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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Machine learning Frenkel Hamiltonian parameters to accelerate simulations of exciton dynamics

In this manuscript, we develop multiple machine learning (ML) models to accelerate a scheme for parameterizing site-based models of exciton dynamics from all-atom configurations of condensed phase sexithiophene systems. This scheme encodes the details of a system’s specific molecular morphology in the correlated distributions of model parameters through the analysis of many single-molecule excited-state electronic-structure calculations. These calculations yield excitation energies for each molecule in the system and the network of pair-wise intermolecular electronic couplings. In this work, we demonstrate that the excitation energies can be accurately predicted using a kernel ridge regression (KRR) model with Coulomb matrix featurization. We present two ML models for predicting intermolecular couplings. The first one utilizes a deep neural network and bi-molecular featurization to predict the coupling directly, which we find to perform poorly. The second one utilizes a KRR model to predict unimolecular transition densities, which can subsequently be analyzed to compute the coupling. We find that the latter approach performs excellently, indicating that an effective, generalizable strategy for predicting simple bimolecular properties is through the indirect application of ML to predict higher-order unimolecular properties. Such an approach necessitates a much smaller feature space and can incorporate the insight of well-established molecular physics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1987

The local interstellar medium

The structure of the local interstellar medium is reviewed with emphasis on the new observations of the cold neutral component. The properties of the high latitude molecular clouds are discussed as well as their relationship to the 'infrared cirrus' and atomic gas. The molecular clouds are shown to lie preferentially along the loops and filaments of local H I gas, but a detailed examination shows the CO and H I peaks are offset from one another. An expansion velocity of 7 km/s is derived for one of the shells, suggesting an expansion energy of about 8 x 10 to the 47th ergs, which is somewhat smaller than that expected for a supernova explosion. If the pressure in the clumps of the high latitude clouds is in equilibrium with the surrounding gas, the pressure in the shells is 10,000-100,000/cu cm K, an order of magnitude higher than what is generally argued to exist in the interstellar medium.

Blitz, Leo↗
DOE OSTI2020

Materials Data on Ge7H18O23 by Materials Project

Ge7H4O17(H5O2)2(H2O)2 crystallizes in the triclinic P1 space group. The structure is three-dimensional and consists of two molecular hydrogen;dihydrate molecules, two water molecules, and one Ge7H4O17 framework. In the Ge7H4O17 framework, there are seven inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.85–2.07 Å. In the second Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.84–2.00 Å. In the third Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.85–2.03 Å. In the fourth Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.84–2.10 Å. In the fifth Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 53–64°. There are a spread of Ge–O bond distances ranging from 1.74–1.85 Å. In the sixth Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 57–61°. There are a spread of Ge–O bond distances ranging from 1.75–1.79 Å. In the seventh Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 53–59°. There are a spread of Ge–O bond distances ranging from 1.73–1.86 Å. There are four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.03 Å) and one longer (1.63 Å) H–O bond length. 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. There are seventeen inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to three Ge4+ atoms. In the second O2- site, O2- is bonded in a distorted T-shaped geometry to three Ge4+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to three Ge4+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ge4+ atoms. In the fifth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to two Ge4+ and one H1+ atom. In the eighth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ge4+ and one H1+ atom. In the ninth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the tenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the eleventh O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the twelfth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the thirteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the fourteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the fifteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the sixteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted water-like geometry to three H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Quantifying Membrane Structure and Dynamics during Bioproduct Production in Zymomonas mobilis by Molecular Simulation

