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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Composite-particle decay widths by the generator coordinate method

We study the feasibility of applying the Generator Coordinate Method (GCM) of self-consistent mean-field theory to calculate decay widths of composite particles to composite-particle final states. The main question is how well the GCM can approximate continuum wave functions in the decay channels. The analysis is straightforward under the assumption that the GCM wave functions are separable into internal and Gaussian center-of-mass wave functions. Two methods are examined for calculating decay widths. In one method, the density of final states is computed entirely in the GCM framework. In the other method, it is determined by matching the GCM wave function to an asymptotic scattering wave function. Both methods are applied to a numerical example and are found to agree within their determined uncertainties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

FELIX-2.0: New version of the finite element solver for the time dependent generator coordinate method with the Gaussian overlap approximation

The time-dependent generator coordinate method (TDGCM) is a powerful method to study the largeamplitude collective motion of quantum many-body systems such as atomic nuclei. Under the GaussianOverlap Approximation (GOA), the TDGCM leads to a local, time-dependent Schrödinger equation in amulti-dimensional collective space. In this paper, we present the version 2.0 of the code FELIX that solvesthe collective Schrödinger equation in a finite element basis. This new version features: (i) the ability tosolve a generalized TDGCM+GOA equation with a metric term in the collective Hamiltonian, (ii) supportfor new kinds of finite elements and different types of quadrature to compute the discretized Hamiltonianand overlap matrices, (iii) the possibility to leverage the spectral element scheme, (iv) an explicit Krylovapproximation of the time propagator for time integration instead of the implicit Crank–Nicolson methodimplemented in the first version, (v) an entirely redesigned workflow. We benchmark this release on ananalytic problem as well as on realistic two-dimensional calculations of the low-energy fission of240Puand256Fm. Low to moderate numerical precision calculations are most efficiently performed with simplexelements with a degree 2 polynomial basis. Higher precision calculations should instead use the spectralelement method with a degree 4 polynomial basis. We emphasize that in a realistic calculation of fissionmass distributions of240Pu, FELIX-2.0 is about 20 times faster than its previous release (within a numericalprecision of a few percents).

Regnier, D.↗
DOE OSTI2022

Intrinsic glassy-metallic transport in an amorphous coordination polymer

Conducting organic materials, such as doped organic polymers, molecular conductors and emerging coordination polymers4, underpin technologies ranging from displays to flexible electronics. Realizing high electrical conductivity in traditionally insulating organic materials necessitates tuning their electronic structure through chemical doping6. Furthermore, even organic materials that are intrinsically conductive, such as single-component molecular conductors, require crystallinity for metallic behavior. However, conducting polymers are often amorphous to aid durability and processability. Using molecular design to produce high conductivity in undoped amorphous materials would enable tunable and robust conductivity in many applications, but there are no intrinsically conducting organic materials that maintain high conductivity when disordered. Here we report an amorphous coordination polymer, Ni tetrathiafulvalene tetrathiolate, which displays markedly high electronic conductivity (up to 1,200 S cm –1 ) and intrinsic glassy-metallic behavior. Theory shows that these properties are enabled by molecular overlap that is robust to structural perturbations. This unusual set of features results in high conductivity that is stable to humid air for weeks, pH 0–14 and temperatures up to 140 °C. Furthermore, these findings demonstrate that molecular design can enable metallic conductivity even in heavily disordered materials, raising fundamental questions about how metallic transport can exist without periodic structure and indicating exciting new applications for these materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

A quantum generalization of intrinsic reaction coordinate using path integral centroid coordinates

We propose a generalization of the intrinsic reaction coordinate (IRC) for quantum many-body systems described in terms of the mass-weighted ring polymer centroids in the imaginary-time path integral theory. This novel kind of reaction coordinate, which may be called the ''centroid IRC,'' corresponds to the minimum free energy path connecting reactant and product states with a least amount of reversible work applied to the center of masses of the quantum nuclei, i.e., the centroids. We provide a numerical procedure to obtain the centroid IRC based on first principles by combining ab initio path integral simulation with the string method. This approach is applied to NH{sub 3} molecule and N{sub 2}H{sub 5}{sup -} ion as well as their deuterated isotopomers to study the importance of nuclear quantum effects in the intramolecular and intermolecular proton transfer reactions. We find that, in the intramolecular proton transfer (inversion) of NH{sub 3}, the free energy barrier for the centroid variables decreases with an amount of about 20% compared to the classical one at the room temperature. In the intermolecular proton transfer of N{sub 2}H{sub 5}{sup -}, the centroid IRC is largely deviated from the ''classical'' IRC, and the free energy barrier is reduced by the quantum effects even more drastically.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Chaotic coordinates for the Large Helical Device

