 They have the advantage over conventional molecular mechanics force fields in that they can, with the same parameters, describe several different bonding states of an atom, and thus to some extent may be able to describe chemical reactions correctly.The potentials were developed partly independently of each other, but share the common idea that the strength of a chemical bond depends on the bonding environment, including the number of bonds and possibly also angles and bond lengths.It is based on the Linus Pauling bond order concept 


and can be written in the form

formula_1

This means that the potential is written as a simple pair potential depending on the distance between two atoms formula_2, but the strength of this bond is modified by the environment of the atom formula_3 via the bond order formula_4.