  An optimized interatomic potential has been constructed for silicon using a
modified Tersoff model. The potential reproduces a wide range of properties of
Si and improves over existing potentials with respect to point defect
structures and energies, surface energies and reconstructions, thermal
expansion, melting temperature and other properties. The proposed potential is
compared with three other potentials from the literature. The potentials
demonstrate reasonable agreement with first-principles binding energies of
small Si clusters as well as single-layer and bilayer silicenes. The four
potentials are used to evaluate the thermal stability of free-standing
silicenes in the form of nano-ribbons, nano-flakes and nano-tubes. While
single-layer silicene is mechanically stable at zero Kelvin, it is predicted to
become unstable and collapse at room temperature. By contrast, the bilayer
silicene demonstrates a larger bending rigidity and remains stable at and even
above room temperature. The results suggest that bilayer silicene might exist
in a free-standing form at ambient conditions.
