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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Benchmark full configuration-interaction calculations on HF and NH2

Full configuration-interaction (FCI) calculations are performed at selected geometries for the 1-sigma(+) state of HF and the 2-B(1) and 2-A(1) states of NH2 using both DZ and DZP gaussian basis sets. Higher excitations become more important when the bonds are stretched and the self-consistent field (SCF) reference becomes a poorer zeroth-order description of the wave function. The complete active space SCF - multireference configuration-interaction (CASSCF-MRCI) procedure gives excellent agreement with the FCI potentials, especially when corrected with a multi-reference analog of the Davidson correction.

Bauschlicher, C. W., Jr.↗
NASA NTRS1988

Symmetry and equivalence restrictions in electronic structure calculations

A simple method for obtaining MCSCF orbitals and CI natural orbitals adapted to degenerate point groups, with full symmetry and equivalnece restrictions, is described. Among several advantages accruing from this method are the ability to perform atomic SCF calculations on states for which the SCF energy expression cannot be written in terms of Coulomb and exchange integrals over real orbitals, and the generation of symmetry-adapted atomic natural orbitals for use in a recently proposed method for basis set contraction.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1992

The calculation of the vibrational frequencies of CuCO+, NiCO and CuCH3

The vibrational frequencies of CuCO+, NiCO, and CuCH3 are computed at both the self-consistent-field (SCF) and coupled-cluster singles and doubles, with a perturbational estimate of the triples (CCSD(T)), levels of theory. Overall the SCF frequencies are in qualitative agreement with the CCSD(T) results. The calculations show that the frequencies for the electrostatically bound CuCO+ are quite different from the datively bound NiCO. The CCSD(T) calculations support a previous suggestion that the C-H stretches in CuCH3 have been misassigned.

Sodupe, M.↗
NASA NTRS1993

Probabilistic and structural reliability analysis of laminated composite structures based on the IPACS code

Probabilistic predictions based on the Integrated Probabilistic Assessment of Composite Structures (IPACS) code are presented for the material and structural response of unnotched and notched, 1M6/3501-6 Gr/Ep laminates. Comparisons of predicted and measured modulus and strength distributions are given for unnotched unidirectional, cross-ply, and quasi-isotropic laminates. The predicted modulus distributions were found to correlate well with the test results for all three unnotched laminates. Correlations of strength distributions for the unnotched laminates are judged good for the unidirectional laminate and fair for the cross-ply laminate, whereas the strength correlation for the quasi-isotropic laminate is deficient because IPACS did not yet have a progressive failure capability. The paper also presents probabilistic and structural reliability analysis predictions for the strain concentration factor (SCF) for an open-hole, quasi-isotropic laminate subjected to longitudinal tension. A special procedure was developed to adapt IPACS for the structural reliability analysis. The reliability results show the importance of identifying the most significant random variables upon which the SCF depends, and of having accurate scatter values for these variables.

Sobel, Larry↗
NASA NTRS1993

Experimental investigation of spherical-convergent-flap thrust-vectoring two-dimensional plug nozzles

An experimental investigation of multiaxis thrust vectoring nozzles with spherical convergent flaps (SCF) and a convertible (in-flight deployable) centerline plug were tested in the NASA-Langley 16-Foot Transonic Tunnel Static Test Facility. Parameters tested during the static test included plug length, external shroud length, shroud internal angle, and yaw vector angle. Results indicated that the SCF convertible-plug nozzle flow is highly three dimensional and characterized by internal flow separation and shock effects. The resultant thrust and discharge coefficient levels were lower than previous wedge nozzle results. In addition, increasing shroud internal angle increased resultant thrust ratio but decreased discharge coefficient. Increasing shroud length increased resultant thrust ratio performance for NPR's greater than 6.0 but for NPR's less than 6.0, resultant thrust ratio decreased as shroud length increased. Increasing plug length caused an increase in resultant thrust ratio and an increase in discharge coefficient. Increasing geometric yaw vector angle had no effect on resultant thrust ratio and little effect on discharge coefficient.

