Crystallinity effects on the surface optical response in metals

We calculate the optical response of a crystalline metal with a surface. Our model uses a single Fourier component of bulk potential, an infinite barrier at the surface, and the random-phase approximation to describe the many-body interactions. Within these constraints the calculations determine the full quantum-mechanical response. The results for an applied long-wavelength field parallel or perpendicular to the surface are characterized by the d parameters, d_∥ and d_⊥. For the latter case we find novel long-ranged oscillations in the induced density near the surface. Although these arise from the simultaneous presence of the surface and lattice scattering, they extend far into the bulk and are incommensurate with the lattice. Using parameters appropriate for Li(110), we find that interband absorption causes both d_⊥ and d_∥ to have frequency dependences significantly different from the jellium limit.