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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Research Update: Spatially resolved mapping of electronic structure on atomic level by multivariate statistical analysis

Atomic level spatial variability of electronic structure in Fe-based superconductor FeTe0.55Se0.45 (Tc = 15 K) is explored using current-imaging tunneling-spectroscopy. Multivariate statistical analysis of the data differentiates regions of dissimilar electronic behavior that can be identified with the segregation of chalcogen atoms, as well as boundaries between terminations and near neighbor interactions. Subsequent clustering analysis allows identification of the spatial localization of these dissimilar regions. Similar statistical analysis of modeled calculated density of states of chemically inhomogeneous FeTe1 x Sex structures further confirms that the two types of chalcogens, i.e., Te and Se, can be identified by their electronic signature and differentiated by their local chemical environment. This approach allows detailed chemical discrimination of the scanning tunneling microscopy data including separation of atomic identities, proximity, and local configuration effects and can be universally applicable to chemically and electronically inhomogeneous surfaces.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

A first-principles density functional theory study of the electronic structural and thermodynamic properties of M2ZrO3 and M2CO3 (M=Na, K) and their capabilities for CO2 capture

Alkali metal zirconates could be used as solid sorbents for CO{sub 2} capture. The structural, electronic, and phonon properties of Na{sub 2}ZrO{sub 3}, K{sub 2}ZrO{sub 3}, Na{sub 2}CO{sub 3}, and K{sub 2}CO{sub 3} are investigated by combining the density functional theory with lattice phonon dynamics. The thermodynamics of CO{sub 2} absorption/desorption reactions of these two zirconates are analyzed. The calculated results show that their optimized structures are in a good agreement with experimental measurements. The calculated band gaps are 4.339 eV (indirect), 3.641 eV (direct), 3.935 eV (indirect), and 3.697 eV (direct) for Na{sub 2}ZrO{sub 3}, K{sub 2}ZrO{sub 3}, Na{sub 2}CO{sub 3}, and K{sub 2}CO{sub 3}, respectively.The calculated phonon dispersions and phonon density of states for M{sub 2}ZrO{sub 3} and M{sub 2}CO{sub 3} (M = K, Na, Li) revealed that from K to Na to Li, their frequency peaks are shifted to high frequencies due to the molecular weight decreased from K to Li. From the calculated reaction heats and relationships of free energy change versus temperatures and CO{sub 2} pressures of the M{sub 2}ZrO{sub 3} (M = K, Na, Li) reacting with CO{sub 2}, we found that the performance of Na{sub 2}ZrO{sub 3} capturing CO{sub 2} is similar to that of Li{sub 2}ZrO{sub 3} and is better than that of K{sub 2}ZrO{sub 3}. Therefore, Na{sub 2}ZrO{sub 3} and Li{sub 2}ZrO{sub 3} are good candidates of high temperature CO{sub 2} sorbents and could be used for post combustion CO{sub 2} capture technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Compositional effects on the electronic structure of ZnSe 1-x S x ternary quantum dots

Here, we report first-principles density functional theory calculations of the electronic structure of ZnSe 1-x S x ternary quantum dots (TQDs) and the impact of composition and compositional distribution on the electron density distribution, electronic density of states, and band gap. We find that the band gaps for ZnSe/ZnS core/shell TQDs are nearly independent of the number of S atoms in the shell, whereas the presence of S in the core of alloyed TQDs modifies the electronic energy levels significantly. Finally, our results imply that distribution of S atoms can be used to achieve quantum confinement in different regions of the TQDs.

charge transport↗
DOE OSTI2016

Ab initio Modeling of the Electronic Structures and Physical Properties of a‐Si 1− x Ge x O 2 Glass ( x = 0 to 1)

The amorphous silica (a‐SiO 2 ) and germania (a‐GeO 2 ) have a wide range of applications in glass industry. Based on a previously constructed near‐perfect continuous random network model with 1296 atoms and periodic boundary conditions, we extend our study to amorphous Si 1− x G e x O 2 models of homogeneous random substitution of Si by Ge with x ranging from 0 to 1. We have calculated the structural, electronic, mechanical, and optical properties for the series by using the first‐principles density functional theory methods. The x ‐dependence of the variations in the properties is analyzed and critically compared with available experimental data. The mass density, volume, total bond order density, bulk mechanical properties, and refractive index are found to vary linearly as a function of x . For x = 0.5, we have also constructed six different kinds of particle immersion models to test the effect of inclusion of spherical particles of one glass of different sizes in the medium of the other glass on their physical properties. It is shown that particle sizes do affect the properties of particle immersion. Our calculations provide deep insight on the properties of mixture and nanocomposites of a‐SiO 2 and a‐GeO 2 glasses.

