Canonical ensemble

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A canonical ensemble in statistical mechanics is an ensemble of dynamically similar systems, each of which can share its energy with a large heat reservoir, or heat bath. Equivalently, the members of the ensemble can be considered loosely-coupled to each other so that they can share the total energy. The distribution of the total energy amongst the possible dynamical states (i.e. the members of the ensemble) is given by the partition function. A generalization of this is the grand canonical ensemble, in which the systems may share particles as well as energy. By contrast, in the microcanonical ensemble, the energy of each individual system is fixed.

A full development of the concept of the canonical ensemble is given in the article on the partition function. An example of the mathematical formulation of the canonical ensemble as a probability measure expressed in the language of measure theory is given in the article on the Potts model.