Surface and Thermodynamic Interatomic Force Fields for Silicon Clusters and Bulk Phases

We show that when the angular dependence of three-body forces is adjusted to describe covalent-metallic phase transitions rather than small-amplitude atomic vibrations, a simple and accurate force field is obtained which is easily extended to describe energies and structures of ${\mathrm{Si}}_n$ vapor-phase clusters ($3\le n\le 10$). Our model may have widespread applications to amorphous phases, melting, and extended defects.