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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Coupling First Principles Calculations of Electron-Electron and Electron-Phonon Scattering, and Applications to Carbon-based Nanostructures

Here, we report first-principles calculations of electronic gaps, lifetimes, and photoelectron spectra of a series of molecules, performed by efficiently combining the computation of electron-electron and electron-phonon self-energies. The dielectric matrix is represented in terms of dielectric eigenpotentials, utilized for both the calculation of G 0 W 0 quasi-particle energies and the diagonalization of the dynamical matrix; virtual electronic states are never explicitly computed and all self-energies are evaluated over the full frequency spectrum. Our formulation enables electronic structure calculations at the many-body perturbation theory level, inclusive of electron-phonon coupling, for systems with hundreds of electrons.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effect of electron–electron interactions on the emission characteristics of ultracold, nanoscale photoemission-based electron sources

For nearly 60 years, cold field emitters have been the source of choice for electron microscopy due to their high brightness and relatively low energy spread. In this paper, we have examined an alternative: nanoscale electron sources based on near-threshold photoemission. While these sources have not yet been realized, they hold the potential to produce significantly brighter beams than cold field emitters. We model electron–electron Coulomb interactions in beams emitted from such sources to calculate the impact of these interactions on the brightness and the energy spread. Our results show that these sources can theoretically deliver more than an order of magnitude brighter electron beams compared to cold field emitters along with more than an order of magnitude smaller energy spread, before being limited by the Coulomb interactions. Electron sources with such high brightness and low energy spread would be transformational for electron microscopy, enabling electron energy loss-based vibrational spectroscopy at the sub-nanometer scale.

Gevorkyan, G S↗
DOE OSTI2025

Extended Gutzwiller Approximation for Nonlocal Electron-Electron and Electron-Boson Correlations (I): The Theory

Understanding electron-electron and electron-photon correlations is central to uncovering the fundamental mechanisms governing material properties, particularly in systems where strong interactions give rise to emergent phenomena such as superconductivity, magnetism, and polaritonic effects. These correlations play a pivotal role in cavity quantum materials, where hybridized light-matter states enable quantum control over electronic properties. However, capturing both local and nonlocal correlations in these systems presents a significant theoretical challenge. In this work, we extend the Gutzwiller wavefunction method to include nonlocal electron-photon and electron-electron interactions, providing a unified framework to study the intricate interplay between these effects. Our approach accurately captures the long-range correlations induced by photon exchange, enabling the exploration of exotic quantum phases and the effects of cavity coupling on electronic structure. By benchmarking the method across coupling regimes, we reveal the critical role of nonlocal correlations in stabilizing phases, such as superconducting and insulating states, that are inaccessible through local interactions alone. This generalized Gutzwiller framework offers a versatile tool for understanding and designing materials that harness the transformative potential of strong light-matter coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Electron-beam energy reconstruction for neutrino oscillation measurements

Neutrinos exist in one of three types or ‘flavours’—electron, muon and tau neutrinos—and oscillate from one flavour to another when propagating through space. This phenomena is one of the few that cannot be described using the standard model of particle physics (reviewed in ref. 1), and so its experimental study can provide new insight into the nature of our Universe (reviewed in ref. 2). Neutrinos oscillate as a function of their propagation distance (L) divided by their energy (E). Therefore, experiments extract oscillation parameters by measuring their energy distribution at different locations. As accelerator-based oscillation experiments cannot directly measure E, the interpretation of these experiments relies heavily on phenomenological models of neutrino–nucleus interactions to infer E. Here we exploit the similarity of electron–nucleus and neutrino–nucleus interactions, and use electron scattering data with known beam energies to test energy reconstruction methods and interaction models. We find that even in simple interactions where no pions are detected, only a small fraction of events reconstruct to the correct incident energy. More importantly, widely used interaction models reproduce the reconstructed energy distribution only qualitatively and the quality of the reproduction varies strongly with beam energy. This shows both the need and the pathway to improve current models to meet the requirements of next-generation, high-precision experiments such as Hyper-Kamiokande (Japan) and DUNE (USA).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Nematic antiferromagnetism and deconfined criticality from the interplay between electron-phonon and electron-electron interactions

