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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Electronic structure of the alternating monolayer-trilayer phase of La 3 Ni 2 O 7

Recent studies of La 3 Ni 2 O 7 have identified a bilayer (2222) structure and an unexpected alternating monolayer-trilayer (1313) structure, both of which feature signatures of superconductivity near 80 K under high pressures. Using angle-resolved photoemission spectroscopy, we measure the electronic structure of 1313 samples. In contrast to the previously studied 2222 structure, we find that the 1313 structure hosts a flat band with a markedly different binding energy, as well as an additional electron pocket and band splittings. By comparison to local-density approximation calculations, we find renormalizations of the Ni-d z 2 and Ni-d x 2 -y 2 derived bands to be about 5 to 7 and about 4 respectively, suggesting strong correlation effects. These results reveal important differences in the electronic structure brought about by the distinct structural motifs with the same stoichiometry. Such differences may be relevant to the putative high temperature superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Two-Photon Photoemission Study of the Coverage-Dependent Electronic Structure of Chemisorbed Alkali Atoms on a Ag(111) Surface

We report a systematic investigation of the electronic structure of chemisorbed alkali atoms (Li-Cs) on a Ag(111) surface by two-photon photoemission spectroscopy. Angle-resolved two-photon photoemission spectra are obtained for 0-0.1 monolayer coverage of alkali atoms. The interfacial electronic structure as a function of periodic properties and the coverage of alkali atoms is observed and interpreted assuming ionic adsorbate/substrate interaction. The energy of the alkali atom σ-resonance at the limit of zero coverage is primarily determined by the image charge interaction, whereas at finite alkali atom coverages, it follows the formation of a dipolar surface field. The coverage- and angle-dependent two-photon photoemission spectra provide information on the photoinduced charge-transfer excitation of adsorbates on metal surfaces. This work complements the previous work on alkali/ Cu(111) chemisorption

Environmental Molecular Sciences Laboratory↗
DOE OSTI2020

Electronic structure and optical properties of quantum crystals from first principles calculations in the Born–Oppenheimer approximation

In this work, we develop a formalism to accurately account for the renormalization of the electronic structure due to quantum and thermal nuclear motions within the Born–Oppenheimer approximation. We focus on the fundamental energy gap obtained from electronic addition and removal energies from quantum Monte Carlo calculations in either the canonical or grand-canonical ensembles. The formalism applies as well to effective single electron theories such as those based on density functional theory. We show that the electronic (Bloch) crystal momentum can be restored by marginalizing the total electron–ion wave function with respect to the nuclear equilibrium distribution, and we describe an explicit procedure to establish the band structure of electronic excitations for quantum crystals within the Born–Oppenheimer approximation. Based on the Kubo–Greenwood equation, we discuss the effects of nuclear motion on optical conductivity. Our methodology applies to the low temperature regime where nuclear motion is quantized and, in general, differs from the semi-classical approximation. We apply our method to study the electronic structure of C2/c-24 crystalline hydrogen at 200 K and 250 GPa and discuss the optical absorption profile of hydrogen crystals at 200 K and carbon diamond at 297 K.

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

Local strain-dependent electronic structure and perpendicular magnetic anisotropy of a MnGaN 2D magnetic monolayer

Local strain-dependent spin-polarized electronic structure of a two-dimensional (2D) magnetic layer is an exciting property for practical applications. For example, it holds the promise for advanced ultrathin spintronic nanodevices with customized electronic and magnetic properties by local strain engineering. Here, we demonstrate that the spin-polarized electronic structure of a 2D manganese gallium nitride (MnGaN-2D) magnetic monolayer is sensitive to intrinsic local lattice strain, as proven by first-principles calculations and indicated by scanning tunneling spectroscopy measurements. Atomic resolution images reveal a highly non-Gaussian lattice spacing/strain distribution, while the spectroscopy reveals variations in the electronic density of states. Simulations of the MnGaN-2D monolayer based on first-principles calculations, including both isotropic and anisotropic strains, confirm a highly strain-dependent manganese partial density of states. Spin-orbit coupling is included which indicates either out-of-plane perpendicular magnetic anisotropy (PMA) or in-plane magnetic anisotropy, dependent on the type of strain whether compressive or tensile, suggesting that MnGaN-2D is magnetoelastic. The MnGaN-2D PMA is further supported by superconducting quantum interference device magnetometry measurements which reveal a high spin polarization of ~ 79 % at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Perspective: Explicitly correlated electronic structure theory for complex systems

