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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Strong-coupling expansion of multi-band interacting models: Mapping onto the transverse-field J 1 - J 2 Ising model

We investigate a class of two-dimensional two-band microscopic models in which the inter-band repulsive interactions play the dominant role. We first demonstrate three different schemes of constraining the ratios between the three types of inter-band interactions – density-density, spin exchange, and pair-hopping – that render the model free of the fermionic sign-problem for any filling and, consequently, amenable to efficient Quantum Monte Carlo simulations. We then study the behavior of these sign-problem-free models in the strong-coupling regime. In the cases where spin-rotational invariance is preserved or lowered to a planar symmetry, the strong-coupling ground state is a quantum paramagnet. However, in the case where there is only a residual Ising symmetry, the strong-coupling expansion maps onto the transverse-field J 1 - J 2 Ising model, whose pseudospins are associated with local inter-band magnetic order. We show that by varying the band structure parameters within a reasonable range of values, a variety of ground states and quantum critical points can be accessed in the strong-coupling regime, some of which are not realized in the weak-coupling regime. Here, we compare these results with the case of the single-band Hubbard model, where only intra-band repulsion is present, and whose strong-coupling behavior is captured by a simple Heisenberg model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Equatorial Electronic Structure in the Uranyl Ion: Cs 2 UO 2 Cl 4 and Cs 2 UO 2 Br 4

Electric field gradient (EFG) tensors in the equatorial plane of the linear UO 2 2+ ion have been measured by nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) experiments and computed by relativistic Kohn–Sham methods with and without environment embedding for Cs 2 UO 2 Cl 4 and Cs 2 UO 2 Br 4 . This approach expands the possibilities for probing the electronic structure in uranyl complexes beyond the strongly covalent U–O bonds. The combined analyses find that one of the two largest principal EFG tensor components at the halogen sites points along the U–X bond (X = Cl, Br), and the second is parallel to the UO 2 2+ ion; in Cs 2 UO 2 Cl 4 , the components are nearly equal in magnitude, whereas in Cs 2 UO 2 Br 4 , due to short-range bromide–cesium interactions, the equatorial component is dominant for one pair of Br sites and the axial component is larger for the second pair. Additionally, the directions and relative magnitudes of the field gradient principal axes are found to be sensitive to the σ and π electron donation by the ligands and the model of the environment. Chlorine-35 NQR spectra of 235 U-depleted and 235 U-enriched Cs 2 UO 2 Cl 4 exhibited no uranium-isotope-dependent shift, but the resonance of the depleted sample displayed a 58% broader line width.

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

Revisiting the Hole Size in Double Helical DNA with Localized Orbital Scaling Corrections

The extent of electronic wave function delocalization for the charge carrier (electron or hole) in double helical DNA plays an important role in determining the DNA charge transfer mechanism and kinetics. The size of the charge carrier’s wave function delocalization is regulated by the solvation induced localization and the quantum delocalization among the π stacked base pairs at any instant of time. Using a newly developed localized orbital scaling correction (LOSC) density functional theory method, we accurately characterized the quantum delocalization of the hole wave function in double helical B-DNA. This approach can be used to diagnose the extent of delocalization in fluctuating DNA structures. Our studies indicate that the hole state tends to delocalize among 4 guanine–cytosine (GC) base pairs and among 3 adenine–thymine (AT) base pairs when these adjacent bases fluctuate into degeneracy. The relatively small delocalization in AT base pairs is caused by the weaker π–π interaction. This extent of delocalization has significant implications for assessing the role of coherent, incoherent, or flickering coherent carrier transport in DNA.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Adsorption and Structure of Chiral Epoxides on Pd(111): Propylene Oxide and Glycidol

Here, the adsorption of enantiopure versus racemic propylene oxide (PO) on Pd(111) is studied by temperature-programmed desorption (TPD) to explore possible differences in their saturation coverage. It is found that that the saturation coverage of enantiopure PO on Pd(111) is identical to that of racemic PO, in contrast to results on Pt(111) where significant coverage differences were found. The surface structures of enantiopure PO on Pd(111) were characterized by scanning tunneling microscopy (STM), which shows the formation of linear chains and hexagonal structures proposed to be due to freely rotating PO, in contrast to the relatively disordered PO overlayers found on Pt(111). STM experiments were carried out for enantiopure glycidol, which contains the same epoxy ring as PO, but where the methyl group of propylene oxide is replaced by a -CH 2 OH group to provide a hydrogen-bonding sites. Glycidol STM images show the formation of completely different surface structures; at low coverages, glycidol forms pseudohexagonal structures which assemble from glycidol dimers, while at high coverages the surface shows extensive hydrogen-bonded networks. Density functional theory (DFT) calculations were carried out to model the enantiopure PO linear chain and the glycidol dimers that are observed by STM. Similar calculations were carried out for racemic PO and glycidol structures. The calculated interaction energies for the enantiopure and the racemic pairs reveal that there is no difference for homochiral versus heterochiral structures for both PO and glycidol on Pd(111).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Dynamical Ion Correlations in Polymer and Membrane Electrolytes: Recent Advances and Open Questions