The theory of quadratic-flux-minimizing (QFM) surfaces is reviewed, and numerical techniques that allow high-order QFM surfaces to be efficiently constructed for experimentally relevant, non-integrable magnetic fields are described. As a practical example, the chaotic edge of the magnetic field in the Large Helical Device (LHD) is examined. A precise technique for finding the boundary surface is implemented, the hierarchy of partial barriers associated with the near-critical cantori is constructed, and a coordinate system, which we call chaotic coordinates, that is based on a selection of QFM surfaces is constructed that simplifies the description of the magnetic field, so that flux surfaces become “straight” and islands become “square.”.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Highly Coupled Heterobicycle‐Fused Porphyrin Dimers: Excitonic Coupling and Charge Separation with Coordinated Fullerene, C 60

Abstract Porphyrin dimers have been widely explored and studied owing to their importance in photosynthetic systems. A vast variety of dimers linked by different groups and at different angles have been synthesized and studied; however, the means by which to synthesize rigidly fused porphyrins with direct conjugation of the chromophores remains limited. Such a class of porphyrins may possess interesting properties that unconjugated or stacked dimers may not exhibit. In this study, bisbenzimidazole‐fused porphyrin dimers and their mono‐ and bis−zinc derivatives are synthesized and characterized. As a consequence of excitonic coupling, these dimers exhibit a split Soret band irrespective of the metal ion in the porphyrin cavity. Steady‐state fluorescence and excitation spectra followed by femtosecond transient absorption spectral studies of the heterometallated dimer, (free‐base and zinc porphyrin) reveals the occurrence of efficient singlet‐singlet energy transfer (>95 % efficiency and rate constant >10 12 s −1 ) within the dyad. Further, donor‐acceptor conjugates were formed by metal‐ligand axial coordination of phenyl imidazole functionalized C 60 and were characterized by a variety of physicochemical techniques. Excited state charge separation from both singlet and triplet excited states of ZnP in the conjugates has been established. The lifetime of the final charge‐separated state was in the 30–40 μs range revealing charge stabilization. Interestingly, no charge separation in the conjugate derived from the heterometallated dimer was observed wherein excitation transfer dominated the process. The present study brings out the importance of the rigid π‐spacer connecting porphyrin dimers in governing the energy and electron transfer events when coupled with an electron acceptor.

Chemistry↗
DOE OSTI2021

AlphaBuilding ResCommunity: A multi-agent virtual testbed for community-level load coordination

Training and validating algorithms in a simulation testbed can accelerate research and applications of optimal control of residential loads to improve energy flexibility and grid resilience. We developed an open-source simulation environment, AlphaBuilding ResCommunity, that can be used to train and validate algorithms to control a single thermostatically controlled load (TCL) or coordinate a group of TCLs. We used reduced-order models to simulate the thermodynamics of TCLs, and the parameter values were determined from the connected smart thermostat data of real households. The environment was built upon the standardized OpenAI Gym interface. Ancillary functions, such as retrieving the parameters and weather forecasts, are provided to facilitate control strategies that require predictive information. Compared with existing efforts, AlphaBuilding ResCommunity has three advantages: (1) more realistic model settings because the parameter values are identified from actual household operating data, and modelling and measurement uncertainty are considered; (2) passive thermal storage control; and (3) ease of use due to a simple software dependency and standardized interface. We demonstrated the applications of the environment by implementing a Kalman Filter and Model Predictive Control on a single TCL and a Priority-Stack-Based Control and Alternating Direction Method of Multipliers to coordinate multiple TCLs for load tracking.

Wang, Z↗
DOE OSTI2018

Examination of Structure and Bonding in 10-Coordinate Europium and Americium Terpyridyl Complexes

M(TpyNO 2 )(NO 3 ) 3 (H 2 O)·THF (M = La, Ce, Nd, Sm, Eu, Am; TpyNO 2 = 4’-nitrophenyl terpyridyl) have been prepared from the reaction of M(NO 3 ) 3 ·nH 2 O with TpyNO 2 in THF. Structural analysis shows that the metal centers are ten-coordinate, providing the first example of Am III with this coordination number. Further spectroscopic and theoretical evaluation of these complexes reveals utilization of the 5f orbitals in bonding in the Am III complex. Comparison of Nd‒L, Eu‒L, and Am‒L bond distances demonstrates that some caution should be taken in comparing Eu III versus Am III in extraction experiments.

anions↗
DOE OSTI2019

Iodosylbenzene Coordination Chemistry Relevant to Metal–Organic Framework Catalysis