The explicitly correlated approach is one of the most important breakthroughs in ab initio electronic structure theory, providing arguably the most compact, accurate, and efficient ansatz for describing the correlated motion of electrons. Since Hylleraas first used an explicitly correlated wave function for the He atom in 1929, numerous attempts have been made to tackle the significant challenges involved in constructing practical explicitly correlated methods that are applicable to larger systems. These include identifying suitable mathematical forms of a correlated wave function and an efficient evaluation of many-electron integrals. R12 theory, which employs the resolution of the identity approximation, emerged in 1985, followed by the introduction of novel correlation factors and wave function ansätze, leading to the establishment of F12 theory in the 2000s. Rapid progress in recent years has significantly extended the application range of explicitly correlated theory, offering the potential of an accurate wave-function treatment of complex systems such as photosystems and semiconductors. In conclusion, this perspective surveys explicitly correlated electronic structure theory, with an emphasis on recent stochastic and deterministic approaches that hold significant promise for applications to large and complex systems including solids.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Ab Initio Study of Structural, Electronic, and Magnetic Properties of A{sub 1−x}{sup III}Mn{sub x}B{sup VI}: In{sub 1−x}Mn{sub x}S-Diluted Magnetic Semiconductor

First-principles density functional calculations on the new class of diluted magnetic semiconductor A{sub 1−x}{sup III}Mn{sub x}B{sup VI} In{sub 1−x}Mn{sub x}S for x = 0.25 and 0.5 are investigated to study the structural, electronic, and magnetic properties, employing the full-potential linearized augmented plane wave method. Electronic band structures and density of states revealed a half-metallic character of In{sub 1−x}Mn{sub x}S and show the stability of anti-ferromagnetic states as compared with ferromagnetic states. The calculated exchange constants J{sub dd} are in good agreement with experimental and theoretical results on magnetic properties of single crystalline A{sub 1−x}{sup III}Mn{sub x}B{sup VI} in the anti-ferromagnetic case. Our predicated calculations on the s,p-d exchange constants N{sub 0}α and N{sub 0}β show that they are lower than in A{sub 1−x}{sup II}Mn{sub x}B{sup VI} DMS. The local environment is found tetrahedral as in the II–VI DMS and other (III,Mn) VI compounds. The total magnetic moment for In{sub 1−x}Mn{sub x}S for different concentrations is in accordance with the exact value 5 μ{sub B} and comes mainly from impurity Mn. The local magnetic moments of Mn ions are reduced from their free space charges values due to the p-d hybridization which produces small magnetic moments on the nonmagnetic In and S sites. The Curie temperature of In{sub 1−x}Mn{sub x}S is calculated within the mean field approximation and compared with other DMS systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Electronic structure and pair potential energy analysis of 4-n-methoxy-4′-cyanobiphenyl: A nematic liquid crystal

Electronic structure properties of 4-n-methoxy-4′-cyanobiphenyl, a pure nematic liquid crystal have been examined using an ab‒initio, HF/6‒31G(d,p) technique with GAMESS program. Conformational and charge distribution analysis have been carried out. MEP, HOMO and LUMO surfaces have been scanned. Ionization potential, electron affinity, electronegativity, global hardness and softness of the liquid crystal molecule have been calculated. Further, stacking, side by side and end to end interactions between a molecular pair have been evaluated. Results have been used to elucidate the physico-chemical and liquid crystalline properties of the system.

