Edge-driven transition in the surface structure of nanoscale silicon

We present an ab initio exploration of the phenomena that might become important for free-standing structures of silicon as they are realized on the nanoscale. We find that not only surface effects, but also edge effects are important considerations in structures of dimensions similar to 3 nm. Specifically, for long nanoscale silicon bars, we find two competing low-energy reconstructions with a transition from one to the other as the cross section of the bar decreases. We predict that this size-dependent phase transition has a signature in the. electronic structure of the bar but little effect on elastic properties. [S0163-1829(98)05419-8].