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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

A comparison of QTP functionals against coupled-cluster methods for EAs of small organic molecules

EA-EOM-CCSD electron affinities and LUMO energies of various Kohn–Sham density functional theory (DFT) methods are calculated for an a priori IP benchmark set of 64 small, closed-shell molecules. The purpose of these calculations was to investigate whether the QTP KS-DFT functionals can emulate EA-EOM-CC with only a mean-field approximation. We show that the accuracy of DFT—relative to CCSD—improves significantly when elements of correlated orbital theory are introduced into the parameterization to define the QTP family of functionals. In particular, QTP(02), which has only a single range separation parameter, provides results accurate to a MAD of <0.15 eV for the whole set of 64 molecules compared to EA-EOM-CCSD, far exceeding the results from the non-QTP family of density functionals.

Chemistry↗
DOE OSTI2024

Observation of a super-tetrahedral cluster of acetonitrile-solvated dodecaborate dianion via dihydrogen bonding

We launched a combined negative ion photoelectron spectroscopy and multiscale theoretical investigation on the geometric and electronic structures of a series of acetonitrile-solvated dodecaborate clusters, i.e., B 12 H 12 2- ·nCH 3 CN (n = 1–4). The electron binding energies of B 12 H 12 2- ·nCH 3 CN are observed to increase with cluster size, suggesting their enhanced electronic stability. B3LYP-D3(BJ)/ma-def2-TZVP geometry optimizations indicate each acetonitrile molecule binds to B 12 H 12 2- via a threefold dihydrogen bond (DHB) B3–H3 ⋮⋮⋮ H3C–CN unit, in which three adjacent nucleophilic H atoms in B 12 H 12 2- interact with the three methyl hydrogens of acetonitrile. The structural evolution from n = 1 to 4 can be rationalized by the surface charge redistributions through the restrained electrostatic potential analysis. Notably, a super-tetrahedral cluster of B 12 H 12 2- solvated by four acetonitrile molecules with 12 DHBs is observed. The post-Hartree–Fock domain-based local pair natural orbital- coupled cluster singles, doubles, and perturbative triples [DLPNO-CCSD(T)] calculated vertical detachment energies agree well with the experimental measurements, confirming the identified isomers as the most stable ones. Furthermore, the nature and strength of the intermolecular interactions between B 12 H 12 2- and CH 3 CN are revealed by the quantum theory of atoms-in-molecules and the energy decomposition analysis. Ab initio molecular dynamics simulations are conducted at various temperatures to reveal the great kinetic and thermodynamic stabilities of the selected B 12 H 12 2- ·CH 3 CN cluster. The binding motif in B 12 H 12 2- ·CH 3 CN is largely retained for the whole halogenated series B 12 X 12 2- ·CH 3 CN (X = F–I). This study provides a molecular-level understanding of structural evolution for acetonitrile-solvated dodecaborate clusters and a fresh view by examining acetonitrile as a real hydrogen bond (HB) donor to form strong HB interactions.

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

Hyperdimensional Imaging Contrast Using an Optical Fiber

Fluorescence properties of a molecule can be used to study the structural and functional nature of biological processes. Physical properties, including fluorescence lifetime, emission spectrum, emission polarization, and others, help researchers probe a molecule, produce desired effects, and infer causes and consequences. Correlative imaging techniques such as hyperdimensional imaging microscopy (HDIM) combine the physical properties and biochemical states of a fluorophore. Here we present a fiber-based imaging system that can generate hyper-dimensional contrast by combining multiple fluorescence properties into a single fluorescence lifetime decay curve. Fluorescence lifetime imaging microscopy (FLIM) with controlled excitation polarization and temporally dispersed emission can generate a spectrally coded, polarization-filtered lifetime distribution for a pixel. This HDIM scheme generates a better contrast between different molecules than that from individual techniques. This setup uses only a single detector and is simpler to implement, modular, cost-efficient, and adaptable to any existing FLIM microscope. We present higher contrast data from Arabidopsis thaliana epidermal cells based on intrinsic anthocyanin emission properties under multiphoton excitation. This work lays the foundation for an alternative hyperdimensional imaging system and demonstrates that contrast-based imaging is useful to study cellular heterogeneity in biological samples.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