The conversion of lignocellulosic biomass into biofuels and bioproducts by microbial biorefineries is central to a sustainable chemical industry. Zymomonas mobilis is one such biorefinery chassis and is resistant to ethanol stress, leading to its use in biomass conversion to biofuels and bioproducts. However, Z. mobilis growth is often inhibited by organic acids, aldehydes, alcohols, ketones, and amides found in biomass hydrolysate. The resulting slow growth inhibits production and as a result drives up the price for the resulting products. One hypothesis is that these molecules interact with or disrupt the bacterial membrane, triggering stress responses and hindering growth. To test this hypothesis at the molecular level, we employ all-atom molecular dynamics (MD) simulations to investigate lignocellulose-derived small molecules and their impact on a biologically relevant Z. mobilis membrane model. Simulations were conducted across a range of inhibitor concentrations from 0 to 2.5 mol %, analyzing key membrane properties such as area per lipid (APL), membrane thickness, lipid-order parameter (−S CH ), lateral diffusion coefficient (D xy ), and permeability coefficient (Pm). From simulation, we observed altered membrane structure and dynamics at these modest small molecule concentrations commonly found in hydrolysates. Generally, the membranes become thinner, with a higher area per lipid and lower-order parameter as the small molecule concentration increases. These trends are stronger for more hydrophobic molecules with greater hydrophobic bulk, as isobutanol, propanol, and propanoic acid showed greater membrane perturbations as the concentration increased compared to other small molecules. Tracking small molecule distributions directly in our equilibrium simulations allows us to determine concentration-dependent free energy profiles for these molecules. While the trends are noisy, generally the barriers to crossing the membrane decrease as the concentration increases, indicating that the membranes become leakier as small molecule concentrations rise. Comparing between native Z. mobilis membranes with hopanoids and membranes sharing the same phospholipid composition but without hopanoids, hopanoids stabilize and order the membrane for smaller molecules to maintain membrane structure but appear insufficient for larger hydrophobic molecules like isobutanol. These findings provide a mechanistic understanding of how small molecules found in biomass degradation streams interact with the Z. mobilis membrane, offering valuable insights for future strain engineering efforts to optimize biofuel and bioproduct synthesis from biomass feedstocks by highlighting limits to small molecule tolerance. This knowledge can guide the modification of membrane composition to develop more robust microbes, thereby improving microbial survival and yields in industrial contexts.

Singh, Nitin Kumar [Michigan State Univ., East Lan↗
DOE OSTI2026

Deciphering the Solvation Structure of Aqueous ZnCl 2 Solutions from X-ray Absorption Spectra Using the Interpretable Graph Neural Network

Machine learning (ML) provides powerful pathways for predicting spectroscopic observables from atomic structures, but its broader impact depends on making model predictions interpretable in terms of physical and chemical principles. Here, we introduce a physics-guided graph neural network (GNN) model that predicts Zn K-edge X-ray spectroscopy (XAS) spectra of aqueous ZnCl 2 solutions. Training data are generated from ab initio XAS calculations on molecular dynamics snapshots obtained using a machine learning interatomic potential. The GNN reproduces experimental spectra across concentrations from dilute (<0.1 m) to highly concentrated (30 m, “water-in-salt”) regimes and scales efficiently to large, disordered liquid systems beyond the reach of conventional ab initio approaches. Gradient-based attribution analysis reveals that the model learns physically meaningful structure-spectrum relationships. Ligand-specific attributions reflect orbital hybridization patterns and the origin of the excitations derived from the density functional theory. Bond-length attributions recover spectral shifts consistent with multiple-scattering theory. Finally, this work bridges data-driven prediction with electronic-structure theory, establishing a general paradigm for interpretable ML that links atomic structure, electronic structure, and spectroscopic observables.

25 ENERGY STORAGE↗
DOE OSTI2020

Materials Data on Zn3P2(HO2)4 by Materials Project

(Zn3P2HO8)2(H2)3 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional and consists of four molecular hydrogen molecules and one Zn3P2HO8 framework. In the Zn3P2HO8 framework, there are two inequivalent Zn2+ sites. In the first Zn2+ site, Zn2+ is bonded in a trigonal planar geometry to one H and two equivalent O2- atoms. The Zn–H bond length is 1.55 Å. Both Zn–O bond lengths are 1.86 Å. In the second Zn2+ site, Zn2+ is bonded to four O2- atoms to form ZnO4 tetrahedra that share corners with two equivalent ZnO4 tetrahedra and corners with four equivalent PO4 tetrahedra. There are a spread of Zn–O bond distances ranging from 1.94–2.03 Å. P5+ is bonded to four O2- atoms to form PO4 tetrahedra that share corners with four equivalent ZnO4 tetrahedra. There is three shorter (1.54 Å) and one longer (1.60 Å) P–O bond length. H is bonded in a single-bond geometry to one Zn2+ atom. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to one Zn2+ and one P5+ atom. In the second O2- site, O2- is bonded in a trigonal planar geometry to two equivalent Zn2+ and one P5+ atom. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to one Zn2+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Zn2+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge7H18O23 by Materials Project

