Dielectric function of media based on conductive particles

The general formula for the dielectric function of a medium containing conductive particles of various sizes (e.g., nanoparticles) is derived, and shown that it is exact in spite of electron-electron interactions for a parabolic confinement of electrons in the particles. The derivation method explains the apparent universal applicability of this formula to other systems. It is also shown, how this formula can be used to design composites with desired dielectric properties.