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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

A new generation of effective core potentials from correlated and spin–orbit calculations: Selected heavy elements

We introduce new correlation consistent effective core potentials (ccECPs) for the elements I, Te, Bi, Ag, Au, Pd, Ir, Mo, and W with 4d, 5d, 6s, and 6p valence spaces. These ccECPs are given as a sum of spin-orbit averaged relativistic effective potential (AREP) and effective spin–orbit (SO) terms. The construction involves several steps with increasing refinements from more simple to fully correlated methods. The optimizations are carried out with objective functions that include weighted many-body atomic spectra, norm-conservation criteria, and SO splittings. Transferability tests involve molecular binding curves of corresponding hydride and oxide dimers. The constructed ccECPs are systematically better and in a few cases on par with previous effective core potential (ECP) tables on all tested criteria and provide a significant increase in accuracy for valence-only calculations with these elements. Our study confirms the importance of the AREP part in determining the overall quality of the ECP even in the presence of sizable spin–orbit effects. The subsequent quantum Monte Carlo calculations point out the importance of accurate trial wave functions that, in some cases (mid-series transition elements), require treatment well beyond a single-reference.

Wang, Guangming (ORCID:0000000231327925)↗
DOE OSTI2022

Composite Correlated Molecular Orbital Theory Calculations of Ring Strain for Use in Predicting Polymerization Reactions

Strained ring systems play an important role in synthesis and can be characterized by the ring strain energy (RSE). The RSE of 3, 4, 5, and 6 membered saturated and unsaturated ring systems containing N, O, P, and S heteroatoms and H, F, SiMe 3 , and SO 2 Me substituents were calculated at the G3(MP2) composite correlated molecular orbital theory level using up to 5 models to predict the RSE. Generally, the RSE decreased as ring size increased with a substantial decrease from 4 to 5 membered rings. Replacement of a ring CH 2 with P or S reduced the RSE, consistent with less angle strain. The RSE for unsaturated systems were generally greater than for saturated systems due to increased angle strain. No general trends were found with respect to substituent effects. In conclusion, the RSE values suggest that 3-pyrroline and 2-pyrroline and their derivatives may be able to support ring opening metathesis polymerization and warrant further study.

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

General framework for calculating spin–orbit couplings using spinless one-particle density matrices: Theory and application to the equation-of-motion coupled-cluster wave functions

Standard implementations of nonrelativistic excited-state calculations compute only one component of spin multiplets (i.e., Ms = 0 triplets); however, matrix elements for all components are necessary for deriving spin-dependent experimental observables. Wigner–Eckart’s theorem allows one to circumvent explicit calculations of all multiplet components. We generate all other spin–orbit matrix elements by applying Wigner–Eckart’s theorem to a reduced one-particle transition density matrix computed for a single multiplet component. In addition to computational efficiency, this approach also resolves the phase issue arising within Born–Oppenheimer’s separation of nuclear and electronic degrees of freedom. A general formalism and its application to the calculation of spin–orbit couplings using equation-of-motion coupled-cluster wave functions are presented. The two-electron contributions are included via the mean-field spin–orbit treatment. Intrinsic issues of constructing spin–orbit mean-field operators for open-shell references are discussed, and a resolution is proposed. The method is benchmarked by using several radicals and diradicals. The merits of the approach are illustrated by a calculation of the barrier for spin inversion in a high-spin tris(pyrrolylmethyl)amine Fe(II) complex.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Isolation and Study of Ruthenium–Cobalt Oxo Cubanes Bearing a High-Valent, Terminal Ru V –Oxo with Significant Oxyl Radical Character

High-valent Ru V -oxo intermediates have long been proposed in catalytic oxidation chemistry, but investigations into their electronic and chemical properties have been limited due to their reactive nature and rarity. The incorporation of Ru into the [Co 3 O 4 ] subcluster via the single-step assembly reaction of Co II (OAc) 2 (H 2 O) 4 (OAc = acetate), perruthenate (RuO 4 - ), and pyridine (py) yielded an unprecedented Ru(O)Co 3 (μ 3 -O) 4 (OAc) 4 (py) 3 cubane featuring an isolable, yet reactive, RuV-oxo moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [Ru V (S = 1/2)Co III 3(S = 0)O 4 ] configuration and non-negligible covalency in the cubane core. Significant oxyl radical character in the Ru V -oxo unit is experimentally demonstrated by radical coupling reactions between the oxo cubane and both 2,4,6-tri-tert-butylphenoxyl and trityl radicals. The oxo cubane oxidizes organic substrates and, notably, reacts with water to form an isolable μ-oxo bis-cubane complex [(py) 3 (OAc) 4 Co 3 (μ 3 -O) 4 Ru]-O-[RuCo 3 (μ 3 -O) 4 (OAc) 4 (py) 3 ]. Redox activity of the Ru V -oxo fragment is easily tuned by the electron-donating ability of the distal pyridyl ligand set at the Co sites demonstrating strong electronic communication throughout the entire cubane cluster. Natural bond orbital calculations reveal cooperative orbital interactions of the [Co 3 O 4 ] unit in supporting the Ru V -oxo moiety via a strong π-electron donation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Orbital-resolved calculations of two-center interferences in linear triatomic molecules

