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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

ORNL_AISD_NiNb

This dataset describes the nickel-niobium solid solution binary alloy, where the two constituent elements nickel (Ni) and niobium (Nb) are randomly placed on an underlying crystal lattice. This dataset for nickel-niobium (Ni-Nb) alloys available includes the formation energy and bulk modulus for each crystal structure. Each atomic sample has a disordered phase which is obtained starting from an initial regular crystal structure of type body-centered cubic (BCC), face-centered cubic (FCC), or hexagonal compact packed (HCP). The geometry optimization ensures that all the alloy samples reached the equilibrium with negative formation energy. We perform geometry optimizations using the LAMMPS simulation package [1], a flexible simulation tool for particle-based materials modeling at the atomic, meso, and continuum scales. We utilized the embedded atom model (EAM) potential for Ni and Nb developed in a previous study [2]. The potential could describe behaviors of the liquid and solid phases of Ni-Nb alloy. The structural factors and angular distributions of three atoms are well-matched with X-ray and ab initio-based molecular dynamics data. We prepared the three different crystals with different initial lattice parameters (3.52 Ã… for FCC, 3.32 Ã… for BCC, and 3.5 Ã… for HCP). We performed energy minimization in two steps. Firstly, we minimized the structures with an isotropic unit cell to minimize the side effects from our arbitrary lattice parameters for all other compositions. Then, we applied geometry optimization with a triclinic (non-orthogonal) unit cell to fully minimize the stress components to calculate the elastic constants. In this procedure, we chose 10,000 as the maximum number of allowable steps aimed at obtaining fully relaxed atomic geometries. The dataset consists of three sets of crystal structures. The first set contains 46,086 irregular crystal structures, each of them with 54 atoms, obtained through optimization starting from a regular BCC crystal structure. The second set contains 24,543 irregular crystal structures, each of them with 32 atoms, obtained through optimization starting from a regular FCC crystal structure. The third set contains 39,303 irregular crystal structures, each of them with 48 atoms, obtained through optimization starting from a regular HCP crystal structure. The atomic configurations within each set span the possible compositional range. The three sets have been unified in a global dataset, which is extremely heterogeneous in terms of crystal structures, lattice volumes, and atomic configurations. Organization of files inside the dataset: the dataset contains three subdirectories called • BCC_opt • FCC_opt • HCP_opt based on the type of initial regular structure used to start the geometry optimization. Inside each of these folders, every atomic structure is identified by a string “A_B_Câ€, where A denotes the number of Nb in the system, B denotes index of structure with a given Nb number, and C denotes the total number of structures generated with a given Nb number. For each optimized crystal structure identified by the unique string of characters “A_B_Câ€, three files are provided: • A_B_C_opt.xyz: The optimized geometries in xyz format • A_B_C_opt.cfg: The optimized geometries in cfg format. It includes cell information and atomic energy, and forces calculated from LAMMPS. • A_B_C.elastic: Raw data of 21 elastic constants from LAMMPS output. • A_B_C.bulk: Calculated upper and lower bounds of bulk modulus and averaged one based on Voigt-Reuss-Hill approach from *.elastic. References: [1] A. P. Thompson, H. M. Aktulga, R. Berger, D. S. Bolintineanu, W. M. Brown, P. S. Crozier, P. J. in 't Veld, A. Kohlmeyer, S. G. Moore, T. D. Nguyen, R. Shan, M. J. Stevens, J. Tranchida, C. Trott, and S. J. Plimpton. LAMMPS - a flexible simulation tool for particle-based materials modeling at the atomic, meso, and continuum scales. Comp. Phys. Comm., 271:108171, 2022. [2] Y Zhang, R Ashcraft, MI Mendelev, CZ Wang, and KF Kelton. Experimental and molecular dynamics simulation study of structure of liquid and amorphous ni62nb38 alloy. The Journal of chemical physics, 145(20):204505, 2016.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Lithiation of Sulfur-Graphene Compounds Using Reactive Force-Field Molecular Dynamics Simulations

