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All sources NASA NTRS DOE OSTI

DOE OSTI2020

Spin Splitting Energy of Transition Metals: A New, More Affordable Wave Function Benchmark Method and Its Use to Test Density Functional Theory

Accurately predicting the spin splitting energy of chemical species is important for understanding their reactivity and magnetic properties, but it is very challenging, especially for molecules containing transition metals. One impediment to progress is the scarcity of accurate benchmark data. Here we report a set of calculations designed to yield reliable benchmarks for simple transition-metal complexes that can be used to test density functional methods that are affordable for large systems of more practical interest. Various wave function methods are tested against experiment for Fe 2+ , Fe 3+ , and Co 3+ , including CASSCF, CASPT2, CASPT3, MRCISD, MRCISD+Q, ACPF, AQCC, CCSD(T), and CASPT2/CCSD(T) and also a new method called CASPT2.5, which is performed by taking the average of the CASPT2 and CASPT3 energies. Furthermore, we find that MRCISD+Q, ACPF, and AQCC require smaller active spaces for good accuracy than are required by CASPT2 and CASPT3, and this aspect may be important for calculations on larger molecules; here we find that CASPT2.5 extrapolated to a complete basis set is the most suitable method—in terms of computational cost and in terms of accuracy on monatomic systems—and therefore we chose this method for molecular benchmarks. Then Kohn–Sham density functional calculations with 60 exchange-correlation functionals are tested for FeF 2 , FeCl 2 , and CoF 2 . We find that MN15-L, M06-SX, and revM06 have very good agreement with CASPT2.5 benchmarks in terms of both the spin splitting energy and the optimized geometry for each spin state. In addition, we recommend def2-TZVP as the most suitable basis set to perform density functional calculations for molecular spin splitting energies; extra polarization functions in the basis set do not help to increase the accuracy of the spin splitting energy in KS calculations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Copper(ii)-photocatalyzed decarboxylative oxygenation of carboxylic acids

Showcasing the concept of light-induced homolysis for the generation of radicals, the Cu II -photocatalyzed decarboxylative oxygenation of carboxylic acids with molecular oxygen as the terminal oxidant is described. Here, two Cu II -carboxylate complexes with different coordination geometries were synthesized and characterized by X-ray analysis, correlating their structure with their ability to initiate light-induced decarboxylations.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRS1983

Friction, wear, transfer and wear surface morphology of ultra-high-molecular-weight polyethylene

Tribological studies at 25 C in a 50-percent-relative-humidity air atmosphere were conducted using hemispherically tipped 440 C HT (high temperature) stainless steel pins sliding against ultra-high-molecular-weight polyethylene (UHMWPE) disks. The results indicate that sliding speed, sliding distance, contact stress and specimen geometry can markedly affect friction, UHMWPE wear, UHMWPE transfer and the type of wear mechanisms that occur. Adhesion appears to be the predominant wear mechanism; but after long sliding distances at slow speeds, heavy ridges of transfer result which can induce fatigue-like wear on the UHMWPE disk wear track. In one instance, abrasive wear to the metallic pin was observed. This was caused by a hard particle embedded in the UHMWPE disk wear track.

Fusaro, R. L.↗

NASA NTRS1982

Shuttle/payload contamination evaluation /SPACE/ program improvements

Performance features, analytic details, and applications of the SPACE computer code for simulating the contaminant environment experienced by Shuttle payloads on-orbit are outlined. A summary is presented of the model preset, input, and output parameters, capabilities, and analytical options. The program was designed to identify the molecular column density, molecular deposition in various scenarios, and the background brightness produced by the contaminant clouds. SPACE covers payload geometries such as the Orbiter and four Spacelab modules, configurations tracing and summing the production of contamination from distributed leakage sources or concentrated sources. A total of ten chemical species can be analyzed, with consideration given to line-of-sight mass transport or scattered molecule transport. Deposition levels can be computed, as can reflection evaluation. Trial results for the analyses of three different payloads are presented. Additionally, the Mini-SPACE code, for quick-look analyses during the payload planning analyses, is outlined.

