Fast and Universal Kohn-Sham Density Functional Theory Algorithm for Warm Dense Matter to Hot Dense Plasma.

Understanding many processes, e.g., fusion experiments, planetary interiors, and dwarf stars, depends strongly on microscopic physics modeling of warm dense matter and hot dense plasma. This complex state of matter consists of a transient mixture of degenerate and nearly free electrons, molecules, and ions. This regime challenges both experiment and analytical modeling, necessitating predictive ab initio atomistic computation, typically based on quantum mechanical Kohn-Sham density functional theory (KS-DFT). However, cubic computational scaling with temperature and system size prohibits the use of DFT through much of the warm dense matter regime. A recently developed stochastic approach to KS-DFT can be used at high temperatures, with the exact same accuracy as the deterministic approach, but the stochastic error can converge slowly and it remains expensive for intermediate temperatures (<50 eV). We have developed a universal mixed stochastic-deterministic algorithm for DFT at any temperature. This approach leverages the physics of KS-DFT to seamlessly integrate the best aspects of these different approaches. We demonstrate that this method significantly accelerated self-consistent field calculations for temperatures from 3 to 50 eV, while producing stable molecular dynamics and accurate diffusion coefficients.

Ab Initio Studies on the Stopping Power of Warm Dense Matter with Time-Dependent Orbital-Free Density Functional Theory.

Electronic transport properties of warm dense matter, such as electrical or thermal conductivities and nonadiabatic stopping power, are of particular interest to geophysics, planetary science, astrophysics, and inertial confinement fusion (ICF). One example is the α-particle stopping power of dense deuterium-tritium (DT) plasmas, which must be precisely known for current small-margin ICF target designs to ignite. We have developed a time-dependent orbital-free density functional theory (TD-OF-DFT) method for ab initio investigations of the charged-particle stopping power of warm dense matter. Our current dependent TD-OF-DFT calculations have reproduced the recently well-characterized stopping power experiment in warm dense beryllium. For α-particle stopping in warm and solid-density DT plasmas, the ab initio TD-OF-DFT simulations show a lower stopping power up to ∼25% in comparison with three stopping-power models often used in the high-energy-density physics community.

Time-dependent density-functional-theory calculations of the nonlocal electron stopping range for inertial confinement fusion applications.

Nonlocal electron transport is important for understanding laser-target coupling for laser-direct-drive (LDD) inertial confinement fusion (ICF) simulations. Current models for the nonlocal electron mean free path in radiation-hydrodynamic codes are based on plasma-physics models developed decades ago; improvements are needed to accurately predict the electron conduction in LDD simulations of ICF target implosions. We utilized time-dependent density functional theory (TD-DFT) to calculate the electron stopping power (SP) in the so-called conduction-zone plasmas of polystyrene in a wide range of densities and temperatures relevant to LDD. Compared with the modified Lee-More model, the TD-DFT calculations indicated a lower SP and a higher stopping range for nonlocal electrons. We fit these electron SP calculations to obtain a global analytical model for the electron stopping range as a function of plasma conditions and the nonlocal electron kinetic energy. This model was implemented in the one-dimensional radiation-hydrodynamic code lilac to perform simulations of LDD ICF implosions, which are further compared with simulations by the standard modified Lee-More model. Results from these integrated simulations are discussed in terms of the implications of this TD-DFT-based mean-free-path model to ICF simulations.

Proton stopping measurements at low velocity in warm dense carbon.

Ion stopping in warm dense matter is a process of fundamental importance for the understanding of the properties of dense plasmas, the realization and the interpretation of experiments involving ion-beam-heated warm dense matter samples, and for inertial confinement fusion research. The theoretical description of the ion stopping power in warm dense matter is difficult notably due to electron coupling and degeneracy, and measurements are still largely missing. In particular, the low-velocity stopping range, that features the largest modelling uncertainties, remains virtually unexplored. Here, we report proton energy-loss measurements in warm dense plasma at unprecedented low projectile velocities. Our energy-loss data, combined with a precise target characterization based on plasma-emission measurements using two independent spectroscopy diagnostics, demonstrate a significant deviation of the stopping power from classical models in this regime. In particular, we show that our results are in closest agreement with recent first-principles simulations based on time-dependent density functional theory.

Attosecond two-photon interferometry for doubly excited states of helium.

We show that the correlation dynamics in coherently excited doubly excited resonances of helium can be followed in real time by two-photon interferometry. This approach promises to map the evolution of the two-electron wave packet onto experimentally easily accessible noncoincident single-electron spectra. We analyze the interferometric signal in terms of a semianalytical model which is validated by a numerical solution of the time-dependent two-electron Schrödinger equation in its full dimensionality.