We performed molecular dynamics simulations of lithium-sulfur-graphene compounds using reactive force fields, providing a time scale to observe atomistic features relevant to the microscopic behavior of the of the bulk of sulfur-based cathodes to be used beyond our present Li-ion batteries. The samples we used were set to realistic geometries through sophisticated protocols to simulate ultrafast reactions that occur within the picosecond range, thus allowing us to get some insights into the characteristics of the bulk material in working cathodes of Li–S batteries, which are mixed with carbon to increase the poor electronic conductivity of S. We report chemical speciation and geometrical data at atomistic levels. We observed that slowly lithiated cathodes were more stable and with higher density than those that were suddenly fully-lithiated. We did not observe molecular Li 2 S formation; however, we observed an amorphous solid arrangement with the same stoichiometry of Li and S, with S–Li–S angles of ~111° and smaller ones due to the interaction between polysulfides that did not reacted totally. In addition, graphene keeps its planar shape; however, S8 changes its shape from rings to chains. Lithiated structures are more stable with lower energies, and more close-packed structures than structures with Li already inserted.

25 ENERGY STORAGE↗
DOE OSTI2023

Americium Oxalate: An Experimental and Computational Investigation of Metal–Ligand Bonding

A novel actinide-containing coordination polymer, [Am(C 2 O 4 )(H 2 O) 3 Cl] (Am-1), has been synthesized and structurally characterized. The crystallographic analysis reveals that the structure is two-dimensional and comprised of pseudo-dimeric Am 3+ nodes that are bridged by oxalate ligands to form sheets. Each metal center is nine-coordinate, forming a distorted capped square antiprism geometry with a C 1 symmetry, and features bound oxalate, aqua, and chloro ligands. The Am 3+ –ligand bonds were probed computationally using the quantum theory of atoms in molecules nd natural localized molecular orbital approaches to investigate the underlying mechanisms and hybrid atomic orbital contributions therein. The analyses indicate that the bonds within Am-1 are predominantly ionic and the 5f shell of the Am 3+ metal centers does not add a significant covalent contribution to the bonds. Further, our bonding assessment is supported by measurements on the optical properties of Am-1 using diffuse reflectance and photoluminescence spectroscopies. The position of the principal absorption band at 507 nm ( 5 L 6' ← 7 F 0' ) is notable because it is consistent with previously reported americium oxalate complexes in solution, indicating similarities in the electronic structure and ionic bonding. Compound Am-1 is an active phosphor, featuring strong bright-blue oxalate-based luminescence with no evidence of metal-centered emission.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis

The application of bimolecular reductive elimination to the activation of iron catalysts for alkene–diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, ( Me PDI)FeCH 3 and ( Et PDI)FeCH 3 ( R PDI = 2,6-(2,6-R 2 -C 6 H 3 N=CMe) 2 C 5 H 3 N), and the alkyl-substituted examples, ( Cy APDI)FeCH 3 ( Cy APDI = 2,6-(C 6 H 11 N=CMe) 2 C 5 H 3 N), have molecular structures significantly distorted from planarity and S = 3/2 ground states. The related N-arylated derivative bearing 2,6-di-isopropyl aryl substituents, ( iPr PDI)FeCH 3 , has an idealized planar geometry and exhibits spin crossover behavior from S = 1/2 to S = 3/2 states. At 23 °C under an N 2 atmosphere, both ( Me PDI)FeCH 3 and ( Et PDI)FeCH 3 underwent reductive elimination of ethane to form the iron dinitrogen precatalysts, [( Me PDI)Fe(N 2 )] 2 (μ-N 2 ) and [( Et PDI)Fe(N 2 )] 2 (μ-N 2 ), respectively, while ( iPr PDI)FeCH 3 proved inert to C–C bond formation. By contrast, addition of butadiene to all three iron methyl complexes induced ethane formation and generated the corresponding iron butadiene complexes, ( R PDI)Fe(η 4 -C 4 H 6 ) (R = Me, Et, i Pr), known precatalysts for the [2+2] cycloaddition of olefins and dienes. Kinetic, crossover experiments, and structural studies were combined with magnetic measurements and Mössbauer spectroscopy to elucidate the electronic and steric features of the iron complexes that enable this unusual reductive elimination and precatalyst activation pathway. Furthermore, transmetalation of methyl groups between iron centers was fast at ambient temperature and independent of steric environment or spin state, while the intermediate dimer underwent the sterically controlled rate-determining reaction with either N 2 or butadiene to access a catalytically active iron compound.

