Arturo O. answered • 01/15/18

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If you have a potential energy V(r), then the force associated with it is just

F(r) = -dV/dr

Note you have 2 different expressions for V in the title of the question and in the wording of the question. Anyway, once you have potential energy V as a function of interatomic distance, evaluate the derivative of V with respect to interatomic distance, and multiply by -1. That will be the force as a function of interatomic distance.