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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

System technology analysis of aeroassisted orbital transfer vehicles. Moderate lift/drag (0.75-1.5): Volume 1A, part 2: Executive summary, phase 2

Significant achievements and activities of Phase 2 of a study to assess aeroassisted orbit transfer vehicle (AOTV) system technology are summarized. Phase 2 was directed towards identification and prioritization of technology payoffs of representative space based mid lift/drag ratio (L/D) AOTV's and the cryofueled propulsion subsystem - configuration interactions. Enhancing technology areas were identified which could provide substantial transport cost reduction. These include: (1) improved lifetime of storable propellant engines; (2) avionics weight reduction; (3) external thermal protection system weight reduction; (4) decrease of uncertainties in aerodynamic and aerothermodynamic performance; electrical power subsystem weight reduction due to incorporation of advanced materials; and (6) structural shell weight reduction. Results indicated that advanced aerothermodynamic methodology and aft end configuring may provide an enlarged allowable zone for engine nozzle protrusions into the separated flow region. Payload manifesting and non-hydrogen propellant manifesting at the space station is recommended.

Source record↗
DOE OSTI2021

Proton decays in 16 Ne and 18 Mg and isospin-symmetry breaking in carbon isotopes and isotones

We report that proton-rich nuclei possess unique properties in the nuclear chart. Due to the presence of both continuum coupling and Coulomb interaction, phenomena such as halos, Thomas-Ehrman shift, and proton emissions can occur. Relevant experimental data are difficult to obtain, so that theoretical calculations are needed to understand nuclei at drip lines and to guide experimentalists. In particular, the 16 Ne and 18 Mg isotopes are supposed to be one-proton and/or two-proton emitting nuclei, but associated experimental data are either incomplete or even unavailable. Consequently, we performed Gamow shell model calculations of carbon isotones bearing A = 15 - 18 . Isospin-symmetry breaking occurring in carbon isotones and isotopes is also discussed. It is hereby shown that the mixed effects of continuum coupling and Coulomb interaction at drip lines generate complex patterns in isospin multiplets. Added to that, it is possible to determine the one-proton and two-proton widths of 16 Ne and 18 Mg . Obtained decay patterns are in agreement with those obtained in previous experimental and theoretical works. Moreover, to our knowledge, this is the first theoretical calculation of binding energy and partial decay widths of 18 Mg in a configuration interaction picture.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Can TDDFT Describe Excited Electronic States of Naphthol Photoacids? A Closer Look with EOM-CCSD

The 1 L b and 1 L a excited states of naphthols are characterized by using time-dependent density functional theory (TDDFT), configuration interaction with singles (CIS), and equation-of-motion coupled cluster singles and doubles (EOM-CCSD) methods. TDDFT fails dramatically at predicting the energy and ordering of the 1 L a and 1 L b excited states as observed experimentally, while EOM-CCSD accurately predicts the excited states as characterized by natural transition orbital analysis. Here, the limitations of TDDFT are attributed to the absence of correlation from doubly excited configurations as well as the inconsistent description of excited electronic states of naphthol photoacids revealed by excitation analysis based on the one-electron transition density matrix.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1996

On the Use of a Mixed Gaussian/Finite-Element Basis Set for the Calculation of Rydberg States

Configuration-interaction studies are reported for the Rydberg states of the helium atom using mixed Gaussian/finite-element (GTO/FE) one particle basis sets. Standard Gaussian valence basis sets are employed, like those, used extensively in quantum chemistry calculations. It is shown that the term values for high-lying Rydberg states of the helium atom can be obtained accurately (within 1 cm -1), even for a small GTO set, by augmenting the n-particle space with configurations, where orthonormalized interpolation polynomials are singly occupied.

