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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Local structure and distortions of mixed methane-carbon dioxide hydrates

A vast source of methane is found in gas hydrate deposits, which form naturally dispersed throughout ocean sediments and arctic permafrost. Methane may be obtained from hydrates by exchange with hydrocarbon byproduct carbon dioxide. It is imperative for the development of safe methane extraction and carbon dioxide sequestration to understand how methane and carbon dioxide co-occupy the same hydrate structure. Pair distribution functions (PDFs) provide atomic-scale structural insight into intermolecular interactions in methane and carbon dioxide hydrates. We present experimental neutron PDFs of methane, carbon dioxide and mixed methane-carbon dioxide hydrates at 10 K analyzed with complementing classical molecular dynamics simulations and Reverse Monte Carlo fitting. Mixed hydrate, which forms during the exchange process, is more locally disordered than methane or carbon dioxide hydrates. The behavior of mixed gas species cannot be interpolated from properties of pure compounds, and PDF measurements provide important understanding of how the guest composition impacts overall order in the hydrate structure.

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

Hydrosilyation of CO 2 using a silatrane hydride: structural characterization of a silyl formate compound

The silatrane hydride compound, [N(CH 2 CH 2 O) 3 ]SiH, reacts with CO 2 in the presence of the [tris(2-pyridylthio)methyl]zinc hydride complex, [Tptm]ZnH, to afford the silyl formate and methoxide derivatives, [N(CH 2 CH 2 O) 3 ]SiO 2 CH and [N(CH 2 CH 2 O) 3 ]SiOCH 3 . The molecular structure of [N(CH 2 CH 2 O) 3 ]SiO 2 CH has been determined by X-ray diffraction, thereby demonstrating that the formate ligand adopts a distal conformation in which the uncoordinated oxygen atom resides with a trans-like disposition relative to silicon. In conclusion, density functional theory calculations indicate that the atrane motif of [N(CH 2 CH 2 O) 3 ]SiO 2 CH is flexible, such that the energy of the molecule changes relatively little as the Si···N distance varies over the range 2.0–3.0 Å.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1994

Ionospheric response to the sustained high geomagnetic activity during the March '89 great storm

A simulation was conducted to model the high-latitude ionospheric to the sustaied level of high geomagnetic activity for the great magnetic storm period of March 13-14, 1989. The geomagnetic and solar activity indices and the Defense Meterological Satellite Program (DMSP) F8 and F9 satellite data for particle precipitation and high-latitude convection were used as inputs to a time-dependent ionospheric model (TDIM). The results of the TDIM were compared to both DMSP plasma density data and ground-based total electron content (TEC) measurements for the great storm period as well as with earlier storm observations. The comparisons show that the overall structure of the high-latitude ionosphere was dominated by an increased convection speed within the polar cap that led to increased ion temperatures. In turn, this enhanced the NO(+) density, raised the atomic-to-molecular ion transition height to over 300 km, decreased N(sub m)F(sub 2), increased h(sub m)F(sub 2), and in places either increased n(sub e) at 800 km or slightly decreased it. The morphology of the ionosphere under these extreme conditions was considerably different than that modeled for less distributed intervals. These differences included the character of the dayside tongue of ionization that no longer extended deep into the polar cap. Instead, as a result of the ion heating and consequent reduction in N(sub m)F(sub 2), a large polar hole occupied much of the polar region. This polar hole extended beyond the auroral oval and merged with the night sector midatitude trough. The limitaions associated with the applicability of the TDIM to the geomagnetic conditions present on March 13 and 14 are discussed. The primary limitations of the TDIM derive from the limited temporal resolution of the model input parameters and the lack of suitably dynamic thermospheric specification for the great storm conditions. These limitations leads to midlatitude ionospheric storm phases that do no follow those observed.