Multicomponent mutual diffusion in the warm, dense matter regime.

We present the formulation, simulations, and results for multicomponent mutual diffusion coefficients in the warm, dense matter regime. While binary mixtures have received considerable attention for mass transport, far fewer studies have addressed ternary and more complex systems. We therefore explicitly examine ternary systems utilizing the Maxwell-Stefan formulation that relates diffusion to gradients in the chemical potential. Onsager coefficients then connect the macroscopic diffusion to microscopic particle motions, evinced in trajectories characterized by positions and velocities, through various autocorrelation functions (ACFs). These trajectories are generated by molecular dynamics (MD) simulations either through the Born-Oppenheimer approximation, which treats the ions classically and the electrons quantum-mechanically by an orbital-free density-functional theory, or through a classical MD approach with Yukawa pair-potentials, whose effective ionizations and electron screening length derive from quantal considerations. We employ the reference-mean form of the ACFs and determine the center-of-mass coefficients through a simple reference-frame-dependent similarity transformation. The Onsager terms in turn determine the mutual diffusion coefficients. We examine a representative sample of ternary mixtures as a function of density and temperature from those with only light elements (D-Li-C, D-Li-Al) to those with highly asymmetric mass components (D-Li-Cu, D-Li-Ag, H-C-Ag). We also follow trends in the diffusion as a function of number concentration and evaluated the efficacy of various approximations such as the Darken approximation.

Energy relaxation rates in dense hydrogen plasmas.

A comprehensive study is made of the energy relaxation rates between ions and electrons in a dense hydrogen plasma. Results of classical molecular dynamics (MD) simulations are compared with quantal calculations using the Fermi golden rule and using dimensional continuation. The rates from the molecular dynamics simulations employing a screened potential are found to be in reasonable agreement with the Landau-Spitzer relaxation rates, and are around 30% higher than the Fermi golden rule rates. By inverting the classical MD relaxation rate vs the quantal result, a semiclassical value for the screening length is suggested. We present energy relaxation rates relevant for radiation-hydrodynamic simulations of inertial confinement fusion devices.

First-principles equation-of-state table of silicon and its effects on high-energy-density plasma simulations.

Using density-functional theory-based molecular-dynamics simulations, we have investigated the equation of state for silicon in a wide range of plasma density and temperature conditions of ρ=0.001-500g/cm^{3} and T=2000-10^{8}K. With these calculations, we have established a first-principles equation-of-state (FPEOS) table of silicon for high-energy-density (HED) plasma simulations. When compared with the widely used SESAME-EOS model (Table 3810), we find that the FPEOS-predicted Hugoniot is ∼20% softer; for off-Hugoniot plasma conditions, the pressure and internal energy in FPEOS are lower than those of SESAME EOS for temperatures above T ≈ 1-10 eV (depending on density), while the former becomes higher in the low-T regime. The pressure difference between FPEOS and SESAME 3810 can reach to ∼50%, especially in the warm-dense-matter regime. Implementing the FPEOS table of silicon into our hydrocodes, we have studied its effects on Si-target implosions. When compared with the one-dimensional radiation-hydrodynamics simulation using the SESAME 3810 EOS model, the FPEOS simulation showed that (1) the shock speed in silicon is ∼10% slower; (2) the peak density of an in-flight Si shell during implosion is ∼20% higher than the SESAME 3810 simulation; (3) the maximum density reached in the FPEOS simulation is ∼40% higher at the peak compression; and (4) the final areal density and neutron yield are, respectively, ∼30% and ∼70% higher predicted by FPEOS versus the traditional simulation using SESAME 3810. All of these features can be attributed to the larger compressibility of silicon predicted by FPEOS. These results indicate that an accurate EOS table, like the FPEOS presented here, could be essential for the precise design of targets for HED experiments.

Simulations of the optical properties of warm dense aluminum.

Using quantum molecular dynamics simulations, we show that the optical properties of aluminum change drastically along the nonmetal metal transition observed experimentally. As the density increases and the many-body effects become important, the optical response gradually evolves from the one characteristic of an atomic fluid to the one of a simple metal. We show that quantum molecular dynamics combined with the Kubo-Greenwood formulation naturally embodies the two limits and provides a powerful tool to calculate and benchmark the optical properties of various systems as they evolve into the warm dense matter regime.

Dynamical and transport properties of liquid gallium at high pressures.

