Sample records for valence electronic state

  1. Ultrafast dynamics of low-energy electron attachment via a non-valence correlation-bound state

    NASA Astrophysics Data System (ADS)

    Rogers, Joshua P.; Anstöter, Cate S.; Verlet, Jan R. R.

    2018-03-01

    The primary electron-attachment process in electron-driven chemistry represents one of the most fundamental chemical transformations with wide-ranging importance in science and technology. However, the mechanistic detail of the seemingly simple reaction of an electron and a neutral molecule to form an anion remains poorly understood, particularly at very low electron energies. Here, time-resolved photoelectron imaging was used to probe the electron-attachment process to a non-polar molecule using time-resolved methods. An initially populated diffuse non-valence state of the anion that is bound by correlation forces evolves coherently in ∼30 fs into a valence state of the anion. The extreme efficiency with which the correlation-bound state serves as a doorway state for low-energy electron attachment explains a number of electron-driven processes, such as anion formation in the interstellar medium and electron attachment to fullerenes.

  2. Real-time observation of valence electron motion.

    PubMed

    Goulielmakis, Eleftherios; Loh, Zhi-Heng; Wirth, Adrian; Santra, Robin; Rohringer, Nina; Yakovlev, Vladislav S; Zherebtsov, Sergey; Pfeifer, Thomas; Azzeer, Abdallah M; Kling, Matthias F; Leone, Stephen R; Krausz, Ferenc

    2010-08-05

    The superposition of quantum states drives motion on the atomic and subatomic scales, with the energy spacing of the states dictating the speed of the motion. In the case of electrons residing in the outer (valence) shells of atoms and molecules which are separated by electronvolt energies, this means that valence electron motion occurs on a subfemtosecond to few-femtosecond timescale (1 fs = 10(-15) s). In the absence of complete measurements, the motion can be characterized in terms of a complex quantity, the density matrix. Here we report an attosecond pump-probe measurement of the density matrix of valence electrons in atomic krypton ions. We generate the ions with a controlled few-cycle laser field and then probe them through the spectrally resolved absorption of an attosecond extreme-ultraviolet pulse, which allows us to observe in real time the subfemtosecond motion of valence electrons over a multifemtosecond time span. We are able to completely characterize the quantum mechanical electron motion and determine its degree of coherence in the specimen of the ensemble. Although the present study uses a simple, prototypical open system, attosecond transient absorption spectroscopy should be applicable to molecules and solid-state materials to reveal the elementary electron motions that control physical, chemical and biological properties and processes.

  3. Study of average valence and valence electron distribution of several oxides using X-ray photoelectron spectra

    NASA Astrophysics Data System (ADS)

    Ding, L. L.; Wu, L. Q.; Ge, X. S.; Du, Y. N.; Qian, J. J.; Tang, G. D.; Zhong, W.

    2018-06-01

    X-ray photoelectron spectra of the O 1s electrons of MnFe2O4, ZnFe2O4, ZnO, and CaO were used to estimate the average valence, ValO, of the oxygen anions in these samples. The absolute values of ValO for these samples were found to be distinctly lower than the traditional value of 2.0, suggesting that the total average valences of the cations are also lower than the conventionally accepted values owing to valence balance in the compounds. In addition, we analyzed the valence band spectra of the samples and investigated the distribution characteristics of the valence electrons.

  4. Pressure-induced valence change and moderate heavy fermion state in Eu-compounds

    NASA Astrophysics Data System (ADS)

    Honda, Fuminori; Okauchi, Keigo; Sato, Yoshiki; Nakamura, Ai; Akamine, Hiromu; Ashitomi, Yosuke; Hedo, Masato; Nakama, Takao; Takeuchi, Tetsuya; Valenta, Jaroslav; Prchal, Jiri; Sechovský, Vladimir; Aoki, Dai; Ōnuki, Yoshichika

    2018-05-01

    A pressure-induced valence transition has attracted much attention in Eu-compounds. Among them, EuRh2Si2, EuNi2Ge2, and EuCo2Ge2 reveal the valence transition around 1, 2, and 3 GPa, respectively. We have succeeded in growing single crystals of EuT2X2 (T: transition metal, X: Si, Ge) and studied electronic properties under pressure. EuRh2Si2 indicates a first-order valence transition between 1 and 2 GPa, with a large and prominent hysteresis in the electrical resistivity. At higher pressures, the first-order valence transition changes to a cross-over regime with an intermediate valence state. Tuning of the valence state with pressure is reflected in a drastic change of the temperature dependence of the electrical resistivity in EuRh2Si2 single crystals. Effect of pressure on the valence states on EuRh2Si2, EuIr2Si2, EuNi2Ge2, and EuCo2Ge2, as well as an isostructural related compound EuGa4, are reviewed.

  5. Valence electronic properties of porphyrin derivatives.

    PubMed

    Stenuit, G; Castellarin-Cudia, C; Plekan, O; Feyer, V; Prince, K C; Goldoni, A; Umari, P

    2010-09-28

    We present a combined experimental and theoretical investigation of the valence electronic structure of porphyrin-derived molecules. The valence photoemission spectra of the free-base tetraphenylporphyrin and of the octaethylporphyrin molecule were measured using synchrotron radiation and compared with theoretical spectra calculated using the GW method and the density-functional method within the generalized gradient approximation. Only the GW results could reproduce the experimental data. We found that the contribution to the orbital energies due to electronic correlations has the same linear behavior in both molecules, with larger deviations in the vicinity of the HOMO level. This shows the importance of adequate treatment of electronic correlations in these organic systems.

  6. Electric-field-driven electron-transfer in mixed-valence molecules.

    PubMed

    Blair, Enrique P; Corcelli, Steven A; Lent, Craig S

    2016-07-07

    Molecular quantum-dot cellular automata is a computing paradigm in which digital information is encoded by the charge configuration of a mixed-valence molecule. General-purpose computing can be achieved by arranging these compounds on a substrate and exploiting intermolecular Coulombic coupling. The operation of such a device relies on nonequilibrium electron transfer (ET), whereby the time-varying electric field of one molecule induces an ET event in a neighboring molecule. The magnitude of the electric fields can be quite large because of close spatial proximity, and the induced ET rate is a measure of the nonequilibrium response of the molecule. We calculate the electric-field-driven ET rate for a model mixed-valence compound. The mixed-valence molecule is regarded as a two-state electronic system coupled to a molecular vibrational mode, which is, in turn, coupled to a thermal environment. Both the electronic and vibrational degrees-of-freedom are treated quantum mechanically, and the dissipative vibrational-bath interaction is modeled with the Lindblad equation. This approach captures both tunneling and nonadiabatic dynamics. Relationships between microscopic molecular properties and the driven ET rate are explored for two time-dependent applied fields: an abruptly switched field and a linearly ramped field. In both cases, the driven ET rate is only weakly temperature dependent. When the model is applied using parameters appropriate to a specific mixed-valence molecule, diferrocenylacetylene, terahertz-range ET transfer rates are predicted.

  7. Electric-field-driven electron-transfer in mixed-valence molecules

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

    Blair, Enrique P., E-mail: enrique-blair@baylor.edu; Corcelli, Steven A., E-mail: scorcell@nd.edu; Lent, Craig S., E-mail: lent@nd.edu

    2016-07-07

    Molecular quantum-dot cellular automata is a computing paradigm in which digital information is encoded by the charge configuration of a mixed-valence molecule. General-purpose computing can be achieved by arranging these compounds on a substrate and exploiting intermolecular Coulombic coupling. The operation of such a device relies on nonequilibrium electron transfer (ET), whereby the time-varying electric field of one molecule induces an ET event in a neighboring molecule. The magnitude of the electric fields can be quite large because of close spatial proximity, and the induced ET rate is a measure of the nonequilibrium response of the molecule. We calculate themore » electric-field-driven ET rate for a model mixed-valence compound. The mixed-valence molecule is regarded as a two-state electronic system coupled to a molecular vibrational mode, which is, in turn, coupled to a thermal environment. Both the electronic and vibrational degrees-of-freedom are treated quantum mechanically, and the dissipative vibrational-bath interaction is modeled with the Lindblad equation. This approach captures both tunneling and nonadiabatic dynamics. Relationships between microscopic molecular properties and the driven ET rate are explored for two time-dependent applied fields: an abruptly switched field and a linearly ramped field. In both cases, the driven ET rate is only weakly temperature dependent. When the model is applied using parameters appropriate to a specific mixed-valence molecule, diferrocenylacetylene, terahertz-range ET transfer rates are predicted.« less

  8. Optoelectronic properties of valence-state-controlled amorphous niobium oxide

    NASA Astrophysics Data System (ADS)

    Onozato, Takaki; Katase, Takayoshi; Yamamoto, Akira; Katayama, Shota; Matsushima, Koichi; Itagaki, Naho; Yoshida, Hisao; Ohta, Hiromichi

    2016-06-01

    In order to understand the optoelectronic properties of amorphous niobium oxide (a-NbO x ), we have investigated the valence states, local structures, electrical resistivity, and optical absorption of a-NbO x thin films with various oxygen contents. It was found that the valence states of Nb ion in a-NbO x films can be controlled from 5+  to 4+  by reducing oxygen pressure during film deposition at room temperature, together with changing the oxide-ion arrangement around Nb ion from Nb2O5-like to NbO2-like local structure. As a result, a four orders of magnitude reduction in the electrical resistivity of a-NbO x films was observed with decreasing oxygen content, due to the carrier generation caused by the appearance and increase of an oxygen-vacancy-related subgap state working as an electron donor. The tunable optoelectronic properties of a-NbO x films by valence-state-control with oxygen-vacancy formation will be useful for potential flexible optoelectronic device applications.

  9. Valence-state reflectometry of complex oxide heterointerfaces

    DOE PAGES

    Hamann-Borrero, Jorge E.; Macke, Sebastian; Choi, Woo Seok; ...

    2016-09-16

    Emergent phenomena in transition-metal-oxide heterostructures such as interface superconductivity and magnetism have been attributed to electronic reconstruction, which, however, is difficult to detect and characterise. Here we overcome the associated difficulties to simultaneously address the electronic degrees of freedom and distinguish interface from bulk effects by implementing a novel approach to resonant X-ray reflectivity (RXR). Our RXR study of the chemical and valance profiles along the polar (001) direction of a LaCoO 3 film on NdGaO 3 reveals a pronounced valence-state reconstruction from Co 3+ in the bulk to Co 2+ at the surface, with an areal density close tomore » 0.5 Co 2+ ions per unit cell. An identical film capped with polar (001) LaAlO 3 maintains the Co 3+ valence over its entire thickness. As a result, we interpret this as evidence for electronic reconstruction in the uncapped film, involving the transfer of 0.5e – per unit cell to the subsurface CoO 2 layer at its LaO-terminated polar surface.« less

  10. Teaching Valence Shell Electron Pair Repulsion (VSEPR) Theory

    ERIC Educational Resources Information Center

    Talbot, Christopher; Neo, Choo Tong

    2013-01-01

    This "Science Note" looks at the way that the shapes of simple molecules can be explained in terms of the number of electron pairs in the valence shell of the central atom. This theory is formally known as valence shell electron pair repulsion (VSEPR) theory. The article explains the preferred shape of chlorine trifluoride (ClF3),…

  11. Fast mapping of the cobalt-valence state in Ba0.5Sr0.5Co0.8Fe0.2O3-d by electron energy loss spectroscopy.

    PubMed

    Müller, Philipp; Meffert, Matthias; Störmer, Heike; Gerthsen, Dagmar

    2013-12-01

    A fast method for determination of the Co-valence state by electron energy loss spectroscopy in a transmission electron microscope is presented. We suggest the distance between the Co-L3 and Co-L2 white-lines as a reliable property for the determination of Co-valence states between 2+ and 3+. The determination of the Co-L2,3 white-line distance can be automated and is therefore well suited for the evaluation of large data sets that are collected for line scans and mappings. Data with a low signal-to-noise due to short acquisition times can be processed by applying principal component analysis. The new technique was applied to study the Co-valence state of Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF), which is hampered by the superposition of the Ba-M4,5 white-lines on the Co-L2,3 white-lines. The Co-valence state of the cubic BSCF phase was determined to be 2.2+ (±0.2) after annealing for 100 h at 650°C, compared to an increased valence state of 2.8+ (±0.2) for the hexagonal phase. These results support models that correlate the instability of the cubic BSCF phase with an increased Co-valence state at temperatures below 840°C.

  12. Direct Electron Impact Excitation of Rydberg-Valence States of Molecular Nitrogen

    NASA Astrophysics Data System (ADS)

    Malone, C. P.; Johnson, P. V.; Liu, X.; Ajdari, B.; Muleady, S.; Kanik, I.; Khakoo, M. A.

    2012-12-01

    Collisions between electrons and neutral N2 molecules result in emissions that provide an important diagnostic probe for understanding the ionospheric energy balance and the effects of space weather in upper atmospheres. Also, transitions to singlet ungerade states cause N2 to be a strong absorber of solar radiation in the EUV spectral range where many ro-vibrational levels of these Rydberg-valence (RV) states are predissociative. Thus, their respective excitation and emission cross sections are important parameters for understanding the [N]/[N2] ratio in the thermosphere of nitrogen dominated atmospheres. The following work provides improved constraints on absolute and relative excitation cross sections of numerous RV states of N2, enabling more physically accurate atmospheric modeling. Here, we present recent integral cross sections (ICSs) for electron impact excitation of RV states of N2 [6], which were based on the differential cross sections (DCSs) derived from electron energy-loss (EEL) spectra of [5]. This work resulted in electronic excitation cross sections over the following measured vibrational levels: b 1Πu (v‧=0-14), c3 1Πu (v‧=0-3), o3 1Πu (v‧=0-3), b‧ 1Σu+ (v‧=0-10), c‧4 1Σu+ (v‧=0-3), G 3Πu (v‧=0-3), and F 3Πu (v‧=0-3). We further adjusted the cross sections of the RV states by extending the vibronic contributions to unmeasured v‧-levels via the relative excitation probabilities (REPs) as discussed in [6]. This resulted in REP-scaled ICSs over the following vibrational levels for the singlet ungerade states: b(0-19), c3(0-4), o3(0-4), b‧(0-16), and c‧4(0-8). Comparison of the ICSs of [6] with available EEL based measurements, theoretical calculations, and emission based work generally shows good agreement within error estimations, except with the recent reevaluation provided by [1]. Further, we have extended these results, using the recent EEL data of [3], to include the unfolding of better resolved features above ~13

  13. Solvent dynamical control of ultrafast ground state electron transfer: implications for Class II-III mixed valency.

    PubMed

    Lear, Benjamin J; Glover, Starla D; Salsman, J Catherine; Londergan, Casey H; Kubiak, Clifford P

    2007-10-24

    We relate the solvent and temperature dependence of the rates of intramolecular electron transfer (ET) of mixed valence complexes of the type {[Ru3O(OAc)6(CO)(L)]2-BL}-1, where L = pyridyl ligand and BL = pyrazine. Complexes were reduced chemically or electrochemically to obtain the mixed valence anions in seven solvents: acetonitrile, methylene chloride, dimethylformamide, tetrahydrofuran, dimethylsulfoxide, chloroform, and hexamethylphosphoramide. Rate constants for intramolecular ET were estimated by simulating the observed degree of nu(CO) IR band shape coalescence in the mixed valence state. Correlations between rate constants for ET and solvent properties including static dielectric constant, optical dielectric constant, the quantity 1/epsilonop - 1/epsilonS, microscopic solvent polarity, viscosity, cardinal rotational moments of inertia, and solvent relaxation times were examined. In the temperature study, the complexes displayed a sharp increase in the ket as the freezing points of the solvents methylene chloride and acetonitrile were approached. The solvent phase transition causes a localized-to-delocalized transition in the mixed valence ions and an acceleration in the rate of ET. This is explained in terms of decoupling the slower solvent motions involved in the frequency factor nuN which increases the value of nuN. The observed solvent and temperature dependence of the ket for these complexes is used in order to formulate a new definition for Robin-Day class II-III mixed valence compounds. Specifically, it is proposed that class II-III compounds are those for which thermodynamic properties of the solvent exert no control over ket, but the dynamic properties of the solvent still influence ket.

  14. Lie algebraic approach to valence bond theory of π-electron systems: a preliminary study of excited states

    NASA Astrophysics Data System (ADS)

    Paldus, J.; Li, X.

    1992-10-01

    Following a brief outline of various developments and exploitations of the unitary group approach (UGA), and its extension referred to as Clifford algebra UGA (CAUGA), in molecular electronic structure calculations, we present a summary of a recently introduced implementation of CAUGA for the valence bond (VB) method based on the Pariser-Parr-Pople (PPP)-type Hamiltonian. The existing applications of this PPP-VB approach have been limited to groundstates of various π-electron systems or, at any rate, to the lowest states of a given multiplicity. In this paper the method is applied to the low-lying excited states of several archetypal models, namely cyclobutadiene and benzene, representing antiaromatic and aromatic systems, hexatriene, representing linear polyenic systems and, finally, naphthalene, representing polyacenes.

  15. The valence-fluctuating ground state of plutonium

    DOE PAGES

    Janoschek, Marc; Das, Pinaki; Chakrabarti, Bismayan; ...

    2015-07-10

    A central issue in material science is to obtain understanding of the electronic correlations that control complex materials. Such electronic correlations frequently arise because of the competition of localized and itinerant electronic degrees of freedom. Although the respective limits of well-localized or entirely itinerant ground states are well understood, the intermediate regime that controls the functional properties of complex materials continues to challenge theoretical understanding. We have used neutron spectroscopy to investigate plutonium, which is a prototypical material at the brink between bonding and nonbonding configurations. In addition, our study reveals that the ground state of plutonium is governed bymore » valence fluctuations, that is, a quantum mechanical superposition of localized and itinerant electronic configurations as recently predicted by dynamical mean field theory. Our results not only resolve the long-standing controversy between experiment and theory on plutonium’s magnetism but also suggest an improved understanding of the effects of such electronic dichotomy in complex materials.« less

  16. XPEEM valence state imaging of mineral micro-intergrowths with a spatial resolution of 100nm

    NASA Astrophysics Data System (ADS)

    Smith, A. D.; Schofield, P. F.; Scholl, A.; Pattrick, R. A. D.; Bridges, J. C.

    2003-03-01

    The crystal chemistry and textural relationships of minerals hold a vast amount of information relating to the formation, history and stability of natural materials. The application of soft X-ray spectroscopy to mineralogical material has revealed that 2p (L{2,3}) spectra provide a sensitive fingerprint of the electronic states of 3d metals. In bulk powdered samples much of the textural and microstructural information is lost, but the area-selectivity capability of X-ray Photo-Emission Electron Microscopy (XPEEM) provides the ability to obtain valence state information from mineral intergrowths with a submicron spatial resolution. Using the state-of-the-art PEEM2 facility on beamline 7.3.1.1 at the Advanced Light Source, Berkeley, USA, a range of minerals, mineral intergrowths and mineralogical textures have been studied for a broad suite of geological, planetary and environmental science materials. High-quality, multi-element valence images have been obtained showing the distribution/variation of the metal valence states across single grains or mineral intergrowths/textures at the l00 nm scale and quantitative valence state ratios can be obtained from areas of 0.01 μ m^2.

  17. Outer-valence Electron Spectra of Prototypical Aromatic Heterocycles from an Optimally Tuned Range-Separated Hybrid Functional

    PubMed Central

    2014-01-01

    Density functional theory with optimally tuned range-separated hybrid (OT-RSH) functionals has been recently suggested [Refaely-Abramson et al. Phys. Rev. Lett.2012, 109, 226405] as a nonempirical approach to predict the outer-valence electronic structure of molecules with the same accuracy as many-body perturbation theory. Here, we provide a quantitative evaluation of the OT-RSH approach by examining its performance in predicting the outer-valence electron spectra of several prototypical gas-phase molecules, from aromatic rings (benzene, pyridine, and pyrimidine) to more complex organic systems (terpyrimidinethiol and copper phthalocyanine). For a range up to several electronvolts away from the frontier orbital energies, we find that the outer-valence electronic structure obtained from the OT-RSH method agrees very well (typically within ∼0.1–0.2 eV) with both experimental photoemission and theoretical many-body perturbation theory data in the GW approximation. In particular, we find that with new strategies for an optimal choice of the short-range fraction of Fock exchange, the OT-RSH approach offers a balanced description of localized and delocalized states. We discuss in detail the sole exception found—a high-symmetry orbital, particular to small aromatic rings, which is relatively deep inside the valence state manifold. Overall, the OT-RSH method is an accurate DFT-based method for outer-valence electronic structure prediction for such systems and is of essentially the same level of accuracy as contemporary GW approaches, at a reduced computational cost. PMID:24839410

  18. In search for an optimal methodology to calculate the valence electron affinities of temporary anions.

    PubMed

    Puiatti, Marcelo; Vera, D Mariano A; Pierini, Adriana B

    2009-10-28

    Recently, we have proposed an approach for finding the valence anion ground state, based on the stabilization exerted by a polar solvent; the methodology used standard DFT methods and relatively inexpensive basis sets and yielded correct electron affinity (EA) values by gradually decreasing the dielectric constant of the medium. In order to address the overall performance of the new methodology, to find the best conditions for stabilizing the valence state and to evaluate its scope and limitations, we gathered a pool of 60 molecules, 25 of them bearing the conventional valence state as the ground anion and 35 for which the lowest anion state found holds the extra electron in a diffuse orbital around the molecule (non valence state). The results obtained by testing this representative set suggest a very good performance for most species having an experimental EA less negative than -3.0 eV; the correlation at the B3LYP/6-311+G(2df,p) level being y = 1.01x + 0.06, with a correlation index of 0.985. As an alternative, the time dependent DFT (TD-DFT) approach was also tested with both B3LYP and PBE0 functionals. The methodology we proposed shows a comparable or better accuracy with respect to TD-DFT, although the TD-DFT approach with the PBE0 functional is suggested as a suitable estimate for species with the most negative EAs (ca.-2.5 to -3.5 eV), for which stabilization strategies can hardly reach the valence state. As an application, a pool of 8 compounds of key biological interest with EAs which remain unknown or unclear were predicted using the new methodology.