In this report we perform ab initio calculations of high-harmonic spectroscopy (HHS) of two-center interference phenomena in oriented carbon-dichalcogen molecules, using time-dependent density functional theory (TDDFT). We show that by resolving the harmonic response into contributions from individual Kohn-Sham orbitals, we can extract target-specific characteristics for both the spectral amplitude and phase. We also discuss that this extraction is predicated on a careful analysis and normalization of the harmonic spectrum. Finally, we present field-free scattering calculations that mimic the recollision step in high-order-harmonic generation and allow the calculation of recombination dipole matrix elements without explicitly calculating the scattering states of a molecule. We show that the orbital-resolved TDDFT HHS results and results based on our field-free scattering calculations are in very good agreement with each other.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

The Separation and Hα Contrasts of Massive Accreting Planets in the Gaps of Transitional Disks: Predicted Hα Protoplanet Yields for Adaptive Optics Surveys

We present a massive accreting gap planet model that ensures large gaps in transitional disks are kept dust free by the scattering action of three coplanar quasi-circular planets in a 1:2:4 mean motion resonance (MMR). This model uses the constraint of the observed gap size, and the dust-free nature of the gap, to determine within ∼10% the possible orbits for three massive planets in an MMR. Calculated orbits are consistent with the observed orbits and Hα emission (the brightest line to observe these planets) for LkCa 15 b, PDS 70 b, and PDS 70 c within observational errors. Moreover, the model suggests that the scarcity of detected Hα planets is likely a selection effect of the current limitations of non-coronagraphic, low (<10%) Strehl, Hα imaging with adaptive optics (AO) systems used in past Hα surveys. We predict that as higher Strehl AO systems (with high-performance custom coronagraphs; like the 6.5 m Magellan Telescope MagAO-X system) are utilized at Hα, the number of detected gap planets will substantially increase by more than tenfold. For example, we show that >25 ± 5 new Hα “gap planets” are potentially discoverable by a survey of the best 19 transitional disks with MagAO-X. Detections of these accreting protoplanets will significantly improve our understanding of planet formation, planet growth and accretion, solar system architectures, and planet–disk interactions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Chemical Bonding Governs Complex Magnetism in MnPt 5 P

Subtle changes in chemical bonds may result in dramatic revolutions in magnetic properties in solid-state materials. MnPt 5 P, a derivative of the rare-earth-free ferromagnetic MnPt 5 As, was discovered and is presented in this work. Specifically, MnPt 5 P was synthesized, and its crystal structure and chemical composition were characterized by X-ray diffraction as well as energy-dispersive X-ray spectroscopy. Accordingly, MnPt 5 P crystallizes in the layered tetragonal structure with the space group P4/mmm (No. 123), in which the face-shared Mn@Pt 12 polyhedral layers are separated by P layers. In contrast to the ferromagnetism observed in MnPt 5 As, the magnetic properties measurements on MnPt 5 P show antiferromagnetic ordering occurs at ~188 K with a strong magnetic anisotropy in and out of the ab-plane. Moreover, a spin-flop transition appears when a high magnetic field is applied. An A-type antiferromagnetic structure was obtained from the analysis of powder neutron diffraction (PND) patterns collected at 150 and 9 K. Calculated electronic structures imply that hybridization of Mn-3d and Pt-5d orbitals is critical for both the structural stability and observed magnetic properties. Semiempirical molecular orbitals calculations on both MnPt 5 P and MnPt 5 As indicate that the lack of 4p character on the P atoms at the highest occupied molecular orbital (HOMO) in MnPt 5 P may cause the different magnetic behavior in MnPt 5 P compared to MnPt 5 As. The discovery of MnPt 5 P, along with our previously reported MnPt5As, parametrizes the end points of a tunable system to study the chemical bonding which tunes the magnetic ordering from ferromagnetism to antiferromagnetism with the strong spin–orbit coupling (SOC) effect.