Ion transport in polymer and membrane electrolytes is often described using uncorrelated models like the Nernst–Einstein (NE) approximation, which link conductivity, transference number, and salt diffusivity to individual ion mobilities. However, growing evidence shows that dynamical ion correlations─arising from ion pairing, polymer-mediated coupling, confinement, and electrostatic interactions─can substantially alter macroscopic transport properties. The Onsager transport formalism offers a rigorous framework to quantify these effects via cross-correlated ionic displacements. This Perspective highlights how such correlations manifest across dry and hydrated systems, including salt-doped polymers, block copolymers, hydrogels, and ion-exchange membranes. Here, we examine key physical origins, the influence of salt chemistry and polymer structure, and open questions in measuring and controlling correlated motion. Embracing correlation-aware design enables new pathways to optimize conductivity, transference number, and selectivity─shifting the focus from individual ion mobility to engineered collective dynamics for next-generation electrolytes in energy storage and separations.

Charge transport↗
DOE OSTI2026

Prediction and Experimental Verification of Electrolyte Solvation Structure from an OMol25-Trained Interatomic Potential

A molecular-level understanding of electrolyte solvation structure and ion–ion correlations is critical to developing next-generation battery chemistries. Atomistic simulation capabilities with sufficient accuracy, speed, and transferability to deliver reliable structural insights while avoiding arduous system-specific reparameterization are thus highly desirable. Machine learning interatomic potentials (MLIPs) trained on large, chemically diverse data sets are revolutionizing computational chemistry, enabling molecular dynamics simulations of battery electrolytes with near-DFT accuracy over 10,000× faster than DFT. While previous MLIP training data sets with suitable elemental coverage for electrolytes have been based on inorganic materials, the Open Molecules 2025 (OMol25) data set provides large-scale molecular DFT MLIP training data with broad elemental coverage and specifically samples tens of millions of electrolyte configurations. Here, we integrate computational modeling with experimental validation to systematically assess the ability of large-scale MLIPs pretrained on materials data or on OMol25 to accurately resolve nanoscale structural organization and ion-solvation characteristics in Na-ion battery electrolytes across diverse physicochemical conditions and compositional regimes. We find that the OMol25-trained Universal Model of Atoms (UMA-OMol) predicts experimentally measured densities and X-ray structure factors in substantially better agreement compared to state-of-the-art models trained only on inorganic materials data. Using UMA-OMol, we further analyze systematic trends in solvation structure as a function of cation identity, anion chemistry, salt concentration, and solvent topology. We observe that increasing system temperature amplifies the heterogeneity within the solvation environment, perturbing cation–solvent interactions and promoting the formation of contact ion pairs (CIPs). Moreover, subtle variations in the solvent topology of glyme-based electrolytes cause pronounced changes in ion correlations and solvation structure. The experimental agreement and microscopic insights shown here position OMol25-trained MLIPs as a practical route to predictive, high-throughput electrolyte simulations beyond the limits of classical force fields and direct DFT molecular dynamics, serving as a powerful tool for accelerating the design of next-generation Na-ion battery electrolytes and beyond.

MLIPs↗
DOE OSTI2018

Record-Low and Anisotropic Thermal Conductivity of a Quasi-One-Dimensional Bulk ZrTe 5 Single Crystal

Zirconium pentatelluride (ZrTe 5 ) has recently attracted renewed interest owing to many of its newly discovered extraordinary physical properties, such as 2D and 3D topological-insulator behavior, pressure-induced superconductivity, Weyl semimetal behavior, Zeeman splitting, and resistivity anomaly. The quasi-one-dimensional structure of single-crystal ZrTe 5 also promises large anisotropy in its thermal properties, which have not yet been studied. In this work, via time-domain thermoreflectance measurements, ZrTe 5 single crystals are discovered to possess a record-low thermal conductivity along the b-axis (through-plane), as small as 0.33 ± 0.03 W m –1 K –1 at room temperature. This ultralow b-axis thermal conductivity is 12 times smaller than its a-axis thermal conductivity (4 ± 1 W m –1 K –1 ) owing to the material’s asymmetrical crystalline structure. First-principles calculations are further conducted to reveal the physical origins of the ultralow b-axis thermal conductivity, which can be attributed to: (1) the resonant bonding and strong lattice anharmonicity induced by electron lone pairs, (2) the weak interlayer van der Waals interactions, and (3) the heavy mass of Te atoms, which results in low phonon group velocity. This work sheds light on the design and engineering of high-efficiency thermal insulators for applications such as thermal barrier coatings, thermoelectrics, thermal energy storage, and thermal management.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Excitonic Mott insulator in a Bose-Fermi-Hubbard system of moiré WS 2 /WSe 2 heterobilayer

