The strength of each bond depends upon the local environment
and is expressed by .
where is the effective coordination
The parameters were chosen to fit :
the cohesive energy of several high-symmetry bulk structures,
the lattice constant of diamond,
the bulk modulus of diamond,
the vacancy formation energy in diamond ( 4 eV).
The potential was tested by calculating :
the elastic constants,
the phonon frequencies, and
defect energies and migration barriers
in diamond and graphite.