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

Cyclically conjugated porphyrin trimers linked through benzo[4,5]imidazo[2,1- a ]isoindole bridges

Cyclically conjugated porphyrin trimers were prepared via a concise synthetic method. Zn-Trimer-1 displayed strong exciton coupling, suggesting the presence of effective electronic interactions. UV-Vis absorption and fluorescence spectra obtained through titration studies on the donor–acceptor adduct (Zn-Trimer-1–C60Im) indicate the occurrence of excited state photo-events. Inspired by nature's photosynthetic process of plants and bacteria, electronically interacting multiporphyrinic systems have long been investigated as synthetic models of natural photosynthetic systems. Remarkable successes have been achieved with cyclic porphyrin arrays, where porphyrins are arranged in a wheel-like structure or nanoring as photosynthetic antennae. Considerable efforts have also been devoted to constructing other porphyrin arrays such as molecular wires for potential applications in sensors, solar energy conversion, non-linear optical (NLO) materials, and more. Due to synthetic difficulties, cyclically conjugated porphyrin arrays in which porphyrins are arranged in planar geometry are very rare. Very recently, Anderson and coworkers have reported unprecedented β,β-directly linked porphyrin trimers and tetramers with different geometries, propeller and saddle, respectively, which result in distinct photophysical and electrochemical properties (Fig. 1a). In this paper, we present novel cyclically conjugated porphyrin trimers, which feature planar geometry with porphyrins assembled around the aromatic triphenylene at the center (Fig. 1b).

Han, Ting↗
DOE OSTI2021

Interfacial intermixing and anti-phase boundaries in GaP/Si(0 0 1) heterostructures

Epitaxial GaP/Si heterostructures grown by molecular beam epitaxy (MBE) and migration-enhanced epitaxy (MEE) have been studied, primarily using aberration-corrected scanning transmission electron microscopy (AC-STEM). Atomically-resolved structure images, which are sensitive to atomic-column intensity revealed the detailed geometry of antiphase boundaries that were both parallel and also inclined to the growth direction. The polar/non-polar GaP/Si interfaces were neither atomically flat laterally nor abrupt vertically. Measurements of intensity profiles using both bright-field and dark-field AC-STEM images, as well as chemically-sensitive g 002 dark-field imaging, indicated substantial interfacial intermixing, which increased significantly from ~1.3 nm (MEE growth at 440 °C) to ~2.1 nm (MBE growth at 600 °C). The finite interface width will impact theoretical predictions of charge imbalance and strong electric fields across the heterointerface.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Halide perovskites enable polaritonic XY spin Hamiltonian at room temperature

Exciton polaritons, the part-light and part-matter quasiparticles in semiconductor optical cavities, are promising for exploring Bose–Einstein condensation, non-equilibrium many-body physics and analogue simulation at elevated temperatures. However, a room-temperature polaritonic platform on par with the GaAs quantum wells grown by molecular beam epitaxy at low temperatures remains elusive. Here, the operation of such a platform calls for long-lifetime, strongly interacting excitons in a stringent material system with large yet nanoscale-thin geometry and homogeneous properties. Here, we address this challenge by adopting a method based on the solution synthesis of excitonic halide perovskites grown under nanoconfinement. Such nanoconfinement growth facilitates the synthesis of smooth and homogeneous single-crystalline large crystals enabling the demonstration of XY Hamiltonian lattices with sizes up to 10 × 10. With this demonstration, we further establish perovskites as a promising platform for room temperature polaritonic physics and pave the way for the realization of robust mode-disorder-free polaritonic devices at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microporous metal–organic frameworks for the purification of propylene