Jarossy, F. J.↗

NASA NTRS1985

Friction, wear, transfer, and wear surface morphology of ultrahigh-molecular-weight polyethylene

Fusaro, R. L.↗

NASA NTRS1998

Burner Emissions Associated with Lobed and Non-Lobed Fuel Injectors

The present experimental study examines NO(sub x), and CO emissions associated with three alternative fuel-injector geometries. These injectors mix fuel and air and strain their interfaces to differing extents and thus create different local equivalence ratios within flow regions upstream of flame ignition and stabilization. Two of the devices studied are lobed fuel injectors, in which molecular mixing of reactants is associated with streamwise vorticity generation, while the third one is a non-lobed fuel injector. Results show that rapid mixing allowed both lobed injector geometries to produce very lean premixed flame structures, with a lower achievable turn-down or fuel/air mass flux ratio than for the analogous non-lobed injector, which largely, produced distinct diffusion flames. All three injectors exhibited some level of sooting near walls and in the far-field region, with the non-lobed injector sooting to the greatest extent. At low fuel flow rates, in which the lobed injectors created locally very lean premixed conditions, there resulted lower NO(sub x) emissions as compared with non-lobed injector emissions. Yet at higher fuel-air mass flux ratios, NO(sub x) emissions from the lobed injectors were actually higher than for the nonlobed injector, likely due to reduced sooting and hence reduced radiative heat losses associated with enhanced mixing. For both lobed injector geometries examined here, CO emissions became high for low values of the fuel/air mass flux ratio, again consistent with locally premixed combustion behavior, despite the fact that fuel was injected separately from air directly into the burner test section. The present study demonstrates that, for fuel-air mixing enhancement devices, control of the local equivalence ratio is critical in order to optimize burner emissions.

Mitchell, M. G.↗

DOE OSTI2025

Confinement-induced chirality in phase-separated achiral polymer solutions

Self-organization of polymers in constrained geometries largely determines their applications in high-strength materials, photonics, and electronics. Chiral organization under confinement is well established for polymers with intrinsic molecular chirality; however, it has not been observed for achiral polymers. Here, we report the emergence of chirality in spatially confined solutions of achiral rigid-rod polymers. We show that kinetically arrested phase separation of polymer solutions confined to narrow capillaries resulted in alternating segments of isotropic and chiral nematic phases. The chiral structure of the nematic segments originated from the interplay between the constrained geometry, surface anchoring, orientational wetting, and elastic anisotropy of rigid-rod polymers. The catenoidal shape of the chiral structure recapitulated the morphology of biological chiral structures. These findings provide insight into the organization of soft matter under spatial confinement and offer a straightforward way to form chiral structures from achiral synthetic polymers.

Science & Technology - Other Topics↗

DOE OSTI2026

Geometry, spin coupling, and dielectric control of redox potentials in [4Fe–4S] Clusters

Iron–sulfur (Fe–S) clusters are common biological cofactors that facilitate vital redox reactions. Despite extensive research, the molecular basis of redox potential tuning in ferredoxin-like proteins remains an active area of debate. In this study, we combine statistical analysis of over one thousand [4Fe–4S]-containing protein structures from the Protein Data Bank (PDB) with broken-symmetry and extended broken-symmetry density functional theory to examine how cysteine ligand orientations and environmental screening affect redox properties of the clusters. We identified five main ligand configurations, three of which are predominant in natural structures. Among these, the adiabatic electron affinity differs by less than 0.1 V, indicating that, while geometry plays a secondary role, it allows localized fine-tuning of redox properties. In contrast, electrostatic and solvation effects primarily determine the overall potential range.

