Plasmons in simple metal slabs: a semi-classical approach

• Published in: Surface science Vol. 384; no. 1; pp. 1 - 14
• Main Authors: Leseduarte, Sergio, Sellarès, Jordi, Travesset, Alex
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 20.07.1997; Amsterdam Elsevier Science; New York, NY
• Subjects: Alkali metals; Applied sciences; Collective effects; Collective excitations (including excitons, polarons, plasmons and other charge-density excitations); Collective excitations (including plasmons and other charge-density excitations); Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron density excitation spectra calculations; Electron states; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Exchange, correlation, dielectric and magnetic functions, plasmons; Jellium models; Many-body and quasi-particle theories; Metallic films; Metals. Metallurgy; Physics; Plasmons; Surface and interface electron states; Jellium models; Metallic films; Plasmons; Electron density excitation spectra calculations; Alkali metals; Many-body and quasi-particle theories; Theoretical study; Electronic structure; Random phase approximation; Dispersion relations; Metals
• DOI: 10.1016/S0039-6028(97)00074-5
• ISSN: 0039-6028

Collective excitations in simple metal systems can be successfully described in terms of a local one-body excitation operator Q, due to the long-range nature of the Coulomb interaction. For the plasmon modes of a simple metal slab, momentum expansions of Q are calculated using a variational procedure equivalent to a restricted RPA calculation. The dispersion relation and the density fluctuation for each mode are found in the sudden approximation using the proper Q operator and the RPA sum rule formalism. The contributions of the exchange and correlation energy are estimated using a local density functional. The positive background is described within a jellium model, while the ground-state electronic density is approximated by a double step profile. The density fluctuation of the plasmon modes above the plasma frequency form standing waves across the slab. The spectra below the plasma frequency are qualitatively different to those of local optics calculations due to the appearance of two multipole plasmon modes which shift the origin of the ω + plasmon down. The dependence of the results on the width of the slab, the density of the simple metal and the surface diffuseness is discussed. The response of the slab to a q- dependent external excitation operator is analyzed. Throughout, the difference with to RPA and TDLDA calculations is stressed.