Cler, Daniel L.↗
NASA NTRS1993

Ab initio study of Fe(+)-benzyne

The interaction of Fe(+) with benzyne is studied using the self-consistent-field (SCF), complete active space SCF, and modified-coupled-pair functional levels of theory. The most stable structure is planar, where the Fe(+) has inserted into the in-plane pi bond, although the C-C bond distance suggests that some in-plane pi bonding remains. This system is compared with Sc(+) bonding to benzyne and other ligands.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1995

Novel composites for wing and fuselage applications

Probabilistic predictions based on the IPACS code are presented for the material and structural response of unnotched and notched, IM6/3501-6 Gr/Ep laminates. Comparisons of predicted and measured modulus and strength distributions are given for unnotched unidirectional, cross-ply and quasi-isotropic laminates. The predicted modulus distributions were found to correlate well with the test results for all three unnotched laminates. Correlations of strength distributions for the unnotched laminates are judged good for the unidirectional laminate and fair for the cross-ply laminate, whereas the strength correlation for the quasi-isotropic laminate is judged poor because IPACS did not have a progressive failure capability at the time this work was performed. The report also presents probabilistic and structural reliability analysis predictions for the strain concentration factor (SCF) for an open-hole, quasi-isotropic laminate subjected to longitudinal tension. A special procedure was developed to adapt IPACS for the structural reliability analysis. The reliability results show the importance of identifying the most significant random variables upon which the SCF depends, and of having accurate scatter values for these variables.

Sobel, L. H.↗
NASA NTRS1994

An Exact Separation of the Spin-Free and Spin-Dependent Terms of the Dirac-Coulomb-Breit Hamiltonian

The Dirac Hamiltonian is transformed by extracting the operator (sigma x p)/2mc from the small component of the wave function and applying it to the operators of the original Hamiltonian. The resultant operators contain products of Paull matrices that can be rearranged to give spin-free and spin-dependent operators. These operators are the ones encountered in the Breit-Pauli Hamiltonian, as well as some of higher order in alpha(sup 2). However, since the transformation of the original Dirac Hamiltonian is exact, the new Hamiltonian can be used in variational calculations, with or without the spin-dependent terms. The new small component functions have the same symmetry properties as the large component. Use of only the spin-free terms of the new Hamiltonian permits the same factorization over spin variables as in nonrelativistic theory, and therefore all the post-Self-Consistent Field (SCF) machinery of nonrelativistic calculations can be applied. However, the single-particle functions are two-component orbitals having a large and small component, and the SCF methods must be modified accordingly. Numerical examples are presented, and comparisons are made with the spin-free second-order Douglas-Kroll transformed Hamiltonian of Hess.

Dyall, Kenneth G.↗
NASA NTRS1998

Static Thrust and Vectoring Performance of a Spherical Convergent Flap Nozzle with a Nonrectangular Divergent Duct

The static internal performance of a multiaxis-thrust-vectoring, spherical convergent flap (SCF) nozzle with a non-rectangular divergent duct was obtained in the model preparation area of the Langley 16-Foot Transonic Tunnel. Duct cross sections of hexagonal and bowtie shapes were tested. Additional geometric parameters included throat area (power setting), pitch flap deflection angle, and yaw gimbal angle. Nozzle pressure ratio was varied from 2 to 12 for dry power configurations and from 2 to 6 for afterburning power configurations. Approximately a 1-percent loss in thrust efficiency from SCF nozzles with a rectangular divergent duct was incurred as a result of internal oblique shocks in the flow field. The internal oblique shocks were the result of cross flow generated by the vee-shaped geometric throat. The hexagonal and bowtie nozzles had mirror-imaged flow fields and therefore similar thrust performance. Thrust vectoring was not hampered by the three-dimensional internal geometry of the nozzles. Flow visualization indicates pitch thrust-vector angles larger than 10' may be achievable with minimal adverse effect on or a possible gain in resultant thrust efficiency as compared with the performance at a pitch thrust-vector angle of 10 deg.

Wing, David J.↗
NASA NTRS1995

The G2(B3LYP/MP2/CC) Approach: A Modification of the G2(MP2) Approach and a Comparison with B3LYP Results

The quadratic configuration interaction calculation in the G2(MP2) approach is replaced by a coupled-cluster singles and doubles calculation including a perturbational estimate of the triples excitations. In addition, the SCF and MP2 geometry optimizations and SCF frequency calculation in the G2(MP2) approach are replaced by a B3LYP geometry optimization and frequency calculation in the proposed G2(B3LYP/MP2/CC) approach. This simplification does not affect the average absolute deviation from experiment, but decreases the maximum error compared with the G2(MP2) approach. The G2(B3LYP/MP2/CC) results are compared with those obtained using the B3LYP approach, and the G2(B3LYP/MP2/CC) model is found to be more reliable, even if the B3LYP calculations are performed using a large basis set.

