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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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

A cheaper, faster, better way to detect water of hydration on Solar System bodies

The 3.0-micrometers water of hydration absorption feature observed in the IR photometry of many low-albedo and some medium-albedo asteroids strongly correlates with the 0.7-micrometers Fe(+2) to Fe(+3) oxidized iron absorption feature observed in narrowband spectrophotometry of these asteroids. Using this relationship, an empirical algorithm for predicting the presence of water of hydration in the surface material of a Solar System body using photometry obtained through the Eight-Color Asteroid Survey nu (0.550 micrometers), w (0.701 micrometers), and x (0.853 micrometers) filters was developed and applied to the ECAS photometry of asteroids and outer planet satellites. The percentage of objects in low-albedo, outer main-belt asteroid classes that test positively for water of hydration increases from P to B to C to G class and correlates linearly with the increasing mean albedos of those objects testing positively. The medium-albedo M-class asteroids do not test positively in large number using this algorithm. Aqueously altered asteroids dominate the Solar System population between heliocentric distances of 2.6 to 3.5 AU, bracketing the Solar System region where the aqueous alteration mechanism operated most strongly. One jovian satellite, J VI Himalia, and one saturnian satellite. Phoebe, tested positively for water of hydration, supporting the hypothesis that these may be captured C-class asteroids from a postaccretional dispersion. The proposed testing technique could be applied to an Earth-based survey of asteroids or a space-probe study of an asteroid's surface characteristic in order to identify a potential water source.

Vilas, Faith↗
DOE OSTI2021

Fully variational incremental CASSCF

We report the complete-active-space self-consistent field (CASSCF) method is a canonical electronic structure theory that holds a central place in conceptualizing and practicing first principles simulations. For application to realistic molecules, however, the CASSCF must be approximated to circumvent its exponentially scaling computational costs. Applying the many-body expansion - also known as the method of increments - to CASSCF (iCASSCF) has been shown to produce a polynomially scaling method that retains much of the accuracy of the parent theory and is capable of treating full valence active spaces. Due to an approximation made in the orbital gradient, the orbital parameters of the original iCASSCF formulation could not be variationally optimized, which limited the accuracy of its nuclear gradient. Herein, a variational iCASSCF is introduced and implemented, where all parameters are fully optimized during energy minimization. This method is able to recover electronic correlations from the full valence space in large systems, produce accurate gradients, and optimize stable geometries as well as transition states. Demonstrations on challenging test cases, such as the oxoMn(salen)Cl complex with 84 electrons in 84 orbitals and the automerization of cyclobutadiene, show that the fully variational iCASSCF is a powerful tool for describing challenging molecular chemistries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Many-Body Dynamical Localization in a Kicked Lieb-Liniger Gas

The kicked rotor system is a textbook example of how classical and quantum dynamics can drastically differ. The energy of a classical particle confined to a ring and kicked periodically will increase linearly in time whereas in the quantum version the energy saturates after a finite number of kicks. The quantum system undergoes Anderson localization in angular-momentum space. Conventional wisdom says that in a many-particle system with short-range interactions the localization will be destroyed due to the coupling of widely separated momentum states. Here we provide evidence that for an interacting one-dimensional Bose gas, the Lieb-Liniger model, the dynamical localization can persist at least for an unexpectedly long time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Magic-angle semimetals

Abstract Breakthroughs in two-dimensional van der Waals heterostructures have revealed that twisting creates a moiré pattern that quenches the kinetic energy of electrons, allowing for exotic many-body states. We show that cold atomic, trapped ion, and metamaterial systems can emulate the effects of a twist in many models from one to three dimensions. Further, we demonstrate at larger angles (and argue at smaller angles) that by considering incommensurate effects, the magic-angle effect becomes a single-particle quantum phase transition (including in a model for twisted bilayer graphene in the chiral limit). We call these models “magic-angle semimetals”. Each contains nodes in the band structure and an incommensurate modulation. At magic-angle criticality, we report a nonanalytic density of states, flat bands, multifractal wave functions that Anderson delocalize in momentum space, and an essentially divergent effective interaction scale. As a particular example, we discuss how to observe this effect in an ultracold Fermi gas.

