Chain-like ground states in three dimensions

We investigate the minimization of configurational energies of Brenner type. These include two- and three-body interaction terms, which favor the alignment of first neighbors. In particular, such configurational energies arise in connection with the molecular-mechanical modeling of covalent$sp$-bonding in carbon. Ground states in three dimensions are characterized and the stability of chains and rings is discussed. The interaction energy is then augmented with terms corresponding to weaker interactions favoring the stratification of configurations. This gives rise to stratified structures, which are reminiscent of nanoscrolls and multi-wall nanotubes. Optimal stratified configurations are identified and their geometry is discussed.

Nanoassembly of meso-Tetraphenylporphines on Surfaces of Carbon Materials: Initial Steps as Studied by Molecular Mechanics and Scanning Tunneling Microscopy

We employed MM+ molecular mechanical modeling and scanning tunneling microscopy (STM) in order to analyze the initial steps of nanoassembly of meso-tetraphenylporphine H2 TPP and its cobalt(II) complex CoTPP on the surface of highly-oriented pyrolytic graphite (HOPG) and single-walled carbon nanotubes (SWNTs). According to the MM+ results, monolayer H2 TPP adsorption is more favorable energetically than the formation of porphyrin stacks on both graphite and nanotube sidewall; the formation of parallel interacting chains of H2 TPP on graphite is more preferable than the growth of long single chains; and the assembly into a long-period helixis favored versus the formation of a short-period helixon SWNT sidewall. STM observations of CoTPP complex deposited onto bare HOPG and onto the graphite with deposited SWNTs are consistent with theoretical results. At the same time, both CoTPP single chains and ribbons were observed on HOPG. The formation of short-period helices on the nanotube sidewalls was concluded to be more likely than the long-period helical nanoassembly.