A Generalized Variational Principle with Applications to Excited State Mean Field Theory

We present a generalization of the variational principle that is compatible with any Hamiltonian eigenstate that can be specified uniquely by a list of properties. This variational principle appears to be compatible with a wide range of electronic structure methods, including mean field theory, density functional theory, multireference theory, and quantum Monte Carlo. Like the standard variational principle, this generalized variational principle amounts to the optimization of a nonlinear function that, in the limit of an arbitrarily flexible wave function, has the desired Hamiltonian eigenstate as its global minimum. Unlike the standard variational principle, it can target excited states and select individual states in cases of degeneracy or near-degeneracy. As an initial demonstration of how this approach can be useful in practice, we employ it to improve the optimization efficiency of excited state mean field theory by an order of magnitude. With this improved optimization, we are able to demonstrate that the accuracy of the corresponding second-order perturbation theory rivals that of singles-and-doubles equation-of-motion coupled cluster in a substantially broader set of molecules than could be explored by our previous optimization methodology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Interference between Franck–Condon and Herzberg–Teller Terms in the Condensed-Phase Molecular Spectra of Metal-Based Tetrapyrrole Derivatives

The commonly used Franck-Condon (FC) approximation is inadequate for explaining the electronic spectra of compounds that possess vibrations with substantial Herzberg-Teller (HT) couplings. Metal-based tetrapyrrole derivatives, which are ubiquitous natural pigments, often exhibit prominent HT activity. In this paper, we compare the condensed phase spectra of zinc-tetraphenylporphyrin (ZnTPP) and zinc-phthalocyanine (ZnPc), which exhibit vastly different spectral features in spite of sharing a common tetrapyrrole backbone. The absorption and emission spectra of ZnTPP are characterized by a lack of mirror symmetry and nontrivial temperature dependence. In contrast, mirror symmetry is restored, and the nontrivial temperature-dependent features disappear in ZnPc. We attribute these differences to FC-HT interference, which is less pronounced in ZnPc because of a larger FC component in the dipole moment that leads to FC-dominated transitions. A single minimalistic FC-HT vibronic model reproduces all the experimental spectral features of these molecules. These observations suggest that FC-HT interference is highly susceptible to chemical modification.

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

Temperature-mediated molecular ladder self-assembly employing Diels–Alder cycloaddition

Dynamic covalent self-assembly processes often exhibit poor capacities for error-correction owing to the relatively low connectivity rearrangement rates of dynamic covalent interactions and the common use of reaction conditions where the equilibrium state remains fixed. Here, we report a dynamic covalent self-assembly technique employing temperature, a conventional, externally-applied stimulus, to mediate the hybridization of peptoid oligomers bearing maleimide- and furan-based pendant groups to afford molecular ladders incorporating Diels–Alder adduct-based rungs. By raising or lowing the reaction temperature, this system enables the equilibrium state to be readily varied without altering reagent concentrations. Both triethylamine and the Lewis acidic scandium triflate were examined as candidate reaction catalysts; however, only scandium triflate increased the rate of single strand conversion. Additionally, as the Diels–Alder cycloaddition reaction does not liberate a small molecule, a registry-dependent mass change was effected by employing a base-catalyzed thiol-Michael addition reaction between any un-reacted maleimide pendant groups and a low molecular weight thiol to enable the number of Diels–Alder adduct rungs to be readily determined by mass spectrometry. Finally, by employing a slow temperature ramp from high to low temperature, approximating the thermal cycle employed for nucleic acid hybridization, sequence-selective hybridization between model, tetra-functional precursor strands was demonstrated.

