Deriving Planck's radiation law from microscopic considerations? In the usual derivation of Planck's radiation law, the energies or frequencies $\omega$ of the oscillators depend on the measurements $L$ of the black body. The model is such that the only characteristic energy is given by these oscillator excitations and in terms of the temperature $T$. Also, the oscillation amplitude vanishes on the walls. Specifically, the structure of the atom walls doesn't enter the computation. After all, that's pretty much the definition of a black body.
My question:

Are there computations (maybe QED + statistical physics?) for more realistic systems, which might model the interaction of photons with the wall atoms and which give results such that one can see the limiting case to an ideal black body?

The question came up when I wondered about the theory behind emission and absorptions of photons on the walls of a black body. 
 A: An old paper that I've enjoyed immensely for its early and unique take on the relationship between the black-body radiation and the Maxwell velocity distribution of molecules is this one:
A. Einstein, On the Quantum Theory of Radiation. Physikalische Zeitschrift 18, 121 (1917).
It is unfortunately not online anywhere that I could find, but you can find it in English in this book (which can also be a bit hard to find):
D. ter Haar, The Old Quantum Theory. Pergamon Press, 1967. See pp. 167-183.
It annoys me to no end that the copy of this book that I got from Amazon was stamped "DISCARDED - SUNY Geneseo". This particular paper has some remarkable (and still valid!) insights by Einstein that were mostly overlooked in the subsequent rush to the new quantum theory.
My view is that old papers by the Greats have value and hidden nuggets even now! Just read how Feynman redefined how all of modern particle physics is done by coming across an old, mostly ignored paper by Dirac on applying Lagrangian methods to quantum theory.
A: Worrying about the walls can be misleading. See 
A blackbody is not a blackbox
for an illuminating account of the derivation of the Planck spectrum without enclosing the field in a box. If you cant get the published version, see the arxiv version.
EDIT (25 March 2012)
Planck's Radiation Law: A Many Body Theory Perspective
discusses blackbody radiation from a many-body viewpoint. Note that they also consider interactions among the photons and electrons, and still show Planck's law is valid. This might perhaps be considered as arising from the interactions of the photons with the electrons in the walls, if you like. This paper is, of course, also referred to in the first paper I mentioned.
