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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

In Silico Guidance for In Vitro Androgen and Glucocorticoid Receptor ToxCast Assays

Molecular initiating events (MIEs) are key events in adverse outcome pathways (AOPs) that link molecular chemistry to target biology. As they are based in chemistry, these interactions are excellent targets for computational chemistry approaches to in silico modelling. In this work, we aim to link ligand chemical structure to MIEs for androgen receptor (AR) and glucocorticoid receptor (GR) binding using ToxCast data. This has been done using an automated computational algorithm to perform maximal common substructure searches on chemical binders for each target from the ToxCast dataset. The models developed show a high level of accuracy, correctly assigning 87.20% of AR binders and 96.81% of GR binders in a 25% test set using holdout cross-validation. The 2D structural alerts developed can be used as in silico models to predict these MIEs, and as guidance for in vitro ToxCast assays to confirm hits. These models can target such experimental work, reducing the number of assays to be performed to gain required toxicological insight. Development of these models has also allowed some structural alerts to be identified as predictors for agonist or antagonist behavior at the receptor target. This work represents a first step in using computational methods to guide and target experimental approaches.

Allen, Timothy H.↗
DOE OSTI2025

Spin Glass Behavior and Giant Magnetoresistance via Aliovalent Fe/Ni Alloying in Amorphous Tetrathiafulvalene-Tetrathiolate Coordination Polymers

The discovery of materials with programmable combinations of charge transport and magnetic properties is a major goal in synthetic chemistry. Molecular materials, such as coordination polymers (CPs), are emerging candidates in this field due to their synthetic modularity. While there are many conductive or magnetic CPs, single-component examples with both properties are still emerging. Here, in this work, we demonstrate how alloying paramagnetic Fe(III) centers into a highly conductive Ni-based CP results in novel amorphous materials with high conductivity and giant magnetoresistance. Aliovalent doping with paramagnetic Fe centers engenders spin-glass transitions, while Ni and the strong π-stacking interactions of tetrathiafulvalene-2,3,6,7-tetrathiolate (TTFtt) ligands support conductivity. Ni 0.69 Fe 0.31 TTFtt has σ ≈ 200 S/cm and a 1.8 K magnetoresistance of −52% at 5 T, among the largest for any coordination solid. This work demonstrates not only how magnetic properties can be rationally incorporated into conductive CPs, but also an unexpected potential for amorphous materials in spintronic applications.

amorphous materials↗
DOE OSTI2026

High-Energy Hybridized States Enable Long-Lived Hot Electrons in Cobaloxime-Silicon Nanocrystal System

Strong electronic coupling is achieved between the molecular catalyst cobaloxime ([Co]) and silicon nanocrystals (Si NCs) bridged by an ethylenepyridine group derived from vinylpyridine (vpy) covalently bound to the Si NC surface (Si-vpy-[Co]). The ethylenepyridine tether in Si-vpy-[Co] is key to dramatic changes to the system’s physical properties which are not observed in the corresponding formylpyridine (fpy) system (Si-fpy-[Co]) consistent with strong electronic coupling previously observed only in dark electrochemical systems. UV−vis absorption spectroscopy reveals new [Co]-centered electronic states in Si-vpy-[Co], and transient absorption spectroscopy finds a strong absorption feature appearing within 250 fs and persisting for at least 5 ns. Astoundingly, spectroelectrochemical measurements reveal that this absorption feature is consistent with both the singly reduced [Co] − and doubly reduced [Co] 2− complexes, leading to the conclusion that these long-lived charges are derived from high-energy “hot” electrons residing in [Co]-centered states. Detailed analysis using cyclic voltammetry, spectroelectrochemistry, electron paramagnetic resonance spectroscopy, and density functional theory (DFT) calculations provides insight into the unique electronic structure created in Si-vpy-[Co]. DFT reveals that the new electronic states arise from hybridization between deep Si NC band states and high-energy molecular orbitals of the ethylenepyridine tether and the [Co] catalyst and are facilitated by σ-bonding character at the ethylenepyridine linkage. This study demonstrates that strong electronic coupling achieved through precise molecular chemistry can change the paradigm of otherwise fixed energy levels in hybrid photoelectrochemical systems for artificial photosynthesis and related applications.

