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Results for “POLARIZABILITY”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Site specific atomic polarizabilities in endohedral fullerenes and carbon onions

We investigate the polarizability of trimetallic nitride endohedral fullerenes by partitioning the total polarizability into site specific components. This analysis indicates that the polarizability of the endohedral fullerene is essentially due to the outer fullerene cage and has insignificant contribution from the encapsulated unit. Thus, the outer fullerene cages effectively shield the encapsulated clusters and behave like Faraday cages. The polarizability of endohedral fullerenes is slightly smaller than the polarizability of the corresponding bare carbon fullerenes. The application of the site specific polarizabilities to C{sub 60}@C{sub 240} and C{sub 60}@C{sub 180} onions shows that, compared to the polarizability of isolated C{sub 60} fullerene, the encapsulation of the C{sub 60} in C{sub 240} and C{sub 180} fullerenes reduces its polarizability by 75% and 83%, respectively. The differences in the polarizability of C{sub 60} in the two onions is a result of differences in the bonding (intershell electron transfer), fullerene shell relaxations, and intershell separations. The site specific analysis further shows that the outer atoms in a fullerene shell contribute most to the fullerene polarizability.

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

Proton spin structure and generalized polarizabilities in the strong quantum chromodynamics regime

The strong interaction is not well understood at low energies or for interactions with low momentum transfer. Chiral perturbation theory gives testable predictions for the nucleonic generalized polarizabilities, which are fundamental quantities describing the nucleon’s response to an external field. We report a measurement of the proton’s generalized spin polarizabilities extracted with a polarized electron beam and a polarized solid ammonia target in the region where chiral perturbation theory is expected to be valid. The investigated structure function g2 characterizes the internal spin structure of the proton. From its moments, we extract the longitudinal–transverse spin polarizability δLT and twist-3 matrix element and polarizability d2¯. Our results provide discriminating power between existing chiral perturbation theory calculations and will help provide a better understanding of this strong quantum chromodynamics regime.

Ruth, D↗
NASA NTRS1979

Finite-field Calculations of Molecular Polarizabilities Using Field-Induced Polarization Functions: Second- and Third-order Perturbation Correlation Corrections to the Coupled Hartree-Fock Polarizability of H2O

Ordinary Rayleigh-Schroudinger perturbation theory with Moller-Plesset (RSMP) partitioning is used to calculate second- and third-order correlation corrections to the CHF polarizability and dipole moment of the water molecule by a finite-field procedure. Pade approximants are found to be useful in accelerating the convergence of the property perturbation expansions. Field-induced polarization functions suitable for polarizability calculations are determined. The average polarizability calculated, neglecting vibrational averaging, with Dunning's (9s5p/4s-4s2p/2s) contracted GTO basis set augmented by field-induced lslp2d/lp polarization functions is within 3 per cent of the experimental result. Correlation corrections to the dipole moment and polarizability of the water molecule calculated by the finite-field RSMP and single + double excitation CI(SDCI) methods for the same basis set are found to be in close agreement. The RSMP approach has the advantages of being size-consistent and of being capable of greater efficiency than the SCDI method. Comparative calculations carried out using Epstein-Nesbet partitioning show that through third order RSEN correlation perturbation expansions for the dipole moment and polarizability are less rapidly convergent than RSMP expansions. However, reasonable accord with RSMP results can be achieved by using Pade approximants to accelerate the convergence of RSEN energy perturbation expansions. The convergence of RSMP property correlation expansions based on the zeroth-order uncoupled-Hartree-Fock (UCHF) and coupled-Hartree-Fock (CHF) approximations are compared through third order. Whereas the CHF + RSMP expansions are for practical purposes fully converged, the UCHF + RSMP expansions are not adequately converged.

