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We develop a first-principles approach to calculate the near-edge absorption spectrum of dense plasmas based on density functional electronic structure calculations and molecular dynamics simulations. We apply the method to the calculation of the K-edge shift along the aluminum shock compressed Hugoniot. We obtain a good agreement with measurements performed at moderate compression and find that the variation of the XANES spectra could be used as a signature for melting along the Hugoniot. We also show that the calculation of the K-edge shift along the Hugoniot formally requires a fully self-consistent calculation beyond the frozen-core approximation and provides an opportunity to test the accuracy of first principle simulation methods in the high-pressure high-temperature regime.

We build an "all-electron" norm-conserving pseudopotential for boron which extends the use of ab initio molecular dynamics simulations up to 50 times the normal density rho0. This allows us to perform ab initio simulations of dense plasmas from the regime where quantum mechanical effects are important to the regime where semiclassical simulations based on the Thomas-Fermi approach are, by default, the only simulation method currently available. This study first allows one to establish, for the case of boron, the density regime from which the semiclassical Thomas-Fermi approach is legitimate and sufficient. It further brings forward various issues pertaining to the construction of pseudopotentials aimed at high-pressure studies.

It is shown that a modified scheme of density functional theory, using the Thomas-Fermi kinetic energy functional for the electrons, is well suited to perform very-high-temperature molecular dynamics simulations on high-Z elements. As an example, iron on the principal Hugoniot is simulated up to 5 keV and 5 times the normal density, giving an equation of state in agreement with current models. Ionic structure is obtained and is given to an excellent level of precision by the structure of the one-component plasma computed for a coupling parameter corresponding to Thomas-Fermi ionization.

We derive a formulation to calculate the excess chemical potential of a fraction of N1 particles interacting with N2 particles of a different species. The excess chemical potential is calculated numerically from first principles by coupling molecular dynamics and Thomas-Fermi density functional theory to take into account the contribution arising from the quantum electrons on the forces acting on the ions. The choice of this simple functional is motivated by the fact that the present paper is devoted to the derivation and the validation of the method but more complicated functionals can and will be implemented in the future. This method is applied in the microcanonical ensemble, the most natural ensemble for molecular dynamics simulations. This avoids the introduction of a thermostat in the simulation and thus uncontrolled modifications of the trajectories calculated from the forces between particles. The calculations are conducted for three values of the input thermodynamic quantities, energy and density, and for different total numbers of particles in order to examine the uncertainties due to finite-size effects. This method and these calculations lie the basic foundation to study the thermodynamic stability of dense mixtures, without any a priori assumption on the degree of ionization of the different species.

Experimental measurements and theoretical calculations of the electrical conductivity of aluminum are presented in the strongly coupled partially degenerate regime (rho=0.3 g/cm(3), 5000

We present and assess a multiscale recursion method to calculate electronic density via the Green's function. The method lies within the framework of finite temperature density functional theory and uses a real space approach. It provides a satisfactory description of the first Brillouin zone without invoking k points. Unlike methods that explicitly calculate eigenstates, the computational workload decreases with temperature. Tests are performed on a system representing a hydrogen plasma with a local pseudopotential. Calculations are distributed on real space grids with different spacings using scaling properties of the recursion. The computational workload increases linearly with the size of the system and can be productively dispatched on an arbitrarily large number of processors.