MICROSCOPIC STRUCTURE OF TETRAHEDRAL AMORPHOUS-CARBON

Simulations are reported of a highly tetrahedral amorphous carbon netw ork at a density of 3 g/cc using Car-Parrinello first principles molec ular dynamics. The simulated structure consists of 65% fourfold and 35 % threefold coordinated carbon sites,in good agreement with experiment . The structure is also in good agreement with recent neutron diffract ion data. An unexpected observation was the presence of small carbon r ings in the structure containing as few as three atoms. These carbon t riangles and quadrilaterals, which resemble the organic compounds cycl opropane and cyclobutane, give the network a topology unique among tet rahedrally bonded amorphous materials.