14 SOLAR ENERGY↗
DOE OSTI2021

Fully variational incremental CASSCF

We report the complete-active-space self-consistent field (CASSCF) method is a canonical electronic structure theory that holds a central place in conceptualizing and practicing first principles simulations. For application to realistic molecules, however, the CASSCF must be approximated to circumvent its exponentially scaling computational costs. Applying the many-body expansion - also known as the method of increments - to CASSCF (iCASSCF) has been shown to produce a polynomially scaling method that retains much of the accuracy of the parent theory and is capable of treating full valence active spaces. Due to an approximation made in the orbital gradient, the orbital parameters of the original iCASSCF formulation could not be variationally optimized, which limited the accuracy of its nuclear gradient. Herein, a variational iCASSCF is introduced and implemented, where all parameters are fully optimized during energy minimization. This method is able to recover electronic correlations from the full valence space in large systems, produce accurate gradients, and optimize stable geometries as well as transition states. Demonstrations on challenging test cases, such as the oxoMn(salen)Cl complex with 84 electrons in 84 orbitals and the automerization of cyclobutadiene, show that the fully variational iCASSCF is a powerful tool for describing challenging molecular chemistries.

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

Contribution to Open Molecules Dataset (coordcomplexsampling)

The Open Molecules Dataset is a project led by external collaborators, focused on the production of a wide diversity of molecular chemistries. This project will include high-throughput electronic structure calculations on metal coordination complexes, biomolecules, and electrolytes. Solvation effects, conformers, chemical reactivity, and spin/charge sampling will be pursued for elements on the periodic table up to, but not including the actinides. We aim to contribute code related to sampling for transition metal complexes, in particular, and expand software capabilities related to other thrusts desired.

Taylor, Michael G. [Los Alamos National Laboratory↗
DOE OSTI2024

A Route to Molecular Quantum Technologies Using Endohedral Metallofullerenes

This project focused on fundamental studies of metal-organic hybrid molecules, including endohedral metallofullerenes (EMFs) and related cage-like structures in which quantum information can be encoded into the magnetic (spin) states associated with lanthanide (Ln) atoms that are encapsulated within a protective organic shell. This approach promises advantages over other current magnetic qubit targets based on inorganic molecules and solids. First and foremost, the organic cage provides a rigid environment devoid of elements that possess magnetic nuclei (the 12C nucleus is non-magnetic), thereby protecting the encapsulated atoms from well-known and stubborn noise sources – random vibrations and fluctuating magnetic fields due to nearby nuclei – that can easily erase fragile quantum information states. Equally important, this approach opens up the vast toolbox of organic molecular chemistry. This allows for large-scale synthesis of chemically identical species, with exquisite control over the quantum information states of the associated Ln atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

On the Efficient Evaluation of the Exchange Correlation Potential on Graphics Processing Unit Clusters

The predominance of Kohn–Sham density functional theory (KS-DFT) for the theoretical treatment of large experimentally relevant systems in molecular chemistry and materials science relies primarily on the existence of efficient software implementations which are capable of leveraging the latest advances in modern high-performance computing (HPC). With recent trends in HPC leading toward increasing reliance on heterogeneous accelerator-based architectures such as graphics processing units (GPU), existing code bases must embrace these architectural advances to maintain the high levels of performance that have come to be expected for these methods. In this work, we purpose a three-level parallelism scheme for the distributed numerical integration of the exchange-correlation (XC) potential in the Gaussian basis set discretization of the Kohn–Sham equations on large computing clusters consisting of multiple GPUs per compute node. In addition, we purpose and demonstrate the efficacy of the use of batched kernels, including batched level-3 BLAS operations, in achieving high levels of performance on the GPU. We demonstrate the performance and scalability of the implementation of the purposed method in the NWChemEx software package by comparing to the existing scalable CPU XC integration in NWChem.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Exploring internal structures and properties of terpolymer fibers via real-space characterizations