Understanding the Hubbard model is crucial for investigating various quantum many-body states and its fermionic and bosonic versions have been largely realized separately. Recently, transition metal dichalcogenides heterobilayers have emerged as a promising platform for simulating the rich physics of the Hubbard model. In this work, we explore the interplay between fermionic and bosonic populations, using a WS 2 /WSe 2 heterobilayer device that hosts this hybrid particle density. We independently tune the fermionic and bosonic populations by electronic doping and optical injection of electron-hole pairs, respectively. This enables us to form strongly interacting excitons that are manifested in a large energy gap in the photoluminescence spectrum. The incompressibility of excitons is further corroborated by observing a suppression of exciton diffusion with increasing pump intensity, as opposed to the expected behavior of a weakly interacting gas of bosons, suggesting the formation of a bosonic Mott insulator. We explain our observations using a two-band model including phase space filling. Our system provides a controllable approach to the exploration of quantum many-body effects in the generalized Bose-Fermi-Hubbard model.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Variation of photon interaction parameters with energy for some Cu-Pb alloys

Various photon interaction parameters (mass attenuation coefficients, effective atomic numbers and effective electron numbers) have been computed for different compositions of Cu-Pb alloys in the wide energy regime of 1 keV to 100 GeV. The mass attenuation coefficients have been computed using mixture rule with the help of WinXCom (mass attenuation coefficient database for elements). The variation of mass attenuation coefficients, effective atomic numbers and electron density has been analysed and discussed in terms of dominance of different photon interaction processes viz. Compton scattering, photoelectric effect and pair production.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Theoretical examination of nuclear spin diffusion in light-induced spin coherences in photosystem I

Microsecond coherence times are predicted in spin dynamics calculations of a donor–acceptor electron spin pair P + A 1A - created upon light excitation of photosystem I (PSI). The effects of nuclear spin diffusion (NSD) due to the anisotropic protein environment on the predicted coherence times T M are studied. Closely positioned pairs and triples of protons located 5–8 Å from the electron spin are shown to largely control T M . Additionally, knowledge of the crystal structure of PSI allows for spin dynamics calculations where specific cofactors and amino acid residues are removed or replaced and the identification of anisotropic environmental features controlling electronic decoherence. Finally, we show that NSD alone cannot explain the >3× shorter experimentally observed coherence times and suggest that methyl groups at key protein sites may explain this discrepancy.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Quantum biological insights into CRISPR-Cas9 sgRNA efficiency from explainable-AI driven feature engineering

Abstract CRISPR-Cas9 tools have transformed genetic manipulation capabilities in the laboratory. Empirical rules-of-thumb have been developed for only a narrow range of model organisms, and mechanistic underpinnings for sgRNA efficiency remain poorly understood. This work establishes a novel feature set and new public resource, produced with quantum chemical tensors, for interpreting and predicting sgRNA efficiency. Feature engineering for sgRNA efficiency is performed using an explainable-artificial intelligence model: iterative Random Forest (iRF). By encoding quantitative attributes of position-specific sequences for Escherichia coli sgRNAs, we identify important traits for sgRNA design in bacterial species. Additionally, we show that expanding positional encoding to quantum descriptors of base-pair, dimer, trimer, and tetramer sequences captures intricate interactions in local and neighboring nucleotides of the target DNA. These features highlight variation in CRISPR-Cas9 sgRNA dynamics between E. coli and H. sapiens genomes. These novel encodings of sgRNAs enhance our understanding of the elaborate quantum biological processes involved in CRISPR-Cas9 machinery.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Photon Frequency Conversion in High-Q Superconducting Resonators: Axion Electrodynamics, QED, and Nonlinear Meissner Radiation

