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At least 289 records · Page 16

All sources NASA NTRS DOE OSTI

DOE OSTI2021

Electronic properties of single-layer CoO 2 /Au(111)

Here we report direct measurements via angle-resolved photoemission spectroscopy (ARPES) of the electronic dispersion of single-layer (SL) CoO 2 . The Fermi contour consists of a large hole pocket centered at the $\overline{\Gamma}$ point. To interpret the ARPES results, we use density functional theory (DFT) in combination with the multi-orbital Gutzwiller Approximation (DFT+GA), basing our calculations on crystalline structure parameters derived from x-ray photoelectron diffraction and low-energy electron diffraction. Our calculations are in good agreement with the measured dispersion. We conclude that the material is a moderately correlated metal. We also discuss substrate effects, and the influence of hydroxylation on the CoO 2 SL electronic structure.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Electron-Ion Dynamics with Time-Dependent Density Functional Theory: Towards Predictive Solar Cell Modeling

This project focussed on two aspects of computational modeling with a view toward application for photovoltaic design: (i) increased reliability of exchange-correlation functionals in time-dependent density functional theory (TDDFT) (a method of choice of the calculation of electronic spectra and dynamics), especially for time-resolved non-perturbative dynamics, and (ii) the development of a practical but rigorously-based method for coupling electronic and nuclear motion via the exact-factorization (EF) approach (a relatively new framework for developing approximations).

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2026

Design Rules for Open-Shell Molecular Wires: Insights from Correlated Many-Body Transport

Open-shell π-conjugated systems have emerged as promising molecular wires that can sustain unusually high low-bias conductance over tens of nanometers. However, predictive design rules remain limited because near-degeneracy and spin polarization give rise to correlated electronic states that are not reliably captured by standard density functional theory and Landauer transport descriptions. Here, we establish physically transparent design rules for long-range, weakly length-dependent charge transport based on the interplay between bond-length alternation and electron–electron interactions. Using a fully correlated transport framework that combines density matrix renormalization group calculations with nonequilibrium Green’s function embedding, we show that weak dimerization maintains spatially extended edge states, while moderate on-site interaction stabilizes open-shell character without excessively separating transport-relevant resonances. This balance yields zero-bias transmission that is largely insensitive to molecular length, providing a route to connect chemically tunable structure to correlated transport beyond mean-field descriptions.

Charge transport↗

DOE OSTI2026

Intertwined charge, spin, and orbital degrees of freedom under electronic correlations in the one-dimensional Fe 3+ chalcogenide chain

Motivated by recent developments in the study of quasi-one-dimensional iron systems with Fe 2+ , we comprehensively study an Fe 3+ chalcogenide chain system. Based on first-principles calculations, the Fe 3+ chain has a similar electronic structure to that discussed before for the Fe 2+ chain, because of the similar Fe⁢𝑋 4 (𝑋 = S or Se) tetrahedron-chain geometry. Furthermore, a three-orbital electronic Hubbard model for this chain was constructed using the density matrix renormalization group method. A robust antiferromagnetic coupling was unveiled in the chain direction. In addition, in the intermediate electronic correlation 𝑈/𝑊 region, we found an interesting orbital-selective Mott phase with the coexistence of localized and itinerant electrons (𝑈 is the on-site Hubbard repulsion, while 𝑊 is the electronic bandwidth) based on the orbital-selective behavior observed in the charge fluctuations. Furthermore, we do not observe any obvious pairing tendency in the Fe 3+ chain in the electronic-correlation 𝑈/𝑊 region, where superconducting pairing tendencies were reported before in iron ladders. This suggests that superconductivity is unlikely to emerge in the Fe 3+ systems. Finally, our results clearly establish the similarities and differences between Fe 2+ and Fe 3+ iron chains, as well as iron ladders.

