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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

Vibrational and Rovibrational Spectroscopy Applied to Astrochemistry

The detection of molecules in astrophysical environments almost always requires remote sensing. While radioastronomical observation and associated rotational spectroscopy are powerful astronomical tools, infrared spectral analysis provides a unique means of examining the observable universe, especially for molecules where permanent dipole moments are small or even non-existent. The molecular vibrations of small molecules are now able to be modeled via quantum chemistry and electronic structure theory conjoined to vibrational analysis to within spectroscopic accuracy in many cases. This chapter will showcase this success and build upon it to show how such advances are now being leveraged to describe molecular vibrations for molecules containing dozens of atoms, electronically excited states, "hot bands," exoplanetary atmospheric opacity data, and even emission of polycyclic aromatic hydrocarbons. All of these are required to prune the interstellar spectral garden of its "weeds" in search of "flowers" that will provide the necessary fingerprints for astronomers to be able to probe the heavens for its past, present, and future secrets.

Ryan C. Fortenberry↗
DOE OSTI2014

Workshop on Field Theoretic Simulations in Particle Physics and Condensed Matter

A two and half day workshop at Boston University, devoted to a discussion of common problems in the theoretical and computational study of particle physics and condensed matter. The phase structure of strongly coupled quantum field theories are of great interest in condensed matter and high energy physics. For example, the study of strongly correlated systems, such as frustrated quantum anti-ferromagnets, have suggested the existence of phases in which the low energy excitations do not have the quantum numbers of electrons but are fractionalized. The field description of such systems are typically topological quantum field theories. The latter have also proved important in constructing supersymmetric lattice gauge theories. Quantum critical systems in condensed matter are described by conformal field theories which have the subject of much recent work in the context of theories of Beyond Standard Model physics. Finally, theoretical holographic techniques originating in string theory may offer a new tool to investigate strongly interacting electrons. In parallel with these theoretical developments there has been rapid progress in computational methods in both fields; from tensor networks and density matrix renormalization group techniques to the rational hybrid Monte Carlo algorithm and techniques to ameliorate the famous sign problem. It is thus a propitious time to bring both communities together to stimulate an exchange of ideas and facilitate possible future collaborations.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Software-defined network abstractions and configuration interfaces for building programmable quantum networks

Well-defined and stable quantum networks are essential to realize functional quantum applications. Quantum networks are complex and must use both quantum and classical channels to support quantum applications like QKD, teleportation, and superdense coding. In particular, the no-cloning theorem prevents the reliable copying of quantum signals such that the quantum and classical channels must be highly coordinated using robust and extensible methods. We develop new network abstractions and interfaces for building programmable quantum networks. Our approach leverages new OpenFlow data structures and table type patterns to build programmable quantum networks and to support quantum applications.

quantum communiction↗
DOE OSTI2017

Effect of electrostatic shielding on the photoelectric properties of heterostructures with deep QWs

The effect of the electrostatic potential induced by charge carriers of the same sign, localized in a deep quantum well, on the current–voltage characteristics of photodetector heterostructures is theoretically analyzed. It is shown for the example of a p–i–n structure with a single deep quantum well in the i-type region that the shielding of an external electric field makes the differential photoconductivity of the heterostructure higher than that in a p–i–n structure without an intermediate 2D layer.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The Li + CaF → Ca + LiF chemical reaction under cold conditions

The calcium monofluoride (CaF) molecule has emerged as a promising candidate for precision measurements, quantum simulation, and ultracold chemistry experiments. Inelastic and reactive collisions of laser cooled CaF molecules in optical tweezers have recently been reported and collisions of cold Li atoms with CaF are of current experimental interest. In this paper, we report ab initio electronic structure and full-dimensional quantum dynamical calculations of the Li + CaF → LiF + Ca chemical reaction. The electronic structure calculations are performed using the internally contracted multi-reference configuration-interaction method with Davidson correction (MRCI + Q). An analytic fit of the interaction energies is obtained using a many-body expansion method. Furthermore, a coupled-channel quantum reactive scattering approach implemented in hyperspherical coordinates is adopted for the scattering calculations under cold conditions. Results show that the Li + CaF reaction populates several low-lying vibrational levels and many rotational levels of the product LiF molecule and that the reaction is inefficient in the 1–100 mK regime allowing sympathetic cooling of CaF by collisions with cold Li atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