While significant research has investigated the processing and properties of high-performance terpolymer fibers, much remains to be understood about the internal nano- and microstructures of these fibers, and how these morphologies relate to fiber properties. Here we use a focused ion beam notch technique and multifrequency atomic force microscope mapping to characterize the internal structure and local mechanical properties within Technora ® fibers. We find a highly fibrillated structure that appears to connect with both the fiber’s molecular chemistry and full-fiber mechanical properties. In addition, through detailed comparisons with Kevlar ® K29 fibers, we find remarkable differences between the internal structures of the two fibers, and posit connections between our measurements and multifunctional performance studies from the literature.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Molecules in celestial objects. III - Study of CO in interstellar diffuse clouds

The absorption lines corresponding to the A-X transition of CO have been looked for in the IUE spectra of 14 stars with varying values of the colour excess, E(B-V) and found to be present in the spectra of nine stars with E(B-V) at least 0.28. The column density of CO has been determined towards these nine stars and its upper limit towards the rest of the stars. The curve of growth analysis has been found to show that the contribution to CO absorption is possibly from a single interstellar cloud for stars with E(B-V) less than 0.4 and from more than one cloud for stars with E(B-V) greater than 0.4. The observed column density of CO as a function of E(B-V) has been found to be in good agreement with that expected from the theory of ion-molecular chemistry.

Tarafdar, S. P.↗
NASA NTRS1993

Reactive control and reasoning assistance for scientific laboratory instruments

Scientific laboratory instruments that are involved in chemical or physical sample identification frequently require substantial human preparation, attention, and interactive control during their operation. Successful real-time analysis of incoming data that supports such interactive control requires: (1) a clear recognition of variance of the data from expected results; and (2) rapid diagnosis of possible alternative hypotheses which might explain the variance. Such analysis then aids in decisions about modifying the experiment protocol, as well as being a goal itself. This paper reports on a collaborative project at the NASA Ames Research Center between artificial intelligence researchers and planetary microbial ecologists. Our team is currently engaged in developing software that autonomously controls science laboratory instruments and that provides data analysis of the real-time data in support of dynamic refinement of the experiment control. the first two instruments to which this technology has been applied are a differential thermal analyzer (DTA) and a gas chromatograph (GC). coupled together, they form a new geochemicstry and microbial analysis tool that is capable of rapid identification of the organiz and mineralogical constituents in soils. The thermal decomposition of the minerals and organics, and the attendance release of evolved gases, provides data about the structural and molecular chemistry of the soil samples.

Thompson, David E.↗
NASA NTRS2020

Eta Carinae & the Homunculus: Far Infrared Sub-millimeter Spectral Lines detected with the Herschel Space Observatory

The evolved massive binary star η Carinae underwent eruptive mass loss events that formed the complex bi-polar “Homunculus” nebula harboring tens of solar masses of unusually nitrogen-rich gas and dust. Despite expectations for the presence of a significant molecular component to the gas, detections have been observationally challenged by limited access to the far-infrared and the intense thermal continuum. A spectral survey of the atomic and rotational molecular transitions was carried out with theHerschel Space Observatory, revealing a rich spectrum of broad emission lines originating in the ejecta. Velocity profiles of selected PACS lines correlate well with known substructures: Hi in the central core; NH and weak [Cii] within the Homunculus; and [Nii] emissions in fast-moving structures external to the Homunculus.We have identified transitions from [Oi], Hi, and 18 separate light C- and O-bearing molecules including CO, CH, CH+, and OH, and a wide set of N-bearing molecules,NH, NH+, N2H+, NH2, NH3, HCN, HNC, CN, and N2H+. Half of these are new detections unprecedented for any early-type massive star environment. A very low ratio[12C/13C]≤4 is estimated from five molecules and their isotopologues. We demonstrate that non-LTE effects due to the strong continuum are significant. Abundance patterns are consistent with line formation in regions of carbon and oxygen depletions with nitrogen enhancements, reflecting an evolved state of the erupting star with efficient transport of CNO-processed material to the outer layers. The results offer many opportunities for further observational and theoretical investigations of the molecular chemistry under extreme physical and chemical conditions around massive stars in their final stages of evolution.