Hypervalent iodine compounds formally feature expanded valence shells at iodine. These reagents are broadly used in synthetic chemistry due to the ability to participate in well-defined oxidation-reduction processes and because the ligand-exchange chemistry intrinsic to the hypervalent center allows hypervalent iodine compounds to be applied to a broad array of oxidative substrate functionalization reactions. We have recently developed methods to generate these compounds from O 2 that are predicated on diverting reactive intermediates of aldehyde autoxidation towards the oxidation of aryl iodides. Coupling the aerobic oxidation of aryliodides with catalysts that effect C–H bond oxidation would provide a strategy to achieve aerobic C–H oxidation chemistry. In this Forum article we discuss the aspects of hypervalent iodine chemistry and bonding that render this class of reagents attractive lynchpins for aerobic oxidation chemistry. We then discuss the oxidation processes relevant to the aerobic preparation of 2-(tertbutylsulfonyl) iodosylbenzene, which is a popular hypervalent iodine reagent for use with porous metal-organic framework-based catalysts because it displays significantly enhanced solubility as compared with unsubstituted iodosylbenzene. We demonstrate that popular synthetic methods to this reagent often provide material that displays unpredictable disproportionation behavior due to the presence of trace impurities. We provide a revised synthetic route that avoids impurities common in the reported methods and provides access to material that displays predictable stability. Lastly, we describe the coordination chemistry of hypervalent iodine compounds with metal clusters relevant to MOF chemistry and discuss the potential implications of this coordination chemistry to catalysis in MOF scaffolds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Strengthening of the Coordination Shell by Counter Ions in Aqueous Th 4+ Solutions

The presence of counter ions in solutions containing highly charged metal cations can trigger processes such as ion-pair formation, hydrogen bond breakages and subsequent reformation, and ligand exchanges. In this work, it is shown how halide (Cl-, Br-) and perchlorate (ClO4-) anions affect the strength of the primary solvent coordination shells around Th4+ using explicit solvent and finite temperature ab initio molecular dynamics modeling methods. The 9-fold solvent geometry was found to be the most stable hydration structure in each aqueous solution. Relative to the dilute aqueous solution, the presence of the counter ions did not significantly alter the geometry of the primary hydration shell. However, the free energy analyses indicated that the 10-fold hydrated states were thermodynamically accessible in dilute and bromide aqueous solutions within 1 kcal/mol. Analysis of the results showed that the hydrogen bond lifetimes were longer and solvent exchange energy barriers were larger in solutions with counter ions in comparison with the solution with no counter ions. This implies that the presence of the counter ions induces a strengthening of the Th4+ hydration shell.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Metal-Coordinated Phthalocyanines as Platform Molecules for Understanding Isolated Metal Sites in the Electrochemical Reduction of CO 2

Single-atom catalysts (SACs) of non-precious transition metals (TMs) often show unique electrochemical performance, including the electrochemical carbon dioxide reduction reaction (CO 2 RR). However, the inhomogeneity in their structures makes it difficult to directly compare SACs of different TM for their CO 2 RR activity, selectivity, and reaction mechanisms. Here, the comparison of isolated TMs (Fe, Co, Ni, Cu, and Zn) is systematically investigated using a series of crystalline molecular catalysts, namely TM-coordinated phthalocyanines (TMPcs), to directly compare the intrinsic role of the TMs with identical local coordination environments on the CO 2 RR performance. The combined experimental measurements, in situ characterization, and density functional theory calculations of TM-Pc catalysts reveal a TM dependent CO 2 RR activity and selectivity, with the free energy difference of ΔG(*HOCO) - ΔG(*CO) being identified as a descriptor for predicting the CO 2 RR performance.

25 ENERGY STORAGE↗
DOE OSTI2019

Redox-Active 1D Coordination Polymers of Iron–Sulfur Clusters

Here we describe the combination of an archetypal redox-active metal sulfide cluster, Fe 4 S 4 , with an organic linker, 1,4-benzenedithiolate, to prepare coordination polymers containing infinite chains of Fe 4 S 4 clusters. The crystal structures of two solid materials have been solved from synchrotron X-ray powder diffraction data using simulated annealing and re-fined by a least-squares Rietveld refinement procedure. The electronic properties of these chains have also been characterized by UV-visible and Mössbauer spectroscopies. Additional experiments demonstrated that these chains can be solubilized by variation of the countercation and that the chain structure is maintained in solution. The redox-activity of the Fe 4 S 4 clusters can be accessed with chemical reagents. Introduction of charge carriers by reduction of the Fe 4 S 4 clusters is found to increase the electrical conductivity of the materials by up to four orders of magnitude. These results highlight the utility of Fe 4 S 4 clusters as redox-active building blocks in preparing new classes of coordination polymers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