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

Report on the 35th Annual Workshop on Recent Developments in Electronic Structure Theory

The 35th Annual Workshop on Recent Developments in Electronic Structure Theory was held June 13 – 16, 2023 at the University of California, Merced, a minority-serving institution with R2 status. This workshop series travels to a different institution within the US each year, and this was the first time it was held in the underserved Central Valley of California. The Local Organizers collected suggestions from the international steering committee to put together a list of topics representing recent major developments in the field and speakers.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electronic structure reconstruction across the antiferromagnetic transition in TaFe₁̣₂₃Te₃ spin ladder

With angle-resolved photoemission spectroscopy, we studied the electronic structure of TaFe₁̣₂₃Te₃, a two-leg spin ladder compound with a novel antiferromagnetic ground state. Quasi-two-dimensional Fermi surface is observed, with sizable inter-ladder hopping. Moreover, instead of observing an energy gap at the Fermi surface in the antiferromagnetic state, we observed the shifts of various bands. Combining these observations with density-functional-theory calculations, we propose that the large scale reconstruction of the electronic structure, caused by the interactions between coexisting itinerant electrons and local moments, is most likely the driving force of the magnetic transition. Thus TaFe₁̣₂₃Te₃ serves as a simpler platform that contains similar ingredients as the parent compounds of iron-based superconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Electronic structure of polycrystalline Cd metal using {sup 241}Am radioisotope

Electronic structure study of the polycrystalline cadmium metal is reported. The experimental measurement is undertaken on a polycrystalline sheet sample using 59.54 keV radioisotope of {sup 241}Am. These results are compared with the ab initio calculations. The theoretical calculations are performed using linear combination of atomic orbitals (LCAO) method employing the density functional theories (DFT) and Hartree-Fock (HF) and augmented plane wave (APW) methods. The spherically averaged APW and LCAO based theoretical Compton profiles are in good agreement with the experimental measurement however the APW based theoretical calculations show best agreement.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Surface and electronic structure of epitaxial PtLuSb (001) thin films

The surface and electronic structure of single crystal thin films of PtLuSb (001) grown by molecular beam epitaxy were studied. Scanning tunneling spectroscopy (STS), photoemission spectroscopy, and temperature dependent Hall measurements of PtLuSb thin films are consistent with a zero-gap semiconductor or semi-metal. STS and photoemission measurements show a decrease in density of states approaching the Fermi level for both valence and conduction bands as well as a slight shift of the Fermi level position into the valence band. Temperature dependent Hall measurements also corroborate the Fermi level position by measurement of p-type carriers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Modeling molecule-plasmon interactions using quantized radiation fields within time-dependent electronic structure theory

We present a combined cavity quantum electrodynamics/ab initio electronic structure approach for simulating plasmon-molecule interactions in the time domain. The simple Jaynes-Cummings-type model Hamiltonian typically utilized in such simulations is replaced with one in which the molecular component of the coupled system is treated in a fully ab initio way, resulting in a computationally efficient description of general plasmon-molecule interactions. Mutual polarization effects are easily incorporated within a standard ground-state Hartree-Fock computation, and time-dependent simulations carry the same formal computational scaling as real-time time-dependent Hartree-Fock theory. As a proof of principle, we apply this generalized method to the emergence of a Fano-like resonance in coupled molecule-plasmon systems; this feature is quite sensitive to the nanoparticle-molecule separation and the orientation of the molecule relative to the polarization of the external electric field.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Atomic and electronic structure of exfoliated black phosphorus

Black phosphorus, a layered two-dimensional crystal with tunable electronic properties and high hole mobility, is quickly emerging as a promising candidate for future electronic and photonic devices. Although theoretical studies using ab initio calculations have tried to predict its atomic and electronic structure, uncertainty in its fundamental properties due to a lack of clear experimental evidence continues to stymie our full understanding and application of this novel material. In this work, aberration-corrected scanning transmission electron microscopy and ab initio calculations are used to study the crystal structure of few-layer black phosphorus. Directly interpretable annular dark-field images provide a three-dimensional atomic-resolution view of this layered material in which its stacking order and all three lattice parameters can be unambiguously identified. In addition, electron energy-loss spectroscopy (EELS) is used to measure the conduction band density of states of black phosphorus, which agrees well with the results of density functional theory calculations performed for the experimentally determined crystal. Furthermore, experimental EELS measurements of interband transitions and surface plasmon excitations are also consistent with simulated results. Finally, the effects of oxidation on both the atomic and electronic structure of black phosphorus are analyzed to explain observed device degradation. The transformation of black phosphorus into amorphous PO{sub 3} or H{sub 3}PO{sub 3} during oxidation may ultimately be responsible for the degradation of devices exposed to atmosphere over time.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Electronic Structures of Iron in Oxide Glasses via 1s3p Resonant Inelastic X-ray Scattering

