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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Discrete discontinuous basis projection method for large-scale electronic structure calculations

We present an approach to accelerate real-space electronic structure methods several fold, without loss of accuracy, by reducing the dimension of the discrete eigenproblem that must be solved. To accomplish this, we construct an efficient, systematically improvable, discontinuous basis spanning the occupied subspace and project the real-space Hamiltonian onto the span. In calculations on a range of systems, we find that accurate energies and forces are obtained with 8–25 basis functions per atom, reducing the dimension of the associated real-space eigenproblems by 1–3 orders of magnitude.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

First-principles calculation of lattice distortion, electronic structure, and bonding properties of GeTe-based and PbSe-based high-entropy chalcogenides

The massive amount of wasted heat energy from industry has pushed the development of thermoelectric (TE) materials that directly convert heat into electricity to a new level of concern. Recently, multicomponent alloys such as GeTe-based and PbSe-based high-entropy (HE) chalcogenides have attracted a great deal of attention due to their potential application as TE materials. The nature of the interatomic bonding, lattice distortion (LD), and the electronic structure in this class of materials is not fully understood. Herein, we report a comprehensive computational investigation of nine GeTe-based HE alloys with eight metallic elements (Ag, Pb, Sb, Bi, Cu, Cd, Mn, and Sn) with large supercells of 1080 atoms each; seven PbSe-based HE solid solutions: Pb0.99−ySb0.012SnySe1−2xTexSx (x = 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, with y = 0) with supercells of 1000 atoms each; and five Pb0.99−ySb0.012SnySe1−2xTexSx (y = 0.05, 0.1, 0.15, 0.2, 0.25 with x = 0.25) solid solutions with supercells of 1000 atoms each. All these HE models are theoretically investigated for the first time. The electronic structure, interatomic bonding, charge transfer, and lattice distortion (LD) are investigated by first-principles calculations based on density functional theory. Multicomponent HE alloys can cause a significant LD, which affects their mechanical, thermal, and TE properties. The calculations for the GeTe-based HE chalcogenides showed that they are semiconductors with a narrow bandgap, except for m8, which has a semi-metallic characteristic, and this makes them good candidates for TE applications. For most of these models, the Fermi level shifts upward and locates deeply in the conduction bands, resulting in the enhancement of the electrical conductivity (σ). The bonding properties showed that most bonds in m5 are more dispersed, indicating highest LD and lower lattice thermal conductivity. For PbSe-based HE solid solutions, the LD calculations showed that the models Pb0.99Sb0.012Se0.5Te0.25S0.25 and Pb0.89Sb0.012Sn0.1Se0.5Te0.25S0.25 have the higher LD, and thus a lower lattice thermal conductivity. Such investigations are in high demand since it enables us to design new HE chalcogenides for TE applications. We use the novel concept of total bond order density as a single quantum mechanical metric to characterize the internal cohesion of these HE alloys and correlate with calculated properties, especially the mechanical properties. This work provides a solid database for HE chalcogenides and a road map for many potential applications. Moreover, the computational procedure we developed can be used to design new HE chalcogenides for specific TE applications.

Physics↗
DOE OSTI2018

Ab Initio Theoretical Prediction of Structural, Electronic, and Magnetic Properties in the 3d (Mn)-Doped Zinc-Blende MgSe: A DFT-mBJ Approach

In this paper, we have investigated the structural, electronic, and magnetic properties of magnesium selenium (MgSe) doped with transition metal manganese (Mn) impurity in the cubic diluted magnetic semiconductor (DMS) zinc blende structure. The compounds which we are interested are as Mg{sub 1−x}Mn{sub x}Se where x change between 0 and 1 by step 0.25. All properties are studied, using first-principles calculation of density functional theory under the framework of the full-potential linearized augmented plane waver (FP-LAPW). In our study, we employed the Wu-Cohen generalized approximation (WC-GGA) to optimize the crystal structure, whereas Tran-Blaha modified Becke-Johnson potential (TB-mBJ) as a new functional was applied to compute the electronic and magnetic properties in order to get some better degree of precision. The electronic band structures and density of state plots reveal ferromagnetic semiconducting behavior in these compounds, and the exchange constants N{sub 0}α and N{sub 0}β are calculated to validate the effects resulting from exchange splitting process. Moreover, for each concentration x, the value of total magnetic moment has been estimated to equal to 5 μ{sub B}. The important magnetic moments values obtained in these compounds indicate the potential for their use in spintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Molecular and Electronic Structure, and Hydrolytic Reactivity of a Samarium(II) Crown Ether Complex

