Quantum dust magnetosonic waves with spin and exchange correlation effects

NASA Astrophysics Data System (ADS)

Maroof, R.; Mushtaq, A.; Qamar, A.

2016-01-01

Dust magnetosonic waves are studied in degenerate dusty plasmas with spin and exchange correlation effects. Using the fluid equations of magnetoplasma with quantum corrections due to the Bohm potential, temperature degeneracy, spin magnetization energy, and exchange correlation, a generalized dispersion relation is derived. Spin effects are incorporated via spin force and macroscopic spin magnetization current. The exchange-correlation potentials are used, based on the adiabatic local-density approximation, and can be described as a function of the electron density. For three different values of angle, the dispersion relation is reduced to three different modes under the low frequency magnetohydrodynamic assumptions. It is found that the effects of quantum corrections in the presence of dust concentration significantly modify the dispersive properties of these modes. The results are useful for understanding numerous collective phenomena in quantum plasmas, such as those in compact astrophysical objects (e.g., the cores of white dwarf stars and giant planets) and in plasma-assisted nanotechnology (e.g., quantum diodes, quantum free-electron lasers, etc.).

Assessing the role of Hartree-Fock exchange, correlation energy and long range corrections in evaluating ionization potential, and electron affinity in density functional theory.

PubMed

Vikramaditya, Talapunur; Lin, Shiang-Tai

2017-06-05

Accurate determination of ionization potentials (IPs), electron affinities (EAs), fundamental gaps (FGs), and HOMO, LUMO energy levels of organic molecules play an important role in modeling and predicting the efficiencies of organic photovoltaics, OLEDs etc. In this work, we investigate the effects of Hartree Fock (HF) Exchange, correlation energy, and long range corrections in predicting IP and EA in Hybrid Functionals. We observe increase in percentage of HF exchange results in increase of IPs and decrease in EAs. Contrary to the general expectations inclusion of both HF exchange and correlation energy (from the second order perturbation theory MP2) leads to poor prediction. Range separated Hybrid Functionals are found to be more reliable among various DFT Functionals investigated. DFT Functionals predict accurate IPs whereas post HF methods predict accurate EAs. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Exchange and correlation energies in silicene illuminated by circularly polarized light

NASA Astrophysics Data System (ADS)

Iurov, Andrii; Gumbs, Godfrey; Huang, Danhong

2017-05-01

Both the exchange and correlation energies due to Coulomb and spin-orbit interactions in a monolayer silicene with a buckled honeycomb lattice are calculated. We use Lindhard formalism for the polarizability. Many-body effects in such Dirac-like materials are studied with an emphasis on the influence of on-site potential difference ? between two sublattices. Our calculations have shown that the presence of an energy bandgap ? leads to a reduced exchange energy, which has some potential applications, such as, tunability of entanglement of electrons for quantum information devices. Since silicene acquires two energy gaps associated with up- and down-pseudospin, we can adjust its electronic properties in a wider range by varying these two bandgaps as compared to graphene. Another way to tune silicene electronic properties is through impurity doping. Our numerical results demonstrate the dependence of exchange and correlation energies on the energy bandgaps, doping and temperature under circularly polarized light.

Accurate and Efficient Approximation to the Optimized Effective Potential for Exchange

NASA Astrophysics Data System (ADS)

Ryabinkin, Ilya G.; Kananenka, Alexei A.; Staroverov, Viktor N.

2013-07-01

We devise an efficient practical method for computing the Kohn-Sham exchange-correlation potential corresponding to a Hartree-Fock electron density. This potential is almost indistinguishable from the exact-exchange optimized effective potential (OEP) and, when used as an approximation to the OEP, is vastly better than all existing models. Using our method one can obtain unambiguous, nearly exact OEPs for any reasonable finite one-electron basis set at the same low cost as the Krieger-Li-Iafrate and Becke-Johnson potentials. For all practical purposes, this solves the long-standing problem of black-box construction of OEPs in exact-exchange calculations.

Approximating the Shifted Hartree-Exchange-Correlation Potential in Direct Energy Kohn-Sham Theory.

PubMed

Sharpe, Daniel J; Levy, Mel; Tozer, David J

2018-02-13

Levy and Zahariev [Phys. Rev. Lett. 113 113002 (2014)] have proposed a new approach for performing density functional theory calculations, termed direct energy Kohn-Sham (DEKS) theory. In this approach, the electronic energy equals the sum of orbital energies, obtained from Kohn-Sham-like orbital equations involving a shifted Hartree-exchange-correlation potential, which must be approximated. In the present study, density scaling homogeneity considerations are used to facilitate DEKS calculations on a series of atoms and molecules, leading to three nonlocal approximations to the shifted potential. The first two rely on preliminary Kohn-Sham calculations using a standard generalized gradient approximation (GGA) exchange-correlation functional and the results illustrate the benefit of describing the dominant Hartree component of the shift exactly. A uniform electron gas analysis is used to eliminate the need for these preliminary Kohn-Sham calculations, leading to a potential with an unconventional form that yields encouraging results, providing strong motivation for further research in DEKS theory.

The Exchange-Correlation Field Effect over the Magnetoacoustic-Gravitational Instability in Plasmas

NASA Astrophysics Data System (ADS)

Rasheed, A.; Jamil, M.; Jung, Young-Dae; Sahar, A.; Asif, M.

2017-09-01

Jeans instability with magnetosonic perturbations is discussed in quantum dusty magnetoplasmas. The quantum and smaller thermal effects are associated only with electrons. The quantum characteristics include exchange-correlation potential, recoil effect, and Fermi degenerate pressure. The multifluid model of plasmas is used for the analytical study of this problem. The significant contribution of electron exchange is noticed on the threshold value of wave vector and Jeans instability. The presence of electron exchange and correlation effects reduce the time to stabilise the phenomenon of self-gravitational collapse of massive species. The results of Jeans instability by magnetosonic perturbations at quantum scale help to disclose the details of the self-gravitating dusty magnetoplasma systems.

Improved correlation corrections to the local-spin-density approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Painter, G.S.

1981-10-15

The accurate correlation energies for the para- and ferromagnetic states of the electron liquid calculated by Ceperley and Alder were recently used by Vosko, Wilk, and Nusair to produce a new correlation-energy density of increased accuracy and proper limiting behavior in the metallic density regime (r/sub s/< or =6). In the present work, the correlation potential in the local-spin-density approximation (LSDA) is derived from the correlation-energy-density representation of Vosko et al. Characteristics of the new exchange-correlation model are compared with those of the LSDA model of Gunnarsson and Lundqvist. Specific comparison is made between these models and exact results inmore » the treatment of atomic and molecular hydrogen. Since the new treatment of correlation primarily affects the region of small r/sub s/, which is exchange dominated, correlation corrections are small compared with errors in the exchange energy. Thus, in light atoms the improved correlation model leads to a reduced cancellation of error between exchange and correlation energies, emphasizing the necessity for improved exchange treatment. For more homogeneous systems, the model should offer real improvement. The present results obtained with precise treatment of correlation within the prescription of Vosko et al. serve to define the present limitations of the LSDA and indicate the importance of nonlocal corrections, particularly for atoms.« less

Dissociation of diatomic molecules and the exact-exchange Kohn-Sham potential: the case of LiF

NASA Astrophysics Data System (ADS)

Makmal, Adi; Kuemmel, Stephan; Kronik, Leeor

2011-03-01

The incorrect fractional-charge dissociation of stretched diatomic molecules, predicted by semi-local exchange-correlation functionals, is revisited. This difficulty can be overcome with asymptotically correct non-local potential operators, but should also be absent in exact Kohn-Sham theory, where the potential is local. Here, we show, for the illustrative case of the LiF dimer, that the exact-exchange local Kohn-Sham potential, constructed within the Krieger, Li, and Iafrate (KLI) approximation, can lead to binding energy and charge dissociation curves that are qualitatively correct. This correct behavior is traced back to a characteristic ``step'' structure in the local exchange potential and its relation to the Kohn-Sham eigenvalues is analyzed.

Discontinuity of the exchange-correlation potential and the functional derivative of the noninteracting kinetic energy as the number of electrons crosses integer boundaries in Li, Be, and B.

PubMed

Morrison, Robert C

2015-01-07

Accurate densities were determined from configuration interaction wave functions for atoms and ions of Li, Be, and B with up to four electrons. Exchange-correlation potentials, Vxc(r), and functional derivatives of the noninteracting kinetic energy, δK[ρ]/δρ(r), obtained from these densities were used to examine their discontinuities as the number of electrons N increases across integer boundaries for N = 1, N = 2, and N = 3. These numerical results are consistent with conclusions that the discontinuities are characterized by a jump in the chemical potential while the shape of Vxc(r) varies continuously as an integer boundary is crossed. The discontinuity of the Vxc(r) is positive, depends on the ionization potential, electron affinity, and orbital energy differences, and the discontinuity in δK[ρ]/δρ(r) depends on the difference between the energies of the highest occupied and lowest unoccupied orbitals. The noninteracting kinetic energy and the exchange correlation energy have been computed for integer and noninteger values of N between 1 and 4.

Importance of the Kinetic Energy Density for Band Gap Calculations in Solids with Density Functional Theory.

PubMed

Tran, Fabien; Blaha, Peter

2017-05-04

Recently, exchange-correlation potentials in density functional theory were developed with the goal of providing improved band gaps in solids. Among them, the semilocal potentials are particularly interesting for large systems since they lead to calculations that are much faster than with hybrid functionals or methods like GW. We present an exhaustive comparison of semilocal exchange-correlation potentials for band gap calculations on a large test set of solids, and particular attention is paid to the potential HLE16 proposed by Verma and Truhlar. It is shown that the most accurate potential is the modified Becke-Johnson potential, which, most noticeably, is much more accurate than all other semilocal potentials for strongly correlated systems. This can be attributed to its additional dependence on the kinetic energy density. It is also shown that the modified Becke-Johnson potential is at least as accurate as the hybrid functionals and more reliable for solids with large band gaps.

Optimized effective potential in real time: Problems and prospects in time-dependent density-functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mundt, Michael; Kuemmel, Stephan

2006-08-15

The integral equation for the time-dependent optimized effective potential (TDOEP) in time-dependent density-functional theory is transformed into a set of partial-differential equations. These equations only involve occupied Kohn-Sham orbitals and orbital shifts resulting from the difference between the exchange-correlation potential and the orbital-dependent potential. Due to the success of an analog scheme in the static case, a scheme that propagates orbitals and orbital shifts in real time is a natural candidate for an exact solution of the TDOEP equation. We investigate the numerical stability of such a scheme. An approximation beyond the Krieger-Li-Iafrate approximation for the time-dependent exchange-correlation potential ismore » analyzed.« less

Quantum effects on compressional Alfven waves in compensated semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amin, M. R.

2015-03-15

Amplitude modulation of a compressional Alfven wave in compensated electron-hole semiconductor plasmas is considered in the quantum magnetohydrodynamic regime in this paper. The important ingredients of this study are the inclusion of the particle degeneracy pressure, exchange-correlation potential, and the quantum diffraction effects via the Bohm potential in the momentum balance equations of the charge carriers. A modified nonlinear Schrödinger equation is derived for the evolution of the slowly varying amplitude of the compressional Alfven wave by employing the standard reductive perturbation technique. Typical values of the parameters for GaAs, GaSb, and GaN semiconductors are considered in analyzing the linearmore » and nonlinear dispersions of the compressional Alfven wave. Detailed analysis of the modulation instability in the long-wavelength regime is presented. For typical parameter ranges of the semiconductor plasmas and at the long-wavelength regime, it is found that the wave is modulationally unstable above a certain critical wavenumber. Effects of the exchange-correlation potential and the Bohm potential in the wave dynamics are also studied. It is found that the effect of the Bohm potential may be neglected in comparison with the effect of the exchange-correlation potential in the linear and nonlinear dispersions of the compressional Alfven wave.« less

Local-spin-density calculations for iron: Effect of spin interpolation on ground-state properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacLaren, J.M.; Clougherty, D.P.; Albers, R.C.

1990-08-15

Scalar-relativistic self-consistent linear muffin-tin orbital (LMTO) calculations for bcc and fcc Fe have been performed with several different local approximations to the exchange and correlation energy density and potential. Overall, in contrast to the conclusions of previous studies, we find that the local-spin-density approximation to exchange and correlation can provide an adequate description of bulk Fe {ital provided} that a proper parametrization of the correlation energy density and potential of the homogeneous electron gas over both spin and density is used. Lattice constants, found from the position of the minimum of the total energy as a function of Wigner-Seitz radius,more » agree to within 1% (for {ital s},{ital p},{ital d} LMTO's only) and within 1--2% (for {ital s},{ital p},{ital d},{ital f} LMTO's) of the experimental lattice constants for all forms used for the local correlation. The best agreement, however, was obtained using a local correlation potential derived from the Vosko-Wilk-Nusair form for the spin dependence of the correlation energy density. The calculation performed with this correlation potential was also the only calculation to correctly predict a bcc ferromagnetic ground state.« less

Augmented potential, energy densities, and virial relations in the weak- and strong-interaction limits of DFT

NASA Astrophysics Data System (ADS)

Vuckovic, Stefan; Levy, Mel; Gori-Giorgi, Paola

2017-12-01

The augmented potential introduced by Levy and Zahariev [Phys. Rev. Lett. 113, 113002 (2014)] is shifted with respect to the standard exchange-correlation potential of the Kohn-Sham density functional theory by a density-dependent constant that makes the total energy become equal to the sum of the occupied orbital energies. In this work, we analyze several features of this approach, focusing on the limit of infinite coupling strength and studying the shift and the corresponding energy density at different correlation regimes. We present and discuss coordinate scaling properties of the augmented potential, study its connection to the response potential, and use the shift to analyze the classical jellium and uniform gas models. We also study other definitions of the energy densities in relation to the functional construction by local interpolations along the adiabatic connection. Our findings indicate that the energy density that is defined in terms of the electrostatic potential of the exchange-correlation hole is particularly well suited for this purpose.

Violation of the continuity equation in the Krieger-Li-Iafrate approximation for current-density functional theory

NASA Astrophysics Data System (ADS)

Siegmund, Marc; Pankratov, Oleg

2011-01-01

We show that the exchange-correlation scalar and vector potentials obtained from the optimized effective potential (OEP) equations and from the Krieger-Li-Iafrate (KLI) approximation for the current-density functional theory (CDFT) change under a gauge transformation such that the energy functional remains invariant. This alone does not assure, however, the theory’s compliance with the continuity equation. Using the model of a quantum ring with a broken angular symmetry which is penetrated by a magnetic flux we demonstrate that the physical current density calculated with the exact-exchange CDFT in the KLI approximation violates the continuity condition. In contrast, the current found from a solution of the full OEP equations satisfies this condition. We argue that the continuity violation stems from the fact that the KLI potentials are not (in general) the exact functional derivatives of a gauge-invariant exchange-correlation functional.

Neural-network Kohn-Sham exchange-correlation potential and its out-of-training transferability

NASA Astrophysics Data System (ADS)

Nagai, Ryo; Akashi, Ryosuke; Sasaki, Shu; Tsuneyuki, Shinji

2018-06-01

We incorporate in the Kohn-Sham self-consistent equation a trained neural-network projection from the charge density distribution to the Hartree-exchange-correlation potential n → VHxc for a possible numerical approach to the exact Kohn-Sham scheme. The potential trained through a newly developed scheme enables us to evaluate the total energy without explicitly treating the formula of the exchange-correlation energy. With a case study of a simple model, we show that the well-trained neural-network VHxc achieves accuracy for the charge density and total energy out of the model parameter range used for the training, indicating that the property of the elusive ideal functional form of VHxc can approximately be encapsulated by the machine-learning construction. We also exemplify a factor that crucially limits the transferability—the boundary in the model parameter space where the number of the one-particle bound states changes—and see that this is cured by setting the training parameter range across that boundary. The training scheme and insights from the model study apply to more general systems, opening a novel path to numerically efficient Kohn-Sham potential.

Prevalence and correlates of exchanging sex for drugs or money among adolescents in the United States.

PubMed

Edwards, J M; Iritani, B J; Hallfors, D D

2006-10-01

This study examined the prevalence and correlates of exchanging sex for drugs or money among a nationally representative sample of 13,294 adolescents in the United States. Data are from the National Longitudinal Study of Adolescent Health, waves I and II. The lifetime prevalence of exchanging sex was estimated and a cross sectional analysis of sociodemographic and behavioural correlates was conducted. Unadjusted odds ratios were obtained. 3.5% of adolescents had ever exchanged sex for drugs or money. Two thirds of these youths were boys. The odds of having exchanged sex were higher for youths who had used drugs, had run away from home, were depressed, and had engaged in various sexual risk behaviours. 15% of boys and 20% of girls who had exchanged sex reported they had ever been told they have HIV or another sexually transmitted infection (STI). Adolescents with a history of exchanging sex have engaged in other high risk behaviours and may experience poor health outcomes, including depression and HIV/STIs. These findings should help inform strategies to prevent this high risk sexual behaviour and its potential consequences.

Effective homogeneity of the exchange-correlation and non-interacting kinetic energy functionals under density scaling.

PubMed

Borgoo, Alex; Teale, Andrew M; Tozer, David J

2012-01-21

Correlated electron densities, experimental ionisation potentials, and experimental electron affinities are used to investigate the homogeneity of the exchange-correlation and non-interacting kinetic energy functionals of Kohn-Sham density functional theory under density scaling. Results are presented for atoms and small molecules, paying attention to the influence of the integer discontinuity and the choice of the electron affinity. For the exchange-correlation functional, effective homogeneities are highly system-dependent on either side of the integer discontinuity. By contrast, the average homogeneity-associated with the potential that averages over the discontinuity-is generally close to 4/3 when the discontinuity is computed using positive affinities for systems that do bind an excess electron and negative affinities for those that do not. The proximity to 4/3 becomes increasingly pronounced with increasing atomic number. Evaluating the discontinuity using a zero affinity in systems that do not bind an excess electron instead leads to effective homogeneities on the electron abundant side that are close to 4/3. For the non-interacting kinetic energy functional, the effective homogeneities are less system-dependent and the effect of the integer discontinuity is less pronounced. Average values are uniformly below 5/3. The study provides information that may aid the development of improved exchange-correlation and non-interacting kinetic energy functionals. © 2012 American Institute of Physics

Density functional theory calculations of III-N based semiconductors with mBJLDA

NASA Astrophysics Data System (ADS)

Gürel, Hikmet Hakan; Akıncı, Özden; Ünlü, Hilmi

2017-02-01

In this work, we present first principles calculations based on a full potential linear augmented plane-wave method (FP-LAPW) to calculate structural and electronic properties of III-V based nitrides such as GaN, AlN, InN in a zinc-blende cubic structure. First principles calculation using the local density approximation (LDA) and generalized gradient approximation (GGA) underestimate the band gap. We proposed a new potential called modified Becke-Johnson local density approximation (MBJLDA) that combines modified Becke-Johnson exchange potential and the LDA correlation potential to get better band gap results compared to experiment. We compared various exchange-correlation potentials (LSDA, GGA, HSE, and MBJLDA) to determine band gaps and structural properties of semiconductors. We show that using MBJLDA density potential gives a better agreement with experimental data for band gaps III-V nitrides based semiconductors.

Exchange-correlation approximations for reduced-density-matrix-functional theory at finite temperature: Capturing magnetic phase transitions in the homogeneous electron gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baldsiefen, Tim; Cangi, Attila; Eich, F. G.

Here, we derive an intrinsically temperature-dependent approximation to the correlation grand potential for many-electron systems in thermodynamical equilibrium in the context of finite-temperature reduced-density-matrix-functional theory (FT-RDMFT). We demonstrate its accuracy by calculating the magnetic phase diagram of the homogeneous electron gas. We compare it to known limits from highly accurate quantum Monte Carlo calculations as well as to phase diagrams obtained within existing exchange-correlation approximations from density functional theory and zero-temperature RDMFT.

Exchange-correlation approximations for reduced-density-matrix-functional theory at finite temperature: Capturing magnetic phase transitions in the homogeneous electron gas

DOE PAGES

Baldsiefen, Tim; Cangi, Attila; Eich, F. G.; ...

2017-12-18

Here, we derive an intrinsically temperature-dependent approximation to the correlation grand potential for many-electron systems in thermodynamical equilibrium in the context of finite-temperature reduced-density-matrix-functional theory (FT-RDMFT). We demonstrate its accuracy by calculating the magnetic phase diagram of the homogeneous electron gas. We compare it to known limits from highly accurate quantum Monte Carlo calculations as well as to phase diagrams obtained within existing exchange-correlation approximations from density functional theory and zero-temperature RDMFT.

Simple iterative construction of the optimized effective potential for orbital functionals, including exact exchange.

PubMed

Kümmel, Stephan; Perdew, John P

2003-01-31

For exchange-correlation functionals that depend explicitly on the Kohn-Sham orbitals, the potential V(xcsigma)(r) must be obtained as the solution of the optimized effective potential (OEP) integral equation. This is very demanding and has limited the use of orbital functionals. We demonstrate that instead the OEP can be obtained iteratively by solving the partial differential equations for the orbital shifts that exactify the Krieger-Li-Iafrate approximation. Unoccupied orbitals do not need to be calculated. Accuracy and efficiency of the method are shown for atoms and clusters using the exact-exchange energy. Counterintuitive asymptotic limits of the exact OEP are presented.

Course 4: Density Functional Theory, Methods, Techniques, and Applications

NASA Astrophysics Data System (ADS)

Chrétien, S.; Salahub, D. R.

Contents 1 Introduction 2 Density functional theory 2.1 Hohenberg and Kohn theorems 2.2 Levy's constrained search 2.3 Kohn-Sham method 3 Density matrices and pair correlation functions 4 Adiabatic connection or coupling strength integration 5 Comparing and constrasting KS-DFT and HF-CI 6 Preparing new functionals 7 Approximate exchange and correlation functionals 7.1 The Local Spin Density Approximation (LSDA) 7.2 Gradient Expansion Approximation (GEA) 7.3 Generalized Gradient Approximation (GGA) 7.4 meta-Generalized Gradient Approximation (meta-GGA) 7.5 Hybrid functionals 7.6 The Optimized Effective Potential method (OEP) 7.7 Comparison between various approximate functionals 8 LAP correlation functional 9 Solving the Kohn-Sham equations 9.1 The Kohn-Sham orbitals 9.2 Coulomb potential 9.3 Exchange-correlation potential 9.4 Core potential 9.5 Other choices and sources of error 9.6 Functionality 10 Applications 10.1 Ab initio molecular dynamics for an alanine dipeptide model 10.2 Transition metal clusters: The ecstasy, and the agony... 10.3 The conversion of acetylene to benzene on Fe clusters 11 Conclusions

Exact Time-Dependent Exchange-Correlation Potential in Electron Scattering Processes

NASA Astrophysics Data System (ADS)

Suzuki, Yasumitsu; Lacombe, Lionel; Watanabe, Kazuyuki; Maitra, Neepa T.

2017-12-01

We identify peak and valley structures in the exact exchange-correlation potential of time-dependent density functional theory that are crucial for time-resolved electron scattering in a model one-dimensional system. These structures are completely missed by adiabatic approximations that, consequently, significantly underestimate the scattering probability. A recently proposed nonadiabatic approximation is shown to correctly capture the approach of the electron to the target when the initial Kohn-Sham state is chosen judiciously, and it is more accurate than standard adiabatic functionals but ultimately fails to accurately capture reflection. These results may explain the underestimation of scattering probabilities in some recent studies on molecules and surfaces.

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

DOE PAGES

Tao, Jianmin; Ye, Lin -Hui; Duan, Yuhua

2017-11-20

The primary goal of Kohn–Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao–Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew–Burke–Ernzerhof (PBE), Tao–Perdew–Staroverov–Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree–Fock density yields the exchange and correlation energies in good agreement with the Optimizedmore » Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Lastly, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.« less

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

NASA Astrophysics Data System (ADS)

Tao, Jianmin; Ye, Lin-Hui; Duan, Yuhua

2017-12-01

The primary goal of Kohn-Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao-Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew-Burke-Ernzerhof (PBE), Tao-Perdew-Staroverov-Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree-Fock density yields the exchange and correlation energies in good agreement with the Optimized Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Finally, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.

Exchange-correlation energies of atoms from efficient density functionals: influence of the electron density

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Jianmin; Ye, Lin -Hui; Duan, Yuhua

The primary goal of Kohn–Sham density functional theory is to evaluate the exchange-correlation contribution to electronic properties. However, the accuracy of a density functional can be affected by the electron density. Here we apply the nonempirical Tao–Mo (TM) semilocal functional to study the influence of the electron density on the exchange and correlation energies of atoms and ions, and compare the results with the commonly used nonempirical semilocal functionals local spin-density approximation (LSDA), Perdew–Burke–Ernzerhof (PBE), Tao–Perdew–Staroverov–Scuseria (TPSS), and hybrid functional PBE0. We find that the spin-restricted Hartree–Fock density yields the exchange and correlation energies in good agreement with the Optimizedmore » Effective Potential method, particularly for spherical atoms and ions. However, the errors of these semilocal and hybrid functionals become larger for self-consistent densities. We further find that the quality of the electron density have greater effect on the exchange-correlation energies of kinetic energy density-dependent meta-GGA functionals TPSS and TM than on those of the LSDA and GGA, and therefore, should have greater influence on the performance of meta-GGA functionals. Lastly, we show that the influence of the density quality on PBE0 is slightly reduced, compared to that of PBE, due to the exact mixing.« less

Renormalization of the Brazilian chiral nucleon-nucleon potential

NASA Astrophysics Data System (ADS)

Da Rocha, Carlos A.; Timóteo, Varese S.

2013-03-01

In this work we present a renormalization of the Brazilian nucleon-nucleon (NN) potential using a subtractive method. We show that the exchange of correlated two pion is important for isovector channels, mainly in tensor and central potentials.

Contrasting dynamics of leaf potential and gas exchange during progressive drought cycles and recovery in Amorpha fruticosa and Robinia pseudoacacia.

PubMed

Yan, Weiming; Zheng, Shuxia; Zhong, Yangquanwei; Shangguan, Zhouping

2017-06-30

Leaf gas exchange is closely associated with water relations; however, less attention has been given to this relationship over successive drought events. Dynamic changes in gas exchange and water potential in the seedlings of two woody species, Amorpha fruticosa and Robinia pseudoacacia, were monitored during recurrent drought. The pre-dawn leaf water potential declined in parallel with gas exchange in both species, and sharp declines in gas exchange occurred with decreasing water potential. A significant correlation between pre-dawn water potential and gas exchange was observed in both species and showed a right shift in R. pseudoacacia in the second drought. The results suggested that stomatal closure in early drought was mediated mainly by elevated foliar abscisic acid (ABA) in R. pseudoacacia, while a shift from ABA-regulated to leaf-water-potential-driven stomatal closure was observed in A. fruticosa. After re-watering, the pre-dawn water potential recovered quickly, whereas stomatal conductance did not fully recover from drought in R. pseudoacacia, which affected the ability to tightly control transpiration post-drought. The dynamics of recovery from drought suggest that stomatal behavior post-drought may be restricted mainly by hydraulic factors, but non-hydraulic factors may also be involved in R. pseudoacacia.

Better band gaps for wide-gap semiconductors from a locally corrected exchange-correlation potential that nearly eliminates self-interaction errors

DOE PAGES

Singh, Prashant; Harbola, Manoj K.; Johnson, Duane D.

2017-09-08

Here, this work constitutes a comprehensive and improved account of electronic-structure and mechanical properties of silicon-nitride (more » $${\\rm Si}_{3}$$ $${\\rm N}_{4}$$ ) polymorphs via van Leeuwen and Baerends (LB) exchange-corrected local density approximation (LDA) that enforces the exact exchange potential asymptotic behavior. The calculated lattice constant, bulk modulus, and electronic band structure of $${\\rm Si}_{3}$$ $${\\rm N}_{4}$$ polymorphs are in good agreement with experimental results. We also show that, for a single electron in a hydrogen atom, spherical well, or harmonic oscillator, the LB-corrected LDA reduces the (self-interaction) error to exact total energy to ~10%, a factor of three to four lower than standard LDA, due to a dramatically improved representation of the exchange-potential.« less

Real-Space Multiple-Scattering Theory and Its Applications at Exascale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eisenbach, Markus; Wang, Yang

In recent decades, the ab initio methods based on density functional theory (DFT) (Hohenberg and Kohn 1964, Kohn and Sham 1965) have become a widely used tool in computational materials science, which allows theoretical prediction of physical properties of materials from the first principles and theoretical interpretation of new physical phenomena found in experiments. In the framework of DFT, the original problem that requires solving a quantum mechanical equation for a many-electron system is reduced to a one-electron problem that involves an electron moving in an effective field, while the effective field potential is made up of an electrostatic potential,more » also known as Hartree potential, arising from the electronic and ion charge distribution in space and an exchange–correlation potential, which is a function of the electron density and encapsulates the exchange and correlation effects of the many-electron system. Even though the exact functional form of the exchange-correlation potential is formally unknown, a local density approximation (LDA) or a generalized gradient approximation (GGA) is usually applied so that the calculation of the exchange–correlation potential, as well as the exchange–correlation energy, becomes tractable while a required accuracy is retained. Based on DFT, ab initio electronic structure calculations for a material generally involve a self-consistent process that iterates between two computational tasks: (1) solving an one-electron Schrödinger equation, also known as Kohn–Sham equation, to obtain the electron density and, if needed, the magnetic moment density, and (2) solving the Poisson equation to obtain the electrostatic potential corresponding to the electron density and constructing the effective potential by adding the exchange–correlation potential to the electrostatic potential. This self-consistent process proceeds until a convergence criteria is reached.« less

Time-dependent density functional theory beyond Kohn-Sham Slater determinants.

PubMed

Fuks, Johanna I; Nielsen, Søren E B; Ruggenthaler, Michael; Maitra, Neepa T

2016-08-03

When running time-dependent density functional theory (TDDFT) calculations for real-time simulations of non-equilibrium dynamics, the user has a choice of initial Kohn-Sham state, and typically a Slater determinant is used. We explore the impact of this choice on the exchange-correlation potential when the physical system begins in a 50 : 50 superposition of the ground and first-excited state of the system. We investigate the possibility of judiciously choosing a Kohn-Sham initial state that minimizes errors when adiabatic functionals are used. We find that if the Kohn-Sham state is chosen to have a configuration matching the one that dominates the interacting state, this can be achieved for a finite time duration for some but not all such choices. When the Kohn-Sham system does not begin in a Slater determinant, we further argue that the conventional splitting of the exchange-correlation potential into exchange and correlation parts has limited value, and instead propose a decomposition into a "single-particle" contribution that we denote v, and a remainder. The single-particle contribution can be readily computed as an explicit orbital-functional, reduces to exchange in the Slater determinant case, and offers an alternative to the adiabatic approximation as a starting point for TDDFT approximations.

Selection during crop diversification involves correlated evolution of the circadian clock and ecophysiological traits in Brassica rapa.

PubMed

Yarkhunova, Yulia; Edwards, Christine E; Ewers, Brent E; Baker, Robert L; Aston, Timothy Llewellyn; McClung, C Robertson; Lou, Ping; Weinig, Cynthia

2016-04-01

Crop selection often leads to dramatic morphological diversification, in which allocation to the harvestable component increases. Shifts in allocation are predicted to impact (as well as rely on) physiological traits; yet, little is known about the evolution of gas exchange and related anatomical features during crop diversification. In Brassica rapa, we tested for physiological differentiation among three crop morphotypes (leaf, turnip, and oilseed) and for correlated evolution of circadian, gas exchange, and phenological traits. We also examined internal and surficial leaf anatomical features and biochemical limits to photosynthesis. Crop types differed in gas exchange; oilseed varieties had higher net carbon assimilation and stomatal conductance relative to vegetable types. Phylogenetically independent contrasts indicated correlated evolution between circadian traits and both gas exchange and biomass accumulation; shifts to shorter circadian period (closer to 24 h) between phylogenetic nodes are associated with higher stomatal conductance, lower photosynthetic rate (when CO2 supply is factored out), and lower biomass accumulation. Crop type differences in gas exchange are also associated with stomatal density, epidermal thickness, numbers of palisade layers, and biochemical limits to photosynthesis. Brassica crop diversification involves correlated evolution of circadian and physiological traits, which is potentially relevant to understanding mechanistic targets for crop improvement. © 2015 The Authors. New Phytologist © 2015 New Phytologist Trust.

Ground-state energies and highest occupied eigenvalues of atoms in exchange-only density-functional theory

NASA Astrophysics Data System (ADS)

Li, Yan; Harbola, Manoj K.; Krieger, J. B.; Sahni, Viraht

1989-11-01

The exchange-correlation potential of the Kohn-Sham density-functional theory has recently been interpreted as the work required to move an electron against the electric field of its Fermi-Coulomb hole charge distribution. In this paper we present self-consistent results for ground-state total energies and highest occupied eigenvalues of closed subshell atoms as obtained by this formalism in the exchange-only approximation. The total energies, which are an upper bound, lie within 50 ppm of Hartree-Fock theory for atoms heavier than Be. The highest occupied eigenvalues, as a consequence of this interpretation, approximate well the experimental ionization potentials. In addition, the self-consistently calculated exchange potentials are very close to those of Talman and co-workers [J. D. Talman and W. F. Shadwick, Phys. Rev. A 14, 36 (1976); K. Aashamar, T. M. Luke, and J. D. Talman, At. Data Nucl. Data Tables 22, 443 (1978)].

Design of exchange-correlation functionals through the correlation factor approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavlíková Přecechtělová, Jana, E-mail: j.precechtelova@gmail.com, E-mail: Matthias.Ernzerhof@UMontreal.ca; Institut für Chemie, Theoretische Chemie / Quantenchemie, Sekr. C7, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin; Bahmann, Hilke

The correlation factor model is developed in which the spherically averaged exchange-correlation hole of Kohn-Sham theory is factorized into an exchange hole model and a correlation factor. The exchange hole model reproduces the exact exchange energy per particle. The correlation factor is constructed in such a manner that the exchange-correlation energy correctly reduces to exact exchange in the high density and rapidly varying limits. Four different correlation factor models are presented which satisfy varying sets of physical constraints. Three models are free from empirical adjustments to experimental data, while one correlation factor model draws on one empirical parameter. The correlationmore » factor models are derived in detail and the resulting exchange-correlation holes are analyzed. Furthermore, the exchange-correlation energies obtained from the correlation factor models are employed to calculate total energies, atomization energies, and barrier heights. It is shown that accurate, non-empirical functionals can be constructed building on exact exchange. Avenues for further improvements are outlined as well.« less

MN15-L: A New Local Exchange-Correlation Functional for Kohn-Sham Density Functional Theory with Broad Accuracy for Atoms, Molecules, and Solids.

PubMed

Yu, Haoyu S; He, Xiao; Truhlar, Donald G

2016-03-08

Kohn-Sham density functional theory is widely used for applications of electronic structure theory in chemistry, materials science, and condensed-matter physics, but the accuracy depends on the quality of the exchange-correlation functional. Here, we present a new local exchange-correlation functional called MN15-L that predicts accurate results for a broad range of molecular and solid-state properties including main-group bond energies, transition metal bond energies, reaction barrier heights, noncovalent interactions, atomic excitation energies, ionization potentials, electron affinities, total atomic energies, hydrocarbon thermochemistry, and lattice constants of solids. The MN15-L functional has the same mathematical form as a previous meta-nonseparable gradient approximation exchange-correlation functional, MN12-L, but it is improved because we optimized it against a larger database, designated 2015A, and included smoothness restraints; the optimization has a much better representation of transition metals. The mean unsigned error on 422 chemical energies is 2.32 kcal/mol, which is the best among all tested functionals, with or without nonlocal exchange. The MN15-L functional also provides good results for test sets that are outside the training set. A key issue is that the functional is local (no nonlocal exchange or nonlocal correlation), which makes it relatively economical for treating large and complex systems and solids. Another key advantage is that medium-range correlation energy is built in so that one does not need to add damped dispersion by molecular mechanics in order to predict accurate noncovalent binding energies. We believe that the MN15-L functional should be useful for a wide variety of applications in chemistry, physics, materials science, and molecular biology.

Experimental and first principle studies on electronic structure of BaTiO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagdeo, Archna, E-mail: archnaj@rrcat.gov.in; Ghosh, Haranath, E-mail: archnaj@rrcat.gov.in; Chakrabarti, Aparna, E-mail: archnaj@rrcat.gov.in

2014-04-24

We have carried out photoemission experiments to obtain valence band spectra of various crystallographic symmetries of BaTiO{sub 3} system which arise as a function of temperature. We also present results of a detailed first principle study of these symmetries of BaTiO{sub 3} using generalized gradient approximation for the exchange-correlation potential. Here we present theoretical results of density of states obtained from DFT based simulations to compare with the experimental valence band spectra. Further, we also perform calculations using post density functional approaches like GGA + U method as well as non-local hybrid exchange-correlation potentials like PBE0, B3LYP, HSE in ordermore » to understand the extent of effect of correlation on band gaps of different available crystallographic symmetries (5 in number) of BaTiO{sub 3}.« less

Single and double multiphoton ionization of Li and Be atoms by strong laser fields

NASA Astrophysics Data System (ADS)

Telnov, Dmitry; Heslar, John; Chu, Shih-I.

2011-05-01

The time-dependent density functional theory with self-interaction correction and proper asymptotic long-range potential is extended for nonperturbative treatment of multiphoton single and double ionization of Li and Be atoms by strong 800 nm laser fields. We make use of the time-dependent Krieger-Li-Iafrate (TDKLI) exchange-correlation potential with the integer discontinuity which improves the description of the double ionization process. However, we have found that the discontinuity of the TDKLI potential is not sufficient to reproduce the characteristic feature of double ionization. This may happen because the discontinuity of the TDKLI potential is related to the spin particle numbers only and not to the total particle number. Introducing a discontinuity with respect to the total particle number to the exchange-correlation potential, we were able to obtain the knee structure in the intensity dependence of the double ionization probability of Be. This work was partially supported by DOE and NSF and by NSC-Taiwan.

Fractional distribution of thallium in paddy soil and its bioavailability to rice.

PubMed

Huang, Xuexia; Li, Ning; Wu, Qihang; Long, Jianyou; Luo, Dinggui; Huang, Xiaowu; Li, Dongmei; Zhao, Dongye

2018-02-01

To investigate the bioavailability of thallium (Tl) in soil and rice in a Tl-contaminated area in Guangdong, China, the topsoil and rice samples were collected from 24 sampling sites and analyzed. Moreover, a modified sequential extraction procedure was applied to determine the different Tl fractions in the soil. The mean pH value of the soil samples was 4.50. The total Tl concentration in the paddy soil was about 4-8 times higher than the Canadian guideline value (1mgkg -1 ) for agricultural land uses. The mean ecological risk index of Tl was determined to be 483, indicating that potential hazard of the paddy soil was serious. The mean content of Tl in rice was 1.42mgkg -1 , which exceeded the German maximum permissible level (0.5mgkg -1 ) of Tl in foods and feedstuffs by a factor of nearly 3. The hazard quotient value via rice intake was 57.6, indicating a high potential health risk to the local residents. The distribution of various Tl fractions followed the order of easily reducible fraction (40.3%) > acid exchangeable fraction (30.5%) > residual fraction (23.8%) > oxidizable fraction (5.4%). Correlation analyses showed that the easily reducible fraction correlates positively with the soil Fe and Mn contents, whereas the acid exchangeable fraction is significantly correlated with the S content. The soil pH was negatively correlated with the Tl content in both soil and rice. The Tl content in rice was more strongly correlated with the exchangeable fraction than the total Tl content in the soil. Overall, the bioavailability of Tl in more acidic soil is higher, and is strongly dependent on the speciation of Tl, especially the content of acid exchangeable fraction. Copyright © 2017 Elsevier Inc. All rights reserved.

Increasing the applicability of density functional theory. IV. Consequences of ionization-potential improved exchange-correlation potentials.

PubMed

Verma, Prakash; Bartlett, Rodney J

2014-05-14

This paper's objective is to create a "consistent" mean-field based Kohn-Sham (KS) density functional theory (DFT) meaning the functional should not only provide good total energy properties, but also the corresponding KS eigenvalues should be accurate approximations to the vertical ionization potentials (VIPs) of the molecule, as the latter condition attests to the viability of the exchange-correlation potential (VXC). None of the prominently used DFT approaches show these properties: the optimized effective potential VXC based ab initio dft does. A local, range-separated hybrid potential cam-QTP-00 is introduced as the basis for a "consistent" KS DFT approach. The computed VIPs as the negative of KS eigenvalue have a mean absolute error of 0.8 eV for an extensive set of molecule's electron ionizations, including the core. Barrier heights, equilibrium geometries, and magnetic properties obtained from the potential are in good agreement with experiment. A similar accuracy with less computational efforts can be achieved by using a non-variational global hybrid variant of the QTP-00 approach.

Global hybrids from the semiclassical atom theory satisfying the local density linear response.

PubMed

Fabiano, Eduardo; Constantin, Lucian A; Cortona, Pietro; Della Sala, Fabio

2015-01-13

We propose global hybrid approximations of the exchange-correlation (XC) energy functional which reproduce well the modified fourth-order gradient expansion of the exchange energy in the semiclassical limit of many-electron neutral atoms and recover the full local density approximation (LDA) linear response. These XC functionals represent the hybrid versions of the APBE functional [Phys. Rev. Lett. 2011, 106, 186406] yet employing an additional correlation functional which uses the localization concept of the correlation energy density to improve the compatibility with the Hartree-Fock exchange as well as the coupling-constant-resolved XC potential energy. Broad energetic and structural testing, including thermochemistry and geometry, transition metal complexes, noncovalent interactions, gold clusters and small gold-molecule interfaces, as well as an analysis of the hybrid parameters, show that our construction is quite robust. In particular, our testing shows that the resulting hybrid, including 20% of Hartree-Fock exchange and named hAPBE, performs remarkably well for a broad palette of systems and properties, being generally better than popular hybrids (PBE0 and B3LYP). Semiempirical dispersion corrections are also provided.

Optical-model potential for electron and positron elastic scattering by atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salvat, Francesc

2003-07-01

An optical-model potential for systematic calculations of elastic scattering of electrons and positrons by atoms and positive ions is proposed. The electrostatic interaction is determined from the Dirac-Hartree-Fock self-consistent atomic electron density. In the case of electron projectiles, the exchange interaction is described by means of the local-approximation of Furness and McCarthy. The correlation-polarization potential is obtained by combining the correlation potential derived from the local density approximation with a long-range polarization interaction, which is represented by means of a Buckingham potential with an empirical energy-dependent cutoff parameter. The absorption potential is obtained from the local-density approximation, using the Born-Ochkurmore » approximation and the Lindhard dielectric function to describe the binary collisions with a free-electron gas. The strength of the absorption potential is adjusted by means of an empirical parameter, which has been determined by fitting available absolute elastic differential cross-section data for noble gases and mercury. The Dirac partial-wave analysis with this optical-model potential provides a realistic description of elastic scattering of electrons and positrons with energies in the range from {approx}100 eV up to {approx}5 keV. At higher energies, correlation-polarization and absorption corrections are small and the usual static-exchange approximation is sufficiently accurate for most practical purposes.« less

Density-Functional Theory with Optimized Effective Potential and Self-Interaction Correction for the Double Ionization of He and Be Atoms

NASA Astrophysics Data System (ADS)

Heslar, John; Telnov, Dmitry; Chu, Shih-I.

2012-06-01

We present a self-interaction-free (SIC) time-dependent density-functional theory (TDDFT) for the treatment of double ionization processes of many-electron systems. The method is based on the Krieger-Li-Iafrate (KLI) treatment of the optimized effective potential (OEP) theory and the incorporation of an explicit self-interaction correction (SIC) term. In the framework of the time-dependent density functional theory, we have performed 3D calculations of double ionization of He and Be atoms by strong near-infrared laser fields. We make use of the exchange-correlation potential with the integer discontinuity which improves the description of the double ionization process. We found that proper description of the double ionization requires the TDDFT exchange-correlation potential with the discontinuity with respect to the variation of the spin particle numbers (SPN) only. The results for the intensity-dependent probabilities of single and double ionization are presented and reproduce the famous ``knee'' structure.

Patching the Exchange-Correlation Potential in Density Functional Theory.

PubMed

Huang, Chen

2016-05-10

A method for directly patching exchange-correlation (XC) potentials in materials is derived. The electron density of a system is partitioned into subsystem densities by dividing its Kohn-Sham (KS) potential among the subsystems. Inside each subsystem, its projected KS potential is required to become the total system's KS potential. This requirement, together with the nearsightedness principle of electronic matters, ensures that the electronic structures inside subsystems can be good approximations to the total system's electronic structure. The nearsightedness principle also ensures that subsystem densities could be well localized in their regions, making it possible to use high-level methods to invert the XC potentials for subsystem densities. Two XC patching methods are developed. In the local XC patching method, the total system's XC potential is improved in the cluster region. We show that the coupling between a cluster and its environment is important for achieving a fast convergence of the electronic structure in the cluster region. In the global XC patching method, we discuss how to patch the subsystem XC potentials to construct the XC potential in the total system, aiming to scale up high-level quantum mechanics simulations of materials. Proof-of-principle examples are given.

Application of the zeta potential for stationary phase characterization in ion chromatography.

PubMed

Buszewski, Bogusław; Jaćkowska, Magdalena; Bocian, Szymon; Dziubakiewicz, Ewelina

2013-01-01

Two series of homemade stationary bonded phases for ion chromatography were investigated according to their zeta potential. One set of dendrimer anion exchanger was synthesized on the polymer support whereas the second material was prepared on the silica gel. The zeta potential data in water environment as well as buffered water solution were obtained. The influence of the length of anion-exchanger chains, the type of the support of the modified surface, and charge distribution on these data was investigated. Additionally, the zeta potential was correlated with retention factor of inorganic ions to describe their influence on the retention mechanism in ion chromatography. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Non-empirical exchange-correlation parameterizations based on exact conditions from correlated orbital theory.

PubMed

Haiduke, Roberto Luiz A; Bartlett, Rodney J

2018-05-14

Some of the exact conditions provided by the correlated orbital theory are employed to propose new non-empirical parameterizations for exchange-correlation functionals from Density Functional Theory (DFT). This reparameterization process is based on range-separated functionals with 100% exact exchange for long-range interelectronic interactions. The functionals developed here, CAM-QTP-02 and LC-QTP, show mitigated self-interaction error, correctly predict vertical ionization potentials as the negative of eigenvalues for occupied orbitals, and provide nice excitation energies, even for challenging charge-transfer excited states. Moreover, some improvements are observed for reaction barrier heights with respect to the other functionals belonging to the quantum theory project (QTP) family. Finally, the most important achievement of these new functionals is an excellent description of vertical electron affinities (EAs) of atoms and molecules as the negative of appropriate virtual orbital eigenvalues. In this case, the mean absolute deviations for EAs in molecules are smaller than 0.10 eV, showing that physical interpretation can indeed be ascribed to some unoccupied orbitals from DFT.

Non-empirical exchange-correlation parameterizations based on exact conditions from correlated orbital theory

NASA Astrophysics Data System (ADS)

Haiduke, Roberto Luiz A.; Bartlett, Rodney J.

2018-05-01

Some of the exact conditions provided by the correlated orbital theory are employed to propose new non-empirical parameterizations for exchange-correlation functionals from Density Functional Theory (DFT). This reparameterization process is based on range-separated functionals with 100% exact exchange for long-range interelectronic interactions. The functionals developed here, CAM-QTP-02 and LC-QTP, show mitigated self-interaction error, correctly predict vertical ionization potentials as the negative of eigenvalues for occupied orbitals, and provide nice excitation energies, even for challenging charge-transfer excited states. Moreover, some improvements are observed for reaction barrier heights with respect to the other functionals belonging to the quantum theory project (QTP) family. Finally, the most important achievement of these new functionals is an excellent description of vertical electron affinities (EAs) of atoms and molecules as the negative of appropriate virtual orbital eigenvalues. In this case, the mean absolute deviations for EAs in molecules are smaller than 0.10 eV, showing that physical interpretation can indeed be ascribed to some unoccupied orbitals from DFT.

The dynamic conditional relationship between stock market returns and implied volatility

NASA Astrophysics Data System (ADS)

Park, Sung Y.; Ryu, Doojin; Song, Jeongseok

2017-09-01

Using the dynamic conditional correlation multivariate generalized autoregressive conditional heteroskedasticity (DCC-MGARCH) model, we empirically examine the dynamic relationship between stock market returns (KOSPI200 returns) and implied volatility (VKOSPI), as well as their statistical mechanics, in the Korean market, a representative and leading emerging market. We consider four macroeconomic variables (exchange rates, risk-free rates, term spreads, and credit spreads) as potential determinants of the dynamic conditional correlation between returns and volatility. Of these macroeconomic variables, the change in exchange rates has a significant impact on the dynamic correlation between KOSPI200 returns and the VKOSPI, especially during the recent financial crisis. We also find that the risk-free rate has a marginal effect on this dynamic conditional relationship.

Stability conditions for exact-exchange Kohn-Sham methods and their relation to correlation energies from the adiabatic-connection fluctuation-dissipation theorem.

PubMed

Bleiziffer, Patrick; Schmidtel, Daniel; Görling, Andreas

2014-11-28

The occurrence of instabilities, in particular singlet-triplet and singlet-singlet instabilities, in the exact-exchange (EXX) Kohn-Sham method is investigated. Hessian matrices of the EXX electronic energy with respect to the expansion coefficients of the EXX effective Kohn-Sham potential in an auxiliary basis set are derived. The eigenvalues of these Hessian matrices determine whether or not instabilities are present. Similar as in the corresponding Hartree-Fock case instabilities in the EXX method are related to symmetry breaking of the Hamiltonian operator for the EXX orbitals. In the EXX methods symmetry breaking can easily be visualized by displaying the local multiplicative exchange potential. Examples (N2, O2, and the polyyne C10H2) for instabilities and symmetry breaking are discussed. The relation of the stability conditions for EXX methods to approaches calculating the Kohn-Sham correlation energy via the adiabatic-connection fluctuation-dissipation (ACFD) theorem is discussed. The existence or nonexistence of singlet-singlet instabilities in an EXX calculation is shown to indicate whether or not the frequency-integration in the evaluation of the correlation energy is singular in the EXX-ACFD method. This method calculates the Kohn-Sham correlation energy through the ACFD theorem theorem employing besides the Coulomb kernel also the full frequency-dependent exchange kernel and yields highly accurate electronic energies. For the case of singular frequency-integrands in the EXX-ACFD method a regularization is suggested. Finally, we present examples of molecular systems for which the self-consistent field procedure of the EXX as well as the Hartree-Fock method can converge to more than one local minimum depending on the initial conditions.

A density difference based analysis of orbital-dependent exchange-correlation functionals

NASA Astrophysics Data System (ADS)

Grabowski, Ireneusz; Teale, Andrew M.; Fabiano, Eduardo; Śmiga, Szymon; Buksztel, Adam; Della Sala, Fabio

2014-03-01

We present a density difference based analysis for a range of orbital-dependent Kohn-Sham functionals. Results for atoms, some members of the neon isoelectronic series and small molecules are reported and compared with ab initio wave function calculations. Particular attention is paid to the quality of approximations to the exchange-only optimised effective potential (OEP) approach: we consider both the localised Hartree-Fock as well as the Krieger-Li-Iafrate methods. Analysis of density differences at the exchange-only level reveals the impact of the approximations on the resulting electronic densities. These differences are further quantified in terms of the ground state energies, frontier orbital energy differences and highest occupied orbital energies obtained. At the correlated level, an OEP approach based on a perturbative second-order correlation energy expression is shown to deliver results comparable with those from traditional wave function approaches, making it suitable for use as a benchmark against which to compare standard density functional approximations.

Surface calculations with asymptotically long-ranged potentials in the full-potential linearized augmented plane-wave method

NASA Astrophysics Data System (ADS)

Ye, Lin-Hui

2015-09-01

Although the supercell method has been widely used for surface calculations, it only works well with short-ranged potentials, but meets difficulty when the potential decays very slowly into the vacuum. Unfortunately, the exact exchange-correlation potential of the density functional theory is asymptotically long ranged, and therefore is not easily handled by use of supercells. This paper illustrates that the authentic slab geometry, another technique for surface calculations, is not affected by this issue: It works equally well with both short- and long-ranged potentials, with the computational cost and the convergence speed being essentially the same. Using the asymptotically long-ranged Becke-Roussel'89 exchange potential as an example, we have calculated six surfaces of various types. We found that accurate potential values can be obtained even in extremely low density regions of more than 100 Å away from the surface. This high performance allows us to explore the asymptotic region, and prove with clean numerical evidence that the Becke-Roussel'89 potential satisfies the correct asymptotic behavior for slab surfaces, as it does for finite systems. Our finding further implies that the Slater component of the exact exchange optimized effective potential is responsible for the asymptotic behavior, not only for jellium slabs, but for slabs of any type. The Becke-Roussel'89 potential may therefore be used to build asymptotically correct model exchange potentials applicable to both finite systems and slab surfaces.

First principles study on the elastic and electronic properties of CdX (X = S, Se and Te)

NASA Astrophysics Data System (ADS)

Sharma, Sheetal; Verma, Ajay Singh; Sarkar, Bimal Kumar; Bhandari, Rajiv; Jindal, Vijay Kumar

2011-12-01

Wide band gap semiconductors are emerging as a potential candidate for optically active materials in blue green spectral region and operating at high power level and high temperature. CdX, X = S, Se and Te are wide band gap semiconductors having applications in optoelectronics devices. In this paper we investigated the elastic and electronic properties of Cadmium chalcogenide (cubic zinc-blende (ZB) structure) using standard Kohn-Sham self consistent density functional theory method (DFT) that uses non conserving pseudopotentials in fully nonlocal form within the generalized gradient approximation (GGA) for the exchange-correlation potential. The independent elastic constants, C11, C12 and C44, are calculated from direct computation of stresses generated by small strains. The shear modulus and Young's modulus are estimated for CdX. Using the GGA for the exchange correlation potential, the calculated direct fundamental band gap value is in very good agreement with the measured one.

Alternative separation of exchange and correlation energies in multi-configuration range-separated density-functional theory.

PubMed

Stoyanova, Alexandrina; Teale, Andrew M; Toulouse, Julien; Helgaker, Trygve; Fromager, Emmanuel

2013-10-07

The alternative separation of exchange and correlation energies proposed by Toulouse et al. [Theor. Chem. Acc. 114, 305 (2005)] is explored in the context of multi-configuration range-separated density-functional theory. The new decomposition of the short-range exchange-correlation energy relies on the auxiliary long-range interacting wavefunction rather than the Kohn-Sham (KS) determinant. The advantage, relative to the traditional KS decomposition, is that the wavefunction part of the energy is now computed with the regular (fully interacting) Hamiltonian. One potential drawback is that, because of double counting, the wavefunction used to compute the energy cannot be obtained by minimizing the energy expression with respect to the wavefunction parameters. The problem is overcome by using short-range optimized effective potentials (OEPs). The resulting combination of OEP techniques with wavefunction theory has been investigated in this work, at the Hartree-Fock (HF) and multi-configuration self-consistent-field (MCSCF) levels. In the HF case, an analytical expression for the energy gradient has been derived and implemented. Calculations have been performed within the short-range local density approximation on H2, N2, Li2, and H2O. Significant improvements in binding energies are obtained with the new decomposition of the short-range energy. The importance of optimizing the short-range OEP at the MCSCF level when static correlation becomes significant has also been demonstrated for H2, using a finite-difference gradient. The implementation of the analytical gradient for MCSCF wavefunctions is currently in progress.

Survey of High-Pressure Effects in Solids.

DTIC Science & Technology

1979-11-01

phenomenological Lennard - Jones and Morse potentials . The resulting study of the GrUneisen parameter is most illuminating. A more am- bitious program would to...the Gordon-Kim-Boyer scheme with our suggested modifications; use of the exchange-correlation potential in the local-density approximation i such an...Xenon Hugoniot Calculations and Experiments .......... 41 3.8. Xenon Intermolecular Potentials ...................... 42 3.9. Xenon Hugoniot Calculations

Development and application of accurate analytical models for single active electron potentials

NASA Astrophysics Data System (ADS)

Miller, Michelle; Jaron-Becker, Agnieszka; Becker, Andreas

2015-05-01

The single active electron (SAE) approximation is a theoretical model frequently employed to study scenarios in which inner-shell electrons may productively be treated as frozen spectators to a physical process of interest, and accurate analytical approximations for these potentials are sought as a useful simulation tool. Density function theory is often used to construct a SAE potential, requiring that a further approximation for the exchange correlation functional be enacted. In this study, we employ the Krieger, Li, and Iafrate (KLI) modification to the optimized-effective-potential (OEP) method to reduce the complexity of the problem to the straightforward solution of a system of linear equations through simple arguments regarding the behavior of the exchange-correlation potential in regions where a single orbital dominates. We employ this method for the solution of atomic and molecular potentials, and use the resultant curve to devise a systematic construction for highly accurate and useful analytical approximations for several systems. Supported by the U.S. Department of Energy (Grant No. DE-FG02-09ER16103), and the U.S. National Science Foundation (Graduate Research Fellowship, Grants No. PHY-1125844 and No. PHY-1068706).

Time-dependent i-DFT exchange-correlation potentials with memory: applications to the out-of-equilibrium Anderson model

NASA Astrophysics Data System (ADS)

Kurth, Stefan; Stefanucci, Gianluca

2018-06-01

We have recently put forward a steady-state density functional theory (i-DFT) to calculate the transport coefficients of quantum junctions. Within i-DFT it is possible to obtain the steady density on and the steady current through an interacting junction using a fictitious noninteracting junction subject to an effective gate and bias potential. In this work we extend i-DFT to the time domain for the single-impurity Anderson model. By a reverse engineering procedure we extract the exchange-correlation (xc) potential and xc bias at temperatures above the Kondo temperature T K. The derivation is based on a generalization of a recent paper by Dittmann et al. [N. Dittmann et al., Phys. Rev. Lett. 120, 157701 (2018)]. Interestingly the time-dependent (TD) i-DFT potentials depend on the system's history only through the first time-derivative of the density. We perform numerical simulations of the early transient current and investigate the role of the history dependence. We also empirically extend the history-dependent TD i-DFT potentials to temperatures below T K. For this purpose we use a recently proposed parametrization of the i-DFT potentials which yields highly accurate results in the steady state.

Time-dependent density-functional theory with optimized effective potential and self-interaction correction and derivative discontinuity for the treatment of double ionization of He and Be atoms in intense laser fields

NASA Astrophysics Data System (ADS)

Heslar, John; Telnov, Dmitry A.; Chu, Shih-I.

2013-05-01

We present a self-interaction-free time-dependent density-functional theory (TDDFT) for the treatment of double-ionization processes of many-electron systems. The method is based on the extension of the Krieger-Li-Iafrate (KLI) treatment of the optimized effective potential (OEP) theory and the incorporation of an explicit self-interaction correction (SIC) term. In the framework of the time-dependent density functional theory, we have performed three-dimensional (3D) calculations of double ionization of He and Be atoms by intense near-infrared laser fields. We make use of the exchange-correlation potential with the integer discontinuity which improves the description of the double-ionization process. We found that a proper description of the double ionization requires the TDDFT exchange-correlation potential with the discontinuity with respect to the variation of the total particle number (TPN). The results for the intensity-dependent rates of double ionization of He and Be atoms are presented.

Increasing the applicability of density functional theory. V. X-ray absorption spectra with ionization potential corrected exchange and correlation potentials.

PubMed

Verma, Prakash; Bartlett, Rodney J

2016-07-21

Core excitation energies are computed with time-dependent density functional theory (TD-DFT) using the ionization energy corrected exchange and correlation potential QTP(0,0). QTP(0,0) provides C, N, and O K-edge spectra to about an electron volt. A mean absolute error (MAE) of 0.77 and a maximum error of 2.6 eV is observed for QTP(0,0) for many small molecules. TD-DFT based on QTP (0,0) is then used to describe the core-excitation spectra of the 22 amino acids. TD-DFT with conventional functionals greatly underestimates core excitation energies, largely due to the significant error in the Kohn-Sham occupied eigenvalues. To the contrary, the ionization energy corrected potential, QTP(0,0), provides excellent approximations (MAE of 0.53 eV) for core ionization energies as eigenvalues of the Kohn-Sham equations. As a consequence, core excitation energies are accurately described with QTP(0,0), as are the core ionization energies important in X-ray photoionization spectra or electron spectroscopy for chemical analysis.

Polarization effects in low-energy electron-CH4 elastic collisions in an exact exchange treatment

NASA Astrophysics Data System (ADS)

Jain, Ashok; Weatherford, C. A.; Thompson, D. G.; McNaughten, P.

1989-12-01

We have investigated the polarization effects in very-low-energy (below 1 eV) electron- CH4 collisions in an exact-exchange treatment. The two models of the parameter-free polarization potential are employed; one, the VpolJT potential, introduced by Jain and Thompson [J. Phys. B 15, L631 (1982)], is based on an approximate polarized-orbital method, and two, the correlation-polarization potential VpolCP, first proposed by O'Connel and Lane [Phys. Rev. A 27, 1893 (1983)], is given as a simple analytic form in terms of the charge density of the target. In this rather very low-energy region, the polarization effects play a decisive role, particularly in creating structure in the differential cross section (DCS) and producing the Ramsauer-Townsend minimum in the total cross section. Our DCS at 0.2, 0.4, and 0.6 eV are compared with recent measurements. We found that a local parameter-free approximation for the polarization potential is quite successful if it is determined under the polarized-orbital-type technique rather than based on the correlation-polarization approach.

Hyperfine coupling constants of the nitrogen and phosphorus atoms: A challenge for exact-exchange density-functional and post-Hartree-Fock methods

NASA Astrophysics Data System (ADS)

Kaupp, Martin; Arbuznikov, Alexei V.; Heßelmann, Andreas; Görling, Andreas

2010-05-01

The isotropic hyperfine coupling constants of the free N(S4) and P(S4) atoms have been evaluated with high-level post-Hartree-Fock and density-functional methods. The phosphorus hyperfine coupling presents a significant challenge to both types of methods. With large basis sets, MP2 and coupled-cluster singles and doubles calculations give much too small values for the phosphorus atom. Triple excitations are needed in coupled-cluster calculations to achieve reasonable agreement with experiment. None of the standard density functionals reproduce even the correct sign of this hyperfine coupling. Similarly, the computed hyperfine couplings depend crucially on the self-consistent treatment in exact-exchange density-functional theory within the optimized effective potential (OEP) method. Well-balanced auxiliary and orbital basis sets are needed for basis-expansion exact-exchange-only OEP approaches to come close to Hartree-Fock or numerical OEP data. Results from the localized Hartree-Fock and Krieger-Li-Iafrate approximations deviate notably from exact OEP data in spite of very similar total energies. Of the functionals tested, only full exact-exchange methods augmented by a correlation functional gave at least the correct sign of the P(S4) hyperfine coupling but with too low absolute values. The subtle interplay between the spin-polarization contributions of the different core shells has been analyzed, and the influence of even very small changes in the exchange-correlation potential could be identified.

Electronic properties of III-nitride semiconductors: A first-principles investigation using the Tran-Blaha modified Becke-Johnson potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Araujo, Rafael B., E-mail: rafaelbna@gmail.com; Almeida, J. S. de, E-mail: jailton-almeida@hotmail.com; Ferreira da Silva, A.

In this work, we use density functional theory to investigate the influence of semilocal exchange and correlation effects on the electronic properties of III-nitride semiconductors considering zinc-blende and wurtzite crystal structures. We find that the inclusion of such effects through the use of the Tran-Blaha modified Becke-Johnson potential yields an excellent description of the electronic structures of these materials giving energy band gaps which are systematically larger than the ones obtained with standard functionals such as the generalized gradient approximation. The discrepancy between the experimental and theoretical band gaps is then significantly reduced with semilocal exchange and correlation effects. However,more » the effective masses are overestimated in the zinc-blende nitrides, but no systematic trend is found in the wurtzite compounds. New results for energy band gaps and effective masses of zinc-blende and wurtzite indium nitrides are presented.« less

Optical spectra and band structure of Ag(x)Ga(x)Ge(1-x)Se2 (x = 0.333, 0.250, 0.200, 0.167) single crystals: experiment and theory.

PubMed

Reshak, A H; Parasyuk, O V; Fedorchuk, A O; Kamarudin, H; Auluck, S; Chyský, J

2013-12-05

Theoretical and experimental studies of the Ag(x)Ga(x)Ge(1-x)Se2 (x = 0.333, 0.250, 0.200, 0.167) single crystals are performed. These crystals possess a lot of intrinsic defects which are responsible for their optoelectronic features. The theoretical investigations were performed by means of DFT calculations using different exchange-correlation potentials. The experimental studies were carried out using the modulated VUV ellipsometry for dielectric constants and birefringence studies. The comparison of the structure obtained from X-ray with the theoretically optimized structure is presented. The crucial role of the intrinsic defect states is manifested in the choice of the exchange correlation potential used. The data may be applicable for a large number of the ternary chalcogenides which are sensitive to the presence of the local disordered states near the band edges.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bleiziffer, Patrick, E-mail: patrick.bleiziffer@fau.de; Krug, Marcel; Görling, Andreas

A self-consistent Kohn-Sham method based on the adiabatic-connection fluctuation-dissipation (ACFD) theorem, employing the frequency-dependent exact exchange kernel f{sub x} is presented. The resulting SC-exact-exchange-only (EXX)-ACFD method leads to even more accurate correlation potentials than those obtained within the direct random phase approximation (dRPA). In contrast to dRPA methods, not only the Coulomb kernel but also the exact exchange kernel f{sub x} is taken into account in the EXX-ACFD correlation which results in a method that, unlike dRPA methods, is free of self-correlations, i.e., a method that treats exactly all one-electron systems, like, e.g., the hydrogen atom. The self-consistent evaluation ofmore » EXX-ACFD total energies improves the accuracy compared to EXX-ACFD total energies evaluated non-self-consistently with EXX or dRPA orbitals and eigenvalues. Reaction energies of a set of small molecules, for which highly accurate experimental reference data are available, are calculated and compared to quantum chemistry methods like Møller-Plesset perturbation theory of second order (MP2) or coupled cluster methods [CCSD, coupled cluster singles, doubles, and perturbative triples (CCSD(T))]. Moreover, we compare our methods to other ACFD variants like dRPA combined with perturbative corrections such as the second order screened exchange corrections or a renormalized singles correction. Similarly, the performance of our EXX-ACFD methods is investigated for the non-covalently bonded dimers of the S22 reference set and for potential energy curves of noble gas, water, and benzene dimers. The computational effort of the SC-EXX-ACFD method exhibits the same scaling of N{sup 5} with respect to the system size N as the non-self-consistent evaluation of only the EXX-ACFD correlation energy; however, the prefactor increases significantly. Reaction energies from the SC-EXX-ACFD method deviate quite little from EXX-ACFD energies obtained non-self-consistently with dRPA orbitals and eigenvalues, and the deviation reduces even further if the Coulomb kernel is scaled by a factor of 0.75 in the dRPA to reduce self-correlations in the dRPA correlation potential. For larger systems, such a non-self-consistent EXX-ACFD method is a competitive alternative to high-level wave-function-based methods, yielding higher accuracy than MP2 and CCSD methods while exhibiting a better scaling of the computational effort than CCSD or CCSD(T) methods. Moreover, EXX-ACFD methods were shown to be applicable in situation characterized by static correlation.« less

Electronic Zero-Point Oscillations in the Strong-Interaction Limit of Density Functional Theory.

PubMed

Gori-Giorgi, Paola; Vignale, Giovanni; Seidl, Michael

2009-04-14

The exchange-correlation energy in Kohn-Sham density functional theory can be expressed exactly in terms of the change in the expectation of the electron-electron repulsion operator when, in the many-electron Hamiltonian, this same operator is multiplied by a real parameter λ varying between 0 (Kohn-Sham system) and 1 (physical system). In this process, usually called adiabatic connection, the one-electron density is kept fixed by a suitable local one-body potential. The strong-interaction limit of density functional theory, defined as the limit λ→∞, turns out to be like the opposite noninteracting Kohn-Sham limit (λ→0) mathematically simpler than the physical (λ = 1) case and can be used to build an approximate interpolation formula between λ→0 and λ→∞ for the exchange-correlation energy. Here we extend the systematic treatment of the λ→∞ limit [Phys. Rev. A 2007, 75, 042511] to the next leading term, describing zero-point oscillations of strictly correlated electrons, with numerical examples for small spherical atoms. We also propose an improved approximate functional for the zero-point term and a revised interpolation formula for the exchange-correlation energy satisfying more exact constraints.