  19. Reactivity of seventeen- and nineteen-valence electron complexes in organometallic chemistry

    NASA Technical Reports Server (NTRS)

    Stiegman, Albert E.; Tyler, David R.

    1986-01-01

    A guideline to the reactivity of 17- and 19-valence electron species in organometallic chemistry is proposed which the authors believe will supersede all others. The thesis holds that the reactions of 17-electron metal radicals are associatively activated with reactions proceeding through a 19-valence electron species. The disparate reaction chemistry of the 17-electron metal radicals are unified in terms of this associative reaction pathway, and the intermediacy of 19-valence electron complexes in producing the observed products is discussed. It is suggested that related associatively activated pathways need to be considered in some reactions that are thought to occur by more conventional routes involving 16- and 18-electron intermediates. The basic reaction chemistry and electronic structures of these species are briefly discussed.

  20. Inelastic collisions of positrons with one-valence-electron targets

    NASA Technical Reports Server (NTRS)

    Abdel-Raouf, Mohamed Assad

    1990-01-01

    The total elastic and positronium formation cross sections of the inelastic collisions between positrons and various one-valence-electron atoms, (namely hydrogen, lithium, sodium, potassium and rubidium), and one-valence-electron ions, (namely hydrogen-like, lithium-like and alkaline-earth positive ions) are determined using an elaborate modified coupled-static approximation. Special attention is devoted to the behavior of the Ps cross sections at the energy regions lying above the Ps formation thresholds.

  1. The stabilities and electron structures of Al-Mg clusters with 18 and 20 valence electrons

    NASA Astrophysics Data System (ADS)

    Yang, Huihui; Chen, Hongshan

    2017-07-01

    The spherical jellium model predicts that metal clusters having 18 and 20 valence electrons correspond to the magic numbers and will show specific stabilities. We explore in detail the geometric structures, stabilities and electronic structures of Al-Mg clusters containing 18 and 20 valence electrons by using genetic algorithm combined with density functional theories. The stabilities of the clusters are governed by the electronic configurations and Mg/Al ratios. The clusters with lower Mg/Al ratios are more stable. The molecular orbitals accord with the shell structures predicted by the jellium model but the 2S level interweaves with the 1D levels and the 2S and 1D orbitals form a subgroup. The clusters having 20 valence electrons form closed 1S21P61D102S2 shells and show enhanced stability. The Al-Mg clusters with a valence electron count of 18 do not form closed shells because one 1D orbital is unoccupied. The ionization potential and electron affinity are closely related to the electronic configurations; their values are determined by the subgroups the HOMO or LUMO belong to. Supplementary material in the form of one pdf file available from the Journal web page at http://https://doi.org/10.1140/epjd/e2017-80042-9

  2. Theory for electron transfer from a mixed-valence dimer with paramagnetic sites to a mononuclear acceptor

    NASA Astrophysics Data System (ADS)

    Bominaar, E. L.; Achim, C.; Borshch, S. A.

    1999-06-01

    Polynuclear transition-metal complexes, such as Fe-S clusters, are the prosthetic groups in a large number of metalloproteins and serve as temporary electron storage units in a number of important redox-based biological processes. Polynuclearity distinguishes clusters from mononuclear centers and confers upon them unique properties, such as spin ordering and the presence of thermally accessible excited spin states in clusters with paramagnetic sites, and fractional valencies in clusters of the mixed-valence type. In an earlier study we presented an effective-mode (EM) analysis of electron transfer from a binuclear mixed-valence donor with paramagnetic sites to a mononuclear acceptor which revealed that the cluster-specific attributes have an important impact on the kinetics of long-range electron transfer. In the present study, the validity of these results is tested in the framework of more detailed theories which we have termed the multimode semiclassical (SC) model and the quantum-mechanical (QM) model. It is found that the qualitative trends in the rate constant are the same in all treatments and that the semiclassical models provide a good approximation of the more rigorous quantum-mechanical description of electron transfer under physiologically relevant conditions. In particular, the present results corroborate the importance of electron transfer via excited spin states in reactions with a low driving force and justify the use of semiclassical theory in cases in which the QM model is computationally too demanding. We consider cases in which either one or two donor sites of a dimer are electronically coupled to the acceptor. In the case of multiconnectivity, the rate constant for electron transfer from a valence-delocalized (class-III) donor is nonadditive with respect to transfer from individual metal sites of the donor and undergoes an order-of-magnitude change by reversing the sign of the intradimer metal-metal resonance parameter (β). In the case of

  3. An electron momentum spectroscopy and density functional theory study of the outer valence electronic structure of stella-2,6-dione

    NASA Astrophysics Data System (ADS)

    Nixon, K. L.; Wang, F.; Campbell, L.; Maddern, T.; Winkler, D.; Gleiter, R.; Loeb, P.; Weigold, E.; Brunger, M. J.

    2003-07-01

    We report on the first electron momentum spectroscopy (EMS) study into the outer valence electronic structure of the ground electronic state for the organic molecule stella-2,6-dione (C8H8O2). Experimentally measured binding-energy spectra are compared against a He(Ialpha) photoelectron spectroscopy result, while our derived momentum distributions (MDs) are compared against corresponding results from the plane wave impulse approximation (PWIA) level calculations. These computations employed density functional theory (DFT) basis states at the triple zeta valence polarization (TZVP) level, with a range of exchange-correlation (XC) functionals. A detailed comparison between the experimental and PWIA DFT-XC/TZVP calculated MDs enabled us to evaluate the accuracy of the various functionals, the Becke-Perdew (BP) XC functional being found to provide the most accurate description here. The importance of the through-bond interaction to the molecular orbitals (MOs) of stella-2,6-dione is demonstrated using the orbital imaging capability of EMS. Finally we show that the molecular geometry of this molecule, as derived from BP/TZVP, is in quite good agreement with corresponding independent experimental data.

  4. The Effect of Cerium Oxide Nanoparticle Valence State on Reactive Oxygen Species and Toxicity.

    PubMed

    Dunnick, Katherine M; Pillai, Rajalekshmi; Pisane, Kelly L; Stefaniak, Aleksandr B; Sabolsky, Edward M; Leonard, Stephen S

    2015-07-01

    Cerium oxide (CeO2) nanoparticles, which are used in a variety of products including solar cells, gas sensors, and catalysts, are expected to increase in industrial use. This will subsequently lead to additional occupational exposures, making toxicology screenings crucial. Previous toxicology studies have presented conflicting results as to the extent of CeO2 toxicity, which is hypothesized to be due to the ability of Ce to exist in both a +3 and +4 valence state. Thus, to study whether valence state and oxygen vacancy concentration are important in CeO2 toxicity, CeO2 nanoparticles were doped with gadolinium to adjust the cation (Ce, Gd) and anion (O) defect states. The hypothesis that doping would increase toxicity and decrease antioxidant abilities as a result of increased oxygen vacancies and inhibition of +3 to +4 transition was tested. Differences in toxicity and reactivity based on valence state were determined in RLE-6TN rat alveolar epithelial and NR8383 rat alveolar macrophage cells using enhanced dark field microscopy, electron paramagnetic resonance (EPR), and annexin V/propidium iodide cell viability stain. Results from EPR indicated that as doping increased, antioxidant potential decreased. Alternatively, doping had no effect on toxicity at 24 h. The present results imply that as doping increases, thus subsequently increasing the Ce(3+)/Ce(4+) ratio, antioxidant potential decreases, suggesting that differences in reactivity of CeO2 are due to the ability of Ce to transition between the two valence states and the presence of increased oxygen vacancies, rather than dependent on a specific valence state.

  5. Exchange Coupling Interactions from the Density Matrix Renormalization Group and N-Electron Valence Perturbation Theory: Application to a Biomimetic Mixed-Valence Manganese Complex.

    PubMed

    Roemelt, Michael; Krewald, Vera; Pantazis, Dimitrios A

    2018-01-09

    The accurate description of magnetic level energetics in oligonuclear exchange-coupled transition-metal complexes remains a formidable challenge for quantum chemistry. The density matrix renormalization group (DMRG) brings such systems for the first time easily within reach of multireference wave function methods by enabling the use of unprecedentedly large active spaces. But does this guarantee systematic improvement in predictive ability and, if so, under which conditions? We identify operational parameters in the use of DMRG using as a test system an experimentally characterized mixed-valence bis-μ-oxo/μ-acetato Mn(III,IV) dimer, a model for the oxygen-evolving complex of photosystem II. A complete active space of all metal 3d and bridge 2p orbitals proved to be the smallest meaningful starting point; this is readily accessible with DMRG and greatly improves on the unrealistic metal-only configuration interaction or complete active space self-consistent field (CASSCF) values. Orbital optimization is critical for stabilizing the antiferromagnetic state, while a state-averaged approach over all spin states involved is required to avoid artificial deviations from isotropic behavior that are associated with state-specific calculations. Selective inclusion of localized orbital subspaces enables probing the relative contributions of different ligands and distinct superexchange pathways. Overall, however, full-valence DMRG-CASSCF calculations fall short of providing a quantitative description of the exchange coupling owing to insufficient recovery of dynamic correlation. Quantitatively accurate results can be achieved through a DMRG implementation of second order N-electron valence perturbation theory (NEVPT2) in conjunction with a full-valence metal and ligand active space. Perspectives for future applications of DMRG-CASSCF/NEVPT2 to exchange coupling in oligonuclear clusters are discussed.

  6. Deduction of the chemical state and the electronic structure of Nd{sub 2}Fe{sub 14}B compound from X-ray photoelectron spectroscopy core-level and valence-band spectra

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

    Wang, Jing; Liang, Le; Zhang, Lanting, E-mail: lantingzh@sjtu.edu.cn, E-mail: lmsun@sjtu.edu.cn

    2014-10-28

    Characterization of chemical state and electronic structure of the technologically important Nd{sub 2}Fe{sub 14}B compound is attractive for understanding the physical nature of its excellent magnetic properties. X-ray photoelectron spectroscopy (XPS) study of such rare-earth compound is important and also challenging due to the easy oxidation of surface and small photoelectron cross-sections of rare-earth 4f electrons and B 2p electrons, etc. Here, we reported an investigation based on XPS spectra of Nd{sub 2}Fe{sub 14}B compound as a function of Ar ion sputtering time. The chemical state of Fe and that of B in Nd{sub 2}Fe{sub 14}B compound can be clearlymore » determined to be 0 and −3, respectively. The Nd in Nd{sub 2}Fe{sub 14}B compound is found to have the chemical state of close to +3 instead of +3 as compared with the Nd in Nd{sub 2}O{sub 3}. In addition, by comparing the valence-band spectrum of Nd{sub 2}Fe{sub 14}B compound to that of the pure Fe, the contributions from Nd, Fe, and B to the valence-band structure of Nd{sub 2}Fe{sub 14}B compound is made more clear. The B 2p states and B 2s states are identified to be at ∼11.2 eV and ∼24.6 eV, respectively, which is reported for the first time. The contribution from Nd 4f states can be identified both in XPS core-level spectrum and XPS valence-band spectrum. Although Nd 4f states partially hybridize with Fe 3d states, Nd 4f states are mainly localized in Nd{sub 2}Fe{sub 14}B compound.« less

  7. Identification of Cr valence states in Cr and Nd co-doped Lu3Al5O12 laser ceramics

    NASA Astrophysics Data System (ADS)

    Zhang, Pande; Jiang, Benxue; Fan, Jintai; Mao, Xiaojian; Zhang, Long

    2017-09-01

    Cr and Nd co-doped laser ceramics, as the potential gain materials in inertial confinement fusion (ICF), have been widely investigated. And the study on valence states of chromium ions is important. The effects of sintering additives and annealing atmosphere on the valence state of chromium were studied in detail, and the results shown that the Cr valence states were demonstrated to be Cr2+ and Cr3+ ions in HIP-sintered Cr(0.2 at.%), Nd(0.8 at.%): LuAG laser ceramics. And the intensity of the near-infrared absorption band caused by Cr2+ ions was attenuated with the decreasing SiO2 concentration and increasing MgO amount. The near-infrared absorption could be eliminated by annealing in air. And the transformation of valence states of Cr ions in the Cr,Nd:LuAG ceramics were also confirmed by electron paramagnetic resonance and X-ray photoelectron spectroscopy.

  8. Coulomb scattering rates of excited states in monolayer electron-doped germanene

    NASA Astrophysics Data System (ADS)

    Shih, Po-Hsin; Chiu, Chih-Wei; Wu, Jhao-Ying; Do, Thi-Nga; Lin, Ming-Fa

    2018-05-01

    Excited conduction electrons, conduction holes, and valence holes in monolayer electron-doped germanene exhibit unusual Coulomb decay rates. The deexcitation processes are studied using the screened exchange energy. They might utilize the intraband single-particle excitations (SPEs), the interband SPEs, and the plasmon modes, depending on the quasiparticle states and the Fermi energies. The low-lying valence holes can decay through the undamped acoustic plasmon, so that they present very fast Coulomb deexcitations, nonmonotonous energy dependence, and anisotropic behavior. However, the low-energy conduction electrons and holes are similar to those in a two-dimensional electron gas. The higher-energy conduction states and the deeper-energy valence ones behave similarly in the available deexcitation channels and have a similar dependence of decay rate on the wave vector k .

  9. Analysis of Ti valence states in resistive switching regions of a rutile TiO2‑ x four-terminal memristive device

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Kengo; Takeuchi, Shotaro; Tohei, Tetsuya; Ikarashi, Nobuyuki; Sakai, Akira

    2018-06-01

    We have performed Ti valence state analysis of our four-terminal rutile TiO2‑ x single-crystal memristors using scanning transmission electron microscopy–electron energy loss spectroscopy (STEM–EELS). Analysis of Ti-L2,3 edge EELS spectra revealed that the electrocolored region formed by the application of voltage includes a valence state reflecting highly reduced TiO2‑ x due to the accumulation of oxygen vacancies. Such a valence state mainly exists within ∼50 nm from the crystal surface and extends along specific crystal directions. These electrically reduced surface layers are considered to directly contribute to the resistive switching (RS) in the four-terminal device. The present results add new insights into the microscopic mechanisms of the RS phenomena and should contribute to further development and improvements of TiO2‑ x based memristive devices.

  10. Electronic and transport properties of Cobalt-based valence tautomeric molecules and polymers

    NASA Astrophysics Data System (ADS)

    Chen, Yifeng; Calzolari, Arrigo; Buongiorno Nardelli, Marco

    2011-03-01

    The advancement of molecular spintronics requires further understandings of the fundamental electronic structures and transport properties of prototypical spintronics molecules and polymers. Here we present a density functional based theoretical study of the electronic structures of Cobalt-based valence tautomeric molecules Co III (SQ)(Cat)L Co II (SQ)2 L and their polymers, where SQ refers to the semiquinone ligand, and Cat the catecholate ligand, while L is a redox innocent backbone ligand. The conversion from low-spin Co III ground state to high-spin Co II excited state is realized by imposing an on-site potential U on the Co atom and elongating the Co-N bond. Transport properties are subsequently calculated by extracting electronic Wannier functions from these systems and computing the charge transport in the ballistic regime using a Non-Equilibrium Green's Function (NEGF) approach. Our transport results show distinct charge transport properties between low-spin ground state and high-spin excited state, hence suggesting potential spintronics devices from these molecules and polymers such as spin valves.

  11. Norbornane: An investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green's function theories

    NASA Astrophysics Data System (ADS)

    Knippenberg, S.; Nixon, K. L.; Brunger, M. J.; Maddern, T.; Campbell, L.; Trout, N.; Wang, F.; Newell, W. R.; Deleuze, M. S.; Francois, J.-P.; Winkler, D. A.

    2004-12-01

    We report on the results of an exhaustive study of the valence electronic structure of norbornane (C7H12), up to binding energies of 29 eV. Experimental electron momentum spectroscopy and theoretical Green's function and density functional theory approaches were all utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among all the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-ζ quality provides the best representation of the electron momentum distributions for all of the 20 valence orbitals of norbornane. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green's function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than 22.5 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet photoemission and newly presented (e,2e) ionization spectra, except for the band associated with the 1a2-1 one-hole state, which is probably subject to rather significant vibronic coupling effects, and a band at ˜25 eV characterized by a momentum distribution of "s-type" symmetry, which Green's function calculations fail to reproduce. We note the vicinity of the vertical double ionization threshold at ˜26 eV.

  12. Temperature and pressure dependences of Sm valence in intermediate valence compound SmB6

    NASA Astrophysics Data System (ADS)

    Emi, N.; Mito, T.; Kawamura, N.; Mizumaki, M.; Ishimatsu, N.; Pristáš, G.; Kagayama, T.; Shimizu, K.; Osanai, Y.; Iga, F.

    2018-05-01

    We report the results of the X-ray absorption spectroscopy (XAS) on the intermediate valence compound SmB6. The XAS measurements were performed near the nonmagnetic-magnetic phase boundary. Mean Sm valence vSm was estimated from absorption spectra, and we found that vSm near the boundary (P ≥ 10 GPa and T ∼ 12 K) is far below a trivalent state with magnetic characteristics. Although the result is markedly different from the cases of pressure induced magnetic orders in Yb and Ce compounds, it is likely that the large deviation from the trivalent state seems to be common in some Sm compounds which possess electronic configuration between 4f5 and 4f6 with multi 4 f electrons.

  13. B-site cation order/disorder and their valence states in Ba3MnNb2O9 perovskite oxide

    NASA Astrophysics Data System (ADS)

    Xin, Yan; Huang, Qing; Shafieizadeh, Zahra; Zhou, Haidong

    2018-06-01

    Polycrystalline samples Ba3MnNb2O9 synthesized by solid state reaction and single crystal samples grown by optical floating zone have been characterized using scanning transmission electron microscopy and electron energy loss spectroscopy. Three types of B-site Mn and Nb ordering phase are observed: fully ordered 1Mn:2Nb; fully disordered; nano-sized 1Mn:1Nb ordered. No electronic structure change for crystals with different ordering/disordering. The Mn valence is determined to be 2+, and Nb valence is 5+. Oxygen 2p orbitals hybridize with Mn 3d and Nb 4d orbitals. Factors that affect the electron energy loss near edge structures of transition metal white-lines in electron energy loss spectroscopy are explicitly illustrated and discussed.

  14. Characterization of Lithium Ion Battery Materials with Valence Electron Energy-Loss Spectroscopy.

    PubMed

    Castro, Fernando C; Dravid, Vinayak P

    2018-06-01

    Cutting-edge research on materials for lithium ion batteries regularly focuses on nanoscale and atomic-scale phenomena. Electron energy-loss spectroscopy (EELS) is one of the most powerful ways of characterizing composition and aspects of the electronic structure of battery materials, particularly lithium and the transition metal mixed oxides found in the electrodes. However, the characteristic EELS signal from battery materials is challenging to analyze when there is strong overlap of spectral features, poor signal-to-background ratios, or thicker and uneven sample areas. A potential alternative or complementary approach comes from utilizing the valence EELS features (<20 eV loss) of battery materials. For example, the valence EELS features in LiCoO2 maintain higher jump ratios than the Li-K edge, most notably when spectra are collected with minimal acquisition times or from thick sample regions. EELS maps of these valence features give comparable results to the Li-K edge EELS maps of LiCoO2. With some spectral processing, the valence EELS maps more accurately highlight the morphology and distribution of LiCoO2 than the Li-K edge maps, especially in thicker sample regions. This approach is beneficial for cases where sample thickness or beam sensitivity limit EELS analysis, and could be used to minimize electron dosage and sample damage or contamination.