The reaction of SmI 2 with dibenzo-30-crown-10 (DB30C10), followed by metathesis with [Bu 4 N][BPh 4 ], allows for the isolation of [Sm II (DB30C10)][BPh 4 ] 2 as bright-red crystals in good yield. Moreover, exposure of [Sm(DB30C10)] 2+ to solvents containing trace water results in the conversion to the dinuclear Sm III complex, Sm 2 (DB30C10)(OH) 2 I 4 . Structural analysis of both complexes shows substantial rearrangement of the crown ether from a folded, Pac-Man form with Sm II to a twisted conformation with Sm III . The optical properties of [Sm II (DB30C10)][BPh 4 ] 2 exhibit a strong temperature dependence and change from broad-band absorption features indicative of domination by 5d states to fine features characteristic of 4f → 4f transitions at low temperatures. Here, exploration of the electronic structure of these complexes via ab initio wave function calculations (SO-CASSCF) reflects that the ground state of Sm II in [Sm II (DB30C10)] 2+ is a 4f 6 state with low-lying 4f 5 5d 1 states, where the latter states have been lowered in energy by ~12 000 cm –1 with respect to the free ion. The decacoordination of the Sm II cation by the crown ether is responsible for this alteration in the energies of the excited state and demonstrates the ability to tune the electronic structure of Sm II .

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

Electronic structure theory with molecular point group symmetries on quantum annealers

Quantum computation has the potential to revolutionize quantum chemistry through major speedups in computation times and an exponential reduction in computational resources. Here, we combine the symmetry-adapted Jordan–Wigner encoding based on the full Boolean symmetry group $\mathbb{Z}$$^{k}_{2}$ with our new implementation of the Xia–Bian–Kais (XBK) method for improving the efficiency of electronic structure theory calculations on quantum annealers, particularly by reducing the number of qubits needed to achieve the same accuracy. By providing a more extensive symmetry-adapted encoding (SAE) than previous work, we are able to simulate molecules larger than those previously reported that have been studied using methods developed for quantum annealers and without using an active space. We calculated the potential energy surfaces of H 2 , LiH, He 2 , H 2 O, O 2 , N 2 , Li 2 , F 2 , CO, BH 3 , NH 3 , and CH 4 , with the largest molecule in the STO-6G basis set requiring 16 qubits with our SAE, and compared them with full configuration interaction results. The application of SAE to the XBK method provides an exponential reduction in the size of the Hilbert space and scales well with the size of the problem. It does not introduce significant additional errors for even or large values of a key variational parameter that determines the number of ancilla qubits used in the XBK method’s Hamiltonian embedding, or for certain molecules such as He 2 and H 2 O. Here, we provide an explanation for this behavior and a recommendation on the usage of our method. In addition, we briefly discuss the potential of extracting electronic excited states from our method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Electronic structure analysis and DFT benchmarking of Rydberg-type alkali-metal-crown ether, -cryptand, and -adamanzane complexes

Density functional theory (DFT) and electron propagator theory (EPT) calculations were performed to study ground and excited electronic structures of alkali-metal (M) coordinated 9-crown-3, 24-crown-8, [2.1.1]cryptand, o-Me 2 -1.1.1, and 3 6 Adamanzane complexes. Each complex bears an expanded electron in the periphery and occupies diffuse 1p-, 1d-, 1f-type molecular orbitals (or superatomic 1P, 1D, 1F orbitals) in excited electronic states. The calculated superatomic shell model of the M(9-crown-3) 2 is 1S, 1P, 1D, 1F, 2S, 2P, 2D, 1G and it is held by all other complexes up to the studied 1F level. Due to the highly diffuse nature of the electron, the ionization energies of these complexes are significantly lower (1.6–2.0 eV) and hence these complexes belong to the superalkali category. Further, the ab initio EPT ionization energy and the excitation energies of the Li(9-crown-3) 2 were used to evaluate DFT errors associated with a series of exchange correlation functionals that span multiple rungs of Jacob's ladder (i.e., GGA, meta-GGA, global GGA hybrid, meta-GGA hybrid, range-separated hybrid, double-hybrid). Among these, the best performing functional is the range-separated hybrid CAM-B3LYP and the errors are within 6% of high-level ab initio EPT results. The accuracy of CAM-B3LYP is indeed transferable to similar complexes and hence the findings are expected to accelerate the progression of studies of Rydberg-type systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

