Understanding Additive Pair Potential in Molecular Dynamics

[calif2a8]

I'm sorry, I wasn't exactly sure where to put this question but this section is probably my best bet. I'm basically trying to understand potential functions of more than 1 parameter... which is basically, most potential functions out there for molecular dynamics, what I just started working with. What is an "additive pair potential"? I can't seem to piece it together

 

[itaischles]

It means that the total potential energy of the system is the sum over all potential energies of pairs of particles in the system. It does not, in general, have to be the case. For example: if the energy between two particles depend on whether there is a third particle nearby than the potential energy is much more complicated than the pair potential. Usually we assume pair potential for simplicity.