  15. Auger electron emission initiated by the creation of valence-band holes in graphene by positron annihilation.

    PubMed

    Chirayath, V A; Callewaert, V; Fairchild, A J; Chrysler, M D; Gladen, R W; Mcdonald, A D; Imam, S K; Shastry, K; Koymen, A R; Saniz, R; Barbiellini, B; Rajeshwar, K; Partoens, B; Weiss, A H

    2017-07-13

    Auger processes involving the filling of holes in the valence band are thought to make important contributions to the low-energy photoelectron and secondary electron spectrum from many solids. However, measurements of the energy spectrum and the efficiency with which electrons are emitted in this process remain elusive due to a large unrelated background resulting from primary beam-induced secondary electrons. Here, we report the direct measurement of the energy spectra of electrons emitted from single layer graphene as a result of the decay of deep holes in the valence band. These measurements were made possible by eliminating competing backgrounds by employing low-energy positrons (<1.25 eV) to create valence-band holes by annihilation. Our experimental results, supported by theoretical calculations, indicate that between 80 and 100% of the deep valence-band holes in graphene are filled via an Auger transition.

  16. Auger electron emission initiated by the creation of valence-band holes in graphene by positron annihilation

    PubMed Central

    Chirayath, V. A.; Callewaert, V.; Fairchild, A. J.; Chrysler, M. D.; Gladen, R. W.; Mcdonald, A. D.; Imam, S. K.; Shastry, K.; Koymen, A. R.; Saniz, R.; Barbiellini, B.; Rajeshwar, K.; Partoens, B.; Weiss, A. H.

    2017-01-01

    Auger processes involving the filling of holes in the valence band are thought to make important contributions to the low-energy photoelectron and secondary electron spectrum from many solids. However, measurements of the energy spectrum and the efficiency with which electrons are emitted in this process remain elusive due to a large unrelated background resulting from primary beam-induced secondary electrons. Here, we report the direct measurement of the energy spectra of electrons emitted from single layer graphene as a result of the decay of deep holes in the valence band. These measurements were made possible by eliminating competing backgrounds by employing low-energy positrons (<1.25 eV) to create valence-band holes by annihilation. Our experimental results, supported by theoretical calculations, indicate that between 80 and 100% of the deep valence-band holes in graphene are filled via an Auger transition. PMID:28703225

  17. Resonant inelastic x-ray scattering and photoemission measurement of O2: Direct evidence for dependence of Rydberg-valence mixing on vibrational states in O 1s → Rydberg states

    NASA Astrophysics Data System (ADS)

    Gejo, T.; Oura, M.; Tokushima, T.; Horikawa, Y.; Arai, H.; Shin, S.; Kimberg, V.; Kosugi, N.

    2017-07-01

    High-resolution resonant inelastic x-ray scattering (RIXS) and low-energy photoemission spectra of oxygen molecules have been measured for investigating the electronic structure of Rydberg states in the O 1s → σ* energy region. The electronic characteristics of each Rydberg state have been successfully observed, and new assignments are made for several states. The RIXS spectra clearly show that vibrational excitation is very sensitive to the electronic characteristics because of Rydberg-valence mixing and vibronic coupling in O2. This observation constitutes direct experimental evidence that the Rydberg-valence mixing characteristic depends on the vibrational excitation near the avoided crossing of potential surfaces. We also measured the photoemission spectra of metastable oxygen atoms (O*) from O2 excited to 1s → Rydberg states. The broadening of the 4p Rydberg states of O* has been found with isotropic behavior, implying that excited oxygen molecules undergo dissociation with a lifetime of the order of 10 fs in 1s → Rydberg states.

  18. One Way to Design a Valence-Skip Compound.

    PubMed

    Hase, I; Yanagisawa, T; Kawashima, K

    2017-12-01

    Valence-skip compound is a good candidate with high T c and low anisotropy because it has a large attractive interaction at the site of valence-skip atom. However, it is not easy to synthesize such compound because of (i) the instability of the skipping valence state, (ii) the competing charge order, and (iii) that formal valence may not be true in some compounds. In the present study, we show several examples of the valence-skip compounds and discuss how we can design them by first principles calculations. Furthermore, we calculated the electronic structure of a promising candidate of valence skipping compound RbTlCl 3 from first principles. We confirmed that the charge-density wave (CDW) is formed in this compound, and the Tl atoms in two crystallographic different sites take the valence Tl 1+ and Tl 3+ . Structure optimization study reveals that this CDW is stable at the ambient pressure, while this CDW gap can be collapsed when we apply pressure with several gigapascals. In this metallic phase, we can expect a large charge fluctuation and a large electron-phonon interaction.

  19. Intermediate-valence state of the Sm and Eu in SmB6 and EuCu2Si2: neutron spectroscopy data and analysis

    NASA Astrophysics Data System (ADS)

    Savchenkov, P. S.; Alekseev, P. A.; Podlesnyak, A.; Kolesnikov, A. I.; Nemkovski, K. S.

    2018-02-01

    Magnetic neutron scattering data for Sm (SmB6, Sm(Y)S) and Eu (EuCu2Si2-x Ge x ) intermediate-valence compounds have been analysed in terms of a generalized model of the intermediate-radius exciton. Special attention is paid to the correlation between the average ion’s valence and parameters of the low-energy excitation in the neutron spectra, such as the resonance mode, including its magnetic form factor. Along with specific features of the formation of the intermediate-valence state for Sm and Eu ions, common physical mechanisms have been revealed for systems based on these elements from the middle of the rare-earth series. A consistent description of the existing experimental data has been obtained by using the concept of a loosely bound hole for the Eu f-electron shell in the intermediate-valence state, in analogy with the previously established loosely bound electron model for the Sm ion.

  20. Intermediate-valence state of the Sm and Eu in SmB 6 and EuCu 2 Si 2 : neutron spectroscopy data and analysis

    DOE PAGES

    Savchenkov, P. S.; Alekseev, P. A.; Podlesnyak, A.; ...

    2018-01-11

    For this study, magnetic neutron scattering data for Sm (SmB 6, Sm(Y)S) and Eu (EuCu 2Si 2- x Ge x ) intermediate-valence compounds have been analysed in terms of a generalized model of the intermediate-radius exciton. Special attention is paid to the correlation between the average ion's valence and parameters of the low-energy excitation in the neutron spectra, such as the resonance mode, including its magnetic form factor. Along with specific features of the formation of the intermediate-valence state for Sm and Eu ions, common physical mechanisms have been revealed for systems based on these elements from the middle ofmore » the rare-earth series. A consistent description of the existing experimental data has been obtained by using the concept of a loosely bound hole for the Eu f-electron shell in the intermediate-valence state, in analogy with the previously established loosely bound electron model for the Sm ion.« less

  1. Intermediate-valence state of the Sm and Eu in SmB 6 and EuCu 2 Si 2 : neutron spectroscopy data and analysis

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

    Savchenkov, P. S.; Alekseev, P. A.; Podlesnyak, A.

    For this study, magnetic neutron scattering data for Sm (SmB 6, Sm(Y)S) and Eu (EuCu 2Si 2- x Ge x ) intermediate-valence compounds have been analysed in terms of a generalized model of the intermediate-radius exciton. Special attention is paid to the correlation between the average ion's valence and parameters of the low-energy excitation in the neutron spectra, such as the resonance mode, including its magnetic form factor. Along with specific features of the formation of the intermediate-valence state for Sm and Eu ions, common physical mechanisms have been revealed for systems based on these elements from the middle ofmore » the rare-earth series. A consistent description of the existing experimental data has been obtained by using the concept of a loosely bound hole for the Eu f-electron shell in the intermediate-valence state, in analogy with the previously established loosely bound electron model for the Sm ion.« less

  2. The electronic characterization of biphenylene—Experimental and theoretical insights from core and valence level spectroscopy

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

    Lüder, Johann; Sanyal, Biplab; Eriksson, Olle

    In this paper, we provide detailed insights into the electronic structure of the gas phase biphenylene molecule through core and valence spectroscopy. By comparing results of X-ray Photoelectron Spectroscopy (XPS) measurements with ΔSCF core-hole calculations in the framework of Density Functional Theory (DFT), we could decompose the characteristic contributions to the total spectra and assign them to non-equivalent carbon atoms. As a difference with similar molecules like biphenyl and naphthalene, an influence of the localized orbitals on the relative XPS shifts was found. The valence spectrum probed by photoelectron spectroscopy at a photon energy of 50 eV in conjunction withmore » hybrid DFT calculations revealed the effects of the localization on the electronic states. Using the transition potential approach to simulate the X-ray absorption spectroscopy measurements, similar contributions from the non-equivalent carbon atoms were determined from the total spectrum, for which the slightly shifted individual components can explain the observed asymmetric features.« less

  3. A revised MRCI-algorithm coupled to an effective valence-shell Hamiltonian. II. Application to the valence excitations of butadiene

    NASA Astrophysics Data System (ADS)

    Strodel, Paul; Tavan, Paul

    2002-09-01

    In Paper I of this work we have sketched an improved MRCI algorithm and its coupling to the effective valence-shell Hamiltonian OM2. To check the quality of the resulting OM2/MRCI approach, it is applied here to the excited valence states of all-trans butadiene. As is explained by a review of previous theoretical work, proper descriptions of these states posed severe problems within correlated ab initio treatments but seemed to be trivial within simple correlated pi-electron models. We now show that an extended MRCI treatment of the correlations among all valence electrons as described by OM2 closely reproduces the experimental evidence, placing the vertical 2 1Ag excitation by about 0.2 eV below the 1 1Bu excitation. By an analysis of sigma]-[pi interactions we explain the corresponding earlier success of correlated pi-electron theory. Exploiting the enhanced capabilities of the new approach we investigate the potential surfaces. Here, OM2/MRCI is shown to predict that the 2 1Ag state is energetically lowered about four times more strongly than the 1 1Bu state upon geometry relaxation constrained to the C2h symmetry. We conclude that OM2/MRCI should be well-suited for the study of excited state surfaces of organic dye molecules.

  4. Oscillator strengths and integral cross sections for the valence-shell excitations of nitric oxide studied by fast electron impact.

    PubMed

    Xu, Xin; Xu, Long-Quan; Xiong, Tao; Chen, Tao; Liu, Ya-Wei; Zhu, Lin-Fan

    2018-01-28

    The generalized oscillator strengths for the valence-shell excitations of A 2 Σ + , C 2 Π, and D 2 Σ + electronic-states of nitric oxide have been determined at an incident electron energy of 1500 eV with an energy resolution of 70 meV. The optical oscillator strengths for these transitions have been obtained by extrapolating the generalized oscillator strengths to the limit that the squared momentum transfer approaches to zero, which give an independent cross-check to the previous experimental and theoretical results. The integral cross sections for the valence-shell excitations of nitric oxide have been determined systematically from the threshold to 2500 eV with the aid of the newly developed BE-scaling method for the first time. The present optical oscillator strengths and integral cross sections of the valence-shell excitations of nitric oxide play an important role in understanding many physics and chemistry of the Earth's upper atmosphere such as the radiative cooling, ozone destruction, day glow, aurora, and so on.

  5. Valence-band states in Bi2(Ca,Sr,La)3Cu2O8

    NASA Astrophysics Data System (ADS)

    Wells, B. O.; Lindberg, P. A. P.; Shen, Z.-X.; Dessau, D. S.; Spicer, W. E.; Lindau, I.; Mitzi, D. B.; Kapitulnik, A.

    1989-09-01

    We have used photoemission spectroscopy to examine the symmetry of the occupied states of the valence band for the La-doped superconductor Bi2(Ca,Sr,La)3Cu2O8. While the oxygen states near the bottom of the 7-eV wide valence band exhibit predominantly O 2pz symmetry, the states at the top of the valence band extending to the Fermi level are found to have primarily O 2px and O 2py character. We have also examined anomalous intensity enhancements in the valence-band features for photon energies near 18 eV. These enhancements, which occur at photon energies ranging from 15.8 to 18.0 eV for the different valence-band features, are not consistent with either simple final-state effects or direct O 2s transitions to unoccupied O 2p states.

  6. Electronic structure and nature of the ground state of the mixed-valence binuclear tetra(mu-1,8-naphthyridine-N,N')-bis(halogenonickel) tetraphenylborate complexes: experimental and DFT characterization.

    PubMed

    Bencini, Alessandro; Berti, Elisabetta; Caneschi, Andrea; Gatteschi, Dante; Giannasi, Elisa; Invernizzi, Ivana

    2002-08-16

    The ground state electronic structure of the mixed-valence systems [Ni(2)(napy)(4)X(2)](BPh(4)) (napy=1,8-naphthyridine; X=Cl, Br, I) was studied with combined experimental (X-ray diffraction, temperature dependence of the magnetic susceptibility, and high-field EPR spectroscopy) and theoretical (DFT) methods. The zero-field splitting (zfs) ground S=3/2 spin state is axial with /D/ approximately 3 cm(-1). The iodide derivative was found to be isostructural with the previously reported bromide complex, but not isomorphous. The compound crystallizes in the monoclinic system, space group P2(1)/n, with a=17.240(5), b=26.200(5), c=11.340(5) A, beta=101.320(5) degrees. DFT calculations were performed on the S=3/2 state to characterize the ground state potential energy surface as a function of the nuclear displacements. The molecules can thus be classified as Class III mixed-valence compounds with a computed delocalization parameter, B=3716, 3583, and 3261 cm(-1) for the Cl, Br, and I derivatives, respectively.

  7. Valence-electron configuration of Fe, Cr, and Ni in binary and ternary alloys from Kβ -to- Kα x-ray intensity ratios

    NASA Astrophysics Data System (ADS)

    Han, I.; Demir, L.

    2009-11-01

    Kβ -to- Kα x-ray intensity ratios of Fe, Cr, and Ni have been measured in pure metals and in alloys of FexNi1-x ( x=0.8 , 0.7, 0.6, 0.5, 0.4, 0.3, and 0.2), NixCr1-x ( x=0.8 , 0.6, 0.5, 0.4, and 0.2), FexCr1-x ( x=0.9 , 0.7, and 0.5), and FexCryNi1-(x+y) ( x=0.7-y=0.1 , x=0.5-y=0.2 , x=0.4-y=0.3 , x=0.3-y=0.3 , x=0.2-y=0.2 , and x=0.1-y=0.2 ) following excitation by 22.69 keV x rays from a 10 mCi C109d radioactive point source. The valence-electron configurations of these metals were determined by corporation of measured Kβ -to- Kα x-ray intensity ratios with the results of multiconfiguration Dirac-Fock calculation for various valence-electron configurations. Valence-electron configurations of 3d transition metals in alloys indicate significant differences with respect to the pure metals. Our analysis indicates that these differences arise from delocalization and/or charge transfer phenomena in alloys. Namely, the observed change of the valence-electron configurations of metals in alloys can be explained with the transfer of 3d electrons from one element to the other element and/or the rearrangement of electrons between 3d and 4s,4p states of individual metal atoms.

  8. Dramatic change of photoexcited quasiparticle relaxation dynamics across Yb valence state transition in YbInCu4

    NASA Astrophysics Data System (ADS)

    Zhang, M. Y.; Chen, R. Y.; Dong, T.; Wang, N. L.

    2017-04-01

    YbInCu4 undergoes a first-order structural phase transition near Tv=40 K associated with an abrupt change of Yb valence state. We perform an ultrafast pump-probe measurement on YbInCu4 and find that the expected heavy-fermion properties arising from the c -f hybridization exist only in a limited temperature range above Tv. Below Tv, the compound behaves as a normal metal though a prominent hybridization energy gap is still present in the infrared measurement. We elaborate that those seemingly controversial phenomena could be well explained by assuming that the Fermi level suddenly shifts up and moves away from the flat f -electron band as well as the indirect hybridization energy gap in the intermediate valence state below Tv.

  9. Valence State Driven Site Preference in the Quaternary Compound Ca5MgAgGe5: An Electron-Deficient Phase with Optimized Bonding

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

    Ponou, Simeon; Lidin, Sven; Zhang, Yuemei

    The quaternary phase Ca5Mg0.95Ag1.05(1)Ge5 (3) was synthesized by high-temperature solid-state techniques, and its crystal structure was determined by single-crystal diffraction methods in the orthorhombic space group Pnma – Wyckoff sequence c12 with a = 23.1481(4) Å, b = 4.4736(1) Å, c = 11.0128(2) Å, V = 1140.43(4) Å3, Z = 4. The crystal structure can be described as linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaMGe (TiNiSi-type; M = Mg, Ag) structures. Hence, 3 is a hettotype of the hitherto missing n = 3 member of the structure series with the general formula R2+nT2X2+n, previously describedmore » with n = 1, 2, and 4. The member with n = 3 was predicted in the space group Cmcm – Wyckoff sequence f5c2. The experimental space group Pnma (in the nonstandard setting Pmcn) corresponds to a klassengleiche symmetry reduction of index two of the predicted space group Cmcm. This transition originates from the switching of one Ge and one Ag position in the TiNiSi-related slab, a process that triggers an uncoupling of each of the five 8f sites in Cmcm into two 4c sites in Pnma. The Mg/Ag site preference was investigated using VASP calculations and revealed a remarkable example of an intermetallic compound for which the electrostatic valency principle is a critical structure-directing force. The compound is deficient by one valence electron according to the Zintl concept, but LMTO electronic structure calculations indicate electronic stabilization and overall bonding optimization in the polyanionic network. Other stability factors beyond the Zintl concept that may account for the electronic stabilization are discussed.« less

  10. Valency configuration of transition metal impurities in ZnO

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

    Petit, Leon; Schulthess, Thomas C; Svane, Axel

    2006-01-01

    We use the self-interaction corrected local spin-density approximation to investigate the ground state valency configuration of transition metal (TM=Mn, Co) impurities in n- and p-type ZnO. We find that in pure Zn{sub 1-x}TM{sub x}O, the localized TM{sup 2+} configuration is energetically favored over the itinerant d-electron configuration of the local spin density (LSD) picture. Our calculations indicate furthermore that the (+/0) donor level is situated in the ZnO gap. Consequently, for n-type conditions, with the Fermi energy {epsilon}F close to the conduction band minimum, TM remains in the 2+ charge state, while for p-type conditions, with {epsilon}F close to themore » valence band maximum, the 3+ charge state is energetically preferred. In the latter scenario, modeled here by co-doping with N, the additional delocalized d-electron charge transfers into the entire states at the top of the valence band, and hole carriers will only exist, if the N concentration exceeds the TM impurity concentration.« less

  11. Low-lying electronic states of Li 2+ and Li 2-

    NASA Astrophysics Data System (ADS)

    Konowalow, Daniel D.; Fish, James L.

    1984-02-01

    Potential curves for the eight lowest lying electronic states of Li2+ and the two lowest-lying states of Li2- are obtained by valence configuration calculations which-utilize an effective core potential. The calculated ionization potential of the ground state of Li2 is found to b. 5.16 eV and its electron affinity is 0.429 eV. Both values are in excellent agreement with recent experimental values and with value deduced from other high quality ab initio quantum mechanical treatments. When our potential curve for the Li2+(12Σg+ state, is corrected for the core-valence correlation error we obtain spectroscopic constants which agree nicely with the experimental values of Bernheim, Gold and Tipton (BGT). For example, we findDe = 10460 ± 140 cm-1 while BGT reportDe = 10469 ± 6 cm-1.

  12. Valence electronic structure of cobalt phthalocyanine from an optimally tuned range-separated hybrid functional.

    PubMed

    Brumboiu, Iulia Emilia; Prokopiou, Georgia; Kronik, Leeor; Brena, Barbara

    2017-07-28

    We analyse the valence electronic structure of cobalt phthalocyanine (CoPc) by means of optimally tuning a range-separated hybrid functional. The tuning is performed by modifying both the amount of short-range exact exchange (α) included in the hybrid functional and the range-separation parameter (γ), with two strategies employed for finding the optimal γ for each α. The influence of these two parameters on the structural, electronic, and magnetic properties of CoPc is thoroughly investigated. The electronic structure is found to be very sensitive to the amount and range in which the exact exchange is included. The electronic structure obtained using the optimal parameters is compared to gas-phase photo-electron data and GW calculations, with the unoccupied states additionally compared with inverse photo-electron spectroscopy measurements. The calculated spectrum with tuned γ, determined for the optimal value of α = 0.1, yields a very good agreement with both experimental results and with GW calculations that well-reproduce the experimental data.

  13. Investigation of the Impact of Different Terms in the Second Order Hamiltonian on Excitation Energies of Valence and Rydberg States.

    PubMed

    Tajti, Attila; Szalay, Péter G

    2016-11-08

    Describing electronically excited states of molecules accurately poses a challenging problem for theoretical methods. Popular second order techniques like Linear Response CC2 (CC2-LR), Partitioned Equation-of-Motion MBPT(2) (P-EOM-MBPT(2)), or Equation-of-Motion CCSD(2) (EOM-CCSD(2)) often produce results that are controversial and are ill-balanced with their accuracy on valence and Rydberg type states. In this study, we connect the theory of these methods and, to investigate the origin of their different behavior, establish a series of intermediate variants. The accuracy of these on excitation energies of singlet valence and Rydberg electronic states is benchmarked on a large sample against high-accuracy Linear Response CC3 references. The results reveal the role of individual terms of the second order similarity transformed Hamiltonian, and the reason for the bad performance of CC2-LR in the description of Rydberg states. We also clarify the importance of the T̂ 1 transformation employed in the CC2 procedure, which is found to be very small for vertical excitation energies.