Separation of propylene from its analogous hydrocarbons such as propane is of great importance in the petrochemical industry to produce valuable chemical feedstocks with desired purity. However, the well-established method currently used for industrial propane/propylene separation is energy intensive. It involves repeated cycling in the cryogenic and high-pressure distillation process and requires multiple columns and high reflux ratios because of the very similar physical properties of the two species. Thus, it is identified as one of the most capital- and energy-intensive processes. Adsorptive separation based on porous adsorbents is regarded as an alternative energy-efficient technology to replace or supplement the traditional heat-driven cryogenic distillation processes. In this context, metal–organic frameworks (MOFs) have emerged as the most promising candidates for propane/propylene separation, taking into consideration their unique tunability with respect to pore geometry and pore functionality. In this highlight, we summarize the latest advancement in developing MOFs as physisorbents for the separation and purification of propylene from propane, with a focus on those that demonstrate selective molecular exclusion and propane-selective adsorption. We discuss the adsorption preferences related to the material design and separation mechanisms, and review the existing challenges. Lastly, we offer our perspectives on various strategies for the future design of MOFs that hold true potential for propylene purification under industrial settings.

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

Materials Data on Ti2H2CSe4Cl16O5 by Materials Project

Ti2C(OCl2)3(HSeOCl)2(SeCl3)2Cl2 crystallizes in the monoclinic P2/c space group. The structure is two-dimensional and consists of two molecular chlorine molecules; four HSeOCl clusters; four SeCl3 clusters; and one Ti2C(OCl2)3 sheet oriented in the (0, 1, 0) direction. In each HSeOCl cluster, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. Se3+ is bonded in a distorted L-shaped geometry to one O2- and one Cl1- atom. The Se–O bond length is 1.83 Å. The Se–Cl bond length is 2.50 Å. O2- is bonded in a distorted water-like geometry to one H1+ and one Se3+ atom. Cl1- is bonded in a distorted single-bond geometry to one Se3+ atom. In each SeCl3 cluster, Se3+ is bonded in a single-bond geometry to one Cl1- atom. The Se–Cl bond length is 2.76 Å. There are three inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 1-coordinate geometry to one Cl1- atom. The Cl–Cl bond length is 2.30 Å. In the second Cl1- site, Cl1- is bonded in a 2-coordinate geometry to one Se3+ and one Cl1- atom. The Cl–Cl bond length is 2.32 Å. In the third Cl1- site, Cl1- is bonded in a distorted linear geometry to two Cl1- atoms. In the Ti2C(OCl2)3 sheet, Ti4+ is bonded in a 5-coordinate geometry to one O2- and four Cl1- atoms. The Ti–O bond length is 2.71 Å. There are a spread of Ti–Cl bond distances ranging from 2.15–2.47 Å. C4+ is bonded in a linear geometry to two equivalent O2- atoms. Both C–O bond lengths are 1.18 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Ti4+ and one C4+ atom. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two equivalent Cl1- atoms. Both O–Cl bond lengths are 1.93 Å. There are three inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Ti4+ atom. In the second Cl1- site, Cl1- is bonded in a water-like geometry to one Ti4+ and one O2- atom. In the third Cl1- site, Cl1- is bonded in an L-shaped geometry to two equivalent Ti4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H12Cl2O13 by Materials Project

H7O3H5O2(ClO4)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four molecular hydrogen;dihydrate molecules, eight ClO4 clusters, and four H7O3 clusters. In each ClO4 cluster, there are four inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.48 Å. In the second O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.46 Å. In the third O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.46 Å. In the fourth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.46 Å. Cl is bonded in a tetrahedral geometry to four O atoms. In each H7O3 cluster, there are seven inequivalent H sites. In the first H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 1.02 Å. In the second H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.05 Å) and one longer (1.53 Å) H–O bond length. In the third H site, H is bonded in a linear geometry to two O atoms. There is one shorter (1.05 Å) and one longer (1.53 Å) H–O bond length. In the fourth 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 fifth 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 sixth H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.99 Å. In the seventh H site, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.98 Å. There are three inequivalent O sites. In the first O site, O is bonded in a 3-coordinate geometry to three H atoms. In the second O site, O is bonded in a trigonal non-coplanar geometry to three H atoms. In the third O site, O is bonded in a 3-coordinate geometry to three H atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Water under hydrophobic confinement: entropy and diffusion