High-Q superconducting resonators have been proposed and developed as detectors of light-by-light scattering mediated by the hypothesized axion or virtual electron–positron pairs in quantum electrodynamics: the Euler–Heisenberg (EH) interaction. Photon frequency and mode conversion is central to the scheme for detecting such rare events. Superconducting resonators are nonlinear devices. The Meissner screening currents that confine the electromagnetic fields to the vacuum region of a superconducting RF cavity are nonlinear functions of the EM field at the vacuum–superconducting interface, and as a result can generate source currents and frequency conversion of microwave photons in the cavity. In this report we consider photon frequency and mode conversion in superconducting resonators with high quality factors from Meissner currents in single- and dual-cavity setups proposed for axion and QED searches based on light-by-light scattering. In a single cavity with two pump modes, photon frequency conversion by the Meissner screening current dominates photon generation by the EH interaction for cavities with Q≲1012⁠. The Meissner currents also generate background photons that limit the operation of the resonator for axion detection in three-mode, single-cavity setups. We also consider the leakage of photons from pump modes into the signal mode for both axion- and EH-mediated light-by-light scattering. Photon frequency conversion by the EH interaction can compete with Meissner and leakage radiation in ultra-high-Q cavities that are beyond the current state of the art. Meissner radiation and leakage backgrounds can be suppressed in dual-cavity setups with appropriate choices for pump and spectator modes, as well as the single-cavity setup proposed for heterodyne detection of galactic axion dark matter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Possible Spin-Triplet Excitonic Insulator in the Ultraquantum Limit of HfTe 5

More than 50 years ago, excitonic insulators formed by the pairing of electrons and holes due to Coulomb interactions were first predicted [A. N. Kozlov and L. A. Maksimov, Sov. J. Exp. Theor. Phys. 21, 790 (1965); L. V. Keldysh and Y. V. Kopaev, Sov. Phys. Solid State 6, 2219 (1965); D. Jérome, T. M. Rice, and W. Kohn, Phys. Rev. 158, 462 (1967)]. Since then, excitonic insulators have been observed in various classes of materials, including quantum Hall bilayers, graphite, transition metal chalcogenides, and more recently in moiré superlattices. In these excitonic insulators, an electron and a hole with the same spin bind together, and the resulting exciton is a spin singlet. Here, we report the experimental observation of a spin-triplet excitonic insulator in the ultra-quantum limit of a three-dimensional topological material HfTe 5 . We observe that the spin-polarized zeroth Landau bands dispersing along the field direction cross each other beyond a characteristic magnetic field in HfTe 5 , forming the one-dimensional Weyl mode. Transport measurements reveal the emergence of a gap of about 2⁢5⁢0 μ⁢eV when the field surpasses a critical threshold. By performing the material-specific modeling, we identify this gap as a consequence of a spin-triplet exciton formation, where electrons and holes with opposite spin form bound states, and the translational symmetry is preserved. The system reaches charge neutrality following the gap opening, as evidenced by the zero Hall conductivity over a wide magnetic field range (10–72 T). In conclusion, our finding of the spin-triplet excitonic insulator paves the way for studying novel spin transport including spin superfluidity, spin Josephson currents, and Coulomb drag of spin currents in analogy to the transport properties associated with the layer pseudospin in quantum Hall bilayers.

36 MATERIALS SCIENCE↗
DOE OSTI2023

$μ^+$ Knight shift in UTe 2 : Evidence for relocalization in a Kondo lattice

The local magnetic susceptibility of the spin-triplet superconductor UTe 2 has been investigated by positive muon (μ + ) Knight shift measurements in the normal state. Three distinct μ + Knight shift components are observed for a magnetic field applied parallel to the c axis. Two of these exhibit a breakdown in the linear relationship with the bulk magnetic susceptibility (χ) below a temperature T*~30K, which points to a gradual emergence of a correlated Kondo liquid. Below T r ~12K linearity is gradually restored, indicating relocalization of the Kondo liquid quasiparticles. The third Knight shift component is two orders of magnitude larger, and despite the c-axis alignment of the external field, scales with the a axis χ above T r ~12K. We conjecture that this component is associated with magnetic clusters and the change in the temperature dependence of all three Knight shift components below T r is associated with a change in magnetic correlations. Finally, our findings indicate that prior to the onset of superconductivity the development of the itinerant heavy-electron fluid is halted by a gradual development of local U 5⁢ƒ-moment fluctuations.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Local volume effects in the generalized pseudopotential theory

