Ab initiocalculations of the dynamical response of copper

Abstract

The role of localized d-bands in the dynamical response of Cu is investigated, on the basis of ab initio pseudopotential calculations. The density-response function is evaluated in both the random-phase approximation (RPA) and a time-dependent local-density functional approximation (TDLDA). Our results indicate that in addition to providing a polarizable background which lowers the free-electron plasma frequency, d-electrons are responsible, at higher energies and small momenta, for a doublepeak structure in the dynamical structure factor. These results are in agreement with the experimentally determined optical response of copper. We also analyze the dependence of dynamical scattering cross sections on the momentum transfer.PACS numbers: 71.45. Gm, 72.30.+q, 78.70.Ck Noble-metal systems have been the focus of much experimental and theoretical work in order to get a better understanding of how electronic properties of delocalized, free-electron-like, electrons are altered by the presence of localized d-electrons. Silver is one of the best understood systems, where the free-electron plasma frequency is strongly renormalized (red-shifted) by the presence of a polarizable background of d-electrons 1 . Unlike silver, copper presents no decoupling between sp and d orbitals, and a combined description of these oneelectron states is needed to address both structural and electronic properties of this material. Though in the case of other materials, as semiconductors, electron-hole interactions (excitonic renormalization) strongly modify the single-particle optical absorption profile 2 , metals offer a valuable playground for investigations of dynamical exchange-correlation effects of interacting many-electron systems within a quasiparticle picture 3 . Indeed, ab initio calculations of the dynamical response of a variety of simple metals, as obtained within the random-phaseapproximation (RPA), successfully account for the experimentally determined plasmon dispersion relations 4 and scattering cross sections 5 . Within the same many-body framework, ab initio calculations of the electronic stopping power of real solids have also been reported 6 .Since the pioneering investigations by Ehrenreich and Philipp 7 on the optical absorption and reflectivity of Ag an Cu, a variety of measurements of the optical properties of copper has been reported 8 . Nevertheless, there have been, to the best of our knowledge, no first-principles calculations of the dielectric response function of Cu that include the full effects of the crystal lattice. Furthermore, the dynamical density-response function is well-known to be a key quantity in discussing one-electron properties in real metals, and it is also of basic importance in the description of low-dimensional copper systems studied in optical and time-resolved femtosecond experiments 9,10 .In this Rapid Communication we report a firstprinciples evaluation of the dynamical density-response function of Cu, as computed in the RPA and a timedependent extension of local-density functional th...

First-principles calculation of the plasmon resonance and of the reflectance spectrum of silver in theGWapproximation

“…These results agree with the general feeling that excitonic effects partially cancel self-energy corrections. A similar result has been found for Cu 11,12 , where the RPA response function calculated without many-body corrections yields good agreement with the experimental EEL and optical spectra.…”

A Many‐body Approach to the Electronic and Optical Properties of Copper and Silver

“…These results agree with the general feeling that excitonic effects partially cancel self-energy corrections (we will discuss in detail this cancellation in the next section). A similar result has been found for copper [4,16], where the RPA response function calculated without many-body corrections yields good agreement with the experimental EEL and optical spectra.…”

Role of occupieddstates in the relaxation of hot electrons in Au

“…These d bands, which are concentrated within a width of ∼ 5.5 eV, are associated with the characteristic d-band wave functions at levels Γ 27 Thus, a kinetic-energy cutoff as large as 75 Ry has been required, thereby keeping ∼ 1200 plane waves in the expansion of each Bloch state. Though all-electron schemes, such as the full-potential linearized augmented plane-wave (LAPW) method, 28 are expected to be better suited for the description of the response of localized d electrons, the plane-wave pseudopotential approach has already been successfully incorporated in the description of the dynamical response 29 and hot-electron lifetimes 19,20,22 of Cu. The sampling over the BZ required for the evaluation of both the dielectric matrix and the hot-electron decay rate of Eqs.…”