Thuemmel, Helmar T.↗
DOE OSTI2014

Ionization satellites of the ArHe dimer

Ionization satellites are key ingredients in the control of post ionization processes such as molecular dissociation and interatomic Coulombic decay. Here, using the high-level ab initio method of multi-reference configuration interaction up to triple excitations, we study the potential energy curves (PECs) of the ionization satellites of the ArHe dimer. With this model system, we demonstrate that the simple model used in alkaline earth metal and rare gas complexes to describe the satellites as a Rydberg electron moving on top of a dicationic core does not fully hold for the rare gas clusters. The more complex valence structure in the rare gas atom leads to the mixing of different electronic configurations of the dimer. This prevents one from assigning a single dicationic parent state to some of the ionization satellites. We further analyze the structure of the different PECs, demonstrating how the density of the Rydberg electron is reflected in the structure of the PEC wherever the simple model is applicable.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Understanding the anharmonic vibrational structure of the carbon dioxide dimer

Understanding the vibrational structure of the CO 2 system is important to confirm the potential energy surface and interactions in such van der Waals complexes. In this work, we use our previously developed mbCO2 potential function to explore the vibrational structure of the CO 2 monomer and dimer. The potential function has been trained to reproduce the potential energies at the CCSD(T)-F12b/aug-cc-pVTZ level of electronic structure theory. The harmonic approximation, as well as anharmonic corrections using vibrational structure theories such as vibrational self-consistent field, vibrational second-order Moller-Plesset perturbation, and vibrational configuration interaction (VCI), is applied to address the vibrational motions. We compare the vibrational results using the mbCO2 potential function with traditional electronic structure theory results and to experimental frequencies. The anharmonic results for the monomer most closely match the experimental data to within 3 cm -1 , including the Fermi dyad frequencies. The intermolecular and intramolecular dimer frequencies were treated separately and show good agreement with the most recent theoretical and experimental results from the literature. The VCI treatment of the dimer vibrational motions accounts for vibrational mixing and delocalization, such that we observe the dimer Fermi resonance phenomena, both in the intramolecular and intermolecular regions.

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

Resonant x-ray emission across the L 3 edge of uranium compounds

A narrow bandwidth x-ray beamline and a multi-crystal von Hamos spectrometer were used to record x-ray absorption and x-ray emission (XES) across the uranium L 3 edge of UO 2 , UO 3 , Cs 2 UO 2 Cl 4 , and Cs 2 UCl 6 . Measurements were made over 17150–17250 eV with an instrumental resolution of ∼2 eV. This resolution allowed the use of Lorentzian peak fits to the L 3 N 4 and L 3 N 5 characteristic x-ray fluorescence lines that have ∼12–13 eV lifetime widths. The fluorescence yields of the four compounds display strong white lines near threshold and multiple scattering features at higher energies. The XES spectra were fit with three Lorentzians, two for the L 3 N 4 and L 3 N 5 lines and one for inelastic scattering by 2p–6d excitations and 4d–6d final states. The intensities of the white lines were largely due to the inelastic scattering component. To support the measurements, relativistic equation-of-motion coupled-cluster and restricted active space configuration interaction calculations were performed for uranium core-excitation energies in Cs 2 UO 2 Cl 4 and Cs 2 UCl 6 . These calculations with rigorous treatments of relativistic effects are shown to provide accurate uranium L 3 -edge binding energies, L 3 N 5 emission energies, as well as the energy losses in the inelastic scattering process. The measured and calculated results show variations between compounds with U(IV) oxidation states that contain 6d 0 5f 2 electrons in their ground configurations (UO 2 and Cs 2 UCl 6 ) compared with U(VI) compounds (UO 3 and Cs 2 UO 2 Cl 4 ) with empty 5f and 6d configurations.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Vibrational levels of a generalized Morse potential

A Generalized Morse Potential (GMP) is an extension of the Morse Potential (MP) with an additional exponential term and an additional parameter that compensate for MP’s erroneous behavior in the long range part of the interaction potential. Because of the additional term and parameter, the vibrational levels of the GMP cannot be solved analytically, unlike the case for the MP. We present several numerical approaches for solving the vibrational problem of the GMP based on Galerkin methods, namely, the Laguerre Polynomial Method (LPM), the Symmetrized LPM, and the Polynomial Expansion Method (PEM), and apply them to the vibrational levels of the homonuclear diatomic molecules B 2 , O 2 , and F 2 , for which high level theoretical near full configuration interaction (CI) electronic ground state potential energy surfaces and experimentally measured vibrational levels have been reported. Overall, the LPM produces vibrational states for the GMP that are converged to within spectroscopic accuracy of 0.01 cm –1 in between 1 and 2 orders of magnitude faster and with much fewer basis functions/grid points than the Colbert–Miller Discrete Variable Representation (CN-DVR) method for the three homonuclear diatomic molecules examined in this study.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

