(810f) Energetics, Structure, and Dynamics of Graphene-Based Nanoparticles

The understanding of the behavior of carbon materials that include nanoparticles composed of a few graphene domains would be greatly aided by the availability of basic properties of the isolated crystalline nanoparticles. In this work, the energetics, structure, and dynamics of three isolated graphitic nanoparticles of different sizes were studied using Molecular Dynamics (MD) simulations.  Results show that the bonded potential energies (stretching, bending, and torsion) and in-plane nonbonded potential energy become less favorable with increasing temperature and particle size, corresponding to increased out of plane ripples. The interplanar binding energy becomes less favorable with increasing temperature and decreasing particle size leading to structural energetics that are more like freestanding graphene. The heat capacity varies little with either nanoparticle size or temperature.  The interplanar spacing increases as the binding energy between the graphene layers is relaxed with decreasing nanoparticle size, in agreement with experimental observations.  Three types of planar motion (breathing, sliding, and rocking) are characterized across a range of temperatures.  The fundamental frequencies were calculated through Fourier transforms of the corresponding motions.  The frequency for sliding is close to that seen for AB-stacking graphite.  Two major frequencies are also observed for the breathing motion.  These frequencies show weak dependence on temperature in the temperature range studied.  The fundamental information on the energetics, structure, and dynamics of these graphitic nanoparticles will help explain such processes as Li-ion diffusion in these kinds of materials in the future.