# How should I calculate total potential in a polymer chain?

Suppose, a polymer has 3 monomers in its chain:
$$\ce{A1-A2-A3}$$

When calculating total LJ potential, do I need to calculate like this: $$E(r_{12})+E(r_{23})+E(r_{31})$$

Or, do I calculate: $$E(r_{12})+E(r_{23})$$

In your case, it's likely you'll want to include all three interactions, unless the monomers themselves are very large such that $$E(r_{31})$$ is very small relative to the other two terms.