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

An under-approximation of entropy for elemental multiconfigurational ground state electronic structures

A combinatorial approach has been applied to the allowable permutations of quantum electronic configurations under the constraints of Hund's rule for established ground state configurations toward an under-approximation of electronic structure entropy. Combined with a previously reported over-approximation, the approximations are used in conjunction in an attempt to bracket the upper and lower entropy limits for multiconfigurational ground state electronic structure entropy and compared to known standard molar entropies for the elements. This formality has been used for the application of a classical statistical mechanics methodology to be applied to the discrete sets of quantum mechanical states of Pu in order to calculate orbital occupancies in Pu's multiconfigurational ground state. Without consideration of the relative energies of various possible electronic configurations contributing to the multiconfigurational ground state, the calculations are performed under a general energy degeneracy assumption weighted to the number of permutations for specific configurations. The number of configurations assumed to significantly contribute is gradually constrained in order to approach a low-order approximation of orbital occupancies in Pu that are then compared to experimental and other calculated results from the literature.

Beaux, II, Miles F. (ORCID:000000032192626X)↗
DOE OSTI2020

Actinide 2-metallabiphenylenes that satisfy Hückel’s rule

Aromaticity and antiaromaticity, as defined by Hückel’s rule, are key ideas in organic chemistry, and are both exemplified in biphenylene—a molecule that consists of two benzene rings joined by a four-membered ring at its core. Biphenylene analogues in which one of the benzene rings has been replaced by a different (4n + 2) π-electron system have so far been associated only with organic compounds. In addition, efforts to prepare a zirconabiphenylene compound resulted in the isolation of a bis(alkyne) zirconocene complex instead. Here we report the synthesis and characterization of, to our knowledge, the first 2-metallabiphenylene compounds. Single-crystal X-ray diffraction studies reveal that these complexes have nearly planar, 11-membered metallatricycles with metrical parameters that compare well with those reported for biphenylene. Nuclear magnetic resonance spectroscopy, in addition to nucleus-independent chemical shift calculations, provides evidence that these complexes contain an antiaromatic cyclobutadiene ring and an aromatic benzene ring. Finally, spectroscopic evidence, Kohn–Sham molecular orbital compositions and natural bond orbital calculations suggest covalency and delocalization of the uranium f 2 electrons with the carbon-containing ligand.

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

Simulation Center for Runaway Electron Avoidance and Mitigation (SCREAM) - NIMROD DIII-D Shattered Pellet Injection Disruption Mitigation and RE Modeling. Final report

Final technical report for UCSD and subcontractor contributions to DE-SC0016420, Simulation Center for Runaway Electron Avoidance and Mitigation (SCREAM). Project description. MHD modeling includeing runaway electron drift orbit calculations will be carried out for DII-D disruption mitigation scenarios. The effects of pitch angle scattering on the energy distribution of runaway electron population will be evaluated using one or more collision models integrated / coupled with the runaway orbit following model in the nimrod code. An extension of the test particle model will be developed to predict runaway electron generation considering both primary and secondary sources of runaway electron production. Simulations simultaneously modelling the effects of generation, confinement, and moderation-space losses during a DII-D rapid shutdown (mitigated disruption) will be completed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Angle-dependent strong-field ionization of halomethanes

We study, experimentally and theoretically, the ionization probability of singly halogenated methane molecules, CH 3 Cl and CH 3 Br, in intense linearly polarized 800 nm laser pulses as a function of the angle between the molecular axis and the laser polarization. Experimentally, the molecules are exposed to two laser pulses with a relative time delay. The first, weaker pulse induces a nuclear rotational wave packet within the molecules, which are then ionized by the second, stronger pulse. The angle-dependent ionization yields are extracted from fits of the measured delay-dependent ionization signal to a superposition of moments of the rotational wave packet’s angular distribution. Angle-dependent strong-field ionization (SFI) yields are also calculated using time-dependent density functional theory. Good agreement between measurements and theory is obtained. Interestingly, we find a marked difference between the angle-dependence of the ionization yields for these two halomethane species despite the similar structure of their highest occupied molecular orbitals. Calculations reveal that these differences are a result of multichannel (CH 3 Cl) vs single-channel (CH 3 Br) ionization and of increased hole localization on Br vs Cl. By adding calculations for CH 3 F, we can discern clear trends in the ionization dynamics with increasing halogen mass. These results are illustrative, as chemical functionalization and molecular alignment are likely to be important parameters for initiating and controlling charge migration dynamics via SFI.