Baral, Khagendra↗
DOE OSTI2018

Occupation probabilities as variables in electronic structure theory: cooper pairing, OP-NSOFT-Cs,t, and the homogeneous electron liquid

The energy functional of a novel electronic structure theory, OP-NSOFT, has as variables the natural spin orbitals (NSO) of the trial function and their joint occupation probabilities in the search for the ground state energy. When occupancy is restricted to the spin-paired NSOs of DOCI, the resulting theory, OP-NSOFT-0, scales as M 3 , with M the size of the one-electron basis set. Accurate results were obtained for small molecules, particularly near dissociation where single reference theories like DFT are inaccurate. The homogeneous electron liquid (HEL) could serve as a test bed of OP-NSOFT for condensed systems, but OP-NSOFT-0 reduces to the Hartree–Fock approximation for the HEL. Cooper pairing is introduced instead, both singlet pairing, OP-NOFT-Cs, and fully polarized triplet pairing, OP-NSOFT-Ct. The former yields 1/3 of the diffusion-Monte-Carlo correlation energy, the latter 1/2 to 1/3 with decreasing electron density for r s values between 1 and 10. Both yield the discontinuity in the single-particle occupation number required by the Luttinger theorem. Furthermore, two-state joint occupation probabilities illustrate the importance of electron–electron small-angle scattering in establishing electron correlation in the unpolarized HEL.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Electronic structure of the primary electron donor of Blastochloris viridis heterodimer mutants : high field EPR study.

High-field electron paramagnetic resonance (HF EPR) has been employed to investigate the primary electron donor electronic structure of Blastochloris viridis heterodimer mutant reaction centers (RCs). In these mutants the amino acid substitution His(M200)Leu or His(L173)Leu eliminates a ligand to the primary electron donor, resulting in the loss of a magnesium in one of the constituent bacteriochlorophylls (BChl). Thus, the native BChl/BChl homodimer primary donor is converted into a BChl/bacteriopheophytin (BPhe) heterodimer. The heterodimer primary donor radical in chemically oxidized RCs exhibits a broadened EPR line indicating a highly asymmetric distribution of the unpaired electron over both dimer constituents. Observed triplet state EPR signals confirm localization of the excitation on the BChl half of the heterodimer primary donor. Theoretical simulation of the triplet EPR lineshapes clearly shows that, in the case of mutants, triplet states are formed by an intersystem crossing mechanism in contrast to the radical pair mechanism in wild type RCs. Photooxidation of the mutant RCs results in formation of a BPhe anion radical within the heterodimer pair. The accumulation of an intradimer BPhe anion is caused by the substantial loss of interaction between constituents of the heterodimer primary donor along with an increase in the reduction potential of the heterodimer primary donor D/D{sup +} couple. This allows oxidation of the cytochrome even at cryogenic temperatures and reduction of each constituent of the heterodimer primary donor individually. Despite a low yield of primary donor radicals, the enhancement of the semiquinone-iron pair EPR signals in these mutants indicates the presence of kinetically viable electron donors.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Nuclear Magnetic Resonance Measurements and Electronic Structure of Pu(IV) in [(Me)4N]2PuCl6

