Structural models of amorphous carbon and its surfaces by tight-binding molecular dynamics

Abstract We use liner-scaling tight-binding molecular dynamics to generate three structural models of amorphous carbon (a-C) with different atomic densities. a-C surfaces are then obtained by imposing tensile strain on these computer generated networks until fracture occurs. Our results show that for a given density, the formation energy of surfaces obtained with different tensile strains differ by only a few 10 −1 eV/atom and their structural properties are qualitatively similar. The presence of sp sites at the surface is observed at all densities, but with different concentrations. The surface thicknesses obtained in our simulations agree with experimental data. Furthermore we find that surface roughness increases with the amount of graphitic component in the bulk sample. The same trends of the macroscopic properties are obtained when using a two-center tight-binding (TC-TB) Hamiltonian, an environmental dependent one, and first principles calculations.