The electronic structure of thorium monoxide: Ligand field assignment of states in the range 0–5 eV

Configuration interaction ligand field theory (CI LFT) calculations of the electronic energy levels of ThO were performed by treating the molecular electronic states as Th 2+ free-ion levels perturbed by the ligand field of O 2- . Twenty nine experimentally characterized ThO v = 0 energy levels, together with the energy difference between the v = 0 levels of the Y and W states were fitted using a CI LFT model that included Th 2+ 7s 2 , 6d7s, 6d 2 , 7s7p, 6d7p, 5f7s, and 7p 2 configurations. Predictions from these calculations were used to provide tentative assignments for 171 out of 250 ThO band heads listed by Gatterer et al. [“Molecular Spectra of Metallic Oxides”, Specola Vaticana (1957)]. Term energies for 30 electronic states have been determined based on these assignments. Subsequently, the CI LFT model was refined by fitting to a set of 59 electronic term energies. The inclusion of CI effects together with integer valence, atomic-in-molecule, ionic bonding ideas reveals atomic energy level patterns that are multiply replicated in the molecular energy level patterns of six Th 2+ O 2- atomic ion configurations (6d7s, 6d 2 , 7s7p, 6d7p, 5f7s, and 7p 2 ) revealing the underlying atomic ion structure that gives rise to the complex and seemingly erratic unassigned bands reported in the Vatican Atlas.

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

Potential surfaces for O atom-polymer reactions

Ab initio quantum chemistry methods are used to study the energetics of interactions of O atoms with organic compounds. Polyethylene (CH2)n has been chosen as the model system to study the interactions of O(3P) and O(1D) atoms with polymers. In particular, H abstraction is investigated and polyethylene is represented by a C3 (propane) oligomeric model. The gradient method, as implemented in the GRADSCF package of programs, is used to determine the geometries and energies of products and reactants. The saddle point, barrier geometry is determined by minimizing the squares of the gradients of the potential with respect to the internal coordinates. To correctly describe the change in bonding during the reaction at least a two configuration MCSCF (multiconfiguration self consistent field) or GVB (generalized valence bond) wave function has to be used. Basis sets include standard Pople and Dunning sets, however, increased with polarization functions and diffuse p functions on both the C and O atoms. The latter is important due to the O(-) character of the wave function at the saddle point and products. Normal modes and vibrational energy levels are given for the reactants, saddle points and products. Finally, quantitative energetics are obtained by implementing a small CAS (complete active space) approach followed by limited configuration interaction (CI) calculations. Comparisons are made with available experimental data.

Laskowski, B. C.↗
DOE OSTI2023

Electronic structure of Co 3 d states in the Kitaev material candidate honeycomb cobaltate Na 3 Co 2 SbO 6 probed with x-ray dichroism

The recent prediction that honeycomb lattices of Co 2+ (3d 7 ) ions could host dominant Kitaev interactions provides an exciting direction for exploration of new routes to stabilizing Kitaev’s quantum spin liquid in real materials. Na 3 Co 2 SbO 6 has been singled out as a potential material candidate provided that spin and orbital moments couple into a J eff = $\frac{1}{2}$ ground state, and that the relative strength of trigonal crystal field and spin-orbit coupling acting on Co ions can be tailored. Using x-ray linear dichroism (XLD) and x-ray magnetic circular dichroism (XMCD) experiments, alongside configuration interaction calculations, we confirm the counterintuitive positive sign of the trigonal crystal field acting on Co 2+ ions and test the validity of the J eff = $\frac{1}{2}$ description of the electronic ground state. Furthermore, the results lend experimental support to recent theoretical predictions that a compression (elongation) of CoO 6 octahedra along (perpendicular to) the trigonal axis would drive this cobaltate toward the Kitaev limit, assuming the J eff = $\frac{1}{2}$ character of the electronic ground state is preserved.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Perspective on Many-Body Methods for Molecular Polaritonic Systems