Materials Science↗
DOE OSTI2025

Advances in Quantum Defect Embedding Theory

Quantum defect embedding theory (QDET) is a many-body embedding method designed to describe condensed systems with strongly correlated electrons localized within a given region of space, for example spin defects in semiconductors and insulators. Although the QDET approach has been successful in predicting the electronic properties of several point defects, several limitations of the method remain. Here, in this work, we propose multiple advances to the QDET formalism. We derive a doublecounting correction that consistently treats the frequency dependence of the screened Coulomb interaction, and we illustrate the effect of including unoccupied orbitals in the active space. In addition, we propose a method to describe hybridization effects between the active space and the environment, and we compare the results of several impurity solvers, providing further insights into improving the reliability and applicability of the method. We present results for defects in diamond and for molecular qubits, including a detailed comparison with experiments.

Chen, Siyuan [University of Chicago, IL (United St↗
DOE OSTI2022

Electron scattering on A = 3 nuclei from quantum Monte Carlo based approaches

We perform first-principle calculations of electron-nucleus scattering on 3 He and 3 H using the Green's function Monte Carlo method and two approaches based on the factorization of the final hadronic state: the spectral-function formalism and the short-time approximation. These three methods are benchmarked among each other and compared to the experimental data for the longitudinal and transverse electromagnetic response functions of 3 He, and the inclusive cross sections of both 3 He and 3 H. Since these three approaches are based on the same description of nuclear dynamics of the initial target state, comparing their results enables a precise quantification of the uncertainties inherent to factorization schemes. At sufficiently large values of the momentum transfer, we find an excellent agreement of the Green's function Monte Carlo calculation with experimental data and with both the spectral-function formalism and the short-time approximation. Here, we also analyze the relevance of relativistic effects, whose inclusion becomes crucial to explain data at high momentum and energy transfer.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Emergent Z 2 Gauge Theories and Topological Excitations in Rydberg Atom Arrays

Strongly interacting arrays of Rydberg atoms provide versatile platforms for exploring exotic many-body phases and dynamics of correlated quantum systems. Motivated by recent experimental advances, we show that the combination of Rydberg interactions and appropriate lattice geometries naturally leads to emergent Z 2 gauge theories endowed with matter fields. Based on this mapping, we describe how Rydberg platforms could realize two distinct classes of topological Z 2 quantum spin liquids, which differ in their patterns of translational symmetry fractionalization. Additionally, we also discuss the natures of the fractionalized excitations of these Z 2 spin liquid states using both fermionic and bosonic parton theories and illustrate their rich interplay with proximate solid phases.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2022

Evidence for a Significant Kuiper Belt Dust Contribution to the Zodiacal Cloud

Interplanetary dust particles (IDPs) are important samples of dust-producing objects in the solar system including many primitive and organic-rich bodies that are not sampled by known meteorites. IDPs spiral in towards the Sun under the influence of Poynting-Robertson (P-R) drag forces and are exposed to solar energetic particles (SEPs) that leave tracks of ionization damage in anhydrous silicate grains. We determined the exposure ages of track-rich IDPs using a new calibration of the SEP track production rate and show that track-rich IDPs have long exposure ages (>1 My) that preclude an origin from main-belt asteroids (MBAs) and Jupiter-family comets (JFCs). We propose that track-rich IDPs represent samples of dust produced by collisions among Edgeworth-Kuiper Belt objects (EKBOs) and that appreciable amounts of EKBO dust are contributing to the Zodiacal cloud. Many track-rich IDPs also contain abundant secondary minerals that provide direct evidence for past aqueous activity on some EKBOs.

Lindsay P. Keller↗
NASA NTRSDate not supplied

Hydrated Interplanetary Dust Particles: Implications for Oxygen Reservoirs in the Outer Solar System

A re-evaluation of solar energetic particle (SEP) track densities in interplanetary dust particles (IDPs) show that many are derived from outer solar system parent bodies such as Kuiper belt objects (KBOs) or beyond. Kuiper belt objects are widely believed to represent the frozen remnants from the birth of the solar system. The population of track-rich IDPs include members from both the anhydrous chondritic-porous and hydrated chondritic-smooth classes and earlier work suggested that the hydrated IDPs may represent anhydrous IDP material that was aqueously altered. We are performing systematic studies of the mineralogy, chemistry and isotopic compositions of track-rich IDPs to gain a fuller understanding of the origin and evolution of KBOs. Here, we focus on the identification of hydrated Kuiper belt dust particles that allows for the direct evaluation of their O isotopic compositions and the implications for the oxygen isotopic composition of outer solar system ices.

