Electron Density Response Research Articles

Multi‐Instrument and SAMI3‐TIDAS Data Assimilation Analysis of Three‐Dimensional Ionospheric Electron Density Variations During the April 2024 Total Solar Eclipse

AbstractThis paper conducts a multi‐instrument and data assimilation analysis of the three‐dimensional ionospheric electron density responses to the total solar eclipse on 08 April 2024. The altitude‐resolved electron density variations over the continental US and adjacent regions are analyzed using the Millstone Hill incoherent scatter radar data, ionosonde observations, Swarm in situ measurements, and a novel TEC‐based ionospheric data assimilation system (TIDAS) with SAMI3 model as the background. The principal findings are summarized as follows: (a) The ionospheric hmF2 exhibited a slight enhancement in the initial phase of the eclipse, followed by a distinct reduction of 20–30 km in the recovery phase of the eclipse. The hmF2 in the umbra region showed a post‐eclipse fluctuation, characterized by wavelike perturbations of 10–25 km in magnitude and a period of 30 min. (b) There was a substantial reduction in ionospheric electron density of 20%–50% during the eclipse, with the maximum depletion observed in the F‐region around 200–250 km. The ionospheric electron density variation exhibited a significant altitude‐dependent feature, wherein the response time gradually delayed with increasing altitude. (c) The bottomside ionospheric electron density displayed an immediate reduction after local eclipse began, reaching maximum depletion 5–10 min after the maximum obscuration. In contrast, the topside ionospheric electron density showed a significantly delayed response, with maximum depletion occurring 1–2.5 hr after the peak obscuration.

Ab initio density response and local field factor of warm dense hydrogen

We present quasi-exact ab initio path integral Monte Carlo (PIMC) results for the partial static density responses and local field factors of hydrogen in the warm dense matter regime, from solid density conditions to the strongly compressed case. The full dynamic treatment of electrons and protons on the same footing allows us to rigorously quantify both electronic and ionic exchange–correlation effects in the system, and to compare the results with those of earlier incomplete models such as the archetypal uniform electron gas or electrons in a fixed ion snapshot potential that do not take into account the interplay between the two constituents. The full electronic density response is highly sensitive to electronic localization around the ions, and our results constitute unambiguous predictions for upcoming X-ray Thomson scattering experiments with hydrogen jets and fusion plasmas. All PIMC results are made freely available and can be used directly for a gamut of applications, including inertial confinement fusion calculations and the modeling of dense astrophysical objects. Moreover, they constitute invaluable benchmark data for approximate but computationally less demanding approaches such as density functional theory or PIMC within the fixed-node approximation.

Ultrafast Laser-Induced Dynamics of Non-Equilibrium Electron Spill-Out in Nanoplasmonic Bilayers.

Contemporary quantum plasmonics capture subtle corrections to the properties of plasmonic nano-objects in equilibrium. Here, we demonstrate non-equilibrium spill-out redistribution of the electronic density at the ultrafast time scale. As revealed by time-resolved 2D spectroscopy of nanoplasmonic Fe/Au bilayers, an injection of the laser-excited non-thermal electrons induces transient electron spill-out thus changing the plasma frequency. The response of the local electronic density switches the electronic density behavior from spill-in to strong (an order of magnitude larger) spill-out at the femtosecond time scale. The superdiffusive transport of hot electrons and the lack of a direct laser heating indicate significantly non-thermal origin of the underlying physics. Our results demonstrate an ultrafast and non-thermal way to control surface plasmon dispersion through transient variations of the spatial electron distribution at the nanoscale. These findings expand quantum plasmonics into previously unexplored directions by introducing ultrashort time scales in the non-equilibrium electronic systems.

Refined interpretation of electron temperature response to neutral beam injection at DIII-D

Accurate particle and power deposition profiles of neutral beam injection (NBI) are essential to transport studies, and that information is usually acquired through Monte Carlo simulations with a given collisional model. The deposition process of the energetic beam particles leads to the informative electron temperature (Te) evolution trajectory, which can be captured by electron cyclotron emission (ECE) system due to its good spatial and temporal resolution. Previously, some work has been done to interpret the Te responses to the pulsed NBI as a linear heating source with Fourier-based techniques, although that approach fell short when the fast ion slowing-down time becomes significant (∼100 ms). It has been observed in DIII-D that the modulated NBI pulses (10–50 Hz) reduce local core Te values ∼0.1 keV through cold electron dilution in high-Te (>2 keV) plasmas alongside accumulative heating. Here, a novel approach to interpret the Te response to NBI was developed by linearizing and modeling the detailed Te evolution trajectory using coherently averaged ECE data based on the different time scales of the terms in the local power and particle balance equations. The technique does not require absolute calibrations of ECE and is independent of collisional models. The resulting beam deposition profiles show good consistency and reasonable agreement with Monte Carlo calculations based on the atomic data from the Atomic Data and Analysis Structure (ADAS). Local electron density response measured by Thomson scattering (TS) also suggests the same features when the beam pulse is large enough for that diagnostic to resolve. The remaining discrepancies are also discussed.

