Structural model of amorphous silicon annealed with tight binding

Abstract

We present a model of amorphous silicon generated by extensive annealing of a continuous random network structure using a molecular dynamics simulation with forces computed by a tight-binding total energy method. We also produce a refined model by relaxing the annealed model using density functional theory. Our annealed structure is primarily a fourfold coordinated continuous random network, with a few coordination defects. The first peak of the pair correlation function of the annealed structure is sharper and more symmetric than the unannealed structure, a result confirmed in the density-function-theory relaxed structure and in good agreement with static disorder results from recent x-ray diffraction analysis by Laaziri et al. The density, bond angle distribution function, elastic constants, and vibrational density of states of the initial and annealed structures are similar. The energy of the annealed structure is lower for both tight-binding and density-functional theory, indicating that the structure with coordination defects is energetically favored. The electronic structure of the annealed structure, computed with both charge-self-consistent tight-binding and density-functional theory, has a wide gap with several occupied gap states.