Improving approximate-optimized effective potentials by imposing exact conditions: Theory and applications to electronic statics and dynamics

NASA Astrophysics Data System (ADS)

Kurzweil, Yair; Head-Gordon, Martin

2009-07-01

We develop a method that can constrain any local exchange-correlation potential to preserve basic exact conditions. Using the method of Lagrange multipliers, we calculate for each set of given Kohn-Sham orbitals a constraint-preserving potential which is closest to the given exchange-correlation potential. The method is applicable to both the time-dependent (TD) and independent cases. The exact conditions that are enforced for the time-independent case are Galilean covariance, zero net force and torque, and Levy-Perdew virial theorem. For the time-dependent case we enforce translational covariance, zero net force, Levy-Perdew virial theorem, and energy balance. We test our method on the exchange (only) Krieger-Li-Iafrate (xKLI) approximate-optimized effective potential for both cases. For the time-independent case, we calculated the ground state properties of some hydrogen chains and small sodium clusters for some constrained xKLI potentials and Hartree-Fock (HF) exchange. The results (total energy, Kohn-Sham eigenvalues, polarizability, and hyperpolarizability) indicate that enforcing the exact conditions is not important for these cases. On the other hand, in the time-dependent case, constraining both energy balance and zero net force yields improved results relative to TDHF calculations. We explored the electron dynamics in small sodium clusters driven by cw laser pulses. For each laser pulse we compared calculations from TD constrained xKLI, TD partially constrained xKLI, and TDHF. We found that electron dynamics such as electron ionization and moment of inertia dynamics for the constrained xKLI are most similar to the TDHF results. Also, energy conservation is better by at least one order of magnitude with respect to the unconstrained xKLI. We also discuss the problems that arise in satisfying constraints in the TD case with a non-cw driving force.

Adaptation of the projector-augmented-wave formalism to the treatment of orbital-dependent exchange-correlation functionals

NASA Astrophysics Data System (ADS)

Xu, Xiao; Holzwarth, N. A. W.

2011-10-01

This paper presents the formulation and numerical implementation of a self-consistent treatment of orbital-dependent exchange-correlation functionals within the projector-augmented-wave method of Blöchl [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.50.17953 50, 17953 (1994)] for electronic structure calculations. The methodology is illustrated with binding energy curves for C in the diamond structure and LiF in the rock salt structure, by comparing results from the Hartree-Fock (HF) formalism and the optimized effective potential formalism in the so-called KLI approximation [Krieger, Li, and Iafrate, Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.45.101 45, 101 (1992)] with those of the local density approximation. While the work here uses pure Fock exchange only, the formalism can be extended to treat orbital-dependent functionals more generally.

Molecular Excitation Energies from Time-Dependent Density Functional Theory Employing Random-Phase Approximation Hessians with Exact Exchange.

PubMed

Heßelmann, Andreas

2015-04-14

Molecular excitation energies have been calculated with time-dependent density-functional theory (TDDFT) using random-phase approximation Hessians augmented with exact exchange contributions in various orders. It has been observed that this approach yields fairly accurate local valence excitations if combined with accurate asymptotically corrected exchange-correlation potentials used in the ground-state Kohn-Sham calculations. The inclusion of long-range particle-particle with hole-hole interactions in the kernel leads to errors of 0.14 eV only for the lowest excitations of a selection of three alkene, three carbonyl, and five azabenzene molecules, thus surpassing the accuracy of a number of common TDDFT and even some wave function correlation methods. In the case of long-range charge-transfer excitations, the method typically underestimates accurate reference excitation energies by 8% on average, which is better than with standard hybrid-GGA functionals but worse compared to range-separated functional approximations.

Comparative Study of Exchange-Correlation Functional and Potential for Evaluating Thermoelectric Transport Properties in d0 Perovskite Oxides

NASA Astrophysics Data System (ADS)

Ohkubo, Isao; Mori, Takao

2017-07-01

The influence of two different types of exchange-correlation functional/potential, namely, the generalized gradient approximation Perdew-Burke-Ernzerhof (GGA-PBE) functional and the modified Becke-Johnson (mBJ) potential, on the thermoelectric transport properties of d0 perovskite oxides (SrTiO3 and KTaO3) was investigated. The reduction of band dispersion induced by the mBJ scheme allows the improved prediction of band gap values by thelocal density approximation (LDA) and GGA, which increases the resolution of the increases in the density of states (DOS), carrier concentration, and effective mass near the conduction band edge. A comparison of the experimental effective mass values of d0 perovskite oxides shows that the effective mass values provided by the mBJ potential are similar to those provided by the GGA-PBE functional. Comparative analysis of the data obtained from Boltzmann theory calculations using the electronic structures determined with the GGA-PBE functional and the mBJ potential shows a difference in the transport coefficients owing to the increases in the DOS, carrier concentration, and effective mass induced by the mBJ scheme.

libvdwxc: a library for exchange-correlation functionals in the vdW-DF family

NASA Astrophysics Data System (ADS)

Hjorth Larsen, Ask; Kuisma, Mikael; Löfgren, Joakim; Pouillon, Yann; Erhart, Paul; Hyldgaard, Per

2017-09-01

We present libvdwxc, a general library for evaluating the energy and potential for the family of vdW-DF exchange-correlation functionals. libvdwxc is written in C and provides an efficient implementation of the vdW-DF method and can be interfaced with various general-purpose DFT codes. Currently, the Gpaw and Octopus codes implement interfaces to libvdwxc. The present implementation emphasizes scalability and parallel performance, and thereby enables ab initio calculations of nanometer-scale complexes. The numerical accuracy is benchmarked on the S22 test set whereas parallel performance is benchmarked on ligand-protected gold nanoparticles ({{Au}}144{({{SC}}11{{NH}}25)}60) up to 9696 atoms.

Dynamical Correlation In Some Liquid Alkaline Earth Metals Near Melting

NASA Astrophysics Data System (ADS)

Thakore, B. Y.; Suthar, P. H.; Khambholja, S. G.; Gajjar, P. N.; Jani, A. R.

2010-12-01

The study of dynamical variables: velocity autocorrelation function (VACF) and power spectrum of liquid alkaline earth metals (Ca, Sr, and Ba) have been presented based on the static harmonic well approximation. The effective interatomic potential for liquid metals is computed using our well recognized model potential with the exchange correlation functions due to Hartree, Taylor, Ichimaru and Utsumi, Farid et al. and Sarkar et al. It is observed that the VACF computed using Sarkar et al. gives the good agreement with available molecular dynamics simulation (MD) results [Phys Rev. B 62, 14818 (2000)]. The shoulder of the power spectrum depends upon the type of local field correlation function used.

Formal expressions and corresponding expansions for the exact Kohn-Sham exchange potential

NASA Astrophysics Data System (ADS)

Bulat, Felipe A.; Levy, Mel

2009-11-01

Formal expressions and their corresponding expansions in terms of Kohn-Sham (KS) orbitals are deduced for the exchange potential vx(r) . After an alternative derivation of the basic optimized effective potential integrodifferential equations is given through a Hartree-Fock adiabatic connection perturbation theory, we present an exact infinite expansion for vx(r) that is particularly simple in structure. It contains the very same occupied-virtual quantities that appear in the well-known optimized effective potential integral equation, but in this new expression vx(r) is isolated on one side of the equation. An orbital-energy modified Slater potential is its leading term which gives encouraging numerical results. Along different lines, while the earlier Krieger-Li-Iafrate approximation truncates completely the necessary first-order perturbation orbitals, we observe that the improved localized Hartree-Fock (LHF) potential, or common energy denominator potential (CEDA), or effective local potential (ELP), incorporates the part of each first-order orbital that consists of the occupied KS orbitals. With this in mind, the exact correction to the LHF, CEDA, or ELP potential (they are all equivalent) is deduced and displayed in terms of the virtual portions of the first-order orbitals. We close by observing that the newly derived exact formal expressions and corresponding expansions apply as well for obtaining the correlation potential from an orbital-dependent correlation energy functional.

Density-functional theory based on the electron distribution on the energy coordinate

NASA Astrophysics Data System (ADS)

Takahashi, Hideaki

2018-03-01

We developed an electronic density functional theory utilizing a novel electron distribution n(ɛ) as a basic variable to compute ground state energy of a system. n(ɛ) is obtained by projecting the electron density n({\\boldsymbol{r}}) defined on the space coordinate {\\boldsymbol{r}} onto the energy coordinate ɛ specified with the external potential {\\upsilon }ext}({\\boldsymbol{r}}) of interest. It was demonstrated that the Kohn-Sham equation can also be formulated with the exchange-correlation functional E xc[n(ɛ)] that employs the density n(ɛ) as an argument. It turned out an exchange functional proposed in our preliminary development suffices to describe properly the potential energies of several types of chemical bonds with comparable accuracies to the corresponding functional based on local density approximation. As a remarkable feature of the distribution n(ɛ) it inherently involves the spatially non-local information of the exchange hole at the bond dissociation limit in contrast to conventional approximate functionals. By taking advantage of this property we also developed a prototype of the static correlation functional E sc including no empirical parameters, which showed marked improvements in describing the dissociations of covalent bonds in {{{H}}}2,{{{C}}}2{{{H}}}4 and {CH}}4 molecules.

Time-dependent spin-density-functional-theory description of He+-He collisions

NASA Astrophysics Data System (ADS)

Baxter, Matthew; Kirchner, Tom; Engel, Eberhard

2017-09-01

Theoretical total cross-section results for all ionization and capture processes in the He+-He collision system are presented in the approximate impact energy range of 10-1000 keV/amu. Calculations were performed within the framework of time-dependent spin-density functional theory. The Krieger-Li-Iafrate approximation was used to determine an accurate exchange-correlation potential in the exchange-only limit. The results of two models, one where electron translation factors in the orbitals used to calculate the potential are ignored and another where partial electron translation factors are included, are compared with available experimental data as well as a selection of previous theoretical calculations.

Novel density functional methodology for the computation of accurate electronic and thermodynamic properties of molecular systems and improved long-range behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kafafi, S.A.

1998-12-10

A novel general purpose density functional methodology for the computation of accurate electronic and thermodynamic properties of molecules and improved long-range behavior is reported. Assuming the separability of the exchange (E{sub x}) and correlation (E{sub c}) contributions to the total exchange-correlation energy functional (E{sub xc}), the E{sub x} term consists of a hybrid mixture of 37.5% Hartree-Fock exchange and the appropriate local spin density exchange using the adiabatic connection formula. He demonstrated that E{sub x} and its corresponding potential V{sub x} [=dE{sub x}/d{rho}(r)] have the proper asymptotic limits at r = 0 and r {r_arrow} {infinity}, E{sub c} consists ofmore » the Vosko, Wilk, and Nusair formula for the free-electron gas correlation energy and a generalized gradient approximation term with one adjustable parameter. V{sub c} [=dE{sub c}/d{rho}(r)] was shown to obey the r {r_arrow} {infinity} limit of the corresponding potential derived from exact atomic exchange-correlation computations; namely, V{sub c} is proportional to r{sup {minus}4}. Most importantly, he demonstrated that, at r values where dispersion forces are operating, V{sub c} is proportional to 1/r{sup n} (n = 4, 6, 8, {hor_ellipsis}). The reported method was denoted by K2-BVWN because it used two adjustable parameters in its formulation. The K2-BVWN scheme scales as N{sup 3}, where N is the number of basis functions, compared to {approximately}N{sup 7} for Gaussian-2 (G2) ab initio theory and related methods, {approximately}N{sup 5} for Barone`s mPW1,3PW, and {approximately}N{sup 4} for Becke`s three-parameter density functional approaches. The G2 data set complemented by the reported molecular systems investigated in this work was recommended as a critical test for evaluating novel ab initio and density functional methodologies. The K2-BVWN method has been implemented in the Gaussian series of programs.« less

Role of modified Becke-Johnson potential in computation of electronic and optical properties of mixed crystals CdxZn1-xSe

NASA Astrophysics Data System (ADS)

Talreja, Sonal; Ahuja, B. L.

2015-08-01

Electronic and optical properties of CdxZn1-xSe (x = 0, 0.25, 0.5, 0.75, 1) compounds are investigated using the first-principles full potential linearized augmented plane wave method. In particular, we have used modified version of the exchange potential of Becke and Johnson, so called mBJ potential. We have discussed the energy bands, density of states, and optical properties such as dielectric constants, refractive indices, reflection spectra, extinction coefficients of all the CdxZn1-xSe compounds. Our mBJ potential based data are found to be in excellent agreement with the available experimental data, which unambiguously validates the applicability of orbital independent exchange-correlation potential in mixed semiconductor crystals. The optical properties are discussed in terms of applicability of Cd-Zn-Se system in light-emitting diodes, UV detectors and filters, etc.

Projector Augmented Wave formulation of orbital-dependent exchange-correlation functionals

NASA Astrophysics Data System (ADS)

Xu, Xiao; Holzwarth, N. A. W.

2012-02-01

The use of orbital-dependent exchange-correlation functionals within electronic structure calculations has recently received renewed attention for improving the accuracy of the calculations, especially correcting self-interaction errors. Since the Projector Augmented Wave (PAW) methodootnotetext P. Bl"ochl, Phys. Rev. B 50, 17953 (1994). is an efficient pseudopotential-like scheme which ensures accurate evaluation of all multipole moments of direct and exchange Coulomb integrals, it is a natural choice for implementing orbital-dependent formalisms. Using Fock exchange as an example of an orbital-dependent functional, we developed the formulation and numerical implementation of the approximate optimized effective potential formalism of Kreiger, Li, and Iafrate (KLI)ootnotetext J. B. Krieger, Y. Li, and G. J. Iafrate Phys. Rev. A 45, 101 (1992). within the PAW method, comparing results with the analogous Hartree-Fock treatment.ootnotetext Xiao Xu and N. A. W. Holzwarth, Phys. Rev. B 81, 245105 (2010); 84, 155113 (2011). Test results are presented for ground state properties of two well-known materials -- diamond and LiF. This formalism can be extended to treat orbital-dependent functionals more generally.

Eikonalization of conformal blocks

DOE PAGES

Fitzpatrick, A. Liam; Kaplan, Jared; Walters, Matthew T.; ...

2015-09-03

Classical field configurations such as the Coulomb potential and Schwarzschild solution are built from the t-channel exchange of many light degrees of freedom. We study the CFT analog of this phenomenon, which we term the 'eikonalization' of conformal blocks. We show that when an operator T appears in the OPE Ο(x)Ο(0), then the large spin Fock space states [TT···T] ℓ also appear in this OPE with a computable coefficient. The sum over the exchange of these Fock space states in an correlator build the classical 'T field' in the dual AdS description. In some limits the sum of all Fockmore » space exchanges can be represented as the exponential of a single T exchange in the 4-pt correlator of O. Our results should be useful for systematizing 1/ℓ perturbation theory in general CFTs and simplifying the computation of large spin OPE coefficients. As examples we obtain the leading log ℓ dependence of Fock space conformal block coefficients, and we directly compute the OPE coefficients of the simplest ‘triple-trace’ operators.« less

Detrended cross-correlation analysis on RMB exchange rate and Hang Seng China Enterprises Index

NASA Astrophysics Data System (ADS)

Ruan, Qingsong; Yang, Bingchan; Ma, Guofeng

2017-02-01

In this paper, we investigate the cross-correlations between the Hang Seng China Enterprises Index and RMB exchange markets on the basis of a cross-correlation statistic test and multifractal detrended cross-correlation analysis (MF-DCCA). MF-DCCA has, at best, serious limitations for most of the signals describing complex natural processes and often indicates multifractal cross-correlations when there are none. In order to prevent these false multifractal cross-correlations, we apply MFCCA to verify the cross-correlations. Qualitatively, we find that the return series of the Hang Seng China Enterprises Index and RMB exchange markets were, overall, significantly cross-correlated based on the statistical analysis. Quantitatively, we find that the cross-correlations between the stock index and RMB exchange markets were strongly multifractal, and the multifractal degree of the onshore RMB exchange markets was somewhat larger than the offshore RMB exchange markets. Moreover, we use the absolute return series to investigate and confirm the fact of multifractality. The results from the rolling windows show that the short-term cross-correlations between volatility series remain high.

Optimised effective potential for ground states, excited states, and time-dependent phenomena

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gross, E.K.U.

1996-12-31

(1) The optimized effective potential method is a variant of the traditional Kohn-Sham scheme. In this variant, the exchange-correlation energy E{sub xc} is an explicit functional of single-particle orbitals. The exchange-correlation potential, given as usual by the functional derivative v{sub xc} = {delta}E{sub xc}/{delta}{rho}, then satisfies as integral equation involving the single-particle orbitals. This integral equation in solved semi-analytically using a scheme recently proposed by Krieger, Li and Iafrate. If the exact (Fock) exchange-energy functional is employed together with the Colle-Salvetti orbital functional for the correlation energy, the mean absolute deviation of the resulting ground-state energies from the exact nonrelativisticmore » values is CT mH for the first-row atoms, as compared to 4.5 mH in a state-of-the-art CI calculation. The proposed scheme is thus significantly more accurate than the conventional Kohn-Sham method while the numerical effort involved is about the same as for an ordinary Hanree-Fock calculation. (2) A time-dependent generalization of the optimized-potential method is presented and applied to the linear-response regime. Since time-dependent density functional theory leads to a formally exact representation of the frequency-dependent linear density response and since the latter, as a function of frequency, has poles at the excitation energies of the fully interacting system, the formalism is suitable for the calculation of excitation energies. A simple additive correction to the Kohn-Sham single-particle excitation energies will be deduced and first results for atomic and molecular singlet and triplet excitation energies will be presented. (3) Beyond the regime of linear response, the time-dependent optimized-potential method is employed to describe atoms in strong emtosecond laser pulses. Ionization yields and harmonic spectra will be presented and compared with experimental data.« less

Cross-correlations between RMB exchange rate and international commodity markets

NASA Astrophysics Data System (ADS)

Lu, Xinsheng; Li, Jianfeng; Zhou, Ying; Qian, Yubo

2017-11-01

This paper employs multifractal detrended analysis (MF-DFA) and multifractal detrended cross-correlation analysis (MF-DCCA) to study cross-correlation behaviors between China's RMB exchange rate market and four international commodity markets, using a comprehensive set of data covering the period from 22 July 2005 to 15 March 2016. Our empirical results from MF-DFA indicate that the RMB exchange rate is the most inefficient among the 4 selected markets. The results from quantitative analysis have testified the existence of cross-correlations and the result from MF-DCCA have further confirmed a strong multifractal behavior between RMB exchange rate and international commodity markets. We also demonstrate that the recent financial crisis has significant impact on the cross-correlated behavior. Through the rolling window analysis, we find that the RMB exchange rates and international commodity prices are anti-persistent cross-correlated. The main sources of multifractality in the cross-correlations are long-range correlations between RMB exchange rate and the aggregate commodity, energy and metals index.

Consequences of a restrictive syringe exchange policy on utilization patterns of a syringe exchange program in Baltimore, Maryland: Implications for HIV risk

PubMed Central

Sherman, Susan G.; Patel, Shivani A.; Ramachandran, Daesha V.; Galai, Noya; Chaulk, Patrick; Serio-Chapman, Chris; Gindi, Renee M.

2016-01-01

Background Syringe distribution policies continue to be debated in many jurisdictions throughout the U.S. The Baltimore Needle and Syringe Exchange Program (NSP) operated under a 1-for-1 syringe exchange policy from its inception in 1994 through 1999, when it implemented a restrictive policy (2000–2004) that dictated less than 1-for-1 exchange for non-program syringes. Methods Data were derived from the Baltimore NSP, which prospectively collected data on all client visits. We examined the impact of this restrictive policy on program-level output measures (i.e., distributed:returned syringe ratio, client volume) before, during, and after the restrictive exchange policy. Through multiple logistic regression, we examined correlates of less than 1-for-1 exchange ratios at the client-level before and during the restrictive exchange policy periods. Results During the restrictive policy period, the average annual program-level ratio of total syringes distributed:returned dropped from 0.99 to 0.88, with a low point of 0.85 in 2000. There were substantial decreases in the average number of syringes distributed, syringes returned, the total number of clients, and new clients enrolling during the restrictive compared to the preceding period. During the restrictive period, 33,508 more syringes were returned to the needle exchange than were distributed. In the presence of other variables, correlates of less than 1-for-1 exchange ratio were being white, female, and less than 30 years old. Discussion With fewer clean syringes in circulation, restrictive policies could increase the risk of exposure to HIV among IDUs and the broader community. The study provides evidence to the potentially harmful effects of such policies. PMID:25919590

Barrierless association of CF2 and dissociation of C2F4 by variational transition-state theory and system-specific quantum Rice–Ramsperger–Kassel theory

PubMed Central

Bao, Junwei Lucas; Zhang, Xin

2016-01-01

Bond dissociation is a fundamental chemical reaction, and the first principles modeling of the kinetics of dissociation reactions with a monotonically increasing potential energy along the dissociation coordinate presents a challenge not only for modern electronic structure methods but also for kinetics theory. In this work, we use multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) to compute the high-pressure limit dissociation rate constant of tetrafluoroethylene (C2F4), in which the potential energies are computed by direct dynamics with the M08-HX exchange correlation functional. To treat the pressure dependence of the unimolecular rate constants, we use the recently developed system-specific quantum Rice–Ramsperger–Kassel theory. The calculations are carried out by direct dynamics using an exchange correlation functional validated against calculations that go beyond coupled-cluster theory with single, double, and triple excitations. Our computed dissociation rate constants agree well with the recent experimental measurements. PMID:27834727

Barrierless association of CF2 and dissociation of C2F4 by variational transition-state theory and system-specific quantum Rice-Ramsperger-Kassel theory.

PubMed

Bao, Junwei Lucas; Zhang, Xin; Truhlar, Donald G

2016-11-29

Bond dissociation is a fundamental chemical reaction, and the first principles modeling of the kinetics of dissociation reactions with a monotonically increasing potential energy along the dissociation coordinate presents a challenge not only for modern electronic structure methods but also for kinetics theory. In this work, we use multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) to compute the high-pressure limit dissociation rate constant of tetrafluoroethylene (C 2 F 4 ), in which the potential energies are computed by direct dynamics with the M08-HX exchange correlation functional. To treat the pressure dependence of the unimolecular rate constants, we use the recently developed system-specific quantum Rice-Ramsperger-Kassel theory. The calculations are carried out by direct dynamics using an exchange correlation functional validated against calculations that go beyond coupled-cluster theory with single, double, and triple excitations. Our computed dissociation rate constants agree well with the recent experimental measurements.

Male Partners' Investment and Alternatives as Correlates of Women's Coerced First Sexual Intercourse in Chinese Dating Relationships: A Social Exchange Perspective.

PubMed

He, Shanshan; Tsang, Sandra

2016-10-01

Social exchange theory has great potential to help our understanding of dating partners' sexual interaction. Yet, to our knowledge, there is still no empirical study applying this theory to explain sexual coercion in the context of intimate relationships. This study examined the relationship between male partners' social exchange variables (investment and alternatives) and women's coerced first sexual intercourse in dating relationships, within both gender samples (not dyadic data). A total of 927 valid questionnaires were collected by purposive snowball sampling in five main cities in China of college students who were currently in a romantic relationship. Results showed that in the male sample, male partners' investment significantly and positively correlated with emotional manipulation coercive tactics, and their alternatives significantly and positively predicted defection threats as coercive tactics. In the female sample, there were no such observations. The research hypotheses of this study have been partially supported, and its implications and limitations are discussed.

Electrical resistivity of Al-Cu liquid binary alloy

NASA Astrophysics Data System (ADS)

Thakor, P. P.; Patel, J. J.; Sonvane, Y. A.; Jani, A. R.

2013-06-01

Present paper deals with the electrical resistivity (ρ) of liquid Al-Cu binary alloy. To describe electron-ion interaction we have used our parameter free model potential along with Faber-Ziman formulation combined with Ashcroft-Langreth (AL) partial structure factor. To see the influence of exchange and correlation effect, Hartree, Taylor and Sarkar et al local field correlation functions are used. From present results, it is seen that good agreements between present results and experimental data have been achieved. Lastly we conclude that our model potential successfully produces the data of electrical resistivity (ρ) of liquid Al-Cu binary alloy.

First-Principles Molecular Dynamics Simulations of NaCl in Water: Performance of Advanced Exchange-Correlation Approximations in Density Functional Theory

NASA Astrophysics Data System (ADS)

Yao, Yi; Kanai, Yosuke

Our ability to correctly model the association of oppositely charged ions in water is fundamental in physical chemistry and essential to various technological and biological applications of molecular dynamics (MD) simulations. MD simulations using classical force fields often show strong clustering of NaCl in the aqueous ionic solutions as a consequence of a deep contact pair minimum in the potential of mean force (PMF) curve. First-Principles Molecular Dynamics (FPMD) based on Density functional theory (DFT) with the popular PBE exchange-correlation approximation, on the other hand, show a different result with a shallow contact pair minimum in the PMF. We employed two of most promising exchange-correlation approximations, ωB97xv by Mardiorossian and Head-Gordon and SCAN by Sun, Ruzsinszky and Perdew, to examine the PMF using FPMD simulations. ωB97xv is highly empirically and optimized in the space of range-separated hybrid functional with a dispersion correction while SCAN is the most recent meta-GGA functional that is constructed by satisfying various known conditions in well-defined physical limits. We will discuss our findings for PMF, charge transfer, water dipoles, etc.

Is the surface oxygen exchange rate linked to bulk ion diffusivity in mixed conducting Ruddlesden–Popper phases?

DOE PAGES

Tomkiewicz, Alex C.; Tamimi, Mazin A.; Huq, Ashfia; ...

2015-03-02

There is a possible link between oxygen surface exchange rate and bulk oxygen anion diffusivity in mixed ionic and electronic conducting oxides; it is a topic of great interest and debate. While a large body of experimental evidence and theoretical analyses support a link, observed differences between bulk and surface composition of these materials are hard to reconcile with this observation. This is further compounded by potential problems with simultaneous measurement of both parameters. Here we utilize separate techniques, in situ neutron diffraction and pulsed isotopic surface exchange, to examine bulk ion mobility and surface oxygen exchange rates of threemore » Ruddlesden-Popper phases, general form A n-1A 2'BnO 3n+1, A n-1A 2'BnX 3n+1; LaSrCo 0.5Fe 0.5O 4-δ (n = 1), La 0.3Sr 2.7CoFeO 7-δ (n = 2) and LaSr 3Co 1.5Fe 1.5O 10-δ (n = 3). These measurements are complemented by surface composition determination via high sensitivity-low energy ion scattering. We observe a correlation between bulk ion mobility and surface exchange rate between materials. The surface exchange rates vary by more than one order of magnitude with high anion mobility in the bulk of an oxygen vacancy-rich n = 2 Ruddlesden-Popper material correlating with rapid oxygen exchange. Furthermore this is in contrast with the similar surface exchange rates which we may expect due to similar surface compositions across all three samples. This paper conclude that experimental limitations lead to inherent convolution of surface and bulk rates, and that surface exchange steps are not likely to be rate limiting in oxygen incorporation.« less

Dependence of Excited State Potential Energy Surfaces on the Spatial Overlap of the Kohn-Sham Orbitals and the Amount of Nonlocal Hartree-Fock Exchange in Time-Dependent Density Functional Theory.

PubMed

Plötner, Jürgen; Tozer, David J; Dreuw, Andreas

2010-08-10

Time-dependent density functional theory (TDDFT) with standard GGA or hybrid exchange-correlation functionals is not capable of describing the potential energy surface of the S1 state of Pigment Yellow 101 correctly; an additional local minimum is observed at a twisted geometry with substantial charge transfer (CT) character. To investigate the influence of nonlocal exact orbital (Hartree-Fock) exchange on the shape of the potential energy surface of the S1 state in detail, it has been computed along the twisting coordinate employing the standard BP86, B3LYP, and BHLYP xc-functionals as well as the long-range separated (LRS) exchange-correlation (xc)-functionals LC-BOP, ωB97X, ωPBE, and CAM-B3LYP and compared to RI-CC2 benchmark results. Additionally, a recently suggested Λ-parameter has been employed that measures the amount of CT in an excited state by calculating the spatial overlap of the occupied and virtual molecular orbitals involved in the transition. Here, the error in the calculated S1 potential energy curves at BP86, B3LYP, and BHLYP can be clearly related to the Λ-parameter, i.e., to the extent of charge transfer. Additionally, it is demonstrated that the CT problem is largely alleviated when the BHLYP xc-functional is employed, although it still exhibits a weak tendency to underestimate the energy of CT states. The situation improves drastically when LRS-functionals are employed within TDDFT excited state calculations. All tested LRS-functionals give qualitatively the correct potential energy curves of the energetically lowest excited states of P. Y. 101 along the twisting coordinate. While LC-BOP and ωB97X overcorrect the CT problem and now tend to give too large excitation energies compared to other non-CT states, ωPBE and CAM-B3LYP are in excellent agreement with the RI-CC2 results, with respect to both the correct shape of the potential energy curve as well as the absolute values of the calculated excitation energies.

Relative contribution of combined kinetic and exchange energy terms vs the electronic component of molecular electrostatic potential in hardness potential derivatives.

PubMed

Bhattacharjee, Rituparna; Roy, Ram Kinkar

2013-11-14

The relative contribution of the sum of kinetic [(10/9)CFρ(r)2/3] and exchange energy [(4/9)CXρ(r)1/3] terms to that of the electronic part of the molecular electrostatic potential [Vel(r)] in the variants of hardness potential is investigated to assess the proposed definition of Δ+h(k) = −[VelN+1(k) – VelN(k)] and Δ–h(k) = −[VelN(k) – VelN–1(k)] (Saha; et al. J. Comput. Chem. 2013, 34, 662). Some substituted benzenes and polycyclic aromatic hydrocarbons (PAHs) (undergoing electrophilic aromatic substitution), carboxylic acids, and their derivatives are chosen to carry out the theoretical investigation as stated above. Intra- and intermolecular reactivity trends generated by Δ+h(k) and Δ–h(k) are found to be satisfactory and are correlated reasonably well with experimental results.

Magnetic exchange in {Gd(III)-radical} complexes: method assessment, mechanism of coupling and magneto-structural correlations.

PubMed

Gupta, Tulika; Rajeshkumar, Thayalan; Rajaraman, Gopalan

2014-07-28

Density functional studies have been performed on ten different {Gd(III)-radical} complexes exhibiting both ferro and antiferromagnetic exchange interaction with an aim to assess a suitable exchange-correlation functional within DFT formalism. This study has also been extended to probe the mechanism of magnetic coupling and to develop suitable magneto-structural correlations for this pair. Our method assessments reveal the following order of increasing accuracy for the evaluation of J values compared to experimental coupling constants: B(40HF)LYP < BHandHLYP < TPSSH < PW91 < PBE < BP86 < OLYP < BLYP < PBE0 < X3LYP < B3LYP < B2PLYP. Grimme's double-hybrid functional is found to be superior compared to other functionals tested and this is followed very closely by the conventional hybrid B3LYP functional. At the basis set front, our calculations reveal that the incorporation of relativistic effect is important in these calculations and the relativistically corrected effective core potential (ECP) basis set is found to yield better Js compared to other methods. The supposedly empty 5d/6s/6p orbitals of Gd(III) are found to play an important role in the mechanism of magnetic coupling and different contributions to the exchange terms are probed using Molecular Orbital (MO) and Natural Bond Orbital (NBO) analysis. Magneto-structural correlations for Gd-O distances, Gd-O-N angles and Gd-O-N-C dihedral angles are developed where the bond angles as well as dihedral angle parameters are found to dictate the sign and strength of the magnetic coupling in this series.

Density functional with full exact exchange, balanced nonlocality of correlations, and constraint satisfaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Jianmin; Perdew, John P; Staroverov, Viktor N

2008-01-01

We construct a nonlocal density functional approximation with full exact exchange, while preserving the constraint-satisfaction approach and justified error cancellations of simpler semilocal functionals. This is achieved by interpolating between different approximations suitable for two extreme regions of the electron density. In a 'normal' region, the exact exchange-correlation hole density around an electron is semilocal because its spatial range is reduced by correlation and because it integrates over a narrow range to -1. These regions are well described by popular semilocal approximations (many of which have been constructed nonempirically), because of proper accuracy for a slowly-varying density or because ofmore » error cancellation between exchange and correlation. 'Abnormal' regions, where non locality is unveiled, include those in which exchange can dominate correlation (one-electron, nonuniform high-density, and rapidly-varying limits), and those open subsystems of fluctuating electron number over which the exact exchange-correlation hole integrates to a value greater than -1. Regions between these extremes are described by a hybrid functional mixing exact and semi local exchange energy densities locally (i.e., with a mixing fraction that is a function of position r and a functional of the density). Because our mixing fraction tends to 1 in the high-density limit, we employ full exact exchange according to the rigorous definition of the exchange component of any exchange-correlation energy functional. Use of full exact exchange permits the satisfaction of many exact constraints, but the nonlocality of exchange also requires balanced nonlocality of correlation. We find that this nonlocality can demand at least five empirical parameters (corresponding roughly to the four kinds of abnormal regions). Our local hybrid functional is perhaps the first accurate size-consistent density functional with full exact exchange. It satisfies other known exact constraints, including exactness for all one-electron densities, and provides an excellent, fit 1.0 the 223 molecular enthalpies of formation of the G3/99 set and the 42 reaction barrier heights of the BH42/03 set, improving both (but especially the latter) over most semilocal functionals and global hybrids. Exact constraints, physical insights, and paradigm examples hopefully suppress 'overfitting'.« less

Comparing ab initio density-functional and wave function theories: the impact of correlation on the electronic density and the role of the correlation potential.

PubMed

Grabowski, Ireneusz; Teale, Andrew M; Śmiga, Szymon; Bartlett, Rodney J

2011-09-21

The framework of ab initio density-functional theory (DFT) has been introduced as a way to provide a seamless connection between the Kohn-Sham (KS) formulation of DFT and wave-function based ab initio approaches [R. J. Bartlett, I. Grabowski, S. Hirata, and S. Ivanov, J. Chem. Phys. 122, 034104 (2005)]. Recently, an analysis of the impact of dynamical correlation effects on the density of the neon atom was presented [K. Jankowski, K. Nowakowski, I. Grabowski, and J. Wasilewski, J. Chem. Phys. 130, 164102 (2009)], contrasting the behaviour for a variety of standard density functionals with that of ab initio approaches based on second-order Møller-Plesset (MP2) and coupled cluster theories at the singles-doubles (CCSD) and singles-doubles perturbative triples [CCSD(T)] levels. In the present work, we consider ab initio density functionals based on second-order many-body perturbation theory and coupled cluster perturbation theory in a similar manner, for a range of small atomic and molecular systems. For comparison, we also consider results obtained from MP2, CCSD, and CCSD(T) calculations. In addition to this density based analysis, we determine the KS correlation potentials corresponding to these densities and compare them with those obtained for a range of ab initio density functionals via the optimized effective potential method. The correlation energies, densities, and potentials calculated using ab initio DFT display a similar systematic behaviour to those derived from electronic densities calculated using ab initio wave function theories. In contrast, typical explicit density functionals for the correlation energy, such as VWN5 and LYP, do not show behaviour consistent with this picture of dynamical correlation, although they may provide some degree of correction for already erroneous explicitly density-dependent exchange-only functionals. The results presented here using orbital dependent ab initio density functionals show that they provide a treatment of exchange and correlation contributions within the KS framework that is more consistent with traditional ab initio wave function based methods.

Physicochemical Properties of Cartilage in the Light of Ion Exchange Theory

PubMed Central

Maroudas, Alice

1968-01-01

Ion exchange theory has been applied to articular cartilage. Relationships were derived between permeability, diffusivity, electrical conductivity, and streaming potential. Systematic measurements were undertaken on these properties. Experimental techniques are described and data tabulated. Theoretical correlations were found to hold within the experimental error. The concentration of fixed negatively-charged groups in cartilage was shown to be the most important parameter. Fixed charge density was found to increase with distance from the articular surface and this variation was reflected in the other properties. PMID:5699797

Oil price and exchange rate co-movements in Asian countries: Detrended cross-correlation approach

NASA Astrophysics Data System (ADS)

Hussain, Muntazir; Zebende, Gilney Figueira; Bashir, Usman; Donghong, Ding

2017-01-01

Most empirical literature investigates the relation between oil prices and exchange rate through different models. These models measure this relationship on two time scales (long and short terms), and often fail to observe the co-movement of these variables at different time scales. We apply a detrended cross-correlation approach (DCCA) to investigate the co-movements of the oil price and exchange rate in 12 Asian countries. This model determines the co-movements of oil price and exchange rate at different time scale. The exchange rate and oil price time series indicate unit root problem. Their correlation and cross-correlation are very difficult to measure. The result becomes spurious when periodic trend or unit root problem occurs in these time series. This approach measures the possible cross-correlation at different time scale and controlling the unit root problem. Our empirical results support the co-movements of oil prices and exchange rate. Our results support a weak negative cross-correlation between oil price and exchange rate for most Asian countries included in our sample. The results have important monetary, fiscal, inflationary, and trade policy implications for these countries.

Collaborative Signaling of Informational Structures by Dynamic Speech Rate.

ERIC Educational Resources Information Center

Koiso, Hanae; Shimojima, Atsushi; Katagiri, Yasuhiro

1998-01-01

Investigated the functions of dynamic speech rates as contextualization cues in conversational Japanese, examining five spontaneous task-oriented dialogs and analyzing the potential of speech-rate changes in signaling the structure of the information being exchanged. Results found a correlation between speech decelerations and the openings of new…

Phase correlation of foreign exchange time series

NASA Astrophysics Data System (ADS)

Wu, Ming-Chya

2007-03-01

Correlation of foreign exchange rates in currency markets is investigated based on the empirical data of USD/DEM and USD/JPY exchange rates for a period from February 1 1986 to December 31 1996. The return of exchange time series is first decomposed into a number of intrinsic mode functions (IMFs) by the empirical mode decomposition method. The instantaneous phases of the resultant IMFs calculated by the Hilbert transform are then used to characterize the behaviors of pricing transmissions, and the correlation is probed by measuring the phase differences between two IMFs in the same order. From the distribution of phase differences, our results show explicitly that the correlations are stronger in daily time scale than in longer time scales. The demonstration for the correlations in periods of 1986-1989 and 1990-1993 indicates two exchange rates in the former period were more correlated than in the latter period. The result is consistent with the observations from the cross-correlation calculation.

Cross-correlations between crude oil and exchange markets for selected oil rich economies

NASA Astrophysics Data System (ADS)

Li, Jianfeng; Lu, Xinsheng; Zhou, Ying

2016-07-01

Using multifractal detrended cross-correlation analysis (MF-DCCA), this paper studies the cross-correlation behavior between crude oil market and five selected exchange rate markets. The dataset covers the period of January 1,1996-December 31,2014, and contains 4,633 observations for each of the series, including daily closing prices of crude oil, Australian Dollars, Canadian Dollars, Mexican Pesos, Russian Rubles, and South African Rand. Our empirical results obtained from cross-correlation statistic and cross-correlation coefficient have confirmed the existence of cross-correlations, and the MF-DCCA results have demonstrated a strong multifractality between cross-correlated crude oil market and exchange rate markets in both short term and long term. Using rolling window analysis, we have also found the persistent cross-correlations between the exchange rates and crude oil returns, and the cross-correlation scaling exponents exhibit volatility during some time periods due to its sensitivity to sudden events.

Exchange-Correlation Hole in Polarized Insulators: Implications for the Microscopic Functional Theory of Dielectrics

NASA Astrophysics Data System (ADS)

Ortiz, Gerardo; Souza, Ivo; Martin, Richard M.

1998-01-01

We present a simple and direct proof that the exchange-correlation hole, and therefore the exchange-correlation energy, in a polarized insulator is not determined by the bulk density alone. It is uniquely characterized by the density and the macroscopic electric polarization of the dielectric medium.

Clinical usefulness of a functional assay for the von Willebrand factor cleaving protease (ADAMTS 13) and its inhibitor in a patient with thrombotic thrombocytopenic purpura.

PubMed

Rick, M E; Austin, H; Leitman, S F; Krizek, D M; Aronson, D L

2004-02-01

Decreased von Willebrand factor cleaving protease activity (VWFCP, ADAMTS 13) leads to persistence of unusually large multimers of von Willebrand factor that bind to platelets, causing platelet aggregates, microangiopathic hemolysis, and thrombocytopenia in patients with thrombotic thrombocytopenic purpura (TTP). The clinical value of measuring ADAMTS 13 and its inhibitor is not fully defined; the case reported here illustrates the usefulness of the assay to help confirm the clinical diagnosis in a patient with other potential causes for thrombotic microangiopathy; the assay also helped in making treatment decisions. A patient with systemic lupus erythematosis (SLE) presented with fever and abdominal pain, thrombocytopenia, and anemia. Thrombotic microangiopathy was diagnosed by the appearance of schistocytes, decreasing platelet count, and evidence of hemolysis. ADAMTS 13 was decreased and an inhibitor was demonstrated in the patient's initial blood sample within 24 hr of admission. Plasma exchange was initiated, and serial assays showed increased ADAMTS 13 activity and decreased inhibitor after each plasma exchange; there was a rebound in inhibitor and a decrease in ADAMTS 13 activity prior to the next exchange that lessened over time. Increasing levels of protease activity correlated with clinical and laboratory improvement. Measurement of ADAMTS 13 activity and its inhibitor aided in the diagnosis of this complicated case of a patient with other potential causes for microangiopathic hemolysis. Subsequent levels correlated with the clinical course, and disappearance of the inhibitor indicated that long-term plasma exchange or other immunosuppressive treatment was not needed.

Evaluating the Development of Biocatalytic Technology for the Targeted Removal of Perchlorate from Drinking Water.

PubMed

Hutchison, Justin M; Guest, Jeremy S; Zilles, Julie L

2017-06-20

Removing micropollutants is challenging in part because of their toxicity at low concentrations. A biocatalytic approach could harness the high affinity of enzymes for their substrates to address this challenge. The potential of biocatalysis relative to mature (nonselective ion exchange, selective ion exchange, and whole-cell biological reduction) and emerging (catalysis) perchlorate-removal technologies was evaluated through a quantitative sustainable design framework, and research objectives were prioritized to advance economic and environmental sustainability. In its current undeveloped state, the biocatalytic technology was approximately 1 order of magnitude higher in cost and environmental impact than nonselective ion exchange. Biocatalyst production was highly correlated with cost and impact. Realistic improvement scenarios targeting biocatalyst yield, biocatalyst immobilization for reuse, and elimination of an electron shuttle could reduce total costs to $0.034 m -3 and global warming potential (GWP) to 0.051 kg CO 2 eq m -3 : roughly 6.5% of cost and 7.3% of GWP of the background from drinking water treatment and competitive with the best performing technology, selective ion exchange. With less stringent perchlorate regulatory limits, ion exchange technologies had increased cost and impact, in contrast to biocatalytic and catalytic technologies. Targeted advances in biocatalysis could provide affordable and sustainable treatment options to protect the public from micropollutants.

Pharmaceuticals' sorptions relative to properties of thirteen different soils.

PubMed

Kodešová, Radka; Grabic, Roman; Kočárek, Martin; Klement, Aleš; Golovko, Oksana; Fér, Miroslav; Nikodem, Antonín; Jakšík, Ondřej

2015-04-01

Transport of human and veterinary pharmaceuticals in soils and consequent ground-water contamination are influenced by many factors, including compound sorption on soil particles. Here we evaluate the sorption isotherms for 7 pharmaceuticals on 13 soils, described by Freundlich equations, and assess the impact of soil properties on various pharmaceuticals' sorption on soils. Sorption of ionizable pharmaceuticals was, in many cases, highly affected by soil pH. The sorption coefficient of sulfamethoxazole was negatively correlated to soil pH, and thus positively related to hydrolytic acidity and exchangeable acidity. Sorption coefficients for clindamycin and clarithromycin were positively related to soil pH and thus negatively related to hydrolytic acidity and exchangeable acidity, and positively related to base cation saturation. The sorption coefficients for the remaining pharmaceuticals (trimethoprim, metoprolol, atenolol, and carbamazepine) were also positively correlated with the base cation saturation and cation exchange capacity. Positive correlations between sorption coefficients and clay content were found for clindamycin, clarithromycin, atenolol, and metoprolol. Positive correlations between sorption coefficients and organic carbon content were obtained for trimethoprim and carbamazepine. Pedotransfer rules for predicting sorption coefficients of various pharmaceuticals included hydrolytic acidity (sulfamethoxazole), organic carbon content (trimethoprimand carbamazepine), base cation saturation (atenolol and metoprolol), exchangeable acidity and clay content (clindamycin), and soil active pH and clay content (clarithromycin). Pedotransfer rules, predicting the Freundlich sorption coefficients, could be applied for prediction of pharmaceutical mobility in soils with similar soil properties. Predicted sorption coefficients together with pharmaceutical half-lives and other imputes (e.g., soil-hydraulic, geological, hydro-geological, climatic) may be used for assessing potential ground-water contamination. Copyright © 2014 Elsevier B.V. All rights reserved.

Improving approximate-optimized effective potentials by imposing exact conditions: Theory and applications to electronic statics and dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kurzweil, Yair; Head-Gordon, Martin

2009-07-15

We develop a method that can constrain any local exchange-correlation potential to preserve basic exact conditions. Using the method of Lagrange multipliers, we calculate for each set of given Kohn-Sham orbitals a constraint-preserving potential which is closest to the given exchange-correlation potential. The method is applicable to both the time-dependent (TD) and independent cases. The exact conditions that are enforced for the time-independent case are Galilean covariance, zero net force and torque, and Levy-Perdew virial theorem. For the time-dependent case we enforce translational covariance, zero net force, Levy-Perdew virial theorem, and energy balance. We test our method on the exchangemore » (only) Krieger-Li-Iafrate (xKLI) approximate-optimized effective potential for both cases. For the time-independent case, we calculated the ground state properties of some hydrogen chains and small sodium clusters for some constrained xKLI potentials and Hartree-Fock (HF) exchange. The results (total energy, Kohn-Sham eigenvalues, polarizability, and hyperpolarizability) indicate that enforcing the exact conditions is not important for these cases. On the other hand, in the time-dependent case, constraining both energy balance and zero net force yields improved results relative to TDHF calculations. We explored the electron dynamics in small sodium clusters driven by cw laser pulses. For each laser pulse we compared calculations from TD constrained xKLI, TD partially constrained xKLI, and TDHF. We found that electron dynamics such as electron ionization and moment of inertia dynamics for the constrained xKLI are most similar to the TDHF results. Also, energy conservation is better by at least one order of magnitude with respect to the unconstrained xKLI. We also discuss the problems that arise in satisfying constraints in the TD case with a non-cw driving force.« less

Super-resolution microscopy reveals structural diversity in molecular exchange among peptide amphiphile nanofibres

DOE PAGES

da Silva, Ricardo M. P.; van der Zwaag, Daan; Albertazzi, Lorenzo; ...

2016-05-19

The dynamic behaviour of supramolecular systems is an important dimension of their potential functions. Here, we report on the use of stochastic optical reconstruction microscopy to study the molecular exchange of peptide amphiphile nanofibres, supramolecular systems known to have important biomedical functions. Solutions of nanofibres labelled with different dyes (Cy3 and Cy5) were mixed, and the distribution of dyes inserting into initially single-colour nanofibres was quantified using correlative image analysis. Our observations are consistent with an exchange mechanism involving monomers or small clusters of molecules inserting randomly into a fibre. Different exchange rates are observed within the same fibre, suggestingmore » that local cohesive structures exist on the basis of beta-sheet discontinuous domains. The results reported here show that peptide amphiphile supramolecular systems can be dynamic and that their intermolecular interactions affect exchange patterns. Lastly, this information can be used to generate useful aggregate morphologies for improved biomedical function.« less

Exchange and Correlation Effects in a Double Barrier Quantum Well

NASA Astrophysics Data System (ADS)

Hasbun, J. E.

2003-03-01

Studies of electronic properties in double barrier resonant tunneling systems usually involve the solution of the BenDaniel-Duke equation (BDK) in the presence of an applied voltage. Electron interactions are included by means of the Hartree term and the wavefunction is self-consistently obtained by coupling the BDK with the Poisson equation. In this work, we go beyond the Hartree approximation by including exchange and correlation effects (v_xc) through the local density functional theory. The analytically parametrized v_xc of Hedin and Lunqvist footnote[1]L. Hedin and B. I. Lundqvist, J. Phys C: Solid. St. Phys. 4, 2064(1971) is employed. While the calculation of v_xc involves extra self-consistency conditions, it is shown that the inclusion of exchange and correlation effects may be important in the electronic characteristics of these devices. For our earlier model footnote[2]J. E. Hasbun, APS Bull. 47, 914(2002) the v_xc potential is comparable to the Hartree electron term at low electric field values, but less so for much higher field. The v_xc employed here ^2 is not appreciably different from the more sophisticated one of Perdew and Zunger footnote[3]J. P. Perdew and A. Zunger, Phys. Rev. B 23, 5048(1981). JH wishes to thank Mei-Yin Chou for helpful discussions

Electronic properties of CdWO{sub 4}: Use of hybrid exchange and correlation functionals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meena, B. S., E-mail: bsmphysics@gmail.com; Mund, H. S.; Ahuja, B. L.

Energy bands, density of states (DOS), Mulliken population (MP) and electron momentum densities (EMDs) of CdWO{sub 4} are presented using hybrid exchange and correlation functionals namely B3LYP, B3PW and PBE0. To validate the present hybrid potentials, theoretical EMDs have been compared with the experimental Compton profile. It is found that LCAO-B3LYP based Compton profile gives a better agreement with experiment than other theoretical profiles. The energy bands and DOS show a wide band gap semiconducting nature of CdWO{sub 4}. The theoretical band gap obtained using B3LYP scheme reconciles well with the available experimental data. In addition, we have also presentedmore » the anisotropies in EMDs along [100], [110] and [001] directions and the bonding effects using the MP data.« less

Influence of different forms of acidities on soil microbiological properties and enzyme activities at an acid mine drainage contaminated site.

PubMed

Sahoo, Prafulla Kumar; Bhattacharyya, Pradip; Tripathy, Subhasish; Equeenuddin, Sk Md; Panigrahi, M K

2010-07-15

Assessment of microbial parameters, viz. microbial biomass, fluorescence diacetate, microbial respiration, acid phosphatase, beta-glucosidase and urease with respect to acidity helps in evaluating the quality of soils. This study was conducted to investigate the effects of different forms of acidities on soil microbial parameters in an acid mine drainage contaminated site around coal deposits in Jainta Hills of India. Total potential and exchangeable acidity, extractable and exchangeable aluminium were significantly higher in contaminated soil compared to the baseline (p<0.01). Different forms of acidity were significantly and positively correlated with each other (p<0.05). Further, all microbial properties were positively and significantly correlated with organic carbon and clay (p<0.05). The ratios of microbial parameters with organic carbon were negatively correlated with different forms of acidity. Principal component analysis and cluster analyses showed that the microbial activities are not directly influenced by the total potential acidity and extractable aluminium. Though acid mine drainage affected soils had higher microbial biomass and activities due to higher organic matter content than those of the baseline soils, the ratios of microbial parameters/organic carbon indicated suppression of microbial growth and activities due to acidity stress. 2010 Elsevier B.V. All rights reserved.

Dynamic relationship between Japanese Yen exchange rates and market anxiety: A new perspective based on MF-DCCA

NASA Astrophysics Data System (ADS)

Lu, Xinsheng; Sun, Xinxin; Ge, Jintian

2017-05-01

This paper investigates the dynamic relationship between Japanese Yen exchange rates and market anxiety during the period from January 5, 1998 to April 18, 2016. A quantitative technique of multifractal detrended cross-correlation analysis (MF-DCCA) is used to explore the multifractal features of the cross-correlations between USD/JPY, AUD/JPY exchange rates and the market anxiety gauge VIX. The investigation shows that the causal relationship between Japanese Yen exchange rates and VIX are bidirectional in general, and the cross-correlations between the two sets of time series are multifractal. Strong evidence suggests that the cross-correlation exponents tend to exhibit different volatility patterns in response to diverse external shocks such as financial distress and widening in interest rate spread, suggesting that the cross-correlated behavior between Japanese Yen exchange rates and VIX are susceptible to economic uncertainties and risks. In addition, the performances of two market anxiety gauges, the VIX and the TED spread, are compared and the sources of multifractality are also traced. Thus, this paper contributes to the literature by shedding light on the unique driving forces of the Yen exchange rate fluctuations in the international foreign exchange market.

Reconsideration of data and correlations for plate finned-tube heat exchangers

NASA Astrophysics Data System (ADS)

Otović, Milena; Mihailović, Miloš; Genić, Srbislav; Jaćimović, Branislav; Milovančević, Uroš; Marković, Saša

2018-04-01

This paper deals with heat exchangers having plain finned tubes in staggered (triangular) pattern. The objective of this paper is to provide the heat transfer and friction factor correlation which can be used in engineering practice. For this purpose, the experimental data of several (most cited) authors who deal with this type of heat exchangers are used. The new correlations are established to predict the air-side heat transfer coefficient and friction factor as a function of the Reynolds number and geometric variables of the heat exchanger - tube diameter, tube pitch, fin spacing, tube rows, etc. In those correlations the characteristic dimension in Reynolds number is calculated by using the new parameter - volumetric porosity. Also, there are given the errors of those correlations.

Impact of anionic ion exchange resins on NOM fractions: Effect on N-DBPs and C-DBPs precursors.

PubMed

Bazri, Mohammad Mahdi; Martijn, Bram; Kroesbergen, Jan; Mohseni, Madjid

2016-02-01

The formation potential of carbonaceous and nitrogenous disinfection by-products (C-DBPs, N-DBPs) after ion exchange treatment (IEX) of three different water types in multiple consecutive loading cycles was investigated. Liquid chromatography with organic carbon detector (LC-OCD) was employed to gauge the impact of IEX on different natural organic matter (NOM) fractions and data obtained were used to correlate these changes to DBPs Formation Potential (FP) under chlorination. Humic (-like) substances fractions of NOM were mainly targeted by ion exchange resins (40-67% removal), whereas hydrophilic, non-ionic fractions such as neutrals and building blocks were poorly removed during the treatment (12-33% removal). Application of ion exchange resins removed 13-20% of total carbonaceous DBPs FP and 3-50% of total nitrogenous DBPs FP. Effect of the inorganic nitrogen (i.e., Nitrate) presence on N-DBPs FP was insignificant while the presence of dissolved organic nitrogen (DON) was found to be a key parameter affecting the formation of N-DBPs. DON especially the portion affiliated with humic substances fraction, was reduced effectively (∼77%) as a result of IEX treatment. Copyright © 2015 Elsevier Ltd. All rights reserved.

A dynamic analysis of S&P 500, FTSE 100 and EURO STOXX 50 indices under different exchange rates.

PubMed

Chen, Yanhua; Mantegna, Rosario N; Pantelous, Athanasios A; Zuev, Konstantin M

2018-01-01

In this study, we assess the dynamic evolution of short-term correlation, long-term cointegration and Error Correction Model (hereafter referred to as ECM)-based long-term Granger causality between each pair of US, UK, and Eurozone stock markets from 1980 to 2015 using the rolling-window technique. A comparative analysis of pairwise dynamic integration and causality of stock markets, measured in common and domestic currency terms, is conducted to evaluate comprehensively how exchange rate fluctuations affect the time-varying integration among the S&P 500, FTSE 100 and EURO STOXX 50 indices. The results obtained show that the dynamic correlation, cointegration and ECM-based long-run Granger causality vary significantly over the whole sample period. The degree of dynamic correlation and cointegration between pairs of stock markets rises in periods of high volatility and uncertainty, especially under the influence of economic, financial and political shocks. Meanwhile, we observe the weaker and decreasing correlation and cointegration among the three developed stock markets during the recovery periods. Interestingly, the most persistent and significant cointegration among the three developed stock markets exists during the 2007-09 global financial crisis. Finally, the exchange rate fluctuations, also influence the dynamic integration and causality between all pairs of stock indices, with that influence increasing under the local currency terms. Our results suggest that the potential for diversifying risk by investing in the US, UK and Eurozone stock markets is limited during the periods of economic, financial and political shocks.

Ab-initio study of (Ga,Cr)N and (Ga,Mn)N DMSs: under hydrostatic pressure

NASA Astrophysics Data System (ADS)

Rani, Anita; Kumar, Ranjan

2018-03-01

The influence of hydrostatic pressure between 0-100 GPa on structural, electronic and magnetic properties of CrxGa1-xN and MnxGa1-xN (x = 0.25) diluted magnetic semiconductors has been studied. The calculations have been performed using DFT as implemented in code SIESTA. LDA + U as exchange-correlation (XC) potential have been used to study the parameters. Under external pressure, shifting in both valence band and conduction band energy levels from their actual positions has been observed, which lead to modification of electronic properties. Also, N0 α, s-d exchange constant and p-d exchange constants, N0 β have been calculated at different pressures. Both the compounds show half metallic nature at studied pressure range.

Pair potentials for liquid sodium near freezing from electron theory and from inversion of the measured structure factor

NASA Astrophysics Data System (ADS)

Perrot, F.; March, N. H.

An effective pair potential for liquid sodium near freezing has been calculated from electron theory using the density-functional method. The main features of the potential extracted by Reatto, Levesque, and Weis [phys. Rev. A 33, 3451 (1986)] by inverting the measured structure factor of Greenfield, Wellendorf, and Wiser [Phys. Rev. A 4, 1607 (1971)] are faithfully reflected by electron theory. To obtain precise agreement between the two methods will evidently require further progress in setting up nonlocal exchange and correlation functionals.

Electronic transport properties of some liquid semiconductor

NASA Astrophysics Data System (ADS)

Sonvane, Y. A.; Thakor, P. B.; Jani, A. R.

2012-06-01

Electronic transport properties like electrical resistivity (ρ) and thermoelectric power (Q) of liquid semiconductor (Si, Ga, Ge, In, Sn, Tl and Bi) are calculated in the present study. Our well established single parametric model potential alongwith Percus Yevick hard sphere (PYHS) reference system are used to describe the structural information. To see the influence of exchange and correlation effect, Hartree, Taylor and Sarkar et al local field correlation functions are used. From present results, it is seen that good agreements between present results and experimental data have been achieved. Lastly we conclude that our model potential successfully produces the data of electronic transport properties for some liquid semiconductor (Si, Ga, Ge, In, Sn, Tl and Bi).

Do foreign exchange and equity markets co-move in Latin American region? Detrended cross-correlation approach

NASA Astrophysics Data System (ADS)

Bashir, Usman; Yu, Yugang; Hussain, Muntazir; Zebende, Gilney F.

2016-11-01

This paper investigates the dynamics of the relationship between foreign exchange markets and stock markets through time varying co-movements. In this sense, we analyzed the time series monthly of Latin American countries for the period from 1991 to 2015. Furthermore, we apply Granger causality to verify the direction of causality between foreign exchange and stock market and detrended cross-correlation approach (ρDCCA) for any co-movements at different time scales. Our empirical results suggest a positive cross correlation between exchange rate and stock price for all Latin American countries. The findings reveal two clear patterns of correlation. First, Brazil and Argentina have positive correlation in both short and long time frames. Second, the remaining countries are negatively correlated in shorter time scale, gradually moving to positive. This paper contributes to the field in three ways. First, we verified the co-movements of exchange rate and stock prices that were rarely discussed in previous empirical studies. Second, ρDCCA coefficient is a robust and powerful methodology to measure the cross correlation when dealing with non stationarity of time series. Third, most of the studies employed one or two time scales using co-integration and vector autoregressive approaches. Not much is known about the co-movements at varying time scales between foreign exchange and stock markets. ρDCCA coefficient facilitates the understanding of its explanatory depth.

Importance of the correlation contribution for local hybrid functionals: range separation and self-interaction corrections.

PubMed

Arbuznikov, Alexei V; Kaupp, Martin

2012-01-07

Local hybrid functionals with their position-dependent exact-exchange admixture are a conceptually simple and promising extension of the concept of a hybrid functional. Local hybrids based on a simple mixing of the local spin density approximation (LSDA) with exact exchange have been shown to be successful for thermochemistry, reaction barriers, and a range of other properties. So far, the combination of this generation of local hybrids with an LSDA correlation functional has been found to give the most favorable results for atomization energies, for a range of local mixing functions (LMFs) governing the exact-exchange admixture. Here, we show that the choice of correlation functional to be used with local hybrid exchange crucially influences the parameterization also of the exchange part as well as the overall performance. A novel ansatz for the correlation part of local hybrids is suggested based on (i) range-separation of LSDA correlation into short-range (SR) and long-range (LR) parts, and (ii) partial or full elimination of the one-electron self-correlation from the SR part. It is shown that such modified correlation functionals allow overall larger exact exchange admixture in thermochemically competitive local hybrids than before. This results in improvements for reaction barriers and for other properties crucially influenced by self-interaction errors, as demonstrated by a number of examples. Based on the range-separation approach, a fresh view on the breakdown of the correlation energy into dynamical and non-dynamical parts is suggested.

The optimized effective potential and the self-interaction correction in density functional theory: Application to molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garza, Jorge; Nichols, Jeffrey A.; Dixon, David A.

2000-05-08

The Krieger, Li, and Iafrate approximation to the optimized effective potential including the self-interaction correction for density functional theory has been implemented in a molecular code, NWChem, that uses Gaussian functions to represent the Kohn and Sham spin-orbitals. The differences between the implementation of the self-interaction correction in codes where planewaves are used with an optimized effective potential are discussed. The importance of the localization of the spin-orbitals to maximize the exchange-correlation of the self-interaction correction is discussed. We carried out exchange-only calculations to compare the results obtained with these approximations, and those obtained with the local spin density approximation,more » the generalized gradient approximation and Hartree-Fock theory. Interesting results for the energy difference (GAP) between the highest occupied molecular orbital, HOMO, and the lowest unoccupied molecular orbital, LUMO, (spin-orbital energies of closed shell atoms and molecules) using the optimized effective potential and the self-interaction correction have been obtained. The effect of the diffuse character of the basis set on the HOMO and LUMO eigenvalues at the various levels is discussed. Total energies obtained with the optimized effective potential and the self-interaction correction show that the exchange energy with these approximations is overestimated and this will be an important topic for future work. (c) 2000 American Institute of Physics.« less

Efficient exact-exchange time-dependent density-functional theory methods and their relation to time-dependent Hartree-Fock.

PubMed

Hesselmann, Andreas; Görling, Andreas

2011-01-21

A recently introduced time-dependent exact-exchange (TDEXX) method, i.e., a response method based on time-dependent density-functional theory that treats the frequency-dependent exchange kernel exactly, is reformulated. In the reformulated version of the TDEXX method electronic excitation energies can be calculated by solving a linear generalized eigenvalue problem while in the original version of the TDEXX method a laborious frequency iteration is required in the calculation of each excitation energy. The lowest eigenvalues of the new TDEXX eigenvalue equation corresponding to the lowest excitation energies can be efficiently obtained by, e.g., a version of the Davidson algorithm appropriate for generalized eigenvalue problems. Alternatively, with the help of a series expansion of the new TDEXX eigenvalue equation, standard eigensolvers for large regular eigenvalue problems, e.g., the standard Davidson algorithm, can be used to efficiently calculate the lowest excitation energies. With the help of the series expansion as well, the relation between the TDEXX method and time-dependent Hartree-Fock is analyzed. Several ways to take into account correlation in addition to the exact treatment of exchange in the TDEXX method are discussed, e.g., a scaling of the Kohn-Sham eigenvalues, the inclusion of (semi)local approximate correlation potentials, or hybrids of the exact-exchange kernel with kernels within the adiabatic local density approximation. The lowest lying excitations of the molecules ethylene, acetaldehyde, and pyridine are considered as examples.

Deorbitalization strategies for meta-generalized-gradient-approximation exchange-correlation functionals

NASA Astrophysics Data System (ADS)

Mejia-Rodriguez, Daniel; Trickey, S. B.

2017-11-01

We explore the simplification of widely used meta-generalized-gradient approximation (mGGA) exchange-correlation functionals to the Laplacian level of refinement by use of approximate kinetic-energy density functionals (KEDFs). Such deorbitalization is motivated by the prospect of reducing computational cost while recovering a strictly Kohn-Sham local potential framework (rather than the usual generalized Kohn-Sham treatment of mGGAs). A KEDF that has been rather successful in solid simulations proves to be inadequate for deorbitalization, but we produce other forms which, with parametrization to Kohn-Sham results (not experimental data) on a small training set, yield rather good results on standard molecular test sets when used to deorbitalize the meta-GGA made very simple, Tao-Perdew-Staroverov-Scuseria, and strongly constrained and appropriately normed functionals. We also study the difference between high-fidelity and best-performing deorbitalizations and discuss possible implications for use in ab initio molecular dynamics simulations of complicated condensed phase systems.

Air mass origins and troposphere-to-stratosphere exchange associated with mid-latitude cyclogenesis and tropopause folding inferred from Be-7 measurements

NASA Technical Reports Server (NTRS)

Kritz, Mark A.; Rosner, Stefan W.; Danielsen, Edwin F.; Selkirk, Henry B.

1991-01-01

The 1984 extratropical mission of NASA's Stratosphere-Troposphere Exchange Project (STEP) studied cross-jet transport in regions of cyclogenesis and tropopause folding. Correlations of Be-7, ozone, water vapor, and potential vorticity measured on a NASA U-2 research aircraft flying in high shear regions above the jet core are indicative of mixing between the cyclonic and the anticyclonic sides of the jet and are consistent with the hypothesis that small-scale entrainments of upper tropospheric air into the lower stratosphere during cyclogenesis are important in maintaining the vertical gradients of Be-7, ozone, water vapor and other trace constituents in the lower few kilometers of the midlatitude stratosphere. Correlations between Be-7, and ozone suggest a lower tropical stratospheric origin for the ozone-poor lamina observed above the jet core.

Theoretical and experimental errors for in situ measurements of plant water potential.

PubMed

Shackel, K A

1984-07-01

Errors in psychrometrically determined values of leaf water potential caused by tissue resistance to water vapor exchange and by lack of thermal equilibrium were evaluated using commercial in situ psychrometers (Wescor Inc., Logan, UT) on leaves of Tradescantia virginiana (L.). Theoretical errors in the dewpoint method of operation for these sensors were demonstrated. After correction for these errors, in situ measurements of leaf water potential indicated substantial errors caused by tissue resistance to water vapor exchange (4 to 6% reduction in apparent water potential per second of cooling time used) resulting from humidity depletions in the psychrometer chamber during the Peltier condensation process. These errors were avoided by use of a modified procedure for dewpoint measurement. Large changes in apparent water potential were caused by leaf and psychrometer exposure to moderate levels of irradiance. These changes were correlated with relatively small shifts in psychrometer zero offsets (-0.6 to -1.0 megapascals per microvolt), indicating substantial errors caused by nonisothermal conditions between the leaf and the psychrometer. Explicit correction for these errors is not possible with the current psychrometer design.

Theoretical and Experimental Errors for In Situ Measurements of Plant Water Potential 1

PubMed Central

Shackel, Kenneth A.

1984-01-01

Errors in psychrometrically determined values of leaf water potential caused by tissue resistance to water vapor exchange and by lack of thermal equilibrium were evaluated using commercial in situ psychrometers (Wescor Inc., Logan, UT) on leaves of Tradescantia virginiana (L.). Theoretical errors in the dewpoint method of operation for these sensors were demonstrated. After correction for these errors, in situ measurements of leaf water potential indicated substantial errors caused by tissue resistance to water vapor exchange (4 to 6% reduction in apparent water potential per second of cooling time used) resulting from humidity depletions in the psychrometer chamber during the Peltier condensation process. These errors were avoided by use of a modified procedure for dewpoint measurement. Large changes in apparent water potential were caused by leaf and psychrometer exposure to moderate levels of irradiance. These changes were correlated with relatively small shifts in psychrometer zero offsets (−0.6 to −1.0 megapascals per microvolt), indicating substantial errors caused by nonisothermal conditions between the leaf and the psychrometer. Explicit correction for these errors is not possible with the current psychrometer design. PMID:16663701

Spatial Distribution and Air-Water Exchange of Organic Flame Retardants in the Lower Great Lakes.

PubMed

McDonough, Carrie A; Puggioni, Gavino; Helm, Paul A; Muir, Derek; Lohmann, Rainer

2016-09-06

Organic flame retardants (OFRs) such as polybrominated diphenyl ethers (PBDEs) and novel halogenated flame retardants (NHFRs) are ubiquitous, persistent, and bioaccumulative contaminants that have been used in consumer goods to slow combustion. In this study, polyethylene passive samplers (PEs) were deployed throughout the lower Great Lakes (Lake Erie and Lake Ontario) to measure OFRs in air and water, calculate air-water exchange fluxes, and investigate spatial trends. Dissolved Σ12BDE was greatest in Lake Ontario near Toronto (18 pg/L), whereas gaseous Σ12BDE was greatest on the southern shoreline of Lake Erie (11 pg/m(3)). NHFRs were generally below detection limits. Air-water exchange was dominated by absorption of BDEs 47 and 99, ranging from -964 pg/m(2)/day to -30 pg/m(2)/day. Σ12BDE in air and water was significantly correlated with surrounding population density, suggesting that phased-out PBDEs continued to be emitted from population centers along the Great Lakes shoreline in 2012. Correlation with dissolved Σ12BDE was strongest when considering population within 25 km while correlation with gaseous Σ12BDE was strongest when using population within 3 km to the south of each site. Bayesian kriging was used to predict dissolved Σ12BDE over the lakes, illustrating the utility of relatively highly spatially resolved measurements in identifying potential hot spots for future study.

