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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

First-Principles Calculations to Investigate the Structural, Electronic, and Half-Metallic Properties of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} (x = 0, 0.25, 0.5, 0.75, and 1) Quaternary Heusler Alloys

The structural, electronic, and magnetic properties of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} (x = 0, 0.25, 0.5, 0.75, and 1) quaternary Heusler alloys have been investigated using first-principles density functional theory within generalized gradient approximation (GGA) and local spin-density approximation with Hubbard-U corrections (LSDA+U). The calculations have been performed using the full-potential linearized augmented Plane wave plus local orbitals method. The crystal structures of Ti{sub 2}RhSn{sub 1-x}Si{sub x}, Ti{sub 2}RhSn{sub 1-x}Ge{sub x}, and Ti{sub 2}RhGe{sub 1-x}Si{sub x} were found to be cubic in (F-43m) symmetry for x = 0, 1 and cubic in (P-43m) symmetry for x = 0.25, 0.75, while tetragonal in (P-4m2) symmetry for x = 0.5. The results show that all Ti{sub 2}RhSn1-xSix, Ti{sub 2}RhGe{sub 0.75}Si{sub 0.25}, and Ti{sub 2}RhGe alloys are half-metallic ferrimagnetic. These new materials are good candidates for potential applications in spintronic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1981

Study of certain features of the electronic structure of the ternary alloys Ni2(Mn, Fe) and Ni3(Mn, Co)

The changes in electronic structure related to transport processes occurring during the alloying of he alloy Ni3Mn with iron and cobalt, and the ordering of the ternary alloys thus formed are presented. The Hall effect, the absolute thermal emf, the internal saturation induction, the Nernst-Ettingshausen constant, and the electrical resistivity were measured. Results show a decrease in the contribution of hole sections of the Fermi surface to the transport process occurs together with a considerable increase in the contribution of electron sections. In this case, the mobility of 3 dimensional holes decreases and the mobility of 4s electrons increases considerably.

Zhukova, V. M.↗
DOE OSTI2023

Pushing the limits of the periodic table — A review on atomic relativistic electronic structure theory and calculations for the superheavy elements

We review the progress in atomic structure theory with a focus on superheavy elements and their predicted ground state configurations important for an element’s placement in the periodic table. To understand the electronic structure and correlations in the regime of large atomic numbers, it is essential to correctly solve the Dirac equation in strong Coulomb fields, and to take into account quantum electrodynamic effects. We specifically focus on the fundamental difficulties encountered when dealing with the many-particle Dirac equation. We further discuss the possibility for future many-electron atomic structure calculations going beyond the critical nuclear charge $Z_{crit}≈170$, where levels such as the $1s$ shell dive into the negative energy continuum ($E_{nκ} < –m_{e}c^2$). The nature of the resulting Gamow states within a rigged Hilbert space formalism is highlighted.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Evolution of the Kondo lattice electronic structure above the transport coherence temperature

Significance The temperature ( T )-dependent evolution of the Kondo lattice electronic structure is a long-standing topic of theoretical and experimental investigation, still lacking a truly microscopic theory that agrees with a full experimental characterization. Here multiple characteristic T scales of the interaction of localized f moments with conduction electrons in the Kondo lattice CeCo I n 5 are identified and investigated using angle-resolved photoemission measurements that substantiate dynamical mean-field theory which newly includes the full realism of crystalline electric-field (CEF) f splittings. Thereby errors in the itinerant versus localized f -state classification from standard density functional theory are corrected, microscopic insight into the broad T -range crossover of f -hybridization effects is gained, and a prediction of CEF degeneracy crossover below the lattice coherence T is made.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1996

Electronic Structure of Tl2Ba2CuO(6+Delta) Epitaxial Films Measured by X-Ray Photoemission

The valence electronic structure and core levels of Tl2Ba2CuO(6 + delta) (Tl-2201) epitaxial films have been measured with X-ray photoelectron spectroscopy and are compared to those of Tl2Ba2CaCu2O(8 + delta) (Tl-2212). Changes in the Tl-2201 core-level binding energies with oxygen doping are consistent with a change in the chemical potential. Differences between the Tl-2201 and Tl-2212 measured densities of states are consistent with the calculated Cu 3d and Tl 6s partial densities of states.

