Yukawa-Friedel-tail pair potentials for warm dense matter applications.

Accurate equations of state (EOS) and plasma transport properties are essential for numerical simulations of warm dense matter encountered in many high-energy-density situations. Molecular dynamics (MD) is a simulation method that generates EOS and transport data using an externally provided potential to dynamically evolve the particles without further reference to the electrons. To minimize computational cost, pair potentials needed in MD may be obtained from the neutral-pseudoatom (NPA) approach, a form of single-ion density functional theory (DFT), where many-ion effects are included via ion-ion correlation functionals.

Ionization of carbon at 10-100 times the diamond density and in the 10^{6} K temperature range.

The behavior of partially ionized hot compressed matter is critical to the study of planetary interiors as well as nuclear fusion studies. A recent quantum study of carbon in the 10-70 Gbar range and at a temperature of 100 eV used N-atom density functional theory (DFT) with N∼32-64 and molecular dynamics (MD). This involves band-structure-type electronic calculations and averaging over many MD-generated ion configurations.

Liquid-Liquid Phase Transitions in Silicon.

We use computationally simple neutral pseudoatom ("average atom") density functional theory (DFT) and standard DFT to elucidate liquid-liquid phase transitions (LPTs) in liquid silicon. An ionization-driven transition and three LPTs including the known LPT near 2.5  g/cm^{3} are found.

Fertilizer usage and cadmium in soils, crops and food.

Phosphate fertilizers were first implicated by Schroeder and Balassa (Science 140(3568):819-820, 1963) for increasing the Cd concentration in cultivated soils and crops. This suggestion has become a part of the accepted paradigm on soil toxicity. Consequently, stringent fertilizer control programs to monitor Cd have been launched.

Ion-ion dynamic structure factor, acoustic modes, and equation of state of two-temperature warm dense aluminum.

The ion-ion dynamical structure factor and the equation of state of warm dense aluminum in a two-temperature quasiequilibrium state, with the electron temperature higher than the ion temperature, are investigated using molecular-dynamics simulations based on ion-ion pair potentials constructed from a neutral pseudoatom model. Such pair potentials based on density functional theory are parameter-free and depend directly on the electron temperature and indirectly on the ion temperature, enabling efficient computation of two-temperature properties. Comparison with ab initio simulations and with other average-atom calculations for equilibrium aluminum shows good agreement, justifying a study of quasiequilibrium situations.

Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime.

We study the conductivities σ of (i) the equilibrium isochoric state σ_{is}, (ii) the equilibrium isobaric state σ_{ib}, and also the (iii) nonequilibrium ultrafast matter state σ_{uf} with the ion temperature T_{i} less than the electron temperature T_{e}. Aluminum, lithium, and carbon are considered, being increasingly complex warm dense matter systems, with carbon having transient covalent bonds. First-principles calculations, i.

Chronic kidney disease of unknown etiology and the effect of multiple-ion interactions.

High incidence of chronic kidney disease of unknown etiology (CKDU) prevalent in many countries (e.g., Sri Lanka, equatorial America) is reviewed in the context of recent experimental work and using our understanding of the hydration of ions and proteins.

Equation of state, phonons, and lattice stability of ultrafast warm dense matter.

Using the two-temperature model for ultrafast matter (UFM), we compare the equation of state, pair-distribution functions g(r), and phonons using the neutral pseudoatom (NPA) model with results from density functional theory (DFT) codes and molecular dynamics (MD) simulations for Al, Li, and Na. The NPA approach uses state-dependent first-principles pseudopotentials from an "all-electron" DFT calculation with finite-T exchange-correlation functional (XCF). It provides pair potentials, structure factors, the "bound" and "free" states, as well as a mean ionization Z[over ¯] unambiguously.

Pair potentials for warm dense matter and their application to x-ray Thomson scattering in aluminum and beryllium.

Ultrafast laser experiments yield increasingly reliable data on warm dense matter, but their interpretation requires theoretical models. We employ an efficient density functional neutral-pseudoatom hypernetted-chain (NPA-HNC) model with accuracy comparable to ab initio simulations and which provides first-principles pseudopotentials and pair potentials for warm-dense matter. It avoids the use of (i) ad hoc core-repulsion models and (ii) "Yukawa screening" and (iii) need not assume ion-electron thermal equilibrium.

Dynamic conductivity and plasmon profile of aluminum in the ultra-fast-matter regime.

We use an explicitly isochoric two-temperature theory to analyze recent x-ray laser scattering data for aluminum in the ultra-fast-matter (UFM) regime up to 6 eV. The observed surprisingly low conductivities are explained by including strong electron-ion scattering effects using the phase shifts calculated via the neutral-pseudo-atom model. The difference between the static conductivity for UFM-Al and equilibrium aluminum in the warm-dense matter state is clearly brought out by comparisons with available density-fucntional+molecular-dynamics simulations.

Chronic kidney disease of unknown aetiology and ground-water ionicity: study based on Sri Lanka.

High incidence of chronic kidney disease of unknown aetiology (CKDU) in Sri Lanka is shown to correlate with the presence of irrigation works and rivers that bring-in 'nonpoint source' fertilizer runoff from intensely agricultural regions. We review previous attempts to link CKDU with As, Cd and other standard toxins. Those studies (e.

Partial ionization in dense plasmas: comparisons among average-atom density functional models.

