Collective excitations in open-shell metal clusters: The time-dependent local-density approximation applied to the self-consistent spheroidal jellium particle

The self-consistent and microscopic time-dependent local-density-approximation (TDLDA) formalism for the calculation of the dynamical electronic response properties of open-shell, axially deformed small metal clusters is presented in detail. The model is based on the self-consistent ground-state calculation of the spheroidal jellium model, giving the optimized cluster shape, driven by its open-valence-shell electronic structure. First results on the static and dynamical electronic polarizability of the strongly axially deformed Na10 cluster are reported and compared with the experimental polarizability and photoabsorption cross-section results. The variety of the future applications of the model is outlined, as well as the possible improvement of the formalism

Comparative study of model potentials for the calculation of dielectric properties of small metal particles

Quite recently the dielectric electronic-response properties of small metal particles were investigated within a strictly self-consistent spherical jellium model. The bottleneck of this kind of calculation for a larger cluster is the self-consistent solution of the single-electron Kohn-Sham equations. Therefore, in this work simple model potentials are investigated and compared with the Kohn-Sham barrier. The result of this comparison is that the widely used model potentials such as finite- or infinite-step potentials are not able to mimic the complex dynamical behavior of a fully self-consistently responding surface

Rough droplet model for spherical metal clusters

We study the thermally activated oscillations, or capillary waves, of a neutral metal cluster within the liquid drop model. These deformations correspond to a surface roughness which we characterize by a single parameter $\Delta$. We derive a simple analytic approximate expression determining $\Delta$ as a function of temperature and cluster size. We then estimate the induced effects on shell structure by means of a periodic orbit analysis and compare with recent data for shell energy of sodium clusters in the size range $50 < N < 250$. A small surface roughness $\Delta\simeq 0.6$ \AA~ is seen to give a reasonable account of the decrease of amplitude of the shell structure observed in experiment. Moreover -- contrary to usual Jahn-Teller type of deformations -- roughness correctly reproduces the shape of the shell energy in the domain of sizes considered in experiment.Comment: 20 pages, 4 figures, important modifications of the presentation, to appear in Phys. Rev.

Self-consistent spheroidal jellium model of metal clusters

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The self-consistent spheroidal jellium model of open-shell monovalent metal clusters

Recently, we have proposed a microscopic model, describing the properties of open-shell, Jahn-Teller deformed monovalent-metal clusters [1]. The model is based on the self-consistent ground-state calculation, allowing the spheroidal (axial) deformation of the ionic jellium background, driven by the open-shell valence electron structure. The ground state electronic properties of such clusters are further investigated and compared to recent experimental data: ionization potentials, electron affinities and binding energies of neutral monomers to cationic clusters [2]

Electronic shell structure and metal clusters: the self-consistent spheroidal jellium model

The electronic properties of small metal particles within the recently proposed self-consistent spheroidal jellium model [1] are further explored and compared to recent experimental data. Physical properties investigated include ionization potentials, electron affinities and the binding energy of neutral monomers to cationic clusters. The formalism is applied within the size-range 2≦N≦41, but could easily be extended beyondN=41. Finally, we discuss briefly the implications for the study of the dynamical response of open-shell clusters. In sharp contrast to earlier studies the functional is now corrected for self-interaction error, in a way first proposed by Pedew and Zunger [2]. This enables us to calculate reliable values for the electron affinities within ajellium-based model. This has the advantage, that we can calculate the affinities for Cu for all particle numbers for which experimental data are available. In all cases investigated we obtain excellent agreement with experiment, with pronounced shell-effects both for the electron affinities and for the binding energies, confirming in this way that the abundances map the relative stability of (Me)N clusters, with Me being a sp-metal atom (Na, K, Li, Cu, Ag, Au etc.)

Temperature effects on the optical absorption of jellium clusters

Temperature broadening of the microscopically obtained optical absorption of open-shell clusters is studied with Na10 as an example. The method used is the time-dependent local-density approximation, combined with the coupling to the shape fluctuations of the cluster, both in the ground state and in the excited state. In sharp contrast to earlier studies by Pacheco and Broglia, the quantum nature of the fluctuations is fully taken into account. The obtained linewidth is in good agreement with recent experimental data of Knight and collaborators. The breakdown of the so-called plasmon-pole approximation is investigated in detail, and it is found that the reason for this is the fragmentation of the oscillator strength stored in the plasmon line, which is a genuine particle-hole effect both in closed-shell jellium clusters (Na20) and in open-shell metal clusters (Na10)