Statistical correlations in an ideal gas of particles obeying fractional exclusion statistics.

PubMed

Pellegrino, F M D; Angilella, G G N; March, N H; Pucci, R

2007-12-01

After a brief discussion of the concepts of fractional exchange and fractional exclusion statistics, we report partly analytical and partly numerical results on thermodynamic properties of assemblies of particles obeying fractional exclusion statistics. The effect of dimensionality is one focal point, the ratio mu/k_(B)T of chemical potential to thermal energy being obtained numerically as a function of a scaled particle density. Pair correlation functions are also presented as a function of the statistical parameter, with Friedel oscillations developing close to the fermion limit, for sufficiently large density.

Interplay between strong correlation and adsorption distances: Co on Cu(001)

NASA Astrophysics Data System (ADS)

Bahlke, Marc Philipp; Karolak, Michael; Herrmann, Carmen

2018-01-01

Adsorbed transition metal atoms can have partially filled d or f shells due to strong on-site Coulomb interaction. Capturing all effects originating from electron correlation in such strongly correlated systems is a challenge for electronic structure methods. It requires a sufficiently accurate description of the atomistic structure (in particular bond distances and angles), which is usually obtained from first-principles Kohn-Sham density functional theory (DFT), which due to the approximate nature of the exchange-correlation functional may provide an unreliable description of strongly correlated systems. To elucidate the consequences of this popular procedure, we apply a combination of DFT with the Anderson impurity model (AIM), as well as DFT + U for a calculation of the potential energy surface along the Co/Cu(001) adsorption coordinate, and compare the results with those obtained from DFT. The adsorption minimum is shifted towards larger distances by applying DFT+AIM, or the much cheaper DFT +U method, compared to the corresponding spin-polarized DFT results, by a magnitude comparable to variations between different approximate exchange-correlation functionals (0.08 to 0.12 Å). This shift originates from an increasing correlation energy at larger adsorption distances, which can be traced back to the Co 3 dx y and 3 dz2 orbitals being more correlated as the adsorption distance is increased. We can show that such considerations are important, as they may strongly affect electronic properties such as the Kondo temperature.

Developing LED UV fluorescence sensors for online monitoring DOM and predicting DBPs formation potential during water treatment.

PubMed

Li, Wen-Tao; Jin, Jing; Li, Qiang; Wu, Chen-Fei; Lu, Hai; Zhou, Qing; Li, Ai-Min

2016-04-15

Online monitoring dissolved organic matter (DOM) is urgent for water treatment management. In this study, high performance size exclusion chromatography with multi-UV absorbance and multi-emission fluorescence scans were applied to spectrally characterize samples from 16 drinking water sources across Yangzi River and Huai River Watersheds. The UV absorbance indices at 254 nm and 280 nm referred to the same DOM components and concentration, and the 280 nm UV light could excite both protein-like and humic-like fluorescence. Hence a novel UV fluorescence sensor was developed out using only one UV280 light-emitting diode (LED) as light source. For all samples, enhanced coagulation was mainly effective for large molecular weight biopolymers; while anion exchange further substantially removed humic substances. During chlorination tests, UVA280 and UVA254 showed similar correlations with yields of disinfection byproducts (DBPs); the humic-like fluorescence obtained from LED sensors correlated well with both trihalomethanes and haloacetic acids yields, while the correlation between protein-like fluorescence and trihalomethanes was relatively poor. Anion exchange exhibited more reduction of DBPs yields as well as UV absorbance and fluorescence signals than enhanced coagulation. The results suggest that the LED UV fluorescence sensors are very promising for online monitoring DOM and predicting DBPs formation potential during water treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Backward jump continuous-time random walk: An application to market trading

NASA Astrophysics Data System (ADS)

Gubiec, Tomasz; Kutner, Ryszard

2010-10-01

The backward jump modification of the continuous-time random walk model or the version of the model driven by the negative feedback was herein derived for spatiotemporal continuum in the context of a share price evolution on a stock exchange. In the frame of the model, we described stochastic evolution of a typical share price on a stock exchange with a moderate liquidity within a high-frequency time scale. The model was validated by satisfactory agreement of the theoretical velocity autocorrelation function with its empirical counterpart obtained for the continuous quotation. This agreement is mainly a result of a sharp backward correlation found and considered in this article. This correlation is a reminiscence of such a bid-ask bounce phenomenon where backward price jump has the same or almost the same length as preceding jump. We suggested that this correlation dominated the dynamics of the stock market with moderate liquidity. Although assumptions of the model were inspired by the market high-frequency empirical data, its potential applications extend beyond the financial market, for instance, to the field covered by the Le Chatelier-Braun principle of contrariness.

Backward jump continuous-time random walk: an application to market trading.

PubMed

Gubiec, Tomasz; Kutner, Ryszard

2010-10-01

The backward jump modification of the continuous-time random walk model or the version of the model driven by the negative feedback was herein derived for spatiotemporal continuum in the context of a share price evolution on a stock exchange. In the frame of the model, we described stochastic evolution of a typical share price on a stock exchange with a moderate liquidity within a high-frequency time scale. The model was validated by satisfactory agreement of the theoretical velocity autocorrelation function with its empirical counterpart obtained for the continuous quotation. This agreement is mainly a result of a sharp backward correlation found and considered in this article. This correlation is a reminiscence of such a bid-ask bounce phenomenon where backward price jump has the same or almost the same length as preceding jump. We suggested that this correlation dominated the dynamics of the stock market with moderate liquidity. Although assumptions of the model were inspired by the market high-frequency empirical data, its potential applications extend beyond the financial market, for instance, to the field covered by the Le Chatelier-Braun principle of contrariness.

Inhomogeneity induced and appropriately parameterized semilocal exchange and correlation energy functionals in two-dimensions.

PubMed

Patra, Abhilash; Jana, Subrata; Samal, Prasanjit

2018-04-07

The construction of meta generalized gradient approximations based on the density matrix expansion (DME) is considered as one of the most accurate techniques to design semilocal exchange energy functionals in two-dimensional density functional formalism. The exchange holes modeled using DME possess unique features that make it a superior entity. Parameterized semilocal exchange energy functionals based on the DME are proposed. The use of different forms of the momentum and flexible parameters is to subsume the non-uniform effects of the density in the newly constructed semilocal functionals. In addition to the exchange functionals, a suitable correlation functional is also constructed by working upon the local correlation functional developed for 2D homogeneous electron gas. The non-local effects are induced into the correlation functional by a parametric form of one of the newly constructed exchange energy functionals. The proposed functionals are applied to the parabolic quantum dots with a varying number of confined electrons and the confinement strength. The results obtained with the aforementioned functionals are quite satisfactory, which indicates why these are suitable for two-dimensional quantum systems.

Inhomogeneity induced and appropriately parameterized semilocal exchange and correlation energy functionals in two-dimensions

NASA Astrophysics Data System (ADS)

Patra, Abhilash; Jana, Subrata; Samal, Prasanjit

2018-04-01

The construction of meta generalized gradient approximations based on the density matrix expansion (DME) is considered as one of the most accurate techniques to design semilocal exchange energy functionals in two-dimensional density functional formalism. The exchange holes modeled using DME possess unique features that make it a superior entity. Parameterized semilocal exchange energy functionals based on the DME are proposed. The use of different forms of the momentum and flexible parameters is to subsume the non-uniform effects of the density in the newly constructed semilocal functionals. In addition to the exchange functionals, a suitable correlation functional is also constructed by working upon the local correlation functional developed for 2D homogeneous electron gas. The non-local effects are induced into the correlation functional by a parametric form of one of the newly constructed exchange energy functionals. The proposed functionals are applied to the parabolic quantum dots with a varying number of confined electrons and the confinement strength. The results obtained with the aforementioned functionals are quite satisfactory, which indicates why these are suitable for two-dimensional quantum systems.

Quantifying NMR relaxation correlation and exchange in articular cartilage with time domain analysis

NASA Astrophysics Data System (ADS)

Mailhiot, Sarah E.; Zong, Fangrong; Maneval, James E.; June, Ronald K.; Galvosas, Petrik; Seymour, Joseph D.

2018-02-01

Measured nuclear magnetic resonance (NMR) transverse relaxation data in articular cartilage has been shown to be multi-exponential and correlated to the health of the tissue. The observed relaxation rates are dependent on experimental parameters such as solvent, data acquisition methods, data analysis methods, and alignment to the magnetic field. In this study, we show that diffusive exchange occurs in porcine articular cartilage and impacts the observed relaxation rates in T1-T2 correlation experiments. By using time domain analysis of T2-T2 exchange spectroscopy, the diffusive exchange time can be quantified by measurements that use a single mixing time. Measured characteristic times for exchange are commensurate with T1 in this material and so impacts the observed T1 behavior. The approach used here allows for reliable quantification of NMR relaxation behavior in cartilage in the presence of diffusive fluid exchange between two environments.

Neutrinoless ββ decay mediated by the exchange of light and heavy neutrinos: the role of nuclear structure correlations

NASA Astrophysics Data System (ADS)

Menéndez, J.

2018-01-01

Neutrinoless β β decay nuclear matrix elements calculated with the shell model and energy-density functional theory typically disagree by more than a factor of two in the standard scenario of light-neutrino exchange. In contrast, for a decay mediated by sterile heavy neutrinos the deviations are reduced to about 50%, an uncertainty similar to the one due to short-range effects. We compare matrix elements in the light- and heavy-neutrino-exchange channels, exploring the radial, momentum transfer and angular momentum-parity matrix element distributions, and considering transitions that involve correlated and uncorrelated nuclear states. We argue that the shorter-range heavy-neutrino exchange is less sensitive to collective nuclear correlations, and that discrepancies in matrix elements are mostly due to the treatment of long-range correlations in many-body calculations. Our analysis supports previous studies suggesting that isoscalar pairing correlations, which affect mostly the longer-range part of the neutrinoless β β decay operator, are partially responsible for the differences between nuclear matrix elements in the standard light-neutrino-exchange mechanism.

Design and investigation of potential Sn-Te-P and Zr-Te-P class of Dirac materials

NASA Astrophysics Data System (ADS)

Sarswat, Prashant; Sarkar, Sayan; Free, Michael

A motivation of new Dirac materials design and synthesis by perturbing the symmetry, was explored by substitution of a Sn vacancy by P that maintains the intrinsic band inversion at the L point but also the direct bandgap shrinkage upon the incorporation of spin-orbit coupling. In a similar line of investigation, Zr-Te-P was also systematically studied. The synthesis of both Sn-Te-P and Zr-Te-P system of compounds resulted in the formation of long needles type crystals and the bulk porous deposits. The exotic morphology of the P-doped SnTe needles possesses the pierced surface throughout its extension. First principle based calculations were also carried out for these sets of compounds using General Gradient Approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. In order to ensure structural optimization, a limited memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) algorithm was employed and the total energy in PBE exchange-correlation functional was considered for the calculation of the formation energy per atom. The new modifications have a potential to establish the new class of Dirac materials ushering upon new frontiers of interest.

Equilibrium Molecular Thermodynamics from Kirkwood Sampling

PubMed Central

2015-01-01

We present two methods for barrierless equilibrium sampling of molecular systems based on the recently proposed Kirkwood method (J. Chem. Phys.2009, 130, 134102). Kirkwood sampling employs low-order correlations among internal coordinates of a molecule for random (or non-Markovian) sampling of the high dimensional conformational space. This is a geometrical sampling method independent of the potential energy surface. The first method is a variant of biased Monte Carlo, where Kirkwood sampling is used for generating trial Monte Carlo moves. Using this method, equilibrium distributions corresponding to different temperatures and potential energy functions can be generated from a given set of low-order correlations. Since Kirkwood samples are generated independently, this method is ideally suited for massively parallel distributed computing. The second approach is a variant of reservoir replica exchange, where Kirkwood sampling is used to construct a reservoir of conformations, which exchanges conformations with the replicas performing equilibrium sampling corresponding to different thermodynamic states. Coupling with the Kirkwood reservoir enhances sampling by facilitating global jumps in the conformational space. The efficiency of both methods depends on the overlap of the Kirkwood distribution with the target equilibrium distribution. We present proof-of-concept results for a model nine-atom linear molecule and alanine dipeptide. PMID:25915525

Analysis of Parent, Teacher, and Consultant Speech Exchanges and Educational Outcomes of Students With Autism During COMPASS Consultation.

PubMed

Ruble, Lisa; Birdwhistell, Jessie; Toland, Michael D; McGrew, John H

2011-01-01

The significant increase in the numbers of students with autism combined with the need for better trained teachers (National Research Council, 2001) call for research on the effectiveness of alternative methods, such as consultation, that have the potential to improve service delivery. Data from 2 randomized controlled single-blind trials indicate that an autism-specific consultation planning framework known as the collaborative model for promoting competence and success (COMPASS) is effective in increasing child Individual Education Programs (IEP) outcomes (Ruble, Dal-rymple, & McGrew, 2010; Ruble, McGrew, & Toland, 2011). In this study, we describe the verbal interactions, defined as speech acts and speech act exchanges that take place during COMPASS consultation, and examine the associations between speech exchanges and child outcomes. We applied the Psychosocial Processes Coding Scheme (Leaper, 1991) to code speech acts. Speech act exchanges were overwhelmingly affiliative, failed to show statistically significant relationships with child IEP outcomes and teacher adherence, but did correlate positively with IEP quality.

Analysis of Parent, Teacher, and Consultant Speech Exchanges and Educational Outcomes of Students With Autism During COMPASS Consultation

PubMed Central

RUBLE, LISA; BIRDWHISTELL, JESSIE; TOLAND, MICHAEL D.; MCGREW, JOHN H.

2011-01-01

The significant increase in the numbers of students with autism combined with the need for better trained teachers (National Research Council, 2001) call for research on the effectiveness of alternative methods, such as consultation, that have the potential to improve service delivery. Data from 2 randomized controlled single-blind trials indicate that an autism-specific consultation planning framework known as the collaborative model for promoting competence and success (COMPASS) is effective in increasing child Individual Education Programs (IEP) outcomes (Ruble, Dal-rymple, & McGrew, 2010; Ruble, McGrew, & Toland, 2011). In this study, we describe the verbal interactions, defined as speech acts and speech act exchanges that take place during COMPASS consultation, and examine the associations between speech exchanges and child outcomes. We applied the Psychosocial Processes Coding Scheme (Leaper, 1991) to code speech acts. Speech act exchanges were overwhelmingly affiliative, failed to show statistically significant relationships with child IEP outcomes and teacher adherence, but did correlate positively with IEP quality. PMID:22639523

Nursing staff and their team: Impact on intention to leave.

PubMed

Trybou, J; Malfait, S; Gemmel, P; Clays, E

2015-12-01

The aim was to examine the relationship between the quality of team-member exchange experienced by nursing staff and their intention to leave. Job satisfaction and affective organizational commitment are considered as mediators. While the shortage of nurses is a management and policy priority, few studies have studied the relationships between nursing staff and their team, key organizational attitudes, and intentions to leave the organization. A questionnaire was administered to 217 registered nurses and nurse assistants in Belgium. Data were collected in 2012. To analyse the data, descriptive statistics, correlation, regression and path analyses were conducted. Team-member exchange has a positive impact on nursing staff satisfaction and affective commitment. Job satisfaction and affective organizational commitment fully mediated the impact of team-member exchange on nursing staff's intention to leave. This study illustrates the potential benefits of the positive influence of team-member exchange on key organizational attitudes of nursing staff, and the negative influence on intention to leave through affective commitment and job satisfaction. © 2015 International Council of Nurses.

A dynamic analysis of S&P 500, FTSE 100 and EURO STOXX 50 indices under different exchange rates

PubMed Central

Chen, Yanhua; Mantegna, Rosario N.; Zuev, Konstantin M.

2018-01-01

In this study, we assess the dynamic evolution of short-term correlation, long-term cointegration and Error Correction Model (hereafter referred to as ECM)-based long-term Granger causality between each pair of US, UK, and Eurozone stock markets from 1980 to 2015 using the rolling-window technique. A comparative analysis of pairwise dynamic integration and causality of stock markets, measured in common and domestic currency terms, is conducted to evaluate comprehensively how exchange rate fluctuations affect the time-varying integration among the S&P 500, FTSE 100 and EURO STOXX 50 indices. The results obtained show that the dynamic correlation, cointegration and ECM-based long-run Granger causality vary significantly over the whole sample period. The degree of dynamic correlation and cointegration between pairs of stock markets rises in periods of high volatility and uncertainty, especially under the influence of economic, financial and political shocks. Meanwhile, we observe the weaker and decreasing correlation and cointegration among the three developed stock markets during the recovery periods. Interestingly, the most persistent and significant cointegration among the three developed stock markets exists during the 2007–09 global financial crisis. Finally, the exchange rate fluctuations, also influence the dynamic integration and causality between all pairs of stock indices, with that influence increasing under the local currency terms. Our results suggest that the potential for diversifying risk by investing in the US, UK and Eurozone stock markets is limited during the periods of economic, financial and political shocks. PMID:29529092

Multifractal detrended Cross Correlation Analysis of Foreign Exchange and SENSEX fluctuation in Indian perspective

NASA Astrophysics Data System (ADS)

Dutta, Srimonti; Ghosh, Dipak; Chatterjee, Sucharita

2016-12-01

The manuscript studies autocorrelation and cross correlation of SENSEX fluctuations and Forex Exchange Rate in respect to Indian scenario. Multifractal detrended fluctuation analysis (MFDFA) and multifractal detrended cross correlation analysis (MFDXA) were employed to study the correlation between the two series. It was observed that the two series are strongly cross correlated. The change of degree of cross correlation with time was studied and the results are interpreted qualitatively.

From Nothing to Something II: Nonlinear Systems via Consistent Correlated Bang

NASA Astrophysics Data System (ADS)

Lou, Sen-Yue

2017-06-01

Chinese ancient sage Laozi said everything comes from \\emph{\\bf \\em "nothing"}. \\rm In the first letter (Chin. Phys. Lett. 30 (2013) 080202), infinitely many discrete integrable systems have been obtained from "nothing" via simple principles (Dao). In this second letter, a new idea, the consistent correlated bang, is introduced to obtain nonlinear dynamic systems including some integrable ones such as the continuous nonlinear Schr\\"odinger equation (NLS), the (potential) Korteweg de Vries (KdV) equation, the (potential) Kadomtsev-Petviashvili (KP) equation and the sine-Gordon (sG) equation. These nonlinear systems are derived from nothing via suitable "Dao", the shifted parity, the charge conjugate, the delayed time reversal, the shifted exchange, the shifted-parity-rotation and so on.

Concerted hydrogen atom exchange between three HF molecules

NASA Technical Reports Server (NTRS)

Komornicki, Andrew; Dixon, David A.; Taylor, Peter R.

1992-01-01

We have investigated the termolecular reaction involving concerted hydrogen exchange between three HF molecules, with particular emphasis on the effects of correlation at the various stationary points along the reaction. Using an extended basis, we have located the geometries of the stable hydrogen-bonded trimer, which is of C(sub 3h) symmetry, and the transition state for hydrogen exchange, which is of D(sub 3h) symmetry. The energies of the exchange reation were then evaluated at the correlated level, using a large atomic natural orbital basis and correlating all valence electrons. Several correlation treatments were used, namely, configration interaction with single and double excitations, coupled-pair functional, and coupled-cluster methods. We are thus able to measure the effect of accounting for size-extensivity. Zero-point corrections to the correlated level energetics were determined using analytic second derivative techniques at the SCF level. Our best calculations, which include the effects of connected triple excitations in the coupled-cluster procedure, indicate that the trimer is bound by 9 +/- 1 kcal/mol relative to three separate monomers, in excellent agreement with previous estimates. The barrier to concerted hydrogen exchange is 15 kcal/mol above the trimer, or only 4.7 kcal/mol above three separated monomers. Thus the barrier to hydrogen exchange between HF molecules via this termolecular process is very low.

Short-range second order screened exchange correction to RPA correlation energies

NASA Astrophysics Data System (ADS)

Beuerle, Matthias; Ochsenfeld, Christian

2017-11-01

Direct random phase approximation (RPA) correlation energies have become increasingly popular as a post-Kohn-Sham correction, due to significant improvements over DFT calculations for properties such as long-range dispersion effects, which are problematic in conventional density functional theory. On the other hand, RPA still has various weaknesses, such as unsatisfactory results for non-isogyric processes. This can in parts be attributed to the self-correlation present in RPA correlation energies, leading to significant self-interaction errors. Therefore a variety of schemes have been devised to include exchange in the calculation of RPA correlation energies in order to correct this shortcoming. One of the most popular RPA plus exchange schemes is the second order screened exchange (SOSEX) correction. RPA + SOSEX delivers more accurate absolute correlation energies and also improves upon RPA for non-isogyric processes. On the other hand, RPA + SOSEX barrier heights are worse than those obtained from plain RPA calculations. To combine the benefits of RPA correlation energies and the SOSEX correction, we introduce a short-range RPA + SOSEX correction. Proof of concept calculations and benchmarks showing the advantages of our method are presented.

Short-range second order screened exchange correction to RPA correlation energies.

PubMed

Beuerle, Matthias; Ochsenfeld, Christian

2017-11-28

Direct random phase approximation (RPA) correlation energies have become increasingly popular as a post-Kohn-Sham correction, due to significant improvements over DFT calculations for properties such as long-range dispersion effects, which are problematic in conventional density functional theory. On the other hand, RPA still has various weaknesses, such as unsatisfactory results for non-isogyric processes. This can in parts be attributed to the self-correlation present in RPA correlation energies, leading to significant self-interaction errors. Therefore a variety of schemes have been devised to include exchange in the calculation of RPA correlation energies in order to correct this shortcoming. One of the most popular RPA plus exchange schemes is the second order screened exchange (SOSEX) correction. RPA + SOSEX delivers more accurate absolute correlation energies and also improves upon RPA for non-isogyric processes. On the other hand, RPA + SOSEX barrier heights are worse than those obtained from plain RPA calculations. To combine the benefits of RPA correlation energies and the SOSEX correction, we introduce a short-range RPA + SOSEX correction. Proof of concept calculations and benchmarks showing the advantages of our method are presented.

Asymmetry in band widening and quasiparticle lifetimes in SrVO3: Competition between screened exchange and local correlations from combined G W and dynamical mean-field theory G W + DMFT

NASA Astrophysics Data System (ADS)

Tomczak, Jan M.; Casula, M.; Miyake, T.; Biermann, S.

2014-10-01

The very first dynamical implementation of the combined GW and dynamical mean-field scheme "G W + DMFT " for a real material was achieved recently [Tomczak et al., Europhys. Lett. 100, 67001 (2012), 10.1209/0295-5075/100/67001], and applied to the ternary transition metal oxide SrVO3. Here, we review and extend that work, giving not only a detailed account of full G W + DMFT calculations, but also discussing and testing simplified approximate schemes. We give insights into the nature of exchange and correlation effects: dynamical renormalizations in the Fermi liquid regime of SrVO3 are essentially local, and nonlocal correlations mainly act to screen the Fock exchange term. The latter substantially widens the quasiparticle band structure, while the band narrowing induced by the former is accompanied by a spectral weight transfer to higher energies. Most interestingly, the exchange broadening is more pronounced in the unoccupied part of the spectrum than in the occupied one. In addition, shorter lifetimes for unoccupied states further contribute to making the corrections to the Kohn-Sham band structure asymmetric with respect to the chemical potential. As a result, the G W + DMFT electronic structure of SrVO3 resembles the conventional density functional based dynamical mean-field (DFT + DMFT ) description for occupied states but is profoundly modified in the empty part. Our work leads to a reinterpretation of inverse photoemission spectroscopy (IPES) data. Indeed, we assign a prominent peak at about 2.7 eV dominantly to eg states, rather than to an upper Hubbard band of t2 g character. Similar surprises can be expected for other transition metal oxides. This prediction urgently calls for more detailed investigations of conduction band states in correlated materials.

[Effect of air temperature and rainfall on wetland ecosystem CO2 exchange in China].

PubMed

Chu, Xiao-jing; Han, Guang-xuan

2015-10-01

Wetland can be a potential efficient sink to reduce global warming due to its higher primary productivity and lower carbon decomposition rate. While there has been a series progress on the influence mechanism of ecosystem CO2 exchange over China' s wetlands, a systematic metaanalysis of data still needs to be improved. We compiled data of ecosystem CO2 exchange of 21 typical wetland vegetation types in China from 29 papers and carried out an integrated analysis of air temperature and precipitation effects on net ecosystem CO2 exchange (NEE), ecosystem respiration (Reco), gross primary productivity (GPP), the response of NEE to PAR, and the response of Reco to temperature. The results showed that there were significant responses (P<0.05) of NEE (R2 = 50%, R2=57%), GPP (R2 = 60%, R2 = 50%) Reco (R2 = 44%, R2=50%) with increasing air temperature and enhanced precipitation on the annual scale. On the growing season scale, air temperature accounted for 50% of the spatial variation of NEE, 36% of GPP and 19% of Reco, respectively. Both NEE (R2 = 33%) and GPP (R2 =25%) were correlated positively with precipitation (P<0.05). However, the relationship between Reco and precipitation was not significant (P>0.05). Across different Chinese wetlands, both precipitation and temperature had no significant effect on apparent quantum yield (α) or ecosystem respiration in the daytime (Reco,day, P>0.05). The maximum photosynthesis rate (Amax) was remarkably correlated with precipitation (P <0.01), but not with air temperature. Besides, there was no significant correlation between basal respiration (Rref) and precipitation (P>0.05). Precipitation was negatively correlated with temperature sensitivity of Reco (Q10, P<0.05). Furthermore, temperature accounted for 35% and 46% of the variations in temperature sensitivity of Reco (Q10) and basal respiration (Rref P<0.05), respectively.

Triangular Arbitrage as an Interaction in Foreign Exchange Markets

NASA Astrophysics Data System (ADS)

Aiba, Yukihiro; Hatano, Naomichi

Analyzing correlation in financial time series is a topic of considerable interest [1]-[17]. In the foreign exchange market, a correlation among the exchange rates can be generated by a triangular arbitrage transaction. The purpose of this article is to review our recent study [18]-[23] on modeling the interaction generated by the triangular arbitrage.

Bonding in the first-row diatomic molecules within the local spin-density approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Painter, G.S.; Averill, F.W.

1982-08-15

The Hohenberg-Kohn-Sham density-functional equations in the local spin-density approximation (LSDA) have been solved with essentially no loss of accuracy for dimers of the first row of the Periodic Table with the use of a fully-self-consistent spin-polarized Gaussian-orbital approach. Spectroscopic constants (binding energies, equilibrium separations, and ground-state vibrational frequencies) have been derived from the calculated potential-energy curves. Intercomparison of results obtained using the exchange-correlation functionals of Slater (scaled exchange or X..cap alpha..), Gunnarsson and Lundqvist (GL), and Vosko, Wilk, and Nusair (VWN) permits assessment of the relative merits of each and serves to identify general shortcomings in the LSDA. Basic trendsmore » are similar for each functional, but the treatment of the spin dependence of the exchange-correlation energy in the GL and VWN functionals yields a variation of the binding energy across the series which is more systematic than that in the X..cap alpha.. approximation. Agreement between the present results and those of Dunlap, Connolly, and Sabin in the X..cap alpha.., approximation confirms the accuracy of the variational charge-density-fit procedure used in the latter work. The refinements in correlation treatment within the VWN functional are reflected in improvements in binding energies which are only slight for most dimers in the series. This behavior is attributed to the error remaining in the exchange channel within the LSDA and demonstrates the necessity for self-interaction corrections for more accurate binding-energy determinations. Within the current LSDA, absolute accuracies of the VWN functional for the first-row dimers are within 2.3 eV for binding energies, 0.07 a.u. for bond lengths, and approx.200 cm/sup -1/ for vibrational frequencies.« less

Wavelets in electronic structure calculations

NASA Astrophysics Data System (ADS)

Modisette, Jason Perry

1997-09-01

Ab initio calculations of the electronic structure of bulk materials and large clusters are not possible on today's computers using current techniques. The storage and diagonalization of the Hamiltonian matrix are the limiting factors in both memory and execution time. The scaling of both quantities with problem size can be reduced by using approximate diagonalization or direct minimization of the total energy with respect to the density matrix in conjunction with a localized basis. Wavelet basis members are much more localized than conventional bases such as Gaussians or numerical atomic orbitals. This localization leads to sparse matrices of the operators that arise in SCF multi-electron calculations. We have investigated the construction of the one-electron Hamiltonian, and also the effective one- electron Hamiltonians that appear in density-functional and Hartree-Fock theories. We develop efficient methods for the generation of the kinetic energy and potential matrices, the Hartree and exchange potentials, and the local exchange-correlation potential of the LDA. Test calculations are performed on one-electron problems with a variety of potentials in one and three dimensions.

Band Formation and Ocean-Surface Interaction on Europa and Ganymede

NASA Astrophysics Data System (ADS)

Howell, Samuel M.; Pappalardo, Robert T.

2018-05-01

Geologic activity in the outer H2O ice shells of Europa and Ganymede, Galilean moons of Jupiter, may facilitate material exchange between global water oceans and the icy surface, fundamentally affecting potential habitability and the future search for life. Spacecraft imagery reveals surfaces rich with tectonic bands, predominantly attributed to the extension of brittle ice overlaying a convecting ice layer. However, the details of band-forming processes and links to potential ocean-surface exchange have remained elusive. We simulate ice shell faulting and convection with two-dimensional numerical models and track the movement of "fossil" ocean material frozen into the base of the ice shell and deformed through geologic time. We find that distinct band types form within a spectrum of extensional terrains correlated to lithosphere strength, governed by lithosphere thickness and cohesion. Furthermore, we find that smooth bands formed in weak lithosphere promote exposure of fossil ocean material at the surface.

The relationship between leaf water status, gas exchange, and spectral reflectance in cotton leaves

NASA Technical Reports Server (NTRS)

Bowman, William D.

1989-01-01

Measurements of leaf spectral reflectance, the components of water potential, and leaf gas exchanges as a function of leaf water content were made to evaluate the use of NIR reflectance as an indicator of plant water status. Significant correlations were determined between spectral reflectance at 810 nm, 1665 nm, and 2210 nm and leaf relative water content, total water potential, and turgor pressure. However, the slopes of these relationships were relatively shallow and, when evaluated over the range of leaf water contents in which physiological activity occurs (e.g., photosynthesis), had lower r-squared values, and some relationships were not statistically significant. NIR reflectance varied primarily as a function of leaf water content, and not independently as a function of turgor pressure, which is a sensitive indicator of leaf water status. The limitations of this approach to measuring plant water stress are discussed.

The double-soft limit in cosmological correlation functions and graviton exchange effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alinea, Allan L.; Kubota, Takahiro; Misumi, Nobuhiko, E-mail: alinea@het.phys.sci.osaka-u.ac.jp, E-mail: kubota@celas.osaka-u.ac.jp, E-mail: misumi.nobu@gmail.com

The graviton exchange effect on cosmological correlation functions is examined by employing the double-soft limit technique. A new relation among correlation functions that contain the effects due to graviton exchange diagrams in addition to those due to scalar-exchange and scalar-contact-interaction, is derived by using the background field method and independently by the method of Ward identities associated with dilatation symmetry. We compare these three terms, putting small values for the slow-roll parameters and (1− n {sub s} ) ≈ 0.042, where n {sub s} is the scalar spectral index. It is argued that the graviton exchange effects are more dominantmore » than the other two and could be observed in the trispectrum in the double-soft limit. Our observation strengthens the previous work by Seery, Sloth and Vernizzi, in which it has been argued that the graviton exchange dominates in the counter-collinear limit for single field slow-roll inflation.« less

Ab initio DFT+U study of He atom incorporation into UO(2) crystals.

PubMed

Gryaznov, Denis; Heifets, Eugene; Kotomin, Eugene

2009-09-07

We present and discuss results of the density functional theory (DFT) for perfect UO(2) crystals with He atoms in octahedral interstitial positions therein. We have calculated basic bulk crystal properties and He incorporation energies into the low temperature anti-ferromagnetic UO(2) phase using several exchange-correlation functionals within the spin-polarized local density (LDA) and generalized gradient (GGA) approximations. In all DFT calculations we included the on-site correlation corrections using the Hubbard model (DFT+U approach). We analysed a potential crystalline symmetry reduction from tetragonal down to orthorhombic structure and confirmed the presence of the Jahn-Teller effect in a perfect UO(2). We discuss also the problem of a conducting electronic state arising when He is placed into a tetragonal antiferromagnetic phase of UO(2) commonly used in defect modelling. Consequently, we found a specific monoclinic lattice distortion which allowed us to restore the semiconducting state and properly estimate He incorporation energies. Unlike the bulk properties, the He incorporation energy strongly depends on several factors, including the supercell size, the use of spin polarization, the exchange-correlation functionals and on-site correlation corrections. We compare our results for the He incorporation with the previous shell model and ab initio DFT calculations.

Exchange-Correlation Effects for Noncovalent Interactions in Density Functional Theory.

PubMed

Otero-de-la-Roza, A; DiLabio, Gino A; Johnson, Erin R

2016-07-12

In this article, we develop an understanding of how errors from exchange-correlation functionals affect the modeling of noncovalent interactions in dispersion-corrected density-functional theory. Computed CCSD(T) reference binding energies for a collection of small-molecule clusters are decomposed via a molecular many-body expansion and are used to benchmark density-functional approximations, including the effect of semilocal approximation, exact-exchange admixture, and range separation. Three sources of error are identified. Repulsion error arises from the choice of semilocal functional approximation. This error affects intermolecular repulsions and is present in all n-body exchange-repulsion energies with a sign that alternates with the order n of the interaction. Delocalization error is independent of the choice of semilocal functional but does depend on the exact exchange fraction. Delocalization error misrepresents the induction energies, leading to overbinding in all induction n-body terms, and underestimates the electrostatic contribution to the 2-body energies. Deformation error affects only monomer relaxation (deformation) energies and behaves similarly to bond-dissociation energy errors. Delocalization and deformation errors affect systems with significant intermolecular orbital interactions (e.g., hydrogen- and halogen-bonded systems), whereas repulsion error is ubiquitous. Many-body errors from the underlying exchange-correlation functional greatly exceed in general the magnitude of the many-body dispersion energy term. A functional built to accurately model noncovalent interactions must contain a dispersion correction, semilocal exchange, and correlation components that minimize the repulsion error independently and must also incorporate exact exchange in such a way that delocalization error is absent.

Nonadiabatic Dynamics in Single-Electron Tunneling Devices with Time-Dependent Density-Functional Theory

NASA Astrophysics Data System (ADS)

Dittmann, Niklas; Splettstoesser, Janine; Helbig, Nicole

2018-04-01

We simulate the dynamics of a single-electron source, modeled as a quantum dot with on-site Coulomb interaction and tunnel coupling to an adjacent lead in time-dependent density-functional theory. Based on this system, we develop a time-nonlocal exchange-correlation potential by exploiting analogies with quantum-transport theory. The time nonlocality manifests itself in a dynamical potential step. We explicitly link the time evolution of the dynamical step to physical relaxation timescales of the electron dynamics. Finally, we discuss prospects for simulations of larger mesoscopic systems.

Nonadiabatic Dynamics in Single-Electron Tunneling Devices with Time-Dependent Density-Functional Theory.

PubMed

Dittmann, Niklas; Splettstoesser, Janine; Helbig, Nicole

2018-04-13

We simulate the dynamics of a single-electron source, modeled as a quantum dot with on-site Coulomb interaction and tunnel coupling to an adjacent lead in time-dependent density-functional theory. Based on this system, we develop a time-nonlocal exchange-correlation potential by exploiting analogies with quantum-transport theory. The time nonlocality manifests itself in a dynamical potential step. We explicitly link the time evolution of the dynamical step to physical relaxation timescales of the electron dynamics. Finally, we discuss prospects for simulations of larger mesoscopic systems.

Correlated Light-Matter Interactions in Cavity QED

NASA Astrophysics Data System (ADS)

Flick, Johannes; Pellegrini, Camilla; Ruggenthaler, Michael; Appel, Heiko; Tokatly, Ilya; Rubio, Angel

2015-03-01

In the last decade, time-dependent density functional theory (TDDFT) has been successfully applied to a large variety of problems, such as calculations of absorption spectra, excitation energies, or dynamics in strong laser fields. Recently, we have generalized TDDFT to also describe electron-photon systems (QED-TDDFT). Here, matter and light are treated on an equal quantized footing. In this work, we present the first numerical calculations in the framework of QED-TDDFT. We show exact solutions for fully quantized prototype systems consisting of atoms or molecules placed in optical high-Q cavities and coupled to quantized electromagnetic modes. We focus on the electron-photon exchange-correlation (xc) contribution by calculating exact Kohn-Sham potentials using fixed-point inversions and present the performance of the first approximated xc-potential based on an optimized effective potential (OEP) approach. Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, and Fritz-Haber-Institut der MPG, Berlin

Orbital dependent functionals: An atom projector augmented wave method implementation

NASA Astrophysics Data System (ADS)

Xu, Xiao

This thesis explores the formulation and numerical implementation of orbital dependent exchange-correlation functionals within electronic structure calculations. These orbital-dependent exchange-correlation functionals have recently received renewed attention as a means to improve the physical representation of electron interactions within electronic structure calculations. In particular, electron self-interaction terms can be avoided. In this thesis, an orbital-dependent functional is considered in the context of Hartree-Fock (HF) theory as well as the Optimized Effective Potential (OEP) method and the approximate OEP method developed by Krieger, Li, and Iafrate, known as the KLI approximation. In this thesis, the Fock exchange term is used as a simple well-defined example of an orbital-dependent functional. The Projected Augmented Wave (PAW) method developed by P. E. Blochl has proven to be accurate and efficient for electronic structure calculations for local and semi-local functions because of its accurate evaluation of interaction integrals by controlling multiple moments. We have extended the PAW method to treat orbital-dependent functionals in Hartree-Fock theory and the Optimized Effective Potential method, particularly in the KLI approximation. In the course of study we develop a frozen-core orbital approximation that accurately treats the core electron contributions for above three methods. The main part of the thesis focuses on the treatment of spherical atoms. We have investigated the behavior of PAW-Hartree Fock and PAW-KLI basis, projector, and pseudopotential functions for several elements throughout the periodic table. We have also extended the formalism to the treatment of solids in a plane wave basis and implemented PWPAW-KLI code, which will appear in future publications.

The Fine-Scale Functional Correlation of Striate Cortex in Sighted and Blind People

PubMed Central

Butt, Omar H.; Benson, Noah C.; Datta, Ritobrato

2013-01-01

To what extent are spontaneous neural signals within striate cortex organized by vision? We examined the fine-scale pattern of striate cortex correlations within and between hemispheres in rest-state BOLD fMRI data from sighted and blind people. In the sighted, we find that corticocortico correlation is well modeled as a Gaussian point-spread function across millimeters of striate cortical surface, rather than degrees of visual angle. Blindness produces a subtle change in the pattern of fine-scale striate correlations between hemispheres. Across participants blind before the age of 18, the degree of pattern alteration covaries with the strength of long-range correlation between left striate cortex and Broca's area. This suggests that early blindness exchanges local, vision-driven pattern synchrony of the striate cortices for long-range functional correlations potentially related to cross-modal representation. PMID:24107953

A study of accurate exchange-correlation functionals through adiabatic connection

NASA Astrophysics Data System (ADS)

Singh, Rabeet; Harbola, Manoj K.

2017-10-01

A systematic way of improving exchange-correlation energy functionals of density functional theory has been to make them satisfy more and more exact relations. Starting from the initial generalized gradient approximation (GGA) functionals, this has culminated into the recently proposed SCAN (strongly constrained and appropriately normed) functional that satisfies several known constraints and is appropriately normed. The ultimate test for the functionals developed is the accuracy of energy calculated by employing them. In this paper, we test these exchange-correlation functionals—the GGA hybrid functionals B3LYP and PBE0 and the meta-GGA functional SCAN—from a different perspective. We study how accurately these functionals reproduce the exchange-correlation energy when electron-electron interaction is scaled as αVee with α varying between 0 and 1. Our study reveals interesting comparison between these functionals and the associated difference Tc between the interacting and the non-interacting kinetic energy for the same density.

Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy

PubMed Central

Zheng, Jie; Sheng, Wenchao; Zhuang, Zhongbin; Xu, Bingjun; Yan, Yushan

2016-01-01

Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER. PMID:27034988

Universal dependence of hydrogen oxidation and evolution reaction activity of platinum-group metals on pH and hydrogen binding energy.

PubMed

Zheng, Jie; Sheng, Wenchao; Zhuang, Zhongbin; Xu, Bingjun; Yan, Yushan

2016-03-01

Understanding how pH affects the activity of hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is key to developing active, stable, and affordable HOR/HER catalysts for hydroxide exchange membrane fuel cells and electrolyzers. A common linear correlation between hydrogen binding energy (HBE) and pH is observed for four supported platinum-group metal catalysts (Pt/C, Ir/C, Pd/C, and Rh/C) over a broad pH range (0 to 13), suggesting that the pH dependence of HBE is metal-independent. A universal correlation between exchange current density and HBE is also observed on the four metals, indicating that they may share the same elementary steps and rate-determining steps and that the HBE is the dominant descriptor for HOR/HER activities. The onset potential of CO stripping on the four metals decreases with pH, indicating a stronger OH adsorption, which provides evidence against the promoting effect of adsorbed OH on HOR/HER.

Hartree-Fock theory of the inhomogeneous electron gas at a jellium metal surface: Rigorous upper bounds to the surface energy and accurate work functions

NASA Astrophysics Data System (ADS)

Sahni, V.; Ma, C. Q.

1980-12-01

The inhomogeneous electron gas at a jellium metal surface is studied in the Hartree-Fock approximation by Kohn-Sham density functional theory. Rigorous upper bounds to the surface energy are derived by application of the Rayleigh-Ritz variational principle for the energy, the surface kinetic, electrostatic, and nonlocal exchange energy functionals being determined exactly for the accurate linear-potential model electronic wave functions. The densities obtained by the energy minimization constraint are then employed to determine work-function results via the variationally accurate "displaced-profile change-in-self-consistent-field" expression. The theoretical basis of this non-self-consistent procedure and its demonstrated accuracy for the fully correlated system (as treated within the local-density approximation for exchange and correlation) leads us to conclude these results for the surface energies and work functions to be essentially exact. Work-function values are also determined by the Koopmans'-theorem expression, both for these densities as well as for those obtained by satisfaction of the constraint set on the electrostatic potential by the Budd-Vannimenus theorem. The use of the Hartree-Fock results in the accurate estimation of correlation-effect contributions to these surface properties of the nonuniform electron gas is also indicated. In addition, the original work and approximations made by Bardeen in this attempt at a solution of the Hartree-Fock problem are briefly reviewed in order to contrast with the present work.

Kinetics of oxygen surface exchange on epitaxial Ruddlesden–Popper phases and correlations to first-principles descriptors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Yueh -Lin; Wang, Xiao Renshaw; Lee, Ho Nyung

2015-12-17

Through alignment of theoretical modeling with experimental measurements of oxygen surface-exchange kinetics on (001)-oriented La 2–xSr xMO 4+δ (M = Co, Ni, Cu) thin films, we demonstrate here the capability of the theoretical bulk O 2p-band centers to correlate with oxygen surface-exchange kinetics of the Ruddlesden–Popper oxide (RP 214) (001)-oriented thin films. In addition, we demonstrate that the bulk O 2p-band centers can also correlate with the experimental activation energies for bulk oxygen transport and oxygen surface exchange of both the RP 214 and the perovskite polycrystalline materials reported in the literature, indicating the effectiveness of the bulk O 2p-bandmore » centers in describing the associated energetics and kinetics. Here, we propose that the opposite slopes of the bulk O 2p-band center correlations between the RP 214 and the perovskite materials are due to the intrinsic mechanistic differences of their oxygen surface-exchange kinetics bulk anionic transport.« less

Seasonal Variations of Indoor Microbial Exposures and Their Relation to Temperature, Relative Humidity, and Air Exchange Rate

PubMed Central

Bekö, Gabriel; Timm, Michael; Gustavsen, Sine; Hansen, Erik Wind

2012-01-01

Indoor microbial exposure has been related to adverse pulmonary health effects. Exposure assessment is not standardized, and various factors may affect the measured exposure. The aim of this study was to investigate the seasonal variation of selected microbial exposures and their associations with temperature, relative humidity, and air exchange rates in Danish homes. Airborne inhalable dust was sampled in five Danish homes throughout the four seasons of 1 year (indoors, n = 127; outdoors, n = 37). Measurements included culturable fungi and bacteria, endotoxin, N-acetyl-beta-d-glucosaminidase, total inflammatory potential, particles (0.75 to 15 μm), temperature, relative humidity, and air exchange rates. Significant seasonal variation was found for all indoor microbial exposures, excluding endotoxin. Indoor fungi peaked in summer (median, 235 CFU/m3) and were lowest in winter (median, 26 CFU/m3). Indoor bacteria peaked in spring (median, 2,165 CFU/m3) and were lowest in summer (median, 240 CFU/m3). Concentrations of fungi were predominately higher outdoors than indoors, whereas bacteria, endotoxin, and inhalable dust concentrations were highest indoors. Bacteria and endotoxin correlated with the mass of inhalable dust and number of particles. Temperature and air exchange rates were positively associated with fungi and N-acetyl-beta-d-glucosaminidase and negatively with bacteria and the total inflammatory potential. Although temperature, relative humidity, and air exchange rates were significantly associated with several indoor microbial exposures, they could not fully explain the observed seasonal variations when tested in a mixed statistical model. In conclusion, the season significantly affects indoor microbial exposures, which are influenced by temperature, relative humidity, and air exchange rates. PMID:23001651

[Correlation between gaseous exchange rate, body temperature, and mitochondrial protein content in the liver of mice].

PubMed

Muradian, Kh K; Utko, N O; Mozzhukhina, T H; Pishel', I M; Litoshenko, O Ia; Bezrukov, V V; Fraĭfel'd, V E

2002-01-01

Correlative and regressive relations between the gaseous exchange, thermoregulation and mitochondrial protein content were analyzed by two- and three-dimensional statistics in mice. It has been shown that the pair wise linear methods of analysis did not reveal any significant correlation between the parameters under exploration. However, it became evident at three-dimensional and non-linear plotting for which the coefficients of multivariable correlation reached and even exceeded 0.7-0.8. The calculations based on partial differentiation of the multivariable regression equations allow to conclude that at certain values of VO2, VCO2 and body temperature negative relations between the systems of gaseous exchange and thermoregulation become dominating.

Electronic and magnetic properties of double perovskite Sr2CoUO6: Heisenberg model

NASA Astrophysics Data System (ADS)

Nid-bahami, A.; Ahmed, S. Sidi; Ait-Tamerd, M.; Zaari, H.; El Kenz, A.; Benyoussef, A.

2018-01-01

This work will be focused on the electronic and magnetic properties of Sr2CoUO6 (SCUO) using ab-initio calculations and Monte Carlo Simulation (MCS). Firstly, we calculate the exchange coupling and the crystal field, then, the electronic and magnetic properties will be studied, using the full-potential linearized augmented plane wave (FP-LAPW) method, as implemented in the Wien2k code. This method employing the generalized gradient approximation (GGA) for exchange-correlation term. The half-metallic ferromagnetic nature implies a potential application of this new compound in spintronics devices. Also, we have presented the results of the band structures and densities of states for the two up and down spin polarizations. The exchange coupling and the crystal field calculated are J = 0 . 567 meV and δ = 0 . 559meV, and total spin magnetic moments is 2.96 μB closed to experimental values 3 μB. Secondly, we have presented the results for the magnetization and the susceptibility as a function of temperature. Finally, we obtain the critical temperature T = 9 . 20 K by MCS in good agreement with the experimental value.

Strong-field ionization of Li and Be: a time-dependent density functional theory with self-interaction correction

NASA Astrophysics Data System (ADS)

Telnov, Dmitry A.; Heslar, John T.; Chu, Shih-I.

2011-11-01

In the framework of the time-dependent density functional theory, we have performed 3D calculations of multiphoton ionization of Li and Be atoms by strong near-infrared laser fields. The results for the intensity-dependent probabilities of single and double ionization are presented. We make use of the time-dependent Krieger-Li-Iafrate exchange-correlation potential with self-interaction correction (TD-KLI-SIC). Such a potential possesses an integer discontinuity which improves description of the ionization process. However, we have found that the discontinuity of the TD-KLI-SIC potential is not sufficient to reproduce characteristic feature of double ionization.

Understanding ferromagnetism and optical absorption in 3d transition metal-doped cubic ZrO{sub 2} with the modified Becke-Johnson exchange-correlation functional

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boujnah, M.; Zaari, H.; El Kenz, A., E-mail: elkenz@fsr.ac.ma

The electronic structure, magnetic, and optical properties in cubic crystalline phase of Zr{sub 1−x}TM{sub x}O{sub 2} (TM = V, Mn, Fe, and Co) at x = 6.25% are studied using density functional theory with the Generalized Gradient Approximation and the modified Becke-Johnson of the exchange-correlation energy and potential. In our calculations, the zirconia is a p-type semiconductor and has a large band gap. We evaluated the possibility of long-range magnetic order for transition metal ions substituting Zr. Our results show that ferromagnetism is the ground state in V, Mn, and Fe-doped ZrO{sub 2} and have a high value of energy in Mn-doped ZrO{sub 2}.more » However, in Co-doped ZrO{sub 2}, antiferromagnetic ordering is more stable than the ferromagnetic one. The exchange interaction mechanism has been discussed to explain the responsible of this stability. Moreover, it has been found that the V, Mn, and Fe transition metals provide half-metallic properties considered to be the leading cause, responsible for ferromagnetism. Furthermore, the optical absorption spectra in the TM -doped cubic ZrO{sub 2} are investigated.« less

Quantitative Chemical Exchange Saturation Transfer MRI of Intervertebral Disc in a Porcine Model

PubMed Central

Zhou, Zhengwei; Bez, Maxim; Tawackoli, Wafa; Giaconi, Joseph; Sheyn, Dmitriy; de Mel, Sandra; Maya, Marcel M.; Pressman, Barry D.; Gazit, Zulma; Pelled, Gadi; Gazit, Dan; Li, Debiao

2017-01-01

Purpose Previous studies have associated low pH in interver-tebral discs (IVDs) with discogenic back pain. The purpose of this study was to determine whether quantitative CEST (qCEST) MRI can be used to detect pH changes in IVDs in vivo. Methods The exchange rate ksw between glycosaminoglycan (GAG) protons and water protons was determined from qCEST analysis. Its dependence on pH value was investigated in GAG phantoms with varying pH and concentrations. The relationship between ksw and pH was studied further in vivo in a porcine model on a 3T MR scanner and validated using a pH meter. Sodium lactate was injected into the IVDs to induce various pH values within the discs ranging from 5 to 7. Results Phantom and animal results revealed that ksw measured using qCEST MRI is highly correlated with pH level. In the animal studies, the relationship can be described as ksw =9.2 × 106 × 10−pH + 196.9, R2 = 0.7883. Conclusion The exchange rate between GAG and water protons determined from qCEST MRI is closely correlated with pH value. This technique has the potential to noninvasively measure pH in the IVDs of patients with discogenic pain. PMID:27670140

Lactate Chemical Exchange Saturation Transfer (LATEST) Imaging in vivo A Biomarker for LDH Activity.

PubMed

DeBrosse, Catherine; Nanga, Ravi Prakash Reddy; Bagga, Puneet; Nath, Kavindra; Haris, Mohammad; Marincola, Francesco; Schnall, Mitchell D; Hariharan, Hari; Reddy, Ravinder

2016-01-22

Non-invasive imaging of lactate is of enormous significance in cancer and metabolic disorders where glycolysis dominates. Here, for the first time, we describe a chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) method (LATEST), based on the exchange between lactate hydroxyl proton and bulk water protons to image lactate with high spatial resolution. We demonstrate the feasibility of imaging lactate with LATEST in lactate phantoms under physiological conditions, in a mouse model of lymphoma tumors, and in skeletal muscle of healthy human subjects pre- and post-exercise. The method is validated by measuring LATEST changes in lymphoma tumors pre- and post-infusion of pyruvate and correlating them with lactate determined from multiple quantum filtered proton magnetic resonance spectroscopy (SEL-MQC (1)H-MRS). Similarly, dynamic LATEST changes in exercising human skeletal muscle are correlated with lactate determined from SEL-MQC (1)H-MRS. The LATEST method does not involve injection of radioactive isotopes or labeled metabolites. It has over two orders of magnitude higher sensitivity compared to conventional (1)H-MRS. It is anticipated that this technique will have a wide range of applications including diagnosis and evaluation of therapeutic response of cancer, diabetes, cardiac, and musculoskeletal diseases. The advantages of LATEST over existing methods and its potential challenges are discussed.

Lactate Chemical Exchange Saturation Transfer (LATEST) Imaging in vivo A Biomarker for LDH Activity

PubMed Central

DeBrosse, Catherine; Nanga, Ravi Prakash Reddy; Bagga, Puneet; Nath, Kavindra; Haris, Mohammad; Marincola, Francesco; Schnall, Mitchell D.; Hariharan, Hari; Reddy, Ravinder

2016-01-01

Non-invasive imaging of lactate is of enormous significance in cancer and metabolic disorders where glycolysis dominates. Here, for the first time, we describe a chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) method (LATEST), based on the exchange between lactate hydroxyl proton and bulk water protons to image lactate with high spatial resolution. We demonstrate the feasibility of imaging lactate with LATEST in lactate phantoms under physiological conditions, in a mouse model of lymphoma tumors, and in skeletal muscle of healthy human subjects pre- and post-exercise. The method is validated by measuring LATEST changes in lymphoma tumors pre- and post-infusion of pyruvate and correlating them with lactate determined from multiple quantum filtered proton magnetic resonance spectroscopy (SEL-MQC 1H-MRS). Similarly, dynamic LATEST changes in exercising human skeletal muscle are correlated with lactate determined from SEL-MQC 1H-MRS. The LATEST method does not involve injection of radioactive isotopes or labeled metabolites. It has over two orders of magnitude higher sensitivity compared to conventional 1H-MRS. It is anticipated that this technique will have a wide range of applications including diagnosis and evaluation of therapeutic response of cancer, diabetes, cardiac, and musculoskeletal diseases. The advantages of LATEST over existing methods and its potential challenges are discussed. PMID:26794265

Invited Paper - Density functional theory: coverage of dynamic and non-dynamic electron correlation effects

NASA Astrophysics Data System (ADS)

Cremer, Dieter

The electron correlation effects covered by density functional theory (DFT) can be assessed qualitatively by comparing DFT densities ρ(r) with suitable reference densities obtained with wavefunction theory (WFT) methods that cover typical electron correlation effects. The analysis of difference densities ρ(DFT)-ρ(WFT) reveals that LDA and GGA exchange (X) functionals mimic non-dynamic correlation effects in an unspecified way. It is shown that these long range correlation effects are caused by the self-interaction error (SIE) of standard X functionals. Self-interaction corrected (SIC) DFT exchange gives, similar to exact exchange, for the bonding region a delocalized exchange hole, and does not cover any correlation effects. Hence, the exchange SIE is responsible for the fact that DFT densities often resemble MP4 or MP2 densities. The correlation functional changes X-only DFT densities in a manner observed when higher order coupling effects between lower order N-electron correlation effects are included. Hybrid functionals lead to changes in the density similar to those caused by SICDFT, which simply reflects the fact that hybrid functionals have been developed to cover part of the SIE and its long range correlation effects in a balanced manner. In the case of spin-unrestricted DFT (UDFT), non-dynamic electron correlation effects enter the calculation both via the X functional and via the wavefunction, which may cause a double-counting of correlation effects. The use of UDFT in the form of permuted orbital and broken-symmetry DFT (PO-UDFT, BS-UDFT) can lead to reasonable descriptions of multireference systems provided certain conditions are fulfilled. More reliable, however, is a combination of DFT and WFT methods, which makes the routine description of multireference systems possible. The development of such methods implies a separation of dynamic and non-dynamic correlation effects. Strategies for accomplishing this goal are discussed in general and tested in practice for CAS (complete active space)-DFT.

Testing time-dependent density functional theory with depopulated molecular orbitals for predicting electronic excitation energies of valence, Rydberg, and charge-transfer states and potential energies near a conical intersection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Shaohong L.; Truhlar, Donald G., E-mail: truhlar@umn.edu

2014-09-14

Kohn-Sham (KS) time-dependent density functional theory (TDDFT) with most exchange-correlation functionals is well known to systematically underestimate the excitation energies of Rydberg and charge-transfer excited states of atomic and molecular systems. To improve the description of Rydberg states within the KS TDDFT framework, Gaiduk et al. [Phys. Rev. Lett. 108, 253005 (2012)] proposed a scheme that may be called HOMO depopulation. In this study, we tested this scheme on an extensive dataset of valence and Rydberg excitation energies of various atoms, ions, and molecules. It is also tested on a charge-transfer excitation of NH{sub 3}-F{sub 2} and on the potentialmore » energy curves of NH{sub 3} near a conical intersection. We found that the method can indeed significantly improve the accuracy of predicted Rydberg excitation energies while preserving reasonable accuracy for valence excitation energies. However, it does not appear to improve the description of charge-transfer excitations that are severely underestimated by standard KS TDDFT with conventional exchange-correlation functionals, nor does it perform appreciably better than standard TDDFT for the calculation of potential energy surfaces.« less

Scaling for quantum tunneling current in nano- and subnano-scale plasmonic junctions.

PubMed

Zhang, Peng

2015-05-19

When two conductors are separated by a sufficiently thin insulator, electrical current can flow between them by quantum tunneling. This paper presents a self-consistent model of tunneling current in a nano- and subnano-meter metal-insulator-metal plasmonic junction, by including the effects of space charge and exchange correlation potential. It is found that the J-V curve of the junction may be divided into three regimes: direct tunneling, field emission, and space-charge-limited regime. In general, the space charge inside the insulator reduces current transfer across the junction, whereas the exchange-correlation potential promotes current transfer. It is shown that these effects may modify the current density by orders of magnitude from the widely used Simmons' formula, which is only accurate for a limited parameter space (insulator thickness > 1 nm and barrier height > 3 eV) in the direct tunneling regime. The proposed self-consistent model may provide a more accurate evaluation of the tunneling current in the other regimes. The effects of anode emission and material properties (i.e. work function of the electrodes, electron affinity and permittivity of the insulator) are examined in detail in various regimes. Our simple model and the general scaling for tunneling current may provide insights to new regimes of quantum plasmonics.

Engel-Vosko GGA calculations of the structural, electronic and optical properties of LiYO2

NASA Astrophysics Data System (ADS)

Muhammad, Nisar; Khan, Afzal; Haidar Khan, Shah; Sajjaj Siraj, Muhammad; Shah, Syed Sarmad Ali; Murtaza, Ghulam

2017-09-01

Structural, electronic and optical properties of lithium yttrium oxide (LiYO2) are investigated using density functional theory (DFT). These calculations are based on full potential linearized augmented plane wave (FP-LAPW) method implemented by WIEN2k. The generalized gradient approximation (GGA) is used as an exchange correlation potential with Perdew-Burk-Ernzerhof (PBE) and Engel-Vosko (EV) as exchange correlation functional. The structural properties are calculated with PBE-GGA as it gives the equilibrium lattice constants very close to the experimental values. While, the band structure and optical properties are calculated with EV-GGA obtain much closer results to their experimental values. Our calculations confirm LiYO2 as large indirect band gap semiconductor having band gap of 5.23 eV exhibiting the characteristics of ultrawide band gap materials showing the properties like higher critical breakdown field, higher temperature operation and higher radiation tolerance. In this article, we report the density of states (DOS) in terms of contribution from s, p, and d-states of the constituent atoms, the band structure, the electronic structure, and the frequency-dependent optical properties of LiYO2. The optical properties presented in this article reveal LiYO2 a suitable candidate for the field of optoelectronic and optical devices.

Scaling for quantum tunneling current in nano- and subnano-scale plasmonic junctions

PubMed Central

Zhang, Peng

2015-01-01

When two conductors are separated by a sufficiently thin insulator, electrical current can flow between them by quantum tunneling. This paper presents a self-consistent model of tunneling current in a nano- and subnano-meter metal-insulator-metal plasmonic junction, by including the effects of space charge and exchange correlation potential. It is found that the J-V curve of the junction may be divided into three regimes: direct tunneling, field emission, and space-charge-limited regime. In general, the space charge inside the insulator reduces current transfer across the junction, whereas the exchange-correlation potential promotes current transfer. It is shown that these effects may modify the current density by orders of magnitude from the widely used Simmons’ formula, which is only accurate for a limited parameter space (insulator thickness > 1 nm and barrier height > 3 eV) in the direct tunneling regime. The proposed self-consistent model may provide a more accurate evaluation of the tunneling current in the other regimes. The effects of anode emission and material properties (i.e. work function of the electrodes, electron affinity and permittivity of the insulator) are examined in detail in various regimes. Our simple model and the general scaling for tunneling current may provide insights to new regimes of quantum plasmonics. PMID:25988951

Spin-polarized structural, elastic, electronic and magnetic properties of half-metallic ferromagnetism in V-doped ZnSe

NASA Astrophysics Data System (ADS)

Monir, M. El Amine.; Baltache, H.; Murtaza, G.; Khenata, R.; Ahmed, Waleed K.; Bouhemadou, A.; Omran, S. Bin; Seddik, T.

2015-01-01

Based on first principles spin-polarized density functional theory, the structural, elastic electronic and magnetic properties of Zn1-xVxSe (for x=0.25, 0.50, 0.75) in zinc blende structure have been studied. The investigation was done using the full-potential augmented plane wave method as implemented in WIEN2k code. The exchange-correlation potential was treated with the generalized gradient approximation PBE-GGA for the structural and elastic properties. Moreover, the PBE-GGA+U approximation (where U is the Hubbard correlation terms) is employed to treat the "d" electrons properly. A comparative study between the band structures, electronic structures, total and partial densities of states and local moments calculated within both GGA and GGA+U schemes is presented. The analysis of spin-polarized band structure and density of states shows the half-metallic ferromagnetic character and are also used to determine s(p)-d exchange constants N0α (conduction band) and N0β (valence band) due to Se(4p)-V(3d) hybridization. It has been clearly evidence that the magnetic moment of V is reduced from its free space change value of 3 μB and the minor atomic magnetic moment on Zn and Se are generated.

Random matrix theory and portfolio optimization in Moroccan stock exchange

NASA Astrophysics Data System (ADS)

El Alaoui, Marwane

2015-09-01

In this work, we use random matrix theory to analyze eigenvalues and see if there is a presence of pertinent information by using Marčenko-Pastur distribution. Thus, we study cross-correlation among stocks of Casablanca Stock Exchange. Moreover, we clean correlation matrix from noisy elements to see if the gap between predicted risk and realized risk would be reduced. We also analyze eigenvectors components distributions and their degree of deviations by computing the inverse participation ratio. This analysis is a way to understand the correlation structure among stocks of Casablanca Stock Exchange portfolio.

Oxygen exchange at gas/oxide interfaces: how the apparent activation energy of the surface exchange coefficient depends on the kinetic regime.

PubMed

Fielitz, Peter; Borchardt, Günter

2016-08-10

In the dedicated literature the oxygen surface exchange coefficient KO and the equilibrium oxygen exchange rate [Fraktur R] are considered to be directly proportional to each other regardless of the experimental circumstances. Recent experimental observations, however, contradict the consequences of this assumption. Most surprising is the finding that the apparent activation energy of KO depends dramatically on the kinetic regime in which it has been determined, i.e. surface exchange controlled vs. mixed or diffusion controlled. This work demonstrates how the diffusion boundary condition at the gas/solid interface inevitably entails a correlation between the oxygen surface exchange coefficient KO and the oxygen self-diffusion coefficient DO in the bulk ("on top" of the correlation between KO and [Fraktur R] for the pure surface exchange regime). The model can thus quantitatively explain the range of apparent activation energies measured in the different regimes: in the surface exchange regime the apparent activation energy only contains the contribution of the equilibrium exchange rate, whereas in the mixed or in the diffusion controlled regime the contribution of the oxygen self-diffusivity has also to be taken into account, which may yield significantly higher apparent activation energies and simultaneously quantifies the correlation KO ∝ DO(1/2) observed for a large number of oxides in the mixed or diffusion controlled regime, respectively.

Beyond the random-phase approximation for the electron correlation energy: the importance of single excitations.

PubMed

Ren, Xinguo; Tkatchenko, Alexandre; Rinke, Patrick; Scheffler, Matthias

2011-04-15

The random-phase approximation (RPA) for the electron correlation energy, combined with the exact-exchange (EX) energy, represents the state-of-the-art exchange-correlation functional within density-functional theory. However, the standard RPA practice--evaluating both the EX and the RPA correlation energies using Kohn-Sham (KS) orbitals from local or semilocal exchange-correlation functionals--leads to a systematic underbinding of molecules and solids. Here we demonstrate that this behavior can be corrected by adding a "single excitation" contribution, so far not included in the standard RPA scheme. A similar improvement can also be achieved by replacing the non-self-consistent EX total energy by the corresponding self-consistent Hartree-Fock total energy, while retaining the RPA correlation energy evaluated using KS orbitals. Both schemes achieve chemical accuracy for a standard benchmark set of noncovalent intermolecular interactions.

Density scaling for multiplets

NASA Astrophysics Data System (ADS)

Nagy, Á.

2011-02-01

Generalized Kohn-Sham equations are presented for lowest-lying multiplets. The way of treating non-integer particle numbers is coupled with an earlier method of the author. The fundamental quantity of the theory is the subspace density. The Kohn-Sham equations are similar to the conventional Kohn-Sham equations. The difference is that the subspace density is used instead of the density and the Kohn-Sham potential is different for different subspaces. The exchange-correlation functional is studied using density scaling. It is shown that there exists a value of the scaling factor ζ for which the correlation energy disappears. Generalized OPM and Krieger-Li-Iafrate (KLI) methods incorporating correlation are presented. The ζKLI method, being as simple as the original KLI method, is proposed for multiplets.

Dynamical implications of bi-directional resource exchange within a meta-ecosystem.

PubMed

Messan, Marisabel Rodriguez; Kopp, Darin; Allen, Daniel C; Kang, Yun

2018-05-05

The exchange of resources across ecosystem boundaries can have large impacts on ecosystem structures and functions at local and regional scales. In this article, we develop a simple model to investigate dynamical implications of bi-directional resource exchanges between two local ecosystems in a meta-ecosystem framework. In our model, we assume that (1) Each local ecosystem acts as both a resource donor and recipient, such that one ecosystem donating resources to another results in a cost to the donating system and a benefit to the recipient; and (2) The costs and benefits of the bi-directional resource exchange between two ecosystems are correlated in a nonlinear fashion. Our model could apply to the resource interactions between terrestrial and aquatic ecosystems that are supported by the literature. Our theoretical results show that bi-directional resource exchange between two ecosystems can indeed generate complicated dynamical outcomes, including the coupled ecosystems having amensalistic, antagonistic, competitive, or mutualistic interactions, with multiple alternative stable states depending on the relative costs and benefits. In addition, if the relative cost for resource exchange for an ecosystem is decreased or the relative benefit for resource exchange for an ecosystem is increased, the production of that ecosystem would increase; however, depending on the local environment, the production of the other ecosystem may increase or decrease. We expect that our work, by evaluating the potential outcomes of resource exchange theoretically, can facilitate empirical evaluations and advance the understanding of spatial ecosystem ecology where resource exchanges occur in varied ecosystems through a complicated network. Copyright © 2018 Elsevier Inc. All rights reserved.

Band gap characterization of ternary BBi1-xNx (0≤x≤1) alloys using modified Becke-Johnson (mBJ) potential

NASA Astrophysics Data System (ADS)

Yalcin, Battal G.