The Response to a Uniform Electric Field in Calculating the Electronic Structure of Crystals with a Basis of Localized Orbitals

The response to the external uniform electric field is calculated for the electronic structure of crystals using the localized basis functions in the form of pseudo-atomic orbitals. The main equations taking into account corrections for incompleteness and nonorthogonality of the basis, including the expressions for dielectric tensor and dynamic charges, are derived, as well. The proposed approach is discussed by the examples of computations for various types of compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic Structure of Cobaltites ScCo{sub 1 –x}Fe{sub x}O{sub 3} (x = 0, 0.05) and BiCoO{sub 3}: X-Ray Photoelectron Spectroscopy

The electronic structure of the Co{sup 3+} cations in perovskite cobaltites Sc{sub 1 –y}Co{sub 1 –x}Fe{sub x}O{sub 3 – (3/2)y} (x = 0, 0.05; y = 0.1) and BiCoO{sub 3} has been studied by X-ray photoelectron spectroscopy. Our measurements have been made in the energy range 0–1250 eV, which has allowed us to determine the binding energies and to characterize the structure of the spectra for both valence and inner electrons of the cobalt cations in detail. Based on the results obtained, we have analyzed the valence and spin states of the cobalt cations and the structure of their local crystalline environment in the oxides under consideration. The influence of the surface etching of cobaltite samples on the electronic state of cobalt has been studied.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Strain induced electronic structure, and magnetic and structural properties in quaternary Heusler alloys ZrRhTiZ (Z = Al, In)

In this work, electronic structure, and magnetic and structural properties of quaternary Heusler alloys ZrRhTiZ (Z = Al, In) have been analyzed from first principles calculations. The ferromagnetic ground state and thermodynamical stability of these compounds are supported by relative total energies, and by derived formation and cohesive energies, respectively. The investigated Curie temperatures of the compounds exceed room temperature indicating that these compounds are promising candidates for beyond room temperature spintronics and magneto-electronics applications. Both compounds follow the Slater-Pauling 18 electron rule and exhibit half-metallic ferromagnetic behavior with magnetic moments of 2 μB with 100% spin polarization in one spin channel at the Fermi-level. The effect of uniform strain on half-metallicity of these compounds inverts the band gap from one spin channel to another spin channel with a mixed spin (magnetic moment) regime that can be mapped to an exchange bias like effect observed in some of the magnetic Heusler compounds. The half metallic ferromagnetic behavior is retained within –2 to 2% strain contrasting with the anomalous spin flip in –1% and 1% strain in ZrRhTiZ (Z = Al, In).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Theoretical Investigation of Structural, Electronic, Magnetic, and Mechanical Properties of Quaternary Heusler Alloys CoVTiX (X = As, Si)

The structural, electronic, magnetic, and mechanical properties of CoVTiAs and CoVTiSi quaternary Heusler alloys are studied using the full-potential linearized augmented plane-wave (FP-LAPW) method in the framework of the density functional theory (DFT). The generalized gradient approximation (GGA) is chosen for the exchange-correlation energy, whereas the modified Becke-Johnson (mBJ) formalism is applied for the electronic properties. Both CoVTiAs and CoVTiSi are stable in the type 2 (FM) structure. The mechanical properties of CoVTiX (X = As, Si) are predicted from the calculated elastic constants. Results identify that these compounds are mechanically stable. Our results with the mBJ approximation predict that CoVTiAs and CoVTiSi alloys are half-metallic ferromagnets with band gaps of 0.450 and 0.424 eV, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Visualization of Chiral Electronic Structure and Anomalous Optical Response in a Material with Chiral Charge Density Waves

