This relation can be converted into a wavevector-dependent dielectric function : (in cgs-Gaussian units) ε ε ( q ) = 1 + k 0 2 q 2 where k 0 = 4 π π e 2 ∂ ∂ n ∂ ∂ μ μ . At long distances (q → 0), the dielectric constant approaches infinity, reflecting the fact that charges get closer and closer to perfectly screened as you observe them from further away.