22 research outputs found
Testing the isomorph invariance of the bridge functions of Yukawa one-component plasmas
It has been conjectured that bridge functions remain nearly invariant along
phase diagram lines of constant excess entropy for the class of R-simple
liquids. In the companion paper, this hypothesis has been confirmed for Yukawa
bridge functions outside the correlation void. In order to complete the testing
of the invariance ansatz, Yukawa bridge functions are here computed inside the
correlation void with the cavity distribution method and input from ultra-long
molecular dynamics simulations featuring a tagged particle pair. A general
methodology is developed for the design of the tagged pair interaction
potential that leads to the acquisition of uniform statistics. An extrapolation
technique is developed to determine the bridge function value at zero
separation. The effect of different sources of errors is quantified. Yukawa
bridge functions are demonstrated to be nearly isomorph invariant also in the
short range. Generalization to all R-simple systems and practical implications
are discussed.Comment: 19 pages, 10 figures, 3 tables, supplementary materia
Quantum version of the integral equation theory based dielectric scheme for strongly coupled electron liquids
A novel dielectric scheme is proposed for strongly coupled electron liquids
that handles quantum mechanical effects beyond the random phase approximation
level and treats electronic correlations within the integral equation theory of
classical liquids. The self-consistent scheme features a complicated dynamic
local field correction functional and its formulation is guided by ab initio
path integral Monte Carlo simulations. Remarkably, our scheme is capable to
provide unprecedently accurate results for the static structure factor with the
exception of the Wigner crystallization vicinity, despite the absence of
adjustable or empirical parameters.Comment: 8 pages, 3 figure
Energy response and spatial alignment of the perturbed electron gas
We present extensive new \emph{ab initio} path integral Monte Carlo (PIMC)
simulations of the harmonically perturbed uniform electron gas (UEG) for
different densities and temperatures. This allows us to study the linear
response of the UEG with respect to different contributions to the total energy
for different wave numbers. We find that the induced change in the interaction
energy exhibits a non-monotonic behaviour, and becomes negative for
intermediate wave numbers. This effect is strongly dependent on the coupling
strength and can be traced back to the spatial alignment of electrons
introduced in earlier works [T.~Dornheim \emph{et al.}, Communications Physics
\textbf{5}, 304 (2022)]. The observed quadratic dependence on the perturbation
amplitude in the limit of weak perturbations and the quartic dependence of the
perturbation amplitude corrections are consistent with linear and non-linear
versions of the density stifness theorem. All PIMC simulation results are
freely available online and can be used to benchmark new methods, or as input
for other calculations
Ab initio path integral Monte Carlo simulations of the uniform electron gas on large length scales
The accurate description of non-ideal quantum many-body systems is of prime
importance for a host of applications within physics, quantum chemistry,
material science, and related disciplines. At finite temperatures, the gold
standard is given by \textit{ab initio} path integral Monte Carlo (PIMC)
simulations, which do not require any empirical input, but exhibit an
exponential increase in the required compute time for fermionic systems with
increasing the system size . Very recently, it has been suggested to compute
fermionic properties without this bottleneck based on PIMC simulations of
fictitious identical particles. In the present work, we use this technique to
carry out very large () PIMC simulations of the warm dense electron
gas and demonstrate that it is capable of providing a highly accurate
description of investigated properties, i.e., the static structure factor, the
static density response function, and local field correction, over the entire
range of length scales
Isomorph invariance and thermodynamics of repulsive dense bi-Yukawa one-component plasmas
In numerous realizations of complex plasmas, dust-dust interactions are
characterized by two screening lengths and are thus better described by a
combination of Yukawa potentials. The present work investigates the static
correlations and the thermodynamics of repulsive dense bi-Yukawa fluids based
on the fact that such strongly coupled systems exhibit isomorph invariance. The
strong virial-potential energy correlations are demonstrated with the aid of
molecular dynamics simulations, an accurate analytical expression for the
isomorph family of curves is obtained and an empirical expression for the
fluid-solid phase-coexistence line is proposed. The isomorph-based empirically
modified hypernetted-chain approach, grounded on the ansatz of isomorph
invariant bridge functions, is then extended to such systems and the resulting
structural properties show an excellent agreement with the results of computer
simulations. A simple and accurate closed-form expression is obtained for the
excess internal energy of dense bi-Yukawa fluids by capitalizing on the compact
parameterization offered by the Rosenfeld-Tarazona decomposition in combination
with the Rosenfeld scaling, which opens up the energy route to thermodynamics.Comment: 11 pages, 6 figure
Wall cratering upon high velocity normal dust impact
Dust-wall high speed impacts, triggered by the termination of runaway
electrons on plasma facing components, constitute a source of erosion. Normal
high velocity mechanical impacts of tungsten dust on bulk tungsten plates are
reproduced in a controlled manner by light gas gun shooting systems.