First-principles investigation of near-field energy transfer between localized quantum emitters in solids

We present a predictive and general approach to investigate near-field energy transfer processes between localized defects in semiconductors, which couples first-principles electronic structure calculations and a nonrelativistic quantum electrodynamics description of photons in the weak-coupling regime. The approach is general and can be readily applied to investigate broad classes of defects in solids. We apply our approach to investigate an exemplar point defect in an oxide, the F center in MgO, and we show that the energy transfer from a magnetic source, e.g., a rare-earth impurity, to the vacancy can lead to spin nonconserving long-lived excitations that are dominant processes in the near field, at distances relevant to the design of photonic devices and ultrahigh dense memories. We also define a descriptor for coherent energy transfer to predict geometrical configurations of emitters to enable long-lived excitations, that are useful to design optical memories in semiconductor and insulators. Published by the American Physical Society 2024

Chattaraj, Swarnabha (ORCID:0000000329333581)↗
DOE OSTI2017

Propagator quantum chemical study of S-cis-(Z)-2-(2-formylethenyl)pyrrole: electronic structure and aspects of intramolecular hydrogen bond manifestation in ionization spectra

For the purpose of investigation of the electronic structures of functionalized pyrroles with potential biological activity the electronic structures and ionization spectra of S-cis-(Z)-2-(2-formylethenyl)pyrrole (FP) were calculated by the propagator quantum chemical method. The calculations were performed using the third-order algebraic diagrammatic construction method (ADC(3)) for one-particle Green´s function (electronic propagator) and the 6–31G** basis set. Going from FP (possessing the intramolecular hydrogen bond H⋯O) to its conformation FPR (without H⋯O bonding), the O1s-ionization energy and the ionization energy of the σ-type lone electron pair orbital of the O atom decrease by ~0.2 eV, which is a consequence of stopping the electron density transfer from the O atom. A strong electron density transfer through the hydrogen bond from the O atom to the NH group occurs in the nitrogen core level ionization spectrum as evidenced by a lower N1s-ionization energy of FP (by ~0.7 eV ) compared to that of FPR. The valence shell ionization spectra of FP and FPR calculated using the ADC(3) method are characterized by a high density of the satellite states. The results obtained indicate that the electronic structures of the compounds of the considered class are characterized by pronounced effects of electron correlation.

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

Finding Electronic Structure Machine Learning Surrogates without Training

A myriad of phenomena in materials science and chemistry rely on quantum-level simulations of the electronic structure in matter. While moving to larger length and time scales has been a pressing issue for decades, such large-scale electronic structure calculations are still challenging despite modern software approaches and advances in high-performance computing. The silver lining in this regard is the use of machine learning to accelerate electronic structure calculations – this line of research has recently gained growing attention. The grand challenge therein is finding a suitable machine-learning model during a process called hyperparameter optimization. This, however, causes a massive computational overhead in addition to that of data generation. We accelerate the construction of machine-learning surrogate models by roughly two orders of magnitude by circumventing excessive training during the hyperparameter optimization phase. We demonstrate our workflow for Kohn-Sham density functional theory, the most popular computational method in materials science and chemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Fermi surface studies of the low-temperature structure of sodium