Response of the F2-peak electron density and height to plasma depletion bays in the equatorial nighttime ionosphere observed by FORMOSAT-7/COSMIC-2

FORMOSAT-7/COSMIC-2 (F7/C2) satellite cluster, launched in June 2019, performs radio occultation experiments observing the vertical electron density profiles in the low-latitude ionosphere. The F7/C2 F2-peak electron density (NmF2) and height (hmF2) are used to identify and examine the behavior of the plasma depletion bay (PDB) structures in the equatorial nighttime ionosphere. The NmF2 reveals three distinct PDBs within 60°W–15°E, 30−90°E, and 110−160°E during June solstice, while a single PDB appears within 150−60°W during December solstice. All the four PDBs’ features simultaneously appear during March and September equinoxes. Asymmetries in the hmF2 over the PDB regions suggests that the electron density increases (decreases) are related to the NmF2 ascending (descending) in the summer (winter) hemispheres. Agreements between F7/C2 observations and HWM93 results show that the asymmetry of vertical motions driven by the neutral wind is the main causal mechanism for the longitudinal variation of PDBs.

Electronic density response of warm dense hydrogen on the nanoscale.

The properties of hydrogen at warm dense matter (WDM) conditions are of high importance for the understanding of astrophysical objects and technological applications such as inertial confinement fusion. In this work, we present extensive ab initio path integral Monte Carlo results for the electronic properties in the Coulomb potential of a fixed ionic configuration. This gives us unique insights into the complex interplay between the electronic localization around the protons with their density response to an external harmonic perturbation. We find qualitative agreement between our simulation data and a heuristic model based on the assumption of a local uniform electron gas model, but important trends are not captured by this simplification. In addition to being interesting in their own right, we are convinced that our results will be of high value for future projects, such as the rigorous benchmarking of approximate theories for the simulation of WDM, most notably density functional theory.

3-D Ionospheric Electron Density Variations during the 2017 Great American Solar Eclipse: A Revisit

This paper studies the three-dimensional (3-D) ionospheric electron density variation over the continental US and adjacent regions during the August 2017 Great American Solar Eclipse event, using Millstone Hill incoherent scatter radar observations, ionosonde data, the Swarm satellite measurements, and a new TEC-based ionospheric data assimilation system (TIDAS). The TIDAS data assimilation system can reconstruct a 3-D electron density distribution over continental US and adjacent regions, with a spatial–temporal resolution of 1∘× 1∘ in latitude and longitude, 20 km in altitude, and 5 min in universal time. The combination of multi-instrumental observations and the high-resolution TIDAS data assimilation products can well represent the dynamic 3-D ionospheric electron density response to the solar eclipse, providing important altitude information and fine-scale details. Results show that the eclipse-induced ionospheric electron density depletion can exceed 50% around the F2-layer peak height between 200 and 300 km. The recovery of electron density following the maximum depletion exhibits an altitude-dependent feature, with lower altitudes exhibiting a faster recovery than the F2 peak region and above. The recovery feature was also characterized by a post-eclipse electron density enhancement of 15–30%, which is particularly prominent in the topside ionosphere at altitudes above 300 km.

A novel diagnostic for dust particle size in a low-pressure nanodusty plasma based on the decay of the electron density released by laser-induced photodetachment

One of the key parameters in low-pressure nanodusty plasmas is the dust particle size. In this work, we introduce a new method for the determination of the dust particle size in a nanodusty plasma, created in a mixture of argon and hexamethyldisiloxane. To this end, an ultraviolet (λ=266 nm) pulsed laser was used to release plasma-collected electrons from the nanoparticles. Subsequently, the response of the free electron density of the plasma was measured using microwave cavity resonance spectroscopy. Using a stochastic model for particle charging using orbital-motion limited (OML) theory, the predicted charging timescale can be directly compared to the experimentally measured decay timescale of the photo-released electron density. Good agreement was found between the experimentally predicted dust particle size and ex situ scanning electron microscopy (SEM) measurements. Furthermore, the sensitivity of the OML model to its input parameters was assessed. Finally, reversing the method can yield an estimate for the positive ion density based on the dust particle size from SEM.