  14. Direct Visualization of Valence Electron Motion Using Strong-Field Photoelectron Holography

    NASA Astrophysics Data System (ADS)

    He, Mingrui; Li, Yang; Zhou, Yueming; Li, Min; Cao, Wei; Lu, Peixiang

    2018-03-01

    Watching the valence electron move in molecules on its intrinsic timescale has been one of the central goals of attosecond science and it requires measurements with subatomic spatial and attosecond temporal resolutions. The time-resolved photoelectron holography in strong-field tunneling ionization holds the promise to access this realm. However, it remains to be a challenging task hitherto. Here we reveal how the information of valence electron motion is encoded in the hologram of the photoelectron momentum distribution (PEMD) and develop a novel approach of retrieval. As a demonstration, applying it to the PEMDs obtained by solving the time-dependent Schrödinger equation for the prototypical molecule H2+ , the attosecond charge migration is directly visualized with picometer spatial and attosecond temporal resolutions. Our method represents a general approach for monitoring attosecond charge migration in more complex polyatomic and biological molecules, which is one of the central tasks in the newly emerging attosecond chemistry.

  15. Direct Visualization of Valence Electron Motion Using Strong-Field Photoelectron Holography.

    PubMed

    He, Mingrui; Li, Yang; Zhou, Yueming; Li, Min; Cao, Wei; Lu, Peixiang

    2018-03-30

    Watching the valence electron move in molecules on its intrinsic timescale has been one of the central goals of attosecond science and it requires measurements with subatomic spatial and attosecond temporal resolutions. The time-resolved photoelectron holography in strong-field tunneling ionization holds the promise to access this realm. However, it remains to be a challenging task hitherto. Here we reveal how the information of valence electron motion is encoded in the hologram of the photoelectron momentum distribution (PEMD) and develop a novel approach of retrieval. As a demonstration, applying it to the PEMDs obtained by solving the time-dependent Schrödinger equation for the prototypical molecule H_{2}^{+}, the attosecond charge migration is directly visualized with picometer spatial and attosecond temporal resolutions. Our method represents a general approach for monitoring attosecond charge migration in more complex polyatomic and biological molecules, which is one of the central tasks in the newly emerging attosecond chemistry.

  16. Electronic absorption and MCD spectra of M sub 2 (TMB) sub 4 sup 2+ , M = Rh and Ir. A valence-bond description of the upper electronic excited states

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

    Smith, D.C.; Miskowski, V.M.; Gray, H.B.

    1990-05-09

    Electronic absorption and magnetic circular dichroism (MCD) spectra of Rh{sub 2}(TMB){sub 4}{sup 2+} and Ir{sub 2}(TMB){sub 4}{sup 2+} are reported along with polarized single-crystal absorption spectra of (Ir{sub 2}(TMB){sub 4})(B(C{sub 6}H{sub 5}){sub 4}){sub 2} {times} CH{sub 3}C{sub 6}H{sub 5} (TMB = 2,5-diisocyano-2,5-dimethylhexane). Interpretation of the spectra is based on a valence-bond model that accommodates highly perturbed dimer transitions as well as monomer-like dimer excitations. In this model, half of the dimer electronic excited states possess ionic character; these states involve metal-to-metal charge transfer (MMCT). The most prominent of the weak features ({approximately} 430 nm) is assigned to the transition tomore » {sup 1}A{sub 1g} (a single-center d{sub z{sup 2}} {yields} p{sub z} excitation). High-energy features ({lambda} < 300 nm) in the spectra of Rh{sub 2}(TMB){sub 4}{sup 2+} and Ir{sub 2}(TMB){sub 4}{sup 2+} are assigned to MMCT arising from d{sub xzyz} {yields} p{sub z} excitations.« less

  17. Nature of the valence band states in Bi2(Ca, Sr, La)3Cu2O8

    NASA Astrophysics Data System (ADS)

    Wells, B. O.; Lindberg, P. A. P.; Shen, Z.-X.; Dessau, D. S.; Spicer, W. E.; Lindau, I.; Mitzi, D. B.; Kapitulnik, A.

    1990-01-01

    We have used photoemission spectroscopy to examine the symmetry of the occupied states of the valence band for the La doped superconductor Bi2(Ca, Sr, La)3Cu2O8. While the oxygen states near the bottom of the 7 eV wide valence band exhibit predominantly O 2pz symmetry, the states at the top of the valence band extending to the Fermi level are found to have primarily O 2px and O 2py character. We have also examined anomalous intensity enhancements in the valence band feature for photon energies near 18 eV. These enhancements, which occur at photon energies ranging from 15.8 to 18.0 eV for the different valence band features, are not consistent with either simple final state effects or direct O2s transitions to unoccupied O2p states.

  18. Use of valence band Auger electron spectroscopy to study thin film growth: oxide and diamond-like carbon films

    NASA Astrophysics Data System (ADS)

    Steffen, H. J.

    1994-12-01

    It is demonstrated how Auger line shape analysis with factor analysis (FA), least-squares fitting and even simple peak height measurements may provide detailed information about the composition, different chemical states and also defect concentration or crystal order. Advantage is taken of the capability of Auger electron spectroscopy to give valence band structure information with high surface sensitivity and the special aspect of FA to identify and discriminate quantitatively unknown chemical species. Valence band spectra obtained from Ni, Fe, Cr and NiFe40Cr20 during oxygen exposure at room temperature reveal the oxidation process in the initial stage of the thin layer formation. Furthermore, the carbon chemical states that were formed during low energy C(+) and Ne(+) ion irradiation of graphite are delineated and the evolution of an amorphous network with sp3 bonds is disclosed. The analysis represents a unique method to quantify the fraction of sp3-hybridized carbon in diamond-like materials.

  19. Valence-Band Electronic Structures of High-Pressure-Phase PdF2-type Platinum-Group Metal Dioxides MO2 (M = Ru, Rh, Ir, and Pt)

    NASA Astrophysics Data System (ADS)

    Soda, Kazuo; Kobayashi, Daichi; Mizui, Tatsuya; Kato, Masahiko; Shirako, Yuichi; Niwa, Ken; Hasegawa, Masashi; Akaogi, Masaki; Kojitani, Hiroshi; Ikenaga, Eiji; Muro, Takayuki

    2018-04-01

    The valence-band electronic structures of high-pressure-phase PdF2-type (HP-PdF2-type) platinum-group metal dioxides MO2 (M = Ru, Rh, Ir, and Pt) were studied by synchrotron radiation photoelectron spectroscopy and first-principles calculations. The obtained photoelectron spectra for HP-PdF2-type RuO2, RhO2, and IrO2 agree well with the calculated valence-band densities of states (DOSs) for these compounds, indicating their metallic properties, whereas the DOS of HP-PdF2-type PtO2 (calculated in the presence and absence of spin-orbit interactions) predicts that this material may be metallic or semimetallic, which is inconsistent with the electric conductivity reported to date and the charging effect observed in current photoelectron measurements. Compared with the calculated results, the valence-band spectrum of PtO2 appears to have shifted toward the high-binding-energy side and reveals a gradual intensity decrease toward the Fermi energy EF, implying a semiconductor-like electronic structure. Spin-dependent calculations predict a ferromagnetic ground state with a magnetization of 0.475 μB per formula unit for HP-PdF2-type RhO2.

  20. Chemical modulation of electronic structure at the excited state

    NASA Astrophysics Data System (ADS)

    Li, F.; Song, C.; Gu, Y. D.; Saleem, M. S.; Pan, F.

    2017-12-01

    Spin-polarized electronic structures are the cornerstone of spintronics, and have thus attracted a significant amount of interest; in particular, researchers are looking into how to modulate the electronic structure to enable multifunctional spintronics applications, especially in half-metallic systems. However, the control of the spin polarization has only been predicted in limited two-dimensional systems with spin-polarized Dirac structures and is difficult to achieve experimentally. Here, we report the modulation of the electronic structure in the light-induced excited state in a typical half-metal, L a1 /2S r1 /2Mn O3 -δ . According to the spin-transport measurements, there appears a light-induced increase in magnetoresistance due to the enhanced spin scattering, which is closely associated with the excited spin polarization. Strikingly, the light-induced variation can be enhanced via alcohol processing and reduced by oxygen annealing. X-ray photoelectron spectroscopy measurements show that in the chemical process, a redox reaction occurs with a change in the valence of Mn. Furthermore, first-principles calculations reveal that the change in the valence of Mn alters the electronic structure and consequently modulates the spin polarization in the excited state. Our findings thus report a chemically tunable electronic structure, demonstrating interesting physics and the potential for multifunctional applications and ultrafast spintronics.

  1. One-electron oxidation of electronically diverse manganese(III) and nickel(II) salen complexes: transition from localized to delocalized mixed-valence ligand radicals.

    PubMed

    Kurahashi, Takuya; Fujii, Hiroshi

    2011-06-01

    Ligand radicals from salen complexes are unique mixed-valence compounds in which a phenoxyl radical is electronically linked to a remote phenolate via a neighboring redox-active metal ion, providing an opportunity to study electron transfer from a phenolate to a phenoxyl radical mediated by a redox-active metal ion as a bridge. We herein synthesize one-electron-oxidized products from electronically diverse manganese(III) salen complexes in which the locus of oxidation is shown to be ligand-centered, not metal-centered, affording manganese(III)-phenoxyl radical species. The key point in the present study is an unambiguous assignment of intervalence charge transfer bands by using nonsymmetrical salen complexes, which enables us to obtain otherwise inaccessible insight into the mixed-valence property. A d(4) high-spin manganese(III) ion forms a Robin-Day class II mixed-valence system, in which electron transfer is occurring between the localized phenoxyl radical and the phenolate. This is in clear contrast to a d(8) low-spin nickel(II) ion with the same salen ligand, which induces a delocalized radical (Robin-Day class III) over the two phenolate rings, as previously reported by others. The present findings point to a fascinating possibility that electron transfer could be drastically modulated by exchanging the metal ion that bridges the two redox centers. © 2011 American Chemical Society

  2. Core Levels, Band Alignments, and Valence-Band States in CuSbS 2 for Solar Cell Applications

    DOE PAGES

    Whittles, Thomas J.; Veal, Tim D.; Savory, Christopher N.; ...

    2017-11-10

    The earth-abundant material CuSbS 2 (CAS) has shown good optical properties as a photovoltaic solar absorber material, but has seen relatively poor solar cell performance. To investigate the reason for this anomaly, the core levels of the constituent elements, surface contaminants, ionization potential, and valence-band spectra are studied by X-ray photoemission spectroscopy. The ionization potential and electron affinity for this material (4.98 and 3.43 eV) are lower than those for other common absorbers, including CuInxGa (1-x)Se 2 (CIGS). Experimentally corroborated density functional theory (DFT) calculations show that the valence band maximum is raised by the lone pair electrons from themore » antimony cations contributing additional states when compared with indium or gallium cations in CIGS. The resulting conduction band misalignment with CdS is a reason for the poor performance of cells incorporating a CAS/CdS heterojunction, supporting the idea that using a cell design analogous to CIGS is unhelpful. These findings underline the critical importance of considering the electronic structure when selecting cell architectures that optimize open-circuit voltages and cell efficiencies.« less

  3. Core Levels, Band Alignments, and Valence-Band States in CuSbS2 for Solar Cell Applications.

    PubMed

    Whittles, Thomas J; Veal, Tim D; Savory, Christopher N; Welch, Adam W; de Souza Lucas, Francisco Willian; Gibbon, James T; Birkett, Max; Potter, Richard J; Scanlon, David O; Zakutayev, Andriy; Dhanak, Vinod R

    2017-12-06

    The earth-abundant material CuSbS 2 (CAS) has shown good optical properties as a photovoltaic solar absorber material, but has seen relatively poor solar cell performance. To investigate the reason for this anomaly, the core levels of the constituent elements, surface contaminants, ionization potential, and valence-band spectra are studied by X-ray photoemission spectroscopy. The ionization potential and electron affinity for this material (4.98 and 3.43 eV) are lower than those for other common absorbers, including CuIn x Ga (1-x) Se 2 (CIGS). Experimentally corroborated density functional theory (DFT) calculations show that the valence band maximum is raised by the lone pair electrons from the antimony cations contributing additional states when compared with indium or gallium cations in CIGS. The resulting conduction band misalignment with CdS is a reason for the poor performance of cells incorporating a CAS/CdS heterojunction, supporting the idea that using a cell design analogous to CIGS is unhelpful. These findings underline the critical importance of considering the electronic structure when selecting cell architectures that optimize open-circuit voltages and cell efficiencies.

  4. Photoelectron Diffraction from Valence States of Oriented Molecules

    NASA Astrophysics Data System (ADS)

    Krüger, Peter

    2018-06-01

    The angular distribution of photoelectrons emitted from valence states of oriented molecules is investigated. The principles underlying the angular pattern formation are explained in terms of photoelectron wave interference, caused by initial state delocalization and final state photoelectron scattering. Computational approaches to photoelectron spectroscopy from molecules are briefly reviewed. Here a combination of molecular orbital calculations for the initial state and multiple scattering theory for the photoelectron final state is used and applied to the 3σ and 4σ orbitals of nitrogen and the highest occupied molecular orbital of pentacene. Appreciable perpendicular emission and circular dichroism in angular distributions is found, two effects that cannot be described by the popular plane wave approximation to the photoelectron final state.

  5. Excited state electron affinity calculations for aluminum

    NASA Astrophysics Data System (ADS)

    Hussein, Adnan Yousif

    2017-08-01

    Excited states of negative aluminum ion are reviewed, and calculations of electron affinities of the states (3s^23p^2)^1D and (3s3p^3){^5}{S}° relative to the (3s^23p)^2P° and (3s3p^2)^4P respectively of the neutral aluminum atom are reported in the framework of nonrelativistic configuration interaction (CI) method. A priori selected CI (SCI) with truncation energy error (Bunge in J Chem Phys 125:014107, 2006) and CI by parts (Bunge and Carbó-Dorca in J Chem Phys 125:014108, 2006) are used to approximate the valence nonrelativistic energy. Systematic studies of convergence of electron affinity with respect to the CI excitation level are reported. The calculated value of the electron affinity for ^1D state is 78.675(3) meV. Detailed Calculations on the ^5S°c state reveals that is 1216.8166(3) meV below the ^4P state.

  6. Electronic Structure of pi Systems: Part II. The Unification of Huckel and Valence Bond Theories.

    ERIC Educational Resources Information Center

    Fox, Marye Anne; Matsen, F. A.

    1985-01-01

    Presents a new view of the electronic structure of pi systems that unifies molecular orbital and valence bond theories. Describes construction of electronic structure diagrams (central to this new view) which demonstrate how configuration interaction can improve qualitative predictions made from simple Huckel theory. (JN)

  7. Valence-band electronic structure evolution of graphene oxide upon thermal annealing for optoelectronics

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

    Yamaguchi, Hisato; Ogawa, Shuichi; Watanabe, Daiki

    We report valence band electronic structure evolution of graphene oxide (GO) upon its thermal reduction. Degree of oxygen functionalization was controlled by annealing temperatures, and an electronic structure evolution was monitored using real-time ultraviolet photoelectron spectroscopy. We observed a drastic increase in density of states around the Fermi level upon thermal annealing at ~600 °C. The result indicates that while there is an apparent band gap for GO prior to a thermal reduction, the gap closes after an annealing around that temperature. This trend of band gap closure was correlated with electrical, chemical, and structural properties to determine a setmore » of GO material properties that is optimal for optoelectronics. The results revealed that annealing at a temperature of ~500 °C leads to the desired properties, demonstrated by a uniform and an order of magnitude enhanced photocurrent map of an individual GO sheet compared to as-synthesized counterpart.« less

  8. Valence-band electronic structure evolution of graphene oxide upon thermal annealing for optoelectronics

    DOE PAGES

    Yamaguchi, Hisato; Ogawa, Shuichi; Watanabe, Daiki; ...

    2016-09-01

    We report valence band electronic structure evolution of graphene oxide (GO) upon its thermal reduction. Degree of oxygen functionalization was controlled by annealing temperatures, and an electronic structure evolution was monitored using real-time ultraviolet photoelectron spectroscopy. We observed a drastic increase in density of states around the Fermi level upon thermal annealing at ~600 °C. The result indicates that while there is an apparent band gap for GO prior to a thermal reduction, the gap closes after an annealing around that temperature. This trend of band gap closure was correlated with electrical, chemical, and structural properties to determine a setmore » of GO material properties that is optimal for optoelectronics. The results revealed that annealing at a temperature of ~500 °C leads to the desired properties, demonstrated by a uniform and an order of magnitude enhanced photocurrent map of an individual GO sheet compared to as-synthesized counterpart.« less

  9. Evaluation of the effect of valence state on cerium oxide nanoparticle toxicity following intratracheal instillation in rats

    PubMed Central

    Dunnick, Katherine M.; Morris, Anna M.; Badding, Melissa A.; Barger, Mark; Stefaniak, Aleksandr B.; Sabolsky, Edward M.; Leonard, Stephen S.

    2016-01-01

    Cerium (Ce) is becoming a popular metal for use in electrochemical applications. When in the form of cerium oxide (CeO2), Ce can exist in both 3 + and 4 + valence states, acting as an ideal catalyst. Previous in vitro and in vivo evidence have demonstrated that CeO2 has either anti- or pro-oxidant properties, possibly due to the ability of the nanoparticles to transition between valence states. Therefore, we chose to chemically modify the nanoparticles to shift the valence state toward 3+. During the hydrothermal synthesis process, 10 mol% gadolinium (Gd) and 20 mol% Gd, were substituted into the lattice of the CeO2 nanoparticles forming a perfect solid solution with various A-site valence states. These two Gd-doped CeO2 nanoparticles were compared to pure CeO2 nanoparticles. Preliminary characteristics indicated that doping results in minimal size and zeta potential changes but alters valence state. Following characterization, male Sprague-Dawley rats were exposed to 0.5 or 1.0 mg/kg nanoparticles via a single intratracheal instillation. Animals were sacrificed and bronchoalveolar lavage fluid and various tissues were collected to determine the effect of valence state and oxygen vacancies on toxicity 1-, 7-, or 84-day post-exposure. Results indicate that damage, as measured by elevations in lactate dehydrogenase, occurred within 1-day post-exposure and was sustained 7-day post-exposure, but subsided to control levels 84-day post-exposure. Furthermore, no inflammatory signaling or lipid peroxidation occurred following exposure with any of the nanoparticles. Our results implicate that valence state has a minimal effect on CeO2 nanoparticle toxicity in vivo. PMID:26898289

  10. Electron-impact excitation of Rydberg and valence electronic states of nitric oxide: II. Integral cross sections

    NASA Astrophysics Data System (ADS)

    Brunger, M. J.; Campbell, L.; Cartwright, D. C.; Middleton, A. G.; Mojarrabi, B.; Teubner, P. J. O.

    2000-02-01

    Integral cross sections (ICSs) for the excitation of 18 excited electronic states, and four composite excited electronic states, in nitric oxide (NO) have been determined for incident electron energies of 15, 20, 30, 40 and 50 eV. These ICSs were derived by extrapolating the respective measured differential cross sections (M J Brunger et al 2000 J. Phys. B: At. Mol. Opt. Phys. 33 783) to 0° and 180° and by performing the appropriate integration. Comparison of the present ICSs with the results of those determined in earlier optical emission measurements, and from theoretical calculations is made. At each incident energy considered, the current ICSs are also summed along with the corresponding elastic and rovibrational excitation ICSs from B Mojarrabi et al (1995 J. Phys. B: At. Mol. Opt. Phys. 28 487) and the ionization cross sections from Rapp and Englander-Golden (1965 J. Chem. Phys. 43 1464), to derive an estimate of the grand total cross sections (GTSs) for e- + NO scattering. The GTSs derived in this manner are compared with the results from independent linear transmission experiments and are found to be entirely consistent with them. The present excited electronic state ICS, and those for elastic and rovibrational excitation from Mojarrabi et al , appear to represent the first set of self-consistent cross sections for electron impact scattering from NO.