Quantum molecular dynamics (QMD) simulations are used to calculate the equation of state, structure, and transport properties of liquid gallium along the principal shock Hugoniot. The calculated Hugoniot is in very good agreement with experimental data up to a pressure of 150 GPa as well as with our earlier classical molecular dynamics calculations using a modified embedded atom method (MEAM) potential. The self-diffusion and viscosity calculated using QMD agree with experimental measurements better than the MEAM results, which we attribute to capturing the complexity of the electronic structure at elevated temperatures. Calculations of the DC conductivity were performed around the Hugoniot. Above a density of 7.5 g/cm(3), the temperature increases rapidly along the Hugoniot, and the optical conductivity decreases, indicating simple liquid metal behavior.

First-principles equation of state of polystyrene and its effect on inertial confinement fusion implosions.

Obtaining an accurate equation of state (EOS) of polystyrene (CH) is crucial to reliably design inertial confinement fusion (ICF) capsules using CH/CH-based ablators. With first-principles calculations, we have investigated the extended EOS of CH over a wide range of plasma conditions (ρ=0.1to100g/cm(3) and T=1000 to 4,000,000 K). When compared with the widely used SESAME-EOS table, the first-principles equation of state (FPEOS) of CH has shown significant differences in the low-temperature regime, in which strong coupling and electron degeneracy play an essential role in determining plasma properties. Hydrodynamic simulations of cryogenic target implosions on OMEGA using the FPEOS table of CH have predicted ∼30% decrease in neutron yield in comparison with the usual SESAME simulations. This is attributed to the ∼5% reduction in implosion velocity that is caused by the ∼10% lower mass ablation rate of CH predicted by FPEOS. Simulations using CH-FPEOS show better agreement with measurements of Hugoniot temperature and scattered light from ICF implosions.

Renal angiotensin receptor mapping in obese spontaneously hypertensive rats.

Obese spontaneously hypertensive rats (SHR) develop nephropathy with severe proteinuria, but lean littermates do not develop renal disease. Intrarenal angiotensin has been suggested to contribute to nephropathy in other experimental models. We examined the regulation of angiotensin receptors as a reflection of target tissue response to possible changes in the renin-angiotensin system. We visualized angiotensin receptors in kidneys of 6-8-month-old obese SHR and their lean littermates. Both obese and lean rats were hypertensive as determined by tail-cuff or by direct measurement. Histologic studies showed early glomerular sclerosis in obese but not lean rats. Autoradiographic visualization of angiotensin receptor binding sites in both obese and lean SHR showed glomeruli and medullary rays having the highest levels of binding with additional diffuse labeling in cortex and outer medulla. In obese rats, binding was reduced relative to lean littermates, particularly in the medulla, while intense binding in glomeruli was preserved. Loss of receptors did not reflect tissue damage, since the medulla showed no pathological changes. Biochemical assays of the binding of subtype-selective antagonists to 125I-angiotensin sites in intact sections showed that both losartan-sensitive and PD 123319-sensitive sites were decreased in nephrotic obese rats. We conclude that specific binding sites for angiotensin are decreased in obese SHR with early glomerular sclerosis, suggesting that angiotensin receptors may be regulated by pathogenic processes in this model of renal disease.

Effect of I1-imidazoline receptor activation on responses of hypoglossal and phrenic nerve to chemical stimulation.

Sedation elicited by some centrally acting antihypertensive agents may interfere with respiratory control, and by selectively inhibiting upper airway dilating muscle activity it may facilitate obstructive sleep apnea. Autoradiographic studies with [125I]p-iodoclonidine in the presence of 10 microM epinephrine to block alpha 2-adrenergic sites or 100 nM moxonidine to mask I1-imidazoline sites show that both I1- as well as alpha 2-sites are localized in putative chemosensory areas of the rostral ventrolateral medulla in the cat. We sought to determine the effect of activating I1 and alpha 2-receptors on central chemosensitivity by using moxonidine as a selective I1 agonist, clonidine as a mixed I1/alpha 2 agonist, SK&F-86466 as a specific alpha 2-antagonist, and efaroxan as a mixed I1/alpha 2 antagonist. We recorded responses of phrenic, hypoglossal, and cervical sympathetic nerve activities to progressive hypercapnia after hyperventilation to apnea. Moxonidine (3-100 micrograms/kg i.v.) caused dose-dependent decreases in tonic cervical sympathetic nerve activity and blood pressure, but had no effect on the CO2 threshold (after 30 or 100 micrograms/kg moxonidine, phrenic nerve activity reappeared at 5.8 +/- 0.2% CO2 versus 5.6 +/- 0.3% CO2 in control). Following moxonidine, the slope of the steep portion of the CO2 response tended to increase (10.3 +/- 1.8 versus 7.3 +/- 0.9). Peak phrenic nerve activity was comparable to control at 7.5% CO2 (20 +/- 2 U in control) and at 9.5% CO2 (30 +/- 3 versus 27. +/- 2 U). Similarly, the response of hypoglossal and inspiratory phasic cervical sympathetic nerve activity to a progressive CO2 rise was not affected by moxonidine. By contrast, clonidine in the same doses decreased CO2 sensitivity, because the CO2 threshold was elevated from 5.3 +/- 0.5% to 6.7 +/- 0.4% (p < 0.001). The slope of the CO2 response was decreased from 9.7 +/- 1.9 to 7.4 +/- 1.3 (p = 0.05). Peak phrenic nerve activity was reduced at 7.5% CO2 (11 +/- 5 versus 25 +/- 2 U; p < 0.05) and at 9.5% CO2 (21 +/- 4 versus 33 +/- 2 U; p = 0.06). Clonidine selectively inhibited the response of hypoglossal nerve activity to CO2. The depressive effects of clonidine were reversed by alpha 2-blockade with SK&F-86466 (0.5 or 1 mg/kg). Inspiratory phasic cervical sympathetic nerve activity increased after SK&F-86466 in parallel with phrenic and hypoglossal nerve activity, but the tonic component of cervical sympathetic nerve activity and blood pressure increased only transiently.(ABSTRACT TRUNCATED AT 400 WORDS)

