B.L. Zhang

Structures of large fullerenes: C60 to C94

Abstract A systematic study of the structures of large carbon fullerenes ranging from C 60 to C 94 is performed. We first generate the topological networks for candidate structures using an efficient cage network generation scheme. The resultant networks were relaxed with tight-binding molecular dynamics to obtain the ground-state structures for various low-energy isomers. Unlike the buckminsterfullerene C 60 , the large carbon fullerenes prefer structures with low symmetry and several isomers can be very close in energy and may coexist in synthesis.

The geometry of large fullerene cages : C72 to C102

Combining an efficient simulated annealing scheme for generating closed, hollow, spheroidal cage structures with a tight‐binding molecular‐dynamics method for energy optimization, the ground‐state structure of every even‐numbered carbon fullerene from C72 to C102 is determined. As a general trend, most ground‐state structures of the large fullerenes have relatively low symmetries. In many cases, several isomers of a fullerene are found to have competitively low energies, which suggests that a mixture of these isomers can be observed in experimental prepared samples.

Search for the ground‐state structure of C84

Using a well‐tested tight‐binding potential, we have studied all twenty‐four isolated‐pentagon isomers of the C84 fullerene. Unlike C76, the helical D2 isomer of C84 is energetically very unfavorable. Two isomers which have D2 and D2d symmetries are found to be much more stable than the rest. The energies of these two isomers are so close that they may coexist in synthesis.

Electronic structures of C82 fullerene isomers

Abstract We have studied the electronic structures of all isolated-pentagon C 82 isomers using a first-principle local-density functional approach. Our results indicate that the ground-state isomer with C 2 symmetry is the most abundant isomer, in agreement with the conclusion obtained by recent experimental 13 C nuclear magnetic resonance spectroscopy. A detailed analysis of the structural and electronic properties of these fullerene isomers is also presented.

STRUCTURE, STABILITY, AND ELECTRONIC PROPERTIES OF LARGE FULLERENES

The recent development in understanding the structures, relative stability, and electronic properties of large fullerenes is reviewed. We describe an efficient scheme to generate the ground-state networks for fullerene clusters. Combining this scheme with quantum-mechanical total-energy calculations, the ground-state structures of fullerenes ranging from C20 to C100 have been studied. Fullerenes of sizes 60, 70, and 84 are found to be energetically more stable than their neighbors. In addition to the energies, the fragmentation stability and the chemical reactivity of the clusters are shown to be important in determining the abundance of fullerene isomers.

Which D2 fullerene isomer of C84 has been observed

Abstract We present the results of a first-principles study for the geometries, energies and electronic properties of four C 84 fullerene isomers that have the D 2 symmetry and satisfy the isolated-pentagon rule. Our approach is based on the all-electron local-density functional method for molecules with complete geometry optimization. Comparison of the results from the present calculation with available experimental data favors the ground-state D 2 isomer over the one proposed by the ring-stacking model.

First-principles study of C96 fullerene isomers

Abstract Four low-energy cage structures of C 96 fullerene isomers have been investigated using a combination of first-principles local-density functional approach and an efficient cage network generating scheme. Our results indicate that a low-symmetry C 2 isomer is the ground-state structure, which provides useful information for experimental characterization. A detailed analysis of the structural and electronic properties of these fullerene isomers is also presented.

Melting of carbon cages

We simulate the melting of carbon fullerenes by molecular dynamics using an accurate tight-binding model. The melting temperatures are obtained for fullerness ranging from C20 to C84. For small cages (n≤58), We found that the melting temperature increases almost linearly with the cluster size. However, the melting temperature of the larger fullerenes (n=60 and n≥70) is fairly constant and does not change much with cluster size.

STRUCTURES AND STABILITIES OF CARBON FULLERENES

The structures and stabilities of carbon fullerenes Cn(n=20–94) are studied with tight-binding molecular dynamics in combination with a new scheme for generating energetically favorable fullerene networks. Magic numbers for fullerene formation energy are observed at n=60, 70 and 84. The experimental observation of the more abundant fullerenes is related to the fragmentation stabilities and chemical reactivities of the fullerenes obtained from our calculations.

Tight-Binding Molecular Dynamics Study of C60 and Other Carbon Clusters

The structure and dynamics of C60 buckyball and carbon clusters C n (n=2–90) have been studied with molecular dynamics simulations using a tight-binding potential model. The studies show that it is possible to nucleate a ‘buckyball-like’ cluster by cooling and compressing carbon atoms from the gas phase. The studies also show that there is a transition from one-dimensional linear and cyclic structures to two-dimensional cage structures as the number of carbon atoms reaches n=20. Magic numbers for fullerene formation energy are observed at n=50,60,70 and 84.