Bauschlicher, Charles W., Jr.↗
NASA NTRS2001

Notch Sensitivity of Woven Ceramic Matrix Composites Under Tensile Loading: An Experimental, Analytical, and Finite Element Study

The stress concentrations associated with circular notches and subjected to uniform tensile loading in woven ceramic matrix composites (CMCs) have been investigated for high-efficient turbine engine applications. The CMC's were composed of Nicalon silicon carbide woven fabric in SiNC matrix manufactured through polymer impregnation process (PIP). Several combinations of hole diameter/plate width ratios and ply orientations were considered in this study. In the first part, the stress concentrations were calculated measuring strain distributions surrounding the hole using strain gages at different locations of the specimens during the initial portion of the stress-strain curve before any microdamage developed. The stress concentration was also calculated analytically using Lekhnitskii's solution for orthotropic plates. A finite-width correction factor for anisotropic and orthotropic composite plate was considered. The stress distributions surrounding the circular hole of a CMC's plate were further studied using finite element analysis. Both solid and shell elements were considered. The experimental results were compared with both the analytical and finite element solutions. Extensive optical and scanning electron microscopic examinations were carried out for identifying the fracture behavior and failure mechanisms of both the notched and notched specimens. The stress concentration factors (SCF) determined by analytical method overpredicted the experimental results. But the numerical solution underpredicted the experimental SCF. Stress concentration factors are shown to increase with enlarged hole size and the effects of ply orientations on stress concentration factors are observed to be negligible. In all the cases, the crack initiated at the notch edge and propagated along the width towards the edge of the specimens.

Haque, A.↗
NASA NTRS1995

The Structure of Li7 and K7

The self-consistent-field (SCF) approach and density functional theory, using the B3LYP hybrid functional, yield three low-lying structures for Li7(-). The relative separations differ for the SCF and B3LYP approaches, however the B3LYP results are in good agreement with the coupled cluster results. For K7(-), only an octahedron with one face capped is found to be a minimum; this the second most stable structure for Li7(-). A comparison of the computed separations between the low-lying states of K7 and the photoelectron detachment spectra does not allow an unambiguous assignment of the structure of K7(-).

Bauschlicher. Charles W., Jr.↗
NASA NTRS1996

The Calculation of Accurate Harmonic Frequencies of Large Molecules: The Polycyclic Aromatic Hydrocarbons, a Case Study

The vibrational frequencies and infrared intensities of naphthalene neutral and cation are studied at the self-consistent-field (SCF), second-order Moller-Plesset (MP2), and density functional theory (DFT) levels using a variety of one-particle basis sets. Very accurate frequencies can be obtained at the DFT level in conjunction with large basis sets if they are scaled with two factors, one for the C-H stretches and a second for all other modes. We also find remarkably good agreement at the B3LYP/4-31G level using only one scale factor. Unlike the neutral PAHs where all methods do reasonably well for the intensities, only the DFT results are accurate for the PAH cations. The failure of the SCF and MP2 methods is caused by symmetry breaking and an inability to describe charge delocalization. We present several interesting cases of symmetry breaking in this study. An assessment is made as to whether an ensemble of PAH neutrals or cations could account for the unidentified infrared bands observed in many astronomical sources.

Bauschlicher, Charles W., Jr.↗
NASA NTRS2005

A Climatology of Midlatitude Continental Clouds from the ARM SGP Site: Low-Level Cloud Macrophysical, Microphysical, and Radiative Properties - Part I

