Hamaker Constant

The Hamaker constant A can be defined for a Van der Waals (VdW) body-body interaction:

where and are the number of atoms per unit volume in two interacting bodies and C is the coefficient in the particle-particle pair interaction.

The Hamaker constant provides the means to determine the interaction parameter C from the Van der Waals pair potential, .

Hamaker's method and the associated Hamaker constant ignores the influence of an intervening medium between the two particles of interaction. In the 1950s Lifshitz developed a description of the VdW energy but with consideration of the dielectric properties of this intervening medium (often a continuous phase).

The Van der Waals forces are effective only up to several hundred angstroms. When the interactions are too far apart the dispersion potential decays faster than ; this is called the retarded regime and the result is a Casimir–Polder force.