Post-mortem surface analysis revealed that three erosion regimes are realized;
plastic deformation, bonding and partial disintegration. The large impact
statistics allowed the extraction of reliable empirical damage laws in the
latter regime, which can be employed for erosion estimates in future reactors.Comment: 7 pages, 7 figures, 1 tabl
Adhesive force distributions for tungsten dust deposited on bulk tungsten and beryllium-coated tungsten surfaces
Comprehensive measurements of the adhesive force for tungsten dust adhered to tungsten surfaces have been performed with the electrostatic detachment method. Monodisperse spherical dust has been deposited with gas dynamics techniques or with gravity mimicking adhesion as it naturally occurs in tokamaks. The adhesive force is confirmed to follow the log-normal distribution and empirical correlations are proposed for the size-dependence of its mean and standard deviation. Systematic differences are observed between the two deposition methods and attributed to plastic deformation during sticking impacts. The presence of thin beryllium coatings on tungsten surfaces is demonstrated to barely affect adhesion
Extraction of the frequency moments of spectral densities from imaginary-time correlation function data
We introduce an exact framework to compute the positive frequency moments
of different dynamic
properties from imaginary-time quantum Monte Carlo data. As a practical
example, we obtain the first five moments of the dynamic structure factor
of the uniform electron gas at the electronic Fermi
temperature based on \emph{ab initio} path integral Monte Carlo simulations. We
find excellent agreement with known sum rules for , and, to our
knowledge, present the first results for . Our idea can be
straightforwardly generalized to other dynamic properties such as the
single-particle spectral function , and will be useful
for a number of applications, including the study of ultracold atoms, exotic
warm dense matter, and condensed matter systems
Diffusion bonding effects on the adhesion of tungsten dust on tungsten surfaces
Abstract High temperature excursions have the potential to strongly enhance the room temperature adhesion of tokamak dust. Planar tungsten substrates containing adhered nearly monodisperse spherical tungsten dust have been exposed to linear plasmas and vacuum furnaces. Prolonged thermal treatments of varying peak temperature and constant duration were followed by room temperature adhesion measurements with the electrostatic detachment method. Adhesive forces have been observed to strongly depend on the thermal pre-history, greatly increasing above a threshold temperature. Adhesive forces have been measured up to an order of magnitude larger than those of untreated samples. This enhancement has been attributed to atomic diffusion that slowly eliminates the omnipresent nanometer-scale surface roughness, ultimately switching the dominant interaction from long-range weak van der Waals forces to short-range strong metallic bonding
X-ray Thomson scattering absolute intensity from the f-sum rule in the imaginary-time domain
We evaluate the f-sum rule on the dynamic structure factor in the
imaginary-time domain as a formally exact and simulation-free means of
normalizing X-Ray Thomson Scattering (XRTS) spectra. This circumvents
error-prone real-time deconvolution of the source function and facilitates
calculating the static structure factor from the properly normalized
imaginary-time correlation function. We apply our technique to two distinct
sets of experimental data, finding that it is effective for both narrow and
broad x-ray sources. This approach could be readily adapted to other scattering
spectroscopies