2015-04-01

The semi-local Becke-Johnson (BJ) exchange-correlation potential and its modified form proposed by Tran and Blaha have attracted a lot of interest recently because of the surprisingly accurate band gaps they can deliver for many semiconductors and insulators (e.g., sp semiconductors, noble-gas solids, and transition-metal oxides). The structural and electronic properties of ternary alloys BBi1-xNx (0≤x≤1) in zinc-blende phase have been reported in this study. The results of the studied binary compounds (BN and BBi) and ternary alloys BBi1-xNx structures are presented by means of density functional theory. The exchange and correlation effects are taken into account by using the generalized gradient approximation (GGA) functional of Wu and Cohen (WC) which is an improved form of the most popular Perdew-Burke-Ernzerhof (PBE). For electronic properties the modified Becke-Johnson (mBJ) potential, which is more accurate than standard semi-local LDA and PBE calculations, has been chosen. Geometric optimization has been implemented before the volume optimization calculations for all the studied alloys structure. The obtained equilibrium lattice constants of the studied binary compounds are in coincidence with experimental works. And, the variation of the lattice parameter of ternary alloys BBi1-xNx almost perfectly matches with Vegard's law. The spin-orbit interaction (SOI) has been also considered for structural and electronic calculations and the results are compared to those of non-SOI calculations.

Molecular excited states from the SCAN functional

NASA Astrophysics Data System (ADS)

Tozer, David J.; Peach, Michael J. G.

2018-06-01

The performance of the strongly constrained and appropriately normed (SCAN) meta-generalised gradient approximation exchange-correlation functional is investigated for the calculation of time-dependent density-functional theory molecular excitation energies of local, charge-transfer and Rydberg character, together with the excited ? potential energy curve in H2. The SCAN results frequently resemble those obtained using a global hybrid functional, with either a standard or increased fraction of exact orbital exchange. For local excitations, SCAN can exhibit significant triplet instability problems, resulting in imaginary triplet excitation energies for a number of cases. The Tamm-Dancoff approximation offers a simple approach to improve the situation, but the excitation energies are still significantly underestimated. Understanding the origin of these (near)-triplet instabilities may provide useful insight into future functional development.

Sex-for-Crack exchanges: associations with risky sexual and drug use niches in an urban Canadian city

PubMed Central

2013-01-01

Background While crack cocaine has been associated with elevated sexual risks and transmission of HIV/STIs, particularly in the context of street-based sex work, few empirical studies have examined correlates of direct sex-for-crack exchanges. This study longitudinally examined the correlates of sex-for-crack exchanges and associated effects on sexual risk outcomes among street-based female sex workers (SW) who use drugs in Vancouver, Canada. Methods Data were drawn from a prospective cohort of street-based SWs (2006–2008), restricted to those who smoke crack cocaine. Multivariable generalized estimating equations (GEE) were employed to examine the correlates of exchanging sex for crack. A confounding model using GEE quasi-Poisson regression modeled the independent effect of exchanging sex for crack on number of clients/week. Results Of 206 SWs, 101 (49%) reported sex-for-crack exchanges over 18 months of follow-up. In multivariable GEE analyses, sharing a crack pipe with a client (aOR = 1.98; 95%CI: 1.27-3.08) and smoking crack in a group of strangers (e.g., in an alley or crackhouse) (aOR = 1.70; 95% CI: 1.13-2.58) were independently correlated with sex-for-crack exchanges. In our confounding model, exchanging sex for crack (aIRR = 1.34; 95% CI: 1.07-1.69) remained significantly associated with servicing a greater number (>10) of clients/week. Conclusions These findings reveal elevated sexual- and drug- risk patterns among those who exchange sex for crack. The physical and social environment featured prominently in our results as a driver of sex-for-crack exchanges, highlighting the need for gender-sensitive multilevel approaches to harm reduction, STI and HIV prevention that address SWs’ environment, individual level factors, and the interplay between them. PMID:24238367

Relationships among foliar chemistry, foliar polyamines, and soil chemistry in red spruce trees growing across the northeastern United States

USGS Publications Warehouse

Minocha, R.; Shortle, W.C.; Lawrence, G.B.; David, M.B.; Minocha, S.C.

1997-01-01

Forest trees are constantly exposed to various types of natural and anthropogenic stressors. A major long-term goal of our research is to develop a set of early physiological and biochemical markers of stress in trees before the appearance of visual symptoms. Six red spruce (Picea rubens Sarg.) stands from the northeastern United States were selected for collection of soil and foliage samples. All of the chosen sites had soil solution pH values below 4.0 in the Oa horizon but varied in their geochemistry. Some of these sites were apparently under some form of environmental stress as indicated by a large number of dead and dying red spruce trees. Samples of soil and needles (from apparently healthy red spruce trees) were collected from these sites four times during a two-year period. The needles were analyzed for perchloric acid-soluble polyamines and exchangeable inorganic ions. Soil and soil solution samples from the Oa and B horizons were analyzed for their exchange chemistry. The data showed a strong positive correlation between Ca and Mg concentrations in the needles and in the Oa horizon of the soil. However, needles from trees growing on relatively Ca-rich soils with a low exchangeable Al concentration and a low Al:Ca soil solution ratio had significantly lower concentrations of putrescine and spermidine than those growing on Ca-poor soils with a high exchangeable Al concentration and a high Al:Ca soil solution in the Oa horizon. The magnitude of this change was several fold higher for putrescine concentrations than for spermidine concentrations. Neither putrescine nor spermidine were correlated with soil solution Ca, Mg, and Al concentrations in the B horizon. The putrescine concentrations of the needles always correlated significantly with exchangeable Al (r2=0.73, p???0.05) and still solution Al:Ca ratios (r2=0.91, p???0.01) of the Oa horizon. This suggests that in conjunction with soil chemistry, putrescine and/or spermidine may be used as a potential early indicator of Al stress before the appearance of visual symptoms in red spruce trees.

Analysis of a 7 year tropospheric ozone vertical distribution at the Observatoire de Haute Provence

NASA Technical Reports Server (NTRS)

Beekmann, Matthias; Ancellet, Gerard; Megie, Gerard

1994-01-01

A seven year (1984-90) climatology of tropospheric vertical ozone soundings, performed by electrochemical sondes at the OHP (44 deg N, 6 deg E, 700 m ASL) in Southern France, is presented. Its seasonal variation shows a broad spring/summer maximum in the troposphere. The contribution of photochemical ozone production and transport from the stratosphere to this seasonal variation are studied by a correlative analysis of ozone concentrations and meteorological variables, with emphasis on potential vorticity. This analysis shows the impact of dynamical and photochemical processes on the spatial and temporal ozone variability. In particular, a positive correlation (r = 04.0, significance greater than 99.9 percent) of ozone with potential vorticity is observed in the middle troposphere, reflecting the impact of stratosphere-troposphere exchange on the vertical ozone distribution.

Quantification of regional early stage gas exchange changes using hyperpolarized (129)Xe MRI in a rat model of radiation-induced lung injury.

PubMed

Doganay, Ozkan; Stirrat, Elaine; McKenzie, Charles; Schulte, Rolf F; Santyr, Giles E

2016-05-01

To assess the feasibility of hyperpolarized (HP) (129)Xe MRI for detection of early stage radiation-induced lung injury (RILI) in a rat model involving unilateral irradiation by assessing differences in gas exchange dynamics between irradiated and unirradiated lungs. The dynamics of gas exchange between alveolar air space and pulmonary tissue (PT), PT and red blood cells (RBCs) was measured using single-shot spiral iterative decomposition of water and fat with echo asymmetry and least-squares estimation images of the right and left lungs of two age-matched cohorts of Sprague Dawley rats. The first cohort (n = 5) received 18 Gy irradiation to the right lung using a (60)Co source and the second cohort (n = 5) was not irradiated and served as the healthy control. Both groups were imaged two weeks following irradiation when radiation pneumonitis (RP) was expected to be present. The gas exchange data were fit to a theoretical gas exchange model to extract measurements of pulmonary tissue thickness (LPT) and relative blood volume (VRBC) from each of the right and left lungs of both cohorts. Following imaging, lung specimens were retrieved and percent tissue area (PTA) was assessed histologically to confirm RP and correlate with MRI measurements. Statistically significant differences in LPT and VRBC were observed between the irradiated and non-irradiated cohorts. In particular, LPT of the right and left lungs was increased approximately 8.2% and 5.0% respectively in the irradiated cohort. Additionally, VRBC of the right and left lungs was decreased approximately 36.1% and 11.7% respectively for the irradiated cohort compared to the non-irradiated cohort. PTA measurements in both right and left lungs were increased in the irradiated group compared to the non-irradiated cohort for both the left (P < 0.05) and right lungs (P < 0.01) confirming the presence of RP. PTA measurements also correlated with the MRI measurements for both the non-irradiated (r = 0.79, P < 0.01) and irradiated groups (r = 0.91, P < 0.01). Regional RILI can be detected two weeks post-irradiation using HP (129)Xe MRI and analysis of gas exchange curves. This approach correlates well with histology and can potentially be used clinically to assess radiation pneumonitis associated with early RILI to improve radiation therapy outcomes.

Constraint on the second functional derivative of the exchange-correlation energy

NASA Astrophysics Data System (ADS)

Joubert, D. P.

2012-09-01

Using the density functional adiabatic connection approach for an N-electron system it is shown that ? γ is the coupling constant that scales the electron-electron interaction strength. For the non-interacting Kohn-Sham Hamiltonian γ = 0 and for the fully interacting system γ = 1. ? is the Hartree plus exchange-correlation energy while f 0(r) and fγ(r) are the Fukui functions of the non-interacting and interacting systems, respectively. This identity can serve to test the internal self-consistency or quality of approximate functionals. The quality of some popular approximate exchange and correlation functionals are tested for a simple model system.

Optimization of a hybrid exchange-correlation functional for silicon carbides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oda, Takuji; Zhang, Yanwen; Weber, William J

2013-01-01

A hybrid exchange-correlation functional is optimized in order to accurately describe the nature of silicon carbides (SiC) in the framework of ab-initio calculations based on density functional theory (DFT), especially with an aim toward future applications in defect studies. It is shown that the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional with the screening parameter of 0.15 -1 outperforms conventional exchange-correlation functionals and other popular hybrid functionals regarding description of band structures in SiC. High transferability is proven through assessment over various SiC polytypes, silicon and diamond. Excellent performance is also confirmed for other fundamental material properties including elastic constants and phonon frequency.

76 FR 39451 - Self-Regulatory Organizations; Chicago Stock Exchange, Inc.; Notice of Filing and Immediate...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-07-06

... the Exchange's rules.\\4\\ In order to remove any potential ambiguity about the nature of the Exchange's... the Exchange's rules.\\7\\ In order to remove any potential ambiguity about the nature of the Exchange's...

Electrical resistivity of liquid lanthanides using charge hard sphere system

NASA Astrophysics Data System (ADS)

Sonvane, Y. A.; Thakor, P. B.; Jani, A. R.

2013-06-01

In the present paper, we have studied electrical resistivity (ρ) of liquid lanthanides. To describe the structural information, the structure factor S(q) due to the charged hard sphere (CHS) reference systems is used along with our newly constructed model potential. To see the influence of exchange and correlation effect on the electrical resistivity (ρ) have used different local field correction functions like Hartree (H), Sarkar et al (S) and Taylor (T). Lastly we conclude that the proper choice of the model potential along with local field correction function plays a vital role to the study of the electrical resistivity (ρ).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choudhury, Sourav; Das, Tushar Kanti; Chatterjee, Prasanta

The influence of exchange-correlation potential, quantum Bohm term, and degenerate pressure on the nature of solitary waves in a quantum semiconductor plasma is investigated. It is found that an amplitude and a width of the solitary waves change with variation of different parameters for different semiconductors. A deformed Korteweg-de Vries equation is obtained for propagation of nonlinear waves in a quantum semiconductor plasma, and the effects of different plasma parameters on the solution of the equation are also presented.

Finite-T correlations and free exchange-correlation energy of quasi-one-dimensional electron gas

NASA Astrophysics Data System (ADS)

Garg, Vinayak; Sharma, Akariti; Moudgil, R. K.

2018-02-01

We have studied the effect of temperature on static density-density correlations and plasmon excitation spectrum of quasi-one-dimensional electron gas (Q1DEG) using the random phase approximation (RPA). Numerical results for static structure factor, pair-correlation function, static density susceptibility, free exchange-correlation energy and plasmon dispersion are presented over a wide range of temperature and electron density. As an interesting result, we find that the short-range correlations exhibit a non-monotonic dependence on temperature T, initially growing stronger (i.e. the pair-correlation function at small inter-electron spacing assuming relatively smaller values) with increasing T and then weakening above a critical T. The cross-over temperature is found to increase with increasing coupling among electrons. Also, the q = 2kF peak in the static density susceptibility χ(q,ω = 0,T) at T = 0 K smears out with rising T. The free exchange-correlation energy and plasmon dispersion show a significant variation with T, and the trend is qualitatively the same as in higher dimensions.

Correlates of exchange sex among a population-based sample of low-income women who have heterosexual sex in Baltimore.

PubMed

Sherman, Susan G; Hast, Marisa; Park, Ju Nyeong; Decker, Michele R; Flynn, Colin; German, Danielle

2018-03-08

Sex exchange is associated with HIV and other morbidities yet has received little research, surveillance, and programmatic attention in the U.S. This study identified correlates of exchange sex and among low-income women in Baltimore, Maryland. Participants were recruited into the National HIV Behavioral Surveillance (NHBS) system in 2013 using respondent driven sampling (RDS) and completed a survey and HIV testing. The analytic sample (n = 253) consisted of women aged ≥18 years who had recent (past year) heterosexual sex. Multivariable logistic regression identified correlates of recent exchange sex. Independently associated with recent exchange sex were history of injection drug use (adjusted odds ratio (AOR) = 3.4, 95% CI: 1.1-10.3), recent prescription painkiller use (AOR = 3.7, 95% CI: 1.4-9.9), recent crack/cocaine use (AOR = 6.6, 95% CI: 2.1-20.9), recent arrest (AOR = 4.1, 95% CI: 1.2-14.8), and recent consistent condom use (AOR 1.1; 95% CI: 1.0-1.3). Women who exchanged sex exhibited heightened social and structural vulnerability and substance use. These data demonstrate the need for further research examining the context of exchange sex among low-income women and synergies between substance use and HIV risk.

Direct mapping between exchange potentials of Hartree-Fock and Kohn-Sham schemes as origin of orbital proximity

NASA Astrophysics Data System (ADS)

Cinal, M.

2010-01-01

It is found that for closed-l-shell atoms, the exact local exchange potential vx(r) calculated in the exchange-only Kohn-Sham (KS) scheme of the density functional theory (DFT) is very well represented within the region of every atomic shell by each of the suitably shifted potentials obtained with the nonlocal Fock exchange operator for the individual Hartree-Fock (HF) orbitals belonging to this shell. This newly revealed property is not related to the well-known steplike shell structure in the response part of vx(r), but it results from specific relations satisfied by the HF orbital exchange potentials. These relations explain the outstanding proximity of the occupied HF and exchange-only KS orbitals as well as the high quality of the Krieger-Li-Iafrate and localized HF (or, equivalently, common-energy-denominator) approximations to the DFT exchange potential vx(r). Another highly accurate representation of vx(r) is given by the continuous piecewise function built of shell-specific exchange potentials, each defined as the weighted average of the shifted orbital exchange potentials corresponding to a given shell. The constant shifts added to the HF orbital exchange potentials, to map them onto vx(r), are nearly equal to the differences between the energies of the corresponding KS and HF orbitals. It is discussed why these differences are positive and grow when the respective orbital energies become lower for inner orbitals.

Zinc distribution in soils amended with different kinds of sewage sludge.

PubMed

Torri, Silvana Irene; Lavado, Raúl

2008-09-01

Sewage sludge (SS) can be applied to cropland to supply and recycle nutrients and organic carbon. Potentially toxic elements in the sludge, however, are of environmental concern. This study evaluates the changes in chemical speciation of Zn in three representative pristine soils of the Pampas Region, Argentina, measured with sequential extraction over a one-year period. Pure SS or SS containing 30% (DM) of its own incineration ash (AS) was applied to the soils at an application rate of 150 Mg ha(-1). Zn was sequentially fractionated into exchangeable, organically bound, inorganic and residual fractions. The application of the SS and AS amendments significantly increased Zn concentration in all soil fractions at each sampling date. At day 1, Zn was mainly found in the residual fraction. A year after the application of the amendments, redistribution towards the inorganic fraction was observed (41-76% of total Zn content). Zn found in exchangeable and inorganic fractions depended on soil pH rather than on the type of soil used. A negative and significant correlation was found between exchangeable Zn concentrations and soil pH (r=0.94), and a positive and significant correlation between inorganic Zn concentrations and soil pH (r=0.92). For each amended soil and sampling date, no significant differences were observed between SS or AS treatments for the exchangeable fraction. Moreover, the use of AS did not cause significant differences in Zn concentration in the other soil fractions compared to SS. Based on these results, land spreading of AS may be similar to SS diaposal in terms of Zn mobility.

Effects of long-term individual and combined water and temperature stress on the growth of rice, wheat and maize: relationship with morphological and physiological acclimation.

PubMed

Perdomo, Juan Alejandro; Conesa, Miquel À; Medrano, Hipólito; Ribas-Carbó, Miquel; Galmés, Jeroni

2015-10-01

This study evaluates the long-term individual and combined effects of high temperature (HT) and water deficit (WD) stress on plant growth, leaf gas-exchange and water use efficiency in cultivars of the three most important crops worldwide, rice, wheat and maize. Total plant biomass (B t ) accumulation decreased under all treatments, being the combined HT-WD treatment the most detrimental in all three species. Although decreases in B t correlated with adjustments in biomass allocation patterns (i.e. the leaf area ratio), most of the variation observed in B t was explained by changes in leaf gas exchange parameters. Thus, integrated values of leaf carbon balance obtained from daily course measurements of photosynthesis and respiration were better predictors of plant growth than the instantaneous measurements of leaf gas exchange. Leaf water use efficiency, assessed both by gas exchange and carbon isotope measurements, was negatively correlated with B t under WD, but not under the combined WD and HT treatment. A comparative analysis of the negative effects of single and combined stresses on the main parameters showed an additive component for WD and HT in rice and maize, in contrast to wheat. Overall, the results of the specific cultivars included in the study suggest that the species native climate plays a role shaping the species acclimation potential to the applied stresses. In this regard, wheat, originated in a cold climate, was the most affected species, which foretells a higher affectation of this crop due to climate change. © 2014 Scandinavian Plant Physiology Society.

Cast and 3D printed ion exchange membranes for monolithic microbial fuel cell fabrication

NASA Astrophysics Data System (ADS)

Philamore, Hemma; Rossiter, Jonathan; Walters, Peter; Winfield, Jonathan; Ieropoulos, Ioannis

2015-09-01

We present novel solutions to a key challenge in microbial fuel cell (MFC) technology; greater power density through increased relative surface area of the ion exchange membrane that separates the anode and cathode electrodes. The first use of a 3D printed polymer and a cast latex membrane are compared to a conventionally used cation exchange membrane. These new techniques significantly expand the geometric versatility available to ion exchange membranes in MFCs, which may be instrumental in answering challenges in the design of MFCs including miniaturisation, cost and ease of fabrication. Under electrical load conditions selected for optimal power transfer, peak power production (mean 10 batch feeds) was 11.39 μW (CEM), 10.51 μW (latex) and 0.92 μW (Tangoplus). Change in conductivity and pH of anolyte were correlated with MFC power production. Digital and environmental scanning electron microscopy show structural changes to and biological precipitation on membrane materials following long term use in an MFC. The cost of the novel membranes was lower than the conventional CEM. The efficacy of two novel membranes for ion exchange indicates that further characterisation of these materials and their fabrication techniques, shows great potential to significantly increase the range and type of MFCs that can be produced.

Forecast in foreign exchange markets

NASA Astrophysics Data System (ADS)

Baviera, R.; Pasquini, M.; Serva, M.; Vergni, D.; Vulpiani, A.

2001-04-01

We perform a statistical study of weak efficiency in Deutschemark/US dollar exchange rates using high frequency data. The presence of correlations in the returns sequence implies the possibility of a statistical forecast of market behavior. We show the existence of correlations and how information theory can be relevant in this context.

Currency co-movement and network correlation structure of foreign exchange market

NASA Astrophysics Data System (ADS)

Mai, Yong; Chen, Huan; Zou, Jun-Zhong; Li, Sai-Ping

2018-02-01

We study the correlations of exchange rate volatility in the global foreign exchange(FX) market based on complex network graphs. Correlation matrices (CM) and the theoretical information flow method (Infomap) are employed to analyze the modular structure of the global foreign exchange network. The analysis demonstrates that there exist currency modules in the network, which is consistent with the geographical nature of currencies. The European and the East Asian currency modules in the FX network are most significant. We introduce a measure of the impact of individual currency based on its partial correlations with other currencies. We further incorporate an impact elimination method to filter out the impact of core nodes and construct subnetworks after the removal of these core nodes. The result reveals that (i) the US Dollar has prominent global influence on the FX market while the Euro has great impact on European currencies; (ii) the East Asian currency module is more strongly correlated than the European currency module. The strong correlation is a result of the strong co-movement of currencies in the region. The co-movement of currencies is further used to study the formation of international monetary bloc and the result is in good agreement with the consideration based on international trade.

Entanglement of Electron Spins in Two Coupled Quantum Dots

NASA Astrophysics Data System (ADS)

Chen, Yuanzhen; Webb, Richard

2004-03-01

We study the entanglement of electron spins in a coupled quantum dots system at 70 mK. Two quantum dots are fabricated in a GaAs/AlGaAs heterostructure containing a high mobility 2-D electron gas. The two dots can be tuned independently and the electron spins in the dots are coupled through an exchange interaction between them. An exchange gate is used to vary the height and width of a potential barrier between the two dots, thus controlling the strength of the exchange interaction. Electrons are injected to the coupled dots by two independent DC currents and the output of the dots is incident on a beam splitter, which introduces quantum interferences. Cross-correlations of the shot noise of currents from the two output channels are measured and compared with theory (1). *Work supported by LPS and ARDA under MDA90401C0903 and NSF under DMR 0103223. (1) Burkard, Loss, & Sukhorukov, Phys. Rev. B61, R16303 (2000).

Air-sea heat exchange, an element of the water cycle

NASA Technical Reports Server (NTRS)

Chahine, M. T.

1984-01-01

The distribution and variation of water vapor, clouds and precipitation are examined. Principal driving forces for these distributions are energy exchange and evaporation at the air-sea interface, which are also important elements of air-sea interaction studies. The overall aim of air-sea interaction studies is to quantitatively determine mass, momentum and energy fluxes, with the goal of understanding the mechanisms controlling them. The results of general circulation simulations indicate that the atmosphere in mid-latitudes responds to changes in the oceanic surface conditions in the tropics. This correlation reflects the strong interaction between tropical and mid-latitude conditions caused by the transport of heat and momentum from the tropics. Studies of air-sea exchanges involve a large number of physica, chemical and dynamical processes including heat flux, radiation, sea-surface temperature, precipitation, winds and ocean currents. The fluxes of latent heat are studied and the potential use of satellite data in determining them evaluated. Alternative ways of inferring heat fluxes will be considered.

Orientation-Dependent Oxygen Evolution on RuO 2 without Lattice Exchange

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoerzinger, Kelsey A.; Diaz-Morales, Oscar; Kolb, Manuel

RuO2 catalysts exhibit record activities towards the oxygen evolution reaction (OER), which is crucial to enable efficient and sustainable energy storage. Here we examine the RuO2 OER kinetics on rutile (110), (100), (101), and (111) orientations, finding (100) the most active. We assess the potential involvement of lattice oxygen in the OER mechanism with online 3 electrochemical mass spectrometry, which showed no evidence of oxygen exchange on these oriented facets in acidic or basic electrolytes. Similar results were obtained for polyoriented RuO2 films and particles, in contrast to previous work, suggesting lattice oxygen is not exchanged in catalyzing OER onmore » crystalline RuO2 surfaces. This hypothesis is supported by the correlation of activity with the number of active Ru-sites calculated by DFT, where more active facets bind oxygen more weakly. This new understanding of the active sites provides a design strategy to enhance the OER activity of RuO2 nanoparticles by facet engineering.« less

Cross-sample entropy of foreign exchange time series

NASA Astrophysics Data System (ADS)

Liu, Li-Zhi; Qian, Xi-Yuan; Lu, Heng-Yao

2010-11-01

The correlation of foreign exchange rates in currency markets is investigated based on the empirical data of DKK/USD, NOK/USD, CAD/USD, JPY/USD, KRW/USD, SGD/USD, THB/USD and TWD/USD for a period from 1995 to 2002. Cross-SampEn (cross-sample entropy) method is used to compare the returns of every two exchange rate time series to assess their degree of asynchrony. The calculation method of confidence interval of SampEn is extended and applied to cross-SampEn. The cross-SampEn and its confidence interval for every two of the exchange rate time series in periods 1995-1998 (before the Asian currency crisis) and 1999-2002 (after the Asian currency crisis) are calculated. The results show that the cross-SampEn of every two of these exchange rates becomes higher after the Asian currency crisis, indicating a higher asynchrony between the exchange rates. Especially for Singapore, Thailand and Taiwan, the cross-SampEn values after the Asian currency crisis are significantly higher than those before the Asian currency crisis. Comparison with the correlation coefficient shows that cross-SampEn is superior to describe the correlation between time series.

Electron correlation and the self-interaction error of density functional theory

NASA Astrophysics Data System (ADS)

Polo, Victor; Kraka, Elfi; Cremer, Dieter

The self-interaction error (SIE) of commonly used DFT functionals has been systematically investigated by comparing the electron density distribution ρ( r ) generated by self-interaction corrected DFT (SIC-DFT) with a series of reference densities obtained by DFT or wavefunction theory (WFT) methods that cover typical electron correlation effects. Although the SIE of GGA functionals is considerably smaller than that of LDA functionals, it has significant consequences for the coverage of electron correlation effects at the DFT level of theory. The exchange SIE mimics long range (non-dynamic) pair correlation effects, and is responsible for the fact that the electron density of DFT exchange-only calculations resembles often that of MP4, MP2 or even CCSD(T) calculations. Changes in the electron density caused by SICDFT exchange are comparable with those that are associated with HF exchange. Correlation functionals contract the density towards the bond and the valence region, thus taking negative charge out of the van der Waals region where these effects are exaggerated by the influence of the SIE of the correlation functional. Hence, SIC-DFT leads in total to a relatively strong redistribution of negative charge from van der Waals, non-bonding, and valence regions of heavy atoms to the bond regions. These changes, although much stronger, resemble those obtained when comparing the densities of hybrid functionals such as B3LYP with the corresponding GGA functional BLYP. Hence, the balanced mixing of local and non-local exchange and correlation effects as it is achieved by hybrid functionals mimics SIC-DFT and can be considered as an economic way to include some SIC into standard DFT. However, the investigation shows also that the SIC-DFT description of molecules is unreliable because the standard functionals used were optimized for DFT including the SIE.

Mimicking the action of folding chaperones by Hamiltonian replica-exchange molecular dynamics simulations: application in the refinement of de novo models.

PubMed

Fan, Hao; Periole, Xavier; Mark, Alan E

2012-07-01

The efficiency of using a variant of Hamiltonian replica-exchange molecular dynamics (Chaperone H-replica-exchange molecular dynamics [CH-REMD]) for the refinement of protein structural models generated de novo is investigated. In CH-REMD, the interaction between the protein and its environment, specifically, the electrostatic interaction between the protein and the solvating water, is varied leading to cycles of partial unfolding and refolding mimicking some aspects of folding chaperones. In 10 of the 15 cases examined, the CH-REMD approach sampled structures in which the root-mean-square deviation (RMSD) of secondary structure elements (SSE-RMSD) with respect to the experimental structure was more than 1.0 Å lower than the initial de novo model. In 14 of the 15 cases, the improvement was more than 0.5 Å. The ability of three different statistical potentials to identify near-native conformations was also examined. Little correlation between the SSE-RMSD of the sampled structures with respect to the experimental structure and any of the scoring functions tested was found. The most effective scoring function tested was the DFIRE potential. Using the DFIRE potential, the SSE-RMSD of the best scoring structures was on average 0.3 Å lower than the initial model. Overall the work demonstrates that targeted enhanced-sampling techniques such as CH-REMD can lead to the systematic refinement of protein structural models generated de novo but that improved potentials for the identification of near-native structures are still needed. Copyright © 2012 Wiley Periodicals, Inc.

Identification of the Dimer Exchange Interface of the Bacterial DNA Damage Response Protein UmuD.

PubMed

Murison, David A; Timson, Rebecca C; Koleva, Bilyana N; Ordazzo, Michael; Beuning, Penny J

2017-09-12

The Escherichia coli SOS response, an induced DNA damage response pathway, confers survival on bacterial cells by providing accurate repair mechanisms as well as the potentially mutagenic pathway translesion synthesis (TLS). The umuD gene products are upregulated after DNA damage and play roles in both nonmutagenic and mutagenic aspects of the SOS response. Full-length UmuD is expressed as a homodimer of 139-amino-acid subunits, which eventually cleaves its N-terminal 24 amino acids to form UmuD'. The cleavage product UmuD' and UmuC form the Y-family polymerase DNA Pol V (UmuD' 2 C) capable of performing TLS. UmuD and UmuD' exist as homodimers, but their subunits can readily exchange to form UmuDD' heterodimers preferentially. Heterodimer formation is an essential step in the degradation pathway of UmuD'. The recognition sequence for ClpXP protease is located within the first 24 amino acids of full-length UmuD, and the partner of full-length UmuD, whether UmuD or UmuD', is degraded by ClpXP. To better understand the mechanism by which UmuD subunits exchange, we measured the kinetics of exchange of a number of fluorescently labeled single-cysteine UmuD variants as detected by Förster resonance energy transfer. Labeling sites near the dimer interface correlate with increased rates of exchange, indicating that weakening the dimer interface facilitates exchange, whereas labeling sites on the exterior decrease the rate of exchange. In most but not all cases, homodimer and heterodimer exchange exhibit similar rates, indicating that somewhat different molecular surfaces mediate homodimer exchange and heterodimer formation.

Multicomponent density functional theory embedding formulation.

PubMed

Culpitt, Tanner; Brorsen, Kurt R; Pak, Michael V; Hammes-Schiffer, Sharon

2016-07-28

Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density is separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF(-) molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.

Multicomponent density functional theory embedding formulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Culpitt, Tanner; Brorsen, Kurt R.; Pak, Michael V.

Multicomponent density functional theory (DFT) methods have been developed to treat two types of particles, such as electrons and nuclei, quantum mechanically at the same level. In the nuclear-electronic orbital (NEO) approach, all electrons and select nuclei, typically key protons, are treated quantum mechanically. For multicomponent DFT methods developed within the NEO framework, electron-proton correlation functionals based on explicitly correlated wavefunctions have been designed and used in conjunction with well-established electronic exchange-correlation functionals. Herein a general theory for multicomponent embedded DFT is developed to enable the accurate treatment of larger systems. In the general theory, the total electronic density ismore » separated into two subsystem densities, denoted as regular and special, and different electron-proton correlation functionals are used for these two electronic densities. In the specific implementation, the special electron density is defined in terms of spatially localized Kohn-Sham electronic orbitals, and electron-proton correlation is included only for the special electron density. The electron-proton correlation functional depends on only the special electron density and the proton density, whereas the electronic exchange-correlation functional depends on the total electronic density. This scheme includes the essential electron-proton correlation, which is a relatively local effect, as well as the electronic exchange-correlation for the entire system. This multicomponent DFT-in-DFT embedding theory is applied to the HCN and FHF{sup −} molecules in conjunction with two different electron-proton correlation functionals and three different electronic exchange-correlation functionals. The results illustrate that this approach provides qualitatively accurate nuclear densities in a computationally tractable manner. The general theory is also easily extended to other types of partitioning schemes for multicomponent systems.« less

Accurate Semilocal Density Functional for Condensed-Matter Physics and Quantum Chemistry.

PubMed

Tao, Jianmin; Mo, Yuxiang

2016-08-12

Most density functionals have been developed by imposing the known exact constraints on the exchange-correlation energy, or by a fit to a set of properties of selected systems, or by both. However, accurate modeling of the conventional exchange hole presents a great challenge, due to the delocalization of the hole. Making use of the property that the hole can be made localized under a general coordinate transformation, here we derive an exchange hole from the density matrix expansion, while the correlation part is obtained by imposing the low-density limit constraint. From the hole, a semilocal exchange-correlation functional is calculated. Our comprehensive test shows that this functional can achieve remarkable accuracy for diverse properties of molecules, solids, and solid surfaces, substantially improving upon the nonempirical functionals proposed in recent years. Accurate semilocal functionals based on their associated holes are physically appealing and practically useful for developing nonlocal functionals.

Exact thermal density functional theory for a model system: Correlation components and accuracy of the zero-temperature exchange-correlation approximation

DOE PAGES

Smith, J. C.; Pribram-Jones, A.; Burke, K.

2016-06-14

Thermal density functional theory calculations often use the Mermin-Kohn-Sham scheme, but employ ground-state approximations to the exchange-correlation (XC) free energy. In the simplest solvable nontrivial model, an asymmetric Hubbard dimer, we calculate the exact many-body energies and the exact Mermin-Kohn-Sham functionals for this system and extract the exact XC free energy. For moderate temperatures and weak correlation, we find this approximation to be excellent. Here we extract various exact free-energy correlation components and the exact adiabatic connection formula.

Exact thermal density functional theory for a model system: Correlation components and accuracy of the zero-temperature exchange-correlation approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, J. C.; Pribram-Jones, A.; Burke, K.

Thermal density functional theory calculations often use the Mermin-Kohn-Sham scheme, but employ ground-state approximations to the exchange-correlation (XC) free energy. In the simplest solvable nontrivial model, an asymmetric Hubbard dimer, we calculate the exact many-body energies and the exact Mermin-Kohn-Sham functionals for this system and extract the exact XC free energy. For moderate temperatures and weak correlation, we find this approximation to be excellent. Here we extract various exact free-energy correlation components and the exact adiabatic connection formula.

Hypernuclear Weak Decays

NASA Astrophysics Data System (ADS)

Itonaga, K.; Motoba, T.

The recent theoretical studies of Lambda-hypernuclear weak decaysof the nonmesonic and pi-mesonic ones are developed with the aim to disclose the link between the experimental decay observables and the underlying basic weak decay interactions and the weak decay mechanisms. The expressions of the nonmesonic decay rates Gamma_{nm} and the decay asymmetry parameter alpha_1 of protons from the polarized hypernuclei are presented in the shell model framework. We then introduce the meson theoretical Lambda N -> NN interactions which include the one-meson exchanges, the correlated-2pi exchanges, and the chiral-pair-meson exchanges. The features of meson exchange potentials and their roles on the nonmesonic decays are discussed. With the adoption of the pi + 2pi/rho + 2pi/sigma + omega + K + rhopi/a_1 + sigmapi/a_1 exchange potentials, we have carried out the systematic calculations of the nonmesonic decay observables for light-to-heavy hypernuclei. The present model can account for the available experimental data of the decay rates, Gamma_n/Gamma_p ratios, and the intrinsic asymmetry parameters alpha_Lambda (alpha_Lambda is related to alpha_1) of emitted protons well and consistently within the error bars. The hypernuclear lifetimes are evaluated by converting the total weak decay rates Gamma_{tot} = Gamma_pi + Gamma_{nm} to tau, which exhibit saturation property for the hypernuclear mass A ≥ 30 and agree grossly well with experimental data for the mass range from light to heavy hypernuclei except for the very light ones. Future extensions of the model and the remaining problems are also mentioned. The pi-mesonic weak processes are briefly surveyed, and the calculations and predictions are compared and confirmed by the recent high precision FINUDA pi-mesonic decay data. This shows that the theoretical basis seems to be firmly grounded.

Scalable properties of metal clusters: A comparative study of modern exchange-correlation functionals

NASA Astrophysics Data System (ADS)

Koitz, Ralph; Soini, Thomas M.; Genest, Alexander; Trickey, S. B.; Rösch, Notker

2012-07-01

The performance of eight generalized gradient approximation exchange-correlation (xc) functionals is assessed by a series of scalar relativistic all-electron calculations on octahedral palladium model clusters Pdn with n = 13, 19, 38, 55, 79, 147 and the analogous clusters Aun (for n up through 79). For these model systems, we determined the cohesive energies and average bond lengths of the optimized octahedral structures. We extrapolate these values to the bulk limits and compare with the corresponding experimental values. While the well-established functionals BP, PBE, and PW91 are the most accurate at predicting energies, the more recent forms PBEsol, VMTsol, and VT{84}sol significantly improve the accuracy of geometries. The observed trends are largely similar for both Pd and Au. In the same spirit, we also studied the scalability of the ionization potentials and electron affinities of the Pd clusters, and extrapolated those quantities to estimates of the work function. Overall, the xc functionals can be classified into four distinct groups according to the accuracy of the computed parameters. These results allow a judicious selection of xc approximations for treating transition metal clusters.

Benchmarking singlet and triplet excitation energies of molecular semiconductors for singlet fission: Tuning the amount of HF exchange and adjusting local correlation to obtain accurate functionals for singlet-triplet gaps

NASA Astrophysics Data System (ADS)

Brückner, Charlotte; Engels, Bernd

2017-01-01

Vertical and adiabatic singlet and triplet excitation energies of molecular p-type semiconductors calculated with various DFT functionals and wave-function based approaches are benchmarked against MS-CASPT2/cc-pVTZ reference values. A special focus lies on the singlet-triplet gaps that are very important in the process of singlet fission. Singlet fission has the potential to boost device efficiencies of organic solar cells, but the scope of existing singlet-fission compounds is still limited. A computational prescreening of candidate molecules could enlarge it; yet it requires efficient methods accurately predicting singlet and triplet excitation energies. Different DFT formulations (Tamm-Dancoff approximation, linear response time-dependent DFT, Δ-SCF) and spin scaling schemes along with several ab initio methods (CC2, ADC(2)/MP2, CIS(D), CIS) are evaluated. While wave-function based methods yield rather reliable singlet-triplet gaps, many DFT functionals are shown to systematically underestimate triplet excitation energies. To gain insight, the impact of exact exchange and correlation is in detail addressed.

REVIEW ARTICLE: On correlation effects in electron spectroscopies and the GW approximation

NASA Astrophysics Data System (ADS)

Hedin, Lars

1999-10-01

The GW approximation (GWA) extends the well-known Hartree-Fock approximation (HFA) for the self-energy (exchange potential), by replacing the bare Coulomb potential v by the dynamically screened potential W, e.g. Vex = iGv is replaced by icons/Journals/Common/Sigma" ALT="Sigma" ALIGN="TOP"/>GW = iGW. Here G is the one-electron Green's function. The GWA like the HFA is self-consistent, which allows for solutions beyond perturbation theory, like say spin-density waves. In a first approximation, iGW is a sum of a statically screened exchange potential plus a Coulomb hole (equal to the electrostatic energy associated with the charge pushed away around a given electron). The Coulomb hole part is larger in magnitude, but the two parts give comparable contributions to the dispersion of the quasi-particle energy. The GWA can be said to describe an electronic polaron (an electron surrounded by an electronic polarization cloud), which has great similarities to the ordinary polaron (an electron surrounded by a cloud of phonons). The dynamical screening adds new crucial features beyond the HFA. With the GWA not only bandstructures but also spectral functions can be calculated, as well as charge densities, momentum distributions, and total energies. We will discuss the ideas behind the GWA, and generalizations which are necessary to improve on the rather poor GWA satellite structures in the spectral functions. We will further extend the GWA approach to fully describe spectroscopies like photoemission, x-ray absorption, and electron scattering. Finally we will comment on the relation between the GWA and theories for strongly correlated electronic systems. In collecting the material for this review, a number of new results and perspectives became apparent, which have not been published elsewhere.

Influence of the nonexchangeable potassium of mica on radiocesium uptake by paddy rice.

PubMed

Eguchi, Tetsuya; Ohta, Takeshi; Ishikawa, Tetsuya; Matsunami, Hisaya; Takahashi, Yoshihiko; Kubo, Katashi; Yamaguchi, Noriko; Kihou, Nobuharu; Shinano, Takuro

2015-09-01

A pot cultivation experiment was conducted to elucidate the influence of the nonexchangeable potassium (K) of mica on radiocesium ((137)Cs) uptake by paddy rice (Oryza sativa L. cv. Koshihikari), and to evaluate the potential of mica application as a countermeasure to reduce radiocesium transfer from soil to paddy rice. The increase in the exchangeable K concentrations of soils, measured before planting, due to mica (muscovite, biotite, and phlogopite) application was negligible. However, in trioctahedral mica (biotite and phlogopite)-treated soil, the release of nonexchangeable K from the mica interlayer maintained the soil-solution K at a higher level during the growing season in comparison to the control, and consequently decreased the (137)Cs transfer factor for brown rice (TF). The sodium tetraphenylboron (TPB)-extractable K concentration of the soils, measured before planting, was strongly negatively correlated with the TF, whereas the exchangeable K concentration of the soils, also measured before planting, was not correlated with the TF. Therefore, we conclude that TPB-extractable K is more reliable than exchangeable K as a basis of fertilizer recommendations for radiocesium-contaminated paddy fields. Phlogopite-treated soils exhibited higher TPB-extractable K concentrations and lower TF values than biotite-treated soils. We thus conclude that phlogopite application is an effective countermeasure to reduce radiocesium uptake in paddy rice. Copyright © 2015 Elsevier Ltd. All rights reserved.

Combining Density Functional Theory and Green's Function Theory: Range-Separated, Nonlocal, Dynamic, and Orbital-Dependent Hybrid Functional.

PubMed

Kananenka, Alexei A; Zgid, Dominika

2017-11-14

We present a rigorous framework which combines single-particle Green's function theory with density functional theory based on a separation of electron-electron interactions into short- and long-range components. Short-range contribution to the total energy and exchange-correlation potential is provided by a density functional approximation, while the long-range contribution is calculated using an explicit many-body Green's function method. Such a hybrid results in a nonlocal, dynamic, and orbital-dependent exchange-correlation functional of a single-particle Green's function. In particular, we present a range-separated hybrid functional called srSVWN5-lrGF2 which combines the local-density approximation and the second-order Green's function theory. We illustrate that similarly to density functional approximations, the new functional is weakly basis-set dependent. Furthermore, it offers an improved description of the short-range dynamic correlation. The many-body contribution to the functional mitigates the many-electron self-interaction error present in many density functional approximations and provides a better description of molecular properties. Additionally, we illustrate that the new functional can be used to scale down the self-energy and, therefore, introduce an additional sparsity to the self-energy matrix that in the future can be exploited in calculations for large molecules or periodic systems.

Effect of alkaline material on phytotoxicity and bioavailability of Cu, Cd, Pb and Zn in stabilized sewage sludge.

PubMed

Zhang, Hongling; Ma, Guofeng; Sun, Lina; Li, Huiying

2017-07-16

The availability and phytotoxicity of heavy metals in sewage sludge is the key restrictive factor that limits sludge application. In this study, municipal sewage sludge was stabilized by alkaline slag or coal fly ash, then the leaching characteristic and fraction distributions of Cu, Cd, Pb and Zn were studied, and their effects on seed germination, root length, and plant accumulating were compared. The results showed that mixed sewage sludge with alkaline slag and coal fly ash decreased the percentage of available heavy metals in sewage sludge. The percentage of exchangeable Cu, Pb, Zn and Cd in stabilized sewage sludge (S1-S4) was 1.50-8.67 times lower than that in SS-only treatment. Leachate Cd, Cu, Pb and Zn from stabilized SS was much lower than the limit threshold. The addition of alkaline materials to SS reduced the inhibitory effect on seed germination and root growth. Pearson's correlation analysis indicated that there was a significant negative correlation between pH and available heavy metals, while a significant positive correlation between the percentage of exchangeable fraction of heavy metals, the leaching potential, tissue concentration and accumulation of heavy metal and toxicity for seed germination was observed.

The QTP family of consistent functionals and potentials in Kohn-Sham density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin, Yifan; Bartlett, Rodney J., E-mail: bartlett@qtp.ufl.edu

This manuscript presents the second, consistent density functional in the QTP (Quantum Theory Project) family, that is, the CAM-QTP(01). It is a new range-separated exchange-correlation functional in which the non-local exchange contribution is 100% at large separation. It follows the same basic principles of this family that the Kohn-Sham eigenvalues of the occupied orbitals approximately equal the vertical ionization energies, which is not fulfilled by most of the traditional density functional methods. This new CAM-QTP(01) functional significantly improves the accuracy of the vertical excitation energies especially for the Rydberg states in the test set. It also reproduces many other propertiesmore » such as geometries, reaction barrier heights, and atomization energies.« less

Observation of Solar Wind Charge Exchange Emission from Exospheric Material in and Outside Earth's Magnetosheath

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Collier, M. R.; Cravens, T.; Kuntz, K. D.; Lepri, S. T.; Robertson, I.; Tomas, L.

2008-01-01

A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth s magnetosheath. The light curve of the O VII (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.36). The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

Correlation of intercalation potential with d-electron configurations for cathode compounds of lithium-ion batteries.

PubMed

Chen, Zhenlian; Zhang, Caixia; Zhang, Zhiyong; Li, Jun

2014-07-14

The d-electron localization is widely recognized as important to transport properties of transition metal compounds, but its role in the energy conversion of intercalation reactions of cathode compounds is still not fully explored. In this work, the correlation of intercalation potential with electron affinity, a key energy term controlling electron intercalation, then with d-electron configuration, is investigated. Firstly, we find that the change of the intercalation potential with respect to the transition metal cations within the same structure class is correlated in an approximately mirror relationship with the electron affinity, based on first-principles calculations on three typical categories of cathode compounds including layered oxides and polyoxyanions Then, by using a new model Hamiltonian based on the crystal-field theory, we reveal that the evolution is governed by the combination of the crystal-field splitting and the on-site d-d exchange interactions. Further, we show that the charge order in solid-solution composites and the compatibility of multi-electron redox steps could be inferred from the energy terms with the d-electron configuration alternations. These findings may be applied to rationally designing new chemistry for the lithium-ion batteries and other metal-ion batteries.

Correlation between Gini index and mobility in a stochastic kinetic model of economic exchange

NASA Astrophysics Data System (ADS)

Bertotti, Maria Letizia; Chattopadhyay, Amit K.; Modanese, Giovanni

Starting from a class of stochastically driven kinetic models of economic exchange, here we present results highlighting the correlation of the Gini inequality index with the social mobility rate, close to dynamical equilibrium. Except for the "canonical-additive case", our numerical results consistently indicate negative values of the correlation coefficient, in agreement with empirical evidence. This confirms that growing inequality is not conducive to social mobility which then requires an "external source" to sustain its dynamics. On the other hand, the sign of the correlation between inequality and total income in the canonical ensemble depends on the way wealth enters or leaves the system. At a technical level, the approach involves a generalization of a stochastic dynamical system formulation, that further paves the way for a probabilistic formulation of perturbed economic exchange models.

Magnetic Exchange Couplings from Semilocal Functionals Evaluated Nonself-Consistently on Hybrid Densities: Insights on Relative Importance of Exchange, Correlation, and Delocalization.

PubMed

Phillips, Jordan J; Peralta, Juan E

2012-09-11

Semilocal functionals generally yield poor magnetic exchange couplings for transition-metal complexes, typically overpredicting in magnitude the experimental values. Here we show that semilocal functionals evaluated nonself-consistently on densities from hybrid functionals can yield magnetic exchange couplings that are greatly improved with respect to their self-consistent semilocal values. Furthermore, when semilocal functionals are evaluated nonself-consistently on densities from a "half-and-half" hybrid, their errors with respect to experimental values can actually be lower than those from self-consistent calculations with standard hybrid functionals such as PBEh or TPSSh. This illustrates that despite their notoriously poor performance for exchange couplings, for many systems semilocal functionals are capable of delivering accurate relative energies for magnetic states provided that their electron delocalization error is corrected. However, while self-consistent calculations with hybrids uniformly improve results for all complexes, evaluating nonself-consistently with semilocal functionals does not give a balanced improvement for both ferro- and antiferromagnetically coupled complexes, indicating that there is more at play with the overestimation problem than simply the delocalization error. Additionally, we show that for some systems the conventional wisdom of choice of exchange functional mattering more than correlation does not hold. This combined with results from the nonself-consistent calculations provide insight on clarifying the relative roles of exchange, correlation, and delocalization in calculating magnetic exchange coupling parameters in Kohn-Sham Density Functional Theory.

Semilocal density functional obeying a strongly tightened bound for exchange

PubMed Central

Sun, Jianwei; Perdew, John P.; Ruzsinszky, Adrienn

2015-01-01

Because of its useful accuracy and efficiency, density functional theory (DFT) is one of the most widely used electronic structure theories in physics, materials science, and chemistry. Only the exchange-correlation energy is unknown, and needs to be approximated in practice. Exact constraints provide useful information about this functional. The local spin-density approximation (LSDA) was the first constraint-based density functional. The Lieb–Oxford lower bound on the exchange-correlation energy for any density is another constraint that plays an important role in the development of generalized gradient approximations (GGAs) and meta-GGAs. Recently, a strongly and optimally tightened lower bound on the exchange energy was proved for one- and two-electron densities, and conjectured for all densities. In this article, we present a realistic “meta-GGA made very simple” (MGGA-MVS) for exchange that respects this optimal bound, which no previous beyond-LSDA approximation satisfies. This constraint might have been expected to worsen predicted thermochemical properties, but in fact they are improved over those of the Perdew–Burke–Ernzerhof GGA, which has nearly the same correlation part. MVS exchange is however radically different from that of other GGAs and meta-GGAs. Its exchange enhancement factor has a very strong dependence upon the orbital kinetic energy density, which permits accurate energies even with the drastically tightened bound. When this nonempirical MVS meta-GGA is hybridized with 25% of exact exchange, the resulting global hybrid gives excellent predictions for atomization energies, reaction barriers, and weak interactions of molecules. PMID:25561554

Semilocal density functional obeying a strongly tightened bound for exchange.

PubMed

Sun, Jianwei; Perdew, John P; Ruzsinszky, Adrienn

2015-01-20

Because of its useful accuracy and efficiency, density functional theory (DFT) is one of the most widely used electronic structure theories in physics, materials science, and chemistry. Only the exchange-correlation energy is unknown, and needs to be approximated in practice. Exact constraints provide useful information about this functional. The local spin-density approximation (LSDA) was the first constraint-based density functional. The Lieb-Oxford lower bound on the exchange-correlation energy for any density is another constraint that plays an important role in the development of generalized gradient approximations (GGAs) and meta-GGAs. Recently, a strongly and optimally tightened lower bound on the exchange energy was proved for one- and two-electron densities, and conjectured for all densities. In this article, we present a realistic "meta-GGA made very simple" (MGGA-MVS) for exchange that respects this optimal bound, which no previous beyond-LSDA approximation satisfies. This constraint might have been expected to worsen predicted thermochemical properties, but in fact they are improved over those of the Perdew-Burke-Ernzerhof GGA, which has nearly the same correlation part. MVS exchange is however radically different from that of other GGAs and meta-GGAs. Its exchange enhancement factor has a very strong dependence upon the orbital kinetic energy density, which permits accurate energies even with the drastically tightened bound. When this nonempirical MVS meta-GGA is hybridized with 25% of exact exchange, the resulting global hybrid gives excellent predictions for atomization energies, reaction barriers, and weak interactions of molecules.

Extent of Fock-exchange mixing for a hybrid van der Waals density functional?

NASA Astrophysics Data System (ADS)

Jiao, Yang; Schröder, Elsebeth; Hyldgaard, Per

2018-05-01

The vdW-DF-cx0 exchange-correlation hybrid design [K. Berland et al., J. Chem. Phys. 146, 234106 (2017)] has a truly nonlocal correlation component and aims to facilitate concurrent descriptions of both covalent and non-covalent molecular interactions. The vdW-DF-cx0 design mixes a fixed ratio, a, of the Fock exchange into the consistent-exchange van der Waals density functional, vdW-DF-cx [K. Berland and P. Hyldgaard, Phys. Rev. B 89, 035412 (2014)]. The mixing value a is sometimes taken as a semi-empirical parameter in hybrid formulations. Here, instead, we assert a plausible optimum average a value for the vdW-DF-cx0 design from a formal analysis; A new, independent determination of the mixing a is necessary since the Becke fit [A. D. Becke, J. Chem. Phys. 98, 5648 (1993)], yielding a' = 0.2, is restricted to semilocal correlation and does not reflect non-covalent interactions. To proceed, we adapt the so-called two-legged hybrid construction [K. Burke et al., Chem. Phys. Lett. 265, 115 (1997)] to a starting point in the vdW-DF-cx functional. For our approach, termed vdW-DF-tlh, we estimate the properties of the adiabatic-connection specification of the exact exchange-correlation functional, by combining calculations of the Fock exchange and of the coupling-constant variation in vdW-DF-cx. We find that such vdW-DF-tlh hybrid constructions yield accurate characterizations of molecular interactions (even if they lack self-consistency). The accuracy motivates trust in the vdW-DF-tlh determination of system-specific values of the Fock-exchange mixing. We find that an average value a' = 0.2 best characterizes the vdW-DF-tlh description of covalent and non-covalent interactions, although there exists some scatter. This finding suggests that the original Becke value, a' = 0.2, also represents an optimal average Fock-exchange mixing for the new, truly nonlocal-correlation hybrids. To enable self-consistent calculations, we furthermore define and test a zero-parameter hybrid functional vdW-DF-cx0p (having fixed mixing a' = 0.2) and document that this truly nonlocal correlation hybrid works for general molecular interactions (at reference and at relaxed geometries). It is encouraging that the vdW-DF-cx0p functional remains useful also for descriptions of some extended systems.

On the exchange-hole model of London dispersion forces

NASA Astrophysics Data System (ADS)

Ángyán, János G.

2007-07-01

First-principles derivation is given for the heuristic exchange-hole model of London dispersion forces by Becke and Johnson [J. Chem. Phys. 122, 154104 (2005)]. A one-term approximation is used for the dynamic charge density response function, and it is shown that a central nonempirical ingredient of the approximate nonexpanded dispersion energy is the charge density autocorrelation function, a two-particle property, related to the exchange-correlation hole. In the framework of a dipolar approximation of the Coulomb interaction around the molecular origin, one obtains the so-called Salem-Tang-Karplus approximation to the C6 dispersion coefficient. Alternatively, by expanding the Coulomb interaction around the center of charge (centroid) of the exchange-correlation hole associated with each point in the molecular volume, a multicenter expansion is obtained around the centroids of electron localization domains, always in terms of the exchange-correlation hole. In order to get a formula analogous to that of Becke and Johnson, which involves the exchange-hole only, further assumptions are needed, related to the difficulties of obtaining the expectation value of a two-electron operator from a single determinant. Thus a connection could be established between the conventional fluctuating charge density model of London dispersion forces and the notion of the "exchange-hole dipole moment" shedding some light on the true nature of the approximations implicit in the Becke-Johnson model.

Influence of substrate structure on turnover of the organic cation/H+ exchanger of the renal luminal membrane.

PubMed

Wright, S H; Wunz, T M

1998-08-01

We examined the influence of organic cation (OC) structure on the rate of turnover of the OC/H+ exchanger in rabbit renal brush-border membrane vesicles (BBMV). The rate of efflux of [14C]tetraethylammonium ([14C]TEA) from BBMV, measured in the presence of an inwardly directed chemical gradient for test agent, provided an indirect measure of activity of the OC/H+(OC) exchanger. The trans-stimulation of [14C]TEA efflux from BBMV was a saturable function of increasing extravesicular concentration of both unlabeled TEA and tetramethylammonium (TMA), with an apparent Michaelis constant (Kt) for the interaction of these compounds with the OC/H+(OC) exchanger of 25 microM and 1 mM, respectively. The effect on [14C]TEA efflux of saturating extravesicular concentrations of a series of n-tetraalkylammonium compounds was examined. Whereas the short-chain compounds TMA and TEA markedly stimulated [14C]TEA efflux (by 830% and 690%, respectively), the long-chain compounds tetrapropylammonium and tetrabutylammonium were less effective, increasing efflux by only 40% and 120%, respectively. When the exchanger was saturated with tetrapentylammonium, mediated efflux of [14C]TEA was reduced. Increasing alkyl chain length was also correlated with an increase in the inhibitory effect (as measured by the apparent inhibition constant, Ki, or the IC50 value) that these compounds had against transport of [14C]TEA by the OC/H+(OC) exchanger; i.e., there was a correlation between decreasing IC50 and decreasing turnover of the OC/H+(OC) exchanger. This same correlation was observed for a broader set of test agents of diverse molecular structure, including a series of n-tetraalkylammonium and -phosphonium compounds and the OCs, choline, N1-methyl nicotinamide, 1-methyl-4-phenylpyridinium, and amiloride. Because high affinity of substrates for the OC/H+(OC) exchanger is correlated with increasing substrate hydrophobicity, we conclude that the interaction of hydrophobic OCs with the renal OC/H+(OC) exchanger results in the formation of a substrate-exchanger complex that has a comparatively low rate of turnover.

Comparison of local exchange potentials of electron-N2 scattering

NASA Astrophysics Data System (ADS)

Rumble, J. R., Jr.; Truhlar, D. G.

1980-05-01

Vibrationally and electronically elastic electron scattering by N2 at 2-30 eV impact energy is considered. Static, static-exchange, and static-exchange-plus-polarization potentials, Cade-Sales-Wahl and INDO/1s wave functions, and semiclassical exchange and Hara free-electron-gas exchange potentials are examined. It is shown that the semiclassical exchange approximation is too attractive at low energy for N2. It is also shown quantitatively by consideration of partial and total integral cross sections how the effects of approximations to exchange become smaller as the incident energy is increased until the differences are about 8% for the total integral cross section at 30 eV.

Approximations to the exact exchange potential: KLI versus semilocal

NASA Astrophysics Data System (ADS)

Tran, Fabien; Blaha, Peter; Betzinger, Markus; Blügel, Stefan

2016-10-01

In the search for an accurate and computationally efficient approximation to the exact exchange potential of Kohn-Sham density functional theory, we recently compared various semilocal exchange potentials to the exact one [F. Tran et al., Phys. Rev. B 91, 165121 (2015), 10.1103/PhysRevB.91.165121]. It was concluded that the Becke-Johnson (BJ) potential is a very good starting point, but requires the use of empirical parameters to obtain good agreement with the exact exchange potential. In this work, we extend the comparison by considering the Krieger-Li-Iafrate (KLI) approximation, which is a beyond-semilocal approximation. It is shown that overall the KLI- and BJ-based potentials are the most reliable approximations to the exact exchange potential, however, sizable differences, especially for the antiferromagnetic transition-metal oxides, can be obtained.

Turbulence and wave breaking effects on air-water gas exchange

PubMed

Boettcher; Fineberg; Lathrop

2000-08-28

We present an experimental characterization of the effects of turbulence and breaking gravity waves on air-water gas exchange in standing waves. We identify two regimes that govern aeration rates: turbulent transport when no wave breaking occurs and bubble dominated transport when wave breaking occurs. In both regimes, we correlate the qualitative changes in the aeration rate with corresponding changes in the wave dynamics. In the latter regime, the strongly enhanced aeration rate is correlated with measured acoustic emissions, indicating that bubble creation and dynamics dominate air-water exchange.

Thermodynamics properties of lanthanide series near melting point-A pseudopotential approach

NASA Astrophysics Data System (ADS)

Suthar, P. H.; Gajjar, P. N.

2018-04-01

The present paper deals with computational study of thermodynamics properties for fifteen elements of lanthanide series. The Helmholtz free energy (F), Internal energy (E) and Entropy (S)have been computed using variational method based on the Gibbs-Bogoliubov (GB) along with Percus-Yevick hard sphere reference system and Gajjar's model potential. The local field correction function proposed by Taylor is applied to introduce the exchange and correlation effects in the study of thermodynamics of these metals. The present results in comparison with available theoretical and experimental are found to be in good agreement and confirm the ability of the model potential.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verma, U. P.; Nayak, V.

Quantum mechanical first principle calculations have been performed to study the electronic and structural properties of TiN and TiAs in zinc blende (ZB) and rock salt (RS) structures. The full-potential linearized augmented plane wave (FP-LAPW) method has been used within the framework of density functional theory (DFT). The exchange correlation functional has been solved employing generalized gradient approximation (GGA). Our predicted results for lattice constants are in good agreement with the earlier findings. The electronic band structures of TiX are metallic in both the phases.

Relativity and the lead-acid battery.

PubMed

Ahuja, Rajeev; Blomqvist, Andreas; Larsson, Peter; Pyykkö, Pekka; Zaleski-Ejgierd, Patryk

2011-01-07

The energies of the solid reactants in the lead-acid battery are calculated ab initio using two different basis sets at nonrelativistic, scalar-relativistic, and fully relativistic levels, and using several exchange-correlation potentials. The average calculated standard voltage is 2.13 V, compared with the experimental value of 2.11 V. All calculations agree in that 1.7-1.8 V of this standard voltage arise from relativistic effects, mainly from PbO2 but also from PbSO4.

Effect of sulfur doping on thermoelectric properties of Sodium Tantalate - A first principles study

NASA Astrophysics Data System (ADS)

Chowdary, Bharadwaj; Jayaraman, Kaushik; Molli, Muralikrishna

2018-05-01

In this work, we report the thermoelectric (TE) transport properties of perovskite-like Sodium Tantalate and studied the effect of Sulfur doping on TE properties of Sodium Tantalate. The band structures are calculated in the purview of density functional theory using the mBJ exchange correlation potential. The transport properties are evaluated using the Boltzmann transport theory in the constant relaxation time approximation. Our results suggest that Sulfur doped Sodium Tantalate is better n-type thermoelectric compared to Sodium Tantalate.

Water on BN doped benzene: A hard test for exchange-correlation functionals and the impact of exact exchange on weak binding

DOE PAGES

Al-Hamdani, Yasmine S.; Alfè, Dario; von Lilienfeld, O. Anatole; ...

2014-10-22

Density functional theory (DFT) studies of weakly interacting complexes have recently focused on the importance of van der Waals dispersion forces, whereas the role of exchange has received far less attention. Here, by exploiting the subtle binding between water and a boron and nitrogen doped benzene derivative (1,2-azaborine) we show how exact exchange can alter the binding conformation within a complex. Benchmark values have been calculated for three orientations of the water monomer on 1,2-azaborine from explicitly correlated quantum chemical methods, and we have also used diffusion quantum Monte Carlo. For a host of popular DFT exchange-correlation functionals we showmore » that the lack of exact exchange leads to the wrong lowest energy orientation of water on 1,2-azaborine. As such, we suggest that a high proportion of exact exchange and the associated improvement in the electronic structure could be needed for the accurate prediction of physisorption sites on doped surfaces and in complex organic molecules. Meanwhile to predict correct absolute interaction energies an accurate description of exchange needs to be augmented by dispersion inclusive functionals, and certain non-local van der Waals functionals (optB88- and optB86b-vdW) perform very well for absolute interaction energies. Through a comparison with water on benzene and borazine (B₃N₃H₆) we show that these results could have implications for the interaction of water with doped graphene surfaces, and suggest a possible way of tuning the interaction energy.« less

An alternative way to track the hot money in turbulent times

NASA Astrophysics Data System (ADS)

Sensoy, Ahmet

2015-02-01

During recent years, networks have proven to be an efficient way to characterize and investigate a wide range of complex financial systems. In this study, we first obtain the dynamic conditional correlations between filtered exchange rates (against US dollar) of several countries and introduce a time-varying threshold correlation level to define dynamic strong correlations between these exchange rates. Then, using evolving networks obtained from strong correlations, we propose an alternative approach to track the hot money in turbulent times. The approach is demonstrated for the time period including the financial turmoil of 2008. Other applications are also discussed.

Individual Basepair Stability of DNA and RNA Studied by NMR-Detected Solvent Exchange

PubMed Central

Steinert, Hannah S.; Rinnenthal, Jörg; Schwalbe, Harald

2012-01-01

In this study, we have optimized NMR methodology to determine the thermodynamic parameters of basepair opening in DNA and RNA duplexes by characterizing the temperature dependence of imino proton exchange rates of individual basepairs. Contributions of the nuclear Overhauser effect to exchange rates measured with inversion recovery experiments are quantified, and the influence of intrinsic and external catalysis exchange mechanisms on the imino proton exchange rates is analyzed. Basepairs in DNA and RNA have an approximately equal stability, and the enthalpy and entropy values of their basepair dissociation are correlated linearly. Furthermore, the compensation temperature, Tc, which is derived from the slope of the correlation, coincides with the melting temperature, and duplex unfolding occurs at that temperature where all basepairs are equally thermodynamically stable. The impact of protium-deuterium exchange of the imino hydrogen on the free energy of RNA basepair opening is investigated, and it is found that two A·U basepairs show distinct fractionation factors. PMID:22713572

Long-range corrected density functional through the density matrix expansion based semilocal exchange hole.

PubMed

Patra, Bikash; Jana, Subrata; Samal, Prasanjit

2018-03-28

The exchange hole, which is one of the principal constituents of the density functional formalism, can be used to design accurate range-separated hybrid functionals in association with appropriate correlation. In this regard, the exchange hole derived from the density matrix expansion has gained attention due to its fulfillment of some of the desired exact constraints. Thus, the new long-range corrected density functional proposed here combines the meta generalized gradient approximation level exchange functional designed from the density matrix expansion based exchange hole coupled with the ab initio Hartree-Fock exchange through the range separation of the Coulomb interaction operator using the standard error function technique. Then, in association with the Lee-Yang-Parr correlation functional, the assessment and benchmarking of the above newly constructed range-separated functional with various well-known test sets shows its reasonable performance for a broad range of molecular properties, such as thermochemistry, non-covalent interaction and barrier heights of the chemical reactions.

Hyperpolarized Xenon-129 Gas-Exchange Imaging of Lung Microstructure: First Case Studies in Subjects with Obstructive Lung Disease

PubMed Central

Dregely, Isabel; Mugler, John P.; Ruset, Iulian C.; Altes, Talissa A.; Mata, Jaime F.; Miller, G. Wilson; Ketel, Jeffrey; Ketel, Steve; Distelbrink, Jan; Hersman, F.W.; Ruppert, Kai

2011-01-01

Purpose To develop and test a method to non-invasively assess the functional lung microstructure. Materials and Methods The Multiple exchange time Xenon polarization Transfer Contrast technique (MXTC) encodes xenon gas-exchange contrast at multiple delay times permitting two lung-function parameters to be derived: 1) MXTC-F, the long exchange-time depolarization value, which is proportional to the tissue to alveolar-volume ratio and 2) MXTC-S, the square root of the xenon exchange-time constant, which characterizes thickness and composition of alveolar septa. Three healthy volunteers, one asthmatic and two COPD (GOLD stage I and II) subjects were imaged with MXTC MRI. In a subset of subjects, hyperpolarized xenon-129 ADC MRI and CT imaging were also performed. Results The MXTC-S parameter was found to be elevated in subjects with lung disease (p-value = 0.018). In the MXTC-F parameter map it was feasible to identify regional loss of functional tissue in a COPD patient. Further, the MXTC-F map showed excellent regional correlation with CT and ADC (ρ ≥ 0.90) in one COPD subject. Conclusion The functional tissue-density parameter MXTC-F showed regional agreement with other imaging techniques. The newly developed parameter MXTC-S, which characterizes the functional thickness of alveolar septa, has potential as a novel biomarker for regional parenchymal inflammation or thickening. PMID:21509861

Potential for noninvasive assessment of lung inhomogeneity using highly precise, highly time-resolved measurements of gas exchange

PubMed Central

Mountain, James E.; Santer, Peter; O’Neill, David P.; Smith, Nicholas M. J.; Ciaffoni, Luca; Couper, John H.; Ritchie, Grant A. D.; Hancock, Gus; Whiteley, Jonathan P.