  11. Influence of polyhedron distortions on calculated bond-valence sums for cations with one lone electron pair.

    PubMed

    Wang, X; Liebau, F

    2007-04-01

    In the present bond-valence model (BVM), the bond-valence parameters r(0) and b are, in general, supposed to be constant for each A-X pair and equal to 0.37 A for all A-X pairs, respectively. For [A(i)(X(j))(n)] coordination polyhedra that do not deviate strongly from regularity, these suppositions are well fulfilled and calculated values for the bond-valence sums (BVS)(i) are nearly equal to the whole-number values of the stoichiometric valence. However, application of the BVM to 2591 [L(i)(X(j))(n)] polyhedra, where L are p-block cations, i.e. cations of the 13th to 17th group of the periodic system of elements, with one lone electron pair and X = O(-II), S(-II) and Se(-II), shows that r(0i) values of individual [LX(n)] polyhedra are correlated with the absolute value /Phi(i)/ of an eccentricity parameter, Phi(i), which is higher for more distorted [LX(n)] polyhedra. As a consequence, calculated (BVS)(i) values for these polyhedra are also correlated with /Phi(i)/, rather than being numerically equal to the stoichiometric valence of L. This is interpreted as the stereochemical influence of the lone electron pair of L. It is shown that the values of the correlation parameters and the R(2) values of the correlation equations depend on the position of the L cation in the periodic system of elements, if the correlations are assumed to be linear. This observation suggests that (BVS)(L) describes a chemical quantity that is different from the stoichiometric valence of L.

  12. Magnetic properties and effect of pressure on the electronic state of EuCo2Ge2

    NASA Astrophysics Data System (ADS)

    Ashitomi, Y.; Kakihana, M.; Honda, F.; Nakamura, A.; Aoki, D.; Uwatoko, Y.; Nakashima, M.; Amako, Y.; Takeuchi, T.; Kida, T.; Tahara, T.; Hagiwara, M.; Haga, Y.; Hedo, M.; Nakama, T.; Ōnuki, Y.

    2018-05-01

    EuCo2Ge2 with the tetragonal structure is a Eu-divalent antiferromagnet with the Néel temperature TN = 23 K. The magnetic easy-axis corresponds to the [100] direction (a-axis), while the [001] direction (c-axis) is a hard-axis. The magnetization for H∥ [ 100 ] indicates a metamagnetic transition at 25 kOe and saturates above 75 kOe. On the other hand, the hard-axis magnetization increases approximately linearly and saturates above 110 kOe. The magnetic phase diagram was constructed. A characteristic feature in EuCo2Ge2 is known as a valence transition under pressure, from Eu 2+δ to Eu 3 - δ ‧(δ, δ ‧ < 1). We also clarified the valence transition by measuring the electrical resistivity under pressure. The valence transition occurs at 3 GPa, with a hysteresis, and terminates at about 4.5 GPa. Further increasing pressure, the electronic state is changed into a moderate heavy fermion state and approaches the nearly trivalent electronic state.

  13. Charge and Spin-State Characterization of Cobalt Bis( o-dioxolene) Valence Tautomers Using Co Kβ X-ray Emission and L-Edge X-ray Absorption Spectroscopies

    DOE PAGES

    Liang, H. Winnie; Kroll, Thomas; Nordlund, Dennis; ...

    2016-12-30

    The valence tautomeric states of Co(phen)(3,5-DBQ) 2 and Co(tmeda)(3,5-DBQ) 2, where 3,5-DBQ is either the semiquinone (SQ –) or catecholate (Cat 2–) form of 3,5-di- tert-butyl-1,2-benzoquinone, have been examined by a series of cobalt-specific X-ray spectroscopies. In this work, we have utilized the sensitivity of 1s3p X-ray emission spectroscopy (Kβ XES) to the oxidation and spin states of 3d transition-metal ions to determine the cobalt-specific electronic structure of valence tautomers. A comparison of their Kβ XES spectra with the spectra of cobalt coordination complexes with known oxidation and spin states demonstrates that the low-temperature valence tautomer can be described asmore » a low-spin Co III configuration and the high-temperature valence tautomer as a high-spin Co II configuration. This conclusion is further supported by Co L-edge X-ray absorption spectroscopy (L-edge XAS) of the high-temperature valence tautomers and ligand-field atomic-multiplet calculations of the Kβ XES and L-edge XAS spectra. In conclusion, the nature and strength of the magnetic exchange interaction between the cobalt center and SQ – in cobalt valence tautomers is discussed in view of the effective spin at the Co site from Kβ XES and the molecular spin moment from magnetic susceptibility measurements.« less

  14. Charge and Spin-State Characterization of Cobalt Bis( o-dioxolene) Valence Tautomers Using Co Kβ X-ray Emission and L-Edge X-ray Absorption Spectroscopies

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

    Liang, H. Winnie; Kroll, Thomas; Nordlund, Dennis

    The valence tautomeric states of Co(phen)(3,5-DBQ) 2 and Co(tmeda)(3,5-DBQ) 2, where 3,5-DBQ is either the semiquinone (SQ –) or catecholate (Cat 2–) form of 3,5-di- tert-butyl-1,2-benzoquinone, have been examined by a series of cobalt-specific X-ray spectroscopies. In this work, we have utilized the sensitivity of 1s3p X-ray emission spectroscopy (Kβ XES) to the oxidation and spin states of 3d transition-metal ions to determine the cobalt-specific electronic structure of valence tautomers. A comparison of their Kβ XES spectra with the spectra of cobalt coordination complexes with known oxidation and spin states demonstrates that the low-temperature valence tautomer can be described asmore » a low-spin Co III configuration and the high-temperature valence tautomer as a high-spin Co II configuration. This conclusion is further supported by Co L-edge X-ray absorption spectroscopy (L-edge XAS) of the high-temperature valence tautomers and ligand-field atomic-multiplet calculations of the Kβ XES and L-edge XAS spectra. In conclusion, the nature and strength of the magnetic exchange interaction between the cobalt center and SQ – in cobalt valence tautomers is discussed in view of the effective spin at the Co site from Kβ XES and the molecular spin moment from magnetic susceptibility measurements.« less

  15. Energies of rare-earth ion states relative to host bands in optical materials from electron photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Thiel, Charles Warren

    There are a vast number of applications for rare-earth-activated materials and much of today's cutting-edge optical technology and emerging innovations are enabled by their unique properties. In many of these applications, interactions between the rare-earth ion and the host material's electronic states can enhance or inhibit performance and provide mechanisms for manipulating the optical properties. Continued advances in these technologies require knowledge of the relative energies of rare-earth and crystal band states so that properties of available materials may be fully understood and new materials may be logically developed. Conventional and resonant electron photoemission techniques were used to measure 4f electron and valence band binding energies in important optical materials, including YAG, YAlO3, and LiYF4. The photoemission spectra were theoretically modeled and analyzed to accurately determine relative energies. By combining these energies with ultraviolet spectroscopy, binding energies of excited 4fN-15d and 4fN+1 states were determined. While the 4fN ground-state energies vary considerably between different trivalent ions and lie near or below the top of the valence band in optical materials, the lowest 4f N-15d states have similar energies and are near the bottom of the conduction band. As an example for YAG, the Tb3+ 4f N ground state is in the band gap at 0.7 eV above the valence band while the Lu3+ ground state is 4.7 eV below the valence band maximum; however, the lowest 4fN-15d states are 2.2 eV below the conduction band for both ions. We found that a simple model accurately describes the binding energies of the 4fN, 4fN-1 5d, and 4fN+1 states. The model's success across the entire rare-earth series indicates that measurements on two different ions in a host are sufficient to predict the energies of all rare-earth ions in that host. This information provides new insight into electron transfer transitions, luminescence quenching, and valence

  16. Puzzle maker in SmB6: accompany-type valence fluctuation state

    NASA Astrophysics Data System (ADS)

    Wu, Qi; Sun, Liling

    2017-11-01

    In recent years, studying the Kondo insulator SmB6, a strongly correlated electron material that has been puzzling the community for decades, has again become an attractive topic due to the discovery of its unusual metallic surface state coexisting with the bulk insulating state. Many efforts have been made to understand the microphysics in SmB6, but some puzzles that have been hotly debated and argued have not been solved. In this article, based on the latest progress made in our high-pressure studies on SmB6 and the accumulating results reported by other groups, we propose a notion named the ‘accompany-type valence fluctuation state’, which possibly coexists with the bulk Kondo insulating ground state of SmB6. We expect that this notion could be taken as a common starting point for understanding in a unified way most of the low-temperature phenomena observed by different experimental investigations on SmB6, thus promoting the deciphering of the puzzles. We also expect that this notion could attract rigorous theoretical interpretation and further experimental investigation, or stimulate better thinking on the physics in SmB6.

  17. Incipient class II mixed valency in a plutonium solid-state compound

    NASA Astrophysics Data System (ADS)

    Cary, Samantha K.; Galley, Shane S.; Marsh, Matthew L.; Hobart, David L.; Baumbach, Ryan E.; Cross, Justin N.; Stritzinger, Jared T.; Polinski, Matthew J.; Maron, Laurent; Albrecht-Schmitt, Thomas E.

    2017-09-01

    Electron transfer in mixed-valent transition-metal complexes, clusters and materials is ubiquitous in both natural and synthetic systems. The degree to which intervalence charge transfer (IVCT) occurs, dependent on the degree of delocalization, places these within class II or III of the Robin-Day system. In contrast to the d-block, compounds of f-block elements typically exhibit class I behaviour (no IVCT) because of localization of the valence electrons and poor spatial overlap between metal and ligand orbitals. Here, we report experimental and computational evidence for delocalization of 5f electrons in the mixed-valent PuIII/PuIV solid-state compound, Pu3(DPA)5(H2O)2 (DPA = 2,6-pyridinedicarboxylate). The properties of this compound are benchmarked by the pure PuIII and PuIV dipicolinate complexes, [PuIII(DPA)(H2O)4]Br and PuIV(DPA)2(H2O)3·3H2O, as well as by a second mixed-valent compound, PuIII[PuIV(DPA)3H0.5]2, that falls into class I instead. Metal-to-ligand charge transfer is involved in both the formation of Pu3(DPA)5(H2O)2 and in the IVCT.

  18. Solid state effects on the electronic structure of H2OEP.

    PubMed

    Marsili, M; Umari, P; Di Santo, G; Caputo, M; Panighel, M; Goldoni, A; Kumar, M; Pedio, M

    2014-12-28

    We present the results of a joint experimental and theoretical investigation concerning the effect of crystal packing on the electronic properties of the H2OEP molecule. Thin films, deposited in ultra high vacuum on metal surfaces, are investigated by combining valence band photoemission, inverse photoemission, and X-ray absorption spectroscopy. The spectra of the films are compared, when possible, with those measured in the gas phase. Once many-body effects are included in the calculations through the GW method, the electronic structure of H2OEP in the film and gas phase are accurately reproduced for both valence and conduction states. Upon going from an isolated molecule to the film phase, the electronic gap shrinks significantly and the lowest unoccupied molecular orbital (LUMO) and LUMO + 1 degeneracy is removed. The calculations show that the reduction of the transport gap in the film is entirely addressable to the enhancement of the electronic screening.

  19. The effects of valence-based and discrete emotional states on aesthetic response.

    PubMed

    Cheng, Yin-Hui

    2013-01-01

    There is increasing recognition that consumer aesthetics--the responses of consumers to the aesthetic or appearance aspects of products--has become an important area of marketing in recent years. Consumer aesthetic responses to a product are a source of pleasure for the consumer. Previous research into the aesthetic responses to products has often emphasized exterior factors and visual design, but studies have seldom considered the psychological aesthetic experience of consumers, and in particular their emotional state. This study attempts to bridge this gap by examining the link between consumers' emotions and their aesthetic response to a product. Thus, the major goal of this study was to determine how valence-based and discrete emotional states influence choice. In Studies 1 and 2, positive and negative emotions were manipulated to implement two different induction techniques and explore the effect of emotions on participants' choices in two separate experiments. The results of both experiments confirmed the predictions, indicating that aesthetic responses and purchase intention are functions of emotional valence, such that both are stronger for people in a positive emotional state than for those in a negative emotional state. Study 2 also used a neutral affective state to establish the robustness of this observed effect of incidental affect. The results of Study 3 demonstrate that aesthetic response and purchase intention are not only a function of affect valence, but also are affected by the certainty appraisal associated with specific affective states. This research, therefore, contributes to the literature by offering empirical evidence that incidental affect is a determinant of aesthetic response.

  20. On the correlations between the polyhedron eccentricity parameters and the bond-valence sums for the cations with one lone electron pair.

    PubMed

    Sidey, Vasyl

    2008-08-01

    Applicability of the Wang-Liebau polyhedron eccentricity parameter in the bond-valence model [Wang & Liebau (2007). Acta Cryst. B63, 216-228] has been found to be doubtful: the correlations between the values of the polyhedron eccentricity parameters and the bond-valence sums calculated for the cations with one lone electron pair are probably an artifact of the poorly determined bond-valence parameters.

  1. Benzonitrile: Electron affinity, excited states, and anion solvation

    NASA Astrophysics Data System (ADS)

    Dixon, Andrew R.; Khuseynov, Dmitry; Sanov, Andrei

    2015-10-01

    We report a negative-ion photoelectron imaging study of benzonitrile and several of its hydrated, oxygenated, and homo-molecularly solvated cluster anions. The photodetachment from the unsolvated benzonitrile anion to the X ˜ 1 A 1 state of the neutral peaks at 58 ± 5 meV. This value is assigned as the vertical detachment energy (VDE) of the valence anion and the upper bound of adiabatic electron affinity (EA) of benzonitrile. The EA of the lowest excited electronic state of benzonitrile, a ˜ 3 A 1 , is determined as 3.41 ± 0.01 eV, corresponding to a 3.35 eV lower bound for the singlet-triplet splitting. The next excited state, the open-shell singlet A ˜ 1 A 1 , is found about an electron-volt above the triplet, with a VDE of 4.45 ± 0.01 eV. These results are in good agreement with ab initio calculations for neutral benzonitrile and its valence anion but do not preclude the existence of a dipole-bound state of similar energy and geometry. The step-wise and cumulative solvation energies of benzonitrile anions by several types of species were determined, including homo-molecular solvation by benzonitrile, hydration by 1-3 waters, oxygenation by 1-3 oxygen molecules, and mixed solvation by various combinations of O2, H2O, and benzonitrile. The plausible structures of the dimer anion of benzonitrile were examined using density functional theory and compared to the experimental observations. It is predicted that the dimer anion favors a stacked geometry capitalizing on the π-π interactions between the two partially charged benzonitrile moieties.

  2. Simultaneous First-Order Valence and Oxygen Vacancy Order/Disorder Transitions in (Pr 0.85 Y 0.15 ) 0.7 Ca 0.3 CoO 3-δ via Analytical Transmission Electron Microscopy

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

    Gulec, Ahmet; Phelan, Daniel; Leighton, Chris

    Perovskite cobaltites have been studied for years as some of the few solids to exhibit thermally driven spin-state crossovers. The unanticipated first-order spin and electronic transitions recently discovered in Pr-based cobaltites are notably different from these conventional crossovers, and are understood in terms of a unique valence transition. In essence, the Pr valence is thought to spontaneously shift from 3+ toward 4+ on cooling, driving subsequent transitions in Co valence and electronic/magnetic properties. Here, we apply temperature-dependent transmission electron microscopy and spectroscopy to study this phenomenon, for the first time with atomic spatial resolution, in the prototypical (Pr 0.85Y 0.15)(0.70)more » Ca 0.30CoO 3-δ. In addition to the direct spectroscopic observation of charge transfer between Pr and Co at the 165 K transition (on both the Pr and O edges), we also find a simultaneous order/disorder transition associated with O vacancies. Remarkably, the first-order valence change drives a transition between ordered and random O vacancies, at constant O vacancy density, demonstrating reversible crystallization of such vacancies even at cryogenic temperatures.« less

  3. Electronic properties and bonding in Zr Hx thin films investigated by valence-band x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Magnuson, Martin; Schmidt, Susann; Hultman, Lars; Högberg, Hans

    2017-11-01

    The electronic structure and chemical bonding in reactively magnetron sputtered Zr Hx (x =0.15 , 0.30, 1.16) thin films with oxygen content as low as 0.2 at.% are investigated by 4d valence band, shallow 4p core-level, and 3d core-level x-ray photoelectron spectroscopy. With increasing hydrogen content, we observe significant reduction of the 4d valence states close to the Fermi level as a result of redistribution of intensity toward the H 1s-Zr 4d hybridization region at ˜6 eV below the Fermi level. For low hydrogen content (x =0.15 , 0.30), the films consist of a superposition of hexagonal closest-packed metal (α phase) and understoichiometric δ -Zr Hx (Ca F2 -type structure) phases, while for x =1.16 , the films form single-phase Zr Hx that largely resembles that of stoichiometric δ -Zr H2 phase. We show that the cubic δ -Zr Hx phase is metastable as thin film up to x =1.16 , while for higher H contents the structure is predicted to be tetragonally distorted. For the investigated Zr H1.16 film, we find chemical shifts of 0.68 and 0.51 eV toward higher binding energies for the Zr 4 p3 /2 and 3 d5 /2 peak positions, respectively. Compared to the Zr metal binding energies of 27.26 and 178.87 eV, this signifies a charge transfer from Zr to H atoms. The change in the electronic structure, spectral line shapes, and chemical shifts as a function of hydrogen content is discussed in relation to the charge transfer from Zr to H that affects the conductivity by charge redistribution in the valence band.

  4. Photoelectron spectrum of valence anions of uracil and first-principles calculations of excess electron binding energies.

    PubMed

    Bachorz, Rafał A; Klopper, Wim; Gutowski, Maciej; Li, Xiang; Bowen, Kit H

    2008-08-07

    The photoelectron spectrum (PES) of the uracil anion is reported and discussed from the perspective of quantum chemical calculations of the vertical detachment energies (VDEs) of the anions of various tautomers of uracil. The PES peak maximum is found at an electron binding energy of 2.4 eV, and the width of the main feature suggests that the parent anions are in a valence rather than a dipole-bound state. The canonical tautomer as well as four tautomers that result from proton transfer from an NH group to a C atom were investigated computationally. At the Hartree-Fock and second-order Moller-Plesset perturbation theory levels, the adiabatic electron affinity (AEA) and the VDE have been converged to the limit of a complete basis set to within +/-1 meV. Post-MP2 electron-correlation effects have been determined at the coupled-cluster level of theory including single, double, and noniterative triple excitations. The quantum chemical calculations suggest that the most stable valence anion of uracil is the anion of a tautomer that results from a proton transfer from N1H to C5. It is characterized by an AEA of 135 meV and a VDE of 1.38 eV. The peak maximum is as much as 1 eV larger, however, and the photoelectron intensity is only very weak at 1.38 eV. The PES does not lend support either to the valence anion of the canonical tautomer, which is the second most stable anion, and whose VDE is computed at about 0.60 eV. Agreement between the peak maximum and the computed VDE is only found for the third most stable tautomer, which shows an AEA of approximately -0.1 eV and a VDE of 2.58 eV. This tautomer results from a proton transfer from N3H to C5. The results illustrate that the characteristics of biomolecular anions are highly dependent on their tautomeric form. If indeed the third most stable anion is observed in the experiment, then it remains an open question why and how this species is formed under the given conditions.

  5. The valence bond glass phase

    NASA Astrophysics Data System (ADS)

    Tarzia, M.; Biroli, G.

    2008-06-01

    We show that a new glassy phase can emerge in the presence of strong magnetic frustration and quantum fluctuations. It is a valence bond glass (VBG). We study its properties solving the Hubbard-Heisenberg model on a Bethe lattice within the large-N limit introduced by Affleck and Marston. We work out the phase diagram that contains Fermi liquid, dimer and valence bond glass phases. This new glassy phase has no electronic or spin gap (although a pseudo-gap is observed), it is characterized by long-range critical valence bond correlations and is not related to any magnetic ordering. As a consequence, it is quite different from both valence bond crystals and spin glasses.

  6. Electrochemical variational study of donor/acceptor orbital mixing and electronic coupling in cyanide-bridged mixed-valence complexes

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

    Dong, Yuhuua; Hupp, J.T.

    1992-07-08

    Cyanide-bridged mixed-valence complexes are interesting examples of strongly covalently linked redox systems which, nevertheless, exist in valence-localized form. As mixed-valence species, they display fairly intense intervalence (or metal-to-metal) charge-transfer transitions ([epsilon] [approx] 3000 M[sup [minus]1] cm[sup [minus]1]), which tend to be shifted toward the visible region from the near-infrared on account of substantial redox asymmetry. The authors have recently succeeded in obtaining (by femtosecond transient absorbance spectroscopy) a direct measure of the thermal kinetics (k[sub ET]) of the highly exothermic back-electron-transfer reaction which follows intervalence excitation in one of these complexes, (H[sub 3]N)[sub 5]Ru-NC-Fe(CN)[sub 5][sup [minus

  7. A Transition from Localized to Strongly Correlated Electron Behavior and Mixed Valence Driven by Physical or Chemical Pressure in ACo 2As 2 (A = Eu and Ca)

    DOE PAGES

    Tan, Xiaoyan; Fabbris, Gilberto; Haskel, Daniel; ...