Systems with strong electron-phonon couplings typically exhibit various forms of charge order, while strong electron-electron interactions lead to magnetism. In this work, we use determinant quantum Monte Carlo calculations to solve a model on a square lattice with a caricature of these interactions. In the limit where electron-electron interactions dominate it has antiferromagnetic order, while where electron-phonon coupling dominates there is columnar valence-bond-solid (VBS) order. We find an intervening phase that hosts coexisting nematic and antiferromagnetic orders. We have also found evidence of a Landau-forbidden continuous quantum phase transition with an emergent O(4) symmetry between the VBS and the nematic antiferromagnetic phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Incorporating Electronic Information into Machine Learning Potential Energy Surfaces via Approaching the Ground-State Electronic Energy as a Function of Atom-Based Electronic Populations

Machine learning (ML) approximations to density functional theory (DFT) potential energy surfaces (PESs) are showing great promise for reducing the computational cost of accurate molecular simulations, but at present, they are not applicable to varying electronic states, and in particular, they are not well suited for molecular systems in which the local electronic structure is sensitive to the medium to long-range electronic environment. With this issue as the focal point, we present a new machine learning approach called "BpopNN" for obtaining efficient approximations to DFT PESs. Conceptually, the methodology is based on approaching the true DFT energy as a function of electron populations on atoms; in practice, this is realized with available density functionals and constrained DFT (CDFT). Additionally, the new approach creates approximations to this function with neural networks. These approximations thereby incorporate electronic information naturally into a ML approach, and optimizing the model energy with respect to populations allows the electronic terms to self-consistently adapt to the environment, as in DFT. We confirm the effectiveness of this approach with a variety of calculations on LinHn clusters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1975

Laboratory observations of RF emission at plasma electron frequency and n + 1/2 times the electron cyclotron frequency in electron beam-plasma and beam-beam interactions

Electric field emissions at frequencies of (n + 1/2) times the electron cyclotron frequency have been generated in a large-scale electron beam experiment in a vacuum facility. These emissions arise when a contrastreaming beam configuration exists, the primary beam consisting of monoenergetic electrons (50 eV to 5 keV) and the other beam of lower-energy backscattered secondary electrons. It is suggested that the same mechanism could also be the source of the observed 3/2 times the electron cyclotron frequency emissions at auroral latitudes. In the absence of the beam-beam instability, weak oscillations were observed at the plasma frequency. In the latter case no significant modifications of the primary beam velocity distribution occurred, and the beam configuration is adequately described by single-particle motion in the ambient magnetic field.

Bernstein, W.↗
DOE OSTI2021

Combined First-Principles Calculations of Electron–Electron and Electron–Phonon Self-Energies in Condensed Systems

In this work, we present a method to efficiently combine the computation of electron–electron and electron–phonon self-energies, which enables the evaluation of electron–phonon coupling at the G 0 W 0 level of theory for systems with hundreds of atoms. In addition, our approach, which is a generalization of a method recently proposed for molecules [J. Chem. Theory Comput.2018, 14, 6269–6275], enables the inclusion of nonadiabatic and temperature effects at no additional computational cost. We present results for diamond and defects in diamond and discuss the importance of numerically accurate G 0 W 0 band structures to obtain robust predictions of zero point renormalization (ZPR) of band gaps, and of the inclusion of nonadiabatic effects to accurately compute the ZPR of defect states in the band gap.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1987

Electron-helium and electron-neon scattering cross sections at low electron energies using a photoelectron source

Absolute electron-helium and electron-neon scattering cross sections have been measured at low electron energies using the powerful technique of photoelectron spectroscopy. The measurements have been carried out at 17 electron energies varying from 0.7 to 10 eV with an accuracy of + or - 2.7 percent. The results obtained in the present work have been compared with other recent measurement and calculations.