The properties of liquid water are known to change drastically in confined geometries. A most interesting and intriguing phenomenon is that the diffusion of water is found to be strongly enhanced by the proximity of a hydrophobic confining wall relative to the bulk diffusion. We report a molecular dynamics simulation using a classical water model investigating the water diffusion near a non-interacting smooth confining wall, which is assumed to imitate a hydrophobic surface, revealing a pronounced diffusion enhancement within several water layers adjacent to the wall. We present evidence that the observed diffusion enhancement can be accounted for, with a quantitative accuracy, using the universal scaling law for liquid diffusion that relates the diffusion rate to the excess entropy. These results show that the scaling law, which has so far only been used for the description of the diffusion in simple liquids, can successfully describe the diffusion in water. It is shown that the law can be used for the analysis of water dynamics under nanoscale hydrophobic confinement, which is currently a subject of intense research activity.

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

Control of Dipolar Dynamics by Geometrical Programming

We propose and theoretically analyze methods for quantum many-body control through geometric reshaping of molecular tweezer arrays. Dynamic rearrangement during entanglement is readily available due to the extended coherence times of molecular rotational qubits. We show how motional dephasing can be suppressed and enhanced spin squeezing can be achieved in an actively rearranged short-range XY model. We also analyze in detail a specific static geometry that significantly suppresses decoherence. These general methods as applied to programmable quantum systems offer robust control modalities that are well suited to molecules.

optical tweezers↗
DOE OSTI2020

Photoelectron spectroscopy and computational investigations of the electronic structures and noncovalent interactions of cyclodextrin-closo-dodecaborate anion complexes x-CD·B12X122- (x = a, ß, y; X = H, F)

We report a joint negative ion photoelectron spectroscopy (NIPES) and computational study on the electronic structures and noncovalent interactions of a series of cyclodextrin-closo-dodecaborate dianion complexes, ?-CD·B12X122- (? = a, ß, ?; X = H, F). The measured vertical / adiabatic detachment energies (VDEs / ADEs) are 1.15/0.93, 3.55/3.20, 3.90/3.60, and 3.85/3.60 eV for B12H122- and its a-, ß-, ?-CD complexes, respectively; while the corresponding values are 1.90/1.70, 4.00/3.60, 4.33/3.95, and 4.30/3.85 eV for the X = F case. These results show that the inclusion of B12X122- into the CD cavities greatly increase the electronic stability of the dianions. The effect of electronic stabilization for ß-CD is roughly the same as for ?-CD, both being considerably stronger than that for a-CD. Density functional theory (DFT) based geometry optimization reveals that B12X122- are inserted into CDs increasingly deeper from a-CD to ?-CD. The calculated VDEs and ADEs agree with the experiments well, particularly, reproducing the electron binding energy (EBE) trends. The molecular orbital analyses indicate that the most loosely bound photodetached electrons origin from the guest B12X122- moieties. In addition to a shift of all signals to larger EBE, significant changes in the signal patterns are observed. At low EBE, this is due to the splitting of highly degenerate B12X122- orbitals, while at high EBE, photodetachment from CD oxygens contributes to the new bands. The guest B12X122- and host CD nocovalent, size-specific interaction based on the independent gradient model (IGM) and energy decomposition analysis (EDA), is dominated by electrostatic interactions. The analysis further unravels unambiguiously the existence of dihydrogen bonding and how it affects the total energy that stabilizes the host-guest complexes of CDs·B12H122- compared to the general hydrogen bonding interaction in CDs·B12F122-. This work clearly exhibits strong influences on the electronic structures of dodecaborates upon clustering with CDs, with both size (a-, ß-, ?-) and molecular (X = H or F) specificities, thus providing critical molecular-level information on the cyclodextrin-closo-dodecaborate interactions of interest to medical applications, e.g. Boron neutron capature therapy. The NIPES experiments done at PNNL were supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Bioscience (X.-B.W.) and was performed at the EMSL, a national scientific user facility sponsored by DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. H.S. and Z.S. acknowledge the funding support of National Natural Science Foundation of China (Nos.11727810, 61720106009 and 21603074), the Science and Technology Commission of Shanghai Municipality (Nos. 19JC1412200), and the Program of Introducing Talents of Discipline to Universities 111 project (B12024). Z. L. thanks the China Scholarship Council (CSC) for financial support. We acknowledge the ECNU Multifunctional Platform for Innovation (001) and HPC Research Computing Team for providing computational and storage resources. J.W. acknowledges support from the Alexander von Humboldt foundation (Feodor Lynen Fellowship and Rückkehrerstipendium), a Freigeist fellowship of the Volkswagenfoundation and Prof. Vladimir A. Azov for helpful discussions.