The generalized pseudopotential theory (GPT) is a compelling approach for deriving real-space transferable interatomic potentials. Using a coarse-grained electronic structure, one can explicitly determine the pair ion-ion and multi-ion interactions in simple and transition metals. While successful in determining bulk properties, in central force metals the GPT fails to describe crystal defects for which there is a significant local volume change. A previous paper [J. A. Moriarty and R. Phillips, Phys. Rev. Lett. 66, 3036 (1991)] found that by allowing the GPT total energy to depend upon some spatially averaged local electron density, the energetics of vacancies and surfaces could be calculated within experimental ranges. In this paper, we develop the formalism further by explicitly calculating the forces and stress tensor associated with this total energy. We call this scheme the adaptive GPT (aGPT) and it is capable of both molecular dynamics (MD) and molecular statics. We apply the aGPT to vacancy formation, divacancy binding, and stacking faults in hcp Mg. We also calculate the local electron density corrections to the bulk elastic constants and phonon dispersion for which there is refinement over the baseline GPT treatment. Furthermore, we demonstrate aGPT-MD simulation through the calculation of thermal expansion in magnesium to 700 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Lead apatites: structural variations among Pb 5 ( B O 4 ) 3 Cl with B = P (pyromorphite), As (mimetite) and V (vanadinite)

The crystal structure of four Pb apatite samples, Pb 5 ( B O 4 ) 3 Cl, was refined with synchrotron high-resolution powder X-ray diffraction data, Rietveld refinements, space group P 6 3 / m and Z = 2. For this isotypic series, B = P 5+ is pyromorphite, B = As 5+ is mimetite and B = V 5+ is vanadinite. The ionic radius for As 5+ (0.355 Å) is similar to that of V 5+ (0.335 Å), and this is twice as large as that for P 5+ (0.170 Å). However, the c unit-cell parameter for mimetite is surprisingly different from that of vanadinite, although their unit-cell volumes, V , are almost equal to each other. No explanation was available for this peculiar c -axis value for mimetite. Structural parameters such as average $\langle$ B —O$\rangle$ [4], $\langle$Pb1—O 9 $\rangle$ [9] and $\langle$Pb2—O 6 Cl 2 $\rangle$ [8] distances increase linearly with V (the coordination numbers for the cations are given in square brackets). Mimetite has a short Pb2—O1 distance, so the O1 oxygen atom interacts with the 6 s 2 lone-pair electrons of the Pb 2+ cation that causes the Cl—Cl distance (= c /2) to increase to the largest value in the series because of repulsion, which causes the c -axis to increase anomalously. Although Pb apatite minerals occur naturally in ore deposits, they are also formed as scaly deposits in lead water pipes that give rise to lead in tap water, as was found recently in Flint, Michigan, USA. It is important to identify Pb-containing phases in water-pipe deposits.

chemistry↗
DOE OSTI2024

Fungi rather than bacteria drive early mass loss from fungal necromass regardless of particle size

Microbial necromass is increasingly recognized as an important fast-cycling component of the long-term carbon present in soils. To better understand how fungi and bacteria individually contribute to the decomposition of fungal necromass, three particle sizes (>500, 250–500, and <250 μm) of Hyaloscypha bicolor necromass were incubated in laboratory microcosms inoculated with individual strains of two fungi and two bacteria. Decomposition was assessed after 15 and 28 days via necromass loss, microbial respiration, and changes in necromass pH, water content, and chemistry. To examine how fungal–bacterial interactions impact microbial growth on necromass, single and paired cultures of bacteria and fungi were grown in microplates containing necromass-infused media. Microbial growth was measured after 5 days through quantitative PCR. Regardless of particle size, necromass colonized by fungi had higher mass loss and respiration than both bacteria and uninoculated controls. Fungal colonization increased necromass pH, water content, and altered chemistry, while necromass colonized by bacteria remained mostly unaltered. Bacteria grew significantly more when co-cultured with a fungus, while fungal growth was not significantly affected by bacteria. Collectively, our results suggest that fungi act as key early decomposers of fungal necromass and that bacteria may require the presence of fungi to actively participate in necromass decomposition.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Regulation of translation by ribosomal RNA pseudouridylation

Pseudouridine is enriched in ribosomal, spliceosomal, transfer, and messenger RNA and thus integral to the central dogma. The chemical basis for how pseudouridine affects the molecular apparatus such as ribosome, however, remains elusive owing to the lack of structures without this natural modification. Here, we studied the translation of a hypopseudouridylated ribosome initiated by the internal ribosome entry site (IRES) elements. We analyzed eight cryo–electron microscopy structures of the ribosome bound with the Taura syndrome virus IRES in multiple functional states. We found widespread loss of pseudouridine-mediated interactions through water and long-range base pairings. In the presence of the translocase, eukaryotic elongation factor 2, and guanosine 5'-triphosphate hydrolysis, the hypopseudouridylated ribosome favors a rare unconducive conformation for decoding that is partially recouped in the ribosome population that remains modified at the P-site uridine. The structural principles learned establish the link between functional defects and modification loss and are likely applicable to other pseudouridine-associated processes.

59 BASIC BIOLOGICAL SCIENCES↗