Minimization studies of elemental carbon using LCBOP semi-empirical potential.

Elemental carbon is interesting to study thanks to its material properties and structural diversity, which ranges from nanotubes through graphite to diamond. In our study of slow-cooled carbon droplets condensed in cool-star atmospheres, computational study with semi-empirical potentials is complementary to experiment and ab initio work. We’ve used the long-range carbon bond-order potential to relax, via conjugate gradient, 1.8 g/cc liquid-like carbon tiled-cube and isolated-cluster systems with 13, 20 and 100 atoms, as well as tetrahedral nanodiamond clusters of 17, 22 and 29 atoms. Tiled-cube simulation nearest neighbor histograms show a bond defining gap between 1.7-2.0 Å. Coordination statistics then show a high percentage of sp and sp2 coordination. Ring sizes of 5 - 7 atoms form more prominently than others, with 5 and 6 atom rings especially abundant. Isolated cluster relaxations show a high amount of sp chains forming, and less ring formation than the tiled-cube simulations. We also see a volume increase for the isolated clusters, unlike comparable density functional theory (DFT) simulations. Our isolated diamond-cluster relaxations saw less surface reconstruction than with DFT.