density matrix renormalization group↗

DOE OSTI2022

Theoretical study of the crystal and electronic properties of α - RuI 3

The material α-RuCl 3 , with a two-dimensional Ru honeycomb sublattice, has attracted considerable attention because it may be a realization of the Kitaev quantum spin liquid. Recently, a new honeycomb material, α-RuCl 3 , was prepared under moderately high pressure, and it is stable under ambient conditions. However, different from α-RuCl 3 , α-RuI 3 was reported to be a paramagnetic metal without long-range magnetic order down to 0.35 K. Here, the structural and electronic properties of the quasi-two-dimensional α-RuI 3 are theoretically studied. First, based on first-principles density functional theory calculations, the ABC stacking honeycomb-layer R$\bar{3}$ (No. 148) structure is found to be the most likely stacking order for α-RuI 3 along the c axis. Furthermore, both R$\bar{3}$ and P$\bar{3}$1c are dynamically stable because no imaginary frequency modes were obtained in the phononic dispersion spectrum without Hubbard U. Moreover, the different physical behavior of α-RuI 3 compared to α-RuCl 3 can be understood naturally. The strong hybridization between Ru 4d and I 5p orbitals decreases the “effective” atomic Hubbard repulsion, leading the electrons of RuI3 to be less localized than in RuCl 3 . As a consequence, the effective electronic correlation is reduced from Cl to I, leading to the metallic nature of α-RuI 3 . Based on the DFT+U (Ueff=2 eV) plus spin-orbital coupling, we obtained a spin-orbit Mott insulating behavior for α-RuCl 3 and, with the same procedure, a metallic behavior for α-RuI 3 , in good agreement with experimental results. Furthermore, when introducing large (unrealistic) U eff =6 eV, the spin-orbit Mott gap opens in α-RuI 3 as well, supporting the physical picture we are proposing. Our results provide guidance to experimentalists and theorists working on two-dimensional transition metal tri-iodide layered materials.

2-dimensional systems↗

DOE OSTI2022

Periodic Trends within Actinyl(VI) Nitrates and Their Structures, Vibrational Spectra, and Electronic Properties

In this work, a series of actinyl(VI) nitrate salts of the form MAnO 2 (NO 3 ) 3 , where M = NH 4 + K + , Rb + , Cs + , and Me 4 N + and AnO 2 2+ = U, Np, Pu, and AnO 2 (NO 3 ) 2 (H 2 O) 2 ·H 2 O, and the uranyl tetranitrates M 2 UO 2 (NO 3 ) 4 have been synthesized from aqueous solution and their structures determined using single-crystal X-ray diffraction. Together, these complexes represent an isostructural series of actinide complexes among the salts crystallized with the same charge-compensating cation and have been studied using vibrational spectroscopy including Raman and Fourier-transform infrared. Periodic trends in both the structural properties of these complexes and their vibrational spectra are presented and discussed, in particular the invariant nature of the O≡An≡O asymmetric stretching frequencies observed across the actinyl series. Electronic structure calculations were performed at a variety of levels of theory to aid in the interpretation of the vibrational data and to correlate trends in the data with the underlying electronic properties of these molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Scaling up the transcorrelated density matrix renormalization group

Explicitly correlated methods, such as the transcorrelated method which shifts a Jastrow or Gutzwiller correlator from the wave function to the Hamiltonian, are designed for high-accuracy calculations of electronic structures, but their application to larger systems has been hampered by the computational cost. We develop improved techniques for the transcorrelated density-matrix renormalization group (DMRG), in which the ground state of the transcorrelated Hamiltonian is represented as a matrix product state (MPS), and demonstrate large-scale calculations of the ground-state energy of the two-dimensional Fermi-Hubbard model. Our developments stem from three technical inventions: (i) constructing matrix product operators (MPOs) of transcorrelated Hamiltonians with low bond dimension and high sparsity, (ii) exploiting the entanglement structure of the ground states to increase the accuracy of the MPS representation, and (iii) optimizing the nonlinear parameter of the Gutzwiller correlator to mitigate the nonvariational nature of the transcorrelated method. Here, we examine systems of size up to 12×12 lattice sites, four times larger than previous transcorrelated DMRG studies, and demonstrate that transcorrelated DMRG yields significant improvements over standard nontranscorrelated DMRG for equivalent computational effort. Transcorrelated DMRG reduces the error of the ground-state energy by 2.4×–14×, with the smallest improvement seen for a small system at half filling and the largest improvement in a dilute closed-shell system.

