  Typical empirical bond-order potentials are short ranged and give ductile
instead of brittle behavior for materials such as crystalline silicon or
diamond. Screening functions can be used to increase the range of these
potentials. We outline a general procedure to combine screening functions with
bond-order potentials that does not require to refit any of the potential's
properties. We use this approach to modify Tersoff's [Phys. Rev. B 39, 5566
(1989)], Erhart & Albe's [Phys. Rev. B 71, 35211 (2005)] and Kumagai et al.'s
[Comp. Mater. Sci. 39, 457 (2007)] Si, C and Si-C potentials. The resulting
potential formulations correctly reproduce brittle materials response, and give
an improved description of amorphous phases.
