36 research outputs found
Correlation energy of the spin-polarized electron liquid by quantum Monte Carlo
Variational and diffusion quantum Monte Carlo (VMC and DMC) methods with
Slater-Jastrow-backflow trial wave functions are used to study the
spin-polarized three-dimensional uniform electron fluid. We report ground state
VMC and DMC energies in the density range .
Finite-size errors are corrected using canonical-ensemble twist-averaged
boundary conditions and extrapolation of the twist-averaged energy per particle
calculated at three system sizes (N=113, 259, and 387) to the thermodynamic
limit of infinite system size. The DMC energies in the thermodynamic limit are
used to parameterize a local spin density approximation correlation function
for inhomogeneous electron systems.Comment: arXiv admin note: substantial text overlap with arXiv:2209.1022
Simulations of Collisional Effects in an Inner-Shell Solid-Density Mg X-Ray Laser
Inner-shell K x-ray lasers have been created by pumping gaseous,
solid, and liquid targets with the intense x-ray output of free-electron-lasers
(FELs). For gaseous targets lasing relies on the creation of K-shell core-holes
on a time-scale short compared with filling via Auger decay. In the case of
solid and liquid density systems, collisional effects will also be important,
affecting not only populations, but also line-widths, both of which impact the
degree of overall gain, and its duration. However, to date such collisional
effects have not been extensively studied. We present here initial simulations
using the CCFLY code of inner-shell lasing in solid density Mg, where we
self-consistently treat the effects of the incoming FEL radiation and the
atomic kinetics of the Mg system, including radiative, Auger, and collisional
effects. We find that the combination of collisional population of the lower
states of the lasing transitions and broadening of the lines precludes lasing
on all but the K of the initially cold system. Even assuming
instantaneous turning on of the FEL pump, we find the duration of the gain in
the solid system to be sub-femtosecond.Comment: This paper has been submitted to Philosophical Transactions
Correlation energy of the paramagnetic electron gas at the thermodynamic limit
The variational and diffusion quantum Monte Carlo methods are used to
calculate the correlation energy of the paramagnetic three-dimensional
homogeneous electron gas at intermediate to high density. Ground state energies
in finite cells are determined using Slater-Jastrow-backflow trial wave
functions, and finite-size errors are removed using twist-averaged boundary
conditions and extrapolation of the energy per particle to the thermodynamic
limit of infinite system size. Our correlation energies in the thermodynamic
limit are lower (i.e., more negative, and therefore more accurate according to
the variational principle) than previous results, and can be used for the
parameterization of density functionals to be applied to high-density systems
Correlation energy of the spin-polarized electron liquid studied using quantum Monte Carlo simulations
Variational and diffusion quantum Monte Carlo (VMC and DMC) methods with Slater-Jastrow-backflow trial wave functions are used to study the spin-polarized three-dimensional uniform electron fluid. We report ground state VMC and DMC energies in the density range 0.5 ≤ r s ≤ 20 . Finite-size errors are corrected using canonical-ensemble twist-averaged boundary conditions and extrapolation of the twist-averaged energy per particle calculated at three system sizes ( N = 113 , 259 , and 387 ) to the thermodynamic limit of infinite system size. The DMC energies in the thermodynamic limit are used to parametrize a local spin density approximation correlation function for inhomogeneous electron systems
Development of a new quantum trajectory molecular dynamics framework
An extension to the wave packet description of quantum plasmas is presented,
where the wave packet can be elongated in arbitrary directions. A generalised
Ewald summation is constructed for the wave packet models accounting for
long-range Coulomb interactions and fermionic effects are approximated by
purpose-built Pauli potentials, self-consistent with the wave packets used. We
demonstrate its numerical implementation with good parallel support and close
to linear scaling in particle number, used for comparisons with the more common
wave packet employing isotropic states. Ground state and thermal properties are
compared between the models with differences occurring primarily in the
electronic subsystem. Especially, the electrical conductivity of dense hydrogen
is investigated where a 15% increase in DC conductivity can be seen in our wave
packet model compared to other models.Comment: 20 pages, 6 figure
Investigating Mechanisms of State Localization in Highly-Ionized Dense Plasmas
We present the first experimental observation of K emission from
highly charged Mg ions at solid density, driven by intense x-rays from a free
electron laser. The presence of K emission indicates the atomic
shell is relocalized for high charge states, providing an upper constraint on
the depression of the ionization potential. We explore the process of state
relocalization in dense plasmas from first principles using finite-temperature
density functional theory alongside a wavefunction localization metric, and
find excellent agreement with experimental results.Comment: 22 pages, 13 figure
Investigating mechanisms of state localization in highly ionized dense plasmas
ProducciĂłn CientĂficaWe present experimental observations of Kβ emission from highly charged Mg ions at solid density, driven by intense x rays from a free electron laser. The presence of Kβ emission indicates the n=3 atomic shell is relocalized for high charge states, providing an upper constraint on the depression of the ionization potential. We explore the process of state relocalization in dense plasmas from first principles using finite-temperature density functional theory alongside a wave-function localization metric, and find excellent agreement with experimental results.This work has been supported by the Spanish Ministry of Science and Innovation under Research Grant No. PID2019-108764RB-I0
Electron population dynamics in resonant non-linear x-ray absorption in nickel at a free-electron laser
Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray–matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the L3-edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm2. We present a simple but predictive rate model that quantitatively describes spectral changes based on the evolution of electronic populations within the pulse duration. Despite its simplicity, the model reaches good agreement with experimental results over more than three orders of magnitude in fluence, while providing a straightforward understanding of the interplay of physical processes driving the non-linear changes. Our findings provide important insights for the design and evaluation of future high-fluence free-electron laser experiments and contribute to the understanding of non-linear electron dynamics in x-ray absorption processes in solids at the femtosecond timescale
Thromboembolic Disease in Patients With Cancer and COVID-19: Risk Factors, Prevention and Practical Thromboprophylaxis Recommendations–State-of-the-Art.
Cancer and COVID-19 are both well-established risk factors predisposing to thrombosis. Both disease entities are correlated with increased incidence of venous thrombotic events through multifaceted pathogenic mechanisms involving the interaction of cancer cells or SARS-CoV2 on the one hand and the coagulation system and endothelial cells on the other hand. Thromboprophylaxis is recommended for hospitalized patients with active cancer and high-risk outpatients with cancer receiving anticancer treatment. Universal thromboprophylaxis with a high prophylactic dose of low molecular weight heparins (LMWH) or therapeutic dose in select patients, is currentlyindicated for hospitalized patients with COVID-19. Also, prophylactic anticoagulation is recommended for outpatients with COVID-19 at high risk for thrombosis or disease worsening. However, whether there is an additive risk of thrombosis when a patient with cancer is infected with SARS-CoV2 remains unclear In the current review, we summarize and critically discuss the literature regarding the epidemiology of thrombotic events in patients with cancer and concomitant COVID-19, the thrombotic risk assessment, and the recommendations on thromboprophylaxis for this subgroup of patients. Current data do not support an additive thrombotic risk for patients with cancer and COVID-19. Of note, patients with cancer have less access to intensive care unit care, a setting associated with high thrombotic risk. Based on current evidence, patients with cancer and COVID-19 should be assessed with well-established risk assessment models for medically ill patients and receive thromboprophylaxis, preferentially with LMWH, according to existing recommendations. Prospective trials on well-characterized populations do not exist