1. The problem statement, all variables and given/known data Consider the metal-vacuum interface located at z = 0,the metal filling the entire half-space z ≥ 0, vacuum filling (!?) the half-space z < 0. The dielectric function in the metal in the long-wavelength limit is given by: where ε0 is the vacuum permittivity. In the metal a solution of Laplace’s equation ∇2φ = 0 is 2. Relevant equations 3. The attempt at a solution Tried to solve this problem for 8 hours, still no result. Maybe some of you might help?