Li, Zhipeng↗
DOE OSTI2025

Improved Treatment of 1–4 Interactions in Force Fields for Molecular Dynamics Simulations

Traditional force fields commonly use a combination of bonded torsional terms and empirically scaled nonbonded interactions to capture 1-4 energies and forces of atoms separated by three bonds in a molecule. While this approach can yield accurate torsional energy barriers, it often leads to inaccurate forces and erroneous geometries and creates an interdependence between dihedral terms and nonbonded interactions, complicating parametrization and reducing transferability. Here, in this paper, we demonstrate that 1-4 interactions can be accurately modeled using only bonded coupling terms, eliminating the need for arbitrarily scaled nonbonded interactions altogether. Furthermore, by leveraging the automated parametrization capabilities of the Q-Force toolkit, we efficiently determine the necessary coupling terms without the need for manual adjustment. Our approach is first validated on a range of small molecule systems, encompassing both flexible and rigid structures, and shows a significant improvement in force field accuracy, obtaining subkcal/mol mean absolute error for every molecule tested. We further extend the bonded-only model for 1-4 interactions to Amber ff14sb, CHARMM36, and OPLS-AA force fields to reproduce ab initio gas and implicit solvent ϕ,ψ surfaces of alanine dipeptide.

Abdullah, Aalim S. [University of California, Berk↗
DOE OSTI2026

Selectivity in gas–liquid interactions: Molecular beam scattering of CD 4 and ND 3 from an aqueous flat liquid jet

The dynamics of polar and nonpolar molecules colliding with an aqueous surface are characterized by scattering molecular beams of deuterated methane and ammonia, CD 4 and ND 3 (E i = 28.9 and 30.3 kJ mol −1 , respectively), from a flat liquid jet of cold salty water (8 m LiBr, 230 K). Translational energy distributions of scattered species collected as a function of collision geometry probe both impulsive scattering (IS) and thermal desorption (TD) mechanisms. Here, we find that CD 4 scattering is dominated by IS and exhibits a super-specular angular distribution. The fraction of TD scattering events is notably smaller for cold salty water than for dodecane, consistent with a higher free energy of solvation for CD 4 in the water jet. In contrast, no scattering signal is seen for ND 3 from the water jet, a result attributed to the high solubility and efficient protonation of ND 3 in liquid water. The IS channel for CD 4 was analyzed using a soft-sphere model, yielding a higher internal energy (E int ) and lower effective surface mass (m eff ) than was seen for Ne/water; the higher value of E int is attributed to rotational excitation of the scattered CD 4 . These findings demonstrate that the outcomes of a gas–liquid collision—scattering trajectory, surface adherence, and energy transfer—are directed at the molecular level by both the gaseous scatterer and liquid surface.

Foreman, Madison M. [University of California, Ber↗
DOE OSTI2023

Aerosol‐Jet‐Printable Covalent Organic Framework Colloidal Inks and Temperature‐Sensitive Nanocomposite Films

