Non-monotonic size effects on the structure and thermodynamics
of Coulomb clusters in three-dimensional harmonic traps |
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Authors: | F Calvo E Yurtsever |
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Institution: | 1.Laboratoire de Chimie et Physique Quantiques, IRSAMC, Université Paul Sabatier,Toulouse Cedex,France;2.Ko? University,Istanbul,Turkey |
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Abstract: | Finite-size effects on the static and thermodynamical
properties of small three-dimensional clusters of identical charged
particles confined by an harmonic trap are investigated using global
optimization and numerical simulations. The relative stabilities of
clusters containing up to 100 particles are estimated from the
second energy derivatives, as well as from the energy gap between
the two lowest-energy structures at a given size. We also provide a
lower bound for the number of permutationally independent minima, as
a function of size, up to n=75. Molecular dynamics and exchange
Monte Carlo simulations are performed to get insight into the finite
temperature behaviour of these clusters. By focusing on specific
sizes, we illustrate the interplay between the stable structures,
the possible competition between different isomers, and the melting
point. In particular, we find that the orientational melting
phenomenon known in two-dimensional clusters has an equivalent form
in some three-dimensional clusters. The vibrational spectra,
computed for all sizes up to 100, shows an increasing number of
low-frequency modes, but comparing to hydrodynamical theory reveals
strong correlation effects. Finally, we investigate the effects
of the trap anisotropy on the general shape of Coulomb clusters, and
on the melting point of a selected case. |
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Keywords: | 36 40 Mr Spectroscopy and geometrical structure of clusters 36 40 Ei Phase transitions in clusters 64 60 Cn Order-disorder transformations statistical mechanics of model systems 68 65 -k Low-dimensional mesoscopic and nanoscale systems: structure and nonelectronic properties |
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