Langhoff, S. R.↗
DOE OSTI2022

Pareto Optimization of Oligomer Polarizability and Dipole Moment Using a Genetic Algorithm

High-performance electronic components are highly sought after in order to produce increasingly smaller and cheaper electronic devices. Drawing inspiration from inorganic dielectric materials, in which both polarizability and polarization contribute, organic materials can also maximize both. For a large set of small molecules drawn from PubChem, a Pareto-like front appears between the polarizability and dipole moment, indicating the presence of an apparent trade-off between these two properties. We tested this balance in π-conjugated materials by searching for novel conjugated hexamers with simultaneously large polar- izabilities and dipole moments with potential use for dielectric materials. Using a genetic algorithm (GA) screening technique in conjunction with an approximate density functional tight-binding method for property calculations, we were able to efficiently search chemical space for optimal hexamers. Given the scope of chemical space, using the GA technique saves considerable time and resources by speeding up molecular searches compared to a systematic search. Here, we also explored the underlying structure–function relationships, including sequence and monomer properties, that characterize large polarizability and dipole moment regimes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Theoretical studies of the global minima and polarizabilities of small lithium clusters

Lithium clusters Lin (n=1-20) have been investigated with density functional theory (DFT) and coupled—cluster (CC) methods. The global-minimum structures are located via an improved basin---hopping algorithm and the lowest energy Lin isomers are confirmed with DFT geometry optimizations, CCSD(T) energy calculations, and by comparing simulated and experimental polarizabilities. The tetrahedral Li4 structure is found to be the basic building block of lithium clusters Lin (n=6-20). Simulated polarizabilities, including thermal effects at room temperature, are in good agreement with measured isotropic polarizabilities.

clusters↗
DOE OSTI2018

Microscopic Behaviors of Tri-n-Butyl Phosphate, n-Dodecane and Their Mixtures at Air/Liquid and Liquid/Liquid Interfaces: An AMBER Polarizable Force Field Study

In solvent extraction processes for recovering metal ions from used nuclear fuel, as well as other industrial applications, a better understanding of the metal complex phase transfer phenomenon would greatly aid ligand design and process optimization. We have approached this challenge by utilizing classical molecular dynamics simulations technique to gain visual appreciation of the vapor/liquid and liquid/liquid interface between tri-n-butyl phosphate (TBP) and n-dodecane with air and water. In this study, we successfully reparameterized polarizable force fields for TBP and n-dodecane that accurately reproduced several of their thermophysical properties such as: density, heat of vaporization, and dipole moment. Our models were able to predict the surface and interfacial tension of different systems when compared to experimental results also performed by us. Through this study, we gained numerous atomistic understanding of the behaviors of TBP and n-dodecane at the interface against air and water, useful in further computational studies of such systems. Lastly, our studies indicate that the initial configuration of a simulation may have a large effect on the final result.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Communication: Accurate higher-order van der Waals coefficients between molecules from a model dynamic multipole polarizability

Due to the absence of the long-range van der Waals (vdW) interaction, conventional density functional theory (DFT) often fails in the description of molecular complexes and solids. In recent years, considerable progress has been made in the development of the vdW correction. However, the vdW correction based on the leading-order coefficient C{sub 6} alone can only achieve limited accuracy, while accurate modeling of higher-order coefficients remains a formidable task, due to the strong non-additivity effect. Here, we apply a model dynamic multipole polarizability within a modified single-frequency approximation to calculate C{sub 8} and C{sub 10} between small molecules. We find that the higher-order vdW coefficients from this model can achieve remarkable accuracy, with mean absolute relative deviations of 5% for C{sub 8} and 7% for C{sub 10}. Inclusion of accurate higher-order contributions in the vdW correction will effectively enhance the predictive power of DFT in condensed matter physics and quantum chemistry.