Ge7H7O18H5O2(H2O)3 crystallizes in the triclinic P1 space group. The structure is three-dimensional and consists of one molecular hydrogen;dihydrate molecule, three water molecules, and one Ge7H7O18 framework. In the Ge7H7O18 framework, there are seven inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.85–2.07 Å. In the second Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.84–2.00 Å. In the third Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.84–2.02 Å. In the fourth Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.82–2.15 Å. In the fifth Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 54–65°. There are a spread of Ge–O bond distances ranging from 1.74–1.84 Å. In the sixth Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–60°. There are a spread of Ge–O bond distances ranging from 1.75–1.82 Å. In the seventh Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 54–58°. There are a spread of Ge–O bond distances ranging from 1.74–1.86 Å. There are seven inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.58 Å) H–O bond length. 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 0.98 Å. In the fourth 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 fifth 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 sixth H1+ site, H1+ is bonded in a linear geometry to two O2- atoms. There is one shorter (1.20 Å) and one longer (1.22 Å) H–O bond length. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. There are eighteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to three Ge4+ atoms. In the second O2- site, O2- is bonded in a distorted T-shaped geometry to three Ge4+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to three Ge4+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ge4+ atoms. In the fifth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the sixth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ge4+ and one H1+ atom. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to two Ge4+ and one H1+ atom. In the eighth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ge4+ and one H1+ atom. In the ninth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the tenth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to two Ge4+ atoms. In the eleventh O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the twelfth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the thirteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the fourteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the fifteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the sixteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three H1+ atoms. In the eighteenth O2- site, O2- is bonded in a trigonal non-coplanar geometry to three H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ge7H18O23 by Materials Project

Ge7H7O18(H2O)3H5O2 crystallizes in the triclinic P1 space group. The structure is three-dimensional and consists of one molecular hydrogen;dihydrate molecule, three water molecules, and one Ge7H7O18 framework. In the Ge7H7O18 framework, there are seven inequivalent Ge4+ sites. In the first Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.85–2.05 Å. In the second Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.87–2.08 Å. In the third Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.83–2.07 Å. In the fourth Ge4+ site, Ge4+ is bonded to six O2- atoms to form GeO6 octahedra that share corners with three GeO4 tetrahedra and edges with three GeO6 octahedra. There are a spread of Ge–O bond distances ranging from 1.82–2.24 Å. In the fifth Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 49–60°. There are a spread of Ge–O bond distances ranging from 1.73–1.84 Å. In the sixth Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 54–61°. There are a spread of Ge–O bond distances ranging from 1.75–1.78 Å. In the seventh Ge4+ site, Ge4+ is bonded to four O2- atoms to form corner-sharing GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 56–59°. There are a spread of Ge–O bond distances ranging from 1.73–1.85 Å. There are seven 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 1.01 Å. In the second H1+ site, H1+ is bonded in a distorted linear geometry to two O2- atoms. There is one shorter (1.04 Å) and one longer (1.61 Å) H–O bond length. In the third H1+ site, H1+ is bonded in a single-bond geometry to two O2- atoms. There is one shorter (1.02 Å) and one longer (1.72 Å) H–O bond length. In the fourth H1+ site, H1+ is bonded in a distorted single-bond geometry to two O2- atoms. There is one shorter (1.03 Å) and one longer (1.65 Å) H–O bond length. In the fifth H1+ site, H1+ is bonded in a distorted single-bond geometry to one O2- atom. The H–O bond length is 1.02 Å. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. In the seventh 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 eighteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ge4+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to three Ge4+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to three Ge4+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Ge4+ atoms. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ge4+ and one H1+ atom. In the sixth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to two Ge4+ and one H1+ atom. In the eighth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the ninth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the tenth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ge4+ and one H1+ atom. In the eleventh O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the twelfth O2- site, O2- is bonded in a trigonal non-coplanar geometry to two Ge4+ and one H1+ atom. In the thirteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the fourteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the fifteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the sixteenth O2- site, O2- is bonded in a bent 120 degrees geometry to two Ge4+ atoms. In the seventeenth O2- site, O2- is bonded in a trigonal non-coplanar geometry to three H1+ atoms. In the eighteenth O2- site, O2- is bonded in a distorted water-like geometry to three H1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Structure and Desorption Kinetics of Acetonitrile Thin Films on Pt(111) and on Graphene on Pt(111)

