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written by
Harvey Gould and Jan Tobochnik *

Because there are only a few problems in statistical mechanics that can be solved exactly, we need to develop techniques for obtaining approximate solutions. In this chapter we introduce several perturbation methods that are applicable when there is a small expansion parameter. Our discussion of the classical monatomic gas will involve many of the same considerations and diffculties encountered in quantum field theory (although knowledge of the latter is not assumed). For example, we will introduce diagrams that are analogous to Feynman diagrams and and divergences analogous to those found in quantum electrodynamics. We also discuss the spatial correlations between particles due to their interactions and the use of hard spheres as a reference system for understanding the properties of liquids.

Published *September 2, 2008*

Last Modified *June 8, 2010*

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