Density matrix renormalization group↗

DOE OSTI2026

An–imidophosphorane (An = U–Pu) bond covalency and proton-coupled electron transfer thermodynamics driven by orbital energy matching

A series of mid-actinide (An = U–Pu) tetrahomoleptic complexes supported by highly electron-donating imidophosphorane ligands, NPC ([NP t Bu(pyrr) 2 ] − , where t Bu = C(CH 3 ) 3 ; pyrr = pyrrolidinyl = N(C 4 H 8 )), are systematically investigated computationally and experimentally to elucidate the nature of actinide–ligand (An–L) covalency across the An 3+/4+/5+ oxidation states. Trends in An–L bonding and redox properties for these complexes, together with their protonated counterparts, are examined using orbital-, electron density-, and energy-decomposition-based methods. This integrated approach reveals progressively improved energy matching between α-spin An 5f and N im 2p orbitals with increasing atomic number and oxidation state, becoming particularly pronounced in the ligand-dominant π-bonding orbitals of An 4+ and An 5+ . In contrast to the An 3+ species, the enhanced An 5f π contributions in the higher-valent counterparts drive the increase in An–N im covalency for later An, thereby inverting the covalency trend to U < Np < Pu. Redistribution of electron density towards the An and N im atomic basins due to the growing energy-matching assisted covalency correlates with higher pKa values and increased N im –H bond dissociation free energies in protonated An 4+ complexes. Electron density at Nim in An 4+ shows a linear correlation with the p K a values calculated via the Bordwell equation. Calculations predict a cathodic shift of 0.84–1.00 V in the redox couples upon protonation, a trend validated when experimentally accessible. These findings demonstrate an increasing role of covalency driven by orbital energy matching from U to Pu in tuning the thermodynamic driving force for proton-coupled electron transfer in the An 5+ species.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗

DOE OSTI2020

High-resolution infrared spectroscopy of jet cooled CH 2 Br radicals: The symmetric CH stretch manifold and absence of nuclear spin cooling

Direct laser absorption of a slit supersonic discharge expansion provides the first high-resolution spectroscopic results on the symmetric CH stretch excitation (ν 1 ) of the bromomethyl (CH 2 Br) radical in the ground electronic state. Narrowband (<1 MHz) mid-infrared radiation is produced by difference-frequency generation of two visible laser beams, with the open shell halohydrocarbon radical generated by electron dissociative attachment of CH 2 Br 2 in a discharge and rapidly cooled to T rot = 18 ± 1 K in the subsequent slit-jet supersonic expansion. A rovibrational structure in the radical spectrum is fully resolved, as well as additional splittings due to spin-rotation effects and 79 Br/ 81 Br isotopologues in natural abundance. Spectroscopic constants and band origins are determined by fitting the transition frequencies to a non-rigid Watson Hamiltonian, yielding results consistent with a vibrationally averaged planar radical and an unpaired electron in the out-of-plane p π orbital. Additionally, extensive satellite band structure from a vibrational hot band is observed and analyzed. The hot band data is compared to CFOUR/VPT2 (CCSD(T)cc-pVQZ) ab initio anharmonic predictions of the vibration rotation alpha matrix, which permits unambiguous assignment to CH 2 symmetric-stretch excitation built on the singly excited CH 2 out-of-plane bending mode (ν 1 + ν 4 ← ν 4 ). Longitudinal cooling of the Doppler width in the slit-jet expansion geometry also reveals partially resolved hyperfine structure on transitions out of the lowest angular momentum states in excellent agreement with predictions based on microwave studies. High level ab initio MOLPRO calculations [CCSD(T)-f12b/VnZ-f12 (n = 3, 4, CBS)] are also performed with explicitly correlated f12 electron methods for the out-of-plane CH 2 bending mode over the halogen series CH 2 X (X = F, Cl, Br, I), which clearly reveals a non-planar geometry for X = F (with a ΔE ≈ 0.3 kcal/mol barrier) and yet planar equilibrium geometries for X = Cl, Br, and I. Finally, a detailed Boltzmann analysis of the transition intensities provides support for negligible collisional equilibration of the entangled H atom nuclear spin states on the few hundred microsecond time scale and high collision densities of a slit supersonic expansion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS2010