Acetonitrile thin films were prepared on Pt(111) and on graphene on Pt(111) using molecular beam techniques. Temperature programed desorption (TPD) experiments of acetonitrile on Pt(111) displayed first-order kinetics for monolayer desorption and zero-order kinetics for multilayer desorption. We used reflection adsorption infrared spectroscopy (RAIRS) to characterize the orientation of the monolayer on Pt(111). Acetonitrile molecules have been shown to adopt a bridging structure where the C=N bond breaks to form two single bonds to underlying platinum atoms. When Tdeposition = 120 K our RAIRS spectra are consistent with this bridging configuration. However, when Tdeposition was lowered to 60 K molecules retained the C=N bond and adopted a vertical orientation with the nitrogen closest to the platinum. On graphene, the TPD experiments show that both the monolayer and multilayer desorb with zero-order kinetics. Our RAIRS spectra suggest that the monolayer consists of acetonitrile molecules oriented with their molecular axes parallel to the graphene substrate. This orientation did not change when Tdeposition was varied from 60 to 120 K. Our results provide a more complete picture of how acetonitrile molecules interact with Pt(111) and with graphene surfaces.

desorption tin films, molecules, thin films, desor↗
DOE OSTI2020

Discontinuous Galerkin discretization for quantum simulation of chemistry

All-electron electronic structure methods based on the linear combination of atomic orbitals method with Gaussian basis set discretization offer a well established, compact representation that forms much of the foundation of modern correlated quantum chemistry calculations—on both classical and quantum computers. Despite their ability to describe essential physics with relatively few basis functions, these representations can suffer from a quartic growth of the number of integrals. Recent results have shown that, for some quantum and classical algorithms, moving to representations with diagonal two-body operators can result in dramatically lower asymptotic costs, even if the number of functions required increases significantly. We introduce a way to interpolate between the two regimes in a systematic and controllable manner, such that the number of functions is minimized while maintaining a block-diagonal structure of the two-body operator and desirable properties of an original, primitive basis. Techniques are analyzed for leveraging the structure of this new representation on quantum computers. Empirical results for hydrogen chains suggest a scaling improvement from O(N 4.5 ) in molecular orbital representations to O(N 2.6 ) in our representation for quantum evolution in a fault-tolerant setting, and exhibit a constant factor crossover at 15 to 20 atoms. Moreover, we test these methods using modern density matrix renormalization group methods classically, and achieve excellent accuracy with respect to the complete basis set limit with a speedup of 1–2 orders of magnitude with respect to using the primitive or Gaussian basis sets alone. These results suggest our representation provides significant cost reductions while maintaining accuracy relative to molecular orbital or strictly diagonal approaches for modest-sized systems in both classical and quantum computation for correlated systems.

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

Observation of attosecond electron dynamics in the photoelectron momentum distribution of atoms using few-cycle laser pulses

The method of time-resolved measurement with ultrashort laser pulses is vital to the development of attosecond science. Pump-probe measurements using a train of attosecond pulses in combination with a near-infrared (NIR) multicycle driving laser have been successful in capturing the intercycle electron dynamics which repeats every optical cycle and leads to above-threshold ionization (ATI) spectra in the frequency domain. Here in this work, we study the effect of a carrier-envelope phase (CEP) in a few-cycle (< 6 fs) NIR laser pulse on the photoelectron momentum distribution (PMD) of a hydrogen atom and show that interference patterns in a PMD change dramatically with CEPs in the few-cycle regime. When the few-cycle driving laser pulse has a sine shape, the double-slit interference with characteristic modulation of ATI peaks dominates the PMD. On the other hand, when the driving pulse has a cosine shape, the holographical interference featured by a spider-like pattern is isolated. Our results suggest that the CEP-stable few-cycle laser pulses can be used to identify different types of intracycle interference structures in a PMD which reveal the underlying subcycle electron dynamics on an attosecond timescale.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Ab initio molecular dynamics simulation of Nd3+ incorporation in calcite