Sodium is the most abundant alkali-metal element and has one of the simplest electronic structures of any metal. At ambient conditions, sodium forms a body-centered-cubic lattice. However, during cooling, it undergoes a partial martensitic phase transition to a complex mixture of rhombohedral polytypes commencing from 36 K. Although the Fermi surface (FS) of bcc sodium has been extensively studied, not much attention has been given to the FS of the martensite structure. Here we report results for the Fermi surface and quantum oscillation (QO) frequencies of several energetically favorable crystal structures of Na at low temperature from first-principles calculations. Interestingly we find that despite drastic differences in the crystal structures of the candidate low-temperature phases of sodium, for all these phases the strongest quantum oscillation peak is centered at 28 kT. Our theoretical results are accompanied by experimental data of QO on a multigrain sodium sample at T = 0.3 K and B max = 18 T exhibiting a sharp peak at 28 kT, independent of the sample orientation. The persistence of this peak even in the presence of the structural transitions has an implication for using the quantum oscillations of polycrystalline sodium for high magnetic field calibration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Rigidifying Fluorescent Linkers by Metal-Organic Framework Formation for Fluorescence Blue Shift and Quantum Yield Enhancement

We demonstrate that rigidifying the structure of fluorescent linkers by structurally constraining them in metal-organic frameworks (MOFs) to control their conformation effectively tunes the fluorescence energy and enhances the quantum yield. Thus, a new tetraphenylethylene-based zirconium MOF exhibits a deep-blue fluorescent emission at 470 nm with a unity quantum yield (99.9 +/- 0.5%) under Ar, representing ca. 3600 cm(-1) blue shift and doubled radiative decay efficiency vs the linker precursor. An anomalous increase in the fluorescence lifetime and relative intensity takes place upon heating the solid MOF from cryogenic to ambient temperatures. The origin of these unusual photoluminescence properties is attributed to twisted linker conformation, intramolecular hindrance, and framework rigidity.

Wei, ZW↗
DOE OSTI2025

Programmable exploration of magnetic states in Lieb-kagome interpolated lattices

We investigate a hybrid modeling framework in which a quantum annealer is used to simulate magnetic interactions in molecular qubit lattices inspired by experimentally realizable systems. Using phthalocyanine assemblies as a structurally constrained prototype, we model a continuous deformation from a Lieb to a kagome lattice, revealing frustration-driven disorder and magnetic field-induced reordering in the spin structure. Here, the goal is to show how a quantum annealer can operate as a physically instantiated, programmable platform to emulate experimentally relevant lattice deformations and produce observables in a manner analogous to an experimental measurement, enabling the characterization of magnetic arrangements beyond the reach of current molecular architectures. This surrogate modeling approach offers a pathway to explore and iteratively design tunable magnetic states in synthetic materials. The synthetic design, structural characterization, and quantum simulation framework established here defines a modular and scalable paradigm for probing the limits of engineered matter across chemistry, condensed matter, and quantum information science.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Helimagnetic Structure and Heavy-Fermion-Like Behavior in the Vicinity of the Quantum Critical Point in Mn 3 P

Antiferromagnet Mn 3 P with Neel temperature T N =30 K is composed of Mn tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and reveal a complex yet well-ordered helimagnetic structure. The itinerant character of this materials is strong, and the ordered state with small magnetic moments is easily suppressed under pressure, exhibiting a quantum critical point at ~1.6 GPa. The remarkable mass renormalization, even in the ordered state, and an incoherent-coherent crossover in the low-temperature region, characterize an unusual electronic state in Mn 3 P, which is most likely effected by the underlying frustration effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Automated chemical resonance generation and structure filtration for kinetic modeling

This study discusses efficient and automated methods for constructing a set of representative resonance structures for arbitrary chemical species, including radicals and biradicals, consisting of the elements H, C, O, N, and S. Determining the representative reactive structures of chemical species is crucial for identification of reactive sites and consequently applying the correct reaction templates to generate the set of important reactions during automated chemical kinetic model generation. We describe a fundamental set of resonance pathway types, accounting for simple resonating structures, as well as global approaches for polycyclic aromatic species. Automatically discovering potential localized structures along with filtration to identify the representative structures was shown to be robust and relatively fast. The algorithms discussed here were recently implemented in the Reaction Mechanism Generator (RMG) software. The final structures proposed by this method were found to be in reasonable agreement with quantum chemical computation results of localized structure contributions to the resonance hybrid.

