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water achieves substantial binding through a localized O–H···O hydrogen bond; benzene achieves a comparable total through a larger set of weaker contacts. In the water dimer, one water is the hydrogen-bond donor and the other presents an oxygen lone pair region as acceptor. The interaction includes electrostatics, induction interaction, dispersion and short-range exchange repulsion; a hydrogen bond is not a separate fundamental force that can simply be added to all those terms again.

For benzene, draw a T-shaped edge-to-face pair or a slipped parallel pair. Its larger, more polarizable electron clouds provide appreciable London dispersion. Its quadrupolar charge distribution also makes the energy orientation dependent, despite each molecule having no permanent dipole by symmetry. An edge C–H approaching the other ring's pi region is therefore preferable to a model of two structureless, noninteracting dipole-free objects. Dispersion attracts while Pauli repulsion limits close overlap. Several distributed contacts can sum to the scale of one water–water hydrogen bond; counting only the number of conventional hydrogen bonds would miss them.

The comparison concerns the given gas-phase pair interaction energies, not an equality of every solvent-dependent association free energy. Correlated primary calculations explicitly identify both T-shaped and parallel-displaced benzene-dimer minima, rather than a uniquely preferred perfectly eclipsed sandwich.^[ref]

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.