Trivalent rare-earth elements (REEs) readily incorporate in Ca-bearing minerals such as calcite (CaCO3), a phenomenon with important implications for the use of REEs as biogeochemical tracers as well as for environmental remediation. Despite substantial efforts, determining the incorporation modes of trivalent REEs in calcite has remained challenging due to their presence in multiple coordination environments. This is particularly problematic for the interpretation of extended X-ray absorption fine structure (EXAFS) spectroscopy. In this work, ab initio molecular dynamics (AIMD) simulations of Nd3+ incorporated in calcite were performed to resolve its incorporation modes. Nd3+ and Ca2+ have very similar ionic radii but the additional positive charge requires a charge compensation scheme (CCS). Five CCSs were considered in AIMD simulations, and the resulting atomic trajectories were then used to compute EXAFS spectra for direct fitting to a published experimental spectrum. The results of the fits indicated that Nd3+ incorporates at the Ca2+ site in calcite in a mixture of six- and seven-fold coordination environments and through three main incorporation modes: associated with a protonated nearest-neighbor Ca2+ vacancy, incorporated as NdOH2+, and charge compensated by a remote species (on the spatial scale probed by EXAFS). The incorporation of Nd3+ in calcite via multiple modes was consistent with previous work, but the AIMD-EXAFS approach allowed for resolving the nature, proportion, and structure of the different coordination environments.

Kerisit, Sebastien N.↗
DOE OSTI2020

Materials Data on Fe2(SO7)3 by Materials Project

FeO6(Fe(SO5)2)3(O2)3 is Tungsten Carbide-like structured and crystallizes in the trigonal P-31c space group. The structure is zero-dimensional and consists of two chebi:30649 molecules, six molecular oxygen molecules, and two Fe(SO5)2 clusters. In each Fe(SO5)2 cluster, there are two inequivalent Fe sites. In the first Fe site, Fe is bonded to six equivalent O atoms to form FeO6 octahedra that share corners with six equivalent SO4 tetrahedra. All Fe–O bond lengths are 2.02 Å. In the second Fe site, Fe is bonded to six O atoms to form FeO6 octahedra that share corners with three equivalent SO4 tetrahedra. There is three shorter (1.78 Å) and three longer (1.94 Å) Fe–O bond length. S is bonded to four O atoms to form SO4 tetrahedra that share corners with two FeO6 octahedra. The corner-sharing octahedra tilt angles range from 42–46°. There are a spread of S–O bond distances ranging from 1.46–1.53 Å. There are five inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Fe atom. In the second O site, O is bonded in a distorted bent 120 degrees geometry to one Fe and one S atom. In the third O site, O is bonded in a single-bond geometry to one S atom. In the fourth O site, O is bonded in a distorted bent 150 degrees geometry to one Fe and one S atom. In the fifth O site, O is bonded in a single-bond geometry to one S atom.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Synergistic Density Functional Theory and Molecular Dynamics Approach to Elucidate PNIPAM–Water Interaction Mechanisms

This study employs Density Functional Theory (DFT) and Molecular Dynamics (MD) simulations to investigate interactions between water molecules and Poly(N-isopropylacrylamide) (PNIPAM). DFT reveals preferential water binding sites, with enhanced binding energy observed in the linker zone. Quantum Theory of Atoms in Molecules (QTAIM) and electron localization function (ELF) analyses highlight the roles of hydrogen bonding and steric hindrance. MD simulations unveil temperature-dependent hydration dynamics, with structural transitions marked by changes in the radius of gyration (Rg) and the radial distribution function (RDF), aligning with DFT findings. Our work goes beyond prior studies by combining a DFT, QTAIM and MD simulations approach across different PNIPAM monomer-to-30mer structures. It introduces a systematic quantification of pseudo-saturation thresholds and explores water clustering dynamics with structural specificity, which have not been previously reported in the literature. These novel insights establish a more complete molecular-level picture of PNIPAM hydration behavior and temperature responsiveness, emphasizing the importance of amide hydrogen and carbonyl oxygen sites in hydrogen bonding, which weakens above the lower critical solution temperature (LCST), resulting in increased hydrophobicity and paving the way for understanding water sorption mechanisms, offering guidance for future applications such as dehumidification and atmospheric water harvesting.