Nuclei interacting with electrons in dense plasmas acquire electronic bound states, modify continuum states, generate resonances and hopping electron states, and generate short-range ionic order. The mean ionization state (MIS), i.e, the mean charge Z of an average ion in such plasmas, is a valuable concept: Pseudopotentials, pair-distribution functions, equations of state, transport properties, energy-relaxation rates, opacity, radiative processes, etc.

Electron-ion and ion-ion potentials for modeling warm dense matter: Applications to laser-heated or shock-compressed Al and Si.

The pair interactions Uij(r) determine the thermodynamics and linear transport properties of matter via the pair-distribution functions (PDFs), i.e., gij(r).

Quantum corrections and bound-state effects in the energy relaxation of hot dense hydrogen.

Simple analytic formulas for energy relaxation (ER) in electron-ion systems, with quantum corrections, ion dynamics, and RPA-type screening are presented. ER in the presence of bound electrons is examined in view of recent simulations for ER in hydrogen in the range 10{20}-10{24} electrons/cc.

Temperature relaxation in hot dense hydrogen.

Temperature equilibration of hydrogen is studied for conditions relevant to inertial confinement fusion. New molecular-dynamics simulations and results from quantum many-body theory are compared with Landau-Spitzer predictions for temperatures T with 50 View Article and Find Full Text PDF

The interaction of nitrogen molecules with (4, 0) single-walled carbon nanotube: electronic and structural effects.

The electronic structure and energetics of (4, 0) single-walled carbon nanotubes (CNTs) interacting with nitrogen have been studied using density-functional calculations. We show that the nanotubes become covered with a stable sheath of N(2) molecules. We have constructed potential energy curves which can be used for the thermodynamic analysis of N(2) adsorption and desorption processes.

Pair-distribution functions of two-temperature two-mass systems: comparison of molecular dynamics, classical-map hypernetted chain, quantum Monte Carlo, and Kohn-Sham calculations for dense hydrogen.

Two-temperature, two-mass quasiequilibrium plasmas may occur in electron-ion plasmas, nuclear-matter, as well as in electron-hole condensed-matter systems. Dense two-temperature hydrogen plasmas straddle the difficult partially degenerate regime of electron densities and temperatures which are important in astrophysics, in inertial-confinement fusion research, and other areas of warm dense-matter physics. Results from quantum Monte Carlo (QMC) are used to benchmark the procedures used in classical molecular-dynamics simulations and hypernetted chain (HNC) and classical-map HNC (CHNC) methods to derive electron-electron and electron-proton pair-distribution functions.

Static and dynamic conductivity of warm dense matter within a density-functional approach: application to aluminum and gold.

The conductivity sigma(omega) of dense Al and Au plasmas is considered where all the needed inputs are obtained from density-functional theory (DFT). These calculations involve a self-consistent determination of (i) the equation of state and the ionization balance, (ii) evaluation of the ion-ion and ion-electron pair-distribution functions, (iii) determination of the scattering amplitudes, and finally the conductivity. We present results for Al and Au for compressions 0.

Spin-polarized stable phases of the 2D electron fluid at finite temperatures.

The Helmholtz free energy F of the 2D electron fluid is calculated using a mapping to a classical Coulomb fluid [Phys. Rev. Lett.

Possibility of an unequivocal test of different models of the equation of state of aluminum in the coupling regime Gamma approximately 1-50.

The equation of state (EOS) in regimes of density (rho) and temperature (T) which are inaccessible to experiment has to be determined using theories which may themselves be out of their range of validity. Even for Al, the EOS in the region 0.1 View Article and Find Full Text PDF

Temperature relaxation in two-temperature states of dense electron-ion systems.

It is shown that the Landau-Spitzer theory for temperature relaxation between electrons and ions, which was originally derived for ideal plasmas, is in fact more general. A relaxation formula is derived, for arbitrary ion-ion coupling that follows from elementary considerations combined with the fluctuation-dissipation theorem and the f-sum rule. The conditions for the validity of this theory are weak electron-ion coupling and that the spectrum of fluctuations of the ions lies at energies far below the resonances of the electrons spectrum.

2D electron gas at arbitrary spin polarizations and coupling strengths: exchange-correlation energies, distribution functions, and spin-polarized phases.

We use the classical mapping of quantum fluids [Phys. Rev. Lett.

Results on the energy-relaxation rates of dense two-temperature aluminum, carbon, and silicon plasmas close to liquid-metal conditions.

We present results for the electron-ion energy relaxation coupling constants g(ei)(T(e),T(i),kappa) for aluminum, carbon, and silicon plasmas at several electron and ion temperatures T(i), T(e) of experimental interest. The calculations use the Fermi golden rule and the Landau-Spitzer model valid at weak electron-ion coupling, as well as the coupled-mode approach suitable for strong coupling. A physically motivated simple derivation of the coupled-mode energy relaxation formula for two-component charged fluids is presented.

Simple classical mapping of the spin-polarized quantum electron gas: distribution functions and local-field corrections.

We use the now well known spin unpolarized exchange-correlation energy E(xc) of the uniform electron gas as the basic "many-body" input to determine the temperature T(q) of a classical Coulomb fluid having the same correlation energy as the quantum system. It is shown that the spin-polarized pair distribution functions (SPDFs) of the classical fluid at T(q), obtained using the hypernetted chain equation, are in excellent agreement with those of the T = 0 quantum fluid obtained by quantum Monte Carlo (QMC) simulations. These methods are computationally simple and easily applied to problems which are currently beyond QMC simulations.