    2016-02-03

    In this paper, we demonstrate that the action of physical pressure, chemical compression, or aliovalent substitution in ACo 2As 2 (A = Eu and Ca) has a general consequence of causing these antiferromagnetic materials to become ferromagnets. In all cases, the mixed valence triggered at the electropositive A site results in the increase of the Co 3d density of states at the Fermi level. Remarkably, the dramatic alteration of magnetic behavior results from the very minor (<0.15 electron) change in the population of the 3d orbitals. The mixed valence state of Eu observed in the high-pressure (HP) form of EuComore » 2As 2 exhibits a remarkable stability, achieving the average oxidation state of +2.25 at 12.6 GPa. In the case of CaCo 2As 2, substituting even 10% of Eu or La into the Ca site causes ferromagnetic ordering of Co moments. Similar to HP-EuCo 2As 2, the itinerant 3d ferromagnetism emerges from electronic doping into the Co layer because of chemical compression of Eu sites in Ca 0.9Eu 0.1Co 1.91As 2 or direct electron doping in Ca 0.85La 0.15Co 1.89As 2. Finally, the results reported herein demonstrate the general possibility of amplifying minor localized electronic effects to achieve major changes in material’s properties via involvement of strongly correlated electrons.« less

  8. Electronic structure and thermoelectric properties of half-Heusler compounds with eight electron valence count—KScX (X = C and Ge)

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

    Ciftci, Yasemin O.; Mahanti, Subhendra D.

    Electronic band structure and structural properties of two representative half-Heusler (HH) compounds with 8 electron valence count (VC), KScC and KScGe, have been studied using first principles methods within density functional theory and generalized gradient approximation. These systems differ from the well studied class of HH compounds like ZrNiSn and ZrCoSb which have VC = 18 because of the absence of d electrons of the transition metal atoms Ni and Co. Electronic transport properties such as Seebeck coefficient (S), electrical conductivity (σ), electronic thermal conductivity (κ{sub e}) (the latter two scaled by electronic relaxation time), and the power factor (S{sup 2}σ) havemore » been calculated using semi-classical Boltzmann transport theory within constant relaxation time approximation. Both the compounds are direct band gap semiconductors with band extrema at the X point. Their electronic structures show a mixture of heavy and light bands near the valance band maximum and highly anisotropic conduction and valence bands near the band extrema, desirable features of good thermoelectric. Optimal p- or n-type doping concentrations have been estimated based on thermopower and maximum power factors. The optimum room temperature values of S are ∼1.5 times larger than that of the best room temperature thermoelectric Bi{sub 2}Te{sub 3}. We also discuss the impact of the band structure on deviations from Weidemann-Franz law as one tunes the chemical potential across the band gap.« less

  9. Measurement of the background in Auger-Photoemission Spectra (APECS) associated with multi-electron and inelastic valence band photoemission processes

    NASA Astrophysics Data System (ADS)

    Joglekar, Prasad; Shastry, Karthik; Hulbert, Steven; Weiss, Alex

    2014-03-01

    Auger Photoelectron Coincidence Spectroscopy (APECS), in which the Auger spectra is measured in coincidence with the core level photoelectron, is capable of pulling difficult to observe low energy Auger peaks out of a large background due mostly to inelastically scattered valence band photoelectrons. However the APECS method alone cannot eliminate the background due to valence band VB photoemission processes in which the initial photon energy is shared by 2 or more electrons and one of the electrons is in the energy range of the core level photoemission peak. Here we describe an experimental method for estimating the contributions from these background processes in the case of an Ag N23VV Auger spectra obtained in coincidence with the 4p photoemission peak. A beam of 180eV photons was incident on a Ag sample and a series of coincidence measurements were made with one cylindrical mirror analyzer (CMA) set at a fixed energies between the core and the valence band and the other CMA scanned over a range corresponding to electrons leaving the surface between 0eV and the 70eV. The spectra obtained were then used to obtain an estimate of the background in the APECS spectra due to multi-electron and inelastic VB photoemission processes. NSF, Welch Foundation.

  10. EELS Valence Mapping in Electron Beam Sensitive FeFx/C Nanocomposites

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

    Cosandey, F.; Al-Sharab, J.F.; Amatucci, Glenn G.

    A new type of positive electrodes for Li-Ion batteries has been synthesized based on FeF{sub 2}/C and FeF3/C nanocomposites with particle size in the 8-12 nm range [1]. The measured high capacities rely on a complete reduction of Fe to its metallic state according to the following reaction: xLi{sup +}+xe{sup -} +Fe{sup x+}Fx = xLiF + Fe{sup 0}, where x=3 and x=2 for FeF3/C and FeF2/C respectively. This electrochemical reaction involves a change in valence state of Fe from 3+ or 2+ to 0 that can be determined uniquely by EELS from the peak energy of the L{sub 3} linemore » and from the L{sub 3}/L{sub 2} line intensity ratio. In this paper, we report EELS mapping results on the electrochemical conversion processes and in particular the mapping of the Fe valence state before and after discharge. This work was performed with a Hitachi HF2000 equipped with a Gatan PEELS and with a FEI CM200 FEG TEM equipped with a Gatan GIF. Both instruments were operated in STEM mode at 200kV with an EELS collection half angle of {beta}=5 mrad and spectrum imaging software.« less

  11. Cluster molecular orbital description of the electronic structures of mixed-valence iron oxides and silicates

    USGS Publications Warehouse

    Sherman, David M.

    1986-01-01

    A molecular orbital description, based on spin-unrestricted X??-scattered wave calculations, is given for the electronic structures of mixed valence iron oxides and silicates. The cluster calculations show that electron hopping and optical intervalence charge-transger result from weak FeFe bonding across shared edges of FeO6 coordination polyhedra. In agreement with Zener's double exchange model, FeFe bonding is found to stabilize ferromagnetic coupling between Fe2+ and Fe3+ cations. ?? 1986.

  12. Experimental and theoretical study of the electronic spectrum of the BAr2 complex: Transition to the excited valence B(2s2p2 2D) state

    NASA Astrophysics Data System (ADS)

    Krumrine, Jennifer R.; Alexander, Millard H.; Yang, Xin; Dagdigian, Paul J.

    2000-03-01

    The 2s2p22D←2s22p 2P valence transition in the BAr2 cluster is investigated in a collaborative experimental and theoretical study. Laser fluorescence excitation spectra of a supersonic expansion of B atoms entrained in Ar at high source backing pressures display several features not assignable to the BAr complex. Resonance fluorescence is not observed, but instead emission from the lower 3s state. Size-selected fluorescence depletion spectra show that these features in the excitation spectrum are primarily due to the BAr2 complex. This electronic transition within BAr2 is modeled theoretically, similarly to our earlier study of the 3s←2p transition [M. H. Alexander et al., J. Chem. Phys. 106, 6320 (1997)]. The excited potential energy surfaces of the fivefold degenerate B(2s2p22D) state within the ternary complex are computed in a pairwise-additive model employing diatomic BAr potential energy curves which reproduce our previous experimental observations on the electronic states emanating from the B(2D)+Ar asymptote. The simulated absorption spectrum reproduces reasonably well the observed fluorescence depletion spectrum. The theoretical model lends insight into the energetics of the approach of B to multiple Ar atoms, and how the orientation of B p-orbitals governs the stability of the complex.

  13. The equation-of-motion coupled cluster method for triple electron attached states

    NASA Astrophysics Data System (ADS)

    Musiał, Monika; Olszówka, Marta; Lyakh, Dmitry I.; Bartlett, Rodney J.

    2012-11-01

    The initial implementation of the triple electron attachment (TEA) equation-of-motion (EOM) coupled cluster (CC) method is presented, aiming at the description of electronic states with three open shell electrons outside a suitably chosen closed shell vacuum. In particular, such an approach can be used for describing dissociation of chemical bonds predominantly formed by three valence electrons, for example, in LiC and NaC molecules. Both ground and excited states are considered while rigorously maintaining the correct spin value. The preliminary results show a correct asymptotic behavior of the dissociation curves. At the same time, we emphasize that a chemically accurate description will require an extension of the minimal TEA-EOM-CC model introduced here, analogous to those already used in the double ionization potential and double electron attachment methods.

  14. Digital modulation of the nickel valence state in a cuprate-nickelate heterostructure

    NASA Astrophysics Data System (ADS)

    Wrobel, F.; Geisler, B.; Wang, Y.; Christiani, G.; Logvenov, G.; Bluschke, M.; Schierle, E.; van Aken, P. A.; Keimer, B.; Pentcheva, R.; Benckiser, E.

    2018-03-01

    Layer-by-layer oxide molecular-beam epitaxy has been used to synthesize cuprate-nickelate multilayer structures of composition (La2CuO4)m/LaO /(LaNiO3)n . In a combined experimental and theoretical study, we show that these structures allow a clean separation of dopant and doped layers. Specifically, the LaO layer separating cuprate and nickelate blocks provides an additional charge that, according to density-functional theory calculations, is predominantly accommodated in the interfacial nickelate layers. This is reflected in an elongation of bond distances and changes in valence state, as observed by scanning transmission electron microscopy and x-ray absorption spectroscopy. Moreover, the predicted charge disproportionation in the nickelate interface layers leads to a metal-to-insulator transition when the thickness is reduced to n =2 , as observed in electrical transport measurements. The results exemplify the perspectives of charge transfer in metal-oxide multilayers to induce doping without introducing chemical and structural disorder.

  15. Recycling of the High Valence States of Heme Proteins by Cysteine Residues of Thimet-Oligopeptidase

    PubMed Central

    Ferreira, Juliana C.; Icimoto, Marcelo Y.; Marcondes, Marcelo F.; Oliveira, Vitor; Nascimento, Otaciro R.; Nantes, Iseli L.

    2013-01-01

    The peptidolytic enzyme THIMET-oligopeptidase (TOP) is able to act as a reducing agent in the peroxidase cycle of myoglobin (Mb) and horseradish peroxidase (HRP). The TOP-promoted recycling of the high valence states of the peroxidases to the respective resting form was accompanied by a significant decrease in the thiol content of the peptidolytic enzyme. EPR (electron paramagnetic resonance) analysis using DBNBS spin trapping revealed that TOP also prevented the formation of tryptophanyl radical in Mb challenged by H2O2. The oxidation of TOP thiol groups by peroxidases did not promote the inactivating oligomerization observed in the oxidation promoted by the enzyme aging. These findings are discussed towards a possible occurrence of these reactions in cells. PMID:24223886

  16. Determining the Oxygen Fugacity of Lunar Pyroclastic Glasses Using Vanadium Valence - An Update

    NASA Technical Reports Server (NTRS)

    Karner, J. M.; Sutton, S. R.; Papike, J. J.; Shearer, C. K.; Jones, J. H.; Newville, M.

    2004-01-01

    We have been developing an oxygen barometer based on the valence state of V (V(2+), V(3+), V(4+), and V(5+)) in solar system basaltic glasses. The V valence is determined by synchrotron micro x-ray absorption near edge structure (XANES), which uses x-ray absorption associated with core-electronic transitions (absorption edges) to reveal a pre-edge peak whose intensity is directly proportional to the valence state of an element. XANES has advantages over other techniques that determine elemental valence because measurements can be made non-destructively in air and in situ on conventional thin sections at a micrometer spatial resolution with elemental sensitivities of approx. 100 ppm. Recent results show that fO2 values derived from the V valence technique are consistent with fO2 estimates determined by other techniques for materials that crystallized above the IW buffer. The fO2's determined by V valence (IW-3.8 to IW-2) for the lunar pyroclastic glasses, however, are on the order of 1 to 2.8 log units below previous estimates. Furthermore, the calculated fO2's decrease with increasing TiO2 contents from the A17 VLT to the A17 Orange glasses. In order to investigate these results further, we have synthesized lunar green and orange glasses and examined them by XANES.

  17. Simulating Ru L 3 -Edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

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

    Van Kuiken, Benjamin E.; Valiev, Marat; Daifuku, Stephanie L.

    2013-05-30

    Ruthenium L3-edge X-ray absorption (XA) spectroscopy probes unoccupied 4d orbitals of the metal atom and is increasingly being used to investigate the local electronic structure in ground and excited electronic states of Ru complexes. The simultaneous development of computational tools for simulating Ru L3-edge spectra is crucial for interpreting the spectral features at a molecular level. This study demonstrates that time-dependent density functional theory (TDDFT) is a viable and predictive tool for simulating ruthenium L3-edge XA spectroscopy. We systematically investigate the effects of exchange correlation functional and implicit and explicit solvent interactions on a series of RuII and RuIII complexesmore » in their ground and electronic excited states. The TDDFT simulations reproduce all of the experimentally observed features in Ru L3-edge XA spectra within the experimental resolution (0.4 eV). Our simulations identify ligand-specific charge transfer features in complicated Ru L3-edge spectra of [Ru(CN)6]4- and RuII polypyridyl complexes illustrating the advantage of using TDDFT in complex systems. We conclude that the B3LYP functional most accurately predicts the transition energies of charge transfer features in these systems. We use our TDDFT approach to simulate experimental Ru L3-edge XA spectra of transition metal mixed-valence dimers of the form [(NC)5MII-CN-RuIII(NH3)5] (where M = Fe or Ru) dissolved in water. Our study determines the spectral signatures of electron delocalization in Ru L3-edge XA spectra. We find that the inclusion of explicit solvent molecules is necessary for reproducing the spectral features and the experimentally determined valencies in these mixed-valence complexes. This study validates the use of TDDFT for simulating Ru 2p excitations using popular quantum chemistry codes and providing a powerful interpretive tool for equilibrium and ultrafast Ru L3-edge XA spectroscopy.« less

  18. Introducing Students to Inner Sphere Electron Transfer Concepts through Electrochemistry Studies in Diferrocene Mixed-Valence Systems

    ERIC Educational Resources Information Center

    Ventura, Karen; Smith, Mark B.; Prat, Jacob R.; Echegoyen, Lourdes E.; Villagran´, Dino

    2017-01-01

    We have designed a 4 h physical chemistry laboratory to introduce upper division students to electrochemistry concepts, including mixed valency and electron transfer (ET), using cyclic and differential pulse voltammetries. In this laboratory practice, students use a ferrocene dimer consisting of two ferrocene centers covalently bonded through a…

  19. Theory of Valence Transition

    NASA Astrophysics Data System (ADS)

    Misawa, S.; Takano, F.

    1981-01-01

    The valence transition phenomena occurring in rare-earth compounds are studied by using the periodic Anderson model with the electron-phonon coupling. This electron-phonon interaction G is treated in the Hartree-Fock approximation. The Coulomb repulsion U between f-electrons on the same site is taken to be ∞, and the decoupling method of Roth is used for the higher order Green function considering the mixing interaction to be small. We put the condition that the total number of electrons is a constant, and calculate the numbers of f- and d-electrons as functions of the original energy of f-electron by using the Green functions. The first order transition is shown to occur if G ≳ (1/2)W, where W is the width of the original d-band. The energy of f-electron at which the insulator and the metallic phase have the same ground state energy is calculated asɛc ≃ (1/2)(G-(1/2)W) + (2V^2/W) log |(G-W/2)/(G+W/2)|- (V^2/8W) log | (G-W/2)(G-(3/2)W) |. The magnetic susceptibilities of both phases are also calculated, but the result is not good, showing the decoupling method used here is not appropriate for the calculation of magnetic properties.

  20. Imaging of the outer valence orbitals of CO by electron momentum spectroscopy — Comparison with high level MRSD-CI and DFT calculations

    NASA Astrophysics Data System (ADS)

    Fan, X. W.; Chen, X. J.; Zhou, S. J.; Zheng, Y.; Brion, C. E.; Frey, R.; Davidson, E. R.

    1997-09-01

    A newly constructed energy dispersive multichannel electron momentum spectrometer has been used to image the electron density of the outer valence orbitals of CO with high precision. Binding energy spectra are obtained at a coincidence energy resolution of 1.2 eV fwhm. The measured electron density profiles in momentum space for the outer valence orbitals of CO are compared with cross sections calculated using SCF wavefunctions with basis sets of varying complexity up to near-Hartree-Fock limit in quality. The effects of correlation and electronic relaxation on the calculated momentum profiles are investigated using large MRSD-CI calculations of the full ion-neutral overlap distributions, as well as large basis set DFT calculations with local and non-local (gradient corrected) functionals.

  1. Effect of valence state and particle size on NO oxidation in fresh and aged Pt-based diesel oxidation catalysts

    NASA Astrophysics Data System (ADS)

    Liang, Yanli; Ding, Xinmei; Zhao, Ming; Wang, Jianli; Chen, Yaoqiang

    2018-06-01

    To stabilize Pt, Magnesium-modified SiO2-Al2O3 materials was used to impregnate with Pt, which could strengthen the bonding effect between Pt and Mg. Before and after aging, both showed a higher dispersion. High valence state of Pt in fresh modified catalyst was unfavorable of NO oxidation, indicating that the valence state of Pt was the leader factor in fresh catalytic performance. While for the aged Mg-modified sample, its reaction temperature of 30% NO conversion lowered by around 30 °C. The Pt stabilization via interacting with Mg derives a relation that the variation of Pt valence state and its exposed sites played a significant role in fresh and aged catalytic NO activity, respectively.

  2. Visible light photoreactivity from hybridization states between carbon nitride bandgap states and valence states in Nb and Ti oxides

    NASA Astrophysics Data System (ADS)

    Lee, Hosik; Ohno, Takahisa

    2013-03-01

    For better efficiency as photocatalysts, N-doping for visible light reactivity has been intensively studied in Lamellar niobic and titanic solid acids (HNb3O8, H2Ti4O9), and its microscopic structures have been debated in this decade. We calculate the layered solid acids' structures and bandgaps. Bandgap reduction by carbon nitride adsorption in interlayer space is observed computationally. It originates from localized nitrogen states which form delocalized top-valence states by hybridizing with the host oxygen states and can contribute to photo-current.

  3. A valence bond study of three-center four-electron pi bonding: electronegativity vs electroneutrality.

    PubMed

    DeBlase, Andrew; Licata, Megan; Galbraith, John Morrison

    2008-12-18

    Three-center four-electron (3c4e) pi bonding systems analogous to that of the ozone molecule have been studied using modern valence bond theory. Molecules studied herein consist of combinations of first row atoms C, N, and O with the addition of H atoms where appropriate in order to preserve the 3c4e pi system. Breathing orbital valence bond (BOVB) calculations were preformed at the B3LYP/6-31G**-optimized geometries in order to determine structural weights, pi charge distributions, resonance energies, and pi bond energies. It is found that the most weighted VB structure depends on atomic electronegativity and charge distribution, with electronegativity as the dominant factor. By nature, these systems are delocalized, and therefore, resonance energy is the main contributor to pi bond energies. Molecules with a single dominant VB structure have low resonance energies and therefore low pi bond energies.

  4. Electronic structure of lanthanide scandates

    NASA Astrophysics Data System (ADS)

    Mizzi, Christopher A.; Koirala, Pratik; Marks, Laurence D.

    2018-02-01

    X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and density functional theory calculations were used to study the electronic structure of three lanthanide scandates: GdSc O3,TbSc O3 , and DySc O3 . X-ray photoelectron spectra simulated from first-principles calculations using a combination of on-site hybrid and GGA +U methods were found to be in good agreement with experimental x-ray photoelectron spectra. The hybrid method was used to model the ground state electronic structure and the GGA +U method accounted for the shift of valence state energies due to photoelectron emission via a Slater-Janak transition state approach. From these results, the lanthanide scandate valence bands were determined to be composed of Ln 4 f ,O 2 p , and Sc 3 d states, in agreement with previous work. However, contrary to previous work the minority Ln 4 f states were found to be located closer to, and in some cases at, the valence band maximum. This suggests that minority Ln 4 f electrons may play a larger role in lanthanide scandate properties than previously thought.

  5. Hierarchy effect on electronic structure and core-to-valence transitions in bone tissue: perspectives in medical nanodiagnostics of mineralized bone

    NASA Astrophysics Data System (ADS)

    Samoilenko, Dmitrii O.; Avrunin, Alexander S.; Pavlychev, Andrey A.

    2017-06-01

    Electronic structure and core-to-valence transitions in bone tissue are examined in the framework of the morphological 3DSL model that takes into account (i) structural and functional organization of the skeleton in the normal and pathological conditions and (ii) peculiarities of electron wave propagation in a three-dimensional superlattice of "black-nanocrystallites-in-muddy-waters". Our focus is on the HAP-to-bone red shifts of core-to-valence transitions near Ca and P 2p and O 1s edges in single-crystal hydroxyapatite (HAP) Ca10(PO4)6(OH)2. The origin of the HAP-to-bone shift is discussed and the extended comparative analysis of the experimental data is performed. The detected spectral shift is assigned with the effect of hierarchical organization of bone tissue. This hierarchy effect on the core-to-valence transition energies is regarded as a promising tool for medical imaging and perspective pathway for nanodiagnostics of mineralized bone. Contribution to the Topical Issue "Dynamics of Systems at the Nanoscale", edited by Andrey Solov'yov and Andrei Korol.

