Atomistic versus two-body central potential models of C-60: A comparative molecular dynamics study

We report on an extensive molecular dynamics investigation of two models of C-60. The first model is based on an effective pair, central potential obtained by integrating the interaction between two carbon atoms over the fullerene cages [L.A. Girifalco, J. Phys. Chem. 96, 858 (1992)]. The second model explicitly takes into account the discrete, "atomistic" structure of the C-60 molecules; we study two different parametrizations of the carbon-carbon interaction, one identical to that employed in the Girifalco approach, the other borrowed from previous studies on graphite [A. Cheng and M.L. Klein, J. Phys. Chem. 95, 6750 (1991)]. We consider a temperature range spanning from 300 to 1900 K, and pressures up to 200 kbar. Results for the lattice spacing and several thermodynamic quantities, as well as for the radial distribution functions, are reported and compared among each other and with experimental data. The central pair model yields only semiquantitative predictions at typical ambient densities, whereas pressures are generally overestimated. Atomistic simulations reproduce to an overall quantitative level of accuracy the experimental C-60 properties. A comparison is also made of the central versus the atomistic potential predictions, when using the same potential parameters in the carbon-carbon interaction. We discuss applications of the adopted modelizations to fullerene systems of current interest, as well as different strategies to optimize the values of the potential parameters.