= Van der Waals potential
A <Van der Waals potential> describes the separation-dependent <potential energy> associated with <Van der Waals forces>. For two neutral, nonpolar particles at separations where the nonretarded dispersion description applies, a familiar attractive contribution is $U(r)=-C_6/r^6$ with $C_6>0$. Its radial force is $-dU/dr=-6C_6/r^7$, directed toward smaller separation.
At sufficiently short separation, overlapping electronic states produce strong <exchange repulsion>; continuing the attractive power law to zero separation is not a physical model. A <Lennard-Jones potential> combines an attractive inverse-sixth-power term with a simple repulsive term to produce a finite-separation minimum. Geometry also changes the effective power law: summing pair interactions over macroscopic bodies gives different distance dependences, as in <Hamaker summation>. The pair potential and a measured force between extended surfaces must therefore be distinguished.
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