Simulation of amorphous carbon with a bond-order potential

Simulations of amorphous carbon were performed at densities ranging from 2.0 to 3.0 g/cm3 with a reactive bond-order potential. The fraction of sp3 bonding increases with increasing density, as is observed experimentally, but with generally too much sp2 content. Ring size distributions are calculated, with a number of large rings observed. It is suggested that structural quantities that are more directly related to physical properties-such as void volumes and coordination numbers-are more useful than ring size distributions in characterizing the structure of amorphous carbon. Void fractions and void volume distributions are calculated, indicating that a percolating void network exists at 2.0 g/cm3, large, non-percolating voids exist at intermediate density, and no voids are found larger than atomic volumes at 3.0 g/cm3