https://doi.org/10.1007/s100530050304
Simulating the thermal stability and phase changes of small carbon clusters and fullerenes
Departamento de Física Teórica,
Universidad de Valladolid, 47011 Valladolid, Spain
Received:
25
March
1998
Revised:
30
October
1998
Published online: 15 May 1999
The thermal stability, phases and phase changes of small carbon clusters
and fullerenes are investigated by constant energy Molecular Dynamics
simulations performed over a wide range of temperatures, i.e., from
to above the melting point of graphitic carbon.
The covalent bonds between the carbon atoms in the clusters are
represented by the many-body Tersoff potential.
The zero temperature structural characteristics of the clusters, i.e.,
the minimum energy structures as well as the isomer hierarchy can be
rationalized in terms of the interplay between the strain energy (due
to the surface curvature) and the number of dangling bonds in the cluster.
Minimization of the strain energy opposes the formation of cage structures
whereas minimization of the number of dangling bonds favors it.
To obtain a reliable picture of the processes experienced by carbon clusters
as a function of temperature, both thermal and dynamical characteristics
of the clusters are carefully analyzed.
We find that higher excitation temperatures are required for producing
structural transformations in the minimum energy structures
than in higher lying isomers.
We have also been able to unambiguously identify some structural changes
of the clusters occurring at temperatures well below the melting-like
transition.
On the other hand, the melting-like transition is interrupted before
completion, i.e., the thermal decomposition of the clusters (evaporation
or ejection of
or
units) occurs, from highly excited
configurations, before the clusters have fully developed a liquid-like
phase.
Comparison with experiments on the thermal decomposition of
and
a discussion of the possible implications of our results on the growth
mechanisms leading to the
formation of different carbon structures are
included.
PACS: 36.40.Ei – Phase transitions in clusters / 61.48.+c – Fullerenes and fullerene-related materials / 82.30.Qt – Isomerization and rearrangement
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 1999