T. R. Gull↗
NASA NTRS2026

The Evolution in Coma Molecular Composition of Comet C/2017 K2 (PanSTARRS) Across the H 2 O Sublimation Zone: ALMA Imaging of an H 2 O-Dominated Coma

We report a survey of molecular emission from cometary volatiles using the Atacama Large Millimeter/Submillimeter Array (ALMA) toward comet C/2017 K2 (PanSTARRS) carried out on UT 2022 September 21, 22, and 23 at a heliocentric distance r H 3 OH, and H 2 CO (along with continuum emission from dust) sampled molecular chemistry in C/2017 K2 at the inner edge of the H 2 O sublimation zone, the region from r H 2 O begins vigorously subliming and increasingly dominating comet activity, discerning parent from daughter or extended source species. This work presents spectrally integrated flux maps, production rates, and parent scale lengths for each molecule. CH 3 OH, CO, and HCN were produced within ~250 km of the nucleus, potentially including contributions from sublimation of icy grains. CS was consistent with production from CS 2 photolysis, and H 2 CO required production from extended sources in the coma. An ortho-to-para ratio of 2.9 ± 0.4 for H 2 CO was derived from simultaneously measured transitions of each spin species. The continuum was extended and spatially resolved, consistent with thermal emission from dust in the coma. Analysis of the continuum visibilities provided an upper limit on the nucleus diameter d <6.6 km and coma dust masses of (1.2-2.4) times10 11 kg.

Nathan X Roth↗
NASA NTRSDate not supplied

Surrogate Fuel Chemistry from ReaxFF Molecular Dynamics

Reactive molecular dynamics with ReaxFF simulations are used to study the chemistry of four component jet fuel mixtures of n-dodecane, iso-octane, n-propylbenzene, and mesitylene. ReaxFF does not require knowledge of the chemistry a priori providing insight into reactions otherwise not seen in established chemical kinetic mechanisms. The results show that a difference in the local chemical environment can change the fuel decomposition pathways across the surrogate mixtures where the same fuel species are used. These simulations highlight the need to consider cross-chemical interactions in chemical kinetic mechanism development and the importance of resonance stabilized polyaromatic hydrocarbon reactions for soot growth and formation. A method for predicting the threshold sooting index from the carbon species formed at the end of the simulations is established. The results of the simulations are consistent with measurements of the threshold sooting index with the predicted values within 20% of the measured data

Surrogate Fuels↗
DOE OSTI2025

An Unconventional Dark Radical Chemistry in Dense Molecular Clouds: Directed Gas-Phase Formation of Naphthyl Radicals

The synthetic pathways to aromatic molecules inside photon-shielded dense molecular clouds remain a fundamental, unsolved enigma in astrochemistry and astrophysics, with low-temperature molecular growth routes involving aromatic radicals, such as prototype bicyclic naphthyl (C 10 H 7 • ), implicated as key sources. Here, exploiting crossed molecular beam experiments augmented by electronic structure calculations, unexpected pathways are exposed leading to the gas-phase formation of 1- and 2-naphthyl via barrierless bimolecular reactions of atomic carbon (C) with indene (C 9 H 8 ) and of dicarbon (C 2 ) with styrene (C 8 H 8 ) accompanied by ring expansion and cyclization together with aromatization. These facile routes challenge conventional wisdom that aromatic radicals are formed in deep space solely via “bright” gas-phase photochemistry of their closed-shell polycyclic aromatic hydrocarbon (PAH) precursors. A hitherto disregarded “dark” aromatic radical chemistry with aromatic radicals synthesized via gas-phase reactions offers new concepts on the chemical evolution of the chemistry of dark molecular clouds eventually culminating in the rapid formation of aromatics, fullerenes, and carbonaceous nanostructures.