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

Molecular catalyst and co-catalyst systems based on transition metal complexes for the electrochemical oxidation of alcohols

Molecular catalysts allow deeper study of underlying mechanisms relative to heterogeneous systems by offering a discrete active site to monitor. Mechanistic study with knowledge of key intermediates subsequently enables the development of design principles through an understanding of how improved reactivity or selectivity can be achieved through modification of the catalyst structure. The co-catalytic inclusion of redox mediators (RM), which are small molecules that can aid in the transfer of protons and electrons, has been shown to improve product conversion and selectivity in many molecular systems, through intercepting key intermediates to direct reaction pathways. The primary focus for the majority of molecular electrocatalysts has been on optimizing design for reductive reactions, such as the hydrogen evolution reaction (HER), the oxygen reduction reaction (ORR), and the carbon dioxide reduction reaction (CO 2 RR). By comparison, there has been much less focus on key oxidative reactions by molecular species, apart from the oxygen evolution reaction (OER). The focus of this review is to highlight molecular catalyst systems optimized for the electrochemical oxidation of alcohols. The electrochemical alcohol oxidation reaction (AOR) can serve a role in synthesizing value-added chemicals and can serve as the counterpart to the CO 2 RR by releasing electricity from energy-rich molecules. State-of-the-art molecular systems for the AOR are divided between single-site catalysts and co-catalytic systems with redox mediators. The AOR is contextualized as an energy relevant reaction, an overview of the area is provided, foundational improvements in catalyst systems are highlighted, and future development principles for incorporating redox mediators are suggested.

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

Electric fields near undulating dielectric membranes

Dielectric interfaces are crucial to the behavior of charged membranes, from graphene to synthetic and biological lipid bilayers. Understanding electrolyte behavior near these interfaces remains a challenge, especially in the case of rough dielectric surfaces. A lack of analytical solutions consigns this problem to numerical treatments. Here, we report an analytic method for determining electrostatic potentials near curved dielectric membranes in a two-dimensional periodic “slab” geometry using a periodic summation of Green’s functions. This method is amenable to simulating arbitrary groups of charges near surfaces with two-dimensional deformations. We concentrate on one-dimensional undulations. We show that increasing membrane undulation increases the asymmetry of interfacial charge distributions due to preferential ionic repulsion from troughs. In the limit of thick membranes, we recover results mimicking those for electrolytes near a single interface. Our work demonstrates that rough surfaces generate charge patterns in electrolytes of charged molecules or mixed-valence ions.

Chemistry↗
DOE OSTI2020

Materials Data on H4INO4 by Materials Project

NH4IO4 is Silicon tetrafluoride-derived structured and crystallizes in the tetragonal I4_1/a space group. The structure is zero-dimensional and consists of four ammonium molecules and four IO4 clusters. In each IO4 cluster, O2- is bonded in a single-bond geometry to one I1- atom. The O–I bond length is 1.80 Å. I1- is bonded in a tetrahedral geometry to four equivalent O2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on B4PF9 by Materials Project

BPF3(BF2)3 is Magnesium tetraboride-derived structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of twelve difluoroborane molecules and four BPF3 clusters. In each BPF3 cluster, B3+ is bonded in a single-bond geometry to one P3- atom. The B–P bond length is 1.85 Å. P3- is bonded in a 4-coordinate geometry to one B3+ and three F1- atoms. All P–F bond lengths are 1.55 Å. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one P3- atom. In the second F1- site, F1- is bonded in a single-bond geometry to one P3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TlClO3 by Materials Project

TlClO3 is Ammonia-derived structured and crystallizes in the trigonal R3m space group. The structure is zero-dimensional and consists of three ramor molecules and three ClO3 clusters. In each ClO3 cluster, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.51 Å. Cl is bonded in a trigonal non-coplanar geometry to three equivalent O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TlClO4 by Materials Project

TlClO4 is Silicon tetrafluoride-derived structured and crystallizes in the cubic F-43m space group. The structure is zero-dimensional and consists of four thallium molecules and four ClO4 clusters. In each ClO4 cluster, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.47 Å. Cl is bonded in a tetrahedral geometry to four equivalent O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AgClO4 by Materials Project

AgClO4 is Silicon tetrafluoride-derived structured and crystallizes in the cubic F-43m space group. The structure is zero-dimensional and consists of four silver molecules and four ClO4 clusters. In each ClO4 cluster, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.47 Å. Cl is bonded in a tetrahedral geometry to four equivalent O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on BrN(OF2)2 by Materials Project

