This means that the potential is written as a simple pair potential depending on the distance between two atoms r i j , but the strength of this bond is modified by the environment of the atom i via the bond order b i j k . b i j k is a function that in Tersoff-type potentials depends inversely on the number of bonds to the atom i , the bond angles between sets of three atoms i j k , and optionally on the relative bond lengths r i j , r i k . In case of only one atomic bond (like in a diatomic molecule), b i j k = 1 which corresponds to the strongest and shortest possible bond. The other limiting case, for increasingly many number of bonds within some interaction range, b i j k → → 0 and the potential turns completely repulsive (as illustrated in the figure to the right).