Electronic oscillations in ionized sodium nanoclusters

Abstract

Irradiation of nanosized metallic clusters by femtosecond laser pulses of moderate intensities ( ) leads to creation of the so-called electron–ion nanoplasma with size-dependent properties. Electron oscillations in such plasma are of interest in view of resonance absorption or probing of cluster dynamics in experiments. We study the electronic oscillations via molecular dynamics simulations for interacting classical electrons and ions. In particular, surface and volume plasmons are analyzed depending on the cluster size, plasma density, the ion ordering parameter and the short range part of the interaction potential. The volume plasmons are observed only for clusters greater than a threshold cluster size. By means of GPU computing, the long-range Coulomb interactions between particles are treated without typical approximations such as PPPM or TreeMD.

Relaxation and collective excitations of cluster nano-plasmas

“…The Mie resonance frequencies depending on the number of ions in the cluster, for different electron temperatures: ♦ -T e = 2.2 eV (this work), -T e = 1.0 eV Ref [28]…”

“…Using this method in Refs. [25][26][27][28] the time evolution of the electron subsystem has been computed in dependence on the above mentioned parameter values R i , n i , and T .…”

Reflecting Boundary Conditions for Classical and Quantum Molecular Dynamics Simulations of Nonideal Plasmas

“…When the wall boundaries are applied the spectra is changed substantially demonstrating well pronounced resonances. These resonances are related to the Mie-like oscillations that are known, for example, for ionized clusters [21,22]. They can not be observed for a periodic system as a shift of all electrons does not produce charge separation and a corresponding returning force.…”

“…N i and N e are the numbers of ions and electrons (N = N i + N e ), R i and q i are the ion coordinates and charges, r k are the electron coordinates, σ ei = σ ee = 0.318 nm are the parameters responsible for the potential correction at short distances, U ext is an external field potential which may include wall boundaries as described below. This form of the interaction potential U has been used in MD studies of uniform nonideal plasmas [30] and simulations of the ionized sodium nanoclusters [22,31]. In our case it is important that this potential is close to the effective particle interaction in WPMD.…”

“…While the state of art simulations of atomic systems reach the scales of nanoseconds and micrometers, the plasma simulations are limited typically by picoseconds and tens of nanometers. Nevertheless, there are plasma objects that fit within these scales, for example, a nanoplasma created by rapid ionization of nanosized atomic clusters by femtosecond laser pulses [21,22]. In this case no boundaries are needed except for those at a very large distance to avoid run away particles.…”