The optical conductivity sigma (omega) for dense Coulomb systems is investigated using molecular dynamics simulations on the basis of pseudopotentials to mimic quantum effects. Starting from linear response theory, the response in the long-wavelength limit k=0 can be expressed by different types of autocorrelation functions (ACF's) such as the current ACF, the force ACF, or the charge density ACF. Consistent simulation data for transverse as well as longitudinal ACF's are shown which are based on calculations with high numerical accuracy. Results are compared with perturbation expansions which are restricted to small values of the plasma parameter. The relevance with respect to a quantum Coulomb plasma is discussed. Finally, results are presented showing a consistent description of these model plasmas in comparison to quantum statistical approaches and to experimental data.

In the long-wavelength limit k = 0, the response function has been investigated with respect to the external and internal fields which is expressed by the external and internal conductivity, respectively. Molecular dynamics (MD) simulations are performed to obtain the current-current correlation function and the dynamical collision frequency which are compared with analytical expressions. Special attention is given to the dynamical collision frequency and the description of plasma oscillations in the case of k = 0. The relation between the external and internal conductivity and to the current-current correlation function is analyzed.

Despite its promise as a method for the simulation of time-dependent many-body quantum mechanics problems, wave packet molecular dynamics (WPMD) is limited in its use by wave packet spreading when applied to dense plasma systems. We employ more accurate methods to determine if spreading really occurs and how WPMD can be improved. A scattering process involving a single dynamic electron interacting with a periodic array of statically screened protons is used as a model problem for the comparison. We compare the numerically exact split operator Fourier transform (SOFT) method, the Wigner trajectory method (WTM), and the time dependent variational principle (TDVP). Within the framework of the TDVP, we use the standard variational form of WPMD, the single Gaussian wave packet (WP). We then generalize this form to include multiple Gaussian for the single electron as in the split WP propagation method. Wave packet spreading is predicted by all methods, so it is not the source of the unphysical behavior of WPMD at high temperatures.Instead, the Gaussian WP's inability to correctly reproduce breakup of the electron's probability density into localized density near the protons is responsible for the deviation from more accurate predictions. Extensions of WPMD must include a mechanism for breakup to occur in order to yield dynamics that lead to accurate electron densities.

Results for the reflection coefficient of shock-compressed dense xenon plasmas at pressures of 1.6-20 GPa and temperatures around 30 000 K using laser beams of wavelengths 1.06 micro m and 0.694 micro m are presented, which indicate metallic behavior at high densities. For the theoretical description of the experiments, a quantum statistical approach to the dielectric function is used. The comparison with molecular dynamics simulations is discussed. We conclude that reflectivity measurements at different wavelengths can provide information about the density profile of the shock wave front.

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.