Pair potential

In physics, a pair potential is a function that describes the potential energy of two interacting objects. Examples of pair potentials include the Coulomb's law in electrodynamics, Newton's law of universal gravitation in mechanics, the Lennard-Jones potential and the Morse potential. 
Pair potentials are very common in physics; exceptions are very rare. An example of a potential energy function that is "not" a pair potential is the three-body Axilrod-Teller potential. Another example is the Stillinger-Weber potential for silicon which includes the angle in a
triangle of silicon atoms as a parameter. 