91 research outputs found
Hugoniot of shocked liquid deuterium up to 300 GPa: Quantum molecular dynamic simulations
Quantum molecular dynamic (QMD) simulations are introduced to study the
thermophysical properties of liquid deuterium under shock compression. The
principal Hugoniot is determined from the equation of states, where
contributions from molecular dissociation and atomic ionization are also added
onto the QMD data. At pressures below 100 GPa, our results show that the local
maximum compression ratio of 4.5 can be achieved at 40 GPa, which is in good
agreement with magnetically driven flyer and convergent-explosive experiments;
At the pressure between 100 and 300 GPa, the compression ratio reaches a
maximum of 4.95, which agrees well with recent high power laser-driven
experiments. In addition, the nonmetal-metal transition and optical properties
are also discussed.Comment: 4.1 pages, 4 figure
Link between K-absorption edges and thermodynamic properties of warm-dense plasmas established by improved first-principles method
A precise calculation that translates shifts of X-ray K-absorption edges to
variations of thermodynamic properties allows quantitative characterization of
interior thermodynamic properties of warm dense plasmas by X-ray absorption
techniques, which provides essential information for inertial confinement
fusion and other astrophysical applications. We show that this interpretation
can be achieved through an improved first-principles method. Our calculation
shows that the shift of K-edges exhibits selective sensitivity to thermal
parameters and thus would be a suitable temperature index to warm dense
plasmas. We also show with a simple model that the shift of K-edges can be used
to detect inhomogeneity inside warm dense plasmas when combined with other
experimental tools
Extended First-Principles Molecular Dynamics Method From Cold Materials to Hot Dense Plasmas
An extended first-principles molecular dynamics (FPMD) method based on
Kohn-Sham scheme is proposed to elevate the temperature limit of the FPMD
method in the calculation of dense plasmas. The extended method treats the wave
functions of high energy electrons as plane waves analytically, and thus
expands the application of the FPMD method to the region of hot dense plasmas
without suffering from the formidable computational costs. In addition, the
extended method inherits the high accuracy of the Kohn-Sham scheme and keeps
the information of elec- tronic structures. This gives an edge to the extended
method in the calculation of the lowering of ionization potential, X-ray
absorption/emission spectra, opacity, and high-Z dense plasmas, which are of
particular interest to astrophysics, inertial confinement fusion engineering,
and laboratory astrophysics
First-Principles Calculation of Principal Hugoniot and K-Shell X-ray Absorption Spectra for Warm Dense KCl
Principal Hugoniot and K-shell X-ray absorption spectra of warm dense KCl are
calculated using the first-principles molecular dynamics method. Evolution of
electronic structures as well as the influence of the approximate description
of ionization on pressure (caused by the underestimation of the energy gap
between conduction bands and valence bands) in the first-principles method are
illustrated by the calculation. Pressure ionization and thermal smearing are
shown as the major factors to prevent the deviation of pressure from global
accumulation along the Hugoniot. In addition, cancellation between electronic
kinetic pressure and virial pressure further reduces the deviation. The
calculation of X-ray absorption spectra shows that the band gap of KCl persists
after the pressure ionization of the electrons of Cl and K taking place at
lower energy, which provides a detailed understanding to the evolution of
electronic structures of warm dense matter
Transport properties of dense deuterium-tritium plasmas
Consistent descriptions of the equation of states, and information about
transport coefficients of deuterium-tritium mixture are demonstrated through
quantum molecular dynamic (QMD) simulations (up to a density of 600 g/cm
and a temperature of eV). Diffusion coefficients and viscosity are
compared with one component plasma model in different regimes from the strong
coupled to the kinetic one. Electronic and radiative transport coefficients,
which are compared with models currently used in hydrodynamic simulations of
inertial confinement fusion, are evaluated up to 800 eV. The Lorentz number is
also discussed from the highly degenerate to the intermediate region.Comment: 4 pages, 3 figure
Ab Initio Simulations of Dense Helium Plasmas
We study the thermophysical properties of dense helium plasmas by using
quantum molecular dynamics and orbital-free molecular dynamics simulations,
where densities are considered from 400 to 800 g/cm and temperatures up
to 800 eV. Results are presented for the equation of state. From the
Kubo-Greenwood formula, we derive the electrical conductivity and electronic
thermal conductivity. In particular, with the increase in temperature, we
discuss the change in the Lorenz number, which indicates a transition from
strong coupling and degenerate state to moderate coupling and partial
degeneracy regime for dense helium.Comment: 4 PRL pages, 3 figure
Thermophysical properties for shock compressed polystyrene
We have performed quantum molecular dynamic simulations for warm dense
polystyrene at high pressures. The principal Hugoniot up to 790 GPa is derived
from wide range equation of states, where contributions from atomic ionizations
are semiclassically determined. The optical conductivity is calculated via the
Kubo-Greenwood formula, from which the dc electrical conductivity and optical
reflectivity are determined. The nonmetal-to-metal transition is identified by
gradual decomposition of the polymer. Our results show good agreement with
recent high precision laser-driven experiments.Comment: 4.2 pages, 3 figure
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