Recent advances in strong light–matter interactions have revealed a wealth of new physical phenomena in molecules embedded in optical cavities, including modified chemical reactivity, altered excitation spectra, and novel quantum correlations. To describe these effects from first-principles, the field of ab initio quantum electrodynamics (QED) has emerged as a compelling extension of quantum chemistry that treats electronic and photonic degrees of freedom on equal footing. In this Perspective, we review the growing landscape of many-body QED methods, including Hartree–Fock, density functional theory (QEDFT), time-dependent DFT (QED-TDDFT), configuration interaction (QED-CI), complete active space (QED-CASSCF), coupled cluster (QED-CC), quantum Monte Carlo (QED-QMC), and density matrix renormalization group (QED-DMRG), highlighting recent developments and implementations. We further explore real-time methods, gradient and Hessian formalisms, and the integration of nonadiabatic nuclear dynamics. Applications range from benchmark simulations of polaritonic chemistry to quantum simulations on emerging quantum hardware. We conclude by outlining future directions for theory development and interdisciplinary efforts at the interface of quantum chemistry, condensed matter, and quantum optics.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Multistate, multichannel coupled diabatic state representations of adiabatic states coupled by conical intersections. CH 2 OH photodissociation

In this work, a coupled diabatic state representation, H d , of the 1, 2, 3 2 A states of CH 2 OH suitable for the description of the three channel, three state photodissociation process CH 2 OH(1 2 A) + hv → CH 2 OH(2, 3 2 A) → CH 2 O(X, A) + H, cis-CHOH + H, trans-CHOH + H, is reported. The representation is based on electronic structure data (energies, energy gradients, and derivative couplings) obtained exclusively from multireference configuration interaction single and double excitation wave functions. Diabat shifting is employed to improve the representation’s agreement with accurate experimental energetics. A careful analysis of the numerous minima, saddle points, and conical intersection seams is reported. The computed T 0 (3 2 A) ~ 35 220 cm -1 is in excellent agreement with the experimental estimate of 35 053 cm -1 , and the computed channel dissociation energies, D 0 , for CH 2 O 9453 (10 160), cis-HCOH 30 310.2 (29 923), and trans-HCOH 28 799 (28 391) cm -1 are in good accord with the measured values given parenthetically. Lastly, these accurate energetics over a wide range of nuclear configurations strongly support the ability of this H d to enable quality simulations of nonadiabatic dynamics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2002

Atomic Data and Spectral Line Intensities for Ne III

A number of satellites and rockets have been launched to observe radiation from the Sun and other astrophysical objects. Line radiation is emitted when the electron impact excited levels decay to the lower levels by photon emission. From this radiation, the physical parameters such as electron temperature and density of the astrophysical plasma, elemental abundance, and opacity can be inferred. Ne III lines have been observed in H II regions, Ne-rich filaments in supernovae, and planetary nebulae. The allowed line at 489.50 Angstroms due to the transition 2s(sup 2) 2p(sup 5) (sup 3) P2 (goes to) 2s(sup 2)2p(sup 4)(sup 3)P2 has been identified in the solar spectrum by Vernazza and Reeves using Skylab observations. Other Ne III lines in the solar EUV spectrum have been reported by Thomas and Neupert based on observations from the Solar EUV Rocket Telescope and Spectrograph (SERTS) instrument. Atomic data for Ne III have been calculated by using a set of programs developed at, University College, London. The Superstructure and Distorted Wave (DW) programs have been updated over the years. In the Superstructure program, configuration interaction can be taken into account and radial functions are calculated in a modified Thomas-Fermi-Amaldi potential. This is a statistical potential and depends on parameters lambda 1 which are determined by optimizing the weighted sum of term energies. They are found to be lambda(sub 0)=1.2467, lambda(sub 1)=1.1617, and lambda(sub 2)=1.0663. The relativistic corrections are included by using the Breit-Pauli Hamiltonian as a perturbation to the nonrelativistic Hamiltonian. The same potential is used to calculate reactance matrices in the DW approximation in LS coupling. Collision strengths in intermediate coupling are obtained by using term coupling coefficients obtained from the Superstructure program. In this calculation, the configurations used are 2s(sup 2)2p(sup 4), 2s2p(sup 5), 2s(sup 2)2p(sup 3)3s, 2s(sup 2)p(sup 3)3d giving rise to 57 fine-structure levels in intermediate coupling.