Aromatic compounds↗
DOE OSTI2020

Reactive Molecular Dynamics Simulations and Quantum Chemistry Calculations To Investigate Soot-Relevant Reaction Pathways for Hexylamine Isomers

Sooting tendencies of a series of nitrogen-containing hydrocarbons (NHCs) have been recently characterized experimentally using the yield sooting index (YSI) methodology. This work aims to identify soot-relevant reaction pathways for three selected C6H15N amines, namely, dipropylamine (DPA), diisopropylamine (DIPA), and 3,3-dimethylbutylamine (DMBA) using ReaxFF molecular dynamics (MD) simulations and quantum mechanical (QM) calculations and to interpret the experimentally observed trends. ReaxFF MD simulations are performed to determine the important intermediate species and radicals involved in the fuel decomposition and soot formation processes. QM calculations are employed to extensively search for chemical reactions involving these species and radicals based on the ReaxFF MD results and also to quantitatively characterize the potential energy surfaces. Specifically, ReaxFF simulations are carried out in the NVT ensemble at 1400, 1600, and 1800 K, where soot has been identified to form in the YSI experiment. These simulations account for the interactions among test fuel molecules and pre-existing radicals and intermediate species generated from rich methane combustion, using a recently proposed simulation framework. ReaxFF simulations predict that the reactivity of the amines decrease in the order DIPA > DPA > DMBA, independent of temperature. Both QM calculations and ReaxFF simulations predict that C2H4, C3H6, and C4H8 are the main nonaromatic soot precursors formed during the decomposition of DPA, DIPA, and DMBA, respectively, and the associated reaction pathways are identified for each amine. Both theoretical methods predict that sooting tendency increases in the order DPA, DIPA, and DMBA, consistent with the experimentally measured trend in YSI. This work demonstrates that sooting tendencies and soot-relevant reaction pathways of fuels with unknown chemical kinetics can be identified efficiently through combined ReaxFF and QM simulations. Overall, predictions from ReaxFF simulations and QM calculations are consistent, in terms of fuel reactivity, major intermediates, and major nonaromatic soot precursors.

fuel decomposition↗
NASA NTRS1985

Time dependent chemistry in dense molecular clouds. I - Grain surface reactions, gas/grain interactions and infrared spectroscopy

For the fist time, a time-dependent model is described which includes the role of grains in the production of molecules in dense clouds including ion-molecule gas phase chemistry. The approach provides information regarding the coupling between the two phases. Although the coupling between the two chemistries is extremely strong, the two domains maintain their own identities. While H2O, CH4, and NH3 are made efficiently, with a high production rate on grains and released back to the gas phase, the gas phase is essentially responsible for the formation of CO, a very stable molecule which may or may not react on grains with atomic oxygen and may or may not form CO2.

Dhendecourt, L. B.↗
DOE OSTI2024

Evidence of both molecular cloud and fluid chemistry in Ryugu regolith

The sulfur chemistry of (162173) Ryugu particles can be a powerful tracer of molecular cloud chemistry and small body processes, but it has not been well explored. We report identification of organosulfurs and a sulfate grain in two Ryugu particles, A0070 and A0093. The sulfate grain shows oxygen isotope ratios (δ 17 O = -11.0 ± 4.3 per mil, δ 18 O = -7.8 ± 2.3 per mil) that are akin to silicates in Ryugu but exhibit mass-independent sulfur isotopic fractionation (Δ 33 S = +5 ± 2 per mil). A methionine-like coating on the sulfate grain is isotopically anomalous (δ 15 N = +62 ± 2 per mil). Both the sulfate and organosulfurs can simultaneously form and survive during aqueous alteration within Ryugu’s parent body, under reduced conditions, low temperature, and a pH >7 in the presence of N-rich organic molecules. This work extends the heliocentric zone where anomalous sulfur, formed by selective photodissociation of H 2 S gas in the molecular cloud, is found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1980

Laboratory and modeling studies of chemistry in dense molecular clouds

A chemical evolutionary model with a large number of species and a large chemical library is used to examine the principal chemical processes in interstellar clouds. Simple chemical equilibrium arguments show the potential for synthesis of very complex organic species by ion-molecule radiative association reactions.

Huntress, W. T., Jr.↗