In molecular physics, the Hamaker constant (denoted A; named for H. C. Hamaker) is a physical constant that can be defined for a van der Waals (vdW) body–body interaction: where ρ1, ρ2 are the number densities of the two interacting kinds of particles, and C is the London coefficient in the particle–particle pair interaction.
In 1956 Lifshitz developed a description of the vdW energy but with consideration of the dielectric properties of this intervening medium (often a continuous phase).
[3] 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.