The synthesis, electronic structure, and characterization via single crystal X-ray diffraction, nuclear magnetic resonance (NMR) spectroscopy, and magnetic susceptibility of (Me4N)2PuCl6 are reported. NMR measurements were performed to both search for the direct 239Pu resonance and to obtain local magnetic and electronic information at the Cl site through 35Cl and 37Cl spectra. No signature of 239Pu NMR was observed. The temperature dependence of the Cl spectra was simulated by diagonalizing the Zeeman and quadrupolar Hamiltonians for 35Cl, 37Cl and 14N isotopes. Electronic structure calculations predict a magnetic ?5 triplet ground state of Pu(IV) in the crystalline electric field of the undistorted PuCl6 octahedron. A tetragonal distortion would result in a very small splitting (20 cm-1) of the triplet ground state into a nonmagnetic singlet and a doublet state. The Cl shifts have an inflection point at T = 15 K, differing from the bulk susceptibility, indicating a nonmagnetic crystal field ground state. The Cl spin-lattice relaxation time is constant down to T = 15 K, below which it rapidly increases, also supporting the nonmagnetic crystal field ground state.

Mounce, Andrew M.↗
DOE OSTI2018

Extended Electronic Structure Inhomogeneity Created by Double Chain Layer Defects Surrounding Columnar Tracks in Heavy-Ion Irradiated YBa{sub 2}Cu{sub 3}O{sub 7-{delta}}.

In YBa2Cu3O7-delta (YBCO), heavy-ion irradiation creates continuous amorphous tracks that are highly effective for vortex pinning. However, the electronic structure landscape of defects and consequently their vortex pinning roles are unclear. Here, we show double chain layer (DCL) defects which intersect the columnar tracks are additionally produced by high energy Pb ion irradiation in YBCO. The DCL defects are similar to 29 nm long, about three times the columnar defect diameter. The electronic structures of the DCL and columnar track defects were determined using atomic-resolution scanning transmission electron microscopy (STEM) and high resolution electron energy loss spectroscopy (EELS). Results show a decrease in the oxygen and copper content at the interface between the track and the YBCO matrix, resulting in interfacial strain. For the DCL defects, the STEM/EELS study revealed a localized electron doped CuO2 plane next to the DCL defect. The DCL defects thus further extend the electronic inhomogeneity into YBCO.

critical current↗
DOE OSTI2016

Influence of Copper Oxidation State on the Bonding and Electronic Structure of Cobalt-Copper Complexes

Heterobimetallic complexes that pair cobalt and copper were synthesized and characterized by a suite of physical methods, including X-ray diffraction, X-ray anomalous scattering, cyclic voltammetry, magnetometry, electronic absorption spectroscopy, electron paramagnetic resonance, and quantum chemical methods. Both Cu(II) and Cu(I) reagents were independently added to a Co(II) metalloligand to provide (py 3 tren)CoCuCl (1-Cl) and (py 3 tren)CoCu(CH 3 CN) (2-CH 3 CN), respectively, where py3tren is the triply deprotonated form of N,N,N-tris(2-(2-pyridylamino)ethyl)amine. Complex 2-CH 3 CN can lose the acetonitrile ligand to generate a coordination polymer consistent with the formula “(py3tren)CoCu” (2). One-electron chemical oxidation of 2-CH 3 CN with AgOTf generated (py 3 tren)CoCuOTf (1-OTf). The Cu(II)/Cu(I) redox couple for 1-OTf and 2-CH 3 CN is reversible at -0.56 and -0.33 V vs Fc + /Fc, respectively. The copper oxidation state impacts the electronic structure of the heterobimetallic core, as well as the nature of the Co–Cu interaction. Quantum chemical calculations showed modest electron delocalization in the (CoCu) +4 state via a Co–Cu σ bond that is weakened by partial population of the Co–Cu σ antibonding orbital. By contrast, no covalent Co–Cu bonding is predicted for the (CoCu) +3 analogue, and the d-electrons are fully localized at individual metals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

GPU implementation of the linear scaling three dimensional fragment method for large scale electronic structure calculations

LS3DF, namely linear scaling three-dimensional fragment method, is an efficient linear scaling ab initio total energy electronic structure calculation code based on a divide-and-conquer strategy. In this paper, we present our GPU implementation of the LS3DF code. Our test results show that the GPU code can calculate systems with about ten thousand atoms fully self-consistently in the order of 10 min using thousands of computing nodes. This makes the electronic structure calculations of 10,000-atom nanosystems routine work. This speed is 4.5–6 times faster than the CPU calculations using the same number of nodes on the Titan machine in the Oak Ridge leadership computing facility (OLCF). Such speedup is achieved by (a) carefully re-designing of the computationally heavy kernels; (b) redesign of the communication pattern for heterogeneous supercomputers.

