Molecular dynamics study of toroidal and helically coiled forms of graphitic carbon

The rotational symmetry, cohesive energies, and thermal stabilities of the toroidal forms, as well as helically coiled forms derived from C-240, C-360, and C-540, are studied by molecular dynamics. For various rotational symmetric helically coiled forms, the dependence of the polygon patterns in the inner ridge line on the coil length is studied. For the short-coil-length limit, the surface consists of pentagons, hexagons, and heptagons. For C-240 and C-360 helices the surface patterns are changed with increasing coil length. By stretching the helically coils along the fiber axis, we found that the surface of C-384 helix, eightfold rotational symmetric form derived from torus C-240, consisting of pentagons and heptagons without heptagons becomes stable as the coil length becomes longer.