  6. Location and valence state of strontium cations on the framework of a carbon dioxide selective porous silicoaluminophosphate

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

    Zhang, Li; Rivera-Ramos, Milton E.; Hernández-Maldonado, Arturo J.

    2014-05-28

    A Sr{sup 2+}-SAPO-34 material that displays superior CO2 adsorption selectivity and capacity was characterized via XPS and UV-vis spectroscopy to elucidate the valence state of strontium cations and framework silicon environment. Most importantly, the location of the strontium has been estimated from a Rietveld refinement analysis of synchrotron diffraction data. The XPS analysis indicated that the apparent valence state of the strontium is less than 2, an indication of its interaction with the large anionic framework. Furthermore, UV-vis tests pointed to changes in the silicon environment, plausibly related to this valence state or framework faulting. For the refinement, the analysismore » found that strontium occupied two unique sites: a site Sr1 slightly displaced from six-membered rings and a site Sr2 positioned at the top or bottom of the eight-membered rings. The latter position favors the interaction of the alkaline earth metal with CO{sub 2}, probably resulting in an enhanced electric field-quadrupole moment interaction.« less

  7. Probability of Two-Step Photoexcitation of Electron from Valence Band to Conduction Band through Doping Level in TiO2.

    PubMed

    Nishikawa, Masami; Shiroishi, Wataru; Honghao, Hou; Suizu, Hiroshi; Nagai, Hideyuki; Saito, Nobuo

    2017-08-17

    For an Ir-doped TiO 2 (Ir:TiO 2 ) photocatalyst, we examined the most dominant electron-transfer path for the visible-light-driven photocatalytic performance. The Ir:TiO 2 photocatalyst showed a much higher photocatalytic activity under visible-light irradiation than nondoped TiO 2 after grafting with the cocatalyst of Fe 3+ . For the Ir:TiO 2 photocatalyst, the two-step photoexcitation of an electron from the valence band to the conduction band through the Ir doping level occurred upon visible-light irradiation, as observed by electron spin resonance spectroscopy. The two-step photoexcitation through the doping level was found to be a more stable process with a lower recombination rate of hole-electron pairs than the two-step photoexcitation process through an oxygen vacancy. Once electrons are photoexcited to the conduction band by the two-step excitation, the electrons can easily transfer to the surface because the conduction band is a continuous electron path, whereas the electrons photoexcited at only the doping level could not easily transfer to the surface because of the discontinuity of this path. The observed two-step photoexcitation from the valence band to the conduction band through the doping level significantly contributes to the enhancement of the photocatalytic performance.

  8. Spin and valence dependence of iron partitioning in Earth’s deep mantle

    PubMed Central

    Piet, Hélène; Badro, James; Nabiei, Farhang; Dennenwaldt, Teresa; Shim, Sang-Heon; Cantoni, Marco; Hébert, Cécile; Gillet, Philippe

    2016-01-01

    We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron microanalysis (focused ion beam and aberration-corrected transmission electron microscopy) to study the distribution and valence of iron in Earth’s lower mantle as a function of depth and composition. Our data reconcile the apparently discrepant existing dataset, by clarifying the effects of spin (high/low) and valence (ferrous/ferric) states on iron partitioning in the deep mantle. In aluminum-bearing compositions relevant to Earth’s mantle, iron concentration in silicates drops above 70 GPa before increasing up to 110 GPa with a minimum at 85 GPa; it then dramatically drops in the postperovskite stability field above 116 GPa. This compositional variation should strengthen the lowermost mantle between 1,800 km depth and 2,000 km depth, and weaken it between 2,000 km depth and the D” layer. The succession of layers could dynamically decouple the mantle above 2,000 km from the lowermost mantle, and provide a rheological basis for the stabilization and nonentrainment of large low-shear-velocity provinces below that depth. PMID:27647917

  9. Unifying Exchange Sensitivity in Transition-Metal Spin-State Ordering and Catalysis through Bond Valence Metrics.

    PubMed

    Gani, Terry Z H; Kulik, Heather J

    2017-11-14

    Accurate predictions of spin-state ordering, reaction energetics, and barrier heights are critical for the computational discovery of open-shell transition-metal (TM) catalysts. Semilocal approximations in density functional theory, such as the generalized gradient approximation (GGA), suffer from delocalization error that causes them to overstabilize strongly bonded states. Descriptions of energetics and bonding are often improved by introducing a fraction of exact exchange (e.g., erroneous low-spin GGA ground states are instead correctly predicted as high-spin with a hybrid functional). The degree of spin-splitting sensitivity to exchange can be understood based on the chemical composition of the complex, but the effect of exchange on reaction energetics within a single spin state is less well-established. Across a number of model iron complexes, we observe strong exchange sensitivities of reaction barriers and energies that are of the same magnitude as those for spin splitting energies. We rationalize trends in both reaction and spin energetics by introducing a measure of delocalization, the bond valence of the metal-ligand bonds in each complex. The bond valence thus represents a simple-to-compute property that unifies understanding of exchange sensitivity for catalytic properties and spin-state ordering in TM complexes. Close agreement of the resulting per-metal-organic-bond sensitivity estimates, together with failure of alternative descriptors demonstrates the utility of the bond valence as a robust descriptor of how differences in metal-ligand delocalization produce differing relative energetics with exchange tuning. Our unified description explains the overall effect of exact exchange tuning on the paradigmatic two-state FeO + /CH 4 reaction that combines challenges of spin-state and reactivity predictions. This new descriptor-sensitivity relationship provides a path to quantifying how predictions in transition-metal complex screening are sensitive to the

  10. Estimation of electronegativity values of elements in different valence states.

    PubMed

    Li, Keyan; Xue, Dongfeng

    2006-10-05

    The electronegativities of 82 elements in different valence states and with the most common coordination numbers have been quantitatively calculated on the basis of an effective ionic potential defined by the ionization energy and ionic radius. It is found that for a given cation, the electronegativity increases with increasing oxidation state and decreases with increasing coordination number. For the transition-metal cations, the electronegativity of the low-spin state is higher than that of the high-spin state. The ligand field stabilization, the first filling of p orbitals, the transition-metal contraction, and especially the lanthanide contraction are well-reflected by the relative values of our proposed electronegativity. This new scale is useful for us to estimate some quantities (e.g., the Lewis acid strength for the main group elements and the hydration free energy for the first transition series) and predict the structure and property of materials.

  11. Influence of metallic surface states on electron affinity of epitaxial AlN films

    NASA Astrophysics Data System (ADS)

    Mishra, Monu; Krishna, Shibin; Aggarwal, Neha; Gupta, Govind

    2017-06-01

    The present article investigates surface metallic states induced alteration in the electron affinity of epitaxial AlN films. AlN films grown by plasma-assisted molecular beam epitaxy system with (30% and 16%) and without metallic aluminium on the surface were probed via photoemission spectroscopic measurements. An in-depth analysis exploring the influence of metallic aluminium and native oxide on the electronic structure of the films is performed. It was observed that the metallic states pinned the Fermi Level (FL) near valence band edge and lead to the reduction of electron affinity (EA). These metallic states initiated charge transfer and induced changes in surface and interface dipoles strength. Therefore, the EA of the films varied between 0.6-1.0 eV due to the variation in contribution of metallic states and native oxide. However, the surface barrier height (SBH) increased (4.2-3.5 eV) adversely due to the availability of donor-like surface states in metallic aluminium rich films.

  12. Valence ionized states of iron pentacarbonyl and eta5-cyclopentadienyl cobalt dicarbonyl studied by symmetry-adapted cluster-configuration interaction calculation and collision-energy resolved Penning ionization electron spectroscopy.

    PubMed

    Fukuda, Ryoichi; Ehara, Masahiro; Nakatsuji, Hiroshi; Kishimoto, Naoki; Ohno, Koichi

    2010-02-28

    Valence ionized states of iron pentacarbonyl Fe(CO)(5) and eta(5)-cyclopentadienyl cobalt dicarbonyl Co(eta(5)-C(5)H(5))(CO)(2) have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy (2D-PIES), and symmetry-adapted cluster-configuration interaction calculations. Theory provided reliable assignments for the complex ionization spectra of these molecules, which have metal-carbonyl bonds. Theoretical ionization energies agreed well with experimental observations and the calculated wave functions could explain the relative intensities of PIES spectra. The collision-energy dependence of partial ionization cross sections (CEDPICS) was obtained by 2D-PIES. To interpret these CEDPICS, the interaction potentials between the molecules and a Li atom were examined in several coordinates by calculations. The relation between the slope of the CEDPICS and the electronic structure of the ionized states, such as molecular symmetry and the spatial distribution of ionizing orbitals, was analyzed. In Fe(CO)(5), an attractive interaction was obtained for the equatorial CO, while the interaction for the axial CO direction was repulsive. For Co(eta(5)-C(5)H(5))(CO)(2), the interaction potential in the direction of both Co-C-O and Co-Cp ring was attractive. These anisotropic interactions and ionizing orbital distributions consistently explain the relative slopes of the CEDPICS.

  13. Electronic and structural ground state of heavy alkali metals at high pressure

    DOE PAGES

    Fabbris, G.; Lim, J.; Veiga, L. S. I.; ...

    2015-02-17

    Here, alkali metals display unexpected properties at high pressure, including emergence of low symmetry crystal structures, that appear to occur due to enhanced electronic correlations among the otherwise nearly-free conduction electrons. We investigate the high pressure electronic and structural ground state of K, Rb, and Cs using x-ray absorption spectroscopy and x-ray diffraction measurements together with ab initio theoretical calculations. The sequence of phase transitions under pressure observed at low temperature is similar in all three heavy alkalis except for the absence of the oC84 phase in Cs. Both the experimental and theoretical results point to pressure-enhanced localization of themore » valence electrons characterized by pseudo-gap formation near the Fermi level and strong spd hybridization. Although the crystal structures predicted to host magnetic order in K are not observed, the localization process appears to drive these alkalis closer to a strongly correlated electron state.« less

  14. Electronic and structural ground state of heavy alkali metals at high pressure

    NASA Astrophysics Data System (ADS)

    Fabbris, G.; Lim, J.; Veiga, L. S. I.; Haskel, D.; Schilling, J. S.

    2015-02-01

    Alkali metals display unexpected properties at high pressure, including emergence of low-symmetry crystal structures, which appear to occur due to enhanced electronic correlations among the otherwise nearly free conduction electrons. We investigate the high-pressure electronic and structural ground state of K, Rb, and Cs using x-ray absorption spectroscopy and x-ray diffraction measurements together with a b i n i t i o theoretical calculations. The sequence of phase transitions under pressure observed at low temperature is similar in all three heavy alkalis except for the absence of the o C 84 phase in Cs. Both the experimental and theoretical results point to pressure-enhanced localization of the valence electrons characterized by pseudogap formation near the Fermi level and strong s p d hybridization. Although the crystal structures predicted to host magnetic order in K are not observed, the localization process appears to drive these alkalis closer to a strongly correlated electron state.

  15. Direct Observation of Pressure-Driven Valence Electron Transfer in Ba 3 BiRu 2 O 9 , Ba 3 BiIr 2 O 9 , and Ba 4 BiIr 3 O 12

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

    Blanchard, Peter E. R.; Chapman, Karena W.; Heald, Steve M.

    The hexagonal perovskites Ba3BiIr2O9, Ba3BiRu2O9 and Ba4BiIr3O12 all undergo pressure-induced 1% volume collapses above 5 GPa. These first-order transitions have been ascribed to internal transfer of valence electrons between bismuth and iridium/ruthenium, which is driven by external applied pressure because the reduction in volume achieved by emptying the 6s shell of bismuth upon oxidation to Bi5+ is greater in magnitude than the increase in volume by reducing iridium or ruthenium. Here, we report direct observation of these valence transfers for the first time, using high-pressure X-ray absorption near-edge spectroscopy (XANES) measurements. Our data also support the highly unusual “4+” nominalmore » oxidation state of bismuth in these compounds, although the possibility of local disproportionation into Bi3+/Bi5+ cannot be definitively ruled out. Ab initio calculations reproduce the transition, support its interpretation as a valence electron transfer from Bi to Ir/Ru, and suggest that the high-pressure phase may show metallic behavior (in contrast to the insulating ambient-pressure phase).« less

  16. Valence-bond theory of linear Hubbard and Pariser-Parr-Pople models

    NASA Astrophysics Data System (ADS)

    Soos, Z. G.; Ramasesha, S.

    1984-05-01

    The ground and low-lying states of finite quantum-cell models with one state per site are obtained exactly through a real-space basis of valence-bond (VB) diagrams that explicitly conserve the total spin. Regular and alternating Hubbard and Pariser-Parr-Pople (PPP) chains and rings with Ne electrons on N(<=12) sites are extrapolated to infinite arrays. The ground-state energy and optical gap of regular U=4|t| Hubbard chains agree with exact results, suggesting comparable accuracy for alternating Hubbard and PPP models, but differ from mean-field results. Molecular PPP parameters describe well the excitations of finite polyenes, odd polyene ions, linear cyanine dyes, and slightly overestimate the absorption peaks in polyacetylene (CH)x. Molecular correlations contrast sharply with uncorrelated descriptions of topological solitons, which are modeled by regular polyene radicals and their ions for both wide and narrow alternation crossovers. Neutral solitons have no midgap absorption and negative spin densities, while the intensity of the in-gap excitation of charged solitons is not enhanced. The properties of correlated states in quantum-cell models with one valence state per site are discussed in the adiabatic limit for excited-state geometries and instabilities to dimerization.

  17. Valence and spin states of iron are invisible in Earth’s lower mantle

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

    Liu, Jiachao; Dorfman, Susannah M.; Zhu, Feng

    Heterogeneity in Earth’s mantle is a record of chemical and dynamic processes over Earth’s history. The geophysical signatures of heterogeneity can only be interpreted with quantitative constraints on effects of major elements such as iron on physical properties including density, compressibility, and electrical conductivity. However, deconvolution of the effects of multiple valence and spin states of iron in bridgmanite (Bdg), the most abundant mineral in the lower mantle, has been challenging. Here we show through a study of a ferric-iron-only (Mg 0.46Fe 3+0.53)(Si 0.49Fe 3+ 0.51)O 3 Bdg that Fe 3+ in the octahedral site undergoes a spin transition betweenmore » 43 and 53 GPa at 300 K. The resolved effects of the spin transition on density, bulk sound velocity, and electrical conductivity are smaller than previous estimations, consistent with the smooth depth profiles from geophysical observations. For likely mantle compositions, the valence state of iron has minor effects on density and sound velocities relative to major cation composition.« less

  18. Valence and spin states of iron are invisible in Earth’s lower mantle

    DOE PAGES

    Liu, Jiachao; Dorfman, Susannah M.; Zhu, Feng; ...

    2018-03-29

    Heterogeneity in Earth’s mantle is a record of chemical and dynamic processes over Earth’s history. The geophysical signatures of heterogeneity can only be interpreted with quantitative constraints on effects of major elements such as iron on physical properties including density, compressibility, and electrical conductivity. However, deconvolution of the effects of multiple valence and spin states of iron in bridgmanite (Bdg), the most abundant mineral in the lower mantle, has been challenging. Here we show through a study of a ferric-iron-only (Mg 0.46Fe 3+0.53)(Si 0.49Fe 3+ 0.51)O 3 Bdg that Fe 3+ in the octahedral site undergoes a spin transition betweenmore » 43 and 53 GPa at 300 K. The resolved effects of the spin transition on density, bulk sound velocity, and electrical conductivity are smaller than previous estimations, consistent with the smooth depth profiles from geophysical observations. For likely mantle compositions, the valence state of iron has minor effects on density and sound velocities relative to major cation composition.« less

  19. Excited state X-ray absorption spectroscopy: Probing both electronic and structural dynamics

    NASA Astrophysics Data System (ADS)

    Neville, Simon P.; Averbukh, Vitali; Ruberti, Marco; Yun, Renjie; Patchkovskii, Serguei; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

    2016-10-01

    We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L 2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. We anticipate that the method presented here can be combined with ab initio molecular dynamics calculations to simulate the time-resolved X-ray spectroscopy of excited state molecular wavepacket dynamics.

  20. Nonresonant valence-to-core x-ray emission spectroscopy of niobium

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

    Ravel, Bruce; Kropf, A. Jeremy; Yang, Dali

    The valence-to-core (V2C) portion of x-ray emission spectroscopy (XES) measures the electron states close to the Fermi level. These states are involved in bonding, thus providing a measure of the chemistry of the material. For this paper, we show the V2C XES spectra for several niobium compounds. The Kβ" peak in the V2C XES results from the transition of a ligand 2s electron into the 1s core-hole of the niobium, a transition allowed by hybridization with the niobium 4p . This location in energy of this weak peak shows a strong ligand dependence, thus providing a sensitive probe of themore » ligand environment about the niobium.« less

  1. Nonresonant valence-to-core x-ray emission spectroscopy of niobium

    DOE PAGES

    Ravel, Bruce; Kropf, A. Jeremy; Yang, Dali; ...

    2018-03-23

    The valence-to-core (V2C) portion of x-ray emission spectroscopy (XES) measures the electron states close to the Fermi level. These states are involved in bonding, thus providing a measure of the chemistry of the material. For this paper, we show the V2C XES spectra for several niobium compounds. The Kβ" peak in the V2C XES results from the transition of a ligand 2s electron into the 1s core-hole of the niobium, a transition allowed by hybridization with the niobium 4p . This location in energy of this weak peak shows a strong ligand dependence, thus providing a sensitive probe of themore » ligand environment about the niobium.« less

  2. Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy

    DOE PAGES

    March, Anne Marie; Assefa, Tadesse A.; Boemer, Christina; ...

    2017-01-17

    Here we probe the dynamics of valence electrons in photoexcited [Fe(terpy) 2] 2+ in solution to gain deeper insight into the Fe-ligand bond changes. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making it a powerful technique for molecular studies in a wide variety of environments. A picosecond-time-resolved measurement of the complete Is X-ray emission spectrum captures the transient photoinduced changes and includes the weak valence-to-core (vtc) emission lines that correspond to transitions from occupied valence orbitals to the nascent core-hole. Vtc-XES offers particular insight into the molecular orbitalsmore » directly involved in the light-driven dynamics; a change in the metal-ligand orbital overlap results in an intensity reduction and a blue energy shift in agreement with our theoretical calculations and more subtle features at the highest energies reflect changes in the frontier orbital populations.« less

  3. Probing Transient Valence Orbital Changes with Picosecond Valence-to-Core X-ray Emission Spectroscopy

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

    March, Anne Marie; Assefa, Tadesse A.; Boemer, Christina

    Here we probe the dynamics of valence electrons in photoexcited [Fe(terpy) 2] 2+ in solution to gain deeper insight into the Fe-ligand bond changes. We use hard X-ray emission spectroscopy (XES), which combines element specificity and high penetration with sensitivity to orbital structure, making it a powerful technique for molecular studies in a wide variety of environments. A picosecond-time-resolved measurement of the complete Is X-ray emission spectrum captures the transient photoinduced changes and includes the weak valence-to-core (vtc) emission lines that correspond to transitions from occupied valence orbitals to the nascent core-hole. Vtc-XES offers particular insight into the molecular orbitalsmore » directly involved in the light-driven dynamics; a change in the metal-ligand orbital overlap results in an intensity reduction and a blue energy shift in agreement with our theoretical calculations and more subtle features at the highest energies reflect changes in the frontier orbital populations.« less

  4. Synthesis, characterization, and photophysical properties of a series of supramolecular mixed-valence compounds.

    PubMed

    Pfennig, B W; Fritchman, V A; Hayman, K A

    2001-01-15

    The synthesis and characterization of 10 cyano-bridged trinuclear mixed-valence compounds of the form [(NH3)5M-NC-FeII(CN)4-CN-M'(NH3)5]n+ (M = RuIII, OsIII, CrIII, or PtIV; n = 2, 3, or 4) is reported. The electronic spectra of these supramolecular compounds exhibit a single intervalent (IT) absorption band for each nondegenerate Fe-->M/M' transition. The redox potential of the Fe(II) center is shifted more positive with the addition of each coordinated metal complex, while the redox potentials of the pendant metals vary only slightly from their dinuclear counterparts. As a result, the Fe-->M IT bands are blue-shifted from those in the corresponding dinuclear mixed-valence compounds. The energies of these IT bands show a linear correlation with the ground-state thermodynamic driving force, as predicted by classical electron transfer theory. Estimates of the degree of electronic coupling (Hab) between the metal centers using a theoretical analysis of the IT band shapes indicate that most of these values are similar to those for the corresponding dinuclear species. Notable exceptions occur for the Fe-->M IT transitions in Os-Fe-M (M = Cr or Pt). The enhanced electronic coupling in these two species can be explained as a result of excited state mixing between electron transfer and/or ligand-based charge transfer states and an intensity-borrowing mechanism. Additionally, the possibility of electronic coupling between the remote metal centers in the Ru-Fe-Ru species is discussed in order to explain the observation of two closely spaced redox waves for the degenerate Ru(III) acceptors.

