Atomic structure and physical properties of amorphous carbon and its hydrogenated analogs

A semiempirical molecular-dynamic density-functional approach is used to perform a systematic investigation of the stability, structure, and properties of quenched pure and hydrogenated amorphous carbon dependent on the mass density and the hydrogen concentration. By comparing the total structure energies for supercell clusters of equal composition and atom number, we obtain the most stable a-C:H configurations characterized by optimal chemical bonding corresponding to certain mass densities and hydrogen concentrations which control the short- and medium-range order in the material. We present a detailed structural analysis of stable and metastable a-C:H modifications comparing theoretically simulated diffraction data with electron-scattering results. In addition, we discuss correlations between the atomic structure and the electronic properties which in turn are mediated by the chemical bonding and the clustering of different hybridized atoms.