Homogeneous electron liquid in arbitrary dimensions beyond the random phase approximation

Abstract The homogeneous electron liquid is a cornerstone in quantum physics and chemistry. It is an archetypal system in the regime of slowly varying densities in which the exchange-correlation energy can be estimated with many methods. For high densities, the behavior of the ground-state energy is well-known for 1, 2, and 3 dimensions. Here, we extend this model to arbitrary integer dimensions and compute its correlation energy beyond the random phase approximation (RPA). We employ the approach developed by Singwi, Tosi, Land, and Sjölander (STLS), whose description of the electronic density response for 2D and 3D for metallic densities is known to be comparable to Quantum Monte-Carlo. For higher dimensions, we compare the results obtained for the correlation energy with the values previously obtained using RPA. We find that in agreement with what is known for 2 and 3 dimensions, the RPA tends to over-correlate the liquid also at higher dimensions. We furthermore provide new analytical formulae for the unconventional-dimensional case both for the real and imaginary parts of the Lindhard polarizability and for the local field correction of the STLS theory, and illustrate the importance of the plasmon contribution at those high dimensions.

Predicting the electronic density response of condensed-phase systems to electric field perturbations.

We present a local and transferable machine-learning approach capable of predicting the real-space density response of both molecules and periodic systems to homogeneous electric fields. The new method, Symmetry-Adapted Learning of Three-dimensional Electron Responses (SALTER), builds on the symmetry-adapted Gaussian process regression symmetry-adapted learning of three-dimensional electron densities framework. SALTER requires only a small, but necessary, modification to the descriptors used to represent the atomic environments. We present the performance of the method on isolated water molecules, bulk water, and a naphthalene crystal. Root mean square errors of the predicted density response lie at or below 10% with barely more than 100 training structures. Derived polarizability tensors and even Raman spectra further derived from these tensors show good agreement with those calculated directly from quantum mechanical methods. Therefore, SALTER shows excellent performance when predicting derived quantities, while retaining all of the information contained in the full electronic response. Thus, this method is capable of predicting vector fields in a chemical context and serves as a landmark for further developments.

Averaging over atom snapshots in linear-response TDDFT of disordered systems: A case study of warm dense hydrogen.

Linear-response time-dependent density functional theory (LR-TDDFT) simulations of disordered extended systems require averaging over different snapshots of ion configurations to minimize finite size effects due to the snapshot-dependence of the electronic density response function and related properties. We present a consistent scheme for the computation of the macroscopic Kohn-Sham (KS) density response function connecting an average over snapshot values of charge density perturbations to the averaged values of KS potential variations. This allows us to formulate the LR-TDDFT within the adiabatic (static) approximation for the exchange-correlation (XC) kernel for disordered systems, where the static XC kernel is computed using the direct perturbation method [Moldabekov et al., J. Chem. Theory Comput. 19, 1286 (2023)]. The presented approach allows one to compute the macroscopic dynamic density response function as well as the dielectric function with a static XC kernel generated for any available XC functional. The application of the developed workflow is demonstrated for the example of warm dense hydrogen. The presented approach is applicable for various types of extended disordered systems, such as warm dense matter, liquid metals, and dense plasmas.

Molecular properties and In silico bioactivity evaluation of (4-fluorophenyl)[5)-3-phen-(4-nitrophenyl yl-4,5-dihydro-1H-pyrazol-1-yl]methanone derivatives: DFT and molecular docking approaches

ObjectivesMolecular structures, spectroscopic properties, charge distributions, frontier orbital energies, nonlinear optical (NLO) properties and molecular docking simulations were analyzed to examine the bio-usefulness of a series of (4-fluorophenyl)[5-(4-nitrophenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl]methanone derivatives. MethodsThe compounds were studied through computational methods. Equilibrium optimization of the compounds was performed at the B3LYP/6-31G(d,p) level of theory, and geometric parameters, frequency vibration, UV–vis spectroscopy and reactivity properties were predicted on the basis of density functional theory (DFT) calculations. ResultsThe energy gap (ΔEg), electron donating/accepting power (ω−/ω+) and electron density response toward electrophiles/nucleophiles calculated for M1 and M2 revealed the importance of substituent positioning on compound chemical behavior. In addition, ω−/ω+ and ΔEn/ΔEe indicated that M6 is more electrophilic because of the presence of two NO2 groups, which enhanced its NLO properties. The hyperpolarizability (β0) of the compounds ranged from 5.21 × 10−30 to 7.26 × 10−30 esu and was greater than that of urea; thus, M1–M6 were considered possible candidates for NLO applications. Docking simulation was also performed on the studied compounds and targets (PDB ID: 5ADH and 1RO6), and the calculated binding affinity and non-bonding interactions are reported. ConclusionThe calculated ω− and ω+ indicated the electrophilic nature of the compounds; M6, a compound with two NO2 groups, showed enhanced effects. Molecular electrostatic potential (MEP) analysis indicated that amide and nitro groups on the compounds were centers of electrophilic attacks. The magnitude of the molecular hyperpolarizability suggested that the entire compound had good NLO properties and therefore could be explored as a candidate NLO material. The docking results indicated that these compounds have excellent antioxidant and anti-inflammatory properties.