NOOBrF4 crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four nitroxyl molecules and four OBrF4 clusters. In each OBrF4 cluster, O2- is bonded in a single-bond geometry to one Br5+ atom. The O–Br bond length is 1.60 Å. Br5+ is bonded in a square pyramidal geometry to one O2- and four F1- atoms. There is two shorter (1.93 Å) and two longer (1.97 Å) Br–F bond length. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one Br5+ atom. In the second F1- site, F1- is bonded in a single-bond geometry to one Br5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K2RuBr5NO by Materials Project

(K)2RuON(Br)5 crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of twenty hydrobromic acid molecules, eight kalium molecules, and four RuON clusters. In each RuON cluster, Ru2+ is bonded in a single-bond geometry to one N3- atom. The Ru–N bond length is 1.74 Å. N3- is bonded in a linear geometry to one Ru2+ and one O2- atom. The N–O bond length is 1.17 Å. O2- is bonded in a single-bond geometry to one N3- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbSNCl6 by Materials Project

NbCl5NSCl crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of four niobium(v) chloride molecules and four NSCl clusters. In each NSCl cluster, N3+ is bonded in a single-bond geometry to one S2- atom. The N–S bond length is 1.46 Å. S2- is bonded in a distorted bent 120 degrees geometry to one N3+ and one Cl1- atom. The S–Cl bond length is 2.14 Å. Cl1- is bonded in a single-bond geometry to one S2- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe3WC14(SO7)2 by Materials Project

WFe3C9S2O9(CO)5 crystallizes in the monoclinic C2/m space group. The structure is zero-dimensional and consists of twenty formaldehyde molecules and four WFe3C9S2O9 clusters. In each WFe3C9S2O9 cluster, W6+ is bonded in a single-bond geometry to one S2- atom. The W–S bond length is 2.54 Å. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to three C+1.21+ and two S2- atoms to form distorted edge-sharing FeC3S2 trigonal bipyramids. There is two shorter (1.78 Å) and one longer (1.81 Å) Fe–C bond length. There are one shorter (2.27 Å) and one longer (2.30 Å) Fe–S bond lengths. In the second Fe3+ site, Fe3+ is bonded to three C+1.21+ and two S2- atoms to form distorted edge-sharing FeC3S2 square pyramids. There are a spread of Fe–C bond distances ranging from 1.78–1.83 Å. There are one shorter (2.24 Å) and one longer (2.26 Å) Fe–S bond lengths. There are five inequivalent C+1.21+ sites. In the first C+1.21+ site, C+1.21+ is bonded in a distorted single-bond geometry to one Fe3+ and one O2- atom. The C–O bond length is 1.15 Å. In the second C+1.21+ site, C+1.21+ is bonded in a distorted single-bond geometry to one Fe3+ and one O2- atom. The C–O bond length is 1.16 Å. In the third C+1.21+ site, C+1.21+ is bonded in a distorted single-bond geometry to one Fe3+ and one O2- atom. The C–O bond length is 1.15 Å. In the fourth C+1.21+ site, C+1.21+ is bonded in a linear geometry to one Fe3+ and one O2- atom. The C–O bond length is 1.16 Å. In the fifth C+1.21+ site, C+1.21+ is bonded in a distorted linear geometry to one Fe3+ and one O2- atom. The C–O bond length is 1.16 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to one W6+ and three Fe3+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Fe3+ atoms. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one C+1.21+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one C+1.21+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one C+1.21+ atom. In the fourth O2- site, O2- is bonded in a single-bond geometry to one C+1.21+ atom. In the fifth O2- site, O2- is bonded in a single-bond geometry to one C+1.21+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H3ClO5 by Materials Project

H3OClO4 is alpha Np structured and crystallizes in the orthorhombic Pnma space group. The structure is zero-dimensional and consists of four water molecules and four HClO4 clusters. In each HClO4 cluster, H is bonded in a single-bond geometry to one O atom. The H–O bond length is 0.99 Å. There are three 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 1.43 Å. In the second O site, O is bonded in a distorted water-like geometry to one H and one Cl atom. The O–Cl bond length is 1.66 Å. In the third O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.43 Å. Cl is bonded in a tetrahedral geometry to four O atoms.

36 MATERIALS SCIENCE↗