C. Kohl

Optical response of Na clusters on NaCl surfaces

Abstract We consider Na clusters on NaCl surfaces as examples of metal clusters attached to an insulating substrate. We concentrate on the cases Na 8 and Na 20 where three-dimensionally extended clusters compete with planar clusters and compute the optical response of ground states and isomers using the time-dependent local-density approximation. The interface interaction leads to strong deformations of the deposited clusters. Nonetheless, one sees a well-developed plasmon response which allows conclusions to be made on the underlying cluster structure (planar or three-dimensional).

Plasmon resonances and triaxial deformations in small Na clusters

Abstract We investigate the (plasmon) resonance spectrum for positively charged Na clusters from Na 3 + up to Na 41 + . We employ a triaxial jellium model for the ionic background and a Kohn-Sham description for the electrons. The (plasmon) resonance spectrum is computed within the local RPA using the same energy functional as for the ground state. The agreement with experimental data is generally very good with a few exceptions which can be explained. The regions of prolate and of oblate clusters can be well discriminated. But the signal of triaxiality in the resonance energies is faint for clusters larger than Na 6 + .

Spin effects in small sodium clusters

We present results on ground state properties for Na clusters withN=2−20 electrons using a jellium model with fully triaxial shapes and employing the spin degree-of-freedom for the electrons. The proper treatment of spin turns out to be crucial for the description of ionization potentials in this range of cluster sizes. Spontaneous spin polarization is observed in some triaxially soft, even clusters.

Nonlinear dynamics of nuclei and metal clusters

SummaryWe discuss and compare dipole resonance modes in nuclei and metal clusters. In both systems, we observe well-developed collectivity with harmonic oscillations which persist high up into the regime of multiple resonances. Deformations tend to induce spectral fragmentation. In clusters, these effects are hardly strong enough to destroy all collectivity, except for the extreme of a fissioning cluster. Nuclear surface modes, on the other hand, are found to interfere strongly with the giant resonances being able to dissolve them completely.

Nonlinear electronic dynamics in free and deposited sodium clusters : Quantal and semi-classical approaches

The optical response of sodium clusters is studied using fully three-dimensional electronic dynamics, in real time, with an explicit ionic background. The obtained spectra are shown to come close to experimental results for free clusters. We use the approach also to compute the response of sodium clusters deposited on a NaCl(1 0 0) surface. The flattening of the clusters induced by the surface results in a shift and a large fragmentation of the plasmon resonance.