Electronic structures of iron in glasses are essential for unraveling the effect of transition metals on amorphous networks and controlling the electro-optical and transport properties of advanced glasses and amorphous energy-storing materials. The electronic configurations around iron in glasses, however, remain not well understood due to the structural disorders arising from multiple iron species with distinct valence, coordination, and spin states. Here, the first 1s3p resonant inelastic X-ray scattering (RIXS) for oxide glasses identifies hidden electronic configurations for Fe 2+ and Fe 3+ in amorphous networks. The results allow us to quantify the composition-induced evolution of oxygen ligand–field interactions of high-spin Fe 3d states with varying valence and coordination environments in complex glasses. The distinct electronic structures account for the electronic origins of iron-induced changes in the glass properties. The results offer prospects for a simultaneous probing of valence, coordination, and spin states of transition metals in diverse multicomponent oxide glasses and functional amorphous solids via 1s3p RIXS.

Kim, Yong-Hyun [Seoul National Univ. (Korea, Repub↗
DOE OSTI2011

Photoelectron spectroscopy of higher bromine and iodine oxide anions: Electron affinities and electronic structures of BrO2,3 and IO2-4 radicals.

This report details a photoelectron spectroscopy (PES) investigation on electron affinities (EAs) and electronic structures of several atmospherically relevant higher bromine and iodine oxide molecules in the gas phase. PES spectra of BrO{sub 2}{sup -} and IO{sub 2}{sup -} were recorded at 12 K and four photon energies--355 nm/3.496 eV, 266 nm/4.661 eV, 193 nm/6.424 eV, and 157 nm/7.867 eV--while BrO{sub 3}{sup -}, IO{sub 3}{sup -}, and IO{sub 4}{sup -} were studied at 193 and 157 nm only due to their expected high electron binding energies. Spectral features corresponding to transitions from the anion ground state to the ground and excited states of the neutral are unraveled and resolved for each species. For the first time, EAs of these bromine and iodine oxides are experimentally determined (except for IO{sub 2}) to be 2.515 {+-} 0.010 (BrO{sub 2}), 2.575 {+-} 0.010 (IO{sub 2}), 4.60 {+-} 0.05 (BrO{sub 3}), 4.70 {+-} 0.05 (IO{sub 3}), and 6.05 {+-} 0.05 eV (IO{sub 4}). Three low-lying excited states with their respective excitation energies are obtained for BrO{sub 2} [1.69 (A {sup 2}B2), 1.79 (B {sup 2}A{sub 1}), 1.99 eV (C {sup 2}A{sub 2})], BrO{sub 3} [0.7 (A {sup 2}A{sub 2}), 1.6 (B {sup 2}E), 3.1 eV (C {sup 2}E)], and IO{sub 3} [0.60 (A {sup 2}A{sub 2}), 1.20 (B {sup 2}E), {approx}3.0 eV (C {sup 2}E)], whereas six excited states of IO{sub 2} are determined with the respective excitation energies of 1.63 (A {sup 2}B{sub 2}), 1.73 (B {sup 2}A{sub 1}), 1.83 (C {sup 2}A{sub 2}), 4.23 (D {sup 2}A{sub 1}), 4.63 (E {sup 2}B{sub 2}), and 5.23 eV (F {sup 2}B{sub 1}). Periodate possesses a very high electron binding energy. Only one excited state feature with 0.95 eV excitation energy is shown in the 157 nm spectrum. The obtained EAs and low-lying excited state information are compared with available theoretical calculations and discussed with their atmospheric implications.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Electronic structure at coarse-grained resolutions from supervised machine learning