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

Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions

We discuss melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions We report a combined experimental and theoretical study of the melting curve and the structural behavior of vanadium under extreme pressure and temperature. We performed powder x-ray-diffraction experiments up to 120 GPa and 4000 K, determining the phase boundary of the body-centered cubic-to-rhombohedral transition and melting temperatures at different pressures. Melting temperatures have also been established from the observation of temperature plateaus during laser heating, and the results from the density-functional theory calculations. Results obtained from our experiments and calculations are fully consistent and lead to an accurate determination of the melting curve of vanadium. These results are discussed in comparison with previous studies. The melting temperatures determined in this study are higher than those previously obtained using the speckle method, but also considerably lower than those obtained from shockwave experiments and linear muffin-tin orbital calculations. Finally, a high-pressure, high-temperature equation of state up to 120 GPa and 2800 K has also been determined.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structure-antioxidant activity relationships, QSAR, DFT calculation, and mechanisms of flavones and flavonols

DFT calculations were performed on nine flavones and flavonols to explain their high antioxidant activity and variations in their activity. Conformational analysis showed that only flavonols with 3-OH directed toward the B-ring are nonplanar; however, flavones and resulted radicals are planar. Hydroxyl group eligible for dissociation is the one with ortho OH directed toward it; otherwise, one of B-ring (in 2′ or 4′-position) hydroxyl group. There are two main factors responsible for stabilizing the resulted radicals and lowering the bond dissociation energy and hence there were found well correlated with the experimental activity. First, driving force resulted from the conversion of nonplanar flavonols to planar radicals accompanied by resonance toward the carbonyl group and H-bond formation with 3-OH and second, radical stabilization by H-bond with ortho hydroxyl group with resonance toward carbonyl or pyrone oxygen. All resonance and H-bonds were confirmed by spin density, bond length, and molecular orbital calculations.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Hydrogenated Gold Clusters from Helium Nanodroplets: Cluster Ionization and Affinities for Protons and Hydrogen Molecules

We report the mass spectrometric detection of hydrogenated gold clusters ionized by electron transfer and proton transfer. The cations appear after the pickup of hydrogen molecules and gold atoms by helium nanodroplets (HNDs) near zero K and subsequent exposure to electron impact. We focus on the size distributions of the gold cluster cations and their hydrogen content, the electron energy dependence of the ion yield, patterns of hydrogenated gold cluster cation stability, and the presence of “magic” clusters. Ab initio molecular orbital calculations were performed to provide insight into ionization energies and proton affinities of gold clusters as well as into molecular hydrogen affinities of the ionized and protonated gold cluster cations. .

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Structural and Electronic Complexities of a Sulfur‐Bridged Di‐Iron Complex Composed of Mono‐ and Di‐Nitrosyl Units

The delocalized, thermodynamically stable cation, [(N 2 S 2 )Fe(NO)•Fe(NO) 2 ] + , an adduct of mono-nitrosyl and dinitrosyl iron units, is analyzed to address the unusual stability of the sulfur-bridged diiron complex in its three overall redox levels, +, 0, and −. X-ray diffraction and myriad spectroscopic techniques probe products of sequential electron uptake in the corresponding neutral and anionic species. Conundrums include unified blueshifts of the overall 3-band, ν(NO), pattern with added electrons. One-electron reduction changes the anti-ferromagnetically coupled, S = 0, cationic diiron species to the neutral analog, S = ½, with unpaired spin mainly localized on the MNIU, which decreases its ∠Fe–N–O angle by 10 degrees in response to the extra electron density. Subsequent reduction to the anionic species, S = 1, involves a major geometric change at the MNIU, which moves the Fe in {Fe(NO)} 8 out of the N 2 S 2 plane. Site-specific 15 N labeling of nitrosyl in the MNIU confirms the IR analysis and shows rapid NO exchange between the MNIU/DNIU (mono-nitrosyl iron unit/dinitrosyl iron unit) pairs during its synthesis at RT. Mössbauer spectroscopy, S K-edge XAS, and molecular orbital calculations confirm the ability of NO and the versatility of sulfur bridges to buffer and distribute electrons, a key to their major importance in metalloenzymes.

DNIC↗
DOE OSTI2023

Insight into the Structural and Emissive Behavior of a Three‐Dimensional Americium(III) Formate Coordination Polymer

Abstract We report the structural, vibrational, and optical properties of americium formate (Am(CHO 2 ) 3 ) crystals synthesized via the in situ hydrolysis of dimethylformamide (DMF). The coordination polymer features Am 3+ ions linked by formate ligands into a three‐dimensional network that is isomorphous to several lanthanide analogs, (e. g., Eu 3+ , Nd 3+ , Tb 3+ ). Structure determination revealed a nine‐coordinate Am 3+ metal center that features a unique local C 3v symmetry. The metal–ligand bonding interactions were investigated by vibrational spectroscopy, natural localized molecular orbital calculations, and the quantum theory of atoms in molecules. The results paint a predominantly ionic bond picture and suggest the metal‐oxygen bonds increase in strength from Nd−O 5 D 1′ → 7 F 0′ emission band is observed and dominates the emission spectrum. This behavior is unusual and is attributed to the C 3v coordination environment of the metal center.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