Electron density pedestal behaviour in strike-point sweeping experiment on JET

Strike-point sweeping, a technique often used to spread heat loads on divertor targets, was employed in JET experiments for the first time to generate an edge-localized modulated particle source for investigating plasma fuelling and particle transport in the edge region. This approach was motivated by the possibility of achieving higher modulation frequencies than those available from traditional gas puff modulation at JET. Higher frequencies would enable the collection of more edge-localized information from the electron density response to the modulated particle source. Various sweeping frequencies, up to 18.5 Hz, were commissioned and utilized in the experiments. Both strong and weak electron density responses were observed in H-mode plasmas, depending on the strike-point configuration and the distance the strike-points moved during the sweep cycle. The electron density response exhibited complex and unconventional behaviour (compared to gas puff modulation), which presented challenges for interpretation. In this study, we analyse one experiment in detail using an optimization framework in which transport and particle source parameters are determined by fitting our forward model parameters to the experimental electron density measurements. We demonstrate that a consistent picture emerges and that our approach can provide new insights into these complex data. However, we note that while strike-point sweeping generates the desired modulated edge-localized particle source, it also modifies the properties of the edge transport barrier. Therefore, the strike-point sweeping methodology is a promising but challenging way to study edge particle transport and edge fuelling properties, requiring very precise measurements.

Assessing the accuracy of hybrid exchange-correlation functionals for the density response of warm dense electrons.

We assess the accuracy of common hybrid exchange-correlation (XC) functionals (PBE0, PBE0-1/3, HSE06, HSE03, and B3LYP) within the Kohn-Sham density functional theory for the harmonically perturbed electron gas at parameters relevant for the challenging conditions of the warm dense matter. Generated by laser-induced compression and heating in the laboratory, the warm dense matter is a state of matter that also occurs in white dwarfs and planetary interiors. We consider both weak and strong degrees of density inhomogeneity induced by the external field at various wavenumbers. We perform an error analysis by comparing with the exact quantum Monte Carlo results. In the case of a weak perturbation, we report the static linear density response function and the static XC kernel at a metallic density for both the degenerate ground-state limit and for partial degeneracy at the electronic Fermi temperature. Overall, we observe an improvement in the density response when the PBE0, PBE0-1/3, HSE06, and HSE03 functionals are used, compared with the previously reported results for the PBE, PBEsol, local-density approximation, and AM05 functionals; B3LYP, on the other hand, does not perform well for the considered system. Additionally, the PBE0, PBE0-1/3, HSE06, and HSE03 functionals are more accurate for the density response properties than SCAN in the regime of partial degeneracy.

Electronic density response of warm dense matter

Matter at extreme temperatures and pressures—commonly known as warm dense matter (WDM)—is ubiquitous throughout our Universe and occurs in astrophysical objects such as giant planet interiors and brown dwarfs. Moreover, WDM is very important for technological applications such as inertial confinement fusion and is realized in the laboratory using different techniques. A particularly important property for the understanding of WDM is given by its electronic density response to an external perturbation. Such response properties are probed in x-ray Thomson scattering (XRTS) experiments and are central for the theoretical description of WDM. In this work, we give an overview of a number of recent developments in this field. To this end, we summarize the relevant theoretical background, covering the regime of linear response theory and nonlinear effects, the fully dynamic response and its static, time-independent limit, and the connection between density response properties and imaginary-time correlation functions (ITCF). In addition, we introduce the most important numerical simulation techniques, including path-integral Monte Carlo simulations and different thermal density functional theory (DFT) approaches. From a practical perspective, we present a variety of simulation results for different density response properties, covering the archetypal model of the uniform electron gas and realistic WDM systems such as hydrogen. Moreover, we show how the concept of ITCFs can be used to infer the temperature from XRTS measurements of arbitrary complex systems without the need for any models or approximations. Finally, we outline a strategy for future developments based on the close interplay between simulations and experiments.

Ab initio path integral Monte Carlo simulations of hydrogen snapshots at warm dense matter conditions.