Chiral materials have attracted significant research interests as they exhibit intriguing physical properties, such as chiral optical response, spin-momentum locking, and chiral induced spin selectivity. Recently, layered transition metal dichalcogenide 1T–TaS 2 has been found to host a chiral charge density wave (CDW) order. Nevertheless, the physical consequences of the chiral order, for example, in electronic structures and the optical properties, are yet to be explored. Here, we report the spectroscopic visualization of an emergent chiral electronic band structure in the CDW phase, characterized by windmill-shaped Fermi surfaces. Further, we uncover a remarkable chirality-dependent circularly polarized Raman response due to the salient in-plane chiral symmetry of CDW, although the ordinary circular dichroism vanishes. Chiral Fermi surfaces and anomalous Raman responses coincide with the CDW transition, proving their lattice origin. Our Letter paves a path to manipulate the chiral electronic and optical properties in two-dimensional materials and explore applications in polarization optics and spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Atomic and Electronic Structure of 3C-SiC(111)-(2√3×2√3)-R30° Surface

The theoretical studies and ab initio calculations have been carried out for the first time for atomic and electronic structure of four variants of 3C-SiC(111)-(2√3×2√3)-R30° surface with Si- terminated surface: initial, relaxed, reconstructed, and relaxed after reconstruction. The surface was simulated in the layered superlattice approximation by a system of thin films (slabs) with a thickness of 12 atomic layers separated by vacuum gaps of ~16 Å. In order to close the dangling carbon bonds, the opposite side of the film was complemented with 12 atoms of hydrogen. Ab initio calculations were performed by means of QUANTUM ESPRESSO program based on the density functional theory. It is shown that the reconstruction makes the atomic layers split. Our previous works and experimental data show that these splits are observed at reconstructions of surface (111) in crystals with the sphalerite structure. The band structures of four alternative slabs are calculated and analyzed. Total and layer-by-layer valence electron state densities are calculated for four top layers. It is shown that the real surface has a metallic conductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Paramagnetic electronic structure of CrSBr: Comparison between ab initio G W theory and angle-resolved photoemission spectroscopy

Here, we explore the electronic structure of paramagnetic CrSBr by comparative first-principles calculations and angle-resolved photoemission spectroscopy. We theoretically approximate the paramagnetic phase using a supercell hosting spin configurations with broken long-range order and applying quasiparticle self-consistent GW theory, without and with the inclusion of excitonic vertex corrections to the screened Coulomb interaction (QS GW and QS $G\widehat{W}$, respectively). Comparing the quasiparticle band-structure calculations to angle-resolved photoemission data collected at 200 K results in excellent agreement. This allows us to qualitatively explain the significant broadening of some bands as arising from the broken magnetic long-range order and/or electronic dispersion perpendicular to the quasi-two-dimensional layers of the crystal structure. The experimental band gap at 200 K is found to be at least 1.51 eV at 200 K. At lower temperature, no photoemission data can be collected as a result of charging effects, pointing towards a significantly larger gap, which is consistent with the calculated band gap of approximately 2.1 eV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Growth of PdCoO 2 films with controlled termination by molecular-beam epitaxy and determination of their electronic structure by angle-resolved photoemission spectroscopy

Utilizing the powerful combination of molecular-beam epitaxy (MBE) and angle-resolved photoemission spectroscopy (ARPES), we produce and study the effect of different terminating layers on the electronic structure of the metallic delafossite PdCoO 2 . Attempts to introduce unpaired electrons and synthesize new antiferromagnetic metals akin to the isostructural compound PdCrO 2 have been made by replacing cobalt with iron in PdCoO 2 films grown by MBE. Using ARPES, we observe similar bulk bands in these PdCoO 2 films with Pd-, CoO 2 -, and FeO 2 -termination. Nevertheless, Pd- and CoO 2 -terminated films show a reduced intensity of surface states. Additionally, we are able to epitaxially stabilize PdFe x Co 1– x O 2 films that show an anomaly in the derivative of the electrical resistance with respect to temperature at 20 K, but do not display pronounced magnetic order.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Performance of Heterostructural TaC/AlGaN Schottky Diodes Based on First Principles Electronic Structure Properties

