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15Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2018
WAVE-PACKET BASED ATOMISTIC MODELLING OF LASER EXCITED
ALUMINUM NANOPARTICLES
Chernyshov A I1,2, Orekhov N D1,2 and Stegailov V V1,2
Joint Institute for High Temperatures of the Russian Academy of Sciences, Izhorskaya 13 Bldg 2,
Moscow 125412, Russia
Moscow Institute of Physics and Technology, Institutskiy Pereulok 9, Dolgoprudny, Moscow Region
141700, Russia [email protected]
Among the most interesting questions, there is the possibility to obtain plasma with near-solid density through interaction with laser pulses of TW/cm2 fluences. Processes of electron-ion relaxation and fragmentation in this unique state of matter - called warm dense matter (WDM) -are of significant interest.
Unfortunately, non-equilibrium WDM remains a very complicated object for a theoretical description. The well-known density functional theory (DFT) describes systems of many electrons taking into account the majority of quantum effects but is quite limited in its ability to handle non-equilibrium phenomena. In this work, we use wave packets molecular dynamics (WPMD) method that provides a unique possibility to describe non-equilibrium and non-adiabatic effects in electron-electron and electron-ion interactions.
We apply the eFF [1] (electron force field) wave packet model for simulation of Al nanoparticles (NP) after an intense laser excitation. In the eFF framework, electrons are represented as floating Gaussians and interactions between electrons are restricted to pairwise components only. Recently, this method has been successfully used to study the response Al NP on irradiation by short laser pulses [2]. In this report, we present a further investigation of thermalization processes in laser excited aluminum NPs.
We examine the evolution of laser-heated Al NPs with diameter 1-3 nm. For simplification, the absorption rate is considered constant as well as the laser fluence. The impulse duration is constant (25 fs) and total energy of impulse was varied from 0.6 eV up to 7 eV per atom. Our study covers different aspects of cluster relaxation process, inter alia the NP radii, charge density, kinetic energy and chaotic temperature.
Much attention is paid to the phase transition process and its dependency on the absorbed energy and the NP size. We examine melting time delay, partial melting and cavity formation inside NPs during relaxing process.
1. J. T. Su h W. A. Goddard, «Excited Electron Dynamics Modeling of Warm Dense Matter,» Phys. Rev. Lett., t. 99, № 18, p. 185003, 11 2007.
2. N. D. Orekhov h V. V. Stegailov, «Electron-ion relaxation in Al nanoplasma: Wave packet molecular dynamics.,» Journal of Physics: Conference Series, t. 774, № 012104, pp. 1-7, 2016.
