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An analytic interatomic bond-order potential ͑BOP͒ is derived that depends explicitly on the group number of the sp-valent element. This is achieved by generalizing the previously published BOP for group-IV elements by extrapolating from half-full occupancy using a simple envelope function for the upper bound of the bond order. This interatomic potential predicts the structural trends across the sp-valent elements that are found by our tight-binding reference calculations and observed by experiment. Unlike empirical interatomic potentials this theoretically derived BOP includes the valence-dependent character of the bonding naturally within its remit.

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Computational studies of atomic assembly processes during GaAs vapor deposition require interatomic potentials that are able to reasonably predict the structures and energies of a molecular arsenic vapor, a variety of elemental gallium and arsenic lattices, binary GaAs lattices, GaAs lattice defects, and ͑001͒ GaAs surfaces. These properties were systematically evaluated and compared to ab initio and experimental data for one Tersoff and two Stillinger-Weber ͑SW͒ GaAs interatomic potentials. It was observed that bulk and arsenic molecular properties calculated by the Tersoff parametrization matched density functional predictions and experimental observations significantly better than either of the SW parametrizations. These trends can be related to the bonding physics included in each potential format. Surface free energy calculations indicate that none of these potentials correctly predict the low-energy surface reconstructions of the GaAs ͑001͒ surface. Simulated As 2 molecular bonding with gallium-rich GaAs ͑001͒ surfaces indicate a high sticking probability for SW potentials, which is in good agreement with experimental observations at low growth temperatures. However, the Tersoff parametrization resulted in an unphysically high desorption probability for As 2 over a wide range of surface temperatures.

Molecular dynamics simulations using a recently developed Ga-N Tersoff type bond order interatomic potential have been used to investigate the growth mechanisms of ͑0001͒ wurtzite GaN films from thermalized atomic gallium and nitrogen fluxes. The crystallinity and stoichiometry of the deposited wurtzite lattice structures were determined as a function of growth temperature and N:Ga flux ratio. The lattice perfection was found to improve as the growth temperature was increased to 500 K. At a fixed growth temperature, the lattice quality and stoichiometry both reached optimum as the N:Ga ratio approached a value between two and three. The optimum flux ratio increased with increasing growth temperature. These three observations are consistent with experimental studies of growth on wurtzite phase promoting substrates. The atomic assembly mechanisms responsible for these effects have been explored using time-resolved atom position images. The analysis revealed that high quality crystalline growth only occurred when off-lattice atoms ͑which are usually associated with amorphous embryos or defect complexes͒ formed during deposition were able to move to unoccupied lattice sites by thermally activated diffusion processes. The need for a high N:Ga flux ratio to synthesize stochiometric films arises because many of the nitrogen adatoms that impact N-rich ͑0001͒ GaN surfaces are re-evaporated. Reductions of the substrate temperature reduce this reevaporation and as a result, the optimum N:Ga ratio for the stoichiometric film formation ͑and best lattice perfection͒ was reduced as the growth temperature was decreased.