Computational Chemistry↗

NASA NTRS1976

A statistical method for treating molecular line opacities

A method for treating atomic and molecular line opacities in cool stellar atmospheres by a statistical opacity sampling is investigated. Under the usual assumptions of plane-parallel geometry, radiative equilibrium, hydrostatic equilibrium, and LTE, each radiative quantity is computed monochromatically at each chosen frequency and depth without any averaging of the opacity. The number of frequencies needed to allow an accurate integration of the energy flux over a given spectral interval is investigated as a function of depth, including opacity for both CN and C2. This method is extended to the calculation of a model atmosphere of a star, and the effect of the number and placement of frequency points is studied. The method is applied to treating molecular lines of CO, C2, and CN in a cool carbon star. Significant advantages of the opacity sampling method are its flexibility, which permits computation of models having arbitrary variations of chemical composition and of opacity with wavelength and depth, and generalizability to include departures from LTE.

Sneden, C.↗

DOE OSTI2021

Molecular dynamics studies of lattice defect effects on tritium diffusion in zirconium

Tritium diffusion in α-Zr containing point defects such as vacancies or self-interstitial atoms (SIAs) is simulated using molecular dynamics. Point defects rapidly aggregate to form extended defects, such as 3D nanoclusters and Frank loops. The geometry of extended defects is affected by the presence of tritium. At low temperature and in the absence of tritium, vacancies aggregate to form stacking fault pyramids. Addition of tritium at these temperatures promotes aggregation of vacancies to form 3D nanoclusters, within which the tritium concentration can be sufficiently high to suggest that these defects may serve as nucleation sites for hydride precipitation. Trapping of tritium in vacancy nanocluster reduces the calculated bulk diffusivity by an amount proportional to the vacancy concentration. At high temperature, vacancy clusters change shape to form planar basal dislocation loops, which bind tritium less strongly, leading to a sharp reduction in the fraction of trapped tritium and a corresponding increase in tritium diffusivity at high temperature. In contrast, SIAs increase tritium diffusion through α-Zr. Analysis of atomic trajectories shows that tritium does not interact directly with SIAs. In conclusion, diffusion enhancement is instead related to expansion of the lattice.

36 MATERIALS SCIENCE↗

DOE OSTI2024

PeleMP: The Multiphysics Solver for the Combustion Pele Adaptive Mesh Refinement Code Suite

Combustion encompasses multiscale, multiphase reacting flow physics spanning a wide range of scales from the molecular scales, where chemical reactions occur, to the device scales, where the turbulent flow is affected by the geometry of the combustor. This scale disparity and the limited measurement capabilities from experiments make modeling combustion a significant challenge. Recent advancements in high-performance computing (HPC), particularly with the Department of Energy's Exascale Computing Project (ECP), have enabled high-fidelity simulations of practical applications to be performed. The major physics submodels, including chemical reactions, turbulence, sprays, soot, and thermal radiation, exhibit distinctive computational characteristics that need to be examined separately to ensure efficient utilization of computational resources. This paper presents the multiphysics solver for the Pele code suite, called PeleMP, which consists of models for spray, soot, and thermal radiation. Here, the mathematical and algorithmic aspects of the model implementations are described in detail as well as the verification process. The computational performance of these models is benchmarked on multiple supercomputers, including Frontier, an exascale machine. Results are presented from production simulations of a turbulent sooting ethylene flame and a bluff-body swirl stabilized spray flame with sustainable aviation fuels to demonstrate the capability of the Pele codes for modeling practical combustion problems with multiphysics. This work is an important step toward the exascale computing era for high-fidelity combustion simulations providing physical insights and data for predictive modeling of real-world devices.