Kumar, Vijay↗
DOE OSTI2024

Use of Grid-Forming Medium-Voltage Power Electronics Hub in a Microgrid Setting

This paper presents the application of a new design of a multiport, modular, medium-voltage power electronics hub (M3PE-HUB) in a microgrid setting. The M3PE-HUB system was modeled in a digital real-time simulator (DRTS) and integrated into the Banshee microgrid test system. This paper presents the preliminary DRTS simulation-based results of the M3PE-HUB system connected in a test microgrid system. Verification and validation of the M3PE-HUB architecture and controls in the test microgrid setting are the primary contributions of this work. The results of the operation during the islanding and resynchronization process indicate the feasibility of the proposed architecture in a microgrid setting. This paper also presents results for a system reconfiguration use case where the M3PE-HUB was used to reconfigure the system under a fault condition.

grid forming↗
NASA NTRS1986

The beta-SiC(100) surface studied by low energy electron diffraction, Auger electron spectroscopy, and electron energy loss spectra

The beta-SiC(100) surface has been studied by low energy electron diffraction, Auger electron spectroscopy, high resolution electron energy loss spectra (HREELS), and core level excitation EELS. Two new Si-terminated phases have been discovered, one with (3 x 2) symmetry, and the other with (2 x 1) symmetry. Models are presented to describe these phases. New results, for the C-rich surface, are presented and discussed. In addition, core level excitation EELS results are given and compared with theory.

Dayan, M.↗
DOE OSTI2019

Electron-Beam Shaping in the Transmission Electron Microscope: Control of Electron-Beam Propagation Along Atomic Columns

We present a detailed analysis of the propagation of high-energy electron beams that have different shapes in a crystal of [100]-oriented zincblende GaN. Our study primarily focuses on Bessel beams and makes use of reformulated Bloch wave and multislice simulations. As a result of the simplicity of the momentum spectrum of a Bessel beam and the symmetry of the crystal, its propagation in the material can be described in a free-space representation, providing a deeper understanding of channeling phenomena and of probe intensity oscillation in the propagation direction. We also consider aperture-limited and Gaussian beams. As a result, the latter probes are shown to be optimal for coupling to 1s Bloch states and achieving minimal spreading along atomic columns.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Nuclear-Electronic Orbital Ehrenfest Dynamics

The recently developed real-time nuclear-electronic orbital (RT-NEO) approach provides an elegant framework for treating electrons and selected nuclei, typically pro- tons, quantum mechanically in nonequilibrium dynamical processes. However, the RT-NEO approach neglects the motion of the other nuclei, preventing a complete de- scription of the coupled nuclear-electronic dynamics and spectroscopy. In this work, we describe the dynamical interaction between the other nuclei and the electron-proton subsystem with the mixed quantum-classical Ehrenfest dynamics method. The NEO- Ehrenfest approach propagates the electrons and quantum protons in a time-dependent variational framework, while the remaining nuclei move classically on the correspond- ing average electron-proton vibronic surface. This approach includes the non-Born- Oppenheimer eects between the electrons and quantum protons with RT-NEO and between the classical nuclei and the electron-proton subsystem with Ehrenfest dynam- ics. Spectral features for vibrational modes involving both quantum and classical nuclei are resolved from the time-dependent dipole moments. Moreover, nuclear quantum ef- fects are included directly in nonadiabatic dynamics simulations. The excited state intramolecular proton transfer in the o-hydroxybenzaldehyde molecule is shown to be faster and to exhibit a larger kinetic isotope eect with NEO-Ehrenfest compared to classical Ehrenfest dynamics. This work shows that the NEO-Ehrenfest method is a powerful tool to study dynamical processes with coupled electronic and nuclear degrees of freedom.

Zhao, Luning↗