Cluster melting equilibrium behavior

The abscissas of the correlation diagrams can be quantified. The quantification is thus far only an ex post facto device with power to classify but not yet to predict. It does not yet have a microscopic interpretation. Nevertheless it satisfies the needs of a theory of the equilibrium behavior of melting and freezing of clusters. Only the existence and not the definition of the nonrigidity parameter or the details of its origins is used in stage 2. However, we make a brief aside here to explain the definition in order to clarify just what information it carries. To understand the order parameter y (not to be confused with the surface tension), it is useful to examine how nonrigidity is traditionally characterized in diatomic and linear, particularly triatomic molecules. For... 

Not all clusters meet these conditions. Some, such as Lia, pass readily among potential minima, even when they are in their ground states. Others possess potential surfaces which do not allow the clear distinction into two kinds of behavior. Nonetheless the equilibrium behavior of the phases of the cluster tells us that the freezing and melting temperatures are not logically linked, except in the limit of N - oo, and that the first-order solid-liquid phase... 

After calibration, the dissociation rate is extrapolated down to low energies, and in the present situation some noteworthy non-monotonic variations are found at energies close to 140 kcal mol These variations are not spurious, but convey some strong anharmonidties in both parent and product clusters assod-ated with the occurrence of melting in this energy range. That dissodation properties relate to the thermodynamical behavior can be understood on the basis that the density of states is important to measure the available phase space open to dissociation, but is also characteristic of statistical properties at equilibrium, in particular the partition ftmction and all other canonical observables. Interestingly, the connection between dissodation properties and thermodynamic features such as phase transitions has been the subject of intense experimental and theoretical research, not only in cluster physics and chemistry, but also in nuclear physics. ... 

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