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

Nonequilibrium Environment Dynamics in a Frequency-Dependent Polarizable Embedding Model

Hybrid quantum mechanical/molecular mechanical (QM/MM) models are some of the most powerful and computationally feasible approaches to account for solvent effects or more general environmental perturbations on quantum chemical systems. In their more recent formulations (known as polarizable embedding) they can account for electrostatic and mutual polarization effects between the QM and the MM subsystems. In this paper, a polarizable embedding scheme based on induced dipoles that is both able to describe electron evolution of the embedded QM system in an efficient manner as well as to capture the frequency dependent behavior of the solvent, is proposed. The effects of this frequency dependent solvent on a time- dependent model system - the Rabi oscillations of H+2 in a resonant - field are considered. The solvent is shown to introduce only mild perturbations when the excitation frequencies of the solvent and the solute are off-resonant. However, the dynamics of the H+2 are fundamentally changed in the presence of a near-resonant excitation solvent.

Wildman, Andrew↗
DOE OSTI2021

Measurement of the Generalized Spin Polarizabilities of the Neutron in the Low-Q{sup 2} Region

Understanding the nucleon spin structure in the regime where the strong interaction becomes truly strong poses a challenge to both experiment and theory. At energy scales below the nucleon mass of about 1 GeV, the intense interaction among the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behaviour causes the emergence of effective degrees of freedom, requiring the application of non-perturbative techniques such as chiral effective field theory1. Here we present measurements of the neutron’s generalized spin polarizabilities that quantify the neutron’s spin precession under electromagnetic fields at very low energy-momentum transfer squared down to 0.035 GeV2. In this regime, chiral effective field theory calculations2–4 are expected to be applicable. Our data, however, show a strong discrepancy with these predictions, presenting a challenge to the current description of the neutron’s spin properties.

Sulkosky, Vincent↗
DOE OSTI2016

A theory of interactions between polarizable dielectric spheres

Surface charging or polarization can strongly affect the nature of interactions between charged dielectric objects, particularly when sharp dielectric discontinuities are involved. The perturbative theory presented here efficiently accounts for this effect by introducing a generalized image method that enables the rapid evaluation of the electrostatic energies and forces that arise in many-body systems. The theory is validated by comparison to full numerical solutions. The importance of polarizability is then examined in the context of clusters of dielectric spheres, as well as a periodic crystal of charged dielectric spheres arranged into an NaCl-type lattice.

Qin, Jian↗
DOE OSTI2019

Time-Dependent Complete Active Space Embedded in Polarizable Force Field

Electron correlation and environmental effects play important roles in electron dynamics and spectroscopic observables of chemical systems in condensed phase. In this paper, we present a time-dependent complete active space configuration interaction (TD-CASCI) approach embedded in a polaraizable force filed, MMPol. The present implementation of TD-CASCI/MMPol utilizes a direct matrix-vector contraction, allowing studies of large systems. This scheme is used to study the solvatochromic shift of coumarin 153 in methanol. The TD-CASCI/MMPol approach captures the double excitation character in the excited state wave function and accurately predicts the solvatochromic red-shift of coumarin 153 dye within the experimental range, outperforming linear response time-dependent density functional theory. The effect of using different reference orbitals for the TD-CASCI/MMPol simulation is also investigated, highlighting the need for an unbiased treatment of all electronic states in the energy range of interest.

Liu, Hongbin↗
DOE OSTI2018

Delineating effects of nuclear symmetry energy on the radii and tidal polarizabilities of neutron stars

Here, what can we learn about the density dependence of nuclear symmetry energy ${E}_{\mathrm{sym}}(\rho)$ from precise measurements of the radius (R 1.4 ) and/or tidal polarizability (Λ 1.4 ) of canonical neutron stars with a mass of 1.4 ${{\rm{M}}}_{\odot }$? With the ${E}_{\mathrm{sym}}(\rho)$ parameterized using three parameters L, K sym, and J sym which have the asymptotic meaning of being respectively the slope, curvature, and skewness of symmetry energy at saturation density, we found that, while both the R 1.4 and Λ 1.4 depend strongly on the slope L, the K sym and J sym parameters characterizing the high-density behavior of ${E}_{\mathrm{sym}}(\rho)$ also play appreciable roles. Thus, there is not a simple relation between the Λ 1.4 /R 1.4 and L alone. Precise measurements of just the Λ 1.4 and R 1.4 cannot completely determine the ${E}_{\mathrm{sym}}(\rho)$ but limit combinations of its parameters. In particular, stringent constraints approximately independent of the J sym on the L–K sym correlations can be obtained. However, infinite combinations of the larger (smaller) L and smaller (larger) K sym can lead to the same Λ 1.4 and R 1.4 . Additional observables including those from terrestrial nuclear experiments are thus necessary to break this degeneracy in order to completely determine the density dependence of nuclear symmetry energy ${E}_{\mathrm{sym}}(\rho)$.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Impact of the neutron star crust on the tidal polarizability