Vasquez, R. P.↗
DOE OSTI2023

Synthesis, crystal and electronic structure of the Zintl phase Ba 16 Sb 11 . A case study uncovering greater structural complexity via monoclinic distortion of the tetragonal Ca 16 Sb 11 structure type

The binary Zintl phase Ba 16 Sb 11 has been synthesized and structurally characterized. Detailed studies via single-crystal X-ray diffraction methods indicate that although Ba 16 Sb 11 appears to crystallize in the tetragonal Ca 16 Sb 11 structure type (space group $P\bar{4}2_1$m with a=13.5647(9) Å, c=12.4124(12)Å, Z=2, R 1 = 3.14%; wR 2 = 4.77%), there exists an extensive structural disorder. Some Ba 16 Sb 11 crystals were found to be monoclinic and the structure was solved and refined in space group P2 1 (a=18.3929(12) Å, b=13.5233(8) Å, c=18.3978(12) Å, β=94.6600(10)°; Z=4, R 1 =5.84 %; wR 2 =9.58 %). The latter corresponds to a 2-fold superstructure of the tetragonal one, which provides a disorder-free structural model. In both descriptions, the disordered tetragonal and the ordered monoclinic superstructure, the basic building units that make up the structure of this Ba-rich compound are pairs of face-shared square antiprisms of Ba atoms, which are centered by Sb atoms. The dimerized antiprisms are linked into parallel chains via square prisms of Ba atoms, which are also centered by Sb atoms. The Zintl concept can be applied in a straightforward manner and as result, the structure of Ba 32 Sb 22 (=2×Ba 16 Sb 11 ) can be rationalized as (Ba 2+ ) 32 (Sb 3– ) 20 [Sb 2 ] 4– . Notably, the partitioning of the valence electrons is done taking into an account the homoatomic Sb–Sb contacts (d=3.01 Å), which can be clearly distinguished in the lower symmetry space group. Electronic structure calculations of Ba 16 Sb 11 are in good accordance with the Zintl rationalization and predict a semiconductor with a band gap of 0.77 eV.

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

Probing the electronic structure and dipole-bound state of the 7-azaindolide anion

We report an investigation of the electronic structure and dipole-bound state (DBS) of the cryogenically-cooled 7-azaindolide anion (7-AI − ) using high-resolution photoelectron imaging, photodetachment spectroscopy, and resonant photoelectron spectroscopy. The electron affinity of the 7-AI radical is measured to be 2.6967(8) eV (21 751 ± 6 cm −1 ). Two excited electronic states of the neutral radical are observed at 0.8 eV and 1.4 eV above the ground state. Two minor isomers of 7-AI − due to deprotonation from the α- and β-carbon on the pyrrole ring are also detected with lower adiabatic detachment energies. A DBS is observed for the 7-AI − anion at 156 cm −1 below the detachment threshold, along with 16 vibrational Feshbach resonances. Resonant two-photon photoelectron imaging reveals that the DBS is relatively long-lived. Resonant photoelectron spectroscopy via the vibrational Feshbach resonances of the DBS gives rise to rich vibrational features for the 7-AI radical not accessible in conventional photoelectron spectroscopy. Fundamental vibrational frequencies for 16 vibrational modes of the 7-AI neutral radical are measured experimentally, including 7 bending modes. The current work provides extensive experimental electronic and vibrational information for the 7-AI − anion and the 7-AI radical.

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

Influence of temperature, doping, and amorphization on the electronic structure and magnetic damping of iron

Hybrid magnonic quantum systems have drawn increased attention in recent years for coherent quantum information processing, but too large magnetic damping is a persistent concern when metallic magnets are used. Their intrinsic damping is largely determined by electron-magnon scattering induced by spin-orbit interactions. In the low scattering limit, damping is dominated by intra-band electronic transitions, which has been theoretically shown to be proportional to the electronic density of states at the Fermi level. In this work, we focus on body-centered-cubic iron as a paradigmatic ferromagnetic material. We comprehensively study its electronic structure using first-principles density functional theory simulations and account for finite lattice temperature, boron (B) doping, and structure amorphization. Our results indicate that temperature induced atomic disorder and amorphous atomic geometries only have a minor influence. Instead, boron doping noticeably decreases the density of states near the Fermi level with an optimal doping level of 6.25%. In addition, we show that this reduction varies significantly for different atomic geometries and report that the highest reduction correlates with a large magnetization of the material. Furthermore, this may suggest materials growth under external magnetic fields as a route to explore in experiment.