Abstract With molecularly well‐defined and tailorable 2D structures, covalent organic frameworks (COFs) have emerged as leading material candidates for chemical sensing, storage, separation, and catalysis. In these contexts, the ability to directly and deterministically print COFs into arbitrary geometries will enable rapid optimization and deployment. However, previous attempts to print COFs have been restricted by low spatial resolution and/or post‐deposition polymerization that limits the range of compatible COFs. Here, these limitations are overcome with a pre‐synthesized, solution‐processable colloidal ink that enables aerosol jet printing of COFs with micron‐scale resolution. The ink formulation utilizes the low‐volatility solvent benzonitrile, which is critical to obtaining homogeneous printed COF film morphologies. This ink formulation is also compatible with other colloidal nanomaterials, thus facilitating the integration of COFs into printable nanocomposite films. As a proof‐of‐concept, boronate‐ester COFs are integrated with carbon nanotubes (CNTs) to form printable COF‐CNT nanocomposite films, in which the CNTs enhance charge transport and temperature sensing performance, ultimately resulting in high‐sensitivity temperature sensors that show electrical conductivity variation by 4 orders of magnitude between room temperature and 300 °C. Overall, this work establishes a flexible platform for COF additive manufacturing that will accelerate the incorporation of COFs into technologically significant applications.

2D materials↗
DOE OSTI2020

Active Learning A Neural Network Model For Gold Clusters & Bulk From Sparse First Principles Training Data

Small metal clusters are of fundamental scientific interest and of tremendous significance in catalysis. These nanoscale clusters display diverse geometries and structural motifs depending on the cluster size; a knowledge of this size-dependent structural motifs and their dynamical evolution has been of longstanding interest. Given the high computational cost of first-principles calculations, molecular modeling and atomistic simulations such as molecular dynamics (MD) has proven to be an important complementary tool to aid this understanding. Classical MD typically employ predefined functional forms which limits their ability to capture such complex size-dependent structural and dynamical transformation. Neural Network (NN) based potentials represent flexible alternatives and in principle, well-trained NN potentials can provide high level of flexibility, transferability and accuracy on-par with the reference model used for training. A major challenge, however, is that NN models are interpolative and requires large quantities (similar to 10 4 or greater) of training data to ensure that the model adequately samples the energy landscape both near and far-from-equilibrium. A highly desirable goal is minimize the number of training data, especially if the underlying reference model is first-principles based and hence expensive. In this work, we introduce an active learning (AL) scheme that trains a NN model on-the-fly with minimal amount of first-principles based training data. Our AL workflow is initiated with a sparse training dataset (similar to 1 to 5 data points) and is updated on-the-fly via a Nested Ensemble Monte Carlo scheme that iteratively queries the energy landscape in regions of failure and updates the training pool to improve the network performance. Using a representative system of gold clusters, we demonstrate that our AL workflow can train a NN with similar to 500 total reference calculations. Using an extensive DFT test set of similar to 1100 configurations, we show that our AL-NN is able to accurately predict both the DFT energies and the forces for clusters of a myriad of different sizes. Our NN predictions are within 30 meV/atom and 40 meV/angstrom of the reference DFT calculations. Moreover, our AL-NN model also adequately captures the various size-dependent structural and dynamical properties of gold clusters in excellent agreement with DFT calculations and available experiments. We finally show that our AL-NN model also captures bulk properties reasonably well, even though they were not included in the training data.

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

Trends in actinide electronic structure revealed from asymmetric, isostructural transuranic metallocenes

The study of actinide electronic structure and bonding within rigorously controlled environments is fundamental to advancing nuclear applications. Here, we report a new set of isostructural actinide organometallics; An(COT big ) 2 , (An = Th, U, Np, and Pu), where COT big is the bulky 1,4-bis(triphenylsilyl)-substituted cyclooctatetraenyl dianion (1,4-(Ph 3 Si) 2 C 8 H 6 ) 2 -. The actinide(IV) metallocene sandwiches have a clam-shell structure, offering a new molecular symmetry to explore f-orbital contributions in bonding. Combined experimental and computational studies reveal that An(COT big ) 2 complexes strongly differ from the previously published coplanar An(COT) 2 sandwiches due to the bent geometry and electron-withdrawing nature of the substituents. While COT big displays comparatively weaker electron donation, the low-energy f-f transitions in An(COT big ) 2 have increased molar absorptivity consistent with the removal of the parity selection rule and better energetic matching between ligand and actinide 5f orbitals as the series is traversed. For Pu(COT big ) 2 , covalent mixing of donor 5f metal orbitals and the ligand-π orbitals is especially strong.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