08 HYDROGEN↗
DOE OSTI2021

Ab Initio Study of Atomic and Electronic Structure of Promising Ba4XMn3O12 (X = Nb, Ce, Pr) Oxides for Solar Thermochemical Hydrogen Production

The two-step metal oxide water-splitting cycle is one of the most viable approach for Solar Thermochemical Hydrogen (STCH) production. Challenges exist in finding suitable oxides that can satisfy thermodynamics of the STCH redox cycle under viable range of temperatures and partial pressures. Recently, BXM family members, i.e., Ba4NbMn3O12 (BNM), Ba4CeMn3O12 (BCM), Ba4PrMn3O12 (BPM) are discovered to exhibit promising STCH performance. However, the magnetic degrees of freedom of their experimental crystal structures is not characterized, and only hypothetical models exist for their electronic structure. We performed Monte-Carlo sampling for the magnetic spin arrangement of Mn atoms to provide explicit atomic structure models for their ground state 12R polytype and determined the most stable spin configuration for each member after structure relaxation using density functional theory (DFT) calculations. We also elucidate the most stable charge configuration (Mn3+/Mn4+ arrangement) for BNM among the existing hypothesis in literature. We investigate these strongly correlated oxides using different levels of theory (DFT+U, Hybrid-DFT) to develop better understanding of their electronic structure. These calculations allowed us to develop a model based on molecular orbital interactions that help explain the observed changes in their experimental x-ray spectroscopy measurements. Thereby, help link differences in electronic structure of BXM family members to their varying water-splitting behavior. These structure models will further facilitate future in-depth defect studies to model STCH redox cycle of these oxides.

