The charge of ionized metal clusters is investigated at high temperatures. Molecular Dynamics (MD) simulations are applied to describe the particle motion. While the electrons are treated as separate particles, the interaction with the ion cores is described as an external jellium potential. The final cluster charge is determined by classifying the particles into free and bound electrons. A relation between the cluster charge and cluster sizes as well as temperatures is derived from MD simulations and simple kinetic model calculations. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Collective excitations in nano-plasmas are described by dynamical bi-local auto-correlation functions. These excitations, which are related to the plasmon excitations in bulk plasmas, arise in the classical as well as the quantum regime. Instead of the wave-vector-dependent dynamical structure factor, which is not well defined in finite systems, two different signatures are considered to characterize collective excitations: the bi-local particle density correlation function and the bi-local current density correlation function. The relation between both signatures is not as trivial as in the homogeneous case and is given here. Exemplary calculations are performed for expanding nearly spherical clusters of sodium atoms after excitation by a high-intensity short pulse laser beam. The lowest collective excitations obtained in the classical regime using molecular dynamics simulations agree well with the lowest collective excitations 6 2 obtained from quantum calculations using fluid dynamics. The energy, damping and structure of the lowest collective modes are given. The dynamical bi-local correlation functions are of relevance for the optical properties, in particular the determination of photo absorption coefficients of nano-plasmas.

Electron density fluctuations as well as current density correlations are considered for excited nano plasmas. Calculations are performed by classical MD simulations at high temperatures for expanding nearly spherical clusters of laser irradiated sodium atoms. The resonance structures observed in the frequency spectrum of the bi‐local correlation functions are analyzed. Mie modes and volume plasmon type excitations are observed as well as breathing modes. We investigate the relation between the bi‐local correlation functions of the electron density fluctuations and current density via the equation of continuity.The collective excitations are of significance for the dielectric function and further properties such as the photo absorption coefficients. Results are presented for an exemplarily taken set of parameter values of the nano plasma (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nano-plasmas produced, e.g. in clusters after short-pulse laser irradiation, can show collective excitations as derived from the time evolution of fluctuations in thermodynamic equilibrium. Molecular dynamical simulations are performed for various cluster sizes. New data are obtained for the minimum value of the stationary cluster charge. The bi-local auto-correlation function gives the spatial structure of the eigenmodes, for which energy eigenvalues are obtained. Varying the cluster size, starting from a few-particles cluster, the emergence of macroscopic properties like collective excitations is shown.