2018-01-01

Inhomogeneity in the lung impairs gas exchange and can be an early marker of lung disease. We hypothesized that highly precise measurements of gas exchange contain sufficient information to quantify many aspects of the inhomogeneity noninvasively. Our aim was to explore whether one parameterization of lung inhomogeneity could both fit such data and provide reliable parameter estimates. A mathematical model of gas exchange in an inhomogeneous lung was developed, containing inhomogeneity parameters for compliance, vascular conductance, and dead space, all relative to lung volume. Inputs were respiratory flow, cardiac output, and the inspiratory and pulmonary arterial gas compositions. Outputs were expiratory and pulmonary venous gas compositions. All values were specified every 10 ms. Some parameters were set to physiologically plausible values. To estimate the remaining unknown parameters and inputs, the model was embedded within a nonlinear estimation routine to minimize the deviations between model and data for CO2, O2, and N2 flows during expiration. Three groups, each of six individuals, were studied: young (20–30 yr); old (70–80 yr); and patients with mild to moderate chronic obstructive pulmonary disease (COPD). Each participant undertook a 15-min measurement protocol six times. For all parameters reflecting inhomogeneity, highly significant differences were found between the three participant groups (P < 0.001, ANOVA). Intraclass correlation coefficients were 0.96, 0.99, and 0.94 for the parameters reflecting inhomogeneity in deadspace, compliance, and vascular conductance, respectively. We conclude that, for the particular participants selected, highly repeatable estimates for parameters reflecting inhomogeneity could be obtained from noninvasive measurements of respiratory gas exchange. NEW & NOTEWORTHY This study describes a new method, based on highly precise measures of gas exchange, that quantifies three distributions that are intrinsic to the lung. These distributions represent three fundamentally different types of inhomogeneity that together give rise to ventilation-perfusion mismatch and result in impaired gas exchange. The measurement technique has potentially broad clinical applicability because it is simple for both patient and operator, it does not involve ionizing radiation, and it is completely noninvasive. PMID:29074714

Individual, network, and neighborhood correlates of exchange sex among female non-injection drug users in Baltimore, MD (2005–2007)

PubMed Central

Rudolph, Abby E; Linton, Sabriya; Dyer, Typhanye Penniman; Latkin, Carl

2012-01-01

The “HIV risk environment” has been characterized as a dynamic interplay between structural and network factors. However, most HIV prevention research has not examined the independent and combined impact of network and structural factors. We aimed to identify individual, network, and neighborhood correlates of exchange sex (≥1 exchange sex partner, past 90 days) among female non-injection drug users (NIDUs). We used baseline data from 417 NIDUs enrolled in a randomized HIV prevention trial in Baltimore (2005–2007). Surveys ascertained demographic variables, drug/sex risk behaviors, neighborhood perceptions, and social/sexual network characteristics. Correlates of exchange sex were identified with descriptive statistics and log-binomial regression. Our findings suggest that sex and drug relationships among female NIDUs are interlinked and may be difficult to modify without altering social norms. Strengthening ties that provide social support but not drug support and reducing ties that provide both drug and social support may facilitate reductions in individual-level HIV-risk behaviors. PMID:22983502

Numerical investigation of transient behaviour of the recuperative heat exchanger in a MR J-T cryocooler using different heat transfer correlations

NASA Astrophysics Data System (ADS)

Damle, R. M.; Ardhapurkar, P. M.; Atrey, M. D.

2016-12-01

In J-T cryocoolers operating with mixed refrigerants (nitrogen-hydrocarbons), the recuperative heat exchange takes place under two-phase conditions. Simultaneous boiling of the low pressure stream and condensation of the high pressure stream results in higher heat transfer coefficients. The mixture composition, operating conditions and the heat exchanger design are crucial for obtaining the required cryogenic temperature. In this work, a one-dimensional transient algorithm is developed for the simulation of the two-phase heat transfer in the recuperative heat exchanger of a mixed refrigerant J-T cryocooler. Modified correlation is used for flow boiling of the high pressure fluid while different condensation correlations are employed with and without the correction for the low pressure fluid. Simulations are carried out for different mixture compositions and numerical predictions are compared with the experimental data. The overall heat transfer is predicted reasonably well and the qualitative trends of the temperature profiles are also captured by the developed numerical model.

Estimating time-varying conditional correlations between stock and foreign exchange markets

NASA Astrophysics Data System (ADS)

Tastan, Hüseyin

2006-02-01

This study explores the dynamic interaction between stock market returns and changes in nominal exchange rates. Many financial variables are known to exhibit fat tails and autoregressive variance structure. It is well-known that unconditional covariance and correlation coefficients also vary significantly over time and multivariate generalized autoregressive model (MGARCH) is able to capture the time-varying variance-covariance matrix for stock market returns and changes in exchange rates. The model is applied to daily Euro-Dollar exchange rates and two stock market indexes from the US economy: Dow-Jones Industrial Average Index and S&P500 Index. The news impact surfaces are also drawn based on the model estimates to see the effects of idiosyncratic shocks in respective markets.

[Characteristics of mercury exchange flux between soil and atmosphere under the snow retention and snow melting control].

PubMed

Zhang, Gang; Wang, Ning; Ai, Jian-Chao; Zhang, Lei; Yang, Jing; Liu, Zi-Qi

2013-02-01

Jiapigou gold mine, located in the upper Songhua River, was once the largest mine in China due to gold output, where gold extraction with algamation was widely applied to extract gold resulting in severe mercury pollution to ambient environmental medium. In order to study the characteristics of mercury exchange flux between soil (snow) and atmosphere under the snow retention and snow melting control, sampling sites were selected in equal distances along the slope which is situated in the typical hill-valley terrain unit. Mercury exchange flux between soil (snow) and atmosphere was determined with the method of dynamic flux chamber and in all sampling sites the atmosphere concentration from 0 to 150 cm near to the earth in the vertical direction was measured. Furthermore, the impact factors including synchronous meteorology, the surface characteristics under the snow retention and snow melting control and the mercury concentration in vertical direction were also investigated. The results are as follows: During the period of snow retention and melting the air mercury tends to gather towards valley bottom along the slope and an obvious deposit tendency process was found from air to the earth's surface under the control of thermal inversion due to the underlying surface of cold source (snow surface). However, during the period of snow melting, mercury exchange flux between the soil and atmosphere on the surface of the earth with the snow being melted demonstrates alternative deposit and release processes. As for the earth with snow covered, the deposit level of mercury exchange flux between soil and atmosphere is lower than that during the period of snow retention. The relationship between mercury exchange flux and impact factors shows that in snow retention there is a remarkable negative linear correlation between mercury exchange flux and air mercury concentration as well as between the former and the air temperature. In addition, in snow melting mercury exchange flux is remarkably negatively linearly correlated to air mercury concentration and positively linearly correlated to air temperature. Furthermore, there is a general positive linear correlation between mercury exchange flux and soil temperature on the surface of earth after snow melting.

Simulation Suggests that medical group mergers won't undermine the potential utility of health information exchanges.

PubMed

Rudin, Robert S; Schneider, Eric C; Volk, Lynn A; Szolovits, Peter; Salzberg, Claudia A; Simon, Steven R; Bates, David W

2012-03-01

Federal and state agencies are investing substantial resources in the creation of community health information exchanges, which are consortia that enable independent health care organizations to exchange clinical data. However, under pressure to form accountable care organizations, medical groups may merge and support private health information exchanges. Such activity could reduce the potential utility of community exchanges-that is, the exchanges' capacity to share patient data across hospitals and physician practices that are independent. Simulations of care transitions based on data from ten Massachusetts communities suggest that there would have to be many such mergers to undermine the potential utility of health information exchanges. At the same time, because hospitals and the largest medical groups account for only 10-20 percent of care transitions in a community, information exchanges will still need to recruit a large proportion of the medical groups in a given community for the exchanges to maintain their usefulness in fostering information exchange across independent providers.

Phase space explorations in time dependent density functional theory

NASA Astrophysics Data System (ADS)

Rajam, Aruna K.

Time dependent density functional theory (TDDFT) is one of the useful tools for the study of the dynamic behavior of correlated electronic systems under the influence of external potentials. The success of this formally exact theory practically relies on approximations for the exchange-correlation potential which is a complicated functional of the co-ordinate density, non-local in space and time. Adiabatic approximations (such as ALDA), which are local in time, are most commonly used in the increasing applications of the field. Going beyond ALDA, has been proved difficult leading to mathematical inconsistencies. We explore the regions where the theory faces challenges, and try to answer some of them via the insights from two electron model systems. In this thesis work we propose a phase-space extension of the TDDFT. We want to answer the challenges the theory is facing currently by exploring the one-body phase-space. We give a general introduction to this theory and its mathematical background in the first chapter. In second chapter, we carryout a detailed study of instantaneous phase-space densities and argue that the functionals of distributions can be a better alternative to the nonlocality issue of the exchange-correlation potentials. For this we study in detail the interacting and the non-interacting phase-space distributions for Hookes atom model. The applicability of ALDA-based TDDFT for the dynamics in strongfields can become severely problematic due to the failure of single-Slater determinant picture.. In the third chapter, we analyze how the phase-space distributions can shine some light into this problem. We do a comparative study of Kohn-Sham and interacting phase-space and momentum distributions for single ionization and double ionization systems. Using a simple model of two-electron systems, we have showed that the momentum distribution computed directly from the exact KS system contains spurious oscillations: a non-classical description of the essentially classical two-electron dynamics. In Time dependent density matrix functional theory (TDDMFT), the evolution scheme of the 1RDM (first order reduced density matrix) contains second-order reduced density matrix (2RDM), which has to be expressed in terms of 1RDMs. Any non-correlated approximations (Hartree-Fock) for 2RDM would fail to capture the natural occupations of the system. In our fourth chapter, we show that by applying the quasi-classical and semi-classical approximations one can capture the natural occupations of the excited systems. We study a time-dependent Moshinsky atom model for this. The fifth chapter contains a comparative work on the existing non-local exchange-correlation kernels that are based on current density response frame work and the co-moving frame work. We show that the two approaches though coinciding with each other in linear response regime, actually turn out to be different in non-linear regime.

Assessing the Chemical Accuracy of Protein Structures via Peptide Acidity

PubMed Central

Anderson, Janet S.; Hernández, Griselda; LeMaster, David M.

2012-01-01

Although the protein native state is a Boltzmann conformational ensemble, practical applications often require a representative model from the most populated region of that distribution. The acidity of the backbone amides, as reflected in hydrogen exchange rates, is exquisitely sensitive to the surrounding charge and dielectric volume distribution. For each of four proteins, three independently determined X-ray structures of differing crystallographic resolution were used to predict exchange for the static solvent-exposed amide hydrogens. The average correlation coefficients range from 0.74 for ubiquitin to 0.93 for Pyrococcus furiosus rubredoxin, reflecting the larger range of experimental exchange rates exhibited by the latter protein. The exchange prediction errors modestly correlate with the crystallographic resolution. MODELLER 9v6-derived homology models at ~60% sequence identity (36% identity for chymotrypsin inhibitor CI2) yielded correlation coefficients that are ~0.1 smaller than for the cognate X-ray structures. The most recently deposited NOE-based ubiquitin structure and the original NMR structure of CI2 fail to provide statistically significant predictions of hydrogen exchange. However, the more recent RECOORD refinement study of CI2 yielded predictions comparable to the X-ray and homology model-based analyses. PMID:23182463

Hydrogen/deuterium (H/D) exchange of gelatinized starch studied by two-dimensional (2D) near-infrared (NIR) correlation spectroscopy

NASA Astrophysics Data System (ADS)

Shinzawa, Hideyuki; Mizukado, Junji

2018-05-01

Hydrogen/deuterium (H/D) exchange of gelatinized starch was probed by in-situ near-infrared (NIR) monitoring coupled with two-dimensional (2D) correlation spectroscopy. Gelatinized starch undergoes spontaneous H/D exchange in D2O. During the substitution, the exchange rate essentially becomes different depending on solvent accessibility of various parts of the molecule. Thus, by analyzing the change in the NIR feature observed during the substitution, it becomes possible to sort out local structure and dynamics of the system. 2D correlation analysis of the time-dependent NIR spectra reveals the presence of different local structure of the starch, each having different solvent accessibility. For example, during the H/D exchange, the D2O is first absorbed by starch molecules especially around the surface area between the starch and water, where the water molecules are weakly interacted with the starch molecules. This absorption is quickly followed by the development of HDO species. Further absorption of the D2O results in the penetration of the molecules inside the starch and eventually develops the relatively strong interaction between the HDO and starch molecules because of the presence of dominant starch molecules.

Communication: Near-locality of exchange and correlation density functionals for 1- and 2-electron systems

NASA Astrophysics Data System (ADS)

Sun, Jianwei; Perdew, John P.; Yang, Zenghui; Peng, Haowei

2016-05-01

The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin density approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Doganay, Ozkan, E-mail: ozkan.doganay@oncology.ox.ac.uk; Imaging Research Laboratories, Robarts Research Institute, London, Ontario N6A5C1; Department of Oncology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Oxford OX3 7DQ

Purpose: To assess the feasibility of hyperpolarized (HP) {sup 129}Xe MRI for detection of early stage radiation-induced lung injury (RILI) in a rat model involving unilateral irradiation by assessing differences in gas exchange dynamics between irradiated and unirradiated lungs. Methods: The dynamics of gas exchange between alveolar air space and pulmonary tissue (PT), PT and red blood cells (RBCs) was measured using single-shot spiral iterative decomposition of water and fat with echo asymmetry and least-squares estimation images of the right and left lungs of two age-matched cohorts of Sprague Dawley rats. The first cohort (n = 5) received 18 Gymore » irradiation to the right lung using a {sup 60}Co source and the second cohort (n = 5) was not irradiated and served as the healthy control. Both groups were imaged two weeks following irradiation when radiation pneumonitis (RP) was expected to be present. The gas exchange data were fit to a theoretical gas exchange model to extract measurements of pulmonary tissue thickness (L{sub PT}) and relative blood volume (V{sub RBC}) from each of the right and left lungs of both cohorts. Following imaging, lung specimens were retrieved and percent tissue area (PTA) was assessed histologically to confirm RP and correlate with MRI measurements. Results: Statistically significant differences in L{sub PT} and V{sub RBC} were observed between the irradiated and non-irradiated cohorts. In particular, L{sub PT} of the right and left lungs was increased approximately 8.2% and 5.0% respectively in the irradiated cohort. Additionally, V{sub RBC} of the right and left lungs was decreased approximately 36.1% and 11.7% respectively for the irradiated cohort compared to the non-irradiated cohort. PTA measurements in both right and left lungs were increased in the irradiated group compared to the non-irradiated cohort for both the left (P < 0.05) and right lungs (P < 0.01) confirming the presence of RP. PTA measurements also correlated with the MRI measurements for both the non-irradiated (r = 0.79, P < 0.01) and irradiated groups (r = 0.91, P < 0.01). Conclusions: Regional RILI can be detected two weeks post-irradiation using HP {sup 129}Xe MRI and analysis of gas exchange curves. This approach correlates well with histology and can potentially be used clinically to assess radiation pneumonitis associated with early RILI to improve radiation therapy outcomes.« less

Source-Free Exchange-Correlation Magnetic Fields in Density Functional Theory.

PubMed

Sharma, S; Gross, E K U; Sanna, A; Dewhurst, J K

2018-03-13

Spin-dependent exchange-correlation energy functionals in use today depend on the charge density and the magnetization density: E xc [ρ, m]. However, it is also correct to define the functional in terms of the curl of m for physical external fields: E xc [ρ,∇ × m]. The exchange-correlation magnetic field, B xc , then becomes source-free. We study this variation of the theory by uniquely removing the source term from local and generalized gradient approximations to the functional. By doing so, the total Kohn-Sham moments are improved for a wide range of materials for both functionals. Significantly, the moments for the pnictides are now in good agreement with experiment. This source-free method is simple to implement in all existing density functional theory codes.

Exact exchange and Wilson-Levy correlation: a pragmatic device for studying complex weakly-bonded systems.

PubMed

Walsh, T R

2005-02-07

The Wilson-Levy (WL) correlation functional is used together with Hartree-Fock (HF) theory to evaluate interaction energies at intermediate separations (i.e. around equilibrium separation) for several weakly-bonded systems. The HF+WL approach reproduces binding trends for all complexes studied: selected rare-gas dimers, isomers of the methane dimer, benzene dimer and naphthalene dimer, and base-pair stacking structures for pyrimidine, cytosine, uracil and guanine dimers. These HF+WL data are contrasted against results obtained from some popular functionals (including B3LYP and PBE), as well as two newly-developed functionals, X3LYP and xPBE. The utility of HF+WL, with reference to exact-exchange (EXX) density-functional theory, is discussed in terms of a suggested EXXWL exchange-correlation functional.

Accuracy of electron densities obtained via Koopmans-compliant hybrid functionals

NASA Astrophysics Data System (ADS)

Elmaslmane, A. R.; Wetherell, J.; Hodgson, M. J. P.; McKenna, K. P.; Godby, R. W.

2018-04-01

We evaluate the accuracy of electron densities and quasiparticle energy gaps given by hybrid functionals by directly comparing these to the exact quantities obtained from solving the many-electron Schrödinger equation. We determine the admixture of Hartree-Fock exchange to approximate exchange-correlation in our hybrid functional via one of several physically justified constraints, including the generalized Koopmans' theorem. We find that hybrid functionals yield strikingly accurate electron densities and gaps in both exchange-dominated and correlated systems. We also discuss the role of the screened Fock operator in the success of hybrid functionals.

Fractionation, Bioaccessibility, and Risk Assessment of Heavy Metals in the Soil of an Urban Recreational Area Amended with Composted Sewage Sludge

PubMed Central

Zhang, Tao; Shao, Yanqiu; Tian, Chao; Cattle, Stephen R.; Zhu, Ying; Song, Jinjuan

2018-01-01

A composted sewage sludge (CSS) was added to the soil of an urban garden at 5%, 10%, and 25% (w/w soil) and stabilised for 180 days. Samples were then collected and analysed for total heavy metal concentrations, chemical fractions, and bioaccessibility, together with some physicochemical properties. The results showed that the total chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) concentrations were increased with CSS addition rate. The CSS addition decreased the residual fractions of these four elements. The exchangeable Cr, Cu, and Pb fractions were very small or not detected, while Zn exhibited an increasing trend in its exchangeable fraction with CSS addition rate. The bioaccessibility of these four elements was increased with the CSS addition rate. Moreover, the Cr, Cu, and Zn bioaccessibility correlated positively with the total concentration, while the bioaccessibility of these four elements exhibited a negative correlation with the residual fraction. The fractionation and bioaccessibility of heavy metals may have also been influenced by pH, cation exchange capacity, and organic matter. The risk assessment code reflected the amended soil showed no or low environmental risks for Cr, Cu, and Pb and a medium risk for Zn. The hazardous index values and cancer risk levels indicated that the heavy metals in the soil amended with 25% CSS posed negligible potential noncarcinogenic and carcinogenic risks to children and adults via incidental ingestion. PMID:29597244

Na+/H+ exchanger 3 inhibitor diminishes hepcidin-enhanced duodenal calcium transport in hemizygous β-globin knockout thalassemic mice.

PubMed

Charoenphandhu, Narattaphol; Kraidith, Kamonshanok; Lertsuwan, Kornkamon; Sripong, Chanakarn; Suntornsaratoon, Panan; Svasti, Saovaros; Krishnamra, Nateetip; Wongdee, Kannikar

2017-03-01

Recent investigation has shown that the liver-derived iron-regulating hormone, hepcidin, can potentiate intestinal calcium absorption in hemizygous β-globin knockout thalassemic (BKO) mice. Since the upregulation of Fe 2+ and H + cotransporter, divalent metal transporter (DMT)-1, has been shown to correlate with thalassemia-induced intestinal calcium absorption impairment, the inhibition of the apical Na + /H + exchanger (NHE)-3 that is essential for cytoplasmic pH regulation and transepithelial sodium absorption was hypothesized to negatively affect hepcidin action. Herein, the positive effect of hepcidin on the duodenal calcium transport was evaluated using Ussing chamber technique. The results showed that BKO mice had lower absorptive surface area and duodenal calcium transport than wild-type mice. Besides, paracellular transport of zinc in BKO mice was compromised. Hepcidin administration completely restored calcium transport. Since this hepcidin action was totally abolished by inhibitors of the basolateral calcium transporters, Na + /Ca 2+ exchanger (NCX1) and plasma membrane Ca 2+ -ATPase (PMCA 1b ), the enhanced calcium flux potentially occurred through the transcellular pathway rather than paracellular pathway. Interestingly, the selective NHE3 inhibitor, 100 nM tenapanor, markedly inhibited hepcidin-enhanced calcium transport. Accordingly, hepcidin is one of the promising therapeutic agents for calcium malabsorption in β-thalassemia. It mainly stimulates the transcellular calcium transport across the duodenal epithelium in an NHE3-dependent manner.

A bias correction for covariance estimators to improve inference with generalized estimating equations that use an unstructured correlation matrix.

PubMed

Westgate, Philip M

2013-07-20

Generalized estimating equations (GEEs) are routinely used for the marginal analysis of correlated data. The efficiency of GEE depends on how closely the working covariance structure resembles the true structure, and therefore accurate modeling of the working correlation of the data is important. A popular approach is the use of an unstructured working correlation matrix, as it is not as restrictive as simpler structures such as exchangeable and AR-1 and thus can theoretically improve efficiency. However, because of the potential for having to estimate a large number of correlation parameters, variances of regression parameter estimates can be larger than theoretically expected when utilizing the unstructured working correlation matrix. Therefore, standard error estimates can be negatively biased. To account for this additional finite-sample variability, we derive a bias correction that can be applied to typical estimators of the covariance matrix of parameter estimates. Via simulation and in application to a longitudinal study, we show that our proposed correction improves standard error estimation and statistical inference. Copyright © 2012 John Wiley & Sons, Ltd.

Subsystem functional and the missing ingredient of confinement physics in density functionals.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Armiento, Rickard Roberto; Mattsson, Ann Elisabet; Hao, Feng

2010-08-01

The subsystem functional scheme is a promising approach recently proposed for constructing exchange-correlation density functionals. In this scheme, the physics in each part of real materials is described by mapping to a characteristic model system. The 'confinement physics,' an essential physical ingredient that has been left out in present functionals, is studied by employing the harmonic-oscillator (HO) gas model. By performing the potential {yields} density and the density {yields} exchange energy per particle mappings based on two model systems characterizing the physics in the interior (uniform electron-gas model) and surface regions (Airy gas model) of materials for the HO gases,more » we show that the confinement physics emerges when only the lowest subband of the HO gas is occupied by electrons. We examine the approximations of the exchange energy by several state-of-the-art functionals for the HO gas, and none of them produces adequate accuracy in the confinement dominated cases. A generic functional that incorporates the description of the confinement physics is needed.« less

Impact of soil properties on selected pharmaceuticals adsorption in soils

NASA Astrophysics Data System (ADS)

Kodesova, Radka; Kocarek, Martin; Klement, Ales; Fer, Miroslav; Golovko, Oksana; Grabic, Roman; Jaksik, Ondrej

2014-05-01

The presence of human and veterinary pharmaceuticals in the environment has been recognized as a potential threat. Pharmaceuticals may contaminate soils and consequently surface and groundwater. Study was therefore focused on the evaluation of selected pharmaceuticals adsorption in soils, as one of the parameters, which are necessary to know when assessing contaminant transport in soils. The goals of this study were: (1) to select representative soils of the Czech Republic and to measure soil physical and chemical properties; (2) to measure adsorption isotherms of selected pharmaceuticals; (3) to evaluate impact of soil properties on pharmaceutical adsorptions and to propose pedotransfer rules for estimating adsorption coefficients from the measured soil properties. Batch sorption tests were performed for 6 selected pharmaceuticals (beta blockers Atenolol and Metoprolol, anticonvulsant Carbamazepin, and antibiotics Clarithromycin, Trimetoprim and Sulfamethoxazol) and 13 representative soils (soil samples from surface horizons of 11 different soil types and 2 substrates). The Freundlich equations were used to describe adsorption isotherms. The simple correlations between measured physical and chemical soil properties (soil particle density, soil texture, oxidable organic carbon content, CaCO3 content, pH_H2O, pH_KCl, exchangeable acidity, cation exchange capacity, hydrolytic acidity, basic cation saturation, sorption complex saturation, salinity), and the Freundlich adsorption coefficients were assessed using Pearson correlation coefficient. Then multiple-linear regressions were applied to predict the Freundlich adsorption coefficients from measured soil properties. The largest adsorption was measured for Clarithromycin (average value of 227.1) and decreased as follows: Trimetoprim (22.5), Metoprolol (9.0), Atenolol (6.6), Carbamazepin (2.7), Sulfamethoxazol (1.9). Absorption coefficients for Atenolol and Metoprolol closely correlated (R=0.85), and both were also related to absorption coefficients of Carbamazepin (R=0.67 and 0.68). Positive correlation was found between Trimetoprim absorption coefficients and Atenolol, Metoprolol or Carbamazepin absorption coefficients. The negative relationship was found between absorption coefficients of Sulfomethoxazol and Clarithromycin (R=-0.80). Sulfamethoxazol absorption coefficient was negatively related to pH_H2O, pH_KCL or sorption complex saturation and positively to the hydrolytic acidity or exchangeable acidity. Trimetoprim absorption coefficient was positively related to the oxidable organic carbon content, cation exchange capacity, basic cation saturation or silt content and negatively to particle density or sand content. Clarithromycin absorption coefficient was positively related to pH_H2O, pH_KCL, CaCO3 content, basic cation saturation or sorption complex saturation and negatively to hydrolytic acidity or exchangeable acidity. Atenolol and Metoprolol absorption coefficients were positively related to the oxidable organic carbon content, cation exchange capacity, basic cation saturation, salinity, clay content or silt content, and negatively to the particle density or sand content. Finally Carbamazepin absorption coefficient was positively related to the oxidable organic carbon content, cation exchange capacity or basic cation saturation, and negatively to the particle density or sand content. Evaluated pedotransfer rules for different pharmaceuticals included different sets of soil properties. Absorption coefficients could be predicted from: the hydrolytic acidity (Sulfamethoxazol), the oxidable organic carbon content (Trimetoprim and Carbamazepin), the oxidable organic carbon content, hydrolytic acidity and cation exchange capacity (Clarithromycin), the basic cation saturation (Atenolol and Metoprolol). Acknowledgement: Authors acknowledge the financial support of the Czech Science Foundation (Project No. 13-12477S).

Thermal Density Functional Theory: Time-Dependent Linear Response and Approximate Functionals from the Fluctuation-Dissipation Theorem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pribram-Jones, Aurora; Grabowski, Paul E.; Burke, Kieron

We present that the van Leeuwen proof of linear-response time-dependent density functional theory (TDDFT) is generalized to thermal ensembles. This allows generalization to finite temperatures of the Gross-Kohn relation, the exchange-correlation kernel of TDDFT, and fluctuation dissipation theorem for DFT. Finally, this produces a natural method for generating new thermal exchange-correlation approximations.

Thermal Density Functional Theory: Time-Dependent Linear Response and Approximate Functionals from the Fluctuation-Dissipation Theorem

DOE PAGES

Pribram-Jones, Aurora; Grabowski, Paul E.; Burke, Kieron

2016-06-08

We present that the van Leeuwen proof of linear-response time-dependent density functional theory (TDDFT) is generalized to thermal ensembles. This allows generalization to finite temperatures of the Gross-Kohn relation, the exchange-correlation kernel of TDDFT, and fluctuation dissipation theorem for DFT. Finally, this produces a natural method for generating new thermal exchange-correlation approximations.

ECOPASS - a multivariate model used as an index of growth performance of poplar clones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ceulemans, R.; Impens, I.

The model (ECOlogical PASSport) reported was constructed by principal component analysis from a combination of biochemical, anatomical/morphological and ecophysiological gas exchange parameters measured on 5 fast growing poplar clones. Productivity data were 10 selected trees in 3 plantations in Belgium and given as m.a.i.(b.a.). The model is shown to be able to reflect not only genetic origin and the relative effects of the different parameters of the clones, but also their production potential. Multiple regression analysis of the 4 principal components showed a high cumulative correlation (96%) between the 3 components related to ecophysiological, biochemical and morphological parameters, and productivity;more » the ecophysiological component alone correlated 85% with productivity.« less

Plane-wave pseudopotential implementation and performance of SCAN meta-GGA exchange-correlation functional for extended systems

NASA Astrophysics Data System (ADS)

Yao, Yi; Kanai, Yosuke

2017-06-01

We present the implementation and performance of the strongly constrained and appropriately normed, SCAN, meta-GGA exchange-correlation (XC) approximation in the planewave-pseudopotential (PW-PP) formalism using the Troullier-Martins pseudopotential scheme. We studied its performance by applying the PW-PP implementation to several practical applications of interest in condensed matter sciences: (a) crystalline silicon and germanium, (b) martensitic phase transition energetics of phosphorene, and (c) a single water molecule physisorption on a graphene sheet. Given the much-improved accuracy over the GGA functionals and its relatively low computational cost compared to hybrid XC functionals, the SCAN functional is highly promising for various practical applications of density functional theory calculations for condensed matter systems. At same time, the SCAN meta-GGA functional appears to require more careful attention to numerical details. The meta-GGA functional shows more significant dependence on the fast Fourier transform grid, which is used for evaluating the XC potential in real space in the PW-PP formalism, than other more conventional GGA functionals do. Additionally, using pseudopotentials that are generated at a different/lower level of XC approximation could introduce noticeable errors in calculating some properties such as phase transition energetics.

Macroscopic and microscopic components of exchange-correlation interactions

NASA Astrophysics Data System (ADS)

Sottile, F.; Karlsson, K.; Reining, L.; Aryasetiawan, F.

2003-11-01

We consider two commonly used approaches for the ab initio calculation of optical-absorption spectra, namely, many-body perturbation theory based on Green’s functions and time-dependent density-functional theory (TDDFT). The former leads to the two-particle Bethe-Salpeter equation that contains a screened electron-hole interaction. We approximate this interaction in various ways, and discuss in particular the results obtained for a local contact potential. This, in fact, allows us to straightforwardly make the link to the TDDFT approach, and to discuss the exchange-correlation kernel fxc that corresponds to the contact exciton. Our main results, illustrated in the examples of bulk silicon, GaAs, argon, and LiF, are the following. (i) The simple contact exciton model, used on top of an ab initio calculated band structure, yields reasonable absorption spectra. (ii) Qualitatively extremely different fxc can be derived approximatively from the same Bethe-Salpeter equation. These kernels can however yield very similar spectra. (iii) A static fxc, both with or without a long-range component, can create transitions in the quasiparticle gap. To the best of our knowledge, this is the first time that TDDFT has been shown to be able to reproduce bound excitons.

Calculation of boron-isotope fractionation between B(OH) 3(aq) and B(OH)4-(aq)

NASA Astrophysics Data System (ADS)

Rustad, James R.; Bylaska, Eric J.; Jackson, Virgil E.; Dixon, David A.

2010-05-01

Density functional and correlated molecular orbital calculations (MP2) are carried out on B(OH) 3· nH 2O clusters ( n = 0, 6, 32), and B(OH)4-· nH 2O ( n = 0, 8, 11, 32) to estimate the equilibrium distribution of 10B and 11B isotopes between boric acid and borate in aqueous solution. For the large 32-water clusters, multiple conformations are generated from ab initio molecular dynamics simulations to account for the effect of solvent fluctuations on the isotopic fractionation. We provide an extrapolated value of the equilibrium constant α34 for the isotope exchange reaction 10B(OH) 3(aq) + 11B(OH)4- (aq) = 11B(OH) 3(aq) + 11B(OH)4- (aq) of 1.026-1.028 near the MP2 complete basis set limit with 32 explicit waters of solvation. With some exchange-correlation functionals we find potentially important contributions from a tetrahedral neutral B(OH) 3·H 2O Lewis acid-base complex. The extrapolations presented here suggest that DFT calculations give a value for 10 3ln α34 about 15% higher than the MP2 calculations.

Reconsidering the roles of gratitude and indebtedness in social exchange.

PubMed

Peng, Cong; Nelissen, Rob M A; Zeelenberg, Marcel

2018-06-01

Receiving favors is often a mixed blessing and commonly triggers two emotions: the positive emotion gratitude and negative emotion indebtedness. In three studies, we examined the hypothesis that gratitude and indebtedness have distinct functions in social exchange. Contrary to current views, we believe that the function of gratitude does not primarily reside in facilitating social exchange. Instead, we propose that indebtedness motivates people to repay favours received, and thus accounts for most of the prosocial effects commonly attributed to gratitude. On the other hand consistent with current views, we believe that gratitude signals the potential for developing a relationship and fosters proximity seeking. Supporting these assumptions, in Study 1 we found that gratitude and indebtedness were associated with aspects of the favour that reflect the concern for relationship and the level of inequity. Studies 2 and 3 provided causal support for these relations, and revealed the unique associations between gratitude and the motivation of proximity seeking, and between indebtedness and the motivation to reciprocate. We argue that this functional distinction has escaped research attention as gratitude and indebtedness are naturally correlated because they stem from the same eliciting event. To appreciate this functional distinction, both emotions should be studied simultaneously in the context of social exchange.

Correlation analysis of the Korean stock market: Revisited to consider the influence of foreign exchange rate

NASA Astrophysics Data System (ADS)

Jo, Sang Kyun; Kim, Min Jae; Lim, Kyuseong; Kim, Soo Yong

2018-02-01

We investigated the effect of foreign exchange rate in a correlation analysis of the Korean stock market using both random matrix theory and minimum spanning tree. We collected data sets which were divided into two types of stock price, the original stock price in Korean Won and the price converted into US dollars at contemporary foreign exchange rates. Comparing the random matrix theory based on the two different prices, a few particular sectors exhibited substantial differences while other sectors changed little. The particular sectors were closely related to economic circumstances and the influence of foreign financial markets during that period. The method introduced in this paper offers a way to pinpoint the effect of exchange rate on an emerging stock market.

Characterizing water-metal interfaces and machine learning potential energy surfaces

NASA Astrophysics Data System (ADS)

Ryczko, Kevin

In this thesis, we first discuss the fundamentals of ab initio electronic structure theory and density functional theory (DFT). We also discuss statistics related to computing thermodynamic averages of molecular dynamics (MD). We then use this theory to analyze and compare the structural, dynamical, and electronic properties of liquid water next to prototypical metals including platinum, graphite, and graphene. Our results are built on Born-Oppenheimer molecular dynamics (BOMD) generated using density functional theory (DFT) which explicitly include van der Waals (vdW) interactions within a first principles approach. All calculations reported use large simulation cells, allowing for an accurate treatment of the water-electrode interfaces. We have included vdW interactions through the use of the optB86b-vdW exchange correlation functional. Comparisons with the Perdew-Burke-Ernzerhof (PBE) exchange correlation functional are also shown. We find an initial peak, due to chemisorption, in the density profile of the liquid water-Pt interface not seen in the liquid water-graphite interface, liquid watergraphene interface, nor interfaces studied previously. To further investigate this chemisorption peak, we also report differences in the electronic structure of single water molecules on both Pt and graphite surfaces. We find that a covalent bond forms between the single water molecule and the platinum surface, but not between the single water molecule and the graphite surface. We also discuss the effects that defects and dopants in the graphite and graphene surfaces have on the structure and dynamics of liquid water. Lastly, we introduce artificial neural networks (ANNs), and demonstrate how they can be used to machine learn electronic structure calculations. As a proof of principle, we show the success of an ANN potential energy surfaces for a dimer molecule with a Lennard-Jones potential.

Homeostatic maintenance of ponderosa pine gas exchange in response to stand density changes.

PubMed

McDowell, Nate G; Adams, Henry D; Bailey, John D; Hess, Marcey; Kolb, Thomas E

2006-06-01

Homeostatic maintenance of gas exchange optimizes carbon gain per water loss. Homeostasis is regulated by short-term physiological and long-term structural mechanisms, both of which may respond to changes in resource availability associated with competition. Therefore, stand density regulation via silvicultural manipulations may facilitate growth and survival through mechanisms operating at both short and long timescales. We investigated the responses of ponderosa pine (Pinus ponderosa) to stand basal area manipulations in Arizona, USA. Stand basal area was manipulated to seven replicated levels in 1962 and was maintained for four decades by decadal thinning. We measured basal area increment (BAI) to assess the response and sustainability of wood growth, carbon isotope discrimination (A) inferred from annual rings to assess the response of crown gas exchange, and ratios of leaf area to sapwood area (A(l):A(s)) to assess longer term structural acclimation. Basal area treatments increased soil water potential (r2 = 0.99) but did not affect photosynthetic capacity. BAI increased within two years of thinning, and the 40-year mean BAI was negatively correlated with stand basal area (r2 = 0.98). delta was negatively correlated with stand basal area for years 5 through 12 after thinning (r2 = 0.90). However, delta was relatively invariant with basal area for the period 13-40 years after initial thinning despite maintenance of treatment basal areas via repeated decadal thinnings. Independent gas exchange measurements verified that the ratio of photosynthesis to stomatal conductance was invariant with basal area, but absolute values of both were elevated at lower basal areas. A(l):A(s) was negatively correlated with basal area (r2 = 0.93). We hypothesize that increased A(l):A(s) is a homeostatic response to increased water availability that maximizes water-use efficiency and whole-tree carbon uptake. Elevated A(l):A(s) of trees at low basal areas was associated with greater resilience to climate, i.e., greater absolute BAI during drought; however, trees with high A(l):A(s) in low basal area stands also exhibited the greatest sensitivity to drought, i.e., greater relative decline in BAI.

76 FR 54277 - Self-Regulatory Organizations; NASDAQ OMX BX, Inc.; Order Approving a Proposed Rule Change...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-31

... members raises potential conflicts of interest, and the potential for unfair competitive advantage.\\25... firm is affiliated with an exchange of which it is a member, the Exchange previously proposed, and the... instances where a member firm is affiliated with an exchange to which it is routing orders, the Exchange...

Electronic and mechanical properties of ZnX (X = S, Se and Te)—An ab initio study

NASA Astrophysics Data System (ADS)

Verma, Ajay Singh; Sharma, Sheetal; Sarkar, Bimal Kumar; Jindal, Vijay Kumar

2011-12-01

Zinc chalcogenides (ZnX, X = S, Se and Te) have been increasing attention as wide and direct band gap semiconductor for blue and ultraviolet optical devices. This paper analyzes electronic and mechanical properties of these materials by ab initio pseudo-potential method that uses non conserving pseudopotentials in fully nonlocal form, as implemented in SIESTA code. In this approach the local density approximation (LDA) is used for the exchange-correlation (XC) potential. The calculations are given for band gap, elastic constants (C11, C12 and C44), shear modulus, and Young's modulus. The results are in very good agreement with previous theoretical calculations and available experimental data.

Impact of Relativistic Electron Beam on Hole Acoustic Instability in Quantum Semiconductor Plasmas

NASA Astrophysics Data System (ADS)

Siddique, M.; Jamil, M.; Rasheed, A.; Areeb, F.; Javed, Asif; Sumera, P.

2018-01-01

We studied the influence of the classical relativistic beam of electrons on the hole acoustic wave (HAW) instability exciting in the semiconductor quantum plasmas. We conducted this study by using the quantum-hydrodynamic model of dense plasmas, incorporating the quantum effects of semiconductor plasma species which include degeneracy pressure, exchange-correlation potential and Bohm potential. Analysis of the quantum characteristics of semiconductor plasma species along with relativistic effect of beam electrons on the dispersion relation of the HAW is given in detail qualitatively and quantitatively by plotting them numerically. It is worth mentioning that the relativistic electron beam (REB) stabilises the HAWs exciting in semiconductor (GaAs) degenerate plasma.

Exchangeable lead from prediction models relates to vetiver lead uptake in different soil types.

PubMed

Andra, Syam S; Sarkar, Dibyendu; Saminathan, Sumathi K M; Datta, Rupali

2011-12-01

Prediction models for exchangeable soil lead, published earlier in this journal (Andra et al. 2010a), were developed using a suite of native lead (Pb) paint-contaminated residential soils from two US cities heavily populated with homes constructed prior to Pb ban in paints. In this study, we tested the feasibility and practical applications of these prediction models for developing a phytoremediation design using vetiver grass (Vetiveria zizanioides), a Pb-tolerant plant. The models were used to estimate the exchangeable fraction of Pb available for vetiver uptake in four lead-spiked soil types, both acidic and alkaline, with varying physico-chemical properties and that are different from those used to build the prediction models. Results indicate a strong correlation for predictable exchangeable Pb with the observed fraction and as well with total Pb accumulated by vetiver grass grown in these soils. The correlation coefficient for the predicted vs. observed exchangeable Pb with p < 0.001 was 0.999, 0.996, 0.949, and 0.998 in the Immokalee, Millhopper, Pahokee Muck, and Tobosa soil type, respectively. Similarly, the correlation coefficient for the predicted exchangeable Pb vs. accumulated Pb in vetiver grass with p < 0.001 was 0.948, 0.983, 0.929, and 0.969 for each soil type, respectively. This study suggests that the success of a phytoremediation design could be assessed upfront by predicting the exchangeable Pb fraction in a given soil type based on its properties. This helps in modifying the soil conditions to enhance phytoextraction of Pb from contaminated soils.

Hydraulics and gas exchange recover more rapidly from severe drought stress in small pot-grown grapevines than in field-grown plants.

PubMed

Romero, Pascual; Botía, Pablo; Keller, Markus

2017-09-01

Modifications of plant hydraulics and shoot resistances (R shoot ) induced by water withholding followed by rewatering, and their relationships with plant water status, leaf gas exchange and water use efficiency at the leaf level, were investigated in pot-grown and field-grown, own-rooted Syrah grapevines in an arid climate. Water stress induced anisohydric behavior, gradually reducing stomatal conductance (g s ) and leaf photosynthesis (A) in response to decreasing midday stem water potential (Ψ s ). Water stress also rapidly increased intrinsic water-use efficiency (A/g s ); this effect persisted for many days after rewatering. Whole-plant (K plant ), canopy (K canopy ), shoot (K shoot ) and leaf (K leaf ) hydraulic conductances decreased during water stress, in tune with the gradual decrease in Ψ s , leaf gas exchange and whole plant water use. Water-stressed vines also had a lower Ψ gradient between stem and leaf (ΔΨ l ), which was correlated with lower leaf transpiration rate (E). E and ΔΨ l increased with increasing vapour pressure deficit (VPD) in non-stressed control vines but not in stressed vines. Perfusion of xylem-mobile dye showed that water flow to petioles and leaves was substantially reduced or even stopped under moderate and severe drought stress. Leaf blade hydraulic resistance accounted for most of the total shoot resistance. However, hydraulic conductance of the whole root system (K root ) was not significantly reduced until water stress became very severe in pot-grown vines. Significant correlations between K plant , K canopy and Ψ s , K canopy and leaf gas exchange, K leaf and Ψ s , and K leaf and A support a link between water supply, leaf water status and gas exchange. Upon re-watering, Ψ s recovered faster than gas exchange and leaf-shoot hydraulics. A gradual recovery of hydraulic functionality of plant organs was also observed, the leaves being the last to recover after rewatering. In pot-grown vines, K canopy recovered rather quickly following restoration of Ψ s , although gas exchange recovery did not directly depend on recovery of K canopy . In field-grown vines, recovery of water status, gas exchange and hydraulic functionality was slower than in pot-grown plants, and low g s after rewatering was related to sustained decreased K plant , K canopy and K shoot and lower water transport to leaves. These results suggest that caution should be exercised when scaling up conclusions from experiments with small pot-grown plants to field conditions. Copyright © 2017 Elsevier GmbH. All rights reserved.

Dynamical Analysis of Stock Market Instability by Cross-correlation Matrix

NASA Astrophysics Data System (ADS)

Takaishi, Tetsuya

2016-08-01

We study stock market instability by using cross-correlations constructed from the return time series of 366 stocks traded on the Tokyo Stock Exchange from January 5, 1998 to December 30, 2013. To investigate the dynamical evolution of the cross-correlations, crosscorrelation matrices are calculated with a rolling window of 400 days. To quantify the volatile market stages where the potential risk is high, we apply the principal components analysis and measure the cumulative risk fraction (CRF), which is the system variance associated with the first few principal components. From the CRF, we detected three volatile market stages corresponding to the bankruptcy of Lehman Brothers, the 2011 Tohoku Region Pacific Coast Earthquake, and the FRB QE3 reduction observation in the study period. We further apply the random matrix theory for the risk analysis and find that the first eigenvector is more equally de-localized when the market is volatile.

Simultaneous acquisition for T2 -T2 Exchange and T1 -T2 correlation NMR experiments

NASA Astrophysics Data System (ADS)

Montrazi, Elton T.; Lucas-Oliveira, Everton; Araujo-Ferreira, Arthur G.; Barsi-Andreeta, Mariane; Bonagamba, Tito J.

2018-04-01

The NMR measurements of longitudinal and transverse relaxation times and its multidimensional correlations provide useful information about molecular dynamics. However, these experiments are very time-consuming, and many researchers proposed faster experiments to reduce this issue. This paper presents a new way to simultaneously perform T2 -T2 Exchange and T1 -T2 correlation experiments by taking the advantage of the storage time and the two steps phase cycling used for running the relaxation exchange experiment. The data corresponding to each step is either summed or subtracted to produce the T2 -T2 and T1 -T2 data, enhancing the information obtained while maintaining the experiment duration. Comparing the results from this technique with traditional NMR experiments it was possible to validate the method.

Subsystem density functional theory with meta-generalized gradient approximation exchange-correlation functionals.

PubMed

Śmiga, Szymon; Fabiano, Eduardo; Laricchia, Savio; Constantin, Lucian A; Della Sala, Fabio

2015-04-21

We analyze the methodology and the performance of subsystem density functional theory (DFT) with meta-generalized gradient approximation (meta-GGA) exchange-correlation functionals for non-bonded molecular systems. Meta-GGA functionals depend on the Kohn-Sham kinetic energy density (KED), which is not known as an explicit functional of the density. Therefore, they cannot be directly applied in subsystem DFT calculations. We propose a Laplacian-level approximation to the KED which overcomes this limitation and provides a simple and accurate way to apply meta-GGA exchange-correlation functionals in subsystem DFT calculations. The so obtained density and energy errors, with respect to the corresponding supermolecular calculations, are comparable with conventional approaches, depending almost exclusively on the approximations in the non-additive kinetic embedding term. An embedding energy error decomposition explains the accuracy of our method.

Scaling Exponents in Financial Markets

NASA Astrophysics Data System (ADS)

Kim, Kyungsik; Kim, Cheol-Hyun; Kim, Soo Yong

2007-03-01

We study the dynamical behavior of four exchange rates in foreign exchange markets. A detrended fluctuation analysis (DFA) is applied to detect the long-range correlation embedded in the non-stationary time series. It is for our case found that there exists a persistent long-range correlation in volatilities, which implies the deviation from the efficient market hypothesis. Particularly, the crossover is shown to exist in the scaling behaviors of the volatilities.

Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

PubMed

Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

2015-08-11

The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.

Correlation between pairing initiation sites, recombination nodules and meiotic recombination in Sordaria macrospora.

PubMed

Zickler, D; Moreau, P J; Huynh, A D; Slezec, A M

1992-09-01

The decrease of meiotic exchanges (crossing over and conversion) in two mutants of Sordaria macrospora correlated strongly with a reduction of chiasmata and of both types of "recombination nodules." Serial section reconstruction electron microscopy was used to compare the synapsis pattern of meiotic prophase I in wild type and mutants. First, synapsis occurred but the number of synaptonemal complex initiation sites was reduced in both mutants. Second, this reduction was accompanied by, or resulted in, modifications of the pattern of synapsis. Genetic and synaptonemal complex maps were compared in three regions along one chromosome arm divided into well marked intervals. Reciprocal exchange frequencies and number of recombination nodules correlated in wild type in the three analyzed intervals, but disparity was found between the location of recombination nodules and exchanges in the mutants. Despite the twofold exchange decrease, sections of the genome such as the short arm of chromosome 2 and telomere regions were sheltered from nodule decrease and from pairing modifications. This indicated a certain amount of diversity in the control of these features and suggested that exchange frequency was dependent not only on the amount of effective pairing but also on the localization of the pairing sites, as revealed by the synaptonemal complex progression in the mutants.

Correlation between Pairing Initiation Sites, Recombination Nodules and Meiotic Recombination in Sordaria Macrospora

PubMed Central

Zickler, D.; Moreau, PJF.; Huynh, A. D.; Slezec, A. M.

1992-01-01

The decrease of meiotic exchanges (crossing over and conversion) in two mutants of Sordaria macrospora correlated strongly with a reduction of chiasmata and of both types of ``recombination nodules.'' Serial section reconstruction electron microscopy was used to compare the synapsis pattern of meiotic prophase I in wild type and mutants. First, synapsis occurred but the number of synaptonemal complex initiation sites was reduced in both mutants. Second, this reduction was accompanied by, or resulted in, modifications of the pattern of synapsis. Genetic and synaptonemal complex maps were compared in three regions along one chromosome arm divided into well marked intervals. Reciprocal exchange frequencies and number of recombination nodules correlated in wild type in the three analyzed intervals, but disparity was found between the location of recombination nodules and exchanges in the mutants. Despite the twofold exchange decrease, sections of the genome such as the short arm of chromosome 2 and telomere regions were sheltered from nodule decrease and from pairing modifications. This indicated a certain amount of diversity in the control of these features and suggested that exchange frequency was dependent not only on the amount of effective pairing but also on the localization of the pairing sites, as revealed by the synaptonemal complex progression in the mutants. PMID:1398050

Effects of communication on the performance of nursing students during the simulation of an emergency situation.

PubMed

Chapelain, Pascal; Morineau, Thierry; Gautier, Claudie

2015-11-01

To explore how nursing performance is impacted by different forms of team communication including a message transmitted through an earpiece which triggers reflective thinking in the simulation of a deteriorating patient situation. Communication can either support team performance or produce interruptions potentially leading to error. Today, technology offers the opportunity to use devices that can permit communication. An experimental protocol was used with quantitative and qualitative analyses. Pairs of nursing students (N = 26) were dispatched to either an experimental group having to wear an earpiece priming reflective thinking, or to a control group. The study was conducted between October 2013-April 2014. The number of spontaneous information exchanges between pairs of participants was positively correlated with overall performance (actions performed and physician call) and with actions performed at the right moment. The number of questions in the team was positively correlated with overall action performance. No quantitative effect of the earpiece message on the performance indicators was found. But, a qualitative observation showed that this message can allow for error avoidance. Subjective evaluation of the earpiece as an aid was negatively correlated with overall action performance. Its evaluation as a disturbance was also negatively correlated with the measurement of actions performed at the right moment. The ability to exchange information and to ask questions seems to contribute to performance in care delivery. The use of communication devices to trigger reflective thinking must be studied in more depth to assess their capacity to improve performance. © 2015 John Wiley & Sons Ltd.

Design of distributed JT (Joule-Thomson) effect heat exchanger for superfluid 2 K cooling device

NASA Astrophysics Data System (ADS)

Jeong, S.; Park, C.; Kim, K.

2018-03-01

Superfluid at 2 K or below is readily obtained from liquid helium at 4.2 K by reducing its vapour pressure. For better cooling performance, however, the cold energy of vaporized helium at 2 K chamber can be effectively utilized in a recuperator which is specially designed in this paper for accomplishing so-called the distributed Joule-Thomson (JT) expansion effect. This paper describes the design methodology of distributed JT effect heat exchanger for 2 K JT cooling device. The newly developed heat exchanger allows continuous significant pressure drop at high-pressure part of the recuperative heat exchanger by using a capillary tube. Being different from conventional recuperative heat exchangers, the efficient JT effect HX must consider the pressure drop effect as well as the heat transfer characteristic. The heat exchanger for the distributed JT effect actively utilizes continuous pressure loss at the hot stream of the heat exchanger by using an OD of 0.64 mm and an ID of 0.4 mm capillary tube. The analysis is performed by dividing the heat exchanger into the multiple sub-units of the heat exchange part and JT valve. For more accurate estimation of the pressure drop of spirally wound capillary tube, preliminary experiments are carried out to investigate the friction factor at high Reynolds number. By using the developed pressure drop correlation and the heat transfer correlation, the specification of the heat exchanger with distributed JT effect for 2 K JT refrigerator is determined.

Modeling Excited States in TiO2 Nanoparticles: On the Accuracy of a TD-DFT Based Description

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berardo, Enrico; Hu, Hanshi; Shevlin, S. A.

2014-03-11

We have investigated the suitability of Time-Dependent Density Functional Theory (TD-DFT) to describe vertical low-energy excitations in naked and hydrated titanium dioxide nanoparticles through a comparison with results from Equation-of-Motion Coupled Cluster (EOM-CC) quantum chemistry methods. We demonstrate that for most TiO2 nanoparticles TD-DFT calculations with commonly used exchange-correlation (XC-)potentials (e.g. B3LYP) and EOM-CC methods give qualitatively similar results. Importantly, however, we also show that for an important subset of structures, TD-DFT gives qualitatively different results depending upon the XC-potential used and that in this case only TD-CAM-B3LYP and TD-BHLYP calculations yield results that are consistent with those obtained usingmore » EOM-CC theory. Moreover, we demonstrate that the discrepancies for such structures arise from a particular combination of defects, excitations involving which are charge-transfer excitations and hence are poorly described by XC-potentials that contain no or low fractions of Hartree-Fock like exchange. Finally, we discuss that such defects are readily healed in the presence of ubiquitously present water and that as a result the description of vertical low-energy excitations for hydrated TiO2 nanoparticles is hence non-problematic.« less

Simulated Tempering Distributed Replica Sampling, Virtual Replica Exchange, and Other Generalized-Ensemble Methods for Conformational Sampling.

PubMed

Rauscher, Sarah; Neale, Chris; Pomès, Régis

2009-10-13

Generalized-ensemble algorithms in temperature space have become popular tools to enhance conformational sampling in biomolecular simulations. A random walk in temperature leads to a corresponding random walk in potential energy, which can be used to cross over energetic barriers and overcome the problem of quasi-nonergodicity. In this paper, we introduce two novel methods: simulated tempering distributed replica sampling (STDR) and virtual replica exchange (VREX). These methods are designed to address the practical issues inherent in the replica exchange (RE), simulated tempering (ST), and serial replica exchange (SREM) algorithms. RE requires a large, dedicated, and homogeneous cluster of CPUs to function efficiently when applied to complex systems. ST and SREM both have the drawback of requiring extensive initial simulations, possibly adaptive, for the calculation of weight factors or potential energy distribution functions. STDR and VREX alleviate the need for lengthy initial simulations, and for synchronization and extensive communication between replicas. Both methods are therefore suitable for distributed or heterogeneous computing platforms. We perform an objective comparison of all five algorithms in terms of both implementation issues and sampling efficiency. We use disordered peptides in explicit water as test systems, for a total simulation time of over 42 μs. Efficiency is defined in terms of both structural convergence and temperature diffusion, and we show that these definitions of efficiency are in fact correlated. Importantly, we find that ST-based methods exhibit faster temperature diffusion and correspondingly faster convergence of structural properties compared to RE-based methods. Within the RE-based methods, VREX is superior to both SREM and RE. On the basis of our observations, we conclude that ST is ideal for simple systems, while STDR is well-suited for complex systems.

Band positions of Rutile surfaces and the possibility of water splitting

NASA Astrophysics Data System (ADS)

Esch, Tobit R.; Bredow, Thomas

2017-11-01

It is well known that both the band gap and the band edge positions of oxide semiconductors are important for the photocatalytic water splitting. In this study, we show that different surface terminations of the same crystalline solid lead to considerable variations of the band gaps and band edges. As an example, we investigate the low-index surfaces of rutile TiO2. A series of hybrid methods based on the PBE exchange-correlation functional, PBE0, HSE06 and HISS, are employed to study the effect of long-range exchange on the electronic properties. In aqueous solution, the oxide particles employed in photocatalysis are fully covered with water molecules. We therefore study the influence of molecularly and dissociatively adsorbed water on the band positions. It is found that water adsorption leads to significant shifts of the band edge positions due to changes of the electrostatic potential at the surface atom positions.

Observation of Solar Wind Charge Exchange Emission From Exospheric Material in and Outside Earth's Magnetosheath 2008 September 25

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Collier, M. R.; Cravens, T.; Kuntz, K. D.; Lepri, S. T.; Robertson, I.; Tomas, L.

2009-01-01

A long XMM-Newton exposure is used to observe solar wind charge exchange (SWCX) emission from exospheric material in and outside Earth's magnetosheath. The light curve of the O vii (0.5-0.62 keV) band is compared with a model for the expected emission, and while the emission is faint and the light curve has considerable scatter, the correlation is significant to better than 99.9%. This result demonstrates the validity of the geocoronal SWCX emission model for predicting a contribution to astrophysical observations to a scale factor of order unity (1.5). In addition, an average value of the SWCX O vii emission from the magnetosheath over the observation of 2.6 +/- 0.5 LU is derived. The results also demonstrate the potential utility of using X-ray observations to study global phenomena of the magnetosheath which currently are only investigated using in situ measurements.

Self-consistent electronic structure of disordered Fe/sub 0. 65/Ni/sub 0. 35/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, D.D.; Pinski, F.J.; Stocks, G.M.

1985-04-15

We present the results of the first ab initio calculation of the electronic structure of the disordered alloy Fe/sub 0.65/Ni/sub 0.35/. The calculation is based on the multiple-scattering coherent-potential approach (KKR-CPA) and is fully self-consistent and spin polarized. Magnetic effects are included within local-spin-density functional theory using the exchange-correlation function of Vosko--Wilk--Nusair. The most striking feature of the calculation is that electrons of different spins experience different degrees of disorder. The minority spin electrons see a very large disorder, whereas the majority spin electrons see little disorder. Consequently, the minority spin density of states is smooth compared to the verymore » structured majority spin density of states. This difference is due to a subtle balance between exchange splitting and charge neutrality.« less

Self-consistent electronic structure of disordered Fe/sub 0/ /sub 65/Ni/sub 0/ /sub 35/

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, D.D.; Pinski, F.J.; Stocks, G.M.

1984-01-01

We present the results of the first ab-initio calculation of the electronic structure of a disordered Fe/sub 0/ /sub 65/Ni/sub 0/ /sub 35/ alloy. The calculation is based on the multiple-scattering coherent-potential approach (KKR-CPA) and is fully self-consistent and spin-polarized. Magnetic effects are included within local-spin-density functional theory using the exchange-correlation function of Vosko-Wilk-Nusair. The most striking feature of the calculation is that electrons of different spins experience different degrees of disorder. The minority spin electrons see a very large disorder; whereas, the majority spin electrons see little disorder. Consequently, the minority spin density of states is smooth compared tomore » the very structured majority spin density of states. This difference is due to a subtle balance between exchange-splitting and charge neutrality. 15 references, 2 figures.« less

Practical auxiliary basis implementation of Rung 3.5 functionals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janesko, Benjamin G., E-mail: b.janesko@tcu.edu; Scalmani, Giovanni; Frisch, Michael J.

2014-07-21

Approximate exchange-correlation functionals for Kohn-Sham density functional theory often benefit from incorporating exact exchange. Exact exchange is constructed from the noninteracting reference system's nonlocal one-particle density matrix γ(r{sup -vector},r{sup -vector}′). Rung 3.5 functionals attempt to balance the strengths and limitations of exact exchange using a new ingredient, a projection of γ(r{sup -vector},r{sup -vector} ′) onto a semilocal model density matrix γ{sub SL}(ρ(r{sup -vector}),∇ρ(r{sup -vector}),r{sup -vector}−r{sup -vector} ′). γ{sub SL} depends on the electron density ρ(r{sup -vector}) at reference point r{sup -vector}, and is closely related to semilocal model exchange holes. We present a practical implementation of Rung 3.5 functionals, expandingmore » the r{sup -vector}−r{sup -vector} ′ dependence of γ{sub SL} in an auxiliary basis set. Energies and energy derivatives are obtained from 3D numerical integration as in standard semilocal functionals. We also present numerical tests of a range of properties, including molecular thermochemistry and kinetics, geometries and vibrational frequencies, and bandgaps and excitation energies. Rung 3.5 functionals typically provide accuracy intermediate between semilocal and hybrid approximations. Nonlocal potential contributions from γ{sub SL} yield interesting successes and failures for band structures and excitation energies. The results enable and motivate continued exploration of Rung 3.5 functional forms.« less

Quantifying potential propagule pressure of aquatic invasive species from the commercial shipping industry in Canada.

PubMed

Lo, Veronica B; Levings, Colin D; Chan, Kai M A

2012-02-01

We quantify and compare different measures of potential propagule pressure (PPP) of aquatic invasive species (AIS) from commercial vessels in Canada. We used ship arrivals and ballast water discharge volumes as proxies for PPP from ballast water organisms, and wetted surface area (WSA) as a proxy for hull fouling PPP, to determine their relative contributions to total PPP. For three regions studied, PPP proxies correlated significantly across ports and some vessel categories. Relative contributions of ship arrivals, ballast discharge, and WSAs to PPP, evidenced by non-significant correlations across these measures, varied across regions, ports, vessel types, and seasons. Flow-through (dominant on east and west coasts) and empty-refill (in Great Lakes-St. Lawrence region) were the major ballast water exchange methods employed by the vessels surveyed. These methods have different biological efficacy for AIS removal, influencing PPP. Our study illustrates benefits and limitations of using different PPP proxies to estimate invasion risk. Copyright © 2011 Elsevier Ltd. All rights reserved.

Calculations with the quasirelativistic local-spin-density-functional theory for high-Z atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Y.; Whitehead, M.A.

1988-10-01

The generalized-exchange local-spin-density-functional theory (LSD-GX) with relativistic corrections of the mass velocity and Darwin terms has been used to calculate statistical total energies for the neutral atoms, the positive ions, and the negative ions for high-Z elements. The effect of the correlation and relaxation correction on the statistical total energy is discussed. Comparing the calculated results for the ionization potentials and electron affinities for the atoms (atomic number Z from 37 to 56 and 72 to 80) with experiment, shows that for the atoms rubidium to barium both the LSD-GX and the quasirelativistic LSD-GX, with self-interaction correction, Gopinathan, Whitehead, andmore » Bogdanovic's Fermi-hole parameters (Phys. Rev. A 14, 1 (1976)), and Vosko, Wilk, and Nusair's correlation correction (Can. J. Phys. 58, 1200 (1980)), are very good methods for calculating ionization potentials and electron affinities. For the atoms hafnium to mercury the relativistic effect has to be considered.« less

Dynamic communities in multichannel data: an application to the foreign exchange market during the 2007-2008 credit crisis.

PubMed

Fenn, Daniel J; Porter, Mason A; McDonald, Mark; Williams, Stacy; Johnson, Neil F; Jones, Nick S

2009-09-01

We study the cluster dynamics of multichannel (multivariate) time series by representing their correlations as time-dependent networks and investigating the evolution of network communities. We employ a node-centric approach that allows us to track the effects of the community evolution on the functional roles of individual nodes without having to track entire communities. As an example, we consider a foreign exchange market network in which each node represents an exchange rate and each edge represents a time-dependent correlation between the rates. We study the period 2005-2008, which includes the recent credit and liquidity crisis. Using community detection, we find that exchange rates that are strongly attached to their community are persistently grouped with the same set of rates, whereas exchange rates that are important for the transfer of information tend to be positioned on the edges of communities. Our analysis successfully uncovers major trading changes that occurred in the market during the credit crisis.

Dynamic communities in multichannel data: An application to the foreign exchange market during the 2007-2008 credit crisis

NASA Astrophysics Data System (ADS)

Fenn, Daniel J.; Porter, Mason A.; McDonald, Mark; Williams, Stacy; Johnson, Neil F.; Jones, Nick S.

2009-09-01

We study the cluster dynamics of multichannel (multivariate) time series by representing their correlations as time-dependent networks and investigating the evolution of network communities. We employ a node-centric approach that allows us to track the effects of the community evolution on the functional roles of individual nodes without having to track entire communities. As an example, we consider a foreign exchange market network in which each node represents an exchange rate and each edge represents a time-dependent correlation between the rates. We study the period 2005-2008, which includes the recent credit and liquidity crisis. Using community detection, we find that exchange rates that are strongly attached to their community are persistently grouped with the same set of rates, whereas exchange rates that are important for the transfer of information tend to be positioned on the edges of communities. Our analysis successfully uncovers major trading changes that occurred in the market during the credit crisis.

Structural and opto-electronic properties of 2D AlSb monolayer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Deobrat, E-mail: deobratsingh9@gmail.com; Sonvane, Yogesh; Gupta, Sanjeev K.

2016-05-23

We have investigated dielectric function related optical properties such as refractive index, absorption coefficient of two-dimensional hexagonal system of aluminum antimony (AlSb). We have also find structural and electronic properties of AlSb which show direct/indirect band gap with planar structure, employing the density functional theory using the generalized gradient approximation (GGA) given by Perdew-Burke-Ernzerhof (PBE) functional for exchange-correlation potential. The refractive index n(ω) increases with frequency in the near infrared region but in visible region n(ω) increasing after decrease.

Rogue waves lead to the instability in GaN semiconductors

PubMed Central

Yahia, M. E.; Tolba, R. E.; El-Bedwehy, N. A.; El-Labany, S. K.; Moslem, W. M.

2015-01-01

A new approach to understand the electron/hole interfaced plasma in GaN high electron mobility transistors (HEMTs). A quantum hydrodynamic model is constructed to include electrons/holes degenerate pressure, Bohm potential, and the exchange/correlation effect and then reduced to the nonlinear Schrödinger equation (NLSE). Numerical analysis of the latter predicts the rough (in)stability domains, which allow for the rogue waves to occur. Our results might give physical solution rather than the engineering one to the intrinsic problems in these high frequency/power transistors. PMID:26206731

Pionic retardation effects in two-pion-exchange three-nucleon forces

NASA Astrophysics Data System (ADS)

Coon, S. A.; Friar, J. L.

1986-09-01

Those two-pion-exchange three-nucleon forces which arise from nuclear processes that involve only pions and nucleons are calculated. Among the processes which contribute are pion seagulls (e.g., nucleon-antinucleon pair terms) and overlapping, retarded pion exchanges. The resulting potential is shown to be a (v/c)2 relativistic correction, and satisfies nontrivial constraints from special relativity. The relativistic ambiguities found before in treatments of relativistic corrections to the one-pion-exchange nuclear charge operator and two-body potential are also present in the three-nucleon potential. The resulting three-nucleon force differs from the original Tucson-Melbourne potential only in the presence of several new nonlocal terms, and in the specification of the choice of ambiguity parameters in the latter potential.

Correlations of multiscale entropy in the FX market

NASA Astrophysics Data System (ADS)

Stosic, Darko; Stosic, Dusan; Ludermir, Teresa; Stosic, Tatijana

2016-09-01

The regularity of price fluctuations in exchange rates plays a crucial role in FX market dynamics. Distinct variations in regularity arise from economic, social and political events, such as interday trading and financial crisis. This paper applies a multiscale time-dependent entropy method on thirty-three exchange rates to analyze price fluctuations in the FX. Correlation matrices of entropy values, termed entropic correlations, are in turn used to describe global behavior of the market. Empirical results suggest a weakly correlated market with pronounced collective behavior at bi-weekly trends. Correlations arise from cycles of low and high regularity in long-term trends. Eigenvalues of the correlation matrix also indicate a dominant European market, followed by shifting American, Asian, African, and Pacific influences. As a result, we find that entropy is a powerful tool for extracting important information from the FX market.

Influence of molecular geometry, exchange-correlation functional, and solvent effects in the modeling of vertical excitation energies in phthalocyanines using time-dependent density functional theory (TDDFT) and polarized continuum model TDDFT methods: can modern computational chemistry methods explain experimental controversies?

PubMed

Nemykin, Victor N; Hadt, Ryan G; Belosludov, Rodion V; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki

2007-12-20

A time-dependent density functional theory (TDDFT) approach coupled with 14 different exchange-correlation functionals was used for the prediction of vertical excitation energies in zinc phthalocyanine (PcZn). In general, the TDDFT approach provides a more accurate description of both visible and ultraviolet regions of the UV-vis and magnetic circular dichroism (MCD) spectra of PcZn in comparison to the more popular semiempirical ZINDO/S and PM3 methods. It was found that the calculated vertical excitation energies of PcZn correlate with the amount of Hartree-Fock exchange involved in the exchange-correlation functional. The correlation was explained on the basis of the calculated difference in energy between occupied and unoccupied molecular orbitals. The influence of PcZn geometry, optimized using different exchange-correlation functionals, on the calculated vertical excitation energies in PcZn was found to be relatively small. The influence of solvents on the calculated vertical excitation energies in PcZn was considered for the first time using a polarized continuum model TDDFT (PCM-TDDFT) method and was found to be relatively small in excellent agreement with the experimental data. For all tested TDDFT and PCM-TDDFT cases, an assignment of the Q-band as an almost pure a1u (HOMO)-->eg (LUMO) transition, initially suggested by Gouterman, was confirmed. Pure exchange-correlation functionals indicate the presence of six 1Eu states in the B-band region of the UV-vis spectrum of PcZn, while hybrid exchange-correlation functionals predict only five 1Eu states for the same energy envelope. The first two symmetry-forbidden n-->pi* transitions were predicted in the Q0-2 region and in the low-energy tail of the B-band, while the first two symmetry-allowed n-->pi* transitions were found within the B-band energy envelope when pure exchange-correlation functionals were used for TDDFT calculations. The presence of a symmetry-forbidden but vibronically allowed n-->pi* transition in the Q0-2 spectral envelope explains the long-time controversy between the experimentally observed low-intensity transition in the Q0-2 region and previous semiempirical and TDDFT calculations, which were unable to predict any electronic transitions in this area. To prove the conceptual possibility of the presence of several degenerate 1Eu states in the B-band region of PcZn, room-temperature UV-vis and MCD spectra of zinc tetra-tert-butylphthalocyanine (PctZn) in non-coordinating solvents were recorded and analyzed using band deconvolution analysis. It was found that the B-band region of the UV-vis and MCD spectra of PctZn can be easily deconvoluted using six MCD Faraday A-terms and two MCD Faraday B-terms with energies close to those predicted by TDDFT calculations for 1Eu and 1A2u excited states, respectively. Such a good agreement between theory and experiment clearly indicates the possibility of employing a TDDFT approach for the accurate prediction of vertical excitation energies in phthalocyanines within a large energy range.

