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 Si sub n vapor-phase clusters (2 =n=10). Our model may have widespread applications to amorphous phases, melting and extended defects.