  The effect of an implicit medium on dispersive interactions of particle pairs
is discussed and simple expressions for the correction relative to vacuum are
derived. We show that a single point Gauss quadrature leads to the intuitive
result that the vacuum van der Waals $C_6$ coefficient is screened by the
permittivity squared of the environment evaluated near to the resonance
frequencies of the interacting particles. This approximation should be
particularly relevant if the medium is transparent at these frequencies. In the
manuscript, we provide simple models and sets of parameters for commonly used
solvents, atoms and small molecules.