36 MATERIALS SCIENCE↗
DOE OSTI2026

SHarmonic: A fast and accurate implementation of spherical harmonics for electronic-structure calculations

The authors present SHarmonic, a new implementation of the spherical harmonics targeted for electronic-structure calculations. Their approach is to use explicit formulas for the harmonics written in terms of normalized Cartesian coordinates. This approach results in a code that is as precise as other implementations while being at least one order of magnitude more computationally efficient. The library can run on graphics processing units as well, achieving an additional order of magnitude in execution speed. This new implementation is simple to use and is provided under an open-source license; it can be readily used by other codes to avoid the error-prone and cumbersome implementation of the spherical harmonics.

Mathematics and Computing↗
DOE OSTI2020

Electronic structures of a diagonally striped lattice: Multiple ( N - 1 ) -fold degenerate flat bands

We investigate the electronic structure of an interesting two-dimensional (2D) diagonally striped lattice (DSL). It consists of arrays of N different types of “atoms” or “molecules” with a fixed sequence in both horizontal and vertical directions. Using a tight-binding model, we show that the DSL (N>2) has the symmetry group Amm2 and Pmm2, and exhibits an oscillatory metallic and insulating phases for the odd- and even- N number, respectively. Some conventional 2D lattices, such as the Lieb lattice, can be related to the derivative DSL via vacancy formation by removing one type of atom in every other (N-1) row of the original DSL. Interestingly, there are multiple (N-1)-fold degenerate flat bands in one group of the derivative DSLs, which affords a unique platform for studying many-body physics. In addition to atomic and molecular lattices, we suggest other artificial DSLs, such as photonic and phononic, to be also constructed with possibly interesting properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Electronic Structure and Optical Absorption Spectra of Gold Fullerenes Au{sub 16} and Au{sub 20}

The electronic and optical properties of gold fullerenes are studied in the framework of the Hubbard model. The expressions of the Fourier transforms of anticommutator Green functions have been obtained for gold fullerenes Au{sub 16} and Au{sub 20}, the poles of which determine the energy spectrum of the system under consideration. The calculations are performed for the thermodynamic means that characterize jumps of electrons from a nanosystem site to a neighboring site, the correlation functions demonstrating the possibility of existing two d electrons with oppositely oriented spin projections on the same site of the fullerenes consisting of gold atoms. The optical absorption spectra are presented. The optical absorption peaks of ions Au{sub 20}{sup −} and Au{sub 16}{sup −} correspond to a near-infrared spectral region, where the light absorption by blood or a soft tissue is vanishingly small; thus, these ions can be used as a new class of contrast improvements and phototherapeutic means for diagnostics and treatment of cancer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Ground and excited electronic structures of electride and alkalide units: The cases of Metal-Tren, -Azacryptand, and -TriPip222 complexes

A systematic electronic structure analysis was conducted for M(L) n molecular electrides and their corresponding alkalide units M(L) n @M' (M/M' = Na, K; L = Tren, Azacryptand, TriPip222; n = 1, 2). All complexes belong to the “superalkali” category due to their low ionization potentials. The saturated molecular electrides display M+(L) n - form with a greatly diffuse quasispherical electron cloud. They were identified as “superatoms” considering the contours of populating atomic-type molecular orbitals. The observed superatomic Aufbau order of M(Tren) 2 is 1S, 1P, 1D, 1F, 2S, 2P, and 1G and it is consistent with those of M(Azacryptand) and M(TriPip222) up to the analyzed 1F level. Their excitation energies decrease gradually moving from M(Tren) 2 to M(Azacryptand) and to M(TriPip222). The studied alkalide complexes carry [M(L) n ] + @M' - ionic structure and their dissociation energies vary in the sequence of K(L) n @Na > Na(L) n @Na > K(L) n @K > Na(L) n @K. Similar to molecular electrides, the anions of alkalide units occupy electrons in diffuse Rydberg-like orbitals. In this work, excited states of [M(L) n @M'] 0/+/- and their trends are also analyzed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Visualizing electronic structure of twisted bilayer MoTe 2 in devices

The pursuit of emergent quantum phenomena lies at the forefront of modern condensed matter physics. A recent breakthrough in this arena is the discovery of the fractional quantum anomalous Hall effect (FQAHE) in twisted bilayer MoTe₂ (tbMoTe₂), marking a paradigm shift and establishing a versatile platform for exploring the intricate interplay among topology, magnetism, and electron correlations. While significant progress has been made through both optical and electrical transport measurements, direct experimental insights into the electronic structure – crucial for understanding and modeling this system – have remained elusive. Here, using spatially and angle-resolved photoemission spectroscopy (μ-ARPES), we directly map the electronic band structure of tbMoTe₂. We identify the valence band maximum, whose partial filling underlies the FQAHE, at the K points, situated approximately 150 meV above the Γ valley. By fine-tuning the doping level via in-situ alkali metal deposition, we also resolve the conduction band minimum at the K point, providing direct evidence that tbMoTe₂ exhibits a direct band gap – distinct from all previously known moiré bilayer transition metal dichalcogenide systems. These results offer critical insights for theoretical modeling and advance our understanding of fractionalized excitations and correlated topological phases in this emergent quantum material.