atomic and magnetic structure↗
DOE OSTI2024

NbZr_BCC_SolidSolution_128atoms_VASP6

We performed density functional theory (DFT) calculations for body-centered-cubic (BCC) structures with 128 lattices sites of solid solution binary alloys niobium-zirconium (Nb-Zr). The electronic structures of alloys have been calculated using Vienna Ab initio Simulation Package (VASP). Within this package the DFT approach is used to reduce many-body Schrodinger equation to set of single particle Kohn-Sham (KS) equations. The generalized electronic exchange-correlation functional is described by generalized gradient approximation with the Perdew-Burke-Ernzerhof parametrization. The electron-ion interactions is described by pseudopotentials developed within the plane-wave basis projector augmented-wave (PAW) approach \cite{PAW}. These pseudopotentials are available at the VASP portal (http://cms.mpi.univie.ac.at/vasp/). Our calculations have been run with the pseudopotentials treating s and p semi-core states as valence in case for the elements Nb and Zr. The electronic densities and potentials are expanded over plane-waves with energy cutoff of 350 eV. 2x2x2 k-mesh and normal precision were used. The alloys were modeled by supercell containing 128 randomly distributed atoms. At initial step the atoms occupy perfect bcc lattice cites. This initial structure was optimized until energy changes less than 1e-6 eV, while forces acting on atoms don't exceed 1e-2 eV/angstrom. The electron-ion interaction is described by PAW pseudopotentials. The calculations have been collected by sampling chemical compositions across the entire compositional range. The chemical compositions have been sampled by progressively changing the number of atoms per constituent by 4. For each chemical composition of binaries and ternaries, the first-principle calculations have been run for 100 randomized arrangements of the constituents on the BCC lattice sites. We collected data for a total of 3,100 randomized atomic structures over 31 chemical compositions. The calculations have been collected on NERSC-Perlmutter and OLCF-Summit using the VASP 6.3.2. The VASP calculations for every atomic structure have been performed in 2 main steps: 1. Starting from an ideal body-centered-cubic (BCC) structure, geometry optimization with low precision has been executed to perform a preliminary optimization of the atomic structure. The output for this calculations is available in the files 0.CONTCAR, 0.OUTCAR, rlx1.out. 2. Using the atomic structure resulting from the preliminary geometry optimization, a second geometry optimization has been performed using normal precision. The output for this calculations is available in the files CONTCAR, OUTCAR, rlx2.out, vaspout.h5, and vasprun.xml. Cases 1-10 have been run without generating the file 'vaspout.h5'. Every chemical composition sampled across the composition range in the dataset has its own directory. The convention used to name the directories for binary alloys is AXBY, where A and B refer to the constituents, whereas X and Y are positive integers that represent the number of atoms for each constituent and their values still sum up to 128. Each atomic structure associated with a specific chemical composition has its own sub-directory within the directory of the corresponding chemical composition. The sub-directories for each atomic structure for each chemical composition are named 'case-*', where * is a positive integer that spans all the values from 1 through 100, extremes included. The files contained in each sub-directory 'case-*' for each atomic structure are as follows: FILES contained in each subdirectory with name "case-N" where N ranges between 11 and 100, extremes included: 1. INCAR: input file that contains various parameters and settings for controlling the behavior of the electronic structure calculations 2. KPOINTS: input file that specifies the Bloch vectors (k points) used to sample the Brillouin zone 3. 0.POSCAR: input file that defines the atomic structure of a system 4. 0.CONTCAR: output file that provides the atomic positions and cell parameters after the first geometry optimization has been run with the precision variable set to PREC=Low in the INCAR file 5. 0.OUTCAR: output file that contains detailed information about the progress of a calculation after the first geometry optimization has been run with the precision variable set to PREC=Low in the INCAR file 6. rlx1.out: file with diagnostic information about the execution of the first geometry optimization with precision variable set to PREC=Low in the INCAR file 7. POSCAR: input file that defines the atomic structure of a system after the first geometry optimization has been run at low precision. This represents the input for the second geometry optimization run with the precision variable set to PREC=Normal in the INCAR file 8. CONTCAR: output file that provides the atomic positions and cell parameters after the second geometry optimization has been run with the precision variable set to PREC=Normal in the INCAR file 9. OUTCAR: output file that contains detailed information about the progress of a calculation after the second geometry optimization has been run with the precision variable set to PREC=Normal in the INCAR file 10. rlx2.out: file with diagnostic information about the execution of the second geometry optimization with precision variable set to PREC=Normal in the INCAR file 11. vaspout.h5: hierarchical HDF5 file containing the inputs and outputs of a VASP calculation. To analyze the data in this file we recommend using py4vasp. This file is only produced if the VASP version used is compiled with HDF5 support 12. vasprun.xml: contains similar information to OUTCAR, but in an xml format. 13. CHGCAR: contains the charge density data of a system. This data is crucial for analyzing electronic structures, calculating electrostatic potential, and studying the distribution of charge in a crystal or molecular system FILES contained in each subdirectory with name "case-N" where N ranges between 1 and 10, extremes included: 1. INCAR: input file that contains various parameters and settings for controlling the behavior of the electronic structure calculations 2. KPOINTS: input file that specifies the Bloch vectors (k points) used to sample the Brillouin zone 3. {ID}.POSCAR: input file that defines the atomic structure of a system at the beginning of ID execution of geometry optimization with PREC=LOW 4. {ID}.CONTCAR: output file that provides the atomic positions and cell parameters at the end of ID execution of geometry optimization with PREC=LOW in the INCAR file 5. {ID}.OUTCAR: output file that contains detailed information about the progress of a calculation after the ID execution of geometry optimization that has been run with the precision variable set to PREC=Low in the INCAR file 6. rlx1.{ID}.out: file with diagnostic information about the execution of the ID execution of the geometry optimization with precision variable set to PREC=Low in the INCAR file 7. N{ID}.POSCAR: input file that defines the atomic structure of a system after the geometry optimization run at low precision. This represents the input for the ID execution of the second geometry optimization run with the precision variable set to PREC=Normal in the INCAR file 8. N{ID}.CONTCAR: output file that provides the atomic positions and cell parameters after the ID execution of the geometry optimization run with the precision variable set to PREC=Normal in the INCAR file 9. N{ID}.OUTCAR: output file that contains detailed information about the progress of a calculation after the ID execution of the geometry optimization run with the precision variable set to PREC=Normal in the INCAR file 10. rlx2.{ID}.out: file with diagnostic information about the ID execution of geometry optimization with precision variable set to PREC=Normal in the INCAR file 11. vaspout.h5: hierarchical HDF5 file containing the inputs and outputs of a VASP calculation. To analyze the data in this file we recommend using py4vasp. This file is only produced if the VASP version used is compiled with HDF5 support 12. vasprun.xml: contains similar information to OUTCAR, but in an xml format. 13. CHGCAR: contains the charge density data of a system. This data is crucial for analyzing electronic structures, calculating electrostatic potential, and studying the distribution of charge in a crystal or molecular system This research is sponsored by the Artificial Intelligence Initiative as part of the Laboratory Directed Research and Development (LDRD) Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the US Department of Energy under contract DE-AC05-00OR22725. This work used resources of the Oak Ridge Leadership Computing Facility, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725, under Directorate Discretionary awards MAT025 (Materials Science) and LRN026 (Machine Learning), and INCITE award MAT201. This work also used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, under award ERCAP0025216. REFERENCES (1) Kresse, G. & Hafner, J. Ab initio molecular dynamics for liquid metals. Phys. review B 47, 558 (1993). (2) Kresse, G. & Hafner, J. Ab initio molecular-dynamics simulation of the liquid-metal–amorphous-semiconductor transition in germanium. Phys. Rev. B 49, 14251 (1994) (3) Kresse, G. & Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. materials science 6, 15–50 (1996) (4) Kresse, G. & Furthmüller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. review B 54, 11169 (1996) (5) Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. review b 59, 1758 (1999)