Sojka, J. J.↗
DOE OSTI2024

Ice Phase Classification Made Easy with Score-Based Denoising

Accurate identification of ice phases is essential for understanding various physicochemical phenomena. However, such classification for structures simulated with molecular dynamics is complicated by the complex symmetries of ice polymorphs and thermal fluctuations. For this purpose, both traditional order parameters and data-driven machine learning approaches have been employed, but they often rely on expert intuition, specific geometric information, or large training data sets. In this work, we present an unsupervised phase classification framework that combines a score-based denoiser model with a subsequent model-free classification method to accurately identify ice phases. Further, the denoiser model is trained on perturbed synthetic data of ideal reference structures, eliminating the need for large data sets and labeling efforts. The classification step utilizes the smooth overlap of atomic position (SOAP) descriptors as the atomic fingerprint, ensuring Euclidean symmetries and transferability to various structural systems. Our approach achieves a remarkable 100% accuracy in distinguishing ice phases of test trajectories using only seven ideal reference structures of ice phases as model inputs. This demonstrates the generalizability of the score-based denoiser model in facilitating phase identification for complex molecular systems. The proposed classification strategy can be broadly applied to investigate structural evolution and phase identification for a wide range of materials, offering new insights into the fundamental understanding of water and other complex systems.

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

Molecular Origins of Temperature-Dependent X-ray Absorption in YAG:Dy

The absorption and emission of X-rays in dysprosium-doped yttrium aluminum garnet (YAG:Dy) has produced unexpected thermographic behavior, which is investigated using a combination of finite temperature ab initio molecular dynamic simulations, structural characterization, and electronic structure calculations of X-ray characteristics. Calculated average peak X-ray absorption spectra (XAS) from simulations between 300 and 600 K result in peak intensity loss due to thermalization effects, matching experimentally measured behavior of YAG:Dy. Here, investigation of atomic snapshots indicates structural factors that correlated with the X-ray behavior, with the first Y–O coordination sphere identified as the primary structural feature unique to high XAS intensity as calculated by radial and pair distribution functions.

Ab initio molecular dynamics↗
DOE OSTI2023

Structural mapping and tuning of mixed halide ions in amorphous sulfides for fast Li-ion conduction and high deformability

Amorphous sulfides are among the most promising candidates for solid electrolytes (SEs) owing to their excellent deformability and acceptable Li-ion conductivity (σion) at room temperature. However, the complex atomic structure of these amorphous materials without long-range ordering results in a lack of structural understanding and difficulties in tuning material properties. Here, in this study, we performed structural mapping of glassy sulfide SEs composed of various anion clusters using a combinatorial atomic level analysis of synchrotron X-ray-based pair distribution function (PDF) and reverse Monte-Carlo (RMC) methods, demonstrating the potential to tune σ ion in glass SEs. First, we prepared a new glassy sulfide with a mixed anion framework of two halogens (Br and I) as atomic anions, with PS 4 3- molecular anions in a Li 2 S–P 2 S 5 -based glass SE. At a specific Br content, [(Li 2 S) 0.658 (LiI 0.9 LiBr 0.1 ) 0.342 ] 0.825 [P 2 S 5 ] 0.175 recorded a σ ion of 2.27 mS cm -1 , the highest value for any glass sulfides reported to date; however, its elastic modulus was still suppressed to 14.48 GPa. PDF and RMC calculations successfully provided structural mapping of anion clusters, including two halogens. Molecular dynamics simulations of each composition confirmed that flexible coordination caused by the rattling of small polarizable Br ions in the mixed halogens of glassy SEs contributed to the superior σ ion . Our results may provide new insights into the design of superior glassy SEs that play key roles in all-solid-state batteries requiring fast Li-ion conduction and high deformability.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multiscale simulations reveal TDP-43 molecular-level interactions driving condensation