L. P. Keller↗
DOE OSTI2023

Active Colloids as Models, Materials, and Machines

Active colloids use energy input at the particle level to propel persistent motion and direct dynamic assemblies. We consider three types of colloids animated by chemical reactions, time-varying magnetic fields, and electric currents. For each type, we review the basic propulsion mechanisms at the particle level and discuss their consequences for collective behaviors in particle ensembles. These microscopic systems provide useful experimental models of nonequilibrium many-body physics in which dissipative currents break time-reversal symmetry. Freed from the constraints of thermodynamic equilibrium, active colloids assemble to form materials that move, reconfigure, heal, and adapt. Colloidal machines based on engineered particles and their assemblies provide a basis for mobile robots with increasing levels of autonomy. This review provides a conceptual framework for understanding and applying active colloids to create material systems that mimic the functions of living matter. We highlight opportunities for chemical engineers to contribute to this growing field.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Record-quality GaAs two-dimensional hole systems

The complex band structure, large spin-orbit induced band splitting, and heavy effective mass of two-dimensional (2D) hole systems hosted in GaAs quantum wells render them rich platforms to study many-body physics and ballistic transport phenomena. Here we report ultra-high-quality (001) GaAs 2D hole systems, fabricated using molecular beam epitaxy and modulation doping, with mobility values as high as 5.8 × 10 6 cm 2 /(V s) at a hole density of p = 1.3 × 10 11 /cm 2 , implying a mean free path of ≃ 27 μm. In the low-temperature magnetoresistance trace of this sample, we observe high-order fractional quantum Hall states up to the Landau level filling ν = 12/25 near ν = 1/2. Furthermore, we see a deep minimum develop at ν = 1/5 in the magnetoresistance of a sample with a much lower hole density of p = 4.0 × 10 10 /cm 2 where we measure a mobility of 3.6 × 10 6 cm2/(V s). Finally, these improvements in sample quality were achieved by the reduction of residual impurities both in the GaAs channel and in the AlGaAs barrier material, as well as optimization in the design of the sample structure.

2-dimensional systems↗
NASA NTRS2000

Laser Technology in Interplanetary Exploration: The Past and the Future

Laser technology has been used in planetary exploration for many years but it has only been in the last decade that laser altimeters and ranging systems have been selected as flight instruments alongside cameras, spectrometers, magnetometers, etc. Today we have an active laser system operating at Mars and another destined for the asteroid Eros. A few years ago a laser ranging system on the Clementine mission changed much of our thinking about the moon and in a few years laser altimeters will be on their way to Mercury, and also to Europa. Along with the increased capabilities and reliability of laser systems has came the realization that precision ranging to the surface of planetary bodies from orbiting spacecraft enables more scientific problems to be addressed, including many associated with planetary rotation, librations, and tides. In addition, new Earth-based laser ranging systems working with similar systems on other planetary bodies in an asynchronous transponder mode will be able to make interplanetary ranging measurements at the few cm level and will advance our understanding of solar system dynamics and relativistic physics.

Smith, David E.↗
DOE OSTI2023

Probing correlated states with plasmons

Understanding the nature of strongly correlated states in flat-band materials (such as moiré heterostructures) is at the forefront of both experimental and theoretical pursuits. While magnetotransport, scanning probe, and optical techniques are often very successful in investigating the properties of the underlying order, the exact nature of the ground state often remains unknown. Here, we propose to leverage strong light-matter coupling present in the flat-band systems to gain insight through dynamical dielectric response into the structure of the many-body ground state. We argue that because of the enlargement of the effective lattice of the system arising from correlations, conventional long-range plasmon becomes “folded” to yield a multiband plasmon spectrum. We detail several mechanisms through which the structure of the plasmon spectrum and that of the dynamical dielectric response is susceptible to the underlying order, revealing valued insights such as the interaction-driven band gaps, spin-structure, and the order periodicity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