Carbon dioxide exchange between an undisturbed old-growth temperate forest and the atmosphere

Treesearch

D.Y. Hollinger; F.M. Kelliher; J.N. Byers; J.E. Hunt; T.M. McSeveny; P.L. Weir

1994-01-01

We used the eddy-correlation technique to investigate the exchange of C02 between an undisturbed old-growth forest and the atmosphere at a remote Southern Hemisphere site on 15 d between 1989 and 1990. Our goal was to determine how environmental factors regulate ecosystem CO2 exchange, and to test whether present knowledge...

76 FR 33795 - Self-Regulatory Organizations; NYSE Arca, Inc.; Notice of Filing and Immediate Effectiveness of...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-09

... with respect to ETP Holders and the equities business of the Exchange that was lost with the... respect to ETP Holders and the equities business of the Exchange. The Exchange will monitor the amount of... raise revenue related to the amount of equity business conducted, which correlates more closely with the...

Carbon dioxide and water vapour exchange in a tropical dry forest as influenced by the North American Monsoon System (NAMS)

USDA-ARS?s Scientific Manuscript database

To better understand the effects and relationship between precipitation, net ecosystem carbon dioxide (NEE) and water vapor exchange (ET), we report a study conducted in the tropical dry forest (TDF) in the northwest of Mexico. Ecosystem gas exchange was measured using the eddy correlation technique...

Modeling the demand-price relations in a high-frequency foreign exchange market

NASA Astrophysics Data System (ADS)

Schmidt, Anatoly B.

1999-09-01

A stochastic nonlinear dynamics model is introduced in terms of observable variables (price and excess demand assumed to be proportional to the number of buyers) to describe a high-frequency foreign exchange market. It is shown how the fundamentalist and chartist patterns of the trader behavior affect the correlation between excess demand and exchange rates.

Analysis of high-resolution foreign exchange data of USD-JPY for 13 years

NASA Astrophysics Data System (ADS)

Mizuno, Takayuki; Kurihara, Shoko; Takayasu, Misako; Takayasu, Hideki

2003-06-01

We analyze high-resolution foreign exchange data consisting of 20 million data points of USD-JPY for 13 years to report firm statistical laws in distributions and correlations of exchange rate fluctuations. A conditional probability density analysis clearly shows the existence of trend-following movements at time scale of 8-ticks, about 1 min.

Statistical properties of the yuan exchange rate index

NASA Astrophysics Data System (ADS)

Wang, Dong-Hua; Yu, Xiao-Wen; Suo, Yuan-Yuan

2012-06-01

We choice the yuan exchange rate index based on a basket of currencies as the effective exchange rate of the yuan and investigate the statistical properties of the yuan exchange rate index after China's exchange rate system reform on the 21st July 2005. After dividing the time series into two parts according to the change in the yuan exchange rate regime in July 2008, we compare the statistical properties of the yuan exchange rate index during these two periods. We find that the distribution of the two return series has the exponential form. We also perform the detrending moving average analysis (DMA) and the multifractal detrending moving average analysis (MFDMA). The two periods possess different degrees of long-range correlations, and the multifractal nature is also unveiled in these two time series. Significant difference is found in the scaling exponents τ(q) and singularity spectra f(α) of the two periods obtained from the MFDMA analysis. Besides, in order to detect the sources of multifractality, shuffling and phase randomization procedures are applied to destroy the long-range temporal correlation and fat-tailed distribution of the yuan exchange rate index respectively. We find that the fat-tailedness plays a critical role in the sources of multifractality in the first period, while the long memory is the major cause in the second period. The results suggest that the change in China's exchange rate regime in July 2008 gives rise to the different multifractal properties of the yuan exchange rate index in these two periods, and thus has an effect on the effective exchange rate of the yuan after the exchange rate reform on the 21st July 2005.

Steady-State Density Functional Theory for Finite Bias Conductances.

PubMed

Stefanucci, G; Kurth, S

2015-12-09

In the framework of density functional theory, a formalism to describe electronic transport in the steady state is proposed which uses the density on the junction and the steady current as basic variables. We prove that, in a finite window around zero bias, there is a one-to-one map between the basic variables and both local potential on as well as bias across the junction. The resulting Kohn-Sham system features two exchange-correlation (xc) potentials, a local xc potential, and an xc contribution to the bias. For weakly coupled junctions the xc potentials exhibit steps in the density-current plane which are shown to be crucial to describe the Coulomb blockade diamonds. At small currents these steps emerge as the equilibrium xc discontinuity bifurcates. The formalism is applied to a model benzene junction, finding perfect agreement with the orthodox theory of Coulomb blockade.

Cluster fusion-fission dynamics in the Singapore stock exchange

NASA Astrophysics Data System (ADS)

Teh, Boon Kin; Cheong, Siew Ann

2015-10-01

In this paper, we investigate how the cross-correlations between stocks in the Singapore stock exchange (SGX) evolve over 2008 and 2009 within overlapping one-month time windows. In particular, we examine how these cross-correlations change before, during, and after the Sep-Oct 2008 Lehman Brothers Crisis. To do this, we extend the complete-linkage hierarchical clustering algorithm, to obtain robust clusters of stocks with stronger intracluster correlations, and weaker intercluster correlations. After we identify the robust clusters in all time windows, we visualize how these change in the form of a fusion-fission diagram. Such a diagram depicts graphically how the cluster sizes evolve, the exchange of stocks between clusters, as well as how strongly the clusters mix. From the fusion-fission diagram, we see a giant cluster growing and disintegrating in the SGX, up till the Lehman Brothers Crisis in September 2008 and the market crashes of October 2008. After the Lehman Brothers Crisis, clusters in the SGX remain small for few months before giant clusters emerge once again. In the aftermath of the crisis, we also find strong mixing of component stocks between clusters. As a result, the correlation between initially strongly-correlated pairs of stocks decay exponentially with average life time of about a month. These observations impact strongly how portfolios and trading strategies should be formulated.

Graphene: A partially ordered non-periodic solid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Dongshan; Wang, Feng, E-mail: fengwang@uark.edu

2014-10-14

Molecular dynamics simulations were performed to study the structural features of graphene over a wide range of temperatures from 50 to 4000 K using the PPBE-G potential [D. Wei, Y. Song, and F. Wang, J. Chem. Phys. 134, 184704 (2011)]. This potential was developed by force matching the Perdew-Burke-Ernzerhof (PBE) exchange correlation functional and has been validated previously to provide accurate potential energy surface for graphene at temperatures as high as 3000 K. Simulations with the PPBE‑G potential are the best available approximation to a direct Car-Parrinello Molecular Dynamics study of graphene. One advantage of the PBE-G potential is to allowmore » large simulation boxes to be modeled efficiently so that properties showing strong finite size effects can be studied. Our simulation box contains more than 600 000 C atoms and is one of the largest graphene boxes ever modeled. With the PPBE-G potential, the thermal-expansion coefficient is negative up to 4000 K. With a large box and an accurate potential, the critical exponent for the scaling properties associated with the normal-normal and height-height correlation functions was confirmed to be 0.85. This exponent remains constant up to 4000 K suggesting graphene to be in the deeply cooled regime even close to the experimental melting temperature. The reduced peak heights in the radial distribution function of graphene show an inverse power law dependence to distance, which indicates that a macroscopic graphene sheet will lose long-range crystalline order as predicted by the Mermin-Wagner instability. Although graphene loses long-range translational order, it retains long range orientational order as indicated by its orientational correlation function; graphene is thus partially ordered but not periodic.« less

Classical technical analysis of Latin American market indices. Correlations in Latin American Currencies (ARS, CLP, MXP) exchange rates with respect to DEM, GBP, JPY and USD

NASA Astrophysics Data System (ADS)

Ausloos, M.; Ivanova, K.

2004-06-01

The classical technical analysis methods of financial time series based on the moving average and momentum is recalled. Illustrations use the IBM share price and Latin American (Argentinian MerVal, Brazilian Bovespa and Mexican IPC) market indices. We have also searched for scaling ranges and exponents in exchange rates between Latin American currencies ($ARS$, $CLP$, $MXP$) and other major currencies $DEM$, $GBP$, $JPY$, $USD$, and $SDR$s. We have sorted out correlations and anticorrelations of such exchange rates with respect to $DEM$, $GBP$, $JPY$ and $USD$. They indicate a very complex or speculative behavior.

Topological Phase Transitions in Zinc-Blende Semimetals Driven Exclusively by Electronic Temperature

NASA Astrophysics Data System (ADS)

Trushin, Egor; Görling, Andreas

2018-04-01

We show that electronic phase transitions in zinc-blende semimetals with quadratic band touching (QBT) at the center of the Brillouin zone, like GaBi, InBi, or HgTe, can occur exclusively due to a change of the electronic temperature without the need to involve structural transformations or electron-phonon coupling. The commonly used Kohn-Sham density-functional methods based on local and semilocal density functionals employing the local density approximation (LDA) or generalized gradient approximations (GGAs), however, are not capable of describing such phenomena because they lack an intrinsic temperature dependence and account for temperature only via the occupation of bands, which essentially leads only to a shift of the Fermi level without changing the shape or topology of bands. Kohn-Sham methods using the exact temperature-dependent exchange potential, not to be confused with the Hartree-Fock exchange potential, on the other hand, describe such phase transitions. A simple modeling of correlation effects can be achieved by screening of the exchange. In the considered zinc-blende compounds the QBT is unstable at low temperatures and a transition to electronic states without QBT takes place. In the case of HgTe and GaBi Weyl points of type I and type II, respectively, emerge during the transitions. This demonstrates that Kohn-Sham methods can describe such topological phase transitions provided they are based on functionals more accurate than those within the LDA or GGA. Moreover, the electronic temperature is identified as a handle to tune topological materials.

Water stress-induced modifications of leaf hydraulic architecture in sunflower: co-ordination with gas exchange.

PubMed

Nardini, Andrea; Salleo, Sebastiano

2005-12-01

The hydraulic architecture, water relationships, and gas exchange of leaves of sunflower plants, grown under different levels of water stress, were measured. Plants were either irrigated with tap water (controls) or with PEG600 solutions with osmotic potential of -0.4 and -0.8 MPa (PEG04 and PEG08 plants, respectively). Mature leaves were measured for hydraulic resistance (R(leaf)) before and after making several cuts across minor veins, thus getting the hydraulic resistance of the venation system (R(venation)). R(leaf) was nearly the same in controls and PEG04 plants but it was reduced by about 30% in PEG08 plants. On the contrary, R(venation) was lowest in controls and increased in PEG04 and PEG08 plants as a likely result of reduction in the diameter of the veins' conduits. As a consequence, the contribution of R(venation) to the overall R(leaf) markedly increased from controls to PEG08 plants. Leaf conductance to water vapour (g(L)) was highest in controls and significantly lower in PEG04 and PEG08 plants. Moreover, g(L) was correlated to R(venation) and to leaf water potential (psi(leaf)) with highly significant linear relationships. It is concluded that water stress has an important effect on the hydraulic construction of leaves. This, in turn, might prove to be a crucial factor in plant-water relationships and gas exchange under water stress conditions.

Methanol exchange dynamics between a temperate cropland soil and the atmosphere

NASA Astrophysics Data System (ADS)

Bachy, A.; Aubinet, M.; Amelynck, C.; Schoon, N.; Bodson, B.; Moureaux, C.; Delaplace, P.; De Ligne, A.; Heinesch, B.

2018-03-01

Soil methanol (CH3OH) exchange is often considered as several orders of magnitude smaller than plant methanol exchange. However, for some ecosystems, it is significant in regard with plant exchange and worth thus better consideration. Our study sought to gain a better understanding of soil exchange. Methanol flux was measured at the ecosystem scale on a bare agricultural soil over two contrasted periods using the disjunct eddy covariance by mass scanning technique. A proton-transfer-reaction mass spectrometer was used for the methanol ambient mixing ratio measurements. Bi-directional exchange dynamics were observed. Methanol emission occurred under dry and warm conditions and correlated best with soil surface temperature, whereas methanol uptake occurred under wet and mild conditions and correlated well with the methanol ambient concentration. After having tested a physical adsorption-desorption model and by confronting our data with the literature, we propose that the exchange was ruled by both a physical adsorption/desorption mechanism and by a methanol source, which still needs to be identified. The soil emission decreased when the vegetation developed. The reasons for the decrease still need to be determined. Overall, the dynamics observed at our site were similar to those reported by other studies for both cropland and forest ecosystems. The mechanism proposed in our work can thus be possibly applied to other sites or ecosystems. In addition, the methanol exchange rate was in the upper range of the exchange rates reported by other soil studies, suggesting that cropland soils are more important methanol exchangers than those in other ecosystems and should therefore be further investigated.

Pionic retardation effects in two-pion-exchange three-nucleon forces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coon, S.A.; Friar, J.L.

1986-09-01

Those two-pion-exchange three-nucleon forces which arise from nuclear processes that involve only pions and nucleons are calculated. Among the processes which contribute are pion seagulls (e.g., nucleon-antinucleon pair terms) and overlapping, retarded pion exchanges. The resulting potential is shown to be a (v-italic/c-italic)/sup 2/ relativistic correction, and satisfies nontrivial constraints from special relativity. The relativistic ambiguities found before in treatments of relativistic corrections to the one-pion-exchange nuclear charge operator and two-body potential are also present in the three-nucleon potential. The resulting three-nucleon force differs from the original Tucson-Melbourne potential only in the presence of several new nonlocal terms, and inmore » the specification of the choice of ambiguity parameters in the latter potential.« less

The use of the Hurst exponent to predict changes in trends on the Warsaw Stock Exchange

NASA Astrophysics Data System (ADS)

Domino, Krzysztof

2011-01-01

The local properties of the time series of the evolution of share prices of 126 significant companies traded on the Warsaw Stock Exchange during the period between 1991-2008 have been investigated. The analysis was applied to daily financial returns. I have used the local DFA to obtain the Hurst exponent (diffusion coefficient) while searching for negative correlations by which changes of long-term trends would be effected. A certain evidence, proving that after the signature of anti-correlation-the drop in the Hurst exponent-the change in the trend and in the return rate of an investment is probable, was pointed out. Hence after further investigation this method may be useful as a part of an investment strategy. As the Warsaw Stock Exchange is relatively smaller and younger than other significant world Stock Exchanges-and as the developing market is less efficient-the generalization for others markets needs further investigation.

Investigation of two-phase heat transfer coefficients of argon-freon cryogenic mixed refrigerants

NASA Astrophysics Data System (ADS)

Baek, Seungwhan; Lee, Cheonkyu; Jeong, Sangkwon

2014-11-01

Mixed refrigerant Joule Thomson refrigerators are widely used in various kinds of cryogenic systems these days. Although heat transfer coefficient estimation for a multi-phase and multi-component fluid in the cryogenic temperature range is necessarily required in the heat exchanger design of mixed refrigerant Joule Thomson refrigerators, it has been rarely discussed so far. In this paper, condensation and evaporation heat transfer coefficients of argon-freon mixed refrigerant are measured in a microchannel heat exchanger. A Printed Circuit Heat Exchanger (PCHE) with 340 μm hydraulic diameter has been developed as a compact microchannel heat exchanger and utilized in the experiment. Several two-phase heat transfer coefficient correlations are examined to discuss the experimental measurement results. The result of this paper shows that cryogenic two-phase mixed refrigerant heat transfer coefficients can be estimated by conventional two-phase heat transfer coefficient correlations.

Self-consistent implementation of meta-GGA functionals for the ONETEP linear-scaling electronic structure package.

PubMed

Womack, James C; Mardirossian, Narbe; Head-Gordon, Martin; Skylaris, Chris-Kriton

2016-11-28

Accurate and computationally efficient exchange-correlation functionals are critical to the successful application of linear-scaling density functional theory (DFT). Local and semi-local functionals of the density are naturally compatible with linear-scaling approaches, having a general form which assumes the locality of electronic interactions and which can be efficiently evaluated by numerical quadrature. Presently, the most sophisticated and flexible semi-local functionals are members of the meta-generalized-gradient approximation (meta-GGA) family, and depend upon the kinetic energy density, τ, in addition to the charge density and its gradient. In order to extend the theoretical and computational advantages of τ-dependent meta-GGA functionals to large-scale DFT calculations on thousands of atoms, we have implemented support for τ-dependent meta-GGA functionals in the ONETEP program. In this paper we lay out the theoretical innovations necessary to implement τ-dependent meta-GGA functionals within ONETEP's linear-scaling formalism. We present expressions for the gradient of the τ-dependent exchange-correlation energy, necessary for direct energy minimization. We also derive the forms of the τ-dependent exchange-correlation potential and kinetic energy density in terms of the strictly localized, self-consistently optimized orbitals used by ONETEP. To validate the numerical accuracy of our self-consistent meta-GGA implementation, we performed calculations using the B97M-V and PKZB meta-GGAs on a variety of small molecules. Using only a minimal basis set of self-consistently optimized local orbitals, we obtain energies in excellent agreement with large basis set calculations performed using other codes. Finally, to establish the linear-scaling computational cost and applicability of our approach to large-scale calculations, we present the outcome of self-consistent meta-GGA calculations on amyloid fibrils of increasing size, up to tens of thousands of atoms.

Self-consistent implementation of meta-GGA functionals for the ONETEP linear-scaling electronic structure package

NASA Astrophysics Data System (ADS)

Womack, James C.; Mardirossian, Narbe; Head-Gordon, Martin; Skylaris, Chris-Kriton

2016-11-01

Accurate and computationally efficient exchange-correlation functionals are critical to the successful application of linear-scaling density functional theory (DFT). Local and semi-local functionals of the density are naturally compatible with linear-scaling approaches, having a general form which assumes the locality of electronic interactions and which can be efficiently evaluated by numerical quadrature. Presently, the most sophisticated and flexible semi-local functionals are members of the meta-generalized-gradient approximation (meta-GGA) family, and depend upon the kinetic energy density, τ, in addition to the charge density and its gradient. In order to extend the theoretical and computational advantages of τ-dependent meta-GGA functionals to large-scale DFT calculations on thousands of atoms, we have implemented support for τ-dependent meta-GGA functionals in the ONETEP program. In this paper we lay out the theoretical innovations necessary to implement τ-dependent meta-GGA functionals within ONETEP's linear-scaling formalism. We present expressions for the gradient of the τ-dependent exchange-correlation energy, necessary for direct energy minimization. We also derive the forms of the τ-dependent exchange-correlation potential and kinetic energy density in terms of the strictly localized, self-consistently optimized orbitals used by ONETEP. To validate the numerical accuracy of our self-consistent meta-GGA implementation, we performed calculations using the B97M-V and PKZB meta-GGAs on a variety of small molecules. Using only a minimal basis set of self-consistently optimized local orbitals, we obtain energies in excellent agreement with large basis set calculations performed using other codes. Finally, to establish the linear-scaling computational cost and applicability of our approach to large-scale calculations, we present the outcome of self-consistent meta-GGA calculations on amyloid fibrils of increasing size, up to tens of thousands of atoms.

What correlation effects are covered by density functional theory?

NASA Astrophysics Data System (ADS)

He, Yuan; Grafenstein, Jurgen; Kraka, Elfi; Cremer, Dieter

The electron density distribution rho(r) generated by a DFT calculation was systematically studied by comparison with a series of reference densities obtained by wavefunction theory (WFT) methods that cover typical electron correlation effects. As a sensitive indicator for correlation effects the dipole moment of the CO molecule was used. The analysis reveals that typical LDA and GGA exchange functionals already simulate effects that are actually reminiscent of pair and three-electron correlation effects covered by MP2, MP4, and CCSD(T) in WFT. Correlation functionals contract the density towards the bond and the valence region thus taking negative charge out of the van der Waals region. It is shown that these improvements are relevant for the description of van der Waals interactions. Similar to certain correlated single-determinant WFT methods, BLYP and other GGA functionals underestimate ionic terms needed for a correct description of polar bonds. This is compensated for in hybrid functionals by mixing in HF exchange. The balanced mixing of local and non-local exchange and correlation effects leads to the correct description of polar bonds as in the B3LYP description of the CO molecule. The density obtained with B3LYP is closer to CCSD and CCSD(T) than to MP2 or MP4, which indicates that the B3LYP hybrid functional mimics those pair and three-electron correlation effects, which in WFT are only covered by coupled cluster methods.

Soft Functionals for Hard Matter

NASA Astrophysics Data System (ADS)

Cooper, Valentino R.; Yuk, Simuck F.; Krogel, Jaron T.

Theory and computation are critical to the materials discovery process. While density functional theory (DFT) has become the standard for predicting materials properties, it is often plagued by inaccuracies in the underlying exchange-correlation functionals. Using high-throughput DFT calculations we explore the accuracy of various exchange-correlation functionals for modeling the structural and thermodynamic properties of a wide range of complex oxides. In particular, we examine the feasibility of using the nonlocal van der Waals density correlation functional with C09 exchange (C09x), which was designed for sparsely packed soft matter, for investigating the properties of hard matter like bulk oxides. Preliminary results show unprecedented performance for some prototypical bulk ferroelectrics, which can be correlated with similarities between C09x and PBEsol. This effort lays the groundwork for understanding how these soft functionals can be employed as general purpose functionals for studying a wide range of materials where strong internal bonds and nonlocal interactions coexist. Research was sponsored by the US DOE, Office of Science, BES, MSED and Early Career Research Programs and used resources at NERSC.

Correlation functional in screened-exchange density functional theory procedures.

PubMed

Chan, Bun; Kawashima, Yukio; Hirao, Kimihiko

2017-10-15

In the present study, we have explored several prospects for the further development of screened-exchange density functional theory (SX-DFT) procedures. Using the performance of HSE06 as our measure, we find that the use of alternative correlation functionals (as oppose to PBEc in HSE06) also yields adequate results for a diverse set of thermochemical properties. We have further examined the performance of new SX-DFT procedures (termed HSEB-type methods) that comprise the HSEx exchange and a (near-optimal) reparametrized B97c (c OS,0  = c SS,0  = 1, c OS,1  = -1.5, c OS,2  = -0.644, c SS,1  = -0.5, and c SS,2  = 1.10) correlation functionals. The different variants of HSEB all perform comparably to or slightly better than the original HSE-type procedures. These results, together with our fundamental analysis of correlation functionals, point toward various directions for advancing SX-DFT methods. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Quantum Monte Carlo analysis of a charge ordered insulating antiferromagnet: The Ti 4O 7 Magneli phase

DOE PAGES

Benali, Anouar; Shulenburger, Luke; Krogel, Jaron T.; ...

2016-06-07

The Magneli phase Ti 4O 7 is an important transition metal oxide with a wide range of applications because of its interplay between charge, spin, and lattice degrees of freedom. At low temperatures, it has non-trivial magnetic states very close in energy, driven by electronic exchange and correlation interactions. We have examined three low- lying states, one ferromagnetic and two antiferromagnetic, and calculated their energies as well as Ti spin moment distributions using highly accurate Quantum Monte Carlo methods. We compare our results to those obtained from density functional theory- based methods that include approximate corrections for exchange and correlation.more » Our results confirm the nature of the states and their ordering in energy, as compared with density-functional theory methods. However, the energy differences and spin distributions differ. Here, a detailed analysis suggests that non-local exchange-correlation functionals, in addition to other approximations such as LDA+U to account for correlations, are needed to simultaneously obtain better estimates for spin moments, distributions, energy differences and energy gaps.« less

Full-Potential Calculation of Structural, Electronic, and Thermodynamic Properties of Fluoroperovskite { CsMF}3 (M = Be and Mg)

NASA Astrophysics Data System (ADS)

Harmel, M.; Khachai, H.; Ameri, A.; Baki, N.; Haddou, A.; Khalfa, M.; Abbar, B.; Omran, S. Bin; Uğur, G.; Uğur, Ş.; Khenata, R.

2012-12-01

The structural and electronic properties of the cubic fluoroperoveskite { CsBeF}3 and { CsMgF}3 have been investigated using the full-potential-linearized augmented plane wave method within the density functional theory. The exchange-correlation potential was treated with the local density approximation and the generalized gradient approximation. The calculations of the electronic band structures show that { CsBeF}_{3 } has an indirect bandgap, whereas { CsMgF}3 has a direct bandgap. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the effect of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and the heat capacity for { CsBeF}3 and { CsMgF}3 compounds are investigated for the first time.

Ab-initio calculations of structural, electronic, and optical properties of Zn3(VO4)2

NASA Astrophysics Data System (ADS)

Ahmed, Nisar; Mukhtar, S.; Gao, Wei; Zafar Ilyas, Syed

2018-03-01

The structural, electronic, and optical properties of Zn3(VO4)2 are investigated using full potential linearized augmented plane wave (FP-LAPW) method within the framework of density functional theory (DFT). Various approaches are adopted to treat the exchange and correlation potential energy such as generalized gradient approximation (GGA), GGA+U, and the Tran–Blaha modified Becke–Johnson (TB-mBJ) potential. The calculated band gap of 3.424 eV by TB-mBJ is found to be close to the experimental result (3.3 eV). The optical anisotropy is analyzed through optical constants, such as dielectric function and absorption coefficient along parallel and perpendicular crystal orientations. The absorption coefficient reveals high absorption (1.5× {10}6 {cm}}-1) of photons in the ultraviolet region.

Self-consistent many-electron theory of electron work functions and surface potential characteristics for selected metals

NASA Technical Reports Server (NTRS)

Smith, J. R.

1969-01-01

Electron work functions, surface potentials, and electron number density distributions and electric fields in the surface region of 26 metals were calculated from first principles within the free electron model. Calculation proceeded from an expression of the total energy as a functional of the electron number density, including exchange and correlation energies, as well as a first inhomogeneity term. The self-consistent solution was obtained via a variational procedure. Surface barriers were due principally to many-body effects; dipole barriers were small only for some alkali metals, becoming quite large for the transition metals. Surface energies were inadequately described by this model, which neglects atomistic effects. Reasonable results were obtained for electron work functions and surface potential characteristics, maximum electron densities varying by a factor of over 60.

Multifractal detrended cross-correlation analysis on gold, crude oil and foreign exchange rate time series

NASA Astrophysics Data System (ADS)

Pal, Mayukha; Madhusudana Rao, P.; Manimaran, P.

2014-12-01

We apply the recently developed multifractal detrended cross-correlation analysis method to investigate the cross-correlation behavior and fractal nature between two non-stationary time series. We analyze the daily return price of gold, West Texas Intermediate and Brent crude oil, foreign exchange rate data, over a period of 18 years. The cross correlation has been measured from the Hurst scaling exponents and the singularity spectrum quantitatively. From the results, the existence of multifractal cross-correlation between all of these time series is found. We also found that the cross correlation between gold and oil prices possess uncorrelated behavior and the remaining bivariate time series possess persistent behavior. It was observed for five bivariate series that the cross-correlation exponents are less than the calculated average generalized Hurst exponents (GHE) for q<0 and greater than GHE when q>0 and for one bivariate series the cross-correlation exponent is greater than GHE for all q values.

The effect of basis set and exchange-correlation functional on time-dependent density functional theory calculations within the Tamm-Dancoff approximation of the x-ray emission spectroscopy of transition metal complexes.

PubMed

Roper, Ian P E; Besley, Nicholas A

2016-03-21

The simulation of X-ray emission spectra of transition metal complexes with time-dependent density functional theory (TDDFT) is investigated. X-ray emission spectra can be computed within TDDFT in conjunction with the Tamm-Dancoff approximation by using a reference determinant with a vacancy in the relevant core orbital, and these calculations can be performed using the frozen orbital approximation or with the relaxation of the orbitals of the intermediate core-ionised state included. Both standard exchange-correlation functionals and functionals specifically designed for X-ray emission spectroscopy are studied, and it is shown that the computed spectral band profiles are sensitive to the exchange-correlation functional used. The computed intensities of the spectral bands can be rationalised by considering the metal p orbital character of the valence molecular orbitals. To compute X-ray emission spectra with the correct energy scale allowing a direct comparison with experiment requires the relaxation of the core-ionised state to be included and the use of specifically designed functionals with increased amounts of Hartree-Fock exchange in conjunction with high quality basis sets. A range-corrected functional with increased Hartree-Fock exchange in the short range provides transition energies close to experiment and spectral band profiles that have a similar accuracy to those from standard functionals.

Performance of the Effective Core Potentials of Ca, Hg and Pb in Complexes with Ligands Containing N and O Donor Atoms.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramirez, Jose Z.; Vargas, Rubicelia; Garza, Jorge

This paper presents a systematic study of the performance of the relativistic effective core potentials (RECPs) proposed by Stoll-Preuss, Christiansen-Ermler and Hay-Wadt for Ca2+, Hg2+ and Pb2+. The RECPs performance is studied when these cations are combined with ethylene glycol, 2-aminoethanol and ethylenediamine to form bidentate complexes. First, the description of the bidentate ligands is analyzed with the Kohn-Sham method by using SVWN, BLYP and B3LYP exchange-correlation functionals and they are compared with the Moeller-Plesset perturbation theory (MP2), for all these methods the TZVP basis set was used. We found that the BLYP exchange-correlation functional gives similar results that thosemore » obtained by the B3LYP and MP2 methods. Thus, the bidentate metal complexes were studied with the BLYP method combined with the RECPs. In order to compare RECPs performance, all the systems considered in this work were studied with the relativistic all-electron Douglas-Kroll (DK3) method. We observed that the Christiansen-Ermler RECPs give the best energetic and geometrical description for Ca and Hg complexes when compared with the all-electron method. For Pb complexes the spin-orbit interaction and Basis Set Superposition error must be taken into account in the RECP. In general, the trend showed in the complexation energies with the all-electron method is followed by the complexation energies computed with all the pseudopotential tested in this work. Battelle operates PNNL for the USDOE.« less

Ab-initio investigations for opto-electronic response of (Cd, Zn)Ga2Te4: Promising solar PV materials

NASA Astrophysics Data System (ADS)

Sahariya, Jagrati; Soni, Amit; Kumar, Pancham

2018-04-01

In this paper, the first principle calculations are performed to analyze the structural, electronic and optical behavior of promising solar materials (Cd,Zn)Ga2Te4. To perform these calculations we have used one of the most accurate Full Potential Linearized Augmented Plane Wave (FP-LAPW) method. The ground state properties of these compounds are confirmed over here after proper examination of energy and charge convergence using Perdew-Burke-Ernzerhof (PBE-sol) exchange correlation potential. The investigations performed such as energy band structure, Density of States (DOS), optical parameters like complex dielectric function and absorption co-efficient are discussed over here to understand the overall response of the chosen system.

Nonlinear beat excitation of low frequency wave in degenerate plasmas

NASA Astrophysics Data System (ADS)

Mir, Zahid; Shahid, M.; Jamil, M.; Rasheed, A.; Shahbaz, A.

2018-03-01

The beat phenomenon due to the coupling of two signals at slightly different frequencies that generates the low frequency signal is studied. The linear dispersive properties of the pump and sideband are analyzed. The modified nonlinear dispersion relation through the field coupling of linear modes against the beat frequency is derived in the homogeneous quantum dusty magnetoplasmas. The dispersion relation is used to derive the modified growth rate of three wave parametric instability. Moreover, significant quantum effects of electrons through the exchange-correlation potential, the Bohm potential, and the Fermi pressure evolved in macroscopic three wave interaction are presented. The analytical results are interpreted graphically describing the significance of the work. The applications of this study are pointed out at the end of introduction.

Electronic properties of excess Cr at Fe site in FeCr{sub 0.02}Se alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Sandeep, E-mail: sandeepk.iitb@gmail.com; Singh, Prabhakar P.

2015-06-24

We have studied the effect of substitution of transition-metal chromium (Cr) in excess on Fe sub-lattice in the electronic structure of iron-selenide alloys, FeCr{sub 0.02}Se. In our calculations, we used Korringa-Kohn-Rostoker coherent potential approximation method in the atomic sphere approximation (KKR-ASA-CPA). We obtained different band structure of this alloy with respect to the parent FeSe and this may be reason of changing their superconducting properties. We did unpolarized calculations for FeCr{sub 0.02}Se alloy in terms of density of states (DOS) and Fermi surfaces. The local density approximation (LDA) is used in terms of exchange correlation potential.

Hole-cyclotron instability in semiconductor quantum plasmas

NASA Astrophysics Data System (ADS)

Areeb, F.; Rasheed, A.; Jamil, M.; Siddique, M.; Sumera, P.

2018-01-01

The excitation of electrostatic hole-cyclotron waves generated by an externally injected electron beam in semiconductor plasmas is examined using a quantum hydrodynamic model. The quantum effects such as tunneling potential, Fermi degenerate pressure, and exchange-correlation potential are taken care of. The growth rate of the wave is analyzed on varying the parameters normalized by hole-plasma frequency, like the angle θ between propagation vector and B0∥z ̂ , speed of the externally injected electron beam v0∥k , thermal temperature of the electron beam τ, external magnetic field B0∥z ̂ that modifies the hole-cyclotron frequency, and finally, the semiconductor electron number density. The instability of the hole-cyclotron wave seeks its applications in semiconductor devices.

Structure factor and radial distribution function of some liquid lanthanides using charged hard sphere

NASA Astrophysics Data System (ADS)

Patel, H. P.; Sonvane, Y. A.; Thakor, P. B.

2017-05-01

The structure factor S(q) and radial distribution function g(r) play vital role to study the various structural properties like electronic, dynamic, magnetic etc. The present paper deals with the structural studies of foresaid properties using our newly constructed parameter free model potential with the Charged Hard Sphere (CHS) approximation. The local field correction due to Sarkar et al. is used to incorporate exchange and correlation among the conduction electrons in dielectric screening. Here we report the S(q) and g(r) for some liquid lanthanides viz: La, Ce, Pr, Nd and Eu. Present computed results are compared with the available experimental data. Lastly we found that our parameter free model potential successfully explains the structural propertiesof4fliquidlanthanides.

Neutrinoless Double Beta Decay Matrix Elements in Light Nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pastore, S.; Carlson, J.; Cirigliano, V.

We present the first ab initio calculations of neutrinoless double-β decay matrix elements in A=6-12 nuclei using variational Monte Carlo wave functions obtained from the Argonne v 18 two-nucleon potential and Illinois-7 three-nucleon interaction. We study both light Majorana neutrino exchange and potentials arising from a large class of multi-TeV mechanisms of lepton-number violation. Our results provide benchmarks to be used in testing many-body methods that can be extended to the heavy nuclei of experimental interest. In light nuclei we also study the impact of two-body short-range correlations and the use of different forms for the transition operators, such asmore » those corresponding to different orders in chiral effective theory.« less

The foreign exchange market: return distributions, multifractality, anomalous multifractality and the Epps effect

NASA Astrophysics Data System (ADS)

Drożdż, Stanisław; Kwapień, Jarosław; Oświȩcimka, Paweł; Rak, Rafał

2010-10-01

We present a systematic study of various statistical characteristics of high-frequency returns from the foreign exchange market. This study is based on six exchange rates forming two triangles: EUR-GBP-USD and GBP-CHF-JPY. It is shown that the exchange rate return fluctuations for all of the pairs considered are well described by the non-extensive statistics in terms of q-Gaussians. There exist some small quantitative variations in the non-extensivity q-parameter values for different exchange rates (which depend also on the time scales studied), and this can be related to the importance of a given exchange rate in the world's currency trade. Temporal correlations organize the series of returns such that they develop the multifractal characteristics for all of the exchange rates, with a varying degree of symmetry of the singularity spectrum f(α), however. The most symmetric spectrum is identified for the GBP/USD. We also form time series of triangular residual returns and find that the distributions of their fluctuations develop disproportionately heavier tails as compared to small fluctuations, which excludes description in terms of q-Gaussians. The multifractal characteristics of these residual returns reveal such anomalous properties as negative singularity exponents and even negative singularity spectra. Such anomalous multifractal measures have so far been considered in the literature in connection with diffusion-limited aggregation and with turbulence. Studying the cross-correlations among different exchange rates, we found that market inefficiency on short time scales leads to the occurrence of the Epps effect on much longer time scales, but comparable to the ones for the stock market. Although the currency market is much more liquid than the stock markets and has a much greater transaction frequency, the building up of correlations takes up to several hours—a duration that does not differ much from what is observed in the stock markets. This may suggest that non-synchronicity of transactions is not the unique source of the observed effect.

First-principles study on half-metallic ferromagnetic properties of Zn1- x V x Se ternary alloys

NASA Astrophysics Data System (ADS)

Khatta, Swati; Tripathi, S. K.; Prakash, Satya

2017-09-01

The spin-polarised density functional theory along with self-consistent plane-wave pseudopotential is used to investigate the half-metallic ferromagnetic properties of ternary alloys Zn1- x V x Se. The generalized gradient approximation is used for exchange-correlation potential. The equilibrium lattice constants, bulk modulus, and its derivatives are calculated. The calculated spin-polarised energy-band structures reveal that these alloys are half-metallic for x = 0.375 and 0.50 and nearly half-metallic for other values of x. The estimated direct and indirect bandgaps may be useful for the magneto-optical absorption experiments. It is found that there is strong Zn 4s, Se 4p, and V 3d orbital hybridization in the conduction bands of both the spins, while Se 4p and V 3d orbital hybridization predominates in the valence bands of both the spins. The s, p-d, and p-d orbital hybridization reduces the local magnetic moment of V atoms and small local magnetic moments are produced on Zn and Se atoms which get coupled with V atoms in ferromagnetic and antiferromagnetic phases, respectively. The conduction and valence-band-edge splittings and exchange constants predict the ferromagnetism in these alloys. The conduction band-impurity (s and p-d) exchange interaction is more significant for ferromagnetism in these alloys than the valence band-impurity (p-d) exchange interaction.

Kinetic theory of Lennard-Jones fluids

NASA Astrophysics Data System (ADS)

Leegwater, Jan A.

1991-12-01

A kinetic theory that describes the time evolution of a fluid consisting of Lennard-Jones particles at all densities is proposed. The kinetic equation assumes binary collisions, but takes into account the finite time duration of a collision. Furthermore, it is an extension of a kinetic equation for the square well fluid as well as the hard sphere Enskog theory. In the low density limit, the Boltzmann theory is obtained. It is shown that the proposed theory obeys all the conservation laws. The exchange of potential and kinetic energies is studied and it is shown that at high density this is a fast process. The dominant mechanism for energy exchange is found to be collisions at the strongly repulsive part of the potential that are disturbed by third particles. The kinetic equation is also used to calculate the Green-Kubo integrands for shear viscosity and heat conductivity. The major structures found in molecular dynamics simulations are reproduced at intermediate densities quantitatively and at high density semiquantitatively. It is found that at high density, not only correlated collisions have to be taken into account, but that even the concept of collisions in the sense of sudden changes in the velocity is no longer useful.

Electron scattering from gas phase cis-diamminedichloroplatinum(II): Quantum analysis of resonance dynamics

NASA Astrophysics Data System (ADS)

Carey, Ralph; Lucchese, Robert R.; Gianturco, F. A.

2013-05-01

We present scattering calculations of electron collisions with the platinum-containing compound cis-diamminedichloroplatinum (CDDP), commonly known as cisplatin, between 0.5 eV and 6 eV, and the corresponding isolated Pt atom from 0.1 eV to 10 eV. We find evidence of resonances in e--CDDP scattering, using an ab initio description of the target. We computed scattering matrix elements from equations incorporating exchange and polarization effects through the use of the static-exchange plus density functional correlation potential. Additionally, we made use of a purely local adiabatic model potential that allows Siegert eigenstates to be calculated, thereby allowing inspection of the possible resonant scattering wave functions. The total cross section for electron scattering from (5d10) 1S Pt displays a large magnitude, monotonic decay from the initial collision energies, with no apparent resonance scattering features in any scattering symmetry. By contrast, the e--CDDP scattering cross section shows a small feature near 3.8 eV, which results from a narrow, well localized resonance of b2 symmetry. These findings are then related to the possible electron-mediated mechanism of the action of CDDP on DNA replication as suggested by recent experiments.

Theory of g-factor enhancement in narrow-gap quantum well heterostructures.

PubMed

Krishtopenko, S S; Gavrilenko, V I; Goiran, M

2011-09-28

We report on the study of the exchange enhancement of the g-factor in the two-dimensional (2D) electron gas in n-type narrow-gap semiconductor heterostructures. Our approach is based on the eight-band k⋅p Hamiltonian and takes into account the band nonparabolicity, the lattice deformation, the spin-orbit coupling and the Landau level broadening in the δ-correlated random potential model. Using the 'screened' Hartree-Fock approximation we demonstrate that the exchange g-factor enhancement not only shows maxima at odd values of Landau level filling factors but, due to the conduction band nonparabolicity, persists at even filling factor values as well. The magnitude of the exchange enhancement, the amplitude and the shape of the g-factor oscillations are determined by both the screening of the electron-electron interaction and the Landau level width. The 'enhanced' g-factor values calculated for the 2D electron gas in InAs/AlSb quantum well heterostructures are compared with our earlier experimental data and with those obtained by Mendez et al (1993 Phys. Rev. B 47 13937) in magnetic fields up to 30 T.

Volatility spillover between crude oil and exchange rate: A copula-CARR approach

NASA Astrophysics Data System (ADS)

Pu, Y. J.; Guo, M. Y.

2017-11-01

Oil provides a powerful impetus for modern society's production and life. The influences of oil price fluctuations on socio-economic development are obvious, and it draws more attention from scholars. However, the distribution of oil is highly centralized, which leads to the vast majority of oil trading through foreign trade. As a result, exchange rate plays an important role in the oil business. Study on the relationship between exchange rate and crude oil gradually becomes a hot research topic in recent years. In this paper, we use copula and CARR model to study correlation structure and relationship between crude oil price and exchange rate. We establish CARR models as marginal models and use five copulas which are Gaussian Copula, Student-t Copula, Gumbel Copula, Clayton Copula and Frank Copula to study the correlation structure between NYMEX crude oil price range and U. S. Dollar Index range. Furthermore, we use Copula-CARR model with structural breaks to detect the change points in the correlation structure between NYMEX crude oil price range and U. S. Dollar Index range. Empirical results show that the change points are closely related to the actual economic events.

Insights into the spurious long-range nature of local rs-dependent non-local exchange-correlation kernels

DOE PAGES

Lu, Deyu

2016-08-05

A systematic route to go beyond the exact exchange plus random phase approximation (RPA) is to include a physical exchange-correlation kernel in the adiabatic-connection fluctuation-dissipation theorem. Previously, [D. Lu, J. Chem. Phys. 140, 18A520 (2014)], we found that non-local kernels with a screening length depending on the local Wigner-Seitz radius, r s(r), suffer an error associated with a spurious long-range repulsion in van der Waals bounded systems, which deteriorates the binding energy curve as compared to RPA. Here, we analyze the source of the error and propose to replace r s(r) by a global, average r s in the kernel.more » Exemplary studies with the Corradini, del Sole, Onida, and Palummo kernel show that while this change does not affect the already outstanding performance in crystalline solids, using an average r s significantly reduces the spurious long-range tail in the exchange-correlation kernel in van der Waals bounded systems. Finally, when this method is combined with further corrections using local dielectric response theory, the binding energy of the Kr dimer is improved three times as compared to RPA.« less

Scaling properties of foreign exchange volatility

NASA Astrophysics Data System (ADS)

Gençay, Ramazan; Selçuk, Faruk; Whitcher, Brandon

2001-01-01

In this paper, we investigate the scaling properties of foreign exchange volatility. Our methodology is based on a wavelet multi-scaling approach which decomposes the variance of a time series and the covariance between two time series on a scale by scale basis through the application of a discrete wavelet transformation. It is shown that foreign exchange rate volatilities follow different scaling laws at different horizons. Particularly, there is a smaller degree of persistence in intra-day volatility as compared to volatility at one day and higher scales. Therefore, a common practice in the risk management industry to convert risk measures calculated at shorter horizons into longer horizons through a global scaling parameter may not be appropriate. This paper also demonstrates that correlation between the foreign exchange volatilities is the lowest at the intra-day scales but exhibits a gradual increase up to a daily scale. The correlation coefficient stabilizes at scales one day and higher. Therefore, the benefit of currency diversification is the greatest at the intra-day scales and diminishes gradually at higher scales (lower frequencies). The wavelet cross-correlation analysis also indicates that the association between two volatilities is stronger at lower frequencies.

CATION EXCHANGE BETWEEN CELLS AND PLASMA OF MAMMALIAN BLOOD

PubMed Central

Sheppard, C. W.; Martin, W. R.; Beyl, Gertrude

1951-01-01

Sodium and potassium exchange has been studied in the blood of the sheep, dog, cow, and man. The potassium exchange rate in human cells is practically unaltered by increasing the plasma potassium concentration approximately threefold. Comparing the results in different species the exchange rate for potassium shows a rough correlation with the intracellular amount of the element. Expressed in per cent of the cellular content sodium tends to exchange more rapidly than potassium. In three instances the specific activity curves deviate from the simple exponential behavior of a two compartment system. In the exchange of potassium in canine blood the deviation is caused by the presence of a rapidly exchanging fraction in the buffy coat cells. Such an effect does not account for the inhomogeneity of sodium exchange in human blood. PMID:14824508

Triangular arbitrage in the foreign exchange market

NASA Astrophysics Data System (ADS)

Aiba, Yukihiro; Hatano, Naomichi

2004-12-01

We first review our previous work, showing what is the triangular arbitrage transaction and how to quantify the triangular arbitrage opportunity. Next we explain that the correlation of the foreign exchange rates can appear without actual triangular arbitrage transaction.

Sensitivity to ocean acidification differs between populations of the Sydney rock oyster: Role of filtration and ion-regulatory capacities.

PubMed

Stapp, Laura S; Parker, Laura M; O'Connor, Wayne A; Bock, Christian; Ross, Pauline M; Pörtner, Hans O; Lannig, G

2018-04-01

Understanding mechanisms of intraspecific variation in resilience to environmental drivers is key to predict species' adaptive potential. Recent studies show a higher CO 2 resilience of Sydney rock oysters selectively bred for increased growth and disease resistance ('selected oysters') compared to the wild population. We tested whether the higher resilience of selected oysters correlates with an increased ability to compensate for CO 2 -induced acid-base disturbances. After 7 weeks of exposure to elevated seawater PCO 2 (1100 μatm), wild oysters had a lower extracellular pH (pH e = 7.54 ± 0.02 (control) vs. 7.40 ± 0.03 (elevated PCO 2 )) and increased hemolymph PCO 2 whereas extracellular acid-base status of selected oysters remained unaffected. However, differing pH e values between oyster types were not linked to altered metabolic costs of major ion regulators (Na + /K + -ATPase, H + -ATPase and Na + /H + -exchanger) in gill and mantle tissues. Our findings suggest that selected oysters possess an increased systemic capacity to eliminate metabolic CO 2 , possibly through higher and energetically more efficient filtration rates and associated gas exchange. Thus, effective filtration and CO 2 resilience might be positively correlated traits in oysters. Copyright © 2017 Elsevier Ltd. All rights reserved.

Leaf hydraulics and drought stress: response, recovery and survivorship in four woody temperate plant species.

PubMed

Blackman, Christopher J; Brodribb, Timothy J; Jordan, Gregory J

2009-11-01

Efficient conduction of water inside leaves is essential for leaf function, yet the hydraulic-mediated impact of drought on gas exchange remains poorly understood. Here we examine the decline and subsequent recovery of leaf water potential (Psi(leaf)), leaf hydraulic conductance (K(leaf)), and midday transpiration (E) in four temperate woody species exposed to controlled drought conditions ranging from mild to lethal. During drought the vulnerability of K(leaf) to declining Psi(leaf) varied greatly among the species sampled. Following drought, plants were rewatered and the rate of E and K(leaf) recovery was found to be strongly dependent on the severity of the drought imposed. Gas exchange recovery was strongly correlated with the relatively slow recovery of K(leaf) for three of the four species, indicating conformity to a hydraulic-stomatal limitation model of plant recovery. However, there was also a shift in the sensitivity of stomata to Psi(leaf) suggesting that the plant hormone abscisic acid may be involved in limiting the rate of stomatal reopening. The level of drought tolerance varied among the four species and was correlated with leaf hydraulic vulnerability. These results suggest that species-specific variation in hydraulic properties plays a fundamental role in steering the dynamic response of plants during recovery.

Introducing False EUR and False EUR exchange rates

NASA Astrophysics Data System (ADS)

Ausloos, M.; Ivanova, K.

2000-10-01

The Euro ( EUR) is a new currency introduced by the European Community. Its exchange rate is very puzzling. We have invented a false Euro ( FEUR) dating back to 1993 and have derived the exchange rates of the FEUR with respect to currencies not belonging to the EUR, i.e., DKK, CHF, JPY and USD. This allows us to search for correlations between the fluctuations preexisting to the introduction of EUR and present ones in such financial data. The detrended fluctuation analysis ( DFA) statistical method is used. This leads to assume a power-law behavior, i.e., a scaling hypothesis, through an exponent α. The latter has demonstrated its usefulness for the investigations of long-range power-law correlations in several types of financial sequences. Our findings show that the α exponent interestingly characterizes fractional Brownian motion of the currency exchange rates between EUR and DKK over a 25 day interval, and usual Brownian motion otherwise and for the three other investigated exchange rates. We can devise an investment strategy based on the localα technique and obtain appreciable gains for the time being.

Mining author relationship in scholarly networks based on tripartite citation analysis

PubMed Central

Wang, Xiaohan; Yang, Siluo

2017-01-01

Following scholars in Scientometrics as examples, we develop five author relationship networks, namely, co-authorship, author co-citation (AC), author bibliographic coupling (ABC), author direct citation (ADC), and author keyword coupling (AKC). The time frame of data sets is divided into two periods: before 2011 (i.e., T1) and after 2011 (i.e., T2). Through quadratic assignment procedure analysis, we found that some authors have ABC or AC relationships (i.e., potential communication relationship, PCR) but do not have actual collaborations or direct citations (i.e., actual communication relationship, ACR) among them. In addition, we noticed that PCR and AKC are highly correlated and that the old PCR and the new ACR are correlated and consistent. Such facts indicate that PCR tends to produce academic exchanges based on similar themes, and ABC bears more advantages in predicting potential relations. Based on tripartite citation analysis, including AC, ABC, and ADC, we also present an author-relation mining process. Such process can be used to detect deep and potential author relationships. We analyze the prediction capacity by comparing between the T1 and T2 periods, which demonstrate that relation mining can be complementary in identifying authors based on similar themes and discovering more potential collaborations and academic communities. PMID:29117198

An Exactly Soluble Model for Hopping Particles Moving with Correlations Between States due to Exchange Sites

NASA Astrophysics Data System (ADS)

Zhao, Xian-Geng; Jia, Sue-Tang

1992-09-01

The motion of hopping particles on an infinite chain is investigated. The model is characterized by the correlations between states due to exchange sites. The analytic solutions for this system are discussed in general case. For some special cases, exact results are obtained with the help of explicit calculations of propagators and mean square displacement deviation. Both probability propagators for the creation and annihilation of two particles or for the deformation and formation of Frenkel excitons are indicated.

Correlation structures in short-term variabilities of stock indices and exchange rates

NASA Astrophysics Data System (ADS)

Nakamura, Tomomichi; Small, Michael

2007-09-01

Financial data usually show irregular fluctuations and some trends. We investigate whether there are correlation structures in short-term variabilities (irregular fluctuations) among financial data from the viewpoint of deterministic dynamical systems. Our method is based on the small-shuffle surrogate method. The data we use are daily closing price of Standard & Poor's 500 and the volume, and daily foreign exchange rates, Euro/US Dollar (USD), British Pound/USD and Japanese Yen/USD. We found that these data are not independent.

First principles study of structural, electronic and optical properties of perovskites CaZrO3 and CaHfO3 in cubic phase

NASA Astrophysics Data System (ADS)

Hoat, D. M.; Silva, J. F. Rivas; Blas, A. Méndez

2018-07-01

In this work, we present the first principles calculations for structural, electronic and optical properties of perovskites CaZrO3 and CaHfO3 using the full-potential linearized augmented plane wave method (FP-LAPW) within the framework of density functional theory (DFT) as implemented in WIEN2k package. The exchange-correlation potential is treated with local density approximation (LDA) and generalized gradient approximation (GGA-PBE and PBESol). Additionally, the Tran Blaha modified Becke-Johnson exchange potential (mBJ) also is employed for electronic and optical calculations due to that it gives very accurate band gap of solids. Our obtained structural parameters are in good agreement with experimental datas and other theoretical results. The energy band gap obtained with mBJ is 4.56 eV for CaZrO3 and 5.27 eV for CaHfO3. The hybridization of states of O atom with those of Zr and Hf atoms in CaZrO3 and CaHfO3, respectively, is observed. The spin-orbit coupling effect on electronic properties of considered compounds also is investigated. Finally, the linear optical properties of CaZrO3 and CaHfO3 are derived from their complex dielectric function calculated with mBJ potential for wide energy range up to 45 eV, and all of them analyzed in details.

The hydraulic conductance of Fraxinus ornus leaves is constrained by soil water availability and coordinated with gas exchange rates.

PubMed

Gortan, Emmanuelle; Nardini, Andrea; Gascó, Antonio; Salleo, Sebastiano

2009-04-01

Leaf hydraulic conductance (Kleaf) is known to be an important determinant of plant gas exchange and photosynthesis. Little is known about the long-term impact of different environmental factors on the hydraulic construction of leaves and its eventual consequences on leaf gas exchange. In this study, we investigate the impact of soil water availability on Kleaf of Fraxinus ornus L. as well as the influence of Kleaf on gas exchange rates and plant water status. With this aim, Kleaf, leaf conductance to water vapour (gL), leaf water potential (Psileaf) and leaf mass per area (LMA) were measured in F. ornus trees, growing in 21 different sites with contrasting water availability. Plants growing in arid sites had lower Kleaf, gL and Psileaf than those growing in sites with higher water availability. On the contrary, LMA was similar in the two groups. The Kleaf values recorded in sites with two different levels of soil water availability were constantly different from each other regardless of the amount of precipitation recorded over 20 days before measurements. Moreover, Kleaf was correlated with gL values. Our data suggest that down-regulation of Kleaf is a component of adaptation of plants to drought-prone habitats. Low Kleaf implies reduced gas exchange which may, in turn, influence the climatic conditions on a local/regional scale. It is concluded that leaf hydraulics and its changes in response to resource availability should receive greater attention in studies aimed at modelling biosphere-atmosphere interactions.

Determination of Ground Heat Exchangers Temperature Field in Geothermal Heat Pumps

NASA Astrophysics Data System (ADS)

Zhurmilova, I.; Shtym, A.

2017-11-01

For the heating and cooling supply of buildings and constructions geothermal heat pumps using low-potential ground energy are applied by means of ground exchangers. The process of heat transfer in a system of ground exchangers is a phenomenon of complex heat transfer. The paper presents a mathematical modeling of heat exchange processes, the temperature fields are built which are necessary for the determination of the ground array that ensures an adequate supply of low potential energy excluding the freezing of soil around the pipes in the ground heat exchangers and guaranteeing a reliable operation of geothermal heat pumps.

Ab Initio Optimized Effective Potentials for Real Molecules in Optical Cavities: Photon Contributions to the Molecular Ground State

PubMed Central

2018-01-01

We introduce a simple scheme to efficiently compute photon exchange-correlation contributions due to the coupling to transversal photons as formulated in the newly developed quantum-electrodynamical density-functional theory (QEDFT).1−5 Our construction employs the optimized-effective potential (OEP) approach by means of the Sternheimer equation to avoid the explicit calculation of unoccupied states. We demonstrate the efficiency of the scheme by applying it to an exactly solvable GaAs quantum ring model system, a single azulene molecule, and chains of sodium dimers, all located in optical cavities and described in full real space. While the first example is a two-dimensional system and allows to benchmark the employed approximations, the latter two examples demonstrate that the correlated electron-photon interaction appreciably distorts the ground-state electronic structure of a real molecule. By using this scheme, we not only construct typical electronic observables, such as the electronic ground-state density, but also illustrate how photon observables, such as the photon number, and mixed electron-photon observables, for example, electron–photon correlation functions, become accessible in a density-functional theory (DFT) framework. This work constitutes the first three-dimensional ab initio calculation within the new QEDFT formalism and thus opens up a new computational route for the ab initio study of correlated electron–photon systems in quantum cavities. PMID:29594185

Willingness to Exchange Health Information via Mobile Devices: Findings From a Population-Based Survey.

PubMed

Serrano, Katrina J; Yu, Mandi; Riley, William T; Patel, Vaishali; Hughes, Penelope; Marchesini, Kathryn; Atienza, Audie A

2016-01-01

The rapid proliferation of mobile devices offers unprecedented opportunities for patients and health care professionals to exchange health information electronically, but little is known about patients' willingness to exchange various types of health information using these devices. We examined willingness to exchange different types of health information via mobile devices, and assessed whether sociodemographic characteristics and trust in clinicians were associated with willingness in a nationally representative sample. We analyzed data for 3,165 patients captured in the 2013 Health Information National Trends Survey. Multinomial logistic regression analysis was conducted to test differences in willingness. Ordinal logistic regression analysis assessed correlates of willingness to exchange 9 types of information separately. Participants were very willing to exchange appointment reminders (odds ratio [OR] = 6.66; 95% CI, 5.68-7.81), general health tips (OR = 2.03; 95% CI, 1.74-2.38), medication reminders (OR = 2.73; 95% CI, 2.35-3.19), laboratory/test results (OR = 1.76; 95% CI, 1.62-1.92), vital signs (OR = 1.63; 95% CI, 1.48-1.80), lifestyle behaviors (OR = 1.40; 95% CI, 1.24-1.58), and symptoms (OR = 1.62; 95% CI, 1.46-1.79) as compared with diagnostic information. Older adults had lower odds of being more willing to exchange any type of information. Education, income, and trust in health care professional information correlated with willingness to exchange certain types of information. Respondents were less willing to exchange via mobile devices information that may be considered sensitive or complex. Age, socioeconomic factors, and trust in professional information were associated with willingness to engage in mobile health information exchange. Both information type and demographic group should be considered when developing and tailoring mobile technologies for patient-clinician communication. © 2016 Annals of Family Medicine, Inc.

Analyzing the Cross-Correlation Between Onshore and Offshore RMB Exchange Rates Based on Multifractal Detrended Cross-Correlation Analysis (MF-DCCA)

NASA Astrophysics Data System (ADS)

Xie, Chi; Zhou, Yingying; Wang, Gangjin; Yan, Xinguo

We use the multifractal detrended cross-correlation analysis (MF-DCCA) method to explore the multifractal behavior of the cross-correlation between exchange rates of onshore RMB (CNY) and offshore RMB (CNH) against US dollar (USD). The empirical data are daily prices of CNY/USD and CNH/USD from May 1, 2012 to February 29, 2016. The results demonstrate that: (i) the cross-correlation between CNY/USD and CNH/USD is persistent and its fluctuation is smaller when the order of fluctuation function is negative than that when the order is positive; (ii) the multifractal behavior of the cross-correlation between CNY/USD and CNH/USD is significant during the sample period; (iii) the dynamic Hurst exponents obtained by the rolling windows analysis show that the cross-correlation is stable when the global economic situation is good and volatile in bad situation; and (iv) the non-normal distribution of original data has a greater effect on the multifractality of the cross-correlation between CNY/USD and CNH/USD than the temporary correlation.

The Hartree product and the description of local and global quantities in atomic systems: A study within Kohn-Sham theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garza, Jorge; Nichols, Jeffrey A.; Dixon, David A.

2000-01-15

The Hartree product is analyzed in the context of Kohn-Sham theory. The differential equations that emerge from this theory are solved with the optimized effective potential using the Krieger, Li, and Iafrate approximation, in order to get a local potential as required by the ordinary Kohn-Sham procedure. Because the diagonal terms of the exact exchange energy are included in Hartree theory, it is self-interaction free and the exchange potential has the proper asymptotic behavior. We have examined the impact of this correct asymptotic behavior on local and global properties using this simple model to approximate the exchange energy. Local quantities,more » such as the exchange potential and the average local electrostatic potential are used to examine whether the shell structure in an atom is revealed by this theory. Global quantities, such as the highest occupied orbital energy (related to the ionization potential) and the exchange energy are also calculated. These quantities are contrasted with those obtained from calculations with the local density approximation, the generalized gradient approximation, and the self-interaction correction approach proposed by Perdew and Zunger. We conclude that the main characteristics in an atomic system are preserved with the Hartree theory. In particular, the behavior of the exchange potential obtained in this theory is similar to those obtained within other Kohn-Sham approximations. (c) 2000 American Institute of Physics.« less

Leaf gas exchange performance and the lethal water potential of five European species during drought.

PubMed

Li, Shan; Feifel, Marion; Karimi, Zohreh; Schuldt, Bernhard; Choat, Brendan; Jansen, Steven

2016-02-01

Establishing physiological thresholds to drought-induced mortality in a range of plant species is crucial in understanding how plants respond to severe drought. Here, five common European tree species were selected (Acer campestre L., Acer pseudoplatanus L., Carpinus betulus L., Corylus avellana L. and Fraxinus excelsior L.) to study their hydraulic thresholds to mortality. Photosynthetic parameters during desiccation and the recovery of leaf gas exchange after rewatering were measured. Stem vulnerability curves and leaf pressure-volume curves were investigated to understand the hydraulic coordination of stem and leaf tissue traits. Stem and root samples from well-watered and severely drought-stressed plants of two species were observed using transmission electron microscopy to visualize mortality of cambial cells. The lethal water potential (ψlethal) correlated with stem P99 (i.e., the xylem water potential at 99% loss of hydraulic conductivity, PLC). However, several plants that were stressed beyond the water potential at 100% PLC showed complete recovery during the next spring, which suggests that the ψlethal values were underestimated. Moreover, we observed a 1 : 1 relationship between the xylem water potential at the onset of embolism and stomatal closure, confirming hydraulic coordination between leaf and stem tissues. Finally, ultrastructural changes in the cytoplasm of cambium tissue and mortality of cambial cells are proposed to provide an alternative approach to investigate the point of no return associated with plant death. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Electronic structures of of PuX (X=S, Se, Te)

NASA Astrophysics Data System (ADS)

Maehira, Takahiro; Sakai, Eijiro; Tatetsu, Yasutomi

2013-08-01

We have calculated the energy band structures and the Fermi surfaces of PuS, PuSe, and PuTe by using a self-consistent relativistic linear augmented-plane-wave method with the exchange and correlation potential in the local density approximation. In general, the energy bands near the Fermi level are mainly caused by the hybridization between the Pu 5 f and the monochalcogenide p electrons. The obtained main Fermi surfaces consisted of two hole sheets and one electron sheet, which were constructed from the band having both the Pu 5 f state and the monochalcogenide p state.

Relativistic density functional theory with picture-change corrected electron density based on infinite-order Douglas-Kroll-Hess method

NASA Astrophysics Data System (ADS)

Oyama, Takuro; Ikabata, Yasuhiro; Seino, Junji; Nakai, Hiromi

2017-07-01

This Letter proposes a density functional treatment based on the two-component relativistic scheme at the infinite-order Douglas-Kroll-Hess (IODKH) level. The exchange-correlation energy and potential are calculated using the electron density based on the picture-change corrected density operator transformed by the IODKH method. Numerical assessments indicated that the picture-change uncorrected density functional terms generate significant errors, on the order of hartree for heavy atoms. The present scheme was found to reproduce the energetics in the four-component treatment with high accuracy.

Replica Exchange Gaussian Accelerated Molecular Dynamics: Improved Enhanced Sampling and Free Energy Calculation.

PubMed

Huang, Yu-Ming M; McCammon, J Andrew; Miao, Yinglong

2018-04-10

Through adding a harmonic boost potential to smooth the system potential energy surface, Gaussian accelerated molecular dynamics (GaMD) provides enhanced sampling and free energy calculation of biomolecules without the need of predefined reaction coordinates. This work continues to improve the acceleration power and energy reweighting of the GaMD by combining the GaMD with replica exchange algorithms. Two versions of replica exchange GaMD (rex-GaMD) are presented: force constant rex-GaMD and threshold energy rex-GaMD. During simulations of force constant rex-GaMD, the boost potential can be exchanged between replicas of different harmonic force constants with fixed threshold energy. However, the algorithm of threshold energy rex-GaMD tends to switch the threshold energy between lower and upper bounds for generating different levels of boost potential. Testing simulations on three model systems, including the alanine dipeptide, chignolin, and HIV protease, demonstrate that through continuous exchanges of the boost potential, the rex-GaMD simulations not only enhance the conformational transitions of the systems but also narrow down the distribution width of the applied boost potential for accurate energetic reweighting to recover biomolecular free energy profiles.

Spin Bose-metal phase in a spin- (1)/(2) model with ring exchange on a two-leg triangular strip

NASA Astrophysics Data System (ADS)

Sheng, D. N.; Motrunich, Olexei I.; Fisher, Matthew P. A.

2009-05-01

Recent experiments on triangular lattice organic Mott insulators have found evidence for a two-dimensional (2D) spin liquid in close proximity to the metal-insulator transition. A Gutzwiller wave function study of the triangular lattice Heisenberg model with a four-spin ring exchange term appropriate in this regime has found that the projected spinon Fermi sea state has a low variational energy. This wave function, together with a slave particle-gauge theory analysis, suggests that this putative spin liquid possesses spin correlations that are singular along surfaces in momentum space, i.e., “Bose surfaces.” Signatures of this state, which we will refer to as a “spin Bose metal” (SBM), are expected to manifest in quasi-one-dimensional (quasi-1D) ladder systems: the discrete transverse momenta cut through the 2D Bose surface leading to a distinct pattern of 1D gapless modes. Here, we search for a quasi-1D descendant of the triangular lattice SBM state by exploring the Heisenberg plus ring model on a two-leg triangular strip (zigzag chain). Using density matrix renormalization group (DMRG) supplemented by variational wave functions and a bosonization analysis, we map out the full phase diagram. In the absence of ring exchange the model is equivalent to the J1-J2 Heisenberg chain, and we find the expected Bethe-chain and dimerized phases. Remarkably, moderate ring exchange reveals a new gapless phase over a large swath of the phase diagram. Spin and dimer correlations possess singular wave vectors at particular “Bose points” (remnants of the 2D Bose surface) and allow us to identify this phase as the hoped for quasi-1D descendant of the triangular lattice SBM state. We use bosonization to derive a low-energy effective theory for the zigzag spin Bose metal and find three gapless modes and one Luttinger parameter controlling all power law correlations. Potential instabilities out of the zigzag SBM give rise to other interesting phases such as a period-3 valence bond solid or a period-4 chirality order, which we discover in the DMRG. Another interesting instability is into a spin Bose-metal phase with partial ferromagnetism (spin polarization of one spinon band), which we also find numerically using the DMRG.

A general range-separated double-hybrid density-functional theory

NASA Astrophysics Data System (ADS)

Kalai, Cairedine; Toulouse, Julien

2018-04-01

A range-separated double-hybrid (RSDH) scheme which generalizes the usual range-separated hybrids and double hybrids is developed. This scheme consistently uses a two-parameter Coulomb-attenuating-method (CAM)-like decomposition of the electron-electron interaction for both exchange and correlation in order to combine Hartree-Fock exchange and second-order Møller-Plesset (MP2) correlation with a density functional. The RSDH scheme relies on an exact theory which is presented in some detail. Several semi-local approximations are developed for the short-range exchange-correlation density functional involved in this scheme. After finding optimal values for the two parameters of the CAM-like decomposition, the RSDH scheme is shown to have a relatively small basis dependence and to provide atomization energies, reaction barrier heights, and weak intermolecular interactions globally more accurate or comparable to range-separated MP2 or standard MP2. The RSDH scheme represents a new family of double hybrids with minimal empiricism which could be useful for general chemical applications.

Influence of the exchange and correlation functional on the structure of amorphous InSb and In3SbTe2 compounds

NASA Astrophysics Data System (ADS)

Gabardi, Silvia; Caravati, Sebastiano; Los, Jan H.; Kühne, Thomas D.; Bernasconi, Marco

2016-05-01

We have investigated the structural, vibrational, and electronic properties of the amorphous phase of InSb and In3SbTe2 compounds of interest for applications in phase change non-volatile memories. Models of the amorphous phase have been generated by quenching from the melt by molecular dynamics simulations based on density functional theory. In particular, we have studied the dependence of the structural properties on the choice of the exchange-correlation functional. It turns out that the use of the Becke-Lee-Yang-Parr functional provides models with a much larger fraction of In atoms in a tetrahedral bonding geometry with respect to previous results obtained with the most commonly used Perdew-Becke-Ernzerhof functional. This outcome is at odd with the properties of Ge2Sb2Te5 phase change compound for which the two exchange-correlation functionals yield very similar results on the structure of the amorphous phase.