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

The hitchhiker's guide to 4d $\mathcal{N}=2$ superconformal field theories

Superconformal field theory with \mathcal{N}=2 𝒩 = 2 supersymmetry in four dimensional spacetime provides a prime playground to study strongly coupled phenomena in quantum field theory. Its rigid structure ensures valuable analytic control over non-perturbative effects, yet the theory is still flexible enough to incorporate a large landscape of quantum systems. Here we aim to offer a guidebook to fundamental features of the 4d \mathcal{N}=2 𝒩 = 2 superconformal field theories and basic tools to construct them in string/M-/F-theory. The content is based on a series of lectures at the Quantum Field Theories and Geometry School in July 2020.

Akhond, Mohammad↗
DOE OSTI2023

Studying light–matter interactions and energy transfer at the nanoscale with a trapped–ion quantum computer

A grand challenge in materials sciences is to control energy transduction, transfer and dissipation at the nanoscale. Meeting this challenge requires progress in nanoscale fabrication and synthesis, but equally importantly, also progress in our understanding of how nanoscale structure influences these phenomena. Although detailed quantum mechanical models exist that capture the structure and physics of materials and molecular species, solving these models to calculate the relevant emergent phenomena, which often occur over vastly different time and energy scales, has so far proven difficult. In this project, we studied how to model energy transfer and light-matter interactions using trapped-ion quantum computers. Our studies focused on emulation of critical processes in natural systems, such as the well-known photosynthetic pigment-protein complexes responsible for capturing and transducing light to electrons. In addition, we implemented proof-of-principle experiments demonstrating that such calculations are possible on trapped-ion quantum computing hardware. These studies and experiments pave the way to investigate energy transport and transduction in a detail not accessible with classical computing technologies. We expect that our studies will allow to extract important guiding principles on how to improve the efficiency of nano-scale light-harvesting and transduction devices.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Strongly Confined Bismuth Antimonide Quantum Dots

Bismuth antimonide (Bi 1−x Sb x ) has emerged as a highly promising material for quantum applications due to its complex band structure. In this study, spherical Bi 1−x Sb x quantum dots (QDs), with a diameter of around 8 ± 2 nm, were successfully synthesized by pulsed laser ablation in liquids. The energy bandgap was determined at 2.02 ± 0.27 eV, which is significantly higher than the bulk value (∼0.025 eV). The strong confinement nature of the dots was confirmed by the Raman peak shifts. The chemical composition of the Bi 1−x Sb x QDs was measured to be around 77 ± 2 at. % of Bi and 23 ± 2 at. % of Sb. The colloid containing the Bi 1−x Sb x QDs was classified as highly stable, displaying a zeta potential of −38 ± 18 mV. Finally, the Bi 1−x Sb x QDs exhibited an electron spin resonance (ESR) signal at room temperature and at cryogenic temperature (4.2 K); consequently, revealing the presence of paramagnetic states.

Alloys↗
DOE OSTI2023

Quantized resistance revealed at the criticality of the quantum anomalous Hall phase transitions

In multilayered magnetic topological insulator structures, magnetization reversal processes can drive topological phase transitions between quantum anomalous Hall, axion insulator, and normal insulator states. Here we report an examination of the critical behavior of two such transitions: the quantum anomalous Hall to normal insulator (QAH-NI), and quantum anomalous Hall to axion insulator (QAH-AXI) transitions. By introducing a new analysis protocol wherein temperature dependent variations in the magnetic coercivity are accounted for, the critical behavior of the QAH-NI and QAH-AXI transitions are evaluated over a wide range of temperature and magnetic field. Despite the uniqueness of these different transitions, quantized longitudinal resistance and Hall conductance are observed at criticality in both cases. Furthermore, critical exponents were extracted for QAH-AXI transitions occurring at magnetization reversals of two different magnetic layers. The observation of consistent critical exponents and resistances in each case, independent of the magnetic layer details, demonstrates critical behaviors in quantum anomalous Hall transitions to be of electronic rather than magnetic origin. Our finding offers a new avenue for studies of phase transition and criticality in QAH insulators.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