NESSi : The N on- E quilibrium S ystems S imulation package

The nonequilibrium dynamics of correlated many-particle systems is of interest in connection with pump–probe experiments on molecular systems and solids, as well as theoretical investigations of transport properties and relaxation processes. Nonequilibrium Green’s functions are a powerful tool to study interaction effects in quantum many-particle systems out of equilibrium, and to extract physically relevant information for the interpretation of experiments. Here, we present the open-source software package NESSi (The Non-Equilibrium Systems Simulation package) which allows to perform many-body dynamics simulations based on Green’s functions on the L-shaped Kadanoff–Baym contour. NESSi contains the library libcntr which implements tools for basic operations on these nonequilibrium Green’s functions, for constructing Feynman diagrams, and for the solution of integral and integro-differential equations involving contour Green’s functions. The library employs a discretization of the Kadanoff–Baym contour into time points and a high-order implementation of integration routines. The total integrated error scales up to $\mathcal{O}(N^{-7})$, which is important since the numerical effort increases at least cubically with the simulation time. A distributed-memory parallelization over reciprocal space allows large-scale simulations of lattice systems. We provide a collection of example programs ranging from dynamics in simple two-level systems to problems relevant in contemporary condensed matter physics, including Hubbard clusters and Hubbard or Holstein lattice models. The libcntr library is the basis of a follow-up software package for nonequilibrium dynamical mean-field theory calculations based on strong-coupling perturbative impurity solvers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Green’s function coupled cluster simulation of the near-valence ionizations of DNA-fragments

Accurate description of the ionization process in DNA is crucial to the understanding of the DNA damage under exposure to ionizing radiation and the exploration of the potential application of DNA strands in nanoelectronics. In this work, by employing our recently developed Green’s function coupled-cluster library on supercomputing facilities, we have studied the spectral functions of several guanine–cytosine (G–C) base pair structures ([G–C]n, n = 1–3) for the first time in a relatively broad near-valence regime ([−25.0, −5.0] eV) in the coupled-cluster with singles and doubles level. Our focus is to give a preliminary many-body coupled-cluster understanding and guideline of the vertical ionization energy (VIE), spectral profile, and ionization feature changes of these systems as the system size expands in this near-valence regime. The results show that, as the system size expands, even though the lowest VIEs keep decreasing, the changes of spectral function profile and the relative peak positions get unexpectedly smaller. Further analysis of the ionized states associated with the most intensive peak in the spectral functions reveals non-negligible |2h, 1p⟩’s in the ionized wave functions of the considered G–C base pair systems. The leading |2h, 1p⟩’s associated with the main ionizations from the cytosine part of the G–C base pairs feature a transition from the intra-base-pair cytosine π → π* excitation to the inter-base-pair electron excitation as the size of G–C base pairs expands, which also indicates the minimum quantum region in the many-body calculations of DNA systems.

Peng, Bo (ORCID:0000000242267294)↗
DOE OSTI2026

Hierarchical Truncations for Many-Body Expansion Potentials

In this work, a new strategy to truncate high-order terms in the many-body expansion (MBE) is proposed. This new approach, which we call a hierarchical many-body expansion (HMBE), is based on a hierarchical partition of the system into multitier fragments and can in principle be applied to any large molecular system. Numerical tests on a series of (H 2 O) 64 structures are presented, demonstrating satisfactory relative energies between the clusters and binding energies of individual clusters compared with full-cluster calculations, with significantly fewer high-order terms computed than conventional MBE. The hierarchical truncation can be augmented by certain many-body terms for fragments at the interface between the partitions (called “Schengen terms”) to further improve accuracy. This work establishes the HMBE scheme as a promising framework to model very large systems (e.g., proteins), which are naturally built on a hierarchical structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Importance of charge self-consistency in first-principles description of strongly correlated systems

First-principles approaches have been successful in solving many-body Hamiltonians for real materials to an extent when correlations are weak or moderate. As the electronic correlations become stronger often embedding methods based on first-principles approaches are used to better treat the correlations by solving a suitably chosen many-body Hamiltonian with a higher level theory. The success of such embedding theories, often referred to as second-principles, is commonly measured by the quality of self-energy Σ which is either a function of energy or momentum or both. However, Σ should, in principle, also modify the electronic eigenfunctions and thus change the real space charge distribution. While such practices are not prevalent, some works that use embedding techniques do take into account these effects. In such cases, choice of partitioning, of the parameters defining the correlated Hamiltonian, of double-counting corrections, and the adequacy of low-level Hamiltonian hosting the correlated subspace hinder a systematic and unambiguous understanding of such effects. Further, for a large variety of correlated systems, strong correlations are largely confined to the charge sector. Then an adequate nonlocal low-order theory is important, and the high-order local correlations embedding contributes become redundant. Here we study the impact of charge self-consistency within two example cases, TiSe 2 and CrBr 3 , and show how real space charge re-distribution due to correlation effects taken into account within a first-principles Green’s function-based many-body perturbative approach is key in driving qualitative changes to the final electronic structure of these materials.

36 MATERIALS SCIENCE↗