Coexistence and Phase Separation in Clusters:
From the Small to the Not-so-Small Regime
David J. Wales and Jonathan P. K. Doye
J. Chem. Phys. 103, 3061-3070 (1995)
We generalise the necessary and sufficient conditions for finite
systems to exhibit Van der Waals-type loops (or `S-bends') in
thermodynamic functions. In the infinite limit such features are
forbidden by Van Hove's theorem, and phase separation occurs instead.
However, in small systems the energetic cost of the interface associated
with phase separation is too great, and there is no contribution to the
partition function from regions of phase
space corresponding to two phases coexisting in contact. We derive a
simple model which can correctly describe both limits, and investigate
how the onset of phase separation will affect observable thermodynamic
The full article can be obtained from JCP online.
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