Influence of the exchange and correlation functional on the structure of amorphous InSb and In3SbTe2 compounds.

PubMed

Gabardi, Silvia; Caravati, Sebastiano; Los, Jan H; Kühne, Thomas D; Bernasconi, Marco

2016-05-28

We have investigated the structural, vibrational, and electronic properties of the amorphous phase of InSb and In3SbTe2 compounds of interest for applications in phase change non-volatile memories. Models of the amorphous phase have been generated by quenching from the melt by molecular dynamics simulations based on density functional theory. In particular, we have studied the dependence of the structural properties on the choice of the exchange-correlation functional. It turns out that the use of the Becke-Lee-Yang-Parr functional provides models with a much larger fraction of In atoms in a tetrahedral bonding geometry with respect to previous results obtained with the most commonly used Perdew-Becke-Ernzerhof functional. This outcome is at odd with the properties of Ge2Sb2Te5 phase change compound for which the two exchange-correlation functionals yield very similar results on the structure of the amorphous phase.

Rapid and quantitative chemical exchange saturation transfer (CEST) imaging with magnetic resonance fingerprinting (MRF).

PubMed

Cohen, Ouri; Huang, Shuning; McMahon, Michael T; Rosen, Matthew S; Farrar, Christian T

2018-05-13

To develop a fast magnetic resonance fingerprinting (MRF) method for quantitative chemical exchange saturation transfer (CEST) imaging. We implemented a CEST-MRF method to quantify the chemical exchange rate and volume fraction of the N α -amine protons of L-arginine (L-Arg) phantoms and the amide and semi-solid exchangeable protons of in vivo rat brain tissue. L-Arg phantoms were made with different concentrations (25-100 mM) and pH (pH 4-6). The MRF acquisition schedule varied the saturation power randomly for 30 iterations (phantom: 0-6 μT; in vivo: 0-4 μT) with a total acquisition time of ≤2 min. The signal trajectories were pattern-matched to a large dictionary of signal trajectories simulated using the Bloch-McConnell equations for different combinations of exchange rate, exchangeable proton volume fraction, and water T 1 and T 2 relaxation times. The chemical exchange rates of the N α -amine protons of L-Arg were significantly (P < 0.0001) correlated with the rates measured with the quantitation of exchange using saturation power method. Similarly, the L-Arg concentrations determined using MRF were significantly (P < 0.0001) correlated with the known concentrations. The pH dependence of the exchange rate was well fit (R 2  = 0.9186) by a base catalyzed exchange model. The amide proton exchange rate measured in rat brain cortex (34.8 ± 11.7 Hz) was in good agreement with that measured previously with the water exchange spectroscopy method (28.6 ± 7.4 Hz). The semi-solid proton volume fraction was elevated in white (12.2 ± 1.7%) compared to gray (8.1 ± 1.1%) matter brain regions in agreement with previous magnetization transfer studies. CEST-MRF provides a method for fast, quantitative CEST imaging. © 2018 International Society for Magnetic Resonance in Medicine.

Methods for converging correlation energies within the dielectric matrix formalism

NASA Astrophysics Data System (ADS)

Dixit, Anant; Claudot, Julien; Gould, Tim; Lebègue, Sébastien; Rocca, Dario

2018-03-01

Within the dielectric matrix formalism, the random-phase approximation (RPA) and analogous methods that include exchange effects are promising approaches to overcome some of the limitations of traditional density functional theory approximations. The RPA-type methods however have a significantly higher computational cost, and, similarly to correlated quantum-chemical methods, are characterized by a slow basis set convergence. In this work we analyzed two different schemes to converge the correlation energy, one based on a more traditional complete basis set extrapolation and one that converges energy differences by accounting for the size-consistency property. These two approaches have been systematically tested on the A24 test set, for six points on the potential-energy surface of the methane-formaldehyde complex, and for reaction energies involving the breaking and formation of covalent bonds. While both methods converge to similar results at similar rates, the computation of size-consistent energy differences has the advantage of not relying on the choice of a specific extrapolation model.

Spin-dependent Otto quantum heat engine based on a molecular substance

NASA Astrophysics Data System (ADS)

Hübner, W.; Lefkidis, G.; Dong, C. D.; Chaudhuri, D.; Chotorlishvili, L.; Berakdar, J.

2014-07-01

We explore the potential of single molecules for thermodynamic cycles. To this end we propose two molecular heat engines based on the Ni2 dimer in the presence of a static magnetic field: (a) a quantum Otto engine and (b) a modified quantum Otto engine for which optical excitations induced by a laser pulse substitute for one of the heat-exchange points. For reliable predictions and to inspect the role of spin and electronic correlations we perform fully correlated ab initio calculations of the molecular electronic structure including spin-orbital effects. We analyze the efficiency of the engines in dependence of the electronic level scheme and the entanglement and find a significant possible enhancement connected to the quantum nature and the heat capacity of the dimer, as well as to the zero-field triplet states splitting.

Parameter motivated mutual correlation analysis: Application to the study of currency exchange rates based on intermittency parameter and Hurst exponent

NASA Astrophysics Data System (ADS)

Cristescu, Constantin P.; Stan, Cristina; Scarlat, Eugen I.; Minea, Teofil; Cristescu, Cristina M.

2012-04-01

We present a novel method for the parameter oriented analysis of mutual correlation between independent time series or between equivalent structures such as ordered data sets. The proposed method is based on the sliding window technique, defines a new type of correlation measure and can be applied to time series from all domains of science and technology, experimental or simulated. A specific parameter that can characterize the time series is computed for each window and a cross correlation analysis is carried out on the set of values obtained for the time series under investigation. We apply this method to the study of some currency daily exchange rates from the point of view of the Hurst exponent and the intermittency parameter. Interesting correlation relationships are revealed and a tentative crisis prediction is presented.

Magnetosonic solitons in semiconductor plasmas in the presence of quantum tunneling and exchange correlation effects

NASA Astrophysics Data System (ADS)

Hussain, S.; Mahmood, S.

2018-01-01

Low frequency magnetosonic wave excitations are investigated in semiconductor hole-electron plasmas. The quantum mechanical effects such as Fermi pressure, quantum tunneling, and exchange-correlation of holes and electrons in the presence of the magnetic field are considered. The two fluid quantum magnetohydrodynamic model is used to study magnetosonic wave dynamics, while electric and magnetic fields are coupled via Maxwell equations. The dispersion relation of the magnetosonic wave in electron-hole semiconductor plasma propagating in the perpendicular direction of the magnetic field is obtained, and its dispersion effects are discussed. The Korteweg-de Vries equation (KdV) for magnetosonic solitons is derived by employing the reductive perturbation method. For numerical analysis, the plasma parameters are taken from the semiconductors such as GaAs, GaSb, GaN, and InP already existing in the literature. It is found that the phase velocity of the magnetosonic wave is increased with the inclusion of exchange-correlation force in the model. The soliton dip structures of the magnetosonic wave in GaN semiconductor plasma are obtained, which satisfy the quantum plasma conditions for electron and hole fluids. The magnetosonic soliton dip structures move with speed less than the magnetosonic wave phase speed in the lab frame. The effects of exchange-correlation force in the model and variations of magnetic field intensity and electron/hole density on the magnetosonic wave dip structures are also investigated numerically for illustration.

Ionization energies and electron affinities from a random-phase-approximation many-body Green's-function method including exchange interactions

NASA Astrophysics Data System (ADS)

Heßelmann, Andreas

2017-06-01

A many-body Green's-function method employing an infinite order summation of ring and exchange-ring contributions to the self-energy is presented. The individual correlation and relaxation contributions to the quasiparticle energies are calculated using an iterative scheme which utilizes density fitting of the particle-hole, particle-particle and hole-hole densities. It is shown that the ionization energies and electron affinities of this approach agree better with highly accurate coupled-cluster singles and doubles with perturbative triples energy difference results than those obtained with second-order Green's-function approaches. An analysis of the correlation and relaxation terms of the self-energy for the direct- and exchange-random-phase-approximation (RPA) Green's-function methods shows that the inclusion of exchange interactions leads to a reduction of the two contributions in magnitude. These differences, however, strongly cancel each other when summing the individual terms to the quasiparticle energies. Due to this, the direct- and exchange-RPA methods perform similarly for the description of ionization energies (IPs) and electron affinities (EAs). The coupled-cluster reference IPs and EAs, if corrected to the adiabatic energy differences between the neutral and charged molecules, were shown to be in very good agreement with experimental measurements.

A review of studies on ion thruster beam and charge-exchange plasmas

NASA Technical Reports Server (NTRS)

Carruth, M. R., Jr.

1982-01-01

Various experimental and analytical studies of the primary beam and charge-exchange plasmas of ion thrusters are reviewed. The history of plasma beam research is recounted, emphasizing experiments on beam neutralization, expansion of the beam, and determination of beam parameters such as electron temperature, plasma density, and plasma potential. The development of modern electron bombardment ion thrusters is treated, detailing experimental results. Studies on charge-exchange plasma are discussed, showing results such as the relationship between neutralizer emission current and plasma beam potential, ion energies as a function of neutralizer bias, charge-exchange ion current collected by an axially moving Faraday cup-RPA for 8-cm and 30-cm ion thrusters, beam density and potential data from a 15-cm ion thruster, and charge-exchange ion flow around a 30-cm thruster. A 20-cm thruster electrical configuration is depicted and facility effects are discussed. Finally, plasma modeling is covered in detail for plasma beam and charge-exchange plasma.

Transport across nanogaps using self-consistent boundary conditions

NASA Astrophysics Data System (ADS)

Biswas, D.; Kumar, R.

2012-06-01

Charge particle transport across nanogaps is studied theoretically within the Schrodinger-Poisson mean field framework. The determination of self-consistent boundary conditions across the gap forms the central theme in order to allow for realistic interface potentials (such as metal-vacuum) which are smooth at the boundary and do not abruptly assume a constant value at the interface. It is shown that a semiclassical expansion of the transmitted wavefunction leads to approximate but self consistent boundary conditions without assuming any specific form of the potential beyond the gap. Neglecting the exchange and correlation potentials, the quantum Child-Langmuir law is investigated. It is shown that at zero injection energy, the quantum limiting current density (Jc) is found to obey the local scaling law Jc ~ Vgα/D5-2α with the gap separation D and voltage Vg. The exponent α > 1.1 with α → 3/2 in the classical regime of small de Broglie wavelengths.

The effective local potential method: Implementation for molecules and relation to approximate optimized effective potential techniques

NASA Astrophysics Data System (ADS)

Izmaylov, Artur F.; Staroverov, Viktor N.; Scuseria, Gustavo E.; Davidson, Ernest R.; Stoltz, Gabriel; Cancès, Eric

2007-02-01

We have recently formulated a new approach, named the effective local potential (ELP) method, for calculating local exchange-correlation potentials for orbital-dependent functionals based on minimizing the variance of the difference between a given nonlocal potential and its desired local counterpart [V. N. Staroverov et al., J. Chem. Phys. 125, 081104 (2006)]. Here we show that under a mildly simplifying assumption of frozen molecular orbitals, the equation defining the ELP has a unique analytic solution which is identical with the expression arising in the localized Hartree-Fock (LHF) and common energy denominator approximations (CEDA) to the optimized effective potential. The ELP procedure differs from the CEDA and LHF in that it yields the target potential as an expansion in auxiliary basis functions. We report extensive calculations of atomic and molecular properties using the frozen-orbital ELP method and its iterative generalization to prove that ELP results agree with the corresponding LHF and CEDA values, as they should. Finally, we make the case for extending the iterative frozen-orbital ELP method to full orbital relaxation.

Convergence behavior of the random phase approximation renormalized correlation energy

NASA Astrophysics Data System (ADS)

Bates, Jefferson E.; Sensenig, Jonathon; Ruzsinszky, Adrienn

2017-05-01

Based on the random phase approximation (RPA), RPA renormalization [J. E. Bates and F. Furche, J. Chem. Phys. 139, 171103 (2013), 10.1063/1.4827254] is a robust many-body perturbation theory that works for molecules and materials because it does not diverge as the Kohn-Sham gap approaches zero. Additionally, RPA renormalization enables the simultaneous calculation of RPA and beyond-RPA correlation energies since the total correlation energy is the sum of a series of independent contributions. The first-order approximation (RPAr1) yields the dominant beyond-RPA contribution to the correlation energy for a given exchange-correlation kernel, but systematically underestimates the total beyond-RPA correction. For both the homogeneous electron gas model and real systems, we demonstrate numerically that RPA renormalization beyond first order converges monotonically to the infinite-order beyond-RPA correlation energy for several model exchange-correlation kernels and that the rate of convergence is principally determined by the choice of the kernel and spin polarization of the ground state. The monotonic convergence is rationalized from an analysis of the RPA renormalized correlation energy corrections, assuming the exchange-correlation kernel and response functions satisfy some reasonable conditions. For spin-unpolarized atoms, molecules, and bulk solids, we find that RPA renormalization is typically converged to 1 meV error or less by fourth order regardless of the band gap or dimensionality. Most spin-polarized systems converge at a slightly slower rate, with errors on the order of 10 meV at fourth order and typically requiring up to sixth order to reach 1 meV error or less. Slowest to converge, however, open-shell atoms present the most challenging case and require many higher orders to converge.

Sorption and degradation of selected pharmaceuticals in representative soils of the Czech Republic

NASA Astrophysics Data System (ADS)

Kodesova, Radka; Kocarek, Martin; Klement, Ales; Golovko, Oksana; Grabic, Roman; Fer, Miroslav; Nikodem, Antonin; Jaksik, Ondrej

2015-04-01

Knowledge of contaminant behavior (e.g. its sorption onto soil particle, degradation etc.) is essential when assessing contaminant migration in soil and groundwater environment. This study was focused on evaluating sorption isotherms and half-lives for 7 pharmaceuticals (clarithromycin, trimethoprim, metoprolol, atenolol, clindamycin, carbamazepine, sulfamethoxazole) on 13 soils of different soil properties. Sorption of ionizable compounds was highly affected by soil pH. The sorption coefficient of sulfamethoxazole was negatively correlated to soil pH and thus positively related to hydrolytic acidity and exchangeable acidity. Sorption coefficients for clindamycin and clarithromycin were positively related to soil pH and thus negatively related to hydrolytic acidity and exchangeable acidity and positively related to base cation saturation. Sorption coefficients for the remaining pharmaceuticals (trimethoprim, metoprolol, atenolol, and carbamazepine) were also positively correlated with the base cation saturation and cation exchange capacity. Degradation rates in some degree reflected sorption of studied pharmaceuticals on soil particles and increased with decreasing sorption. The highest mobility in studied soils was observed for sulfamethoxazole, but this pharmaceutical was relatively quickly degraded. The second highest mobility was found for carbamazepine, which mostly did not noticeably degrade during our experiments. Thus this pharmaceutical has the highest potential to migrate in water environment. The lowest mobility was observed for clarithromycin. However, this pharmaceutical due to its stability may be retained in an environment for a long time. Acknowledgement: The authors acknowledge the financial support of the Czech Science Foundation (Project No. 13-12477S, Transport of pharmaceuticals in soils). References: Kodesova, R., Grabic, R., Kocarek, M., Klement, A., Golovko, O., Fer, M., Nikodem, A., Jaksik, O., Pharmaceuticals' sorptions relative to properties of thirteen different soils. Science of the Total Environment 511 (2015) 435-443.

Correlation of the antimicrobial activity of salicylaldehydes with broadening of the NMR signal of the hydroxyl proton. Possible involvement of proton exchange processes in the antimicrobial activity.

PubMed

Elo, Hannu; Kuure, Matti; Pelttari, Eila

2015-03-06

Certain substituted salicylaldehydes are potent antibacterial and antifungal agents and some of them merit consideration as potential chemotherapeutic agents against Candida infections, but their mechanism of action has remained obscure. We report here a distinct correlation between broadening of the NMR signal of the hydroxyl proton of salicylaldehydes and their activity against several types of bacteria and fungi. When proton NMR spectra of the compounds were determined using hexadeuterodimethylsulfoxide as solvent and the height of the OH proton signal was measured, using the signal of the aldehyde proton as an internal standard, it was discovered that a prerequisite of potent antimicrobial activity is that the proton signal is either unobservable or relatively very low, i.e. that it is extremely broadened. Thus, none of the congeners whose OH proton signal was high were potent antimicrobial agents. Some congeners that gave a very low OH signal were, however, essentially inactive against the microbes, indicating that although drastic broadening of the OH signal appears to be a prerequisite, also other (so far unknown) factors are needed for high antimicrobial activity. Because broadening of the hydroxyl proton signal is related to the speed of the proton exchange process(es) involving that proton, proton exchange may be involved in the mechanism of action of the compounds. Further studies are needed to analyze the relative importance of different factors (such as electronic effects, strength of the internal hydrogen bond, co-planarity of the ring and the formyl group) that determine the rates of those processes. Copyright © 2015 Elsevier Masson SAS. All rights reserved.

Novel Approaches to Spectral Properties of Correlated Electron Materials: From Generalized Kohn-Sham Theory to Screened Exchange Dynamical Mean Field Theory

NASA Astrophysics Data System (ADS)

Delange, Pascal; Backes, Steffen; van Roekeghem, Ambroise; Pourovskii, Leonid; Jiang, Hong; Biermann, Silke

2018-04-01

The most intriguing properties of emergent materials are typically consequences of highly correlated quantum states of their electronic degrees of freedom. Describing those materials from first principles remains a challenge for modern condensed matter theory. Here, we review, apply and discuss novel approaches to spectral properties of correlated electron materials, assessing current day predictive capabilities of electronic structure calculations. In particular, we focus on the recent Screened Exchange Dynamical Mean-Field Theory scheme and its relation to generalized Kohn-Sham Theory. These concepts are illustrated on the transition metal pnictide BaCo2As2 and elemental zinc and cadmium.

3d-4f magnetic interaction with density functional theory plus u approach: local Coulomb correlation and exchange pathways.

PubMed

Zhang, Yachao; Yang, Yang; Jiang, Hong

2013-12-12

The 3d-4f exchange interaction plays an important role in many lanthanide based molecular magnetic materials such as single-molecule magnets and magnetic refrigerants. In this work, we study the 3d-4f magnetic exchange interactions in a series of Cu(II)-Gd(III) (3d(9)-4f(7)) dinuclear complexes based on the numerical atomic basis-norm-conserving pseudopotential method and density functional theory plus the Hubbard U correction approach (DFT+U). We obtain improved description of the 4f electrons by including the semicore 5s5p states in the valence part of the Gd-pseudopotential. The Hubbard U correction is employed to treat the strongly correlated Cu-3d and Gd-4f electrons, which significantly improve the agreement of the predicted exchange constants, J, with experiment, indicating the importance of accurate description of the local Coulomb correlation. The high efficiency of the DFT+U approach enables us to perform calculations with molecular crystals, which in general improve the agreement between theory and experiment, achieving a mean absolute error smaller than 2 cm(-1). In addition, through analyzing the physical effects of U, we identify two magnetic exchange pathways. One is ferromagnetic and involves an interaction between the Cu-3d, O-2p (bridge ligand), and the majority-spin Gd-5d orbitals. The other one is antiferromagnetic and involves Cu-3d, O-2p, and the empty minority-spin Gd-4f orbitals, which is suppressed by the planar Cu-O-O-Gd structure. This study demonstrates the accuracy of the DFT+U method for evaluating the 3d-4f exchange interactions, provides a better understanding of the exchange mechanism in the Cu(II)-Gd(III) complexes, and paves the way for exploiting the magnetic properties of the 3d-4f compounds containing lanthanides other than Gd.

Nonequilibrium Green's functions and atom-surface dynamics: Simple views from a simple model system

NASA Astrophysics Data System (ADS)

Boström, E.; Hopjan, M.; Kartsev, A.; Verdozzi, C.; Almbladh, C.-O.

2016-03-01

We employ Non-equilibrium Green's functions (NEGF) to describe the real-time dynamics of an adsorbate-surface model system exposed to ultrafast laser pulses. For a finite number of electronic orbitals, the system is solved exactly and within different levels of approximation. Specifically i) the full exact quantum mechanical solution for electron and nuclear degrees of freedom is used to benchmark ii) the Ehrenfest approximation (EA) for the nuclei, with the electron dynamics still treated exactly. Then, using the EA, electronic correlations are treated with NEGF within iii) 2nd Born and with iv) a recently introduced hybrid scheme, which mixes 2nd Born self-energies with non-perturbative, local exchange- correlation potentials of Density Functional Theory (DFT). Finally, the effect of a semi-infinite substrate is considered: we observe that a macroscopic number of de-excitation channels can hinder desorption. While very preliminary in character and based on a simple and rather specific model system, our results clearly illustrate the large potential of NEGF to investigate atomic desorption, and more generally, the non equilibrium dynamics of material surfaces subject to ultrafast laser fields.

Photolithography and Fluorescence Correlation Spectroscopy used to examine the rates of exchange in reverse micelle systems

NASA Astrophysics Data System (ADS)

Norris, Zach; Mawson, Cara; Johnson, Kyron; Kessler, Sarah; Rebecca, Anne; Wolf, Nathan; Lim, Michael; Nucci, Nathaniel

Reverse micelles are molecular complexes that encapsulate a nanoscale pool of water in a surfactant shell dissolved in non-polar solvent. These complexes have a wide range of applications, and in all cases, the degree to which reverse micelles (RM) exchange their contents is relevant for their use. Despite its importance, this aspect of RM behavior is poorly understood. Photolithography is employed here to create micro and nano scale fluidic systems in which mixing rates can be precisely measured using fluorescence correlation spectroscopy (FCS). Micro-channel patterns are etched using reactive ion etching process into a layer of silicon dioxide on crystalline silicon substrates. Solutions containing mixtures of reverse micelles, proteins, and fluorophores are placed into reservoirs in the patterns, while diffusion and exchange between RMs is monitored using a FCS system built from a modified confocal Raman spectrometer. Using this approach, the diffusion and exchange rates for RM systems are measured as a function of the components of the RM mixture. Funding provided by Rowan University.

Correlational and thermodynamic properties of finite-temperature electron liquids in the hypernetted-chain approximation.

PubMed

Tanaka, Shigenori

2016-12-07

Correlational and thermodynamic properties of homogeneous electron liquids at finite temperatures are theoretically analyzed in terms of dielectric response formalism with the hypernetted-chain (HNC) approximation and its modified version. The static structure factor and the local-field correction to describe the strong Coulomb-coupling effects beyond the random-phase approximation are self-consistently calculated through solution to integral equations in the paramagnetic (spin unpolarized) and ferromagnetic (spin polarized) states. In the ground state with the normalized temperature θ=0, the present HNC scheme well reproduces the exchange-correlation energies obtained by quantum Monte Carlo (QMC) simulations over the whole fluid phase (the coupling constant r s ≤100), i.e., within 1% and 2% deviations from putative best QMC values in the paramagnetic and ferromagnetic states, respectively. As compared with earlier studies based on the Singwi-Tosi-Land-Sjölander and modified convolution approximations, some improvements on the correlation energies and the correlation functions including the compressibility sum rule are found in the intermediate to strong coupling regimes. When applied to the electron fluids at intermediate Fermi degeneracies (θ≈1), the static structure factors calculated in the HNC scheme show good agreements with the results obtained by the path integral Monte Carlo (PIMC) simulation, while a small negative region in the radial distribution function is observed near the origin, which may be associated with a slight overestimation for the exchange-correlation hole in the HNC approximation. The interaction energies are calculated for various combinations of density and temperature parameters ranging from strong to weak degeneracy and from weak to strong coupling, and the HNC values are then parametrized as functions of r s and θ. The HNC exchange-correlation free energies obtained through the coupling-constant integration show reasonable agreements with earlier results including the PIMC-based fitting over the whole fluid region at finite degeneracies in the paramagnetic state. In contrast, a systematic difference between the HNC and PIMC results is observed in the ferromagnetic state, which suggests a necessity of further studies on the exchange-correlation free energies from both aspects of analytical theory and simulation.

Structural, electronic, magnetic and thermodynamic properties of Ni1-xTixO alloys an ab initio calculation and Monte Carlo study

NASA Astrophysics Data System (ADS)

Klaa, K.; Labidi, S.; Masrour, R.; Jabar, A.; Labidi, M.; Amara, A.; Drici, A.; Hlil, E. K.; Ellouze, M.

2018-06-01

Structural, electronic, magnetic and thermodynamic main features for Ni1-xTixO ternary alloys in rock-salt structure with Ti content in the range ? were studied using the full potential Linearized augmented plane wave (FP-LAPW) method within density functional theory. The exchange-correlation potential was calculated by the generalized gradient approximation. The analysis of the electronic density of states curves allowed the computation of the magnetic moments which are considered to lie along (010) axes. The thermodynamic stability of this alloy was investigated by calculating the excess enthalpy of mixing ? as well as the phase diagram. In addition, the Monte Carlo simulations have been exploited to calculate the transition temperature and magnetic coercive field in the alloy.

Effective potential kinetic theory for strongly coupled plasmas

NASA Astrophysics Data System (ADS)

Baalrud, Scott D.; Daligault, Jérôme

2016-11-01

The effective potential theory (EPT) is a recently proposed method for extending traditional plasma kinetic and transport theory into the strongly coupled regime. Validation from experiments and molecular dynamics simulations have shown it to be accurate up to the onset of liquid-like correlation parameters (corresponding to Γ ≃ 10-50 for the one-component plasma, depending on the process of interest). Here, this theory is briefly reviewed along with comparisons between the theory and molecular dynamics simulations for self-diffusivity and viscosity of the one-component plasma. A number of new results are also provided, including calculations of friction coefficients, energy exchange rates, stopping power, and mobility. The theory is also cast in the Landau and Fokker-Planck kinetic forms, which may prove useful for enabling efficient kinetic computations.

Influence of Rb/Cs Cation-Exchange on Inorganic Sn Halide Perovskites: From Chemical Structure to Physical Properties.

PubMed

Jung, Young-Kwang; Lee, Ji-Hwan; Walsh, Aron; Soon, Aloysius

2017-04-11

CsSnI 3 is a potential lead-free inorganic perovskite for solar energy applications due to its nontoxicity and attractive optoelectronic properties. Despite these advantages, photovoltaic cells using CsSnI 3 have not been successful to date, in part due to low stability. We demonstrate how gradual substitution of Rb for Cs influences the structural, thermodynamic, and electronic properties on the basis of first-principles density functional theory calculations. By examining the effect of the Rb:Cs ratio, we reveal a correlation between octahedral distortion and band gap, including spin-orbit coupling. We further highlight the cation-induced variation of the ionization potential (work function) and the importance of surface termination for tin-based halide perovskites for engineering high-performance solar cells.

Modulation of the reaction cycle of the Na+:Ca2+, K+ exchanger.

PubMed

Vedovato, Natascia; Rispoli, Giorgio

2007-09-01

Ca(2+) concentration in retinal photoreceptor rod outer segment (OS) strongly affects the generator potential kinetics and the receptor light adaptation. The response to intense light stimuli delivered in the dark produce potential changes exceeding 40 mV: since the Ca(2+) extrusion in the OS is entirely controlled by the Na(+):Ca(2+), K(+) exchanger, it is important to assess how the exchanger ion transport rate is affected by the voltage and, in general, by intracellular factors. It is indeed known that the cardiac Na(+):Ca(2+) exchanger is regulated by Mg-ATP via a still unknown metabolic pathway. In the present work, the Na(+):Ca(2+), K(+) exchanger regulation was investigated in isolated OS, recorded in whole-cell configuration, using ionic conditions that activated maximally the exchanger in both forward and reverse mode. In all species examined (amphibia: Rana esculenta and Ambystoma mexicanum; reptilia: Gecko gecko), the forward (reverse) exchange current increased about linearly for negative (positive) voltages and exhibited outward (inward) rectification for positive (negative) voltages. Since hyperpolarisation increases Ca(2+) extrusion rate, the recovery of the dark level of Ca(2+) (and, in turn, of the generator potential) after intense light stimuli results accelerated. Mg-ATP increased the size of forward and reverse exchange current by a factor of approximately 2.3 and approximately 2.6, respectively, without modifying their voltage dependence. This indicates that Mg-ATP regulates the number of active exchanger sites and/or the exchanger turnover number, although via an unknown mechanism.

Recent developments in LIBXC - A comprehensive library of functionals for density functional theory

NASA Astrophysics Data System (ADS)

Lehtola, Susi; Steigemann, Conrad; Oliveira, Micael J. T.; Marques, Miguel A. L.

2018-01-01

LIBXC is a library of exchange-correlation functionals for density-functional theory. We are concerned with semi-local functionals (or the semi-local part of hybrid functionals), namely local-density approximations, generalized-gradient approximations, and meta-generalized-gradient approximations. Currently we include around 400 functionals for the exchange, correlation, and the kinetic energy, spanning more than 50 years of research. Moreover, LIBXC is by now used by more than 20 codes, not only from the atomic, molecular, and solid-state physics, but also from the quantum chemistry communities.

Density functional study of double ionization energies

NASA Astrophysics Data System (ADS)

Chong, D. P.

2008-02-01

In this paper, double ionization energies (DIEs) of gas-phase atoms and molecules are calculated by energy difference method with density functional theory. To determine the best functional for double ionization energies, we first study 24 main group atoms in the second, third, and fourth periods. An approximation is used in which the electron density is first obtained from a density functional computation with the exchange-correlation potential Vxc known as statistical average of orbital potentials, after which the energy is computed from that density with 59 different exchange-correlation energy functionals Exc. For the 24 atoms, the two best Exc functional providing DIEs with average absolute deviation (AAD) of only 0.25eV are the Perdew-Burke-Ernzerhof functional modified by Hammer et al. [Phys. Rev. B 59, 6413 (1999)] and one known as the Krieger-Chen-Iafrate-Savin functional modified by Krieger et al. (unpublished). Surprisingly, none of the 20 available hybrid functionals is among the top 15 functionals for the DIEs of the 24 atoms. A similar procedure is then applied to molecules, with opposite results: Only hybrid functionals are among the top 15 functionals for a selection of 29molecules. The best Exc functional for the 29molecules is found to be the Becke 1997 functional modified by Wilson et al. [J. Chem. Phys. 115, 9233 (2001)]. With that functional, the AAD from experiment for DIEs of 29molecules is just under 0.5eV. If the two suspected values for C2H2 and Fe(CO)5 are excluded, the AAD improves to 0.32eV. Many other hybrid functionals perform almost as well.

Low-Dimensional Materials for Optoelectronic and Bioelectronic Applications

NASA Astrophysics Data System (ADS)

Hong, Tu

In this thesis, we first discuss the fundamentals of ab initio electronic structure theory and density functional theory (DFT). We also discuss statistics related to computing thermodynamic averages of molecular dynamics (MD). We then use this theory to analyze and compare the structural, dynamical, and electronic properties of liquid water next to prototypical metals including platinum, graphite, and graphene. Our results are built on Born-Oppenheimer molecular dynamics (BOMD) generated using density functional theory (DFT) which explicitly include van der Waals (vdW) interactions within a first principles approach. All calculations reported use large simulation cells, allowing for an accurate treatment of the water-electrode interfaces. We have included vdW interactions through the use of the optB86b-vdW exchange correlation functional. Comparisons with the Perdew-Burke-Ernzerhof (PBE) exchange correlation functional are also shown. We find an initial peak, due to chemisorption, in the density profile of the liquid water-Pt interface not seen in the liquid water-graphite interface, liquid watergraphene interface, nor interfaces studied previously. To further investigate this chemisorption peak, we also report differences in the electronic structure of single water molecules on both Pt and graphite surfaces. We find that a covalent bond forms between the single water molecule and the platinum surface, but not between the single water molecule and the graphite surface. We also discuss the effects that defects and dopants in the graphite and graphene surfaces have on the structure and dynamics of liquid water. Lastly, we introduce artificial neural networks (ANNs), and demonstrate how they can be used to machine learn electronic structure calculations. As a proof of principle, we show the success of an ANN potential energy surfaces for a dimer molecule with a Lennard-Jones potential.

Net ecosystem CO2 exchange of a primary tropical peat swamp forest in Sarawak, Malaysia

NASA Astrophysics Data System (ADS)

Tang Che Ing, A.; Stoy, P. C.; Melling, L.

2014-12-01

Tropical peat swamp forests are widely recognized as one of the world's most efficient ecosystems for the sequestration and storage of carbon through both their aboveground biomass and underlying thick deposits of peat. As the peat characteristics exhibit high spatial and temporal variability as well as the structural and functional complexity of forests, tropical peat ecosystems can act naturally as both carbon sinks and sources over their life cycles. Nonetheless, few reports of studies on the ecosystem-scale CO2 exchange of tropical peat swamp forests are available to-date and their present roles in the global carbon cycle remain uncertain. To quantify CO2 exchange and unravel the prevailing factors and potential underlying mechanism regulating net CO2 fluxes, an eddy covariance tower was erected in a tropical peat swamp forest in Sarawak, Malaysia. We observed that the diurnal and seasonal patterns of net ecosystem CO2 exchange (NEE) and its components (gross primary productivity (GPP) and ecosystem respiration (RE)) varied between seasons and years. Rates of NEE declined in the wet season relative to the dry season. Conversely, both the gross primary productivity (GPP) and ecosystem respiration (RE) were found to be higher during the wet season than the dry season, in which GPP was strongly negatively correlated with NEE. The average annual NEE was 385 ± 74 g C m-2 yr-1, indicating the primary peat swamp forest functioned as net source of CO2 to the atmosphere over the observation period.

Spherical ion oscillations in a positive polarity gridded inertial-electrostatic confinement device

NASA Astrophysics Data System (ADS)

Bandara, R.; Khachan, J.

2013-07-01

A pulsed, positive polarity gridded inertial electrostatic confinement device has been investigated experimentally, using a differential emissive probe and potential traces as primary diagnostics. Large amplitude oscillations in the plasma current and plasma potential were observed within a microsecond of the discharge onset, which are indicative of coherent ion oscillations about a temporarily confined excess of recirculating electron space charge. The magnitude of the depth of the potential well in the established virtual cathode was determined using a differential emissive Langmuir probe, which correlated well to the potential well inferred from the ion oscillation frequency for both hydrogen and argon experiments. It was found that the timescale for ion oscillation dispersion is strongly dependent on the neutral gas density, and weakly dependent on the peak anode voltage. The cessation of the oscillations was found to be due to charge exchange processes converting ions to high velocity neutrals, causing the abrupt de-coherence of the oscillations through an avalanche dispersion in phase space.

Alternative derivation of an exchange-only density-functional optimized effective potential

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joubert, D. P.

2007-10-15

An alternative derivation of the exchange-only density-functional optimized effective potential equation is given. It is shown that the localized Hartree-Fock-common energy denominator Green's function approximation (LHF-CEDA) for the density-functional exchange potential proposed independently by Della Sala and Goerling [J. Chem. Phys. 115, 5718 (2001)] and Gritsenko and Baerends [Phys. Rev. A 64, 42506 (2001)] can be derived as an approximation to the OEP exchange potential in a similar way that the KLI approximation [Phys. Rev. A 45, 5453 (1992)] was derived. An exact expression for the correction term to the LHF-CEDA approximation can thus be found. The correction term canmore » be expressed in terms of the first-order perturbation-theory many-electron wave function shift when the Kohn-Sham Hamiltonian is subjected to a perturbation equal to the difference between the density-functional exchange potential and the Hartree-Fock nonlocal potential, expressed in terms of the Kohn-Sham orbitals. An explicit calculation shows that the density weighted mean of the correction term is zero, confirming that the LHF-CEDA approximation can be interpreted as a mean-field approximation. The corrected LHF-CEDA equation and the optimized effective potential equation are shown to be identical, with information distributed differently between terms in the equations. For a finite system the correction term falls off at least as fast as 1/r{sup 4} for large r.« less

Alternative derivation of an exchange-only density-functional optimized effective potential

NASA Astrophysics Data System (ADS)

Joubert, D. P.

2007-10-01

An alternative derivation of the exchange-only density-functional optimized effective potential equation is given. It is shown that the localized Hartree-Fock common energy denominator Green’s function approximation (LHF-CEDA) for the density-functional exchange potential proposed independently by Della Sala and Görling [J. Chem. Phys. 115, 5718 (2001)] and Gritsenko and Baerends [Phys. Rev. A 64, 42506 (2001)] can be derived as an approximation to the OEP exchange potential in a similar way that the KLI approximation [Phys. Rev. A 45, 5453 (1992)] was derived. An exact expression for the correction term to the LHF-CEDA approximation can thus be found. The correction term can be expressed in terms of the first-order perturbation-theory many-electron wave function shift when the Kohn-Sham Hamiltonian is subjected to a perturbation equal to the difference between the density-functional exchange potential and the Hartree-Fock nonlocal potential, expressed in terms of the Kohn-Sham orbitals. An explicit calculation shows that the density weighted mean of the correction term is zero, confirming that the LHF-CEDA approximation can be interpreted as a mean-field approximation. The corrected LHF-CEDA equation and the optimized effective potential equation are shown to be identical, with information distributed differently between terms in the equations. For a finite system the correction term falls off at least as fast as 1/r4 for large r .

The use of multiobjective calibration and regional sensitivity analysis in simulating hyporheic exchange

USGS Publications Warehouse

Naranjo, Ramon C.; Niswonger, Richard G.; Stone, Mark; Davis, Clinton; McKay, Alan

2012-01-01

We describe an approach for calibrating a two-dimensional (2-D) flow model of hyporheic exchange using observations of temperature and pressure to estimate hydraulic and thermal properties. A longitudinal 2-D heat and flow model was constructed for a riffle-pool sequence to simulate flow paths and flux rates for variable discharge conditions. A uniform random sampling approach was used to examine the solution space and identify optimal values at local and regional scales. We used a regional sensitivity analysis to examine the effects of parameter correlation and nonuniqueness commonly encountered in multidimensional modeling. The results from this study demonstrate the ability to estimate hydraulic and thermal parameters using measurements of temperature and pressure to simulate exchange and flow paths. Examination of the local parameter space provides the potential for refinement of zones that are used to represent sediment heterogeneity within the model. The results indicate vertical hydraulic conductivity was not identifiable solely using pressure observations; however, a distinct minimum was identified using temperature observations. The measured temperature and pressure and estimated vertical hydraulic conductivity values indicate the presence of a discontinuous low-permeability deposit that limits the vertical penetration of seepage beneath the riffle, whereas there is a much greater exchange where the low-permeability deposit is absent. Using both temperature and pressure to constrain the parameter estimation process provides the lowest overall root-mean-square error as compared to using solely temperature or pressure observations. This study demonstrates the benefits of combining continuous temperature and pressure for simulating hyporheic exchange and flow in a riffle-pool sequence. Copyright 2012 by the American Geophysical Union.

Seasonal and Inter-Annual Variations in Carbon Dioxide Exchange over an Alpine Grassland in the Eastern Qinghai-Tibetan Plateau.

PubMed

Shang, Lunyu; Zhang, Yu; Lyu, Shihua; Wang, Shaoying

2016-01-01

This work analyzed carbon dioxide exchange and its controlling factors over an alpine grassland on the eastern Qinghai-Tibetan Plateau. The main results show that air temperature and photosynthetically active radiation are two dominant factors controlling daily gross primary production. Soil temperature and soil water content are the main factors controlling ecosystem respiration. Canopy photosynthetic activity is also responsible for the variation of daily ecosystem respiration other than environmental factors. No clear correlation between net ecosystem exchange and environmental factors was observed at daily scale. Temperature sensitive coefficient was observed to increase with larger soil water content. High values of temperature sensitive coefficient occurred during the periods when soil water content was high and grass was active. Annual integrated net ecosystem exchange, gross primary production and ecosystem respiration were -191, 1145 and 954 g C m-2 for 2010, and -250, 975 and 725 g C m-2 for 2011, respectively. Thus, this alpine grassland was a moderate carbon sink in both of the two years. Compared to alpine grasslands on the Qinghai-Tibetan Plateau, this alpine grassland demonstrated a much greater potential for carbon sequestration than others. Annual precipitation is a dominant factor controlling the variation of annual net ecosystem exchange over this grassland. The difference in gross primary production between the two years was not caused by the variation in annual precipitation. Instead, air temperature and the length of growing season had an important impact on annual gross primary production. Variation of annual ecosystem respiration was closely related to annual gross primary production and soil water content during the growing season.

Seasonal and Inter-Annual Variations in Carbon Dioxide Exchange over an Alpine Grassland in the Eastern Qinghai-Tibetan Plateau

PubMed Central

Shang, Lunyu; Zhang, Yu; Lyu, Shihua; Wang, Shaoying

2016-01-01

This work analyzed carbon dioxide exchange and its controlling factors over an alpine grassland on the eastern Qinghai-Tibetan Plateau. The main results show that air temperature and photosynthetically active radiation are two dominant factors controlling daily gross primary production. Soil temperature and soil water content are the main factors controlling ecosystem respiration. Canopy photosynthetic activity is also responsible for the variation of daily ecosystem respiration other than environmental factors. No clear correlation between net ecosystem exchange and environmental factors was observed at daily scale. Temperature sensitive coefficient was observed to increase with larger soil water content. High values of temperature sensitive coefficient occurred during the periods when soil water content was high and grass was active. Annual integrated net ecosystem exchange, gross primary production and ecosystem respiration were -191, 1145 and 954 g C m-2 for 2010, and -250, 975 and 725 g C m-2 for 2011, respectively. Thus, this alpine grassland was a moderate carbon sink in both of the two years. Compared to alpine grasslands on the Qinghai-Tibetan Plateau, this alpine grassland demonstrated a much greater potential for carbon sequestration than others. Annual precipitation is a dominant factor controlling the variation of annual net ecosystem exchange over this grassland. The difference in gross primary production between the two years was not caused by the variation in annual precipitation. Instead, air temperature and the length of growing season had an important impact on annual gross primary production. Variation of annual ecosystem respiration was closely related to annual gross primary production and soil water content during the growing season. PMID:27861616

Asymptotic behavior of the Kohn-Sham exchange potential at a metal surface

NASA Astrophysics Data System (ADS)

Qian, Zhixin

2012-03-01

The asymptotic structure of the Kohn-Sham exchange potential vx(r) in the classically forbidden region of a metal surface is investigated, together with that of the Slater exchange potential VxS(r) and those of the approximate Krieger-Li-Iafrate VxKLI(r) and Harbola-Sahni Wx(r) exchange potentials. Particularly, the former is shown to have the form of vx(z→∞)=-αx/z with αx a constant dependent only of bulk electron density. The same result in previous work is thus confirmed; in the meanwhile, a controversy raised recently gets resolved. The structure of the exchange hole ρx(r,r') is examined, and the delocalization of it in the metal bulk when the electron is at large distance from the metal surface is demonstrated with analytical expressions. The asymptotic structures of vx(r), VxS(r), VxKLI(r), and Wx(r) at a slab metal surface are also investigated. Particularly, vx(z→∞)=-1/z in the slab case. The distinction, in this respect, between the semi-infinite and the slab metal surfaces is elucidated.

Correlation between physicochemical properties of modified clinoptilolite and its performance in the removal of ammonia-nitrogen.

PubMed

Dong, Yingbo; Lin, Hai; He, Yinhai

2017-03-01

The physicochemical properties of the 24 modified clinoptilolite samples and their ammonia-nitrogen removal rates were measured to investigate the correlation between them. The modified clinoptilolites obtained by acid modification, alkali modification, salt modification, and thermal modification were used to adsorb ammonia-nitrogen. The surface area, average pore width, macropore volume, mecropore volume, micropore volume, cation exchange capacity (CEC), zeta potential, silicon-aluminum ratios, and ammonia-nitrogen removal rate of the 24 modified clinoptilolite samples were measured. Subsequently, the linear regression analysis method was used to research the correlation between the physicochemical property of the different modified clinoptilolite samples and the ammonia-nitrogen removal rate. Results showed that the CEC was the major physicochemical property affecting the ammonia-nitrogen removal performance. According to the impacts from strong to weak, the order was CEC > silicon-aluminum ratios > mesopore volume > micropore volume > surface area. On the contrary, the macropore volume, average pore width, and zeta potential had a negligible effect on the ammonia-nitrogen removal rate. The relational model of physicochemical property and ammonia-nitrogen removal rate of the modified clinoptilolite was established, which was ammonia-nitrogen removal rate = 1.415[CEC] + 173.533 [macropore volume] + 0.683 [surface area] + 4.789[Si/Al] - 201.248. The correlation coefficient of this model was 0.982, which passed the validation of regression equation and regression coefficients. The results of the significance test showed a good fit to the correlation model.

Breakdown of the single-exchange approximation in third-order symmetry-adapted perturbation theory.

PubMed

Lao, Ka Un; Herbert, John M

2012-03-22

We report third-order symmetry-adapted perturbation theory (SAPT) calculations for several dimers whose intermolecular interactions are dominated by induction. We demonstrate that the single-exchange approximation (SEA) employed to derive the third-order exchange-induction correction (E(exch-ind)((30))) fails to quench the attractive nature of the third-order induction (E(ind)((30))), leading to one-dimensional potential curves that become attractive rather than repulsive at short intermolecular separations. A scaling equation for (E(exch-ind)((30))), based on an exact formula for the first-order exchange correction, is introduced to approximate exchange effects beyond the SEA, and qualitatively correct potential energy curves that include third-order induction are thereby obtained. For induction-dominated systems, our results indicate that a "hybrid" SAPT approach, in which a dimer Hartree-Fock calculation is performed in order to obtain a correction for higher-order induction, is necessary not only to obtain quantitative binding energies but also to obtain qualitatively correct potential energy surfaces. These results underscore the need to develop higher-order exchange-induction formulas that go beyond the SEA. © 2012 American Chemical Society

Carbonate and Bicarbonate Ion Transport in Alkaline Anion Exchange Membranes

DTIC Science & Technology

2013-06-25

membranes (AEMs) are being developed for potential use in fuel cell systems which include portable power applications. In a fuel cell , these membranes...Alkaline Anion Exchange Membranes Report Title ABSTRACT Anion exchange membranes (AEMs) are being developed for potential use in fuel cell systems which...include portable power applications. In a fuel cell , these membranes transport hydroxide ions from the cathode to the anode. If carbon dioxide is

Power-law behaviour evaluation from foreign exchange market data using a wavelet transform method

NASA Astrophysics Data System (ADS)

Wei, H. L.; Billings, S. A.

2009-09-01

Numerous studies in the literature have shown that the dynamics of many time series including observations in foreign exchange markets exhibit scaling behaviours. A simple new statistical approach, derived from the concept of the continuous wavelet transform correlation function (WTCF), is proposed for the evaluation of power-law properties from observed data. The new method reveals that foreign exchange rates obey power-laws and thus belong to the class of self-similarity processes.

Effects of metal ions on the reactivity and corrosion electrochemistry of Fe/FeS nanoparticles.

PubMed

Kim, Eun-Ju; Kim, Jae-Hwan; Chang, Yoon-Seok; Turcio-Ortega, David; Tratnyek, Paul G

2014-04-01

Nano-zerovalent iron (nZVI) formed under sulfidic conditions results in a biphasic material (Fe/FeS) that reduces trichloroethene (TCE) more rapidly than nZVI associated only with iron oxides (Fe/FeO). Exposing Fe/FeS to dissolved metals (Pd(2+), Cu(2+), Ni(2+), Co(2+), and Mn(2+)) results in their sequestration by coprecipitation as dopants into FeS and FeO and/or by electroless precipitation as zerovalent metals that are hydrogenation catalysts. Using TCE reduction rates to probe the effect of metal amendments on the reactivity of Fe/FeS, it was found that Mn(2+) and Cu(2+) decreased TCE reduction rates, while Pd(2+), Co(2+), and Ni(2+) increased them. Electrochemical characterization of metal-amended Fe/FeS showed that aging caused passivation by growth of FeO and FeS phases and poisoning of catalytic metal deposits by sulfide. Correlation of rate constants for TCE reduction (kobs) with electrochemical parameters (corrosion potentials and currents, Tafel slopes, and polarization resistance) and descriptors of hydrogen activation by metals (exchange current density for hydrogen reduction and enthalpy of solution into metals) showed the controlling process changed with aging. For fresh Fe/FeS, kobs was best described by the exchange current density for activation of hydrogen, whereas kobs for aged Fe/FeS correlated with electrochemical descriptors of electron transfer.

Detecting a currency's dominance or dependence using foreign exchange network trees

NASA Astrophysics Data System (ADS)

McDonald, Mark; Suleman, Omer; Williams, Stacy; Howison, Sam; Johnson, Neil F.

2005-10-01

In a system containing a large number of interacting stochastic processes, there will typically be many nonzero correlation coefficients. This makes it difficult to either visualize the system’s interdependencies, or identify its dominant elements. Such a situation arises in foreign exchange (FX), which is the world’s biggest market. Here we develop a network analysis of these correlations using minimum spanning trees (MSTs). We show that not only do the MSTs provide a meaningful representation of the global FX dynamics, but they also enable one to determine momentarily dominant and dependent currencies. We find that information about a country’s geographical ties emerges from the raw exchange-rate data. Most importantly from a trading perspective, we discuss how to infer which currencies are “in play” during a particular period of time.

A third-generation density-functional-theory-based method for calculating canonical molecular orbitals of large molecules.

PubMed

Hirano, Toshiyuki; Sato, Fumitoshi

2014-07-28

We used grid-free modified Cholesky decomposition (CD) to develop a density-functional-theory (DFT)-based method for calculating the canonical molecular orbitals (CMOs) of large molecules. Our method can be used to calculate standard CMOs, analytically compute exchange-correlation terms, and maximise the capacity of next-generation supercomputers. Cholesky vectors were first analytically downscaled using low-rank pivoted CD and CD with adaptive metric (CDAM). The obtained Cholesky vectors were distributed and stored on each computer node in a parallel computer, and the Coulomb, Fock exchange, and pure exchange-correlation terms were calculated by multiplying the Cholesky vectors without evaluating molecular integrals in self-consistent field iterations. Our method enables DFT and massively distributed memory parallel computers to be used in order to very efficiently calculate the CMOs of large molecules.

Influence of the exchange and correlation functional on the structure of amorphous InSb and In{sub 3}SbTe{sub 2} compounds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gabardi, Silvia; Caravati, Sebastiano; Bernasconi, Marco, E-mail: marco.bernasconi@mater.unimib.it

2016-05-28

We have investigated the structural, vibrational, and electronic properties of the amorphous phase of InSb and In{sub 3}SbTe{sub 2} compounds of interest for applications in phase change non-volatile memories. Models of the amorphous phase have been generated by quenching from the melt by molecular dynamics simulations based on density functional theory. In particular, we have studied the dependence of the structural properties on the choice of the exchange-correlation functional. It turns out that the use of the Becke-Lee-Yang-Parr functional provides models with a much larger fraction of In atoms in a tetrahedral bonding geometry with respect to previous results obtainedmore » with the most commonly used Perdew-Becke-Ernzerhof functional. This outcome is at odd with the properties of Ge{sub 2}Sb{sub 2}Te{sub 5} phase change compound for which the two exchange-correlation functionals yield very similar results on the structure of the amorphous phase.« less

Inclusion of electron correlation for the target wave function in low- to intermediate-energy e-N2 scattering

NASA Technical Reports Server (NTRS)

Weatherford, C. A.; Brown, F. B.; Temkin, A.

1987-01-01

In a recent calculation, an exact exchange method was developed for use in the partial-differential-equation approach to electron-molecule scattering and was applied to e-N2 scattering in the fixed-nuclei approximation with an adiabatic polarization potential at low energies (0-10 eV). Integrated elastic cross sections were calculated and found to be lower than experiment at energies both below and above the Pi(g) resonance. It was speculated at that time that improved experimental agreement could be obtained if a correlated target representation were used in place of the uncorrelated one. The present paper implements this suggestion and demonstrates the improved agreement. These calculations are also extended to higher energies (0-30 eV) so asd to include the Sigma(u) resonance. Some discrepancies among the experiments and between experiment and the various calculations at very low energy are noted.

From The Cover: The X3LYP extended density functional for accurate descriptions of nonbond interactions, spin states, and thermochemical properties.

PubMed

Xu, Xin; Goddard, William A

2004-03-02

We derive the form for an exact exchange energy density for a density decaying with Gaussian-like behavior at long range. Based on this, we develop the X3LYP (extended hybrid functional combined with Lee-Yang-Parr correlation functional) extended functional for density functional theory to significantly improve the accuracy for hydrogen-bonded and van der Waals complexes while also improving the accuracy in heats of formation, ionization potentials, electron affinities, and total atomic energies [over the most popular and accurate method, B3LYP (Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional)]. X3LYP also leads to a good description of dipole moments, polarizabilities, and accurate excitation energies from s to d orbitals for transition metal atoms and ions. We suggest that X3LYP will be useful for predicting ligand binding in proteins and DNA.

From The Cover: The X3LYP extended density functional for accurate descriptions of nonbond interactions, spin states, and thermochemical properties

NASA Astrophysics Data System (ADS)

Xu, Xin; Goddard, William A., III

2004-03-01

We derive the form for an exact exchange energy density for a density decaying with Gaussian-like behavior at long range. Based on this, we develop the X3LYP (extended hybrid functional combined with Lee-Yang-Parr correlation functional) extended functional for density functional theory to significantly improve the accuracy for hydrogen-bonded and van der Waals complexes while also improving the accuracy in heats of formation, ionization potentials, electron affinities, and total atomic energies [over the most popular and accurate method, B3LYP (Becke three-parameter hybrid functional combined with Lee-Yang-Parr correlation functional)]. X3LYP also leads to a good description of dipole moments, polarizabilities, and accurate excitation energies from s to d orbitals for transition metal atoms and ions. We suggest that X3LYP will be useful for predicting ligand binding in proteins and DNA.

The X3LYP extended density functional for accurate descriptions of nonbond interactions, spin states, and thermochemical properties

PubMed Central

Xu, Xin; Goddard, William A.

2004-01-01

We derive the form for an exact exchange energy density for a density decaying with Gaussian-like behavior at long range. Based on this, we develop the X3LYP (extended hybrid functional combined with Lee–Yang–Parr correlation functional) extended functional for density functional theory to significantly improve the accuracy for hydrogen-bonded and van der Waals complexes while also improving the accuracy in heats of formation, ionization potentials, electron affinities, and total atomic energies [over the most popular and accurate method, B3LYP (Becke three-parameter hybrid functional combined with Lee–Yang–Parr correlation functional)]. X3LYP also leads to a good description of dipole moments, polarizabilities, and accurate excitation energies from s to d orbitals for transition metal atoms and ions. We suggest that X3LYP will be useful for predicting ligand binding in proteins and DNA. PMID:14981235

Electron binding energy of uranium-ligand and uranyl-ligand anions

NASA Astrophysics Data System (ADS)

Wang, Lei; Horowitz, Steven; Marston, Brad

2012-02-01

Electron binding energies of the early actinide element uranium in gas-phase anion complexes are calculated by relativistic density functional theory (DFT) with two different exchange-correlation functions (RPBE and B3LYP) and also in the Hartree-Fock (HF) approximationootnotetextADF2010.02, SCM.com. Scalar and spin-orbit calculations are performed, and the calculated energies are compared to available experimental measurements and shown to disagree by energies of order 1 eV. Strong correlations that are poorly treated in DFT and HF can be included by a hybrid approach in which a generalized Anderson impurity model is numerically diagonalized. Reduction-oxidation (redox) potentials of aqueous actinide ions show improved agreement with measured values in the hybrid approachootnotetextS. E. Horowitz and J. B. Marston, J. Chem. Phys 134 064510 (2011).. We test whether or not similar improvements are found in the gas-phase.

Willingness to Exchange Health Information via Mobile Devices: Findings From a Population-Based Survey

PubMed Central

Serrano, Katrina J.; Yu, Mandi; Riley, William T.; Patel, Vaishali; Hughes, Penelope; Marchesini, Kathryn; Atienza, Audie A.

2016-01-01

PURPOSE The rapid proliferation of mobile devices offers unprecedented opportunities for patients and health care professionals to exchange health information electronically, but little is known about patients’ willingness to exchange various types of health information using these devices. We examined willingness to exchange different types of health information via mobile devices, and assessed whether sociodemographic characteristics and trust in clinicians were associated with willingness in a nationally representative sample. METHODS We analyzed data for 3,165 patients captured in the 2013 Health Information National Trends Survey. Multinomial logistic regression analysis was conducted to test differences in willingness. Ordinal logistic regression analysis assessed correlates of willingness to exchange 9 types of information separately. RESULTS Participants were very willing to exchange appointment reminders (odds ratio [OR] = 6.66; 95% CI, 5.68–7.81), general health tips (OR = 2.03; 95% CI, 1.74–2.38), medication reminders (OR = 2.73; 95% CI, 2.35–3.19), laboratory/test results (OR = 1.76; 95% CI, 1.62–1.92), vital signs (OR = 1.63; 95% CI, 1.48–1.80), lifestyle behaviors (OR = 1.40; 95% CI, 1.24–1.58), and symptoms (OR = 1.62; 95% CI, 1.46–1.79) as compared with diagnostic information. Older adults had lower odds of being more willing to exchange any type of information. Education, income, and trust in health care professional information correlated with willingness to exchange certain types of information. CONCLUSIONS Respondents were less willing to exchange via mobile devices information that may be considered sensitive or complex. Age, socioeconomic factors, and trust in professional information were associated with willingness to engage in mobile health information exchange. Both information type and demographic group should be considered when developing and tailoring mobile technologies for patient-clinician communication. PMID:26755781

Cooling field and temperature dependent exchange bias in Gd substituted YFe0.5Cr0.5O3

NASA Astrophysics Data System (ADS)

Singh, Karan; Mukherjee, K.

2018-04-01

We report the results of our investigation of cooling field and temperature dependence of exchange bias on Gd substituted mixed metal oxide YFe0.5Cr0.5O3. A negative exchange bias is observed in the Gd-substituted compounds, in contrast to the positive exchange bias in parent compound, YFe0.5Cr0.5O3 [1]. With the increase in Gd concentration it is noted that the exchange bias decreases. It was noted that the paramagnetic contribution from Gd ions plays the leading role in comparison to the antiferromagnetic type correlations among spins as is observed for the parent compound. Due to magnetic rare earth ion, additional exchange interaction of the form Gd-O-Fe/Cr dominates the magnetic interaction arising due to the transition metal ions, resulting in the reduction in exchange bias value.

Coexisting exchange bias effect and ferroelectricity in geometrically frustrated ZnCr2O4

NASA Astrophysics Data System (ADS)

Dey, J. K.; Majumdar, S.; Giri, S.

2018-06-01

Concomitant occurrence of exchange bias effect and ferroelectric order is revealed in antiferromagnetic spinel ZnCr2O4. The exchange bias effect is observed below antiferromagnetic Neél temperature (T N) with a reasonable value of exchange bias field ( Oe at 2 K). Intriguingly, the ratio is found unusually high as  ∼2.2, where H C is the coercivity. This indicates that large H C is not always primary for obtaining large exchange bias effect. Ferroelectric order is observed at T N, where non-centrosymmetric magnetic structure with space group associated with the magnetoelectric coupling correlates the ferroelectric order, proposing that, ZnCr2O4 is an improper multiferroic material. Rare occurrence of exchange bias effect and ferroelectric order in ZnCr2O4 attracts the community for fundamental interest and draws special attention in designing new materials for possible electric field control of exchange bias effect.

Social preferences influence the short-term exchange of social grooming among male bonobos.

PubMed

Surbeck, Martin; Hohmann, Gottfried

2015-03-01

The emotional mediation hypothesis proposes a mediating role of social bonds in the exchange of services. This model predicts that the form of short-term exchange of services depends on the relationship between the individuals involved. Here, we test this prediction in the exchange of grooming among males in a wild bonobo community for which close relatedness could be excluded. As bonobo males hardly engage in food sharing or agonistic support, grooming is mainly exchanged for grooming. While overall grooming, both given and received, correlates across dyads and within sessions, the form of grooming exchange within a given session differs according to dyadic association preferences. Individuals with a higher tendency to associate, ergo more familiar individuals, exhibit larger time differences and reduced reciprocation in consecutive grooming bouts than less familiar individuals. These results support the idea that emotional components are involved in the exchange of services between unrelated individuals.

Electronic structures of Plutonium compounds with the NaCl-type monochalcogenides structure

NASA Astrophysics Data System (ADS)

Maehira, Takahiro; Tatetsu, Yasutomi

2012-12-01

We calculate the energy band structure and the Fermi surface of PuS, PuSe and PuTe by using a self-consistent relativistic linear augmented-plane-wave method with the exchange and correlation potential in a local density approximation. It is found in common that the energy bands in the vicinity of the Fermi level are mainly due to the hybridization between Pu 5/ and monochalcogenide p electrons. The obtained main Fermi surfaces are composed of two hole sheets and one electron sheet, all of which are constructed from the band having the Pu 5/ state and the monochalcogenide p state.

Numerical methods for the inverse problem of density functional theory

DOE PAGES

Jensen, Daniel S.; Wasserman, Adam

2017-07-17

Here, the inverse problem of Kohn–Sham density functional theory (DFT) is often solved in an effort to benchmark and design approximate exchange-correlation potentials. The forward and inverse problems of DFT rely on the same equations but the numerical methods for solving each problem are substantially different. We examine both problems in this tutorial with a special emphasis on the algorithms and error analysis needed for solving the inverse problem. Two inversion methods based on partial differential equation constrained optimization and constrained variational ideas are introduced. We compare and contrast several different inversion methods applied to one-dimensional finite and periodic modelmore » systems.« less

Thermodynamical study of boron doped CeX{sub 3} (X=Pd, Rh)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Ramesh; Dwivedi, Shalini; Sharma, Yamini, E-mail: sharma.yamini62@gmail.com

2016-05-06

The structural, electronic, thermal, and optical properties of cubic non magnetic CeX{sub 3}(X=Pd, Rh) compounds which crystallize in the Au{sub 3}Cu structure have been studied using the projected augmented wave (PAW) method within the density functional theory (DFT) with generalized gradient approximation (GGA) for exchange correlation potential. In this paper we have calculated the band structure which are interpreted using the density of states. The optical properties such as extinction coefficients clearly illustrate the changes in CeX{sub 3} due to intercalation of boron. Lattice instability is observed in CePd{sub 3}B from the calculated dynamical properties.

Electronic cooling design and test validation

NASA Astrophysics Data System (ADS)

Murtha, W. B.

1983-07-01

An analytical computer model has been used to design a counterflow air-cooled heat exchanger according to the cooling, structural and geometric requirements of a U.S. Navy shipboard electronics cabinet, emphasizing high reliability performance through the maintenance of electronic component junction temperatures lower than 110 C. Environmental testing of the design obtained has verified that the analytical predictions were conservative. Model correlation to the test data furnishes an upgraded capability for the evaluation of tactical effects, and has established a two-orders of magnitude growth potential for increased electronics capabilities through enhanced heat dissipation. Electronics cabinets of this type are destined for use with Vertical Launching System-type combatant vessel magazines.

Numerical methods for the inverse problem of density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jensen, Daniel S.; Wasserman, Adam

Here, the inverse problem of Kohn–Sham density functional theory (DFT) is often solved in an effort to benchmark and design approximate exchange-correlation potentials. The forward and inverse problems of DFT rely on the same equations but the numerical methods for solving each problem are substantially different. We examine both problems in this tutorial with a special emphasis on the algorithms and error analysis needed for solving the inverse problem. Two inversion methods based on partial differential equation constrained optimization and constrained variational ideas are introduced. We compare and contrast several different inversion methods applied to one-dimensional finite and periodic modelmore » systems.« less

The first principles study of elastic and thermodynamic properties of ZnSe

NASA Astrophysics Data System (ADS)

Khatta, Swati; Kaur, Veerpal; Tripathi, S. K.; Prakash, Satya

2018-05-01

The elastic and thermodynamic properties of ZnSe are investigated using thermo_pw package implemented in Quantum espresso code within the framework of density functional theory. The pseudopotential method within the local density approximation is used for the exchange-correlation potential. The physical parameters of ZnSe bulk modulus and shear modulus, anisotropy factor, Young's modulus, Poisson's ratio, Pugh's ratio and Frantsevich's ratio are calculated. The sound velocity and Debye temperature are obtained from elastic constant calculations. The Helmholtz free energy and internal energy of ZnSe are also calculated. The results are compared with available theoretical calculations and experimental data.

Equilibrium finite-frequency noise of an interacting mesoscopic capacitor studied in time-dependent density functional theory

NASA Astrophysics Data System (ADS)

Dittmann, Niklas; Splettstoesser, Janine; Helbig, Nicole

2018-03-01

We calculate the frequency-dependent equilibrium noise of a mesoscopic capacitor in time-dependent density functional theory (TDDFT). The capacitor is modeled as a single-level quantum dot with on-site Coulomb interaction and tunnel coupling to a nearby reservoir. The noise spectra are derived from linear-response conductances via the fluctuation-dissipation theorem. Thereby, we analyze the performance of a recently derived exchange-correlation potential with time-nonlocal density dependence in the finite-frequency linear-response regime. We compare our TDDFT noise spectra with real-time perturbation theory and find excellent agreement for noise frequencies below the reservoir temperature.

Organo-Zintl-based superatoms: [Ge9(CHO)3] and [Ge9(CHO)

NASA Astrophysics Data System (ADS)

Reddy, G. Naaresh; Jena, Puru; Giri, Santanab

2017-10-01

A systematic study, based on density functional theory and different hybrid functionals for exchange-correlation potential, shows that the electron affinities of organo-zintl clusters [Ge9(R)n] [R = CHO; n = 1, 3] are close to that of chlorine (3.6 eV) and iodine (3.0 eV). A detailed study of the molecular orbitals of these complexes, when compared to those of Al13-, Cl- and I-, confirm that they behave as superatoms, mimicking the chemistry of halogens. This study expands the scope of superatoms by including a new class of pseudo-halogens based on ligated organo-Zintl ions.

Modeling and relationship of respiratory exchange ratio to athletic performance.

PubMed

Bellar, David; Judge, Lawrence W

2012-09-01

Previous research has related the results of tests of maximum aerobic capacity to performance for endurance athletes. These results are often only able to predict the running velocity of races such as the marathon. This investigation sought to determine the absolute V[Combining Dot Above]O2 at various respiratory exchange ratio (RER) values (0.85, 0.90, 0.95, 1.0, 1.05, and 1.10) by using a third-order polynomial regression to model the physiological responses for V[Combining Dot Above]O2 and RER obtained from an assessment of maximum aerobic capacity. The V[Combining Dot Above]O2 determined was subsequently correlated to race performance. The participants in the study were selected from a population of National Collegiate Athletic Association Division 1 crosscountry runners (male n = 7, female n = 7, age 20.5 ± 0.9 years; height 170.3 ± 8.2 cm; weight 59.7 ± 8.7 kg; V[Combining Dot Above]O2max 57.0 ± 7.8 ml O2·kg·min). Third-order regression analysis resulted in strong curve fitting between the variables (r = 0.949 ± 0.03). Partial correlations (controlled for weight) were used to assess the relationship between oxygen consumption at the desired points of RER and race performance. The partial correlations revealed that the absolute oxygen consumptions at all RER points of interest were significantly correlated to race performance (r > 0.740, p < 0.01). There was a significant difference in the strength of the correlations for the points RER 0.95 (t = 2.68957, p = 0.01), 1.0 (t = 2.18516, p = 0.03), and 1.05 (t = 1.85668, p = 0.04) and the correlations found for RER 0.85. After converting the oxygen consumption at the RER points to estimated horizontal running speeds, only the estimate at RER 1.05 was not statistically different from the actual speed achieved in the culminating XC race. It can be suggested based upon these results that coaches of collegiate crosscountry runners who engage in metabolic testing of athletes examine the estimated running pace at RER 1.05 to gain an insight into a runner's potential.

Approximate correlations for chevron-type plate heat exchangers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wanniarachchi, A.S.; Ratnam, U.; Tilton, B.E.

1995-12-31

There exists very little useful data representing the performance of industrial plate heat exchangers (PHEs) in the open literature. As a result, it has been difficult to arrive at any generalized correlations. While every PHE manufacturer is believed to have a comprehensive set of performance curves for their own designs, there exists the need to generate an approximate set of generalized correlations for the heat-transfer community. Such correlations can be used for preliminary designs and analytical studies. This paper attempts to develop such a set of generalized correlations to quantify the heat-transfer and pressure-drop performance of chevron-type PHEs. For thismore » purpose, the experimental data reported by Heavner et al. were used for the turbulent region. For the laminar region, a semi-theoretical approach was used to express, for example, the friction factor as a function of the Reynolds number and the chevron angle. Asymptotic curves were used for the transitional region. Physical explanations are provided for the trends shown by the generalized correlations. The correlations are compared against the open-literature data, where appropriate. These correlations are expected to be improved in the future when more data become available.« less

The Index cohesive effect on stock market correlations

NASA Astrophysics Data System (ADS)

Shapira, Y.; Kenett, D. Y.; Ben-Jacob, E.

