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We present classical and DFT-based molecular dynamics (MD) simulations of carbon in the warm dense matter regime (ρ= 3.7 g/cc, 0.86 eV < T <8.62 eV [T < 100 eV for classical MD]). Two different classical interatomic potentials are used: 1. LCBOP, designed to simulate condensed (e.g. solid) phases of C, and 2. linearly screened Coulomb (Yukawa) potentials. It is shown that LCBOP over-predicts minima and maxima in the pair correlation functions of liquid-C in this regime when compared to the DFT-MD results. The screened Coulomb model, while under-correlating at low-T, seems to produce the correct qualitative features in the static ionic pair distributions at the highest-T. However, both approaches predict the decay in the ionic contribution of the specific heat as T → ∞ to be much slower than that predicted by a model based on DFT-MD. These differences in the MD-derived equations of state in warm dense regimes could have important consequences when using classical inter-ionic forces such as these in large-scale MD simulations aimed at studying, for instance, processes of relevance to inertial confinement fusion when C is used as an ablator material. [ABSTRACT FROM AUTHOR]

For planets other than Earth, particularly exoplanets, interpretation of the composition and structure depends largely on comparing the mass and radius with the composition expected given their distance from the parent star. The composition implies a mass--radius relation which relies heavily on equations of state calculated from electronic structure theory and measured experimentally on Earth. We lay out a method for deriving and testing equations of state, and deduce mass--radius and mass-pressure relations for key, relevant materials whose equation of state (EOS) is reasonably well established, and for differentiated Fe/rock. We find that variations in the EOS, such as may arise when extrapolating from low-pressure data, can have significant effects on predicted mass-radius relations and on planetary pressure profiles. The relations are compared with the observed masses and radii of planets and exoplanets, broadly supporting recent inferences about exoplanet structures. Kepler-10b is apparently "Earth-like," likely with a proportionately larger core than Earth's, nominally 2/3 of the mass of the planet. CoRoT-7b is consistent with a rocky mantle over an Fe-based core which is likely to be proportionately smaller than Earth's. GJ 1214b lies between the mass-radius curves for H2O and CH4, suggesting an "icy" composition with a relatively large core or a relatively large proportion of H2O. CoRoT-2b is less dense than the hydrogen relation, which could be explained by an anomalously high degree of heating or by higher than assumed atmospheric opacity. HAT-P-2b is slightly denser than the mass-radius relation for hydrogen, suggesting the presence of a significant amount of matter of higher atomic number. CoRoT-3b lies close to the hydrogen relation. The pressure at the center of Kepler-10b is Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. The central pressure in CoRoT-7b is probably close to 0.8 TPa, though may be up to 2 TPa. These pressures are accessible by planar shock and ramp-loading experiments at large laser facilities. The center of HAT-P-2b is probably around 210 TPa, in the range of planned National Ignition Facility experiments, and that of CoRoT-3b around 1900 TPa. [ABSTRACT FROM AUTHOR]

We present laser-driven shock compression experiments on cryogenic liquid deuterium to 550 GPa along the principal Hugoniot and reflected-shock data up to 1 TPa. High-precision interferometric Doppler velocimetry and impedance-matching analysis were used to determine the compression accurately enough to reveal a significant difference as compared to state-of-the-art ab initio calculations and thus, no single equation of state model fully matches the principal Hugoniot of deuterium over the observed pressure range. In the molecular-to-atomic transition pressure range, models based on density functional theory calculations predict the maximum compression accurately. However, beyond 250 GPa along the principal Hugoniot, first-principles models exhibit a stiffer response than the experimental data. Similarly, above 500 GPa the reflected shock data show 5%-7% higher compression than predicted by all current models. [ABSTRACT FROM AUTHOR]

A equation of state (EOS) experimental technique that enables the study of thermodynamic derivatives into the TPa regime is described and applied to boron carbide (B4C). Data presented here are principal Hugoniot sound speed measurements reported using a laser-driven shock platform, providing a means to explore the high-pressure off-Hugoniot response of opaque materials. The extended B4C Hugoniot suggests the presence of a high-pressure phase, as recently predicted by molecular dynamics simulations, adding to the complexity of the existing phase diagram. [ABSTRACT FROM AUTHOR]