The RNA-binding protein TDP-43 is associated with mRNA processing and transport from the nucleus to the cytoplasm. TDP-43 localizes in the nucleus as well as accumulating in cytoplasmic condensates such as stress granules. Aggregation and formation of amyloid-like fibrils of cytoplasmic TDP-43 are hallmarks of numerous neurodegenerative diseases, most strikingly present in >90% of amyotrophic lateral sclerosis (ALS) patients. If excessive accumulation of cytoplasmic TDP-43 causes, or is caused by, neurodegeneration is presently not known. In this work, we use molecular dynamics simulations at multiple resolutions to explore TDP-43 self- and cross-interaction dynamics. A full-length molecular model of TDP-43, all 414 amino acids, was constructed from select structures of the protein functional domains (N-terminal domain, and two RNA recognition motifs, RRM1 and RRM2) and modeling of disordered connecting loops and the low complexity glycine-rich C-terminus domain. All-atom CHARMM36m simulations of single TDP-43 proteins served as guides to construct a coarse-grained Martini 3 model of TDP-43. The Martini model and a coarser implicit solvent Cα model, optimized for disordered proteins, were subsequently used to probe TDP-43 interactions; self-interactions from single-chain full-length TDP-43 simulations, cross-interactions from simulations with two proteins and simulations with assemblies of dozens to hundreds of proteins. Our findings illustrate the utility of different modeling scales for accessing TDP-43 molecular-level interactions and suggest that TDP-43 has numerous interaction preferences or patterns, exhibiting an overall strong, but dynamic, association and driving the formation of biomolecular condensates.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Reinforcement learning based hybrid bond-order coarse-grained interatomic potentials for exploring mesoscale aggregation in liquid–liquid mixtures

Exploring mesoscopic physical phenomena has always been a challenge for brute-force all-atom molecular dynamics simulations. Although recent advances in computing hardware have improved the accessible length scales, reaching mesoscopic timescales is still a significant bottleneck. Coarse-graining of all-atom models allows robust investigation of mesoscale physics with a reduced spatial and temporal resolution but preserves desired structural features of molecules, unlike continuum-based methods. Here, we present a hybrid bond-order coarse-grained forcefield (HyCG) for modeling mesoscale aggregation phenomena in liquid–liquid mixtures. The intuitive hybrid functional form of the potential offers interpretability to our model, unlike many machine learning based interatomic potentials. We parameterize the potential with the continuous action Monte Carlo Tree Search (cMCTS) algorithm, a reinforcement learning (RL) based global optimizing scheme, using training data from all-atom simulations. The resulting RL-HyCG correctly describes mesoscale critical fluctuations in binary liquid–liquid extraction systems. cMCTS, the RL algorithm, accurately captures the mean behavior of various geometrical properties of the molecule of interest, which were excluded from the training set. The developed potential model along with the RL-based training workflow could be applied to explore a variety of other mesoscale physical phenomena that are typically inaccessible to all-atom molecular dynamics simulations.

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

Materials Data on ScH16I3O8 by Materials Project

ScH10O7IH2OHI1IH3 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four hydriodic acid molecules, four molecular hydrogen;hydroiodide molecules, four water molecules, and four ScH10O7I clusters. In each ScH10O7I cluster, Sc3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Sc–O bond distances ranging from 1.97–2.35 Å. There are ten inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- and one I1- atom. The H–O bond length is 1.00 Å. The H–I bond length is 2.42 Å. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.97 Å. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted water-like geometry to one Sc3+ and two H1+ atoms. In the second O2- site, O2- is bonded in a single-bond geometry to one Sc3+, one H1+, and one O2- atom. The O–O bond length is 1.48 Å. In the third O2- site, O2- is bonded in a distorted water-like geometry to one Sc3+ and two H1+ atoms. In the fourth O2- site, O2- is bonded in a distorted water-like geometry to one Sc3+ and two H1+ atoms. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to one Sc3+ and one O2- atom. In the sixth O2- site, O2- is bonded in a distorted water-like geometry to one Sc3+ and one H1+ atom. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one Sc3+ and two H1+ atoms. I1- is bonded in a 1-coordinate geometry to one H1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MgH20C4Br2(N4O3)2 by Materials Project

