Comparison of bonding in amorphous silicon and carbon

We present detailed calculations using the total energy pseudopotential method of relaxed amorphous structures at various densities formed metastably in silicon and carbon. These calculations show a number of interesting features: fivefold coordination of atoms in silicon but not in carbon, bond lengths in carbon increased at reduced volume, with the opposite trend in silicon, and three-center orbitals in carbon. Also, the energy is nearly independent of volume in carbon, suggesting that properties of amorphous carbon will depend strongly on the growth process.