Time-dependent local-density-response theory for strongly charged metal surfaces

Abstract

We present a microscopic calculation of nonlocal effects on the optical response of strongly charged metal surfaces. Exchange and correlation effects are included within the time-dependent local-density-functional theory. We use the jellium model for the ionic background, and consider, for computational reasons, a thin metal slab. The background density is given by the Wigner–Seitz radius rs=3, and the surface charge is varied from −2.4 to 23.9 × 10−3 ‖e‖/Å2. In the long-wavelength limit, i.e., to lowest order in the (small) ratio of Fermi velocity to velocity of light, the nonlocal effects can be summarized in two surface-response functions. Our slab calculation yields a good approximation for the surface-response functions of a semi-infinite system. We show results for the relative deviation of the reflectance from its classical value and the power absorptance as a function of frequency for differently charged surfaces. They agree qualitatively with our previous results obtained in the conventional random-phase approximation. At high positive surface charges, the power absorption is drastically diminished, since certain surface excitations are suppressed. We discuss the relevance of these findings for experiments in nonaqueous electrolytic cells.