Advances in ultra-wide bandgap materials, such as high Al-content AlxGa1-xN (AlGaN), are essential for next generation power electronics, but the requirement for lattice matched substrates is currently a significant obstacle. Recently, conductive TaC has emerged as a promising virtual substrate for AlGaN heteroepitaxy, with wurtzite (0001) AlxGa1-xN lattice-matched to rocksalt (111) TaC at x ~ 0.5. Thus, understanding and controlling the electronic properties of the TaC/AlGaN interface is key for developing technological applications based on TaC/AlGaN devices. Using density functional theory and electronic structure calculations, we here investigate TaC/Al0.5Ga0.5N interfaces, where we include explicit alloy models in the slab calculations. We predict the Schottky barrier height and the electric field discontinuity resulting from interface charges. Considering all possible combinations of (Ta, C) substrate termination, (Al/Ga, N) nucleation, and (Al/Ga, N) polarity, we construct a chemical potential phase diagram to identify the stable interfaces that can be accessed through variation of the synthesis conditions. The predicted interface electronic properties are implemented in device performance simulations to demonstrate a practical design for a strain-free, high-efficiency TaC/AlGaN Schottky diode with a low barrier height and without interface charges, underscoring the potential of TaC as a substrate for ultra-wide bandgap devices.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Complex Dirac-like Electronic Structure in Atomic Site-Ordered Rh 3 In 3.4 Ge 3.6

We report the synthesis via an indium flux method of a novel single-crystalline compound Rh 3 In 3.4 Ge 3.6 that belongs to the cubic Ir 3 Ge 7 structure type. In Rh 3 In 3.4 Ge 3.6 , the In and Ge atoms preferentially occupy, respectively, the 12d and 16f sites of the Im3¯m space group, thus creating a colored variant of the Ir 3 Ge 7 structure. Like the other compounds of the Ir 3 Ge 7 family, Rh 3 In 3.4 Ge 3.6 shows potential as a thermoelectric, displaying a relatively large power factor, PF ~ 2 mW/cm K 2 , at a temperature T ~ 225 K, albeit showing a modest figure of merit, ZT = 8 x 10 -4 , because of the lack of a finite band gap. These figures might improve through a use of chemical substitution strategies to achieve band gap opening. Remarkably, electronic band structure calculations reveal that this compound displays a complex Dirac-like electronic structure relatively close to the Fermi level. The electronic structure is composed of several Dirac type-I and type-II nodes, and even Dirac type-III nodes that result from the touching between a flat band and a linearly dispersing band. Here, this rich Dirac-like electronic dispersion suggests the possibility to observe experimentally Dirac type-III nodes and study their role in the physical properties of Rh 3 In 3.4 Ge 3.6 and related Ir 3 Ge 7 -type materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Resonant inelastic X-ray scattering determination of the electronic structure of oxyhemoglobin and its model complex

Hemoglobin and myoglobin are oxygen-binding proteins with S = 0 heme {FeO 2 } 8 active sites. The electronic structure of these sites has been the subject of much debate. This study uses Fe K-edge X-ray absorption spectroscopy (XAS) and 1s2p resonant inelastic X-ray scattering (RIXS) to study oxyhemoglobin and a related heme {FeO 2 } 8 model compound, [(pfp)Fe(1-MeIm)(O 2 )] (pfp = meso-tetra(α,α,α,α- o -pivalamido-phenyl)porphyrin, or TpivPP, 1-MeIm = 1-methylimidazole) (pfpO 2 ), which was previously analyzed using L-edge XAS. The K-edge XAS and RIXS data of pfpO 2 and oxyhemoglobin are compared with the data for low-spin Fe II and Fe III [Fe(tpp)(Im) 2 ] 0/+ (tpp = tetra-phenyl porphyrin) compounds, which serve as heme references. The X-ray data demonstrate that pfpO 2 is similar to Fe II , while oxyhemoglobin is qualitatively similar to Fe III , but with significant quantitative differences. Density-functional theory (DFT) calculations show that the cjontrast between pfpO 2 and oxyhemoglobin is due to a distal histidine H bond to O 2 and the less hydrophobic environment in the protein, which lead to more backbonding into the O 2 . A valence bond configuration interaction multiplet model is used to analyze the RIXS data and show that pfpO 2 is dominantly Fe II with 6–8% Fe III character, while oxyhemoglobin has a very mixed wave function that has 50–77% Fe III character and a partially polarized Fe–O 2 π-bond.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