Influence of Electronic Entropy on Shell Effects

In the previous sections, we showed that consideration of triaxial (ellipsoidal) shapes in the framework of the SCM leads to overall substantial systematic improvement in the agreement between theory and experimental observations pertaining to the major and the fine structure of the size-evolutionary patterns associated with the energetics of fragmentation processes (monomer/dimer dissociation energies and fission energetics) and ionization. 

The theoretical methods and discussion of deformation effects in the previous sections were restricted to zero temperature. However, the experiments are necessarily made with clusters at finite temperatures, a fact that strongly motivates the development of finite-temperature theoretical approaches. 

Due to the difficulty of the subject, to date only a few finite-temperature theoretical studies of metal clusters have been performed. In this section, we discuss briefly some of the conclusions of a recent SCM study [41] regarding the importance of thermal effects. The theoretical details pertaining to this finite-temperature (FT) SE-SCM will not be elaborated here, but they can be found in the aforementioned reference. 

The influence of the electronic entropy on the height of fission barriers has not been studied as yet, but it will undoubtedly be the subject of future research in metal-cluster physics. In any case, based on the results of this section, it is natural to conjecture that electronic-entropy effects will tend to quench the barrier heights, especially in the case of larger multiply charged clusters. 

This research was supported by a grant from the US Department of Energy (Grant No. FG05-86ER45234). Calculations were performed on CRAY computers at the Supercomputer Center at Livermore, California, and the Georgia Institute of Technology Center for Computational Materials Science. 

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