Carbon clusters: From ring structures to nanographene

The lowest energy configurations of Cn(n =< 55) clusters are obtained using the energy mini- mization technique with the conjugate gradient (CG) method where a modified Brenner potential is invoked to describe the carbon and hydrocarbon interaction. We found that the ground state configuration consists of a single ring for small number of C atoms and multi-ring structures are found with increasing n, which can be in planar, bowl-like or cap-like form. Contrary to previous predictions, the binding energy Eb does not show even-odd oscillations and only small jumps are found in the Eb(n) curve as a consequence of specific types of edges or equivalently the number of secondary atoms. We found that hydrogenation of the edge atoms may change the ground state configuration of the nanocluster. In both cases we determined the magic clusters. Special attention is paid to trigonal and hexagonal shaped carbon clusters and to clusters having a graphene-like configuration. Trigonal clusters are never the ground state, while hexagonal shaped clusters are only the ground state when they have zigzag edges.Comment: Accepted for publication in Phys. Rev.

Theoretical study of the stable states of small carbon clusters Cn (n = 2-10)

Both even- and odd-numbered neutral carbon clusters Cn (n = 2-10) are systematically studied using the energy minimization method and the modified Brenner potential for the carbon-carbon interactions. Many stable configurations were found and several new isomers are predicted. For the lowest energy stable configurations we obtained their binding energies and bond lengths. We found that for n < 6 the linear isomer is the most stable one while for n > 5 the monocyclic isomer becomes the most stable. The latter was found to be regular for all studied clusters. The dependence of the binding energy for linear and cyclic clusters versus the cluster size n (n = 2-10) is found to be in good agreement with several previous calculations, in particular with ab initio calculations as well as with experimental data for n = 2-5.Comment: Submitted to Phys. Rev.

First-principles modeling of the polycyclic aromatic hydrocarbons reduction

Density functional theory modelling of the reduction of realistic nanographene molecules (C42H18, C48H18 and C60H24) by molecular hydrogen evidences for the presence of limits in the hydrogenation process. These limits caused the contentions between three-fold symmetry of polycyclic aromatic hydrocarbon molecules and two-fold symmetry of adsorbed hydrogen pairs. Increase of the binding energy between nanographenes during reduction is also discussed as possible cause of the experimentally observed limited hydrogenation of studied nanographenes.Comment: 18 pages, 7 figures, accepted to J. Phys. Chem.

The Study on the Medium-Sized Carbon Islands on Ru(0001) Surface

During chemical vapor deposition (CVD) growth of graphene on Ru(0001) surface, a specific C cluster, which has 13 C atoms arranged as three connected hexagons (so called 3-C-6), was supposed to be extremely stable. To verify this, we systemically explored the stabilities of carbon clusters C-N (N = 12, 13, 14) on the Ru(0001) surface by using first principle approach. While, it is surprising that neither 3-C-6 is the ground state of C-13 nor the C-13 cluster shows exceptional stability. So, based on the experimental STM image with C-3v symmetry and a dimmer of 1 nm, the magic cluster was proposed as C-21 or C-21-3C, which have the same core composed of six hexagons and three pentagons, as that studied before. This study is helpful to resolve the debate on the dominating clusters observed during graphene CVD growth and is helpful for understanding the growth mechanism of graphene CVD growth