Computational studies aimed at understanding conformationally dependent electronic structure in soft materials require a combination of classical and quantum-mechanical simulations, for which the sampling of conformational space can be particularly demanding. Coarse-grained (CG) models provide a means of accessing relevant time scales, but CG configurations must be back-mapped into atomistic representations to perform quantum-chemical calculations, which is computationally intensive and inconsistent with the spatial resolution of the CG models. A machine learning approach, denoted as artificial neural network electronic coarse graining (ANN-ECG), is presented here in which the conformationally dependent electronic structure of a molecule is mapped directly to CG pseudo-atom configurations. By averaging over decimated degrees of freedom, ANN-ECG accelerates simulations by eliminating backmapping and repeated quantum-chemical calculations. The approach is accurate, consistent with the CG spatial resolution, and can be used to identify computationally optimal CG resolutions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Applications of Nickelate perovskites for neuromorphic computing from electronic structure and Machine Learning

While the limit of Moore's law is presently being reached with current microelectronic technologies, we need to develop new paradigms that overcome this limitation. In that respect, neuromorphic computing is a concept that emulates the neural behavior and response of the human brain, and it has been recognized as a promising alternative approach. In this research project, we will perform multi-fidelity scale bridging to explore the potential use of materials with metal to insulator transition for neuromorphic applications. In particular, rare earth nickelates are promising for such purposes, as the transition in these materials is quite sensitive to a broad set of different external stimuli. Our multi-fidelity approach will bridge the high-fidelity electronic structure calculations with classical potentials. We will bridge dynamical mean field theory with a classical atomistic representation via a deep learning force field. The neural network is trained with energies, charges, and forces obtained by accurate electronic structure theories based on Dynamical Mean Field Theory. The configurational space is generated from known crystal phases, ab initio molecular dynamics with exchange-correlation functionals corrected with the Hubbard model, disordered phases with different concentrations of oxygen vacancies, and nonsymmetrical positions and induced strain by grain interfaces or contact with a substrate. Strategies to train the model with a reduced number of training examples are obtained from active learning methods, and new structures for improving the learning process are generated by using machine learning autoencoders. This classical potential will be validated through a diversity of electronic structure methods and represents an important step to combine the flexibility and accuracy of first-principles with the speed of classical potentials. The generated multi-fidelity surrogate model will be used to understand the role of strain, oxygen vacancies, proton doping, the variation of the crystal phase, substrate effects, vibrational effects as the octahedral rotation, grain boundaries and defect effects on the response of a Metal to Insulator Transition (MIT) in correlated materials. Long time and large-scale simulations will help understand the role of different stimuli to control the hysteresis of the MIT, as it has been experimentally suggested. Selected configurations will be analyzed with higher-level theories to provide an accurate electronic description and to study how the orbitals and charges are rearranged under different conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2015

The electronic structure, mechanical and thermodynamic properties of Mo{sub 2}XB{sub 2} and MoX{sub 2}B{sub 4} (X = Fe, Co, Ni) ternary borides

The mechanical properties, electronic structure and thermodynamic properties of the Mo{sub 2}XB{sub 2} and MoX{sub 2}B{sub 4} (X = Fe, Co, Ni) ternary borides were calculated by first-principles methods. The elastic constants show that these ternary borides are mechanically stable. Formation enthalpy of Mo{sub 2}XB{sub 2} and MoX{sub 2}B{sub 4} (X = Fe, Co, Ni) ternary borides are at the range of −118.09 kJ/mol to −40.14 kJ/mol. The electronic structures and chemical bonding characteristics are analyzed by the density of states. Mo{sub 2}FeB{sub 2} has the largest shear and Young's modulus because of its strong chemical bonding, and the values are 204.3 GPa and 500.3 GPa, respectively. MoCo{sub 2}B{sub 4} shows the lowest degree of anisotropy due to the lack of strong direction in the bonding. The Debye temperature of MoFe{sub 2}B{sub 4} is the largest among the six phases, which means that MoFe{sub 2}B{sub 4} possesses the best thermal conductivity. Enthalpy shows an approximately linear function of the temperature above 300 K. The entropy of these compounds increase rapidly when the temperature is below 450 K. The Gibbs free energy decreases with the increase in temperature. MoCo{sub 2}B{sub 4} has the lowest Gibbs free energy, which indicates the strongest formation ability in Mo{sub 2}XB{sub 2} and MoX{sub 2}B{sub 4} (X = Fe, Co, Ni) ternary borides.

36 MATERIALS SCIENCE↗