Bastian Holst

Ab Initio Equation of State Data for Hydrogen, Helium, and Water and the Internal Structure of Jupiter

The equation of state of hydrogen, helium, and water affects interior structure models of giant planets significantly. We present a new equation of state data table, LM-REOS, generated by large-scale quantum molecular dynamics simulations for hydrogen, helium, and water in the warm dense matter regime, i.e., for megabar pressures and temperatures of several thousand kelvins, and by advanced chemical methods in the complementary regions. The influence of LM-REOS on the structure of Jupiter is investigated and compared with state-of-the-art results within a standard three-layer model consistent with astrophysical observations of Jupiter. Our new Jupiter models predict an important impact of mixing effects of helium in hydrogen with respect to an altered compressibility and immiscibility.

Thermophysical properties of warm dense hydrogen using quantum molecular dynamics simulations

We study the thermophysical properties of warm dense hydrogen by using quantum molecular dynamics simulations. Results are presented for the pair distribution functions, the equation of state, and the Hugoniot curve. From the dynamic conductivity, we derive the dc electrical conductivity and the reflectivity. We compare with available experimental data and predictions of the chemical picture. In particular, we discuss the nonmetal-to-metal transition, which occurs at about 40 GPa in the dense fluid.

Electronic transport coefficients from ab initio simulations and application to dense liquid hydrogen

Using Kubos linear response theory, we derive expressions for the frequency-dependent electrical conductivity (Kubo-Greenwood formula), thermopower, and thermal conductivity in a strongly correlated electron system. These are evaluated within ab initio molecular dynamics simulations in order to study the thermoelectric transport coefficients in dense liquid hydrogen, especially near the nonmetal-to-metal transition region. We also observe significant deviations from the widely used Wiedemann-Franz law, which is strictly valid only for degenerate systems, and give an estimate for its valid scope of application toward lower densities.

Quantum molecular dynamics simulations for the nonmetal-to-metal transition in fluid helium.

We have performed quantum molecular dynamics simulations for dense helium to study the nonmetal-to-metal transition at high pressures. We present new results for the equation of state and the Hugoniot curve in the warm dense matter region. The optical conductivity is calculated via the Kubo-Greenwood formula from which the dc conductivity is derived. The nonmetal-to-metal transition is identified at about 1 g/cm(3). We compare with experimental results as well as with other theoretical approaches, especially with predictions of chemical models.

Ab initiomodel of optical properties of two-temperature warm dense matter

We present a model to describe thermophysical and optical properties of two-temperature systems consisted of heated electrons and cold ions in a solid lattice that occur during ultrafast heating experiments. Our model is based on ab initio simulations within the framework of density functional theory. The optical properties are obtained by evaluating the Kubo-Greenwood formula. By applying the material parameters of our ab initio model to a two-temperature model we are able to describe the temperature relaxation process of femtosecond-laser-heated gold and its optical properties within the same theoretical framework. Recent time-resolved measurements of optical properties of ultrafast heated gold revealed the dynamics of the interaction between femtosecond laser pulses and solid state matter. Different scenarios obtained from simulations of our study are compared with experimental data [Chen, Holst, Kirkwood, Sametoglu, Reid, Tsui, Recoules, and Ng, Phys. Rev. Lett. 110, 135001 (2013)].

Equation of State for Dense Hydrogen and Plasma Phase Transition

We calculate the equation of state of dense hydrogen within the chemical picture. Fluid variational theory is generalized for a multi-component system of molecules, atoms, electrons, and protons. Chemical equilibrium is supposed for the reactions dissociation and ionization. We identify the region of thermodynamic instability which is related to the plasma phase transition. The reflectivity is calculated along the Hugoniot curve and compared with experimental results. The equation-of-state data is used to calculate the pressure and temperature profiles for the interior of Jupiter. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Metal-to-nonmetal transitions

Luttinger, Peierls or Mott? Quantum Phase Transitions in Strongly Correlated 1D Electron#x2013 Phonon Systems.- The Metal#x2013 Nonmetal Transition in Fluid Mercury: Landau#x2013 Zeldovich Revisited.- The Influence of Pauli Blocking Effects on the Mott Transition in Dense Hydrogen.- Metal#x2013 Insulator Transition in Dense Hydrogen.- Resolving the Ion and Electron Dynamics in Finite Systems Exposed to Intense Optical Laser Fields.- Mott Effect in Nuclear Matter.- BEC#x2013 BCS Crossover in Strongly Interacting Matter.

Hydrogen and deuterium in shock wave experiments, ab initio simulations and chemical picture modeling

We present equation of state data of shock compressed hydrogen and deuterium. These have been calculated in the physical picture by using ab initio molecular dynamics simulations based on finite temperature density functional theory as well as in the chemical picture via the Saha-D model. The results are compared in detail with data of shock wave experiments obtained for condensed and gaseous precompressed hydrogen and deuterium targets in a wide range of shock compressions from low pressures up to megabars.

Thomson scattering in dense plasmas with density and temperature gradients

Abstract Collective X-ray Thomson scattering has become a versatile tool for the diagnostics of dense plasmas. Assuming homogeneous density and temperature throughout the target sample, these parameters can be determined directly from the plasmon dispersion and the ratio of plasmon amplitudes via detailed balance. In inhomogeneous media, the scattering signal is an average of the density and temperature dependent scattering cross-section weighted with the density and temperature profiles. We analyse Thomson scattering spectra in the XUV range from near solid density hydrogen targets generated by free electron laser radiation. The influence of plasma inhomogeneities on the scattering spectrum is investigated by comparing density and temperature averaged scattering signals to calculations assuming homogeneous targets. We find discrepancies larger than 10% between the mean electron density and the effective density as well as between the mean temperature and the effective temperature.

Equation of state for dense hydrogen and helium: application to astrophysics

We present theoretical results for the equation of state of hydrogen and helium applying the chemical picture which treats the elementary charged particles (electrons, ions) and neutral bound states (atoms, molecules) on an equal footing. The chemical equilibrium for dissociation and ionization processes is solved accounting for nonideality corrections. We compare our results with experiments and other theoretical models and calculate pressures and temperatures in jupiters interior.