Scaling procedure for simulations of extreme ionizations and Coulomb explosion of large clusters

Abstract

We advance a scaling procedure for molecular dynamics (MD) simulations which allows for the computation of extreme ionization levels, multielectron dynamics, and Coulomb explosion (CE) energetics of very large elemental and molecular clusters driven by ultraintense (peak intensities ${I}_{M}={10}^{15}--{10}^{21}\phantom{\rule{0.3em}{0ex}}\mathrm{W}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$) laser fields. The procedure of scaled particle dynamics uses a standard MD code for a scaled cluster with a reduced number of composite ions (nuclei) (heavy pseudoparticles) and of composite electrons (light pseudoparticles). A single scaling parameter $s$ was used for the composition, charge, and mass of all the pseudoparticles, while the initial distances between pseudoparticles and the short-range potential parameters were scaled by ${s}^{1∕3}$. The scaling procedure was applied for the computation of the ion energies from CE of ${({\mathrm{D}}_{2})}_{n∕2}$ and ${(\mathrm{C}{\mathrm{H}}_{4})}_{n}$ clusters over the size domain of $n={10}^{3}--{10}^{7}$, bridging between clusters and nanodroplets. Deuterons with a maximal energy of $110\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ can be effectively produced and utilized for nuclear fusion driven by CE of ${(\mathrm{D})}_{n}$ clusters with $n=1.7\ifmmode\times\else\texttimes\fi{}{10}^{6}$. The intensity dependence of the ionization levels of ${(\mathrm{C}{\mathrm{H}}_{4})}_{n}$ clusters $(n=8\ifmmode\times\else\texttimes\fi{}{10}^{4}--{10}^{6})$ manifests ignition and nanoplasma screening effects, establishing the conditions for the production of bare ${\mathrm{C}}^{6+}+{\mathrm{H}}^{+}$ nuclear matter for nucleosynthesis. The scaling procedure will be applicable for large finite systems where the particle motion is mainly governed by long-range (e.g., Coulomb) interactions.