Matter and stopping in matter under extreme conditions

For the dynamic behaviour of a target under irradiation with dense particle beams, it is essential to study static and transport properties of matter over a wide range of densities and temperatures. Of particular interest are the formation of neutral atoms and molecules through recombination in a dense plasma, and the eventual emergence of ordered structures, as well as the delocalization and the lowering of the continuum edge that precurses the transition to a metallic state. As a theoretical tool, we employ wave packet molecular dynamics, in which electrons are represented by Gaussian wave packets, whose parameters follow pseudo-Hamiltonian dynamics. To exclude artifacts from the finite size of the simulation box, about 103 particles must be simulated. For reasons of numerical economy, the wave function is only pairwise symmetrized at present. As stationary observables, we study the energy-resolved electron-proton pair distribution function for hydrogen and the spectral density of the electrons. With increasing density, we observe the delocalization of the states and the lowering of the continuum edge. As a dynamical observable, we consider the stopping of ions. In comparison with classical point particles, the finite width of the wave packet leads to a smoothing of the singular Coulomb potential and a reduction of the stopping power. This is confirmed by actual calculations of the stopping of ions in matter.