Atoms of a noble gas reach an equilibrium distance from each other when an attracting van der Waals force balances a repelling force the result of overlapping electron orbits. The strength at which these two forces balance is the so-called Lennard-Jones potential (L-J potential).
Subject to assumptions about the physical properties of the molecules, the L-J potential may be used to calculate an approximation for their separation. Other more recent methods, such as the Stockmayer equation and the so-called multi equation, describe the interaction of molecules more accurately.
The L-J potential is of the form
![V(r) = 4\varepsilon \left[ \left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^{6} \right],](a/../upload/math/f657c4957747fc136443224e3e77b26d.png)
where ε is the well depth and σ is the hard sphere radius.