet no one is the least bit curious about this???
  4. Feb 11, 2007 #3


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    don't understand your notation
    what is to the power of +/-? as you know, you get either (1-e^x) or (1+e^x)
  5. Feb 11, 2007 #4
    no...it means you get "a" or "1/a"...

    this is the standard way of writing Fermi-Dirac or Bose-Einstein statistics as combined in one expression, the notation isn't mine...
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