42 ENGINEERING↗

DOE OSTI2020

Materials Data on SbH5(Cl3O)2 by Materials Project

SbCl6H5O2 is Molybdenum Carbide MAX Phase-like structured and crystallizes in the triclinic P1 space group. The structure is zero-dimensional and consists of two molecular hydrogen;dihydrate molecules and two SbCl6 clusters. In each SbCl6 cluster, Sb5+ is bonded in an octahedral geometry to six Cl1- atoms. There are a spread of Sb–Cl bond distances ranging from 2.39–2.44 Å. There are six inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom. In the fourth Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom. In the fifth Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom. In the sixth Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on NaCaB5(H7O4)3 by Materials Project

NaCaB5H13O12(H2)4 crystallizes in the triclinic P-1 space group. The structure is three-dimensional and consists of two hydrogen molecules, four molecular hydrogen molecules, and one NaCaB5H13O12 framework. In the NaCaB5H13O12 framework, Na is bonded in a 7-coordinate geometry to five H and two equivalent O atoms. There are a spread of Na–H bond distances ranging from 2.33–2.52 Å. There are one shorter (2.39 Å) and one longer (2.57 Å) Na–O bond lengths. Ca is bonded in a 6-coordinate geometry to one H and five O atoms. The Ca–H bond length is 2.45 Å. There are a spread of Ca–O bond distances ranging from 2.30–2.54 Å. There are five inequivalent B sites. In the first B site, B is bonded in a trigonal planar geometry to three O atoms. There are a spread of B–O bond distances ranging from 1.36–1.43 Å. In the second B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.47–1.50 Å. In the third B site, B is bonded in a trigonal planar geometry to three O atoms. There is two shorter (1.37 Å) and one longer (1.40 Å) B–O bond length. In the fourth B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.46–1.52 Å. In the fifth B site, B is bonded to four O atoms to form corner-sharing BO4 tetrahedra. There are a spread of B–O bond distances ranging from 1.48–1.50 Å. There are thirteen inequivalent H sites. In the first H site, H is bonded in a distorted L-shaped geometry to one Na and one H atom. The H–H bond length is 0.77 Å. In the second H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the third H site, H is bonded in an L-shaped geometry to one Ca and one H atom. The H–H bond length is 0.76 Å. In the fourth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. In the fifth H site, H is bonded in a single-bond geometry to one Na and one H atom. In the sixth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 1.00 Å. In the seventh H site, H is bonded in a distorted single-bond geometry to two O atoms. There is one shorter (1.00 Å) and one longer (1.67 Å) H–O bond length. In the eighth H site, H is bonded in a distorted single-bond geometry to one Na atom. In the ninth H site, H is bonded in a distorted linear geometry to two O atoms. There is one shorter (1.02 Å) and one longer (1.62 Å) H–O bond length. In the tenth H site, H is bonded in a distorted L-shaped geometry to one Na and one H atom. The H–H bond length is 0.75 Å. In the eleventh H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.97 Å. In the twelfth H site, H is bonded in a distorted single-bond geometry to one Na and one H atom. In the thirteenth H site, H is bonded in a single-bond geometry to one H atom. There are twelve inequivalent O sites. In the first O site, O is bonded in a 2-coordinate geometry to two equivalent Na, one B, and one H atom. In the second O site, O is bonded in a 2-coordinate geometry to one B and two H atoms. In the third O site, O is bonded in a 3-coordinate geometry to one B and two H atoms. In the fourth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the fifth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the sixth O site, O is bonded in a bent 120 degrees geometry to two B atoms. In the seventh O site, O is bonded in a distorted trigonal planar geometry to one Ca and two B atoms. In the eighth O site, O is bonded in a distorted bent 120 degrees geometry to two equivalent Ca and two B atoms. In the ninth O site, O is bonded in a 2-coordinate geometry to one Ca, one B, and one H atom. In the tenth O site, O is bonded in a distorted water-like geometry to one B and one H atom. In the eleventh O site, O is bonded in a 2-coordinate geometry to one Ca, one B, and one H atom. In the twelfth O site, O is bonded in a bent 120 degrees geometry to two B atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on SbH5(Cl3O)2 by Materials Project