MgC4H4(N2O3)2(NH2)4(H2)2(H2Br)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight ammonia molecules, four hydrogen molecules, four molecular hydrogen;hydrobromide molecules, and two MgC4H4(N2O3)2 clusters. In each MgC4H4(N2O3)2 cluster, Mg2+ is bonded in an octahedral geometry to six O2- atoms. There are a spread of Mg–O bond distances ranging from 1.97–2.23 Å. There are two inequivalent C4+ sites. In the first C4+ site, C4+ is bonded in a 1-coordinate geometry to two N3- and one O2- atom. Both C–N bond lengths are 1.33 Å. The C–O bond length is 1.26 Å. In the second C4+ site, C4+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.17 Å. There are two inequivalent N3- sites. In the first N3- site, N3- is bonded in a distorted single-bond geometry to one C4+ atom. In the second N3- site, N3- is bonded in a distorted single-bond geometry to one C4+ atom. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 120 degrees geometry to one Mg2+ and one C4+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to one Mg2+ and one C4+ atom. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to one Mg2+ and two H1+ atoms.

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

Perspective on Kramers symmetry breaking and restoration in relativistic electronic structure methods for open-shell systems

Without rigorous symmetry constraints, solutions to approximate electronic structure methods may artificially break symmetry. In the case of the relativistic electronic structure, if time-reversal symmetry is not enforced in calculations of molecules not subject to a magnetic field, it is possible to artificially break Kramers degeneracy in open shell systems. This leads to a description of excited states that may be qualitatively incorrect. Despite this, different electronic structure methods to incorporate correlation and excited states can partially restore Kramers degeneracy from a broken symmetry solution. For single-reference techniques, the inclusion of double and possibly triple excitations in the ground state provides much of the needed correction. Formally, however, this imbalanced treatment of the Kramers-paired spaces is a multi-reference problem, and so methods such as complete-active-space methods perform much better at recovering much of the correct symmetry by state averaging. Using multi-reference configuration interaction, any additional corrections can be obtained as the solution approaches the full configuration interaction limit. A recently proposed “Kramers contamination” value is also used to assess the magnitude of symmetry breaking.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Molecular-based analysis of nanoparticle solvation: Classical density functional approach

Proper statistical mechanics understanding of nanoparticle solvation processes requires an accurate description of the molecular structure of the solvent. Achieving this goal with standard molecular dynamics (MD) simulation methods is challenging due to large length scales. An alternative approach to this problem can be formulated using classical density functional theory (cDFT), where a full configurational description of the positions of all the atoms is replaced by collective atomic site densities in the molecule. Using an example of the negatively charged silica-like system in an aqueous polar environment represented by a two-site water model, we demonstrate here that cDFT can reproduce MD data at a fraction of the computational cost. An important implication of this result is the ability to understand how the solvent molecular features may affect the system’s properties at the macroscopic scale. A concrete example highlighted in this work is the analysis of nanoparticle interactions with sizes of up to 100 nm in diameter.

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

Polarizable Water Potential Derived from a Model Electron Density

A new empirical potential for efficient, large scale molecular dynamics simulation of water is presented. The HIPPO (Hydrogen-like Intermolecular Polarizable POtential) force field is based upon the model electron density of a hydrogen-like atom. This framework is used to derive and parametrize individual terms describing charge penetration damped permanent electrostatics, damped polarization, charge transfer, anisotropic Pauli repulsion, and damped dispersion interactions. Initial parameter values were fit to Symmetry Adapted Perturbation Theory (SAPT) energy components for ten water dimer configurations, as well as the radial and angular dependence of the canonical dimer. The SAPT-based parameters were then systematically refined to extend the treatment to water bulk phases. The final HIPPO water model provides a balanced representation of a wide variety of properties of gas phase clusters, liquid water, and ice polymorphs, across a range of temperatures and pressures. This water potential yields a rationalization of water structure, dynamics, and thermodynamics explicitly correlated with an ab initio energy decomposition, while providing a level of accuracy comparable or superior to previous polarizable atomic multipole force fields. The HIPPO water model serves as a cornerstone around which similarly detailed physics-based models can be developed for additional molecular species.

