Tersoff-style potential for silicon, carbon and silicon carbide.

Parameters from
Erhart and Albe
"Analytical potential for atomistic simulations of silicon, carbon,
and silicon carbide"
Phys. Rev. B 71 (2005), 035211

Parameter file copied as-is from LAMMPS, see comments in the file for
details.

Contact: Tobias Brink <brink@mm.tu-darmstadt.de>
