 formula_4 is a function that in Tersoff-type potentials depends inversely on the number of bonds to the atom formula_3, the bond angles between sets of three atoms formula_7, and optionally on the relative bond lengths formula_2, formula_9.In case of only one atomic bond (like in a diatomic molecule), formula_10 which corresponds to the strongest and shortest possible bond.The other limiting case, for increasingly many number of bonds within some interaction range, formula_11 and the potential turns completely repulsive (as illustrated in the figure to the right).