Structural correlations in silicon microclusters

The pair-correlation and angle-distribution functions for silicon microclusters containing 620 atoms have been calculated through molecular-dynamics (MD) simulation with use of the Stillinger-Weber three-body potential. To model the experimental situation where the investigation of the structure of small clusters usually involves a size distribution, we have determined an effective pair-correlation function by folding together the pair correlations of individual clusters. The simulation results indicate that small covalently bonded clusters may undergo structural transformations at temperatures lower than 20% of their bulk melting temperature. This necessitates detailed knowledge of the ensemble of configurations lying above the ground state to explain the experimentally determined structure as well as to explain the existence of the so-called magic numbers. Our results also show that the presence of a distribution of silicon cluster sizes, each with different topologies, yields an amorphouslike pair-correlation function with the nearest-neighbor distance of crystalline silicon and an angle distribution peaked about 90°and 108°. © 1988 The American Physical Society.