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

Materials Data on UH14(SeO5)2 by Materials Project

(UH3(SeO5)2)2(H2)11 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of sixteen hydrogen molecules; four molecular hydrogen molecules; and one UH3(SeO5)2 sheet oriented in the (1, 0, 0) direction. In the UH3(SeO5)2 sheet, U4+ is bonded to seven O2- atoms to form distorted UO7 pentagonal bipyramids that share corners with three equivalent SeO4 tetrahedra and corners with two equivalent SeO4 trigonal pyramids. There are a spread of U–O bond distances ranging from 1.80–2.49 Å. There are three inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.00 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 1.01 Å. In the third H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are two inequivalent Se1+ sites. In the first Se1+ site, Se1+ is bonded to four O2- atoms to form SeO4 tetrahedra that share corners with three equivalent UO7 pentagonal bipyramids. There are a spread of Se–O bond distances ranging from 1.65–1.76 Å. In the second Se1+ site, Se1+ is bonded to four O2- atoms to form distorted SeO4 trigonal pyramids that share corners with two equivalent UO7 pentagonal bipyramids. There are a spread of Se–O bond distances ranging from 1.69–1.97 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one U4+ and one Se1+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to one H1+ and one Se1+ atom. In the third O2- site, O2- is bonded in a water-like geometry to one H1+ and one Se1+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one U4+ and one Se1+ atom. In the fifth O2- site, O2- is bonded in a bent 150 degrees geometry to one U4+ and one Se1+ atom. In the sixth O2- site, O2- is bonded in a single-bond geometry to one U4+ atom. In the seventh O2- site, O2- is bonded in a distorted water-like geometry to one H1+ and one Se1+ atom. In the eighth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one U4+ and one Se1+ atom. In the ninth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one U4+ and one Se1+ atom. In the tenth O2- site, O2- is bonded in a distorted single-bond geometry to one U4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Signature of 0 + excited state and shape coexistence in 94 Kr through 93 Kr(d,p) 94 Kr reaction

A measurement of the excitation spectrum of 94 Kr via one-neutron transfer to the ground state of 93 Kr using the 93 Kr(d,p) 94 Kr reaction at 8A MeV, observing the outgoing protons, performed with the IRIS facility at TRIUMF is reported. Two states in 94 Kr, at 1.50±0.14 MeV and 2.20±0.14 MeV, were observed. An adiabatic-wave approximation analysis of the differential cross sections leads us to identify the lower energy state as being populated with neutron transfer to the 3 s1/2 orbital. This leads to the first observation of the lowest 0 + excited state in 94 Kr, hence signaling shape co-existence. Theoretical calculations performed within the in-medium similarity renormalization group framework are presented that also show the existence of a low-energy 0 + state, aligning qualitatively with the observation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Confinement-mediated phase behavior of hydrocarbon fluids: Insights from Monte Carlo simulations

The phase behavior of hydrocarbon fluids confined in porous media has been discussed to deviate significantly from that in the bulk environment due to the existence of sub-10nm pores. Though experiments and simulations have measured the bubble/dew points and sorption isotherms of hydrocarbons confined in both natural and synthetic nanopores, the confinement effects in terms of the strength of fluid-pore interactions tuned by surface wettability and chemistry have received comparably less discussion. More significantly, the underlying physics of confinement-induced phenomena remain obfuscated. In this work, we studied the phase behavior and capillary condensation of n-hexane to understand the effects of confinement at the molecular level. To systematically investigate the pore effects, we constructed two types of wall confinements; one is a structureless virtual wall described by the Steele potential and the other one is an all-atom amorphous silica structure with surface modified by hydroxyl groups. Our numerical results demonstrated the importance of fluid-pore interaction, pore size, and pore morphology effects in mediating the pressure-volume-temperature (PVT) properties of hydrocarbons. The most remarkable finding of this work was that the saturation pressure predicted from the van der Waals-type adsorption isothermal loop could be elevated or suppressed relative to the bulk phase, as illustrated in the graphical abstract. As the surface energy (i.e., fluid-pore interaction) decreased, the isothermal vapor pressure increased, indicating a greater preference for the fluid to exist in the vapor state. Sufficient reduction of the fluid-pore interactions could even elevate the vapor pressure above that of the bulk fluid.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