SbCl6H5O2 is Halite, Rock Salt-like structured and crystallizes in the monoclinic C2/c space group. The structure is zero-dimensional and consists of four molecular hydrogen;dihydrate molecules and four SbCl6 clusters. In each SbCl6 cluster, Sb5+ is bonded in an octahedral geometry to six Cl1- atoms. There are a spread of Sb–Cl bond distances ranging from 2.39–2.44 Å. There are three inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Sb5+ atom.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on PtCl4O5 by Materials Project

PtO3Cl4O2 crystallizes in the monoclinic Cc space group. The structure is zero-dimensional and consists of four molecular oxygen molecules and four PtO3Cl4 clusters. In each PtO3Cl4 cluster, Pt is bonded in a 6-coordinate geometry to two O and four Cl atoms. There are one shorter (1.83 Å) and one longer (2.69 Å) Pt–O bond lengths. There are a spread of Pt–Cl bond distances ranging from 2.27–2.34 Å. There are three inequivalent O sites. In the first O site, O is bonded in a bent 120 degrees geometry to one Pt and one O atom. The O–O bond length is 1.22 Å. In the second O site, O is bonded in a single-bond geometry to one Pt atom. In the third O site, O is bonded in a single-bond geometry to one O atom. There are four inequivalent Cl sites. In the first Cl site, Cl is bonded in a single-bond geometry to one Pt atom. In the second Cl site, Cl is bonded in a single-bond geometry to one Pt atom. In the third Cl site, Cl is bonded in a single-bond geometry to one Pt atom. In the fourth Cl site, Cl is bonded in a single-bond geometry to one Pt atom.

36 MATERIALS SCIENCE↗

NASA NTRS1975

Comments on unmixedness

Unmixedness in flames refers to the condition in which eddies of fuel and oxidant have engulfed each other but where the molecular mixing necessary for complete reaction has not taken place. This phenomenon is studied experimentally using a flow geometry consisting of a coaxial Mach 2 hydrogen jet surrounded by a parallel cold Mach 2 air stream. Gas sample measurements taken downstream in the region near the flame revealed the presence of unreacted hydrogen and oxygen in the same sample. The data were analyzed by means of the CHARNAL program which uses a step function variation with time for instantaneous concentration.

Eggers, J. M.↗

NASA NTRS1993

Nongray gas analyses for reflecting walls utilizing a flux technique

A flux formulation for a planar slab of molecular gas radiation bounded by diffuse reflecting walls is developed. While this formulation is limited to the planar geometry, it is useful for studying approximations necessary in modeling nongray radiative heat transfer. The governing equations are derived by considering the history of multiple reflections between the walls. Accurate solutions are obtained by explicitly accounting for a finite number of reflections and approximating the spectral effects of the remaining reflections. Four approximate methods are presented and compared using a single absorption band of H2O. All four methods reduce to an identical zeroth-order formulation, which accounts for all reflections approximately but does handle nonreflected radiation correctly. A single absorption band of CO2 is also considered using the best-behaved approximation for higher orders. A zeroth-order formulation is sufficient to predict the radiative transfer accurately for many cases considered. For highly reflecting walls, higher order solutions are necessary for better accuracy. Including all the important bands of H2O, the radiative source distributions are also obtained for two different temperature and concentration profiles.

Menart, J. A.↗

DOE OSTI2022

Current rectification by nanoparticles in bipolar nanopores

Bipolar nanochannels comprising two domains of positively and negatively charged walls along the pore axis are known to rectify current when exposed to an electric potential bias. We find that addition of charged nanoparticles can increase rectification considerably, by approximately one order of magnitude. Two bipolar channel geometries are considered here; their behavior is examined at rest and under the influence of a negative bias and a positive bias, respectively. We do so by relying on a molecular-level model of the electrolyte solution in the channels. The large increase in current rectification can be explained by the inherent electric field that charged nanoparticles generate within the channel. This effect is found to be largely dependent on the pore's geometry, its charge distribution, and the sign of the nanoparticles' charge, thereby offering new opportunities for design of engineered nanopore membrane-nanoparticle systems for energy storage.

77 NANOSCIENCE AND NANOTECHNOLOGY↗