I1-imidazoline receptors. Definition, characterization, distribution, and transmembrane signaling.

Data were presented showing that I1-imidazoline sites show a unique ligand specificity that differs markedly from that of any of the alpha 2-adrenergic subtypes or the I2-imidazoline sites labeled by [3H]idazoxan. On the other hand, the ligand specificity of I1-imidazoline sites is maintained across mammalian species (cow, rat, dog, and human) and between different tissues and cell types. I1-Imidazoline sites can be further distinguished from I2 sites because the latter, unlike I1 sites, were not present in RVLM membranes from bovine brain stem. Furthermore, I1-imidazoline sites were modulated by guanine nucleotides with a specificity appropriate for a receptor coupled to G-protein and were mainly localized to plasma membranes. I1-Imidazoline sites show a unique pattern of distribution between diverse tissues and cell types and appear to be a neuroepithelial marker as well as being present in secretory cells of the pancreatic islets. The widespread distribution of I1-imidazoline sites implies that the functional significance of this putative receptor may have been underestimated. The signaling pathway associated with the I1-imidazoline receptor remains to be fully elucidated, but is likely that activation of phospholipase A2 leading to release of arachidonic acid and subsequent generation of prostaglandins plays a major role.

Electrical conductivity for warm, dense aluminum plasmas and liquids.

The electrical conductivity of warm, dense aluminum plasmas and liquids is calculated using ab initio molecular dynamics and the Kubo-Greenwood formula. The density range extends from near solid to one-hundredth of solid density, and the temperature range extends from 6000 K to 30 000 K. This density and temperature range allows direct comparison with experimental results obtained with the tamped exploding wire technique.

Ultrastructure of the foveal glands of the ticks, Dermacentor andersoni Stiles and D. variabilis (Say).

The foveal glands of Dermacentor variabilis appear to consist of 2 cell types. The outer cells (Type I) are active, with large areas of abundant finely granular material, apparently precursors of the mature secretory granules. The inner cells (Type II) are apparently storage cells. They are highly vacuolated and contain coarsely granular material as well as presumably mature secretory granules. The foveal glands of D. andersoni contain only Type II cells with extensive accumulations of presumably mature secretory granules.

Properties of warm dense polystyrene plasmas along the principal Hugoniot.

Polystyrene (CH) is often chosen as the ablator material for inertial confinement fusion (ICF) targets. Its static, dynamical, and optical properties in warm, dense conditions (due to shock compression) are important for ICF designs. Using the first-principles quantum molecular dynamics (QMD) method, we have investigated the equation of state (EOS) and optical reflectivity of shock-compressed CH up to an unprecedentedly high pressure of 62 Mbar along the principal Hugoniot. The QMD results are compared with existing experimental measurements as well as the SESAME EOS model. Although the Hugoniot pressure and/or temperature from QMD calculations agrees with experiments and the SESAME EOS model at low pressures below 10 Mbar, we have identified for the first time a stiffer behavior of shocked CH at higher pressures (>10 Mbar). Such a stiffer behavior of warm, dense CH can affect the ablation pressure (shock strength), shock coalescence dynamics, and nonuniformity growth in ICF implosions. In addition, we corrected the mistake made in literature for calculating the reflectivity of shocked CH and obtained good agreements with experimental measurements, which should lend credence to future opacity calculations in a first-principles fashion.

