367 research outputs found
Correlations in Hot Dense Helium
Hot dense helium is studied with first-principles computer simulations. By
combining path integral Monte Carlo and density functional molecular dynamics,
a large temperature and density interval ranging from 1000 to 1000000 K and 0.4
to 5.4 g/cc becomes accessible to first-principles simulations and the changes
in the structure of dense hot fluids can be investigated. The focus of this
article are pair correlation functions between nuclei, between electrons, and
between electrons and nuclei. The density and temperature dependence of these
correlation functions is analyzed in order to describe the structure of the
dense fluid helium at extreme conditions.Comment: accepted for publication in Journal of Physics
Path Integral Monte Carlo Simulation of the Low-Density Hydrogen Plasma
Restricted path integral Monte Carlo simulations are used to calculate the
equilibrium properties of hydrogen in the density and temperature range of
and . We test the accuracy of the pair density matrix and
analyze the dependence on the system size, on the time step of the path
integral and on the type of nodal surface. We calculate the equation of state
and compare with other models for hydrogen valid in this regime. Further, we
characterize the state of hydrogen and describe the changes from a plasma to an
atomic and molecular liquid by analyzing the pair correlation functions and
estimating the number of atoms and molecules present.Comment: 12 pages, 21 figures, submitted for Phys. Rev.
Sequestration of noble gases in giant planet interiors
The Galileo probe showed that Jupiter's atmosphere is severely depleted in
neon compared to protosolar values. We show, via ab initio simulations of the
partitioning of neon between hydrogen and helium phases, that the observed
depletion can be explained by the sequestration of neon into helium-rich
droplets within the postulated hydrogen-helium immiscibility layer of the
planet's interior. We also demonstrate that this mechanism will not affect
argon, explaining the observed lack of depletion of this gas. This provides
strong indirect evidence for hydrogen-helium immiscibility in Jupiter
Tidal Response of Preliminary Jupiter Model
In anticipation of improved observational data for Jupiter's gravitational
field from the Juno spacecraft, we predict the static tidal response for a
variety of Jupiter interior models based on ab initio computer simulations of
hydrogen-helium mixtures. We calculate hydrostatic-equilibrium gravity terms
using the non-perturbative concentric Maclaurin Spheroid (CMS) method that
eliminates lengthy expansions used in the theory of figures. Our method
captures terms arising from the coupled tidal and rotational perturbations,
which we find to be important for a rapidly-rotating planet like Jupiter. Our
predicted static tidal Love number is 10\% larger than
previous estimates. The value is, as expected, highly correlated with the zonal
harmonic coefficient , and is thus nearly constant when plausible changes
are made to interior structure while holding fixed at the observed value.
We note that the predicted static might change due to Jupiter's dynamical
response to the Galilean moons, and find reasons to argue that the change may
be detectable, although we do not present here a theory of dynamical tides for
highly oblate Jovian planets. An accurate model of Jupiter's tidal response
will be essential for interpreting Juno observations and identifying tidal
signals from effects of other interior dynamics in Jupiter's gravitational
field.Comment: 10 Pages, 6 figures, 4 table
Structure and bonding of dense liquid oxygen from first principles simulations
Using first principles simulations we have investigated the structural and
bonding properties of dense fluid oxygen up to 180 GPa. We have found that band
gap closure occurs in the molecular liquid, with a "slow" transition from a
semi-conducting to a poor metallic state occurring over a wide pressure range.
At approximately 80 GPa, molecular dissociation is observed in the metallic
fluid. Spin fluctuations play a key role in determining the electronic
structure of the low pressure fluid, while they are suppressed at high
pressure.Comment: 4 figure
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