Isotherma-Isobaric Ensemble

Symbols: denotes the partition function for the canonical ensemble, for the isotherma-isobaric ensemble, and for the grand canonical ensemble.

In the isotherma-isobaric ensemble the volume of the system is not fixed. Thus the system is also in pressure equillibrium as well a thermal one. (, and are fixed)

With the partition function being given by

for the continuous case, or alternatively

Note that for the discrete case

Where is the Gibbs Free Energy. Similar to before, this leads us to conclude that .