The first direct detection of a binary neutron star merger by the LIGO Scientific Collaboration and the Virgo Collaboration (LIGO-Virgo) has opened the brand new era of multimessenger astronomy. Here, this historic detection has been instrumental in providing initial constraints on the tidal polarizability (or deformability) of neutron stars. In turn, the tidal polarizability—an observable highly sensitive to stellar compactness—has been used to impose limits on stellar radii and ultimately on the underlying equation of state (EOS). Besides its strong dependence on the stellar compactness, the tidal polarizability is also sensitive to the second tidal Love number k 2 . It is the main purpose of this paper to perform a detailed study of k 2 which, for a given compactness parameter, encodes the entire sensitivity of the tidal polarizability to the underlying equation of state. In particular, we examine the important role that the crustal component of the EOS plays in the determination of k 2 . A set of realistic models of the equation of state that yield an accurate description of the properties of finite nuclei support neutron stars of two solar masses and provide a Lorentz covariant extrapolation to dense matter are used to solve both the Tolman-Oppenheimer-Volkoff and the differential equations for the induced quadrupole gravitational field from which k 2 is extracted. Given that the tidal polarizability scales as the fifth power of the compactness parameter, a universal relation exists among the tidal polarizability and the compactness parameter that is highly insensitive to the underlying equation of state. Thus, besides an extraction of the tidal polarizabilities, a measurement of the individual stellar masses is also required to impact the mass-radius relation. However, we observe a strong sensitivity of the second Love number to the underlying equation of state—particularly to the contribution from the inner crust. Although by itself the tidal polarizability cannot contribute to the determination of the mass-radius relation, future detections of binary neutron star mergers by the LIGO-Virgo Collaborations during the third observing run and beyond are poised to provide significant constraints on both the tidal polarizabilities and the masses of the individual stars, and thus ultimately on the mass-radius relation. Yet, subleading corrections to the tidal polarizability are encoded in the second Love number k 2 , which displays a large sensitivity to the entire—crust-plus-core—equation of state.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Local-Field Effects in Linear Response Properties within a Polarizable Frozen Density Embedding Method

In this work, we present a polarizable frozen density embedding (FDE) method for calculating polarizabilities of coupled subsystems. The method (FDE-pol) combines a FDE method with an explicit polarization model such that the expensive freeze/thaw cycles can be bypassed, and approximate nonadditive kinetic potentials are avoided by enforcing external orthogonality between the subsystems. To describe the polarization of the frozen environment, we introduce a Hirshfeld partition-based density-dependent method for calculating the atomic polarizabilities of atoms in molecules, which alleviates the need to fit the atomic parameters to a specific system of interest or to a larger general set of molecules. Further, we show that the Hirshfeld partition-based method predicts molecular polarizabilities close to the basis set limit, and thus, a single basis set-dependent scaling parameter can be introduced to improve the agreement against the reference polarizability data. To test the model, we characterized the uncoupled and coupled response of small interacting molecular complexes. Here, the coupled response properties include the perturbation of the frozen system due to the external perturbation which is ignored in the uncoupled response. We show that FDE-pol can accurately reproduce both the exact uncoupled polarizability and the coupled polarizabilities of the supermolecular systems. Using damped response theory, we also demonstrate that the coupled frequency-dependent polarizability can be described by including local field effects. The results emphasize the necessity of including local-field effects for describing the response properties of coupled subsystems, as well as the importance of accurate atomic polarizability models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