We combine ab initio path integral Monte Carlo (PIMC) simulations with fixed ion configurations from density functional theory molecular dynamics (DFT-MD) simulations to solve the electronic problem for hydrogen under warm dense matter conditions [Böhme et al., Phys. Rev. Lett. 129, 066402 (2022)0031-900710.1103/PhysRevLett.129.066402]. The problem of path collapse due to the Coulomb attraction is avoided by utilizing the pair approximation, which is compared against the simpler Kelbg pair potential. We find very favorable convergence behavior towards the former. Since we do not impose any nodal restrictions, our PIMC simulations are afflicted with the notorious fermion sign problem, which we analyze in detail. While computationally demanding, our results constitute an exact benchmark for other methods and approximations within DFT. Our setup gives us the unique capability to study important properties of warm dense hydrogen such as the electronic static density response and exchange-correlation kernel without any model assumptions, which will be very valuable for a variety of applications such as the interpretation of experiments and the development of new XC functionals.

Comment on “The effects of radio-frequency bias on electron density in an inductively coupled plasma reactor” [J. Appl. hys. 102, 113302 (2007)

Sobolewski et al. [J. Appl. Phys. 102, 113302 (2007)] obtained the complex responses of electron density to the long-pulsed RF bias and proposed the gas composition effect as a key underlying factor. In this Comment, the consistent explanations on the complex responses indicate that the ignored slow wall heating should be taken into account.

Diffusive density response of electrons in anisotropic multiband systems

We explicitly calculate the density-density response function with conserving vertex corrections for anisotropic multiband systems in the presence of impurities including long-range disorder. The direction dependence of the vertex corrections is correctly considered to obtain the diffusion constant which is given by a combination of componentwise transport relaxation times and velocities on the Fermi surface. We also investigate the diffusive density response of various anisotropic systems, propose some empirical rules for the corresponding diffusion constant, and demonstrate that it is crucial to consider the component dependence of the transport relaxation times to correctly interpret the transport properties of anisotropic systems, especially various topological materials with a different power-law dispersion in each direction.

Static Electronic Density Response of Warm Dense Hydrogen: AbInitio Path Integral MonteCarlo Simulations.

The properties of hydrogen under extreme conditions are important for many applications, including inertial confinement fusion and astrophysical models. A key quantity is given by the electronic density response to an external perturbation, which is probed in x-ray Thomson scattering experiments-the state of the art diagnostics from which system parameters like the free electron density n_{e}, the electronic temperature T_{e}, and the charge state Z can be inferred. In this work, we present highly accurate path integral MonteCarlo results for the static electronic density response of hydrogen. We obtain the static exchange-correlation (XC) kernel K_{XC}, which is of central relevance for many applications, such as time-dependent density functional theory. This gives us a first unbiased look into the electronic density response of hydrogen in the warm-dense matter regime, thereby opening up a gamut of avenues for future research.

Interhemispheric Asymmetries in Ionospheric Electron Density Responses During Geomagnetic Storms: A Study Using Space‐Based and Ground‐Based GNSS and AMPERE Observations

AbstractWe utilize Total Electron Content (TEC) measurements and electron density (Ne) retrieval profiles from Global Navigation Satellite System (GNSS) receivers onboard multiple Low Earth Orbit (LEO) satellites to characterize large‐scale ionosphere‐thermosphere system responses during geomagnetic storms. We also analyze TEC measurements from GNSS receivers in a worldwide ground‐based network. Measurements from four storms during June and July 2012 (boreal summer months), December 2015 (austral summer month), and March 2015 (equinoctial month) are analyzed to study global ionospheric responses and the interhemispheric asymmetry of these responses. We find that the space‐based and ground‐based TECs and their responses are consistent in all four geomagnetic storms. The global 3D view from GNSS‐Radio Occultation (RO) Ne observations captures enhancements and the uplifting of Ne structures at high latitudes during the initial and main phases. Subsequently, Ne depletion occurs at high latitudes and starts progressing into midlatitude and low latitude as the storm reaches its recovery phase. A clear time lag is evident in the storm‐induced Ne perturbations at high latitudes between the summer and winter hemispheres. The interhemispheric asymmetry in TEC and Ne appears to be consistent with the magnitudes of the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) high latitude integrated field‐aligned currents (FACs), which are 3–4 MA higher in the summer hemisphere than in the winter hemisphere during these storms. The ionospheric TEC and Ne responses combined with the AMPERE‐observed FACs indicate that summer preconditioning in the ionosphere‐thermosphere system plays a key role in the interhemispheric asymmetric storm responses.