Polarizabilites and Rydberg States in the Presence of a Debye Potential

Polarizabilities and hyperpolarizabilities, alpha(1), beta(1),gamma(1), alpha(2), beta(2),gamma(2), alpha(3), beta(3),gamma(3), delta and epsilon of hydrogenic systems have been calculated by Drachman. We have now calculated these quantities by using pseudostates for the S. P. D and F states. All of them converge very fast as the number of terms in the pseudostates is increased, and are essentially independent of the nonlinear parameters. All the results are in good agreement with the results obtained by Drachman. except for delta, which is of the third-order in perturbation formalism. We have calculated Rydberg states of He for high N and L. The effective potential is -alpha(sub 1)/x(exp 4)+{6 * Beta(sub 1) -alpha(sub 2)/x(exp6), where x is the distance of the outer electron from the nucleus. The exchange and electron-electron correlations are unimportant because the outer electron is far away from the nucleus. This implies that the conventional variational calculations are not necessary. The results agree well with the results of Drachman. We have generalized this approach in the presence of a Debye potential.

Bhatia, A. K.↗

DOE OSTI2025

Interplay of 𝑑- and 𝑝-states in RbTi3⁢Bi5 and CsTi3⁢Bi5 flat-band kagome metals

Shifting the Fermi level of the celebrated 𝐴⁢𝑀3⁢𝑋5 (135) compounds into proximity of flat bands strongly enhances electronic correlations and severely affects the formation of density waves and superconductivity. Our broadband infrared spectroscopy measurements of RbTi3⁢Bi5 and CsTi3⁢Bi5 combined with density-functional band-structure calculations reveal that the correlated Ti 𝑑-states are intricately coupled with the Bi 𝑝-states that form a tilted Dirac crossing. Electron-phonon coupling manifests itself in the strong damping of itinerant carriers and in the anomalous shape of the phonon line in RbTi3⁢Bi5. An anomaly in these spectral features around 150 K can be paralleled to the onset of nematicity detected by low-temperature probes. Our findings show that the materials with low band filling open unexplored directions in the physics of kagome metals and involve electronic states of different nature strongly coupled with lattice dynamics.

Wenzel, Matthew [ORNL]↗

NASA NTRS1992

Theoretical study of metal ions bound to He, Ne, and Ar

Accurate ab initio calculations for all of the first-row transition-metal ions with He, Ne, and Ar were performed at the modified coupled-pair functional level of electron correlation treatment. It is concluded that there is a strong correlation between the binding energy and bond length, since the bonding is predominantly electrostatic. The calculated binding energies are found to be about 20 pct less than the experimental values due to the theoretical limitations.

Partridge, Harry↗

NASA NTRS2018

Hybrid Theory of Scattering and Its Applications

A number of formulations have been used to investigate scattering of low-energy electrons and positrons from various targets. The hybrid theory of scattering, which takes into account the short-range correlations, and is variationally correct, is described in this article. This approach has been applied to calculate phase shifts for scattering of electrons and positrons, resonances in two-electron systems, photo detachment, and photoionization of two-electron systems. This approach has also been applied to calculate excitation of 2s state of atomic hydrogen by electron impact. In photo absorption the target can be left in 2p state instead of 1s state, resulting in the emission of Lyman-alpha radiation. Cross sections for this process are also calculated.

Bhatia, Anand K.↗

DOE OSTI2020

Understanding the origin of magneto-crystalline anisotropy in pure and Fe/Si substituted SmCo 5

In this paper, we report magneto-crystalline anisotropy of pure and Fe/Si substituted SmCo5. The calculations were performed using the advanced density functional theory (DFT) including onsite electron-electron correlation and spin-orbit coupling. Si substitution substantially reduces both the uniaxial magnetic anisotropy and the magnetic moment. Fe substitution with the selective site, on the other hand, enhances the magnetic moment with a limited chemical stability. The magnetic hardness of the SmCo5 is governed by the Sm 4f localized orbital contribution. The 4f density of states (DOS) becomes flat and split with the substitution of Co (2c) with Si/Fe atoms, except with the Fe substitution at 3 g sites. It is also confirmed that Si substitution favors the thermodynamic stability on contrary to the diminished magnetic and anisotropic effects in SmCo5 at either sites.