Bhatia, A. K.↗
DOE OSTI2013

Unusual Inorganic Biradicals: A Theoretical Analysis

Triatomic ions in the series FX 2 + , where X = O, S, Se, Te and Po are the terminal atoms, exhibit unusually high biradical characters (0.76 < β < 0.92), as measured from the analysis of Multi-Reference Configuration Interaction (MRCI) wavefunctions. Candidates in this series have the largest biradical character among the homologous, 18 valence electron CX 2 2- , NX 2 - , X 3 and OX 2 (X = O, S, Se, Te and Po) systems. In the same scale the biradical character of ozone (O 3 ) is just 0.19, whereas that of trimethylenemethane [C(CH 2 ) 3 ] is 0.97 (β=1 for an "ideal" biradical). For the 24 electron XO 2 series, consisting of molecules with two oxygen atoms and a moiety X that is isoelectronic to oxygen, i.e. X= CH 2 , NH, O, F + , the singlet (S) state is lower than the triplet (T) one and the S-T splitting as well the barrier between their "open" and "ring" configurations was found to depend linearly with the inverse of the biradical character.

Miliordos, Evangelos↗
DOE OSTI2022

Generator coordinate method for transition-state dynamics in nuclear fission

Since its beginnings, fission theory has assumed that low-energy induced fission takes place through transition-state channels at the barrier tops. Nevertheless, up to now there is no microscopic theory applicable to those conditions. We suggest that modern reaction theory is suitable for this purpose, and propose a methodology based on a configuration-interaction framework using the generator coordinate method (GCM). Simple reaction-theoretic models are constructed with the Gaussian overlap approximation to parametrize both the dynamics within the channels and their incoherent couplings to states outside the barrier. The physical characteristics of the channels examined here are their effective bandwidths and the quality of the coupling to compound-nucleus states as measured by the transmission factor T. We also investigate the spacing of GCM states with respect to their degree of overlap. We find that a rather coarse mesh provides an acceptable accuracy for estimating the bandwidths and transmission factors. The common numerical stability problem in using the GCM is avoided due to the choice of meshes and the finite bandwidths of the channels. Here, the bandwidths of the channels are largely controlled by the zero-point energy with respect to the collective coordinate in the GCM configurations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Strategies to Obtain Reliable Energy Landscapes from Embedded Multireference Correlated Wavefunction Methods for Surface Reactions

Embedded correlated wavefunction (ECW) theory is a powerful tool for studying ground- and excited-state reaction mechanisms and associated energetics in heterogeneous catalysis. Several factors are important to obtaining reliable ECW energies, critically the construction of consistent active spaces (ASs) along reaction pathways when using a multireference correlated wavefunction (CW) method that relies on a subset of orbital spaces in the configuration interaction expansion to account for static electron correlation, e.g., complete AS self-consistent field theory, in addition to the adequate partitioning of the system into a cluster and environment, as well as the choice of a suitable basis set and number of states included in excited-state simulations. Here, in this work, we conducted a series of systematic studies to develop best-practice guidelines for ground- and excited-state ECW theory simulations, utilizing the decomposition of NH 3 on Pd(111) as an example. We determine that ECW theory results are relatively insensitive to cluster size, the aug-cc-pVDZ basis set provides an adequate compromise between computational complexity and accuracy, and that a fixed-clean-surface approximation holds well for the derivation of the embedding potential. Additionally, we demonstrate that a merging approach, which involves generating ASs from the molecular fragments at each configuration, is preferable to a creeping approach, which utilizes ASs from adjacent structures as an initial guess, for the generation of consistent potential energy curves involving open-d-shell metal surfaces, and, finally, we show that it is essential to include bands of excited states in their entirety when simulating excited-state reaction pathways.

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

Cross-shell excited configurations in the structure of 34 Si

The cross-shell excited states of 34 Si have been investigated via β decays of the 4 − ground state and the 1 + isomeric state of 34 Al. Since the valence protons and valence neutrons occupy different major shells in the ground state as well as the intruder 1 + isomeric state of 34 Al, intruder levels of 34 Si are populated via allowed β decays. Spin assignments to such intruder levels of 34 Si were established through γ-γ angular correlation analysis for the negative-parity states. The configurations of such intruder states play crucial roles in our understanding of the N = 20 shell gap evolution. A configuration interaction model derived from the FSU Hamiltonian was utilized in order to interpret the intruder states in 34 Si. Furthermore, shell model interaction derived from a more fundamental theory with the valence space in medium similarity renormalization group method was also employed to interpret the structure of 34 Si.

20 ≤ A ≤ 38↗