Computer Science↗
DOE OSTI2015

Physical properties and electronic structure of a new barium titanate suboxide Ba{sub 1+δ}Ti{sub 13−δ}O{sub 12} (δ = 0.11)

The structure, transport, thermodynamic properties, x-ray absorption spectra (XAS), and electronic structure of a new barium titanate suboxide, Ba{sub 1+δ}Ti{sub 13−δ}O{sub 12} (δ = 0.11), are reported. It is a paramagnetic poor metal with hole carriers dominating the transport. Fermi liquid behavior appears at low temperature. The oxidization state of Ti obtained by the XAS is consistent with the metallic Ti{sup 2+} state. Local density approximation band structure calculations reveal the material is near the Van Hove singularity. The pseudogap behavior in the Ti-d band and the strong hybridization between the Ti-d and O-p orbitals reflect the characteristics of the building blocks of the Ti{sub 13} semi-cluster and the TiO{sub 4} quasi-squares, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Occupied and unoccupied electronic structure of Na doped MoS{sub 2}(0001)

The influence of sodium on the band structure of MoS{sub 2}(0001) and the comparison of the experimental band dispersion with density functional theory show excellent agreement for the occupied states (angle-resolved photoemission) and qualitative agreement for the unoccupied states (inverse photoemission spectroscopy). Na-adsorption leads to charge transfer to the MoS{sub 2} surface causing an effect similar to n-type doping of a semiconductor. The MoS{sub 2} occupied valence band structure shifts rigidly to greater binding with little change in the occupied state dispersion. Likewise, the unoccupied states shift downward, approaching the Fermi level, yet the amount of the shift for the unoccupied states is greater than that of the occupied states, effectively causing a narrowing of the MoS{sub 2} bandgap.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Ab initio GGA+U investigations of the structural, electronic, and magnetic properties of Cd 1-x Mn x Te alloy

The structural, electronic and magnetic properties of Cd 1-x Mn x Te alloy in the zinc-blende (ZB) phase within the framework of spin-polarized density functional theory using the generalized gradient approximation (GGA) are studied. In particular, we employ GGA+U SIC method that gives a better description of systems with strong Coulomb correlations of the d-electrons. First, we discuss implementation of GGA+U method to the ground state calculations of pure CdTe and ferromagnetic MnTe. The alloy is modelled at some selected compositions by ordered structures described in terms of periodically repeated supercells for the compositions x = 0.25, 0.5, and 0.75. The compositional dependence of the lattice constant, electronic band structure and partial densities of states of ferromagnetic Cd 1-x Mn x Te alloy are studied. We estimate the spin-exchange splitting energies produced by the Mn 3d-states and determine the exchange constants for the conduction and valence bands of the alloy. The energy positions of the occupied and unoccupied Mn 3d-bands in the electronic structure of ferromagnetic Cd 1-x Mn x Te alloy are also presented. Our calculations using GGA+U SIC approach agree well with the available experimental data and other calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Momentum-space electronic structures and charge orders of the high-temperature superconductors Ca 2-x Na x CuO₂Cl₂ and Bi₂Sr₂CaCu₂O 8+δ

We study the electronic structure of Ca 2-x Na x CuO₂Cl₂ and Bi₂Sr₂CaCu₂O 8+δ samples in a wide range of doping, using angle-resolved photoemission spectroscopy, with emphasis on the Fermi surface (FS) in the near antinodal region. The “nesting wave vector,” i.e., the wave vector that connects two nearly flat pieces of the FS in the antinodal region, reveals a universal monotonic decrease in magnitude as a function of doping. Comparing our results to the charge order recently observed by scanning tunneling spectroscopy (STS), we conclude that the FS nesting and the charge order pattern seen in STS do not have a direct relationship. Therefore, the charge order likely arises due to strong-correlation physics rather than FS nesting physics

Meng, Jian-Qiao↗
NASA NTRS1986

Analysis of boron carbides' electronic structure

The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

Howard, Iris A.↗