Spatially resolved dynamic structure factor of finite systems from molecular dynamics simulations

Abstract

The dynamical response of metallic clusters up to 10 3 atoms is investigated using the restricted molecular dynamics simulations scheme. Exemplarily, sodium like material is considered. Correlation functions are evaluated to investigate the spatial structure of collective electron excitations and optical response of laser excited clusters. In particular, the spectrum of bi-local correlation functions shows resonances representing different modes of collective excitations inside the nano plasma. The spatial structure, the resonance energy and width of the eigenmodes have been investigated for various values of electron density, temperature, cluster size and ionization degree. Comparison with bulk properties is performed and the dispersion relation of collective excitations is discussed.

Spatially Resolved Electronic Correlations in Nanoclusters

“…For example, the very narrow rightmost plasmon resonance shows several satellites towards lower frequencies for the larger systems. Similar resonance fragmentation has also been observed in [7] for clusters consisting of N ion = N el = 1, 000 ions and electrons. Additionally, a significant resonance appears below ω Mie in some cases.…”

“…Furthermore, the spatially resolved spectra can be compared to bilocal correlation functions [7] for identifying excitation modes and to deduce the spatially dependent dispersion relation inside the cluster. The identified features in the collective behavior of the cluster's electronic subsystem will be relevant for understanding transport and optical properties in finite size-limited systems, such as microstructured targets in experiments on laser-matter interaction as well as nanoelectronics that is currently rapidly developing towards system sizes that were studied in this work.…”

“…In contrast to the bilocal correlation functions analyzed in [7] a simpler, more direct diagnostic is applied here to obtain spatially resolved information on the features in the observed spectra. Since the self-consistent electrical field experienced by each electron contributes to the driving force for its collective motion, it is logical to exploit this as an observable.…”

“…In particular, the need for investigating systems with large but finite particle numbers and nontrivial surfaces makes them an indispensable tool to bridge the gap from nano-to microscale and further towards bulk matter -the latter usually simulated by extension via periodic boundary conditions. Previous work by Raitza et al [6,7] considered nanoclusters with up to 1,000 particles, hinting at sizedependent shifts of optical resonances. In this paper we extend this line of investigation to much larger systems containing more than half a million particles.…”

Spatially resolved collective excitations of nano-plasmas via molecular dynamics simulations and fluid dynamics

“…So far [11][12][13], we have obtained excitation spectra for bulk and cluster materials via correlation functions. In the case of clusters, the correlation functions were analyzed using spherical harmonics.…”