First principles nonequilibrium plasma mixing.

We have performed nonequilibrium classical and quantum-mechanical molecular dynamics simulations that follow the interpenetration of deuterium-tritium (DT) and carbon (C) components through an interface initially in hydrostatic and thermal equilibrium. We concentrate on the warm, dense matter regime with initial densities of 2.5-5.5 g/cm3 and temperatures from 10 to 100 eV. The classical treatment employs a Yukawa pair-potential with the parameters adjusted to the plasma conditions, and the quantum treatment rests on an orbital-free density functional theory at the Thomas-Fermi-Dirac level. For times greater than about a picosecond, the component concentrations evolve in accordance with Fick's law for a classically diffusing fluid with the motion, though, described by the mutual diffusion coefficient of the mixed system rather than the self-diffusion of the individual components. For shorter times, microscopic processes control the clearly non-Fickian dynamics and require a detailed representation of the electron probability density in space and time.

First-principles thermal conductivity of warm-dense deuterium plasmas for inertial confinement fusion applications.

Thermal conductivity (κ) of both the ablator materials and deuterium-tritium (DT) fuel plays an important role in understanding and designing inertial confinement fusion (ICF) implosions. The extensively used Spitzer model for thermal conduction in ideal plasmas breaks down for high-density, low-temperature shells that are compressed by shocks and spherical convergence in imploding targets. A variety of thermal-conductivity models have been proposed for ICF hydrodynamic simulations of such coupled and degenerate plasmas. The accuracy of these κ models for DT plasmas has recently been tested against first-principles calculations using the quantum molecular-dynamics (QMD) method; although mainly for high densities (ρ > 100 g/cm3), large discrepancies in κ have been identified for the peak-compression conditions in ICF. To cover the wide range of density-temperature conditions undergone by ICF imploding fuel shells, we have performed QMD calculations of κ for a variety of deuterium densities of ρ = 1.0 to 673.518 g/cm3, at temperatures varying from T = 5 × 103 K to T = 8 × 106 K. The resulting κQMD of deuterium is fitted with a polynomial function of the coupling and degeneracy parameters Γ and θ, which can then be used in hydrodynamic simulation codes. Compared with the "hybrid" Spitzer-Lee-More model currently adopted in our hydrocode lilac, the hydrosimulations using the fitted κQMD have shown up to ∼20% variations in predicting target performance for different ICF implosions on OMEGA and direct-drive-ignition designs for the National Ignition Facility (NIF). The lower the adiabat of an imploding shell, the more variations in predicting target performance using κQMD. Moreover, the use of κQMD also modifies the shock conditions and the density-temperature profiles of the imploding shell at early implosion stage, which predominantly affects the final target performance. This is in contrast to the previous speculation that κQMD changes mainly the inside ablation process during the hot-spot formation of an ICF implosion.

First-principles opacity table of warm dense deuterium for inertial-confinement-fusion applications.

Accurate knowledge of the optical properties of a warm dense deuterium-tritium (DT) mixture is important for reliable design of inertial confinement fusion (ICF) implosions using radiation-hydrodynamics simulations. The opacity of a warm dense DT shell essentially determines how much radiation from hot coronal plasmas can be deposited in the DT fuel of an imploding capsule. Even for the simplest species of hydrogen, the accurate calculation of their opacities remains a challenge in the warm-dense matter regime because strong-coupling and quantum effects play an important role in such plasmas. With quantum-molecular-dynamics (QMD) simulations, we have derived a first-principles opacity table (FPOT) of deuterium (and the DT mixture by mass scaling) for a wide range of densities from ρ(D)=0.5 to 673.518g/cm(3) and temperatures from T=5000K up to the Fermi temperature T(F) for each density. Compared with results from the astrophysics opacity table (AOT) currently used in our hydrocodes, the FPOT of deuterium from our QMD calculations has shown a significant increase in opacity for strongly coupled and degenerate plasma conditions by a factor of 3-100 in the ICF-relevant photon-energy range. As conditions approach those of classical plasma, the opacity from the FPOT converges to the corresponding values of the AOT. By implementing the FPOT of deuterium and the DT mixture into our hydrocodes, we have performed radiation-hydrodynamics simulations for low-adiabat cryogenic DT implosions on the OMEGA laser and for direct-drive-ignition designs for the National Ignition Facility. The simulation results using the FPOT show that the target performance (in terms of neutron yield and energy gain) could vary from ∼10% up to a factor of ∼2 depending on the adiabat of the imploding DT capsule; the lower the adiabat, the more variation is seen in the prediction of target performance when compared to the AOT modeling.