The Potential of Mean Force of a system with N molecules is strictly the potential that gives the average force over all the configurations of all the n+1...N molecules acting on a particle at any fixed configuration keeping fixed a set of molecules 1...n

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

Radial distribution function

In statistical mechanics, a radial distribution function , g, describes how the atomic density varies as a function of the distance from one particular atom....

 of the system, , by:

Further reading

• McQuarrie, D. A. Statistical Mechanics.
• Chandler, D.
  David Chandler (chemist)
  David Chandler is a physical chemist who is currently a professor at the University of California, Berkeley. He is a member of the United States National Academy of Sciences and a winner of the Irving Langmuir Award. He has published two books and over 200 scientific articles.-Biography:David...
  
   (1987). Introduction to Modern Statistical Mechanics. Oxford University Press.