The Potential of Mean Force of a system with N particles is by construction the potential that gives the average force over all the configurations of all the n+1...N particles acting on a particle j at any fixed configuration keeping fixed a set of particles 1...n
Above,  is the averaged force, i.e. "mean force" on particle j. And  is the so-called potential of mean force. For ,  is the average work needed to bring the two particles from infinite separation to a distance . It is also related to the radial distribution function of the system, , by: