  We develop an empirical potential for silicon which represents a considerable
improvement over existing models in describing local bonding for bulk defects
and disordered phases. The model consists of two- and three-body interactions
with theoretically motivated functional forms that capture chemical and
physical trends as explained in a companion paper. The numerical parameters in
the functional form are obtained by fitting to a set of ab initio results from
quantum mechanical calculations based on density functional theory in the local
density approximation, which include various bulk phases and defect structures.
We test the potential by applying it to the relaxation of point defects, core
properties of partial dislocations and the structure of disordered phases, none
of which are included in the fitting procedure. For dislocations, our model
makes predictions in excellent agreement with ab initio and tight-binding
calculations. It is the only potential known to describe both the 30$^\circ$-
and 90$^\circ$-partial dislocations in the glide set {111}. The structural and
thermodynamic properties of the liquid and amorphous phases are also in good
agreement with experimental and ab initio results. Our potential is the first
capable of simulating a quench directly from the liquid to the amorphous phase,
and the resulting amorphous structure is more realistic than with existing
empirical preparation methods. These advances in transferability come with no
extra computational cost, since force evaluation with our model is faster than
with the popular potential of Stillinger-Weber, thus allowing reliable
atomistic simulations of very large atomic systems.