A record of single-layer and overcast low cloud (stratus) properties has been generated using approximately 4000 hours of data collected from January 1997 to December 2002 at the Atmospheric Radiation Measurement (ARM) Southern Great Plains Central Facility (SCF). The cloud properties include liquid-phase and liquid-dominant, mixed-phase, low cloud macrophysical, microphysical, and radiative properties including cloud-base and -top heights and temperatures, and cloud physical thickness derived from a ground-based radar and lidar pair, and rawinsonde sounding; cloud liquid water path (LWP) and content (LWC), and cloud-droplet effective radius (r(sub e)) and number concentration (N) derived from the macrophysical properties and radiometer data; and cloud optical depth (tau), effective solar transmission (gamma), and cloud/top-of-atmosphere albedos (R(sub cldy)/R(sub TOA)) derived from Eppley precision spectral pyranometer measurements. The cloud properties were analyzed in terms of their seasonal, monthly, and hourly variations. In general, more stratus clouds occur during winter and spring than in summer. Cloud-layer altitudes and physical thicknesses were higher and greater in summer than in winter with averaged physical thicknesses of 0.85 km and 0.73 km for day and night, respectively. The seasonal variations of LWP, LWC, N. tau, R(sub cldy), and R(sub TOA) basically follow the same pattern with maxima and minima during winter and summer, respectively. There is no significant variation in mean r(sub e), however, despite a summertime peak in aerosol loading, Although a considerable degree of variability exists, the 6-yr average values of LWP, LWC, r(sub e), N, tau, gamma, R(sub cldy) and R(sub TOA) are 150 gm(exp -2) (138), 0.245 gm(exp -3) (0.268), 8.7 micrometers (8.5), 213 cm(exp -3) (238), 26.8 (24.8), 0.331, 0.672, 0.563 for daytime (nighttime). A new conceptual model of midlatitude continental low clouds at the ARM SGP site has been developed from this study. The low stratus cloud amount monotonically increases from midnight to early morning (0930 LT), and remains large until around local noon, then declines until 1930 LT when it levels off for the remainder of the night. In the morning, the stratus cloud layer is low, warm, and thick with less LWC, while in the afternoon it is high, cold, and thin with more LWC. Future parts of this series will consider other cloud types and cloud radiative forcing at the ARM SCF.

Dong, Xiquan↗
NASA NTRS2014

Secure Naming and Addressing Operations for Store, Carry and Forward Networks

This paper describes concepts for secure naming and addressing directed at Store, Carry and Forward (SCF) distributed applications, where disconnection and intermittent connectivity between forwarding systems is the norm. The paper provides a brief overview of store, carry and forward distributed applications followed by an in depth discussion of how to securely: create a namespace; allocate names within the namespace; query for names known within a local processing system or connected subnetwork; validate ownership of a given name; authenticate data from a given name; and, encrypt data to a given name. Critical issues such as revocation of names, mobility and the ability to use various namespaces to secure operations or for Quality-of-Service are also presented. Although the concepts presented for naming and addressing have been developed for SCF, they are directly applicable to fully connected systems.

computer security↗
NASA NTRS1967

Confirmation of the predicted Hartree-Fock limit in BeH sub 2.

We have recently estimated the total energy of the BeH 2 molecule as -15.918 ± 0.015 au. One of the steps in the analysis was to estimate the difference between the SCF energies computed with a minimal basis set of Slater orbits and with the best possible single-determinant wave function, the so-called Hartree-Fock limit and was predicted to be -15.773 ± 0.007 au for BeH 2 .

Molecular energy↗
DOE OSTI2021

Synthesis, Electronic Structure, and Reactivity of a Planar Four‐Coordinate, Cobalt–Imido Complex

Abstract A four‐coordinate cobalt–imido complex, ( t Bu mPNP)Co=NMes ( t Bu mPNP=modified PNP pincer ligand) has been synthesized from addition of 2,4,6‐trimethylphenylazide (Mes–N 3 ) to the corresponding dinitrogen complex. The solid‐state structure determined by X‐ray diffraction established a rare, idealized planar geometry with a Co=N bond distance of 1.716(2) Å. Magnetic measurements revealed an S =1 ground state with CAS‐SCF calculations supporting radical character on the imide nitrogen. Thermolysis of the cobalt–imido compound induced selective insertion of the imido group into a Co−P bond and yielded a three‐coordinate cobalt complex with a distorted T‐shaped geometry. Transition state analysis conducted with DFT calculations established the thermodynamic stability of the P–N coupled product and provided insight into the exclusive selectivity.

Park, Yoonsu↗
DOE OSTI2021

Synthesis, Electronic Structure, and Reactivity of a Planar Four–Coordinate, Cobalt–Imido Complex

A four-coordinate cobalt imido complex, ( tBu mPNP)Co=NMes ( tBu mPNP = modified PNP pincer ligand) has been synthesized from addition of 2,4,6-trimethylphenylazide (Mes–N 3 ) to the corresponding dinitrogen complex. The solid-state structure determined by X-ray diffraction established a rare, idealized planar geometry with a Co=N bond distance of 1.716(2) Å. Magnetic measurements revealed an S = 1 ground state with CAS-SCF calculations supporting radical character on the imide nitrogen. Here, thermolysis of the cobalt-imido compound induced selective insertion of the imido group into a Co–P bond and yielded a three-coordinate cobalt complex with a distorted T-shaped geometry. Transition state analysis conducted with DFT calculations established the thermodynamic stability of the P–N coupled product and provided insight into the exclusive selectivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