Absorption of low-frequency radiation by small metal particles: a semiclassical random-phase-approximation

Calculations of low-frequency absorption of electromagnetic radiation by small conducting particles must take account of screening of the externally applied field due to polarization charges. In this paper we introduce a 'semiclassical' variant of the random-phase-approximation (RPA) method for obtaining the self-consistent field. Electric and magnetic dipole absorption are treated within a unified scheme, and we also demonstrate the equivalence of this approach to a superficially dissimilar perturbative method. The approach is more tractable than the full RPA equations, and allows us to discuss the effective potential for both diffusive and ballistic electron dynamics.