Surface and thermodynamic interatomic force fields for silicon clusters and bulk phases

We have developed new interatomic force fields which describe the phase stability of crystalline silicon and small clusters of silicon. We show that when three-body forces are adjusted to describe ‘‘covalent→metallic’’ phase transitions instead of small-amplitude atomic vibrations, a simple and accurate force field is obtained. This force field can be easily modified to describe energies and structures of ${\mathrm{Si}}_{\mathit{n}}$ vapor-phase clusters. A key aspect of the cluster problem is the transfer of bond strength from dangling bonds to back bonds. We expect our potential will have widespread applications to the formation and activation energies for diffusion of defects in crystalline Si and to the structural properties of amorphous and liquid silicon.