Chen, Cheng [Univ. of Oxford (United Kingdom)]↗
DOE OSTI2021

Ab-initio predictions of phase stability, electronic structure, and optical properties of (0001)-MAX surfaces in M 2 AC (M = Cr, Zr, Hf; A = Al, Ga)

In this work, we report MAX phases' surface properties, which are essential for thin-film technology due to their excellent resistance to high-temperature oxidation, corrosion, and wear. The surface stability, electronic, and optical properties of 0001-surfaces in M 2 AC (M = Zr, Hf, Cr; A = Al, Ga) are investigated and compared with their bulk counterparts. The interplay between chemical bonding and charge distribution is discussed from electronic structure, including the Fermi surfaces. Four possible (0001)-terminated surfaces are considered by breaking M - C and M-A bonds in which cleavage energy of M - C is higher than M-A. The Cr–Al bond in Cr 2 AlC is stronger than other M-A bonds. The charge density of valance A-p electrons redistributes in the surface area, distinct from that of the bulk. The A- and M(C)-terminated (0001)-surfaces are the most stable and energetically favorable terminations due to lower surface energies. The optical properties of the most stable (0001)-surfaces were also investigated to understand the dielectric and photoconductive behavior in the (0001)-terminated surfaces of M 2 AC.

36 MATERIALS SCIENCE↗
NASA NTRS1988

Recent advances in electronic structure theory and their influence on the accuracy of ab initio potential energy surfaces

Recent advances in electronic structure theory and the availability of high speed vector processors have substantially increased the accuracy of ab initio potential energy surfaces. The recently developed atomic natural orbital approach for basis set contraction has reduced both the basis set incompleteness and superposition errors in molecular calculations. Furthermore, full CI calculations can often be used to calibrate a CASSCF/MRCI approach that quantitatively accounts for the valence correlation energy. These computational advances also provide a vehicle for systematically improving the calculations and for estimating the residual error in the calculations. Calculations on selected diatomic and triatomic systems will be used to illustrate the accuracy that currently can be achieved for molecular systems. In particular, the F+H2 yields HF+H potential energy hypersurface is used to illustrate the impact of these computational advances on the calculation of potential energy surfaces.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1989

Recent advances in electronic structure theory and their influence on the accuracy of ab initio potential energy surfaces

Recent advances in electronic structure theory and the availability of high speed vector processors have substantially increased the accuracy of ab initio potential energy surfaces. The recently developed atomic natural orbital approach for basis set contraction has reduced both the basis set incompleteness and superposition errors in molecular calculations. Furthermore, full CI calculations can often be used to calibrate a CASSCF/MRCI approach that quantitatively accounts for the valence correlation energy. These computational advances also provide a vehicle for systematically improving the calculations and for estimating the residual error in the calculations. Calculations on selected diatomic and triatomic systems will be used to illustrate the accuracy that currently can be achieved for molecular systems. In particular, the F + H2 yields HF + H potential energy hypersurface is used to illustrate the impact of these computational advances on the calculation of potential energy surfaces.

Bauschlicher, Charles W., Jr.↗
DOE OSTI2025

Sensitivity of electronic structure to crystal distortions in infinite-layered LaNiO 2

Recent observations of unconventional superconductivity (SC) in thin films of LaNiO 2 (critical temperature T c ≃ 10 K) and in bulk single crystals of La 3 ⁢Ni 2 ⁢O 7 under pressure T c ≃ 80K have cemented a long sought-after class of SC nickelates. In La 1–x ⁢Sr⁢ x ⁢NiO 2 , SC appears only in films for reasons not understood. We perform a combination of experiments to probe the crystal structure and magnetic order in bulk LaNiO 2 together with ab initio calculations of the electronic structure. We find that the infinite layers are naturally buckled out-of-plane. The electronic bands are largely unaffected by the buckling, but uniaxial compression along the c axis may lead to a Lifshitz transition.

36 MATERIALS SCIENCE↗