36 MATERIALS SCIENCE↗
DOE OSTI2021

Spectral Denoising for Accelerated Analysis of Correlated Ionic Transport

Computation of correlated ionic transport properties from molecular dynamics in the Green-Kubo formalism is expensive, as one cannot rely on the affordable mean square displacement approach. We use spectral decomposition of the short-time ionic displacement covariance to learn a set of diffusion eigenmodes that encode the correlation structure and form a basis for analyzing the ionic trajectories. This allows systematic reduction of the uncertainty and accelerate computations of ionic conductivity in systems with a steady-state correlation structure. We provide mathematical and numerical proofs of the method’s robustness and demonstrate it on realistic electrolyte materials.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Materials Data on Zn2Hg2H3(SO5)2 by Materials Project

(HgZnSO5)4(H2)3 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional and consists of four molecular hydrogen molecules and one HgZnSO5 framework. In the HgZnSO5 framework, there are two inequivalent Hg+1.50+ sites. In the first Hg+1.50+ site, Hg+1.50+ is bonded in a 2-coordinate geometry to six O2- atoms. There are a spread of Hg–O bond distances ranging from 2.10–2.97 Å. In the second Hg+1.50+ site, Hg+1.50+ is bonded in a distorted linear geometry to two O2- atoms. There are one shorter (2.07 Å) and one longer (2.10 Å) Hg–O bond lengths. Zn2+ is bonded to five O2- atoms to form ZnO5 trigonal bipyramids that share corners with three equivalent SO4 tetrahedra and an edgeedge with one ZnO5 trigonal bipyramid. There are a spread of Zn–O bond distances ranging from 2.01–2.21 Å. S5+ is bonded to four O2- atoms to form SO4 tetrahedra that share corners with three equivalent ZnO5 trigonal bipyramids. There are a spread of S–O bond distances ranging from 1.46–1.52 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to one Hg+1.50+, one Zn2+, and one S5+ atom. In the second O2- site, O2- is bonded to two Hg+1.50+ and two equivalent Zn2+ atoms to form a mixture of corner and edge-sharing OZn2Hg2 tetrahedra. In the third O2- site, O2- is bonded in a bent 150 degrees geometry to one Zn2+ and one S5+ atom. In the fourth O2- site, O2- is bonded to two Hg+1.50+ and two equivalent Zn2+ atoms to form a mixture of corner and edge-sharing OZn2Hg2 tetrahedra. In the fifth O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Zn2+ and one S5+ atom. In the sixth O2- site, O2- is bonded in a single-bond geometry to one Hg+1.50+ and one S5+ atom.

36 MATERIALS SCIENCE↗