2009-12-01

We present empirical examination and reassessment of the functional role of the market Index, using datasets of stock returns for eight years, by analyzing and comparing the results for two very different markets: 1) the New York Stock Exchange (NYSE), representing a large, mature market, and 2) the Tel Aviv Stock Exchange (TASE), representing a small, young market. Our method includes special collective (holographic) analysis of stock-Index correlations, of nested stock correlations (including the Index as an additional ghost stock) and of bare stock correlations (after subtraction of the Index return from the stocks returns). Our findings verify and strongly substantiate the assumed functional role of the index in the financial system as a cohesive force between stocks, i.e., the correlations between stocks are largely due to the strong correlation between each stock and the Index (the adhesive effect), rather than inter-stock dependencies. The Index adhesive and cohesive effects on the market correlations in the two markets are presented and compared in a reduced 3-D principal component space of the correlation matrices (holographic presentation). The results provide new insights into the interplay between an index and its constituent stocks in TASE-like versus NYSE-like markets.

Toward structural dynamics: protein motions viewed by chemical shift modulations and direct detection of C'N multiple-quantum relaxation.

PubMed

Mori, Mirko; Kateb, Fatiha; Bodenhausen, Geoffrey; Piccioli, Mario; Abergel, Daniel

2010-03-17

Multiple quantum relaxation in proteins reveals unexpected relationships between correlated or anti-correlated conformational backbone dynamics in alpha-helices or beta-sheets. The contributions of conformational exchange to the relaxation rates of C'N coherences (i.e., double- and zero-quantum coherences involving backbone carbonyl (13)C' and neighboring amide (15)N nuclei) depend on the kinetics of slow exchange processes, as well as on the populations of the conformations and chemical shift differences of (13)C' and (15)N nuclei. The relaxation rates of C'N coherences, which reflect concerted fluctuations due to slow chemical shift modulations (CSMs), were determined by direct (13)C detection in diamagnetic and paramagnetic proteins. In well-folded proteins such as lanthanide-substituted calbindin (CaLnCb), copper,zinc superoxide dismutase (Cu,Zn SOD), and matrix metalloproteinase (MMP12), slow conformational exchange occurs along the entire backbone. Our observations demonstrate that relaxation rates of C'N coherences arising from slow backbone dynamics have positive signs (characteristic of correlated fluctuations) in beta-sheets and negative signs (characteristic of anti-correlated fluctuations) in alpha-helices. This extends the prospects of structure-dynamics relationships to slow time scales that are relevant for protein function and enzymatic activity.

Developing a food exchange list for Middle Eastern appetizers and desserts commonly consumed in Jordan

PubMed Central

BAWADI, Hiba A.; AL-SHWAIYAT, Naseem M.; TAYYEM, Reema F.; MEKARY, Rania; TUURI, Georgianna

2011-01-01

Aim This study was conducted to develop a meal-planning exchange list for Middle Eastern foods commonly included in the Jordanian cuisine. Forty types of appetizers and another 40 types of desserts were selected; with five different recipes for each item. Recipes were collected from different housewives and Arabic cookbooks. Ingredients’ weight and dish net weight were recorded based on an average recipe, and dishes were prepared accordingly. Dishes were proximately analyzed following the AOAC procedures. Proximate analysis was compared to the WHO-food composition tables (FCT) for the use in the Middle East, and with food analysis software (ESHA). Results Significant correlations (P < 0.001) were found between macronutrient content obtained from proximate analysis and those obtained from ESHA. The correlation coefficients (r) were 0.92 for carbohydrate, 0.86 for protein, and 0.86 for fat. Strong correlations were also detected between proximate analysis FCT for carbohydrate (r=0.91, P<0.001) and protein (r=0.81; P<0.001) contents. However, this significant correlation was not found as strong, yet significant for fat (r=0. 62, P<0.001). Conclusion A valid exchange system for traditional desserts and appetizers is now available and ready to be used by dietitians and health care providers in Jordan and Arab World. PMID:21841913

Developing a food exchange list for Middle Eastern appetizers and desserts commonly consumed in Jordan.

PubMed

Bawadi, Hiba A; Al-Shwaiyat, Naseem M; Tayyem, Reema F; Mekary, Rania; Tuuri, Georgianna

2009-03-01

AIM: This study was conducted to develop a meal-planning exchange list for Middle Eastern foods commonly included in the Jordanian cuisine. Forty types of appetizers and another 40 types of desserts were selected; with five different recipes for each item. Recipes were collected from different housewives and Arabic cookbooks. Ingredients' weight and dish net weight were recorded based on an average recipe, and dishes were prepared accordingly. Dishes were proximately analyzed following the AOAC procedures. Proximate analysis was compared to the WHO-food composition tables (FCT) for the use in the Middle East, and with food analysis software (ESHA). RESULTS: Significant correlations (P < 0.001) were found between macronutrient content obtained from proximate analysis and those obtained from ESHA. The correlation coefficients (r) were 0.92 for carbohydrate, 0.86 for protein, and 0.86 for fat. Strong correlations were also detected between proximate analysis FCT for carbohydrate (r=0.91, P<0.001) and protein (r=0.81; P<0.001) contents. However, this significant correlation was not found as strong, yet significant for fat (r=0. 62, P<0.001). CONCLUSION: A valid exchange system for traditional desserts and appetizers is now available and ready to be used by dietitians and health care providers in Jordan and Arab World.

Regulation and acclimation of leaf gas exchange in a piñon-juniper woodland exposed to three different precipitation regimes.

PubMed

Limousin, Jean-Marc; Bickford, Christopher P; Dickman, Lee T; Pangle, Robert E; Hudson, Patrick J; Boutz, Amanda L; Gehres, Nathan; Osuna, Jessica L; Pockman, William T; McDowell, Nate G

2013-10-01

Leaf gas-exchange regulation plays a central role in the ability of trees to survive drought, but forecasting the future response of gas exchange to prolonged drought is hampered by our lack of knowledge regarding potential acclimation. To investigate whether leaf gas-exchange rates and sensitivity to drought acclimate to precipitation regimes, we measured the seasonal variations of leaf gas exchange in a mature piñon-juniper Pinus edulis-Juniperus monosperma woodland after 3 years of precipitation manipulation. We compared trees receiving ambient precipitation with those in an irrigated treatment (+30% of ambient precipitation) and a partial rainfall exclusion (-45%). Treatments significantly affected leaf water potential, stomatal conductance and photosynthesis for both isohydric piñon and anisohydric juniper. Leaf gas exchange acclimated to the precipitation regimes in both species. Maximum gas-exchange rates under well-watered conditions, leaf-specific hydraulic conductance and leaf water potential at zero photosynthetic assimilation all decreased with decreasing precipitation. Despite their distinct drought resistance and stomatal regulation strategies, both species experienced hydraulic limitation on leaf gas exchange when precipitation decreased, leading to an intraspecific trade-off between maximum photosynthetic assimilation and resistance of photosynthesis to drought. This response will be most detrimental to the carbon balance of piñon under predicted increases in aridity in the southwestern USA. © 2013 John Wiley & Sons Ltd.

Theoretical reflections on the structural polymorphism of the oxygen-evolving complex in the S2 state and the correlations to substrate water exchange and water oxidation mechanism in photosynthesis.

PubMed

Guo, Yu; Li, Hui; He, Lan-Lan; Zhao, Dong-Xia; Gong, Li-Dong; Yang, Zhong-Zhi

2017-10-01

The structural polymorphism of the oxygen-evolving complex is of great significance to photosynthetic water oxidation. Employing density functional theory calculations, we have made further advisement on the interconversion mechanism of O5 transfer in the S 2 state, mainly focusing on the potentiality of multi-state reactivity and spin transitions. Then, O5 protonation is proven impossible in S 2 for irreversibility of the interconversion, which serves as an auxiliary judgment for the protonation state of O5 in S 1 . Besides, the structural polymorphism could also be archived by alternative mechanisms involving Mn3 ligand exchange, one of which with Mn3(III) makes sense to substrate water exchange in S 2 , although being irresponsible for the derivations of the observed EPR signals. During the water exchange, high-spin states would prevail to facilitate electron transfer between the ferromagnetically coupled Mn centers. In addition, water exchange in S 1 could account for the closed-cubane structure as the initial form entering S 2 at cryogenic temperatures. With regard to water oxidation, the structural flexibility and variability in both S 2 and S 3 guarantee smooth W2-O5 coupling in S 4 , according to the substrate assignments from water exchange kinetics. Within this theoretical framework, the new XFEL findings on S 1 -S 3 can be readily rationalized. Finally, an alternative mechanistic scenario for OO bond formation with ·OH radical near O4 is presented, followed by water binding to the pivot Mn4(III) from O4 side during S 4 -S 0 . This may diversify the substrate sources combined with the Ca channel in water delivery for the forthcoming S-cycle. Copyright © 2017. Published by Elsevier B.V.

Fluidized-Bed Heat Transfer Modeling for the Development of Particle/Supercritical-CO2 Heat Exchanger

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Zhiwen; Martinek, Janna G

Concentrating solar power (CSP) technology is moving toward high-temperature and high-performance design. One technology approach is to explore high-temperature heat-transfer fluids and storage, integrated with a high-efficiency power cycle such as the supercritical carbon dioxide (s-CO2) Brayton power cycle. The s-CO2 Brayton power system has great potential to enable the future CSP system to achieve high solar-to-electricity conversion efficiency and to reduce the cost of power generation. Solid particles have been proposed as a possible high-temperature heat-transfer medium that is inexpensive and stable at high temperatures above 1,000 degrees C. The particle/heat exchanger provides a connection between the particles andmore » s-CO2 fluid in the emerging s-CO2 power cycles in order to meet CSP power-cycle performance targets of 50% thermal-to-electric efficiency, and dry cooling at an ambient temperature of 40 degrees C. The development goals for a particle/s-CO2 heat exchanger are to heat s-CO2 to =720 degrees C and to use direct thermal storage with low-cost, stable solid particles. This paper presents heat-transfer modeling to inform the particle/s-CO2 heat-exchanger design and assess design tradeoffs. The heat-transfer process was modeled based on a particle/s-CO2 counterflow configuration. Empirical heat-transfer correlations for the fluidized bed and s-CO2 were used in calculating the heat-transfer area and optimizing the tube layout. A 2-D computational fluid-dynamics simulation was applied for particle distribution and fluidization characterization. The operating conditions were studied from the heat-transfer analysis, and cost was estimated from the sizing of the heat exchanger. The paper shows the path in achieving the cost and performance objectives for a heat-exchanger design.« less

The impact of wood stove technology upgrades on indoor residential air quality

NASA Astrophysics Data System (ADS)

Allen, Ryan W.; Leckie, Sara; Millar, Gail; Brauer, Michael

2009-12-01

Fine particulate matter (PM 2.5) air pollution has been linked to adverse health impacts, and combustion sources including residential wood-burning may play an important role in some regions. Recent evidence suggests that indoor air quality may improve in homes where older, non-certified wood stoves are exchanged for lower emissions EPA-certified alternatives. As part of a wood stove exchange program in northern British Columbia, Canada, we sampled outdoor and indoor air at 15 homes during 6-day sampling sessions both before and after non-certified wood stoves were exchanged. During each sampling session two consecutive 3-day PM 2.5 samples were collected onto Teflon filters, which were weighed and analyzed for the wood smoke tracer levoglucosan. Residential PM 2.5 infiltration efficiencies ( Finf) were estimated from continuous light scattering measurements made with nephelometers, and estimates of Finf were used to calculate the outdoor- and indoor-generated contributions to indoor air. There was not a consistent relationship between stove technology and outdoor or indoor concentrations of PM 2.5 or levoglucosan. Mean Finf estimates were low and similar during pre- and post-exchange periods (0.32 ± 0.17 and 0.33 ± 0.17, respectively). Indoor sources contributed the majority (˜65%) of the indoor PM 2.5 concentrations, independent of stove technology, although low indoor-outdoor levoglucosan ratios (median ≤ 0.19) and low indoor PM 2.5-levoglucosan correlations ( r ≤ 0.19) suggested that wood smoke was not a major indoor PM 2.5 source in most of these homes. In summary, despite the potential for extensive wood stove exchange programs to reduce outdoor PM 2.5 concentrations in wood smoke-impacted communities, we did not find a consistent relationship between stove technology upgrades and indoor air quality improvements in homes where stoves were exchanged.

Quantum correlated pulse-pair generation during pulse-trapping propagation in optical fibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirosawa, Kenichi; Kannari, Fumihiko; Takeoka, Masahiro

2007-10-15

We study a different scheme for generating photon number correlation and squeezing for two copropagating pulses, a soliton and a trapped pulse, in an optical fiber. When the center wavelength of a trapped pulse is close to that of a soliton pulse, the two pulses interact with each other through the third-order optical nonlinear process and exchange photons between the two pulses. The soliton pulse exhibits photon number squeezing. When the center wavelengths of the two pulses are sufficiently separated and no photon-number exchange takes place, the strong negative correlation in the photon number between the parts of the trappedmore » pulse and the soliton pulse is formed via cross-phase modulation. By measuring the photon number of the negatively correlated part of the trapped pulse, we can obtain the photon number of the soliton pulse with a variance less than the shot-noise limit.« less

Bond breaking and bond formation: how electron correlation is captured in many-body perturbation theory and density-functional theory.

PubMed

Caruso, Fabio; Rohr, Daniel R; Hellgren, Maria; Ren, Xinguo; Rinke, Patrick; Rubio, Angel; Scheffler, Matthias

2013-04-05

For the paradigmatic case of H(2) dissociation, we compare state-of-the-art many-body perturbation theory in the GW approximation and density-functional theory in the exact-exchange plus random-phase approximation (RPA) for the correlation energy. For an unbiased comparison and to prevent spurious starting point effects, both approaches are iterated to full self-consistency (i.e., sc-RPA and sc-GW). The exchange-correlation diagrams in both approaches are topologically identical, but in sc-RPA they are evaluated with noninteracting and in sc-GW with interacting Green functions. This has a profound consequence for the dissociation region, where sc-RPA is superior to sc-GW. We argue that for a given diagrammatic expansion, sc-RPA outperforms sc-GW when it comes to bond breaking. We attribute this to the difference in the correlation energy rather than the treatment of the kinetic energy.

The structural role of weak and strong links in a financial market network

NASA Astrophysics Data System (ADS)

Garas, A.; Argyrakis, P.; Havlin, S.

2008-05-01

We investigate the properties of correlation based networks originating from economic complex systems, such as the network of stocks traded at the New York Stock Exchange (NYSE). The weaker links (low correlation) of the system are found to contribute to the overall connectivity of the network significantly more than the strong links (high correlation). We find that nodes connected through strong links form well defined communities. These communities are clustered together in more complex ways compared to the widely used classification according to the economic activity. We find that some companies, such as General Electric (GE), Coca Cola (KO), and others, can be involved in different communities. The communities are found to be quite stable over time. Similar results were obtained by investigating markets completely different in size and properties, such as the Athens Stock Exchange (ASE). The present method may be also useful for other networks generated through correlations.

Correlation Equations for Condensing Heat Exchangers Based on an Algorithmic Performance-Data Classification

NASA Astrophysics Data System (ADS)

Pacheco-Vega, Arturo

2016-09-01

In this work a new set of correlation equations is developed and introduced to accurately describe the thermal performance of compact heat exchangers with possible condensation. The feasible operating conditions for the thermal system correspond to dry- surface, dropwise condensation, and film condensation. Using a prescribed form for each condition, a global regression analysis for the best-fit correlation to experimental data is carried out with a simulated annealing optimization technique. The experimental data were taken from the literature and algorithmically classified into three groups -related to the possible operating conditions- with a previously-introduced Gaussian-mixture-based methodology. Prior to their use in the analysis, the correct data classification was assessed and confirmed via artificial neural networks. Predictions from the correlations obtained for the different conditions are within the uncertainty of the experiments and substantially more accurate than those commonly used.

Exchangeable hydrogen explains the pH of spodosol Oa horizons

USGS Publications Warehouse

Ross, D.S.; David, M.B.; Lawrence, G.B.; Bartlett, R.J.

1996-01-01

The chemistry of extremely acid Oa horizons does not conform to traditional pH, Al, and base saturation relationships. Results from two separate studies of northeastern U.S. forested soils were used to investigate relationships between pH in water or dilute salt solutions and other soil characteristics. In Oa horizons with pH below 4, soil pH in dilute CaCl2 solution was correlated with exchangeable H+ measured either by titration (r = -0.88, P = 0.0001, n = 142) or by electrode (r = -0.89, P = 0.0001, n = 45). Exchangeable H+ expressed as a percentage of the cation-exchange capacity (CEC) was linear with pH and showed similar slopes for data from both studies. For all samples, pHw = 4.21 - 1.80 x H+/CEC (R2 = 0.69, n = 194). The reciprocal of the H+/CEC ratio is base saturation with Al added to the bases. Because of the low pH, exchangeable Al does not appear to behave as an acid. Exchangeable H+ remains an operationally defined quantity because of the difficulty in separating exchange and hydrolysis reactions. In a variety of neutral-salt extractants, concentration of H+ were correlated with 0.1 M BaCl2-exchangeable H+ (r > 0.91, P = 0.0001, n = 26) regardless of the strength of the extract. Nine successive extractions with 0.33 mM CaCl2 removed more H+ than was removed by single batch extractions with either 1 M KCl or 0.1 M BaCl2 (average H+ of 70, 43, and 49 mmol kg-1, respectively for 26 samples). The data showed little difference in the chemical behavior of Oa horizons from a variety of geographical sites and vegetation types.

Heat transfer and flow friction correlations for perforated plate matrix heat exchangers

NASA Astrophysics Data System (ADS)

Ratna Raju, L.; Kumar, S. Sunil; Chowdhury, K.; Nandi, T. K.

2017-02-01

Perforated plate matrix heat exchangers (MHE) are constructed of high conductivity perforated plates stacked alternately with low conductivity spacers. They are being increasingly used in many cryogenic applications including Claude cycle or Reversed Brayton cycle cryo-refrigerators and liquefiers. Design of high NTU (number of (heat) transfer unit) cryogenic MHEs requires accurate heat transfer coefficient and flow friction factor. Thermo-hydraulic behaviour of perforated plates strongly depends on the geometrical parameters. Existing correlations, however, are mostly expressed as functions of Reynolds number only. This causes, for a given configuration, significant variations in coefficients from one correlation to the other. In this paper we present heat transfer and flow friction correlations as functions of all geometrical and other controlling variables. A FluentTM based numerical model has been developed for heat transfer and pressure drop studies over a stack of alternately arranged perforated plates and spacers. The model is validated with the data from literature. Generalized correlations are obtained through regression analysis over a large number of computed data.

Dispersion- and Exchange-Corrected Density Functional Theory for Sodium Ion Hydration.

PubMed

Soniat, Marielle; Rogers, David M; Rempe, Susan B

2015-07-14

A challenge in density functional theory is developing functionals that simultaneously describe intermolecular electron correlation and electron delocalization. Recent exchange-correlation functionals address those two issues by adding corrections important at long ranges: an atom-centered pairwise dispersion term to account for correlation and a modified long-range component of the electron exchange term to correct for delocalization. Here we investigate how those corrections influence the accuracy of binding free energy predictions for sodium-water clusters. We find that the dual-corrected ωB97X-D functional gives cluster binding energies closest to high-level ab initio methods (CCSD(T)). Binding energy decomposition shows that the ωB97X-D functional predicts the smallest ion-water (pairwise) interaction energy and larger multibody contributions for a four-water cluster than most other functionals - a trend consistent with CCSD(T) results. Also, ωB97X-D produces the smallest amounts of charge transfer and the least polarizable waters of the density functionals studied, which mimics the lower polarizability of CCSD. When compared with experimental binding free energies, however, the exchange-corrected CAM-B3LYP functional performs best (error <1 kcal/mol), possibly because of its parametrization to experimental formation enthalpies. For clusters containing more than four waters, "split-shell" coordination must be considered to obtain accurate free energies in comparison with experiment.

Adaptable interaction between aquaporin-1 and band 3 reveals a potential role of water channel in blood CO2 transport.

PubMed

Hsu, Kate; Lee, Ting-Ying; Periasamy, Ammasi; Kao, Fu-Jen; Li, Li-Tzu; Lin, Chuang-Yu; Lin, Hui-Ju; Lin, Marie

2017-10-01

Human CO 2 respiration requires rapid conversion between CO 2 and HCO 3 - Carbonic anhydrase II facilitates this reversible reaction inside red blood cells, and band 3 [anion exchanger 1 (AE1)] provides a passage for HCO 3 - flux across the cell membrane. These 2 proteins are core components of the CO 2 transport metabolon. Intracellular H 2 O is necessary for CO 2 /HCO 3 - conversion. However, abundantly expressed aquaporin 1 (AQP1) in erythrocytes is thought not to be part of band 3 complexes or the CO 2 transport metabolon. To solve this conundrum, we used Förster resonance energy transfer (FRET) measured by fluorescence lifetime imaging (FLIM-FRET) and identified interaction between aquaporin-1 and band 3 at a distance of 8 nm, within the range of dipole-dipole interaction. Notably, their interaction was adaptable to membrane tonicity changes. This suggests that the function of AQP1 in tonicity response could be coupled or correlated to its function in band 3-mediated CO 2 /HCO 3 - exchange. By demonstrating AQP1 as a mobile component of the CO 2 transport metabolon, our results uncover a potential role of water channel in blood CO 2 transport and respiration.-Hsu, K., Lee, T.-Y., Periasamy, A., Kao, F.-J., Li, L.-T., Lin, C.-Y., Lin, H.-J., Lin, M. Adaptable interaction between aquaporin-1 and band 3 reveals a potential role of water channel in blood CO 2 transport. © FASEB.

The use of the Hurst exponent to investigate the global maximum of the Warsaw Stock Exchange WIG20 index

NASA Astrophysics Data System (ADS)

Domino, Krzysztof

2012-01-01

The WIG20 index-the index of the 20 biggest companies traded on the Warsaw Stock Exchange-reached the global maximum on 29th October 2007. I have used the local DFA (Detrended Functional Analysis) to obtain the Hurst exponent (diffusion exponent) and investigate the signature of anti-correlation of share price evolution around the maximum. The analysis was applied to the share price evolution for variable DFA parameters. For many values of parameters, the evidence of anti-correlation near the WIG20 maximum was pointed out.

Electronic and Transport Properties of LaNi4Sb12 Skutterudite: Modified Becke-Johnson Approach

NASA Astrophysics Data System (ADS)

Bhat, Tahir Mohiuddin; Singh, Srishti; Gupta, Dinesh C.

2018-05-01

We carried out an ab initio study of structural, electronic, thermodynamic, and thermoelectric properties of the lanthanum-filled skutterudite, LaNi4Sb12. Generalized gradient approximation and modified Becke-Johnson potentials were employed for the exchange-correlation potential. The electronic structure calculations display the metallic behavior of the compound. The alloy offers low lattice thermal conductivity along with a high Seebeck coefficient with a value of - 158 (μVK-1) at room temperature. The effect of high pressure and temperature on thermal properties like thermal expansion coefficient, heat capacity, and Grüneisen parameter are also investigated by means of a quasi-harmonic Debye model. The large Seebeck coefficient and high power factor exhibited by LaNi4Sb12 make it an attractive candidate for thermoelectric materials.

75 FR 68660 - Self-Regulatory Organizations; EDGX Exchange, Inc.; Notice of Filing and Immediate Effectiveness...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-08

... proposed rule change reflects a competitive pricing structure designed to incent market participants to... Exchange believes that the above pricing is appropriate since higher rebates are directly correlated with... notes that it operates in a highly competitive market in which market participants can readily direct...

A hydrogeomorphic river network model predicts where and why hyporheic exchange is important in large basins

USGS Publications Warehouse

Gomez-Velez, Jesus D.; Harvey, Judson

2014-01-01

Hyporheic exchange has been hypothesized to have basin-scale consequences; however, predictions throughout river networks are limited by available geomorphic and hydrogeologic data and by models that can analyze and aggregate hyporheic exchange flows across large spatial scales. We developed a parsimonious but physically based model of hyporheic flow for application in large river basins: Networks with EXchange and Subsurface Storage (NEXSS). We applied NEXSS across a broad range of geomorphic diversity in river reaches and synthetic river networks. NEXSS demonstrates that vertical exchange beneath submerged bed forms rather than lateral exchange through meanders dominates hyporheic fluxes and turnover rates along river corridors. Per kilometer, low-order streams have a biogeochemical potential at least 2 orders of magnitude larger than higher-order streams. However, when biogeochemical potential is examined per average length of each stream order, low- and high-order streams were often found to be comparable. As a result, the hyporheic zone's intrinsic potential for biogeochemical transformations is comparable across different stream orders, but the greater river miles and larger total streambed area of lower order streams result in the highest cumulative impact from low-order streams. Lateral exchange through meander banks may be important in some cases but generally only in large rivers.

A hydrogeomorphic river network model predicts where and why hyporheic exchange is important in large basins

NASA Astrophysics Data System (ADS)

Gomez-Velez, Jesus D.; Harvey, Judson W.

2014-09-01

Hyporheic exchange has been hypothesized to have basin-scale consequences; however, predictions throughout river networks are limited by available geomorphic and hydrogeologic data and by models that can analyze and aggregate hyporheic exchange flows across large spatial scales. We developed a parsimonious but physically based model of hyporheic flow for application in large river basins: Networks with EXchange and Subsurface Storage (NEXSS). We applied NEXSS across a broad range of geomorphic diversity in river reaches and synthetic river networks. NEXSS demonstrates that vertical exchange beneath submerged bed forms rather than lateral exchange through meanders dominates hyporheic fluxes and turnover rates along river corridors. Per kilometer, low-order streams have a biogeochemical potential at least 2 orders of magnitude larger than higher-order streams. However, when biogeochemical potential is examined per average length of each stream order, low- and high-order streams were often found to be comparable. As a result, the hyporheic zone's intrinsic potential for biogeochemical transformations is comparable across different stream orders, but the greater river miles and larger total streambed area of lower order streams result in the highest cumulative impact from low-order streams. Lateral exchange through meander banks may be important in some cases but generally only in large rivers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Jianwei; Yang, Zenghui; Peng, Haowei

The uniform electron gas and the hydrogen atom play fundamental roles in condensed matter physics and quantum chemistry. The former has an infinite number of electrons uniformly distributed over the neutralizing positively charged background, and the latter only one electron bound to the proton. The uniform electron gas was used to derive the local spin density approximation to the exchange-correlation functional that undergirds the development of the Kohn-Sham density functional theory. We show here that the ground-state exchange-correlation energies of the hydrogen atom and many other 1- and 2-electron systems are modeled surprisingly well by a different local spin densitymore » approximation (LSDA0). LSDA0 is constructed to satisfy exact constraints but agrees surprisingly well with the exact results for a uniform two-electron density in a finite, curved three-dimensional space. We also apply LSDA0 to excited or noded 1-electron densities, where it works less well. Furthermore, we show that the localization of the exact exchange hole for a 1- or 2-electron ground state can be measured by the ratio of the exact exchange energy to its optimal lower bound.« less

Positive exchange-bias and giant vertical hysteretic shift in La0.3Sr0.7FeO3/SrRuO3 bilayers

PubMed Central

Rana, Rakesh; Pandey, Parul; Singh, R. P.; Rana, D. S.

2014-01-01

The exchange-bias effects in the mosaic epitaxial bilayers of the itinerant ferromagnet (FM) SrRuO3 and the antiferromagnetic (AFM) charge-ordered La0.3Sr0.7FeO3 were investigated. An uncharacteristic low-field positive exchange bias, a cooling-field driven reversal of positive to negative exchange-bias and a layer thickness optimised unusual vertical magnetization shift were all novel facets of exchange bias realized for the first time in magnetic oxides. The successive magnetic training induces a transition from positive to negative exchange bias regime with changes in domain configurations. These observations are well corroborated by the hysteretic loop asymmetries which display the modifications in the AFM spin correlations. These exotic features emphasize the key role of i) mosaic disorder induced subtle interplay of competing AFM-superexchange and FM double exchange at the exchange biased interface and, ii) training induced irrecoverable alterations in the AFM spin structure. PMID:24569516

Semi-Local DFT Functionals with Exact-Exchange-Like Features: Beyond the AK13

NASA Astrophysics Data System (ADS)

Armiento, Rickard

The Armiento-Kümmel functional from 2013 (AK13) is a non-empirical semi-local exchange functional on generalized gradient approximation form (GGA) in Kohn-Sham (KS) density functional theory (DFT). Recent works have established that AK13 gives improved electronic-structure exchange features over other semi-local methods, with a qualitatively improved orbital description and band structure. For example, the Kohn-Sham band gap is greatly extended, as it is for exact exchange. This talk outlines recent efforts towards new exchange-correlation functionals based on, and extending, the AK13 design ideas. The aim is to improve the quantitative accuracy, the description of energetics, and to address other issues found with the original formulation. Swedish e-Science Research Centre (SeRC).

Role of non-local exchange in the electronic structure of correlated oxides

NASA Astrophysics Data System (ADS)

Iori, Federico; Gatti, Matteo; Rubio Secades, Angel

Transition-metal oxides (TMO) with partially filled d or f shells are a prototype of correlated materials. They exhibit very interesting properties, like metal-insulator phase transitions (MIT). In this work we consider several TMO insulators in which Kohn-Sham LDA band structures are metallic: VO2, V2O3, Ti2O3, LaTiO3 and YTiO3. In the past, this failure of LDA has been explained in terms of its inadequacy to capture the strong interactions taking place between correlated electrons. In the spirit of the Hubbard model, possible corrections to improve onsite correlation are the LDA +U and LDA +DMFT approaches. Here we make use of the HSE06 hybrid functional. We show that, without invoking strong-correlation effects, the contribution of the non-local Fock exchange is essential to correct the LDA results, by curing its delocalization error. In fact, HSE06 provides insulating band structures and correctly describes the MIT in all the considered compounds. We further discuss the advantages and the limitations of the HSE06 hybrid functional in correlated TMO

Experimental investigation of heat transfer coefficient of mini-channel PCHE (printed circuit heat exchanger)

NASA Astrophysics Data System (ADS)

Kwon, Dohoon; Jin, Lingxue; Jung, WooSeok; Jeong, Sangkwon

2018-06-01

Heat transfer coefficient of a mini-channel printed circuit heat exchanger (PCHE) with counter-flow configuration is investigated. The PCHE used in the experiments is two layered (10 channels per layer) and has the hydraulic diameter of 1.83 mm. Experiments are conducted under various cryogenic heat transfer conditions: single-phase, boiling and condensation heat transfer. Heat transfer coefficients of each experiments are presented and compared with established correlations. In the case of the single-phase experiment, empiricial correlation of modified Dittus-Boelter correlation was proposed, which predicts the experimental results with 5% error at Reynolds number range from 8500 to 17,000. In the case of the boiling experiment, film boiling phenomenon occurred dominantly due to large temperature difference between the hot side and the cold side fluids. Empirical correlation is proposed which predicts experimental results with 20% error at Reynolds number range from 2100 to 2500. In the case of the condensation experiment, empirical correlation of modified Akers correlation was proposed, which predicts experimental results with 10% error at Reynolds number range from 3100 to 6200.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. I. Theory for a dimer

NASA Astrophysics Data System (ADS)

Tiwari, Vivek; Peters, William K.; Jonas, David M.

2017-10-01

Non-adiabatic vibrational-electronic resonance in the excited electronic states of natural photosynthetic antennas drastically alters the adiabatic framework, in which electronic energy transfer has been conventionally studied, and suggests the possibility of exploiting non-adiabatic dynamics for directed energy transfer. Here, a generalized dimer model incorporates asymmetries between pigments, coupling to the environment, and the doubly excited state relevant for nonlinear spectroscopy. For this generalized dimer model, the vibrational tuning vector that drives energy transfer is derived and connected to decoherence between singly excited states. A correlation vector is connected to decoherence between the ground state and the doubly excited state. Optical decoherence between the ground and singly excited states involves linear combinations of the correlation and tuning vectors. Excitonic coupling modifies the tuning vector. The correlation and tuning vectors are not always orthogonal, and both can be asymmetric under pigment exchange, which affects energy transfer. For equal pigment vibrational frequencies, the nonadiabatic tuning vector becomes an anti-correlated delocalized linear combination of intramolecular vibrations of the two pigments, and the nonadiabatic energy transfer dynamics become separable. With exchange symmetry, the correlation and tuning vectors become delocalized intramolecular vibrations that are symmetric and antisymmetric under pigment exchange. Diabatic criteria for vibrational-excitonic resonance demonstrate that anti-correlated vibrations increase the range and speed of vibronically resonant energy transfer (the Golden Rule rate is a factor of 2 faster). A partial trace analysis shows that vibronic decoherence for a vibrational-excitonic resonance between two excitons is slower than their purely excitonic decoherence.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. I. Theory for a dimer.

PubMed

Tiwari, Vivek; Peters, William K; Jonas, David M

2017-10-21

Non-adiabatic vibrational-electronic resonance in the excited electronic states of natural photosynthetic antennas drastically alters the adiabatic framework, in which electronic energy transfer has been conventionally studied, and suggests the possibility of exploiting non-adiabatic dynamics for directed energy transfer. Here, a generalized dimer model incorporates asymmetries between pigments, coupling to the environment, and the doubly excited state relevant for nonlinear spectroscopy. For this generalized dimer model, the vibrational tuning vector that drives energy transfer is derived and connected to decoherence between singly excited states. A correlation vector is connected to decoherence between the ground state and the doubly excited state. Optical decoherence between the ground and singly excited states involves linear combinations of the correlation and tuning vectors. Excitonic coupling modifies the tuning vector. The correlation and tuning vectors are not always orthogonal, and both can be asymmetric under pigment exchange, which affects energy transfer. For equal pigment vibrational frequencies, the nonadiabatic tuning vector becomes an anti-correlated delocalized linear combination of intramolecular vibrations of the two pigments, and the nonadiabatic energy transfer dynamics become separable. With exchange symmetry, the correlation and tuning vectors become delocalized intramolecular vibrations that are symmetric and antisymmetric under pigment exchange. Diabatic criteria for vibrational-excitonic resonance demonstrate that anti-correlated vibrations increase the range and speed of vibronically resonant energy transfer (the Golden Rule rate is a factor of 2 faster). A partial trace analysis shows that vibronic decoherence for a vibrational-excitonic resonance between two excitons is slower than their purely excitonic decoherence.

[Effect of phosphate on the exchangeable form and the bioavailability of exogenous neodymium in soil].

PubMed

Xu, Z; Li, D; Yang, J; Peng, A

2001-05-01

Effects of phosphate on the exchangeable form and the bioavailability of exogenous neodymium (Nd) in soil were studied with 147Nd isotopic tracer. Exchangeable Nd was extracted with solution (pH8.2) of NaAc. The results indicated that Nd beyond 99.5% was adsorbed by soil whether phosphate exists in soil or not. Phosphate can precipitate dramatically Nd3+. And the Nd phosphate precipitates may set limits on the concentration of exchangeable Nd observed in soil. KH2PO4 ranging from 0.3 g.kg-1 to 1.5 g.kg-1 make a uniform impact on the exchangeable form of Nd. In addition, phosphate in soil can inhibit wheat seedling to absorb Nd. The concentration of exchangeable Nd is correlated significantly with the content of Nd in wheat seedling.

Modeling the adiabatic connection in H2.

PubMed

Peach, Michael J G; Teale, Andrew M; Tozer, David J

2007-06-28

Full configuration interaction (FCI) data are used to quantify the accuracy of approximate adiabatic connection (AC) forms in describing the ground state potential energy curve of H2, within spin-restricted density functional theory (DFT). For each internuclear separation R, accurate properties of the AC are determined from large basis set FCI calculations. The parameters in the approximate AC form are then determined so as to reproduce these FCI values exactly, yielding an exchange-correlation energy expressed entirely in terms of FCI-derived quantities. This is combined with other FCI-derived energy components to give the total electronic energy; comparison with the FCI energy quantifies the accuracy of the AC form. Initial calculations focus on a [1/1]-Padé-based form. The potential energy curve determined using the procedure is a notable improvement over those from existing DFT functionals. The accuracy near equilibrium is quantified by calculating the bond length and vibrational wave numbers; errors in the latter are below 0.5%. The molecule dissociates correctly, which can be traced to the use of virtual orbital eigenvalues in the slope in the noninteracting limit, capturing static correlation. At intermediate R, the potential energy curve exhibits an unphysical barrier, similar to that noted previously using the random phase approximation. Alternative forms of the AC are also considered, paying attention to size extensivity and the behavior in the strong-interaction limit; none provide an accurate potential energy curve for all R, although good accuracy can be achieved near equilibrium. The study demonstrates how data from correlated ab initio calculations can provide valuable information about AC forms and highlight areas where further theoretical progress is required.

75 FR 39608 - Self-Regulatory Organizations; Chicago Board Options Exchange, Incorporated; Notice of Filing and...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-09

... rule proposal is available on the Exchange's website ( http://www.cboe.org/legal ), at the Exchange's... have the necessary systems capacity to handle the potential additional traffic associated with the...

Effects of Co doping on the metamagnetic states of the ferromagnetic fcc Fe-Co alloy.

PubMed

Ortiz-Chi, Filiberto; Aguayo, Aarón; de Coss, Romeo

2013-01-16

The evolution of the metamagnetic states in the ferromagnetic face centered cubic (fcc) Fe(1-x)Co(x) alloy as a function of Co concentration has been studied by means of first-principles calculations. The ground state properties were obtained using the full-potential linear augmented plane wave method and the generalized gradient approximation for the exchange-correlation functional. The alloying was modeled using the virtual crystal approximation and the magnetic states were obtained from the calculations of the total energy as a function of the spin moment, using the fixed spin moment method. For ferromagnetic fcc Fe, the binding-energy curve shows metamagnetic behavior, with two minima corresponding to a small-volume, low-spin (LS) state and a large-volume, high-spin (HS) state, which are separated by a small energy (E(LS) ≲ E(HS)). The evolution of the magnetic moment, the exchange integral (J), and the binding-energy curve is analyzed in the whole range of Co concentrations (x). The magnetic moment corresponding to the HS state decreases monotonically from 2.6 μ(B)/atom in fcc Fe to 1.7 μ(B)/atom in fcc Co. In contrast, the exchange integral for the HS state shows a maximum at around x = 0.45. The thermal dependence of the lattice parameter is evaluated with a method based on statistical mechanics using the binding-energy curve as an effective potential. It is observed that the behavior of the lattice parameter with temperature is tuned by Co doping, from negative thermal expansion in fcc Fe to positive thermal expansion in fcc Co, through the modification of the energetics of the metamagnetic states.

Endogenous minerals have influences on surface electrochemistry and ion exchange properties of biochar.

PubMed

Zhao, Ling; Cao, Xinde; Zheng, Wei; Wang, Qun; Yang, Fan

2015-10-01

The feedstocks for biochar production are diverse and many of them contain various minerals in addition to being rich in carbon. Twelve types of biomass classified into 2 categories: plant-based and municipal waste, were employed to produce biochars under 350 °C and 500 °C. Their pH, point of zero net charge (PZNC), zeta potential, cation and anion exchange capacity (CEC and AEC) were analyzed. The municipal waste-based biochars (MW-BC) had higher mineral levels than the plant-based biochars (PB-BC). However, the water soluble mineral levels were lower in the MW-BCs due to the dominant presence of less soluble minerals, such as CaCO3 and (Ca,Mg)3(PO4)2. The higher total minerals in MW-BCs accounted for the higher PZNC (5.47-9.95) than in PB-BCs (1.91-8.18), though the PZNCs of the PB-BCs increased more than that of the MW-BCs as the production temperature rose. The minerals had influence on the zeta potentials via affecting the negative charges of biochars and the ionic strength of solution. The organic functional groups in PB-BCs such as -COOH and -OH had a greater effect on the CEC and AEC, while the minerals had a greater effect on that of MW-BCs. The measured CEC and AEC values had a strong positive correlation with the total amount of soluble cations and anions, respectively. Results indicated that biochar surface charges depend not only on the organic functional groups, but also on the minerals present and to some extent, minerals have more influences on the surface electrochemistry and ion exchange properties of biochar. Copyright © 2015 Elsevier Ltd. All rights reserved.

Jump spillover between oil prices and exchange rates

NASA Astrophysics Data System (ADS)

Li, Xiao-Ping; Zhou, Chun-Yang; Wu, Chong-Feng

2017-11-01

In this paper, we investigate the jump spillover effects between oil prices and exchange rates. To identify the latent historical jumps for exchange rates and oil prices, we use a Bayesian MCMC approach to estimate the stochastic volatility model with correlated jumps in both returns and volatilities for each. We examine the simultaneous jump intensities and the conditional jump spillover probabilities between oil prices and exchange rates, finding strong evidence of jump spillover effects. Further analysis shows that the jump spillovers are mainly due to exogenous events such as financial crises and geopolitical events. Thus, the findings have important implications for financial risk management.

Covalent bond orders and atomic valences from correlated wavefunctions

NASA Astrophysics Data System (ADS)

Ángyán, János G.; Rosta, Edina; Surján, Péter R.

1999-01-01

A comparison is made between two alternative definitions for covalent bond orders: one derived from the exchange part of the two-particle density matrix and the other expressed as the correlation of fluctuations (covariance) of the number of electrons between the atomic centers. Although these definitions lead to identical formulae for mono-determinantal SCF wavefunctions, they predict different bond orders for correlated wavefunctions. It is shown that, in this case, the fluctuation-based definition leads to slightly lower values of the bond order than does the exchange-based definition, provided one uses an appropriate space-partitioning technique like that of Bader's topological theory of atoms in a molecule; however, use of Mulliken partitioning in this context leads to unphysical behaviour. The example of H 2 is discussed in detail.

Currency crises and the evolution of foreign exchange market: Evidence from minimum spanning tree

NASA Astrophysics Data System (ADS)

Jang, Wooseok; Lee, Junghoon; Chang, Woojin

2011-02-01

We examined the time series properties of the foreign exchange market for 1990-2008 in relation to the history of the currency crises using the minimum spanning tree (MST) approach and made several meaningful observations about the MST of currencies. First, around currency crises, the mean correlation coefficient between currencies decreased whereas the normalized tree length increased. The mean correlation coefficient dropped dramatically passing through the Asian crisis and remained at the lowered level after that. Second, the Euro and the US dollar showed a strong negative correlation after 1997, implying that the prices of the two currencies moved in opposite directions. Third, we observed that Asian countries and Latin American countries moved away from the cluster center (USA) passing through the Asian crisis and Argentine crisis, respectively.

Foreign exchange market as a lattice gauge theory

NASA Astrophysics Data System (ADS)

Young, K.

1999-10-01

A simple model of the foreign exchange market is exactly a lattice gauge theory. Exchange rates are the exponentials of gauge potentials defined on spatial links while interest rates are related to gauge potentials on temporal links. Arbitrage opportunities are given by nonzero values of the gauge-invariant field tensor or curvature defined on closed loops. Arbitrage opportunities involving cross-rates at one time are "magnetic fields," while arbitrage opportunities involving future contracts are "electric fields."

Chromium uptake by rice and accumulation in soil amended with municipal solid waste compost.

PubMed

Bhattacharyya, P; Chakraborty, A; Chakrabarti, K; Tripathy, S; Powell, M A

2005-09-01

Effect of addition of municipal solid waste compost (MSWC) on chromium (Cr) content of submerged rice paddies was studied. Experiments were conducted during the three consecutive wet seasons from 1997 to 1999 on rice grown under submergence, at the Experimental Farm of Calcutta University, India. A sequential extraction method was used to determine the various chromium fractions in MSWC and cow dung manure (CDM). Chromium was significantly bound to the organic matter and Fe and Mn oxides in MSWC and CDM. Chromium content in rice straw was higher than in rice grain. Chromium bound with organic matter in MSWC best correlated with straw Cr (r=0.99**) followed by Fe and Mn oxides (r=0.97*) and water soluble as well as exchangeable fractions (r=0.96*). The water soluble and the exchangeable fractions in MSWC best correlated with grain Cr (r=0.98*). The Cr content of rice grain had the highest correlation with water soluble and exchangeable Cr (r=0.99**) while the straw Cr best correlated with the Fe and Mn oxides (r=0.98*). Both the carbonate bound and residual fractions in MSWC and CDM did not significantly correlate with rice straw and grain Cr. MSWC would be a valuable resource for agriculture if it can be used safely, but long-term use may require the cessation of the dumping by the leather tanneries and other major contributors of pollutants.

Anisotropic exchange interaction induced by a single photon in semiconductor microcavities

NASA Astrophysics Data System (ADS)

Chiappe, G.; Fernández-Rossier, J.; Louis, E.; Anda, E. V.

2005-12-01

We investigate coupling of localized spins in a semiconductor quantum dot embedded in a microcavity. The lowest cavity mode and the quantum dot exciton are coupled and close in energy, forming a polariton. The fermions forming the exciton interact with localized spins via exchange. Exact diagonalization of a Hamiltonian in which photons, spins, and excitons are treated quantum mechanically shows that a single polariton induces a sizable indirect anisotropic exchange interaction between spins. At sufficiently low temperatures strong ferromagnetic correlations show up without an appreciable increase in exciton population. In the case of a (Cd,Mn)Te quantum dot, Mn-Mn ferromagnetic coupling is still significant at 1 K : spin-spin correlation around 3 for exciton occupation smaller than 0.3. We find that the interaction mediated by photon-polaritons is 10 times stronger than the one induced by a classical field for equal Rabi splitting.

Emotional Intelligence predicts individual differences in social exchange reasoning.

PubMed

Reis, Deidre L; Brackett, Marc A; Shamosh, Noah A; Kiehl, Kent A; Salovey, Peter; Gray, Jeremy R

2007-04-15

When assessed with performance measures, Emotional Intelligence (EI) correlates positively with the quality of social relationships. However, the bases of such correlations are not understood in terms of cognitive and neural information processing mechanisms. We investigated whether a performance measure of EI is related to reasoning about social situations (specifically social exchange reasoning) using versions of the Wason Card Selection Task. In an fMRI study (N=16), higher EI predicted hemodynamic responses during social reasoning in the left frontal polar and left anterior temporal brain regions, even when controlling for responses on a very closely matched task (precautionary reasoning). In a larger behavioral study (N=48), higher EI predicted faster social exchange reasoning, after controlling for precautionary reasoning. The results are the first to directly suggest that EI is mediated in part by mechanisms supporting social reasoning and validate a new approach to investigating EI in terms of more basic information processing mechanisms.

Thermally Cross-Linked Anion Exchange Membranes from Solvent Processable Isoprene Containing Ionomers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, Tsung-Han; Ertem, S. Piril; Maes, Ashley M.

2015-01-28

Random copolymers of isoprene and 4-vinylbenzyl chloride (VBCl) with varying compositions were synthesized via nitroxide-mediated polymerization. Subsequent quaternization afforded solvent processable and cross-linkable ionomers with a wide range of ion exchange capacities (IECs). Solution cast membranes were thermally cross-linked to form anion exchange membranes. Cross-linking was achieved by taking advantage of the unsaturations on the polyisoprene backbone, without added cross-linkers. A strong correlation was found between water uptake and ion conductivity of the membranes: conductivities of the membranes with IECs beyond a critical value were found to be constant related to their high water absorption. Environmentally controlled small-angle X-ray scatteringmore » experiments revealed a correlation between the average distance between ionic clusters and the ion conductivity, indicating that a well-connected network of ion clusters is necessary for efficient ion conduction and high ion conductivity.« less

Transport through correlated systems with density functional theory

NASA Astrophysics Data System (ADS)

Kurth, S.; Stefanucci, G.

2017-10-01

We present recent advances in density functional theory (DFT) for applications in the field of quantum transport, with particular emphasis on transport through strongly correlated systems. We review the foundations of the popular Landauer-Büttiker(LB)  +  DFT approach. This formalism, when using approximations to the exchange-correlation (xc) potential with steps at integer occupation, correctly captures the Kondo plateau in the zero bias conductance at zero temperature but completely fails to capture the transition to the Coulomb blockade (CB) regime as the temperature increases. To overcome the limitations of LB  +  DFT, the quantum transport problem is treated from a time-dependent (TD) perspective using TDDFT, an exact framework to deal with nonequilibrium situations. The steady-state limit of TDDFT shows that in addition to an xc potential in the junction, there also exists an xc correction to the applied bias. Open shell molecules in the CB regime provide the most striking examples of the importance of the xc bias correction. Using the Anderson model as guidance we estimate these corrections in the limit of zero bias. For the general case we put forward a steady-state DFT which is based on one-to-one correspondence between the pair of basic variables, steady density on and steady current across the junction and the pair local potential on and bias across the junction. Like TDDFT, this framework also leads to both an xc potential in the junction and an xc correction to the bias. Unlike TDDFT, these potentials are independent of history. We highlight the universal features of both xc potential and xc bias corrections for junctions in the CB regime and provide an accurate parametrization for the Anderson model at arbitrary temperatures and interaction strengths, thus providing a unified DFT description for both Kondo and CB regimes and the transition between them.

Physical Forces between Humans and How Humans Attract and Repel Each Other Based on Their Social Interactions in an Online World

PubMed Central

Thurner, Stefan; Fuchs, Benedikt

2015-01-01

Physical interactions between particles are the result of the exchange of gauge bosons. Human interactions are mediated by the exchange of messages, goods, money, promises, hostilities, etc. While in the physical world interactions and their associated forces have immediate dynamical consequences (Newton’s laws) the situation is not clear for human interactions. Here we quantify the relative acceleration between humans who interact through the exchange of messages, goods and hostilities in a massive multiplayer online game. For this game we have complete information about all interactions (exchange events) between about 430,000 players, and about their trajectories (movements) in the metric space of the game universe at any point in time. We use this information to derive “interaction potentials" for communication, trade and attacks and show that they are harmonic in nature. Individuals who exchange messages and trade goods generally attract each other and start to separate immediately after exchange events end. The form of the interaction potential for attacks mirrors the usual “hit-and-run" tactics of aggressive players. By measuring interaction intensities as a function of distance, velocity and acceleration, we show that “forces" between players are directly related to the number of exchange events. We find an approximate power-law decay of the likelihood for interactions as a function of distance, which is in accordance with previous real world empirical work. We show that the obtained potentials can be understood with a simple model assuming an exchange-driven force in combination with a distance-dependent exchange rate. PMID:26196505

Physical Forces between Humans and How Humans Attract and Repel Each Other Based on Their Social Interactions in an Online World.

PubMed

Thurner, Stefan; Fuchs, Benedikt

2015-01-01

Physical interactions between particles are the result of the exchange of gauge bosons. Human interactions are mediated by the exchange of messages, goods, money, promises, hostilities, etc. While in the physical world interactions and their associated forces have immediate dynamical consequences (Newton's laws) the situation is not clear for human interactions. Here we quantify the relative acceleration between humans who interact through the exchange of messages, goods and hostilities in a massive multiplayer online game. For this game we have complete information about all interactions (exchange events) between about 430,000 players, and about their trajectories (movements) in the metric space of the game universe at any point in time. We use this information to derive "interaction potentials" for communication, trade and attacks and show that they are harmonic in nature. Individuals who exchange messages and trade goods generally attract each other and start to separate immediately after exchange events end. The form of the interaction potential for attacks mirrors the usual "hit-and-run" tactics of aggressive players. By measuring interaction intensities as a function of distance, velocity and acceleration, we show that "forces" between players are directly related to the number of exchange events. We find an approximate power-law decay of the likelihood for interactions as a function of distance, which is in accordance with previous real world empirical work. We show that the obtained potentials can be understood with a simple model assuming an exchange-driven force in combination with a distance-dependent exchange rate.

Carbon dioxide exchange in Norway spruce at the shoot, tree and ecosystem scale.

PubMed

Wallin, G; Linder, S; Lindroth, A; Räntfors, M; Flemberg, S; Grelle, A

2001-08-01

Net CO2 exchange in a 35-year-old boreal Norway spruce (Picea abies (L.) Karst.) forest in northern Sweden was measured at the shoot (NSE), tree (NTE) and ecosystem levels (NEE) by means of shoot cuvettes, whole-tree chambers and the eddy covariance technique, respectively. We compared the dynamics of gross primary production (GPP) at the three levels during the course of a single week. The diurnal dynamics of GPP at each level were estimated by subtracting half-hourly or hourly model-estimated values of total respiration (excluding light-dependent respiration) from net CO(2) exchange. The relationship between temperature and total respiration at each level was derived from nighttime measurements of NSE, NTE and NEE over the course of 1 month. There was a strong linear relationship (r2 = 0.93) between the hourly estimates of GPP at the shoot and tree levels, but the correlation between shoot- and ecosystem-level GPP was weaker (r2 = 0.69). However, the correlation between shoot- and ecosystem-level GPP was improved (r2 = 0.88) if eddy covariance measurements were restricted to periods when friction velocity was > or = 0.5 m s(-1). Daily means were less dependent on friction velocity, giving an r2 value of 0.94 between shoot- and ecosystem-level GPP. The correlation between shoot and tree levels also increased when daily means were compared (r2 = 0.98). Most of the measured variation in carbon exchange rate among the shoot, tree and ecosystem levels was the result of periodic low coupling between vegetation and the atmosphere at the ecosystem level. The results validate the use of measurements at the shoot and tree level for analyzing the contribution of different compartments to net ecosystem CO2 exchange.

Correlated XANES, TEM, and NanoSIMS of presolar graphite grains

NASA Astrophysics Data System (ADS)

Groopman, Evan E.; Nittler, Larry R.

2018-01-01

We report correlated XANES, TEM, and NanoSIMS measurements of twelve presolar graphite grains extracted from primitive meteorites and for which isotopic data indicate predominantly Type-II supernovae origins. We find continued evidence for isotopic heterogeneities in presolar graphite grains, including the first observation of a radial gradient in the inferred initial 26Al/27Al within a presolar graphite grain. The XANES spectra of these samples show a variety of minor absorbances near the C K-edge, attributable to vinyl-keto, aliphatic, carboxyl, and carbonate molecules, as well as possible damage during sample preparation. Each sample exhibits homogeneous C K-edge XANES spectra within the graphite, however, showing no correlation with isotopic heterogeneities. Gradients in the isotope ratios of C, N, O, and Al could be due to both processes during condensation, e.g., mixing in stellar ejecta and granular transport, and post-condensation effects, such as isotope dilution and exchange with isotopically normal material in the early Solar System or laboratory, the latter of which is a significant issue for high-density presolar graphite grains. It remains unknown whether the mechanisms behind isotope exchange would also affect the local chemistry and therefore the XANES spectra. Ti L-edge XANES from most Ti-rich subgrains match standard spectra for TiC and potentially TiCN. A rare rutile (TiO2) subgrain has been identified, though it lacks the lowest energy L3 peak typically seen in standard spectra. Ca has also been identified by EDXS in TiC subgrains, likely due to the decay of live 44Ti at the time of formation. Future NanoSIMS measurements will determine the variability of initial 44Ti in TiC subgrains, an important constraint on mixing in the ejecta of the grains' parent supernovae.

The RPA Atomization Energy Puzzle.

PubMed

Ruzsinszky, Adrienn; Perdew, John P; Csonka, Gábor I

2010-01-12

There is current interest in the random phase approximation (RPA), a "fifth-rung" density functional for the exchange-correlation energy. RPA has full exact exchange and constructs the correlation with the help of the unoccupied Kohn-Sham orbitals. In many cases (uniform electron gas, jellium surface, and free atom), the correction to RPA is a short-ranged effect that is captured by a local spin density approximation (LSDA) or a generalized gradient approximation (GGA). Nonempirical density functionals for the correction to RPA were constructed earlier at the LSDA and GGA levels (RPA+), but they are constructed here at the fully nonlocal level (RPA++), using the van der Waals density functional (vdW-DF) of Langreth, Lundqvist, and collaborators. While they make important and helpful corrections to RPA total and ionization energies of free atoms, they correct the RPA atomization energies of molecules by only about 1 kcal/mol. Thus, it is puzzling that RPA atomization energies are, on average, about 10 kcal/mol lower than those of accurate values from experiment. We find here that a hybrid of 50% Perdew-Burke-Ernzerhof GGA with 50% RPA+ yields atomization energies much more accurate than either one does alone. This suggests a solution to the puzzle: While the proper correction to RPA is short-ranged in some systems, its contribution to the correlation hole can spread out in a molecule with multiple atomic centers, canceling part of the spread of the exact exchange hole (more so than in RPA or RPA+), making the true exchange-correlation hole more localized than in RPA or RPA+. This effect is not captured even by the vdW-DF nonlocality, but it requires the different kind of full nonlocality present in a hybrid functional.

In situ fluorescence spectroscopy correlates ionomer degradation to reactive oxygen species generation in an operating fuel cell.

PubMed

Prabhakaran, Venkateshkumar; Arges, Christopher G; Ramani, Vijay

2013-11-21

The rate of generation of reactive oxygen species (ROS) within the polymer electrolyte membrane (PEM) of an operating proton exchange member fuel cell (PEMFC) was monitored using in situ fluorescence spectroscopy. A modified barrier layer was introduced between the PEM and the electrocatalyst layer to eliminate metal-dye interactions and fluorescence resonance energy transfer (FRET) effects during measurements. Standard fuel cell operating parameters (temperature, relative humidity, and electrode potential) were systematically varied to evaluate their influence on the rate of ROS generation during PEMFC operation. Independently, the macroscopic rate of PEM degradation was measured by monitoring the fluoride ion emission rate (FER) in the effluent stream at each operating condition. The ROS generation reaction rate constant (estimated from the in situ fluorescence experiments) correlated perfectly with the measured FER across all conditions, demonstrating unequivocally for the first time that a direct correlation exists between in situ ROS generation and PEM macroscopic degradation. The activation energy for ROS generation within the PEM was estimated to be 12.5 kJ mol(-1).

Ex vivo assessment and validation of water exchange performance of 23 heat and moisture exchangers for laryngectomized patients.

PubMed

van den Boer, Cindy; Muller, Sara H; Vincent, Andrew D; van den Brekel, Michiel W M; Hilgers, Frans J M

2014-08-01

Breathing through a tracheostoma results in insufficient warming and humidification of the inspired air. This loss of air conditioning, especially humidification, can be partially restored with the application of a heat and moisture exchanger (HME) over the tracheostoma. For medical professionals, it is not easy to judge differences in water exchange performance of various HMEs owing to the lack of universal outcome measures. This study has three aims: assessment of the water exchange performance of commercially available HMEs for laryngectomized patients, validation of these results with absolute humidity outcomes, and assessment of the role of hygroscopic salt present in some of the tested HMEs. Measurements of weight and absolute humidity at end inspiration and end expiration at different breathing volumes of a healthy volunteer were performed using a microbalance and humidity sensor. Twenty-three HMEs from 6 different manufacturers were tested. Associations were determined between core weight, weight change, breathing volume, and absolute humidity, using both linear and nonlinear mixed effects models. Water exchange of the 23 HMEs at a breathing volume of 0.5 L varies between 0.5 and 3.6 mg. Both water exchange and wet core weight correlate strongly with the end-inspiratory absolute humidity values (r2 =0.89/0.87). Hygroscopic salt increases core weight. The 23 tested HMEs for laryngectomized patients show wide variation in water exchange performance. Water exchange correlates well with the end-inspiratory absolute humidity outcome, which validates the ex vivo weight change method. Wet core weight is a predictor of HME performance. Hygroscopic salt increases the weight of the core material. The results of this study can help medical professionals to obtain a more founded opinion about the performance of available HMEs for pulmonary rehabilitation in laryngectomized patients, and allow them to make an informed decision about which HME type to use.

Exchange and Inelastic OH(+) + H Collisions on the Doublet and Quartet Electronic States.

PubMed

Bulut, Niyazi; Lique, François; Roncero, Octavio

2015-12-17

The exchange and inelastic state-to-state cross sections for the OH(+) + H collisions are computed from wave packet calculations using the doublet and quartet ground electronic potential energy surface (PES) correlating to the open shell reactants, for collision energies in the range of 1 meV to 0.7 eV. The doublet PES presents a deep insertion well, of ≈6 eV, but the exchange reaction has a rather low probability, showing that the mechanism is not statistical. This well is also responsible of a rather high rotational energy transfer, which makes the rigid-rotor approach overestimate the cross section for low Δj transitions and for high collisonal energies. The quartet PES, with a much shallower well, also presents a low exchange reaction cross section, but the inelastic state-to-state cross sections are very well reproduced by rigid-rotor calculations. When the electronic partition is used to obtain the total state-to-state cross section, the contribution of the doublet state becomes small, and the resulting total cross sections become close to those obtained for the quartet state. Thus, the total (quartet and doublet) cross sections for this open shell system can be reproduced rather satisfactorily by those obtained with the rigid-rotor approximation on the quartet state. Finally, we compare the new OH(+)-H cross sections with OH(+)-He ones recently computed. We found significant differences, especially for transitions with large Δj showing that specific OH(+)-H calculations had to be performed to accurately analyze the OH(+) emission from interstellar molecular clouds.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Hamdani, Yasmine S.; Alfè, Dario; von Lilienfeld, O. Anatole

Density functional theory (DFT) studies of weakly interacting complexes have recently focused on the importance of van der Waals dispersion forces, whereas the role of exchange has received far less attention. Here, by exploiting the subtle binding between water and a boron and nitrogen doped benzene derivative (1,2-azaborine) we show how exact exchange can alter the binding conformation within a complex. Benchmark values have been calculated for three orientations of the water monomer on 1,2-azaborine from explicitly correlated quantum chemical methods, and we have also used diffusion quantum Monte Carlo. For a host of popular DFT exchange-correlation functionals we showmore » that the lack of exact exchange leads to the wrong lowest energy orientation of water on 1,2-azaborine. As such, we suggest that a high proportion of exact exchange and the associated improvement in the electronic structure could be needed for the accurate prediction of physisorption sites on doped surfaces and in complex organic molecules. Meanwhile to predict correct absolute interaction energies an accurate description of exchange needs to be augmented by dispersion inclusive functionals, and certain non-local van der Waals functionals (optB88- and optB86b-vdW) perform very well for absolute interaction energies. Through a comparison with water on benzene and borazine (B₃N₃H₆) we show that these results could have implications for the interaction of water with doped graphene surfaces, and suggest a possible way of tuning the interaction energy.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Hamdani, Yasmine S.; Michaelides, Angelos, E-mail: angelos.michaelides@ucl.ac.uk; Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ

Density functional theory (DFT) studies of weakly interacting complexes have recently focused on the importance of van der Waals dispersion forces, whereas the role of exchange has received far less attention. Here, by exploiting the subtle binding between water and a boron and nitrogen doped benzene derivative (1,2-azaborine) we show how exact exchange can alter the binding conformation within a complex. Benchmark values have been calculated for three orientations of the water monomer on 1,2-azaborine from explicitly correlated quantum chemical methods, and we have also used diffusion quantum Monte Carlo. For a host of popular DFT exchange-correlation functionals we showmore » that the lack of exact exchange leads to the wrong lowest energy orientation of water on 1,2-azaborine. As such, we suggest that a high proportion of exact exchange and the associated improvement in the electronic structure could be needed for the accurate prediction of physisorption sites on doped surfaces and in complex organic molecules. Meanwhile to predict correct absolute interaction energies an accurate description of exchange needs to be augmented by dispersion inclusive functionals, and certain non-local van der Waals functionals (optB88- and optB86b-vdW) perform very well for absolute interaction energies. Through a comparison with water on benzene and borazine (B{sub 3}N{sub 3}H{sub 6}) we show that these results could have implications for the interaction of water with doped graphene surfaces, and suggest a possible way of tuning the interaction energy.« less

Compressibility of the protein-water interface

NASA Astrophysics Data System (ADS)

Persson, Filip; Halle, Bertil

2018-06-01

The compressibility of a protein relates to its stability, flexibility, and hydrophobic interactions, but the measurement, interpretation, and computation of this important thermodynamic parameter present technical and conceptual challenges. Here, we present a theoretical analysis of protein compressibility and apply it to molecular dynamics simulations of four globular proteins. Using additively weighted Voronoi tessellation, we decompose the solution compressibility into contributions from the protein and its hydration shells. We find that positively cross-correlated protein-water volume fluctuations account for more than half of the protein compressibility that governs the protein's pressure response, while the self correlations correspond to small (˜0.7%) fluctuations of the protein volume. The self compressibility is nearly the same as for ice, whereas the total protein compressibility, including cross correlations, is ˜45% of the bulk-water value. Taking the inhomogeneous solvent density into account, we decompose the experimentally accessible protein partial compressibility into intrinsic, hydration, and molecular exchange contributions and show how they can be computed with good statistical accuracy despite the dominant bulk-water contribution. The exchange contribution describes how the protein solution responds to an applied pressure by redistributing water molecules from lower to higher density; it is negligibly small for native proteins, but potentially important for non-native states. Because the hydration shell is an open system, the conventional closed-system compressibility definitions yield a pseudo-compressibility. We define an intrinsic shell compressibility, unaffected by occupation number fluctuations, and show that it approaches the bulk-water value exponentially with a decay "length" of one shell, less than the bulk-water compressibility correlation length. In the first hydration shell, the intrinsic compressibility is 25%-30% lower than in bulk water, whereas its self part is 15%-20% lower. These large reductions are caused mainly by the proximity to the more rigid protein and are not a consequence of the perturbed water structure.

Compressibility of the protein-water interface.

PubMed

Persson, Filip; Halle, Bertil

2018-06-07

The compressibility of a protein relates to its stability, flexibility, and hydrophobic interactions, but the measurement, interpretation, and computation of this important thermodynamic parameter present technical and conceptual challenges. Here, we present a theoretical analysis of protein compressibility and apply it to molecular dynamics simulations of four globular proteins. Using additively weighted Voronoi tessellation, we decompose the solution compressibility into contributions from the protein and its hydration shells. We find that positively cross-correlated protein-water volume fluctuations account for more than half of the protein compressibility that governs the protein's pressure response, while the self correlations correspond to small (∼0.7%) fluctuations of the protein volume. The self compressibility is nearly the same as for ice, whereas the total protein compressibility, including cross correlations, is ∼45% of the bulk-water value. Taking the inhomogeneous solvent density into account, we decompose the experimentally accessible protein partial compressibility into intrinsic, hydration, and molecular exchange contributions and show how they can be computed with good statistical accuracy despite the dominant bulk-water contribution. The exchange contribution describes how the protein solution responds to an applied pressure by redistributing water molecules from lower to higher density; it is negligibly small for native proteins, but potentially important for non-native states. Because the hydration shell is an open system, the conventional closed-system compressibility definitions yield a pseudo-compressibility. We define an intrinsic shell compressibility, unaffected by occupation number fluctuations, and show that it approaches the bulk-water value exponentially with a decay "length" of one shell, less than the bulk-water compressibility correlation length. In the first hydration shell, the intrinsic compressibility is 25%-30% lower than in bulk water, whereas its self part is 15%-20% lower. These large reductions are caused mainly by the proximity to the more rigid protein and are not a consequence of the perturbed water structure.

75 FR 39074 - Self-Regulatory Organizations; EDGA Exchange, Inc.; Notice of Filing of Proposed Rule Change To...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-07-07

... but not in the stocks that underlie that ETF, what consequences might that have for the underlying stocks or other products? What are the potential effects on price discovery for the ETF, the underlying..., ETPs include Exchange Traded Funds (``ETF''),\\3\\ Exchange Traded Vehicles (``ETV''),\\4\\ and Exchange...

Simulation of angular-resolved RABBITT measurements in noble-gas atoms

NASA Astrophysics Data System (ADS)

Bray, Alexander W.; Naseem, Faiza; Kheifets, Anatoli S.

2018-06-01

We simulate angular-resolved RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) measurements on valence shells of noble-gas atoms (Ne, Ar, Kr, and Xe). Our nonperturbative numerical simulation is based on solution of the time-dependent Schrödinger equation (TDSE) for a target atom driven by an ionizing XUV and dressing IR fields. From these simulations we extract the angular-dependent magnitude and phase of the RABBITT oscillations and deduce the corresponding angular anisotropy β parameter and Wigner time delay τW for the single XUV photon absorption that initiates the RABBITT process. Said β and τW parameters are compared with calculations in the random-phase approximation with exchange (RPAE), which includes intershell correlation. This comparison is used to test various effective potentials employed in the one-electron TDSE. In lighter atoms (Ne and Ar), several effective potentials are found to provide accurate simulations of RABBITT measurements for a wide range of photon energies up to 100 eV above the valence-shell threshold. In heavier atoms (Kr and Xe), the onset of strong correlation with the d shell restricts the validity of the single active electron approximation to several tens of eV above the valence-shell threshold.