A reactive interatomic potential based on an analytic bond-order scheme is developed for the ternary system W-C-H. The model combines Brenner's hydrocarbon potential with parameter sets for W-W, W-C and W-H interactions and is adjusted to materials properties of reference structures with different local atomic coordinations including tungsten carbide, W-H molecules as well as H dissolved in bulk W. The potential has been tested in various scenarios, like surface, defect, and melting properties, none of which were considered in the fitting. The intended area of application is simulations of hydrogen and hydrocarbon interactions with tungsten, that have a crucial role in fusion reactor plasma-walls. Furthermore, this study shows that the angular dependent bond-order scheme can be extended to second-nearest neighbor interactions, which are relevant in body-centered cubic metals. Moreover, it provides a possibly general route for modeling metal carbides.

An analytical bond-order potential for GaN is presented that describes a wide range of structural properties of GaN as well as bonding and structure of the pure constituents. For the systematic fit of the potential parameters reference data are taken from total-energy calculations within the density functional theory if not available from experiments. Although long-range interactions are not explicitly included in the potential, the present model provides a good fit to different structural geometries including defects and high-pressure phases of GaN.

An analytical bond-order potential for GaAs is presented, that allows one to model a wide range of properties of GaAs compound structures, as well as the pure phases of gallium and arsenide, including nonequilibrium configurations. The functional form is based on the bond-order scheme as devised by Abell-Tersoff and Brenner, while a systematic fitting scheme starting from the Pauling relation is used for determining all adjustable parameters. Reference data were taken from experiments if available, or computed by self-consistent total-energy calculations within the local density-functional theory otherwise. For fitting the parameters, only structural data of the metallic phases of gallium and arsenide as well as those of different GaAs phases were used. A number of tests on point defect properties, surface properties, and melting behavior have been performed afterward in order to validate the accuracy and transferability of the potential model, but were not part of the fitting procedure. While point defect properties and surfaces with low As content are found to be in good agreement with literature data, the description of As-rich surface reconstructions is not satisfactory. In the case of molten GaAs we find support for a structural model based on experiment that indicates a polymerized arsenic phase in the melt.

We are studying ion-irradiation-induced amorphization in Si, Ge, and GaAs using molecular-dynamics simulations. Although high-energy recoils produce defects and amorphous pockets, we show that low-energy recoils ͑about 5-10 eV͒ can lead to a significant component of the athermal recrystallization of preexisting damage. For typical experimental irradiation conditions this recrystallization is, however, not sufficient to fully recrystallize larger amorphous pockets, which grow and induce full amorphization. We also examine the coordination and topological defect structures in Si, Ge, and GaAs observed in the simulations, and find that these structures can explain some experimentally observed features found in amorphous semiconductors. For irradiated amorphous GaAs, we suggest that long ͑about 2.8 Å͒ and weak Ga-Ga bonds, also present in pure Ga, are produced during irradiation.