36 MATERIALS SCIENCE↗

DOE OSTI2025

The Reaction Rates of Amidogen and Ammonia with Nitrous Oxide: Implications for Combustion Mechanisms

Pulsed laser photolysis experiments with laser-induced fluorescence detection of NH 2 set an upper limit to the rate constant for reaction with N 2 O of k < 1 × 10 −15 cm 3 molecule −1 s −1 at 513 K. Computations were based on geometries and anharmonic frequency analysis (B2PLYP-D3/cc-pVTZ) followed by coupled cluster calculations extrapolated to the infinite basis set limit, with corrections for core−valence electron correlation, scalar relativistic effects, and correlation up to CCSDT(Q). Species that showed multireference character were quantified with MRCI(7,7)+Q/cc-pVTZ theory. Rate constants were obtained for the dominant product channel H 2 NN + NO, along with HN 3 + OH, H 2 NO + N 2 , NNH + HNO, ON(NH) 2 and HNNH + NO. The last channel is slow even at 2500 K, contrary to an early empirical estimate and confirming recent suggestions. Modeling of literature experiments on oxidation of NH 3 by N 2 O shows that all channels are too slow to make a significant impact on the loss of N 2 O in ammonia flames. Similarly, the direct NH 3 + N 2 O reaction is found to be negligibly slow.

Ammonia↗

NASA NTRSDate not supplied

Ab Initio Electronic Structure Calculations of CNN for CN Excitation Studies

The CN molecule is an important contributor to radiative heat flux in shock layers around vehicles entering Titan’s atmosphere. Current data for heavy particle (de)excitation rate coefficients of CN leads to uncertainties in the population of CN in its first and second excited states. This in turn leads to uncertainties in the radiative heat flux predicted by Computational Fluid Dynamics (CFD) simulations of Titan atmospheric entry. This work performs ab initio electronic structure calculations of the CNN complex to create Potential Energy Surfaces (PESs) that correlate to the ground and first and second excited states of CN. Specifically, the state combinations of CN(X,A,B) + N(4S𝑜) correlate to six states of CNN (three Quintet A” and three Triplet A”). Initial calculations of these states suggest that heavy particle (de)excitation of CN by N atoms is likely to proceed through collinear geometries on triplet surfaces. Complete PESs will show all of the reaction pathways in detail, and will be used in nonadiabatic dynamics calculations to evaluate improved rate coefficients and reduce uncertainty in the radiative heat flux during Titan entry.

Eric C Geistfeld↗

NASA NTRSDate not supplied

Ab Initio Electronic Structure Calculations of CNN for CN Excitation Studies

Eric Geistfeld↗

DOE OSTI2025

Analysis of correlations between intrinsic ductility and electronic density of states in refractory alloys

High entropy alloys (HEAs) correspond to a new and emerging class of materials that allows us to explore a large composition space to tune mechanical strength and thermal stability. Therefore, to design better alloys, it is important to scan the high-dimensional space of chemistry, composition and temperature. Here, to facilitate this search, we present a method to screen intrinsically ductile body centered cubic (BCC) refractory alloys from electronic structure calculations by using the density of states (DOS) at the Fermi level, g(μ F ). This correlation between intrinsic ductility and g(μ F ) is tested by analyzing group V (V, Nb, Ta) and VI (Mo, W) refractory metals, binary alloys, such as W-Nb, W-V, Mo-Nb and Mo-V, and refractory alloys for which experimental stress-strain measurements are available. In addition, we perform a high-throughput exploration of the entire composition space of a recently proposed alloy system, CrMoNbV, and identify compositions that exhibit high intrinsic ductility.

36 MATERIALS SCIENCE↗