  5. Levels of Valence

    PubMed Central

    Shuman, Vera; Sander, David; Scherer, Klaus R.

    2013-01-01

    The distinction between the positive and the negative is fundamental in our emotional life. In appraisal theories, in particular in the component process model of emotion (Scherer, 1984, 2010), qualitatively different types of valence are proposed based on appraisals of (un)pleasantness, goal obstructiveness/conduciveness, low or high power, self-(in)congruence, and moral badness/goodness. This multifaceted conceptualization of valence is highly compatible with the frequent observation of mixed feelings in real life. However, it seems to contradict the one-dimensional conceptualization of valence often encountered in psychological theories, and the notion of valence as a common currency used to explain choice behavior. Here, we propose a framework to integrate the seemingly disparate conceptualizations of multifaceted valence and one-dimensional valence by suggesting that valence should be conceived at different levels, micro and macro. Micro-valences correspond to qualitatively different types of evaluations, potentially resulting in mixed feelings, whereas one-dimensional macro-valence corresponds to an integrative “common currency” to compare alternatives for choices. We propose that conceptualizing levels of valence may focus research attention on the mechanisms that relate valence at one level (micro) to valence at another level (macro), leading to new hypotheses, and addressing various concerns that have been raised about the valence concept, such as the valence-emotion relation. PMID:23717292

  6. Decay rates of inner-valence excitations in noble gas atoms.

    PubMed

    Gokhberg, K; Averbukh, V; Cederbaum, L S

    2007-04-21

    A Fano - algebraic diagrammatic construction - Stieltjes method has been recently developed for ab initio calculations of nonradiative decay rates [V. Averbukh and L. S. Cederbaum, J. Chem. Phys. 123, 204107 (2005)] of singly ionized states. In the present work this method is generalized for the case of electronic decay of excited states. The decay widths of autoionizing inner-valence-excited states of Ne, Ar, and Kr are calculated. Apart from the lowest excitation of Kr, they are found to be in good to excellent agreement with the experimental values. Comparison with the other theoretical studies shows that in many cases the new method performs better than the previously available techniques.

  7. Authentic Assessment Tool for the Measurement of Students' Understanding of the Valence Shell Electron Pair Repulsion Theory

    ERIC Educational Resources Information Center

    Wuttisela, Karntarat

    2017-01-01

    There are various types of instructional media related to Valence Shell Electron Pair Repulsion (VSEPR) but there is a lack of diversity of resources devoted to assessment. This research presents an assessment and comparison of students' understanding of VSEPR theory before and after tuition involving the use of the foam molecule model (FMM) and…

  8. Correlating valence state, site preference and co-substitution to the magnetoelastic properties of cobalt ferrite

    NASA Astrophysics Data System (ADS)

    Nlebedim, Cajetan; Jiles, David

    2015-03-01

    Understanding how to influence the physics of magnetism, especially the relationship between magnetic susceptibility and stress, can be very useful in designing non-contact stress and torque sensors using magnetoelastic materials. This is particularly important considering that materials rarely occur in states desirable for direct applications. In this work we show that the magnetoelastic properties of cobalt ferrite are strongly dependent on the valence states and site preferences of substituted cations. It was found that co-substitution of magnetic and non-magnetic cations, is key to achieving simultaneous improvement in magnetostriction amplitude and strain sensitivity to applied magnetic field. Nevertheless, Curie temperature decreased, irrespective of the valence state, site preference or co-substitution. This presentation will show why tetravalent Ge resulted in superior magnetostrictive properties compared to other tetravalent, trivalent and divalent cations substituted into the crystal lattice of cobalt ferrite. This work was supported by the U.S. DOE, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division. The research was performed at Ames Laboratory, operated for the USDoE by Iowa State University (Contract #DE-AC02-07CH11358).

  9. Electronic spectroscopy of diatomic molecules

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.

    1994-01-01

    This article provides an overview of the principal computational approaches and their accuracy for the study of electronic spectroscopy of diatomic molecules. We include a number of examples from our work that illustrate the range of application. We show how full configuration interaction benchmark calculations were instrumental in improving the understanding of the computational requirements for obtaining accurate results for diatomic spectroscopy. With this understanding it is now possible to compute radiative lifetimes accurate to within 10% for systems involving first- and second-row atoms. We consider the determination of the infrared vibrational transition probabilities for the ground states of SiO and NO, based on a globally accurate dipole moment function. We show how we were able to assign the a(sup "5)II state of CO as the upper state in the recently observed emission bands of CO in an Ar matrix. We next discuss the assignment of the photoelectron detachment spectra of NO and the alkali oxide negative ions. We then present several examples illustrating the state-of-the-art in determining radiative lifetimes for valence-valence and valence-Rydberg transitions. We next compare the molecular spectroscopy of the valence isoelectronic B2, Al2, and AlB molecules. The final examples consider systems involving transition metal atoms, which illustrate the difficulty in describing states with different numbers of d electrons.

  10. Correlation between valence electronic structure and magnetic properties in RCo5 (R = rare earth) intermetallic compound

    NASA Astrophysics Data System (ADS)

    Zhi-Qin, Xue; Yong-Quan, Guo

    2016-06-01

    The magnetisms of RCo5 (R = rare earth) intermetallics are systematically studied with the empirical electron theory of solids and molecules (EET). The theoretical moments and Curie temperatures agree well with experimental ones. The calculated results show strong correlations between the valence electronic structure and the magnetic properties in RCo5 intermetallic compounds. The moments of RCo5 intermetallics originate mainly from the 3d electrons of Co atoms and 4f electrons of rare earth, and the s electrons also affect the magnetic moments by the hybridization of d and s electrons. It is found that moment of Co atom at 2c site is higher than that at 3g site due to the fact that the bonding effect between R and Co is associated with an electron transformation from 3d electrons into covalence electrons. In the heavy rare-earth-based RCo5 intermetallics, the contribution to magnetic moment originates from the 3d and 4f electrons. The covalence electrons and lattice electrons also affect the Curie temperature, which is proportional to the average moment along the various bonds. Project supported by the National Natural Science Foundation of China (Grant No. 11274110).

  11. Valence holes observed in nanodiamonds dispersed in water

    NASA Astrophysics Data System (ADS)

    Petit, Tristan; Pflüger, Mika; Tolksdorf, Daniel; Xiao, Jie; Aziz, Emad F.

    2015-02-01

    Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed.Colloidal dispersion is essential for most nanodiamond applications, but its influence on nanodiamond electronic properties remains unknown. Here we have probed the electronic structure of oxidized detonation nanodiamonds dispersed in water by using soft X-ray absorption and emission spectroscopies at the carbon and oxygen K edges. Upon dispersion in water, the π* transitions from sp2-hybridized carbon disappear, and holes in the valence band are observed. Electronic supplementary information (ESI) available: Experimental methods, details on XAS/XES normalization and background correction procedures. See DOI: 10.1039/c4nr06639a

  12. A theoretical study of the dissociative recombination of SH+ with electrons through the 2Π states of SH.

    PubMed

    Kashinski, D O; Talbi, D; Hickman, A P; Di Nallo, O E; Colboc, F; Chakrabarti, K; Schneider, I F; Mezei, J Zs

    2017-05-28

    A quantitative theoretical study of the dissociative recombination of SH + with electrons has been carried out. Multireference, configuration interaction calculations were used to determine accurate potential energy curves for SH + and SH. The block diagonalization method was used to disentangle strongly interacting SH valence and Rydberg states and to construct a diabatic Hamiltonian whose diagonal matrix elements provide the diabatic potential energy curves. The off-diagonal elements are related to the electronic valence-Rydberg couplings. Cross sections and rate coefficients for the dissociative recombination reaction were calculated with a stepwise version of the multichannel quantum defect theory, using the molecular data provided by the block diagonalization method. The calculated rates are compared with the most recent measurements performed on the ion Test Storage Ring (TSR) in Heidelberg, Germany.

  13. The Valence- and Conduction-Band Structure of the Sapphire (1102) Surface.

    DTIC Science & Technology

    1984-12-01

    surface. The pbotomission spectrum of the valece-baud region has boon adjusted to rmove croas-section effect s and comparod to the recent theoretical ...transitions in Al203. Several theoretical deteminations of the electron structure of various A1203 analoaues have bes performed. These calculations were...picture of the valence sad core density of states in sapphire. The rew, 31 velesee-bend data of Fit. I& and the theoretical 003 shows is Fig. 1.. which

  14. Molybdenum Valence in Basaltic Silicate Melts

    NASA Technical Reports Server (NTRS)

    Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Pando, K.

    2010-01-01

    The moderately siderophile element molybdenum has been used as an indicator in planetary differentiation processes, and is particularly relevant to core formation [for example, 1-6]. However, models that apply experimental data to an equilibrium differentiation scenario infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Partitioning behavior of molybdenum, a multivalent element with a transition near the J02 of interest for core formation (IW-2) will be sensitive to changes in JO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo6+ can be either octahedrally or tetrahedrally coordinated. Here we present first XANES measurements of Mo valence in basaltic run products at a range of P, T, and JO2 and further quantify the valence transition of Mo.

  15. Electric Field Generation and Control of Bipartite Quantum Entanglement between Electronic Spins in Mixed Valence Polyoxovanadate [GeV14O40]8.

    PubMed

    Palii, Andrew; Aldoshin, Sergey; Tsukerblat, Boris; Borràs-Almenar, Juan José; Clemente-Juan, Juan Modesto; Cardona-Serra, Salvador; Coronado, Eugenio

    2017-08-21

    As part of the search for systems in which control of quantum entanglement can be achieved, here we consider the paramagnetic mixed valence polyoxometalate K 2 Na 6 [GeV 14 O 40 ]·10H 2 O in which two electrons are delocalized over the 14 vanadium ions. Applying a homogeneous electric field can induce an antiferromagnetic coupling between the two delocalized electronic spins that behave independently in the absence of the field. On the basis of the proposed theoretical model, we show that the external field can be used to generate controllable quantum entanglement between the two electronic spins traveling over a vanadium network of mixed valence polyoxoanion [GeV 14 O 40 ] 8- . Within a simplified two-level picture of the energy pattern of the electronic pair based on the previous ab initio analysis, we evaluate the temperature and field dependencies of concurrence and thus indicate that the entanglement can be controlled via the temperature, magnitude, and orientation of the electric field with respect to molecular axes of [GeV 14 O 40 ] 8- .

  16. Protected Fe valence in quasi-two-dimensional α-FeSi2.

    PubMed

    Miiller, W; Tomczak, J M; Simonson, J W; Smith, G; Kotliar, G; Aronson, M C

    2015-05-08

    We report the first comprehensive study of the high temperature form (α-phase) of iron disilicide. Measurements of the magnetic susceptibility, magnetization, heat capacity and resistivity were performed on well characterized single crystals. With a nominal iron d(6) configuration and a quasi-two-dimensional crystal structure that strongly resembles that of LiFeAs, α-FeSi2 is a potential candidate for unconventional superconductivity. Akin to LiFeAs, α-FeSi2 does not develop any magnetic order and we confirm its metallic state down to the lowest temperatures (T = 1.8 K). However, our experiments reveal that paramagnetism and electronic correlation effects in α-FeSi2 are considerably weaker than in the pnictides. Band theory calculations yield small Sommerfeld coefficients of the electronic specific heat γ = Ce/T that are in excellent agreement with experiment. Additionally, realistic many-body calculations further corroborate that quasi-particle mass enhancements are only modest in α-FeSi2. Remarkably, we find that the natural tendency to vacancy formation in the iron sublattice has little influence on the iron valence and the density of states at the Fermi level. Moreover, Mn doping does not significantly change the electronic state of the Fe ion. This suggests that the iron valence is protected against hole doping and indeed the substitution of Co for Fe causes a rigid-band like response of the electronic properties. As a key difference from the pnictides, we identify the smaller inter-iron layer spacing, which causes the active orbitals near the Fermi level to be of a different symmetry in α-FeSi2. This change in orbital character might be responsible for the lack of superconductivity in this system, providing constraints on pairing theories in the iron based pnictides and chalcogenides.

  17. THE VALENCE AND METHYLATION STATE OF ARSENIC DETERMINES ITS POTENCY IN INTERACTION WITH THE MITOTIC APPARATUS

    EPA Science Inventory

    We have previously shown that the cytotoxic and genotoxic potency of arsenicals is dependent upon their valence and methylation state. Trivalent methylated arsenicals are much more potent DNA damaging agents than are their inorganic and pentavalent counterparts. Furthermore, thei...

  18. Role of valence electrons in phase transformation kinetics of thallium and its dilute alloys

    NASA Technical Reports Server (NTRS)

    Ahmed, R.; Ahmed, S.

    1991-01-01

    The kinetics of the phase transformation of thallium and its dilute alloys were investigated using XRD and calorimetry. Pure thallium exhibits a beta(bcc) to alpha(hcp) phase transformation on cooling at 508 K. With alloying additions, the crystal structure for each phase does not change, although the size of the unit cell increases. The enthalpy and the temperature of phase transformation of each alloy have been determined. The chemical free energy change associated with the phase transformation of each alloy was calculated. The valence electrons make an outstanding contribution to the chemical free energy change required for the phase change.

  19. Barrier-free proton transfer in the valence anion of 2'-deoxyadenosine-5'-monophosphate. II. A computational study.

    PubMed

    Kobyłecka, Monika; Gu, Jiande; Rak, Janusz; Leszczynski, Jerzy

    2008-01-28

    The propensity of four representative conformations of 2(')-deoxyadenosine-5(')-monophosphate (5(')-dAMPH) to bind an excess electron has been studied at the B3LYP6-31++G(d,p) level. While isolated canonical adenine does not support stable valence anions in the gas phase, all considered neutral conformations of 5(')-dAMPH form adiabatically stable anions. The type of an anionic 5(')-dAMPH state, i.e., the valence, dipole bound, or mixed (valence/dipole bound), depends on the internal hydrogen bond(s) pattern exhibited by a particular tautomer. The most stable anion results from an electron attachment to the neutral syn-south conformer. The formation of this anion is associated with a barrier-free proton transfer triggered by electron attachment and the internal rotation around the C4(')-C5(') bond. The adiabatic electron affinity of the a_south-syn anion is 1.19 eV, while its vertical detachment energy is 1.89 eV. Our results are compared with the photoelectron spectrum (PES) of 5(')-dAMPH(-) measured recently by Stokes et al., [J. Chem. Phys. 128, 044314 (2008)]. The computational VDE obtained for the most stable anionic structure matches well with the experimental electron binding energy region of maximum intensity. A further understanding of DNA damage might require experimental and computational studies on the systems in which purine nucleotides are engaged in hydrogen bonding.

  20. Synthesis of High Valence Silver-Loaded Mesoporous Silica with Strong Antibacterial Properties

    PubMed Central

    Chen, Chun-Chi; Wu, Hsin-Hsien; Huang, Hsin-Yi; Liu, Chen-Wei; Chen, Yi-Ning

    2016-01-01

    A simple chemical method was developed for preparing high valence silver (Ag)-loaded mesoporous silica (Ag-ethylenediaminetetraacetic acid (EDTA)-SBA-15), which showed strong antibacterial activity. Ag-EDTA-SBA-15 exhibited stronger and more effective antibacterial activity than commercial Ag nanoparticles did, and it offered high stability of high valence silver in the porous matrix and long-lasting antibacterial activity. The synthesized materials were characterized using Fourier transform infrared spectroscopy, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) analysis, and transmission electron microscopy (TEM). Ag existed in both surface complexation and Ag particles. EDTA anchored within a porous structure chelated Ag ions in higher oxidation states and prevented their agglomeration and oxidation reduction. The XRD results showed that most Ag in the Ag-EDTA-SBA-15 existed in higher oxidation states such as Ag(II) and Ag(III). However, the XPS and TEM results showed that Ag easily reduced in lower oxidation states and agglomerated as Ag particles on the exterior layer of the SBA-15. PMID:26742050

  1. The electronic states of cyclopropane studied by VUV absorption and electron energy-loss spectroscopies

    NASA Astrophysics Data System (ADS)

    Gingell, M.; Mason, N. J.; Walker, I. C.; Marston, G.; Zhao, H.; Siggel, M. R. F.

    1999-06-01

    Absolute optical (VUV) absorption cross sections for cyclopropane have been measured from 5.0 to 11.2 and 20-40 eV using synchrotron radiation. Also, electron energy-loss (EEL) spectra have been obtained using incident electrons of (a) 150 eV energy scattered through small angles (energy loss 5.0-15 eV) and (b) near-threshold energies scattered through large angles (energy loss 0-10.5 eV). Taken together these confirm that the low-lying excited electronic states of cyclopropane are of Rydberg type and, although spectral bands are diffuse, a known Rydberg series has been extended. Recent computations (Galasso V 1996 Chem. Phys. 206 289) appear to give a good account of the experimental spectrum from threshold to about 11 eV, but these must be extended if valence-excited states are to be characterized. Particular attention has been directed at the evaluation of absolute optical cross sections. These are now believed to be established over the energy ranges 5-15 and 20-40 eV. In the gap region (15-20 eV) second-order radiation may affect the optical measurements. From consideration of second-order effects, and comparison of the present studies with earlier measurements, we propose a best-estimate cross section in this energy region also.

  2. ULTRASONIC NEBULIZATION AND ARSENIC VALENCE STATE CONSIDERATIONS PRIOR TO DETERMINATION VIA INDUCTIVELY COUPLED PLASMA MASS SPECTROMETRY

    EPA Science Inventory

    An ultrasonic nebulizer (USN) was utilized as a sample introduction device for an inductively coupled plasma mass spectrometer in an attempt to increase the sensitivity for As. The USN produced a valence state response difference for As. The As response was suppressed approximate...

  3. Ab initio investigation on the valence and dipole-bound states of CNa - and SiNa -

    NASA Astrophysics Data System (ADS)

    Kalcher, Josef; Sax, Alexander F.

    2000-08-01

    CNa - and SiNa - have been studied by the CAS-ACPF method. The 3Σ- ground states have binding energies of 5420 and 7517 cm -1, respectively. The 5Σ- excited states are 494 and 1551 cm -1 above the respective ground states. The 1Δ , 3Π , and 1Π valence-excited states for SiNa - should be at least metastable. CNa - and SiNa - possess dipole-bound 5Σ- and 3Σ- states. Binding energies of these states in CNa - are 217 and 236 cm -1, respectively. SiNa - has two stable 5Σ- dipole-bound states, whose binding energies are 246 and 118 cm -1, respectively.

  4. Organic Electronic Devices Using Crosslinked Polyelectrolyte Multilayers as an Ultra-Thin Dielectric Material

    DTIC Science & Technology

    2006-09-01

    energy band diagram illustrating the allowed energies for valence and conducting electrons. The dashes within the band gap (Eg) represent localized ...allowed energies for valence and conducting electrons. The dashes within the band gap (Eg) represent localized electron energy states, or traps, that...been observed with the formation of alternating bond lengths along the backbone.43 The localization of the π-electrons while forming the shorter double

  5. Understanding valence-shell electron-pair repulsion (VSEPR) theory using origami molecular models

    NASA Astrophysics Data System (ADS)

    Endah Saraswati, Teguh; Saputro, Sulistyo; Ramli, Murni; Praseptiangga, Danar; Khasanah, Nurul; Marwati, Sri

    2017-01-01

    Valence-shell electron-pair repulsion (VSEPR) theory is conventionally used to predict molecular geometry. However, it is difficult to explore the full implications of this theory by simply drawing chemical structures. Here, we introduce origami modelling as a more accessible approach for exploration of the VSEPR theory. Our technique is simple, readily accessible and inexpensive compared with other sophisticated methods such as computer simulation or commercial three-dimensional modelling kits. This method can be implemented in chemistry education at both the high school and university levels. We discuss the example of a simple molecular structure prediction for ammonia (NH3). Using the origami model, both molecular shape and the scientific justification can be visualized easily. This ‘hands-on’ approach to building molecules will help promote understanding of VSEPR theory.

  6. Low-temperature spin dynamics of a valence bond glass in Ba2YMoO6

    NASA Astrophysics Data System (ADS)

    de Vries, M. A.; Piatek, J. O.; Misek, M.; Lord, J. S.; Rønnow, H. M.; Bos, J.-W. G.

    2013-04-01

    We carried out ac magnetic susceptibility measurements and muon spin relaxation spectroscopy on the cubic double perovskite Ba2YMoO6, down to 50 mK. Below ∼1 K the muon relaxation is typical of a magnetic insulator with a spin-liquid type ground state, i.e. without broken symmetries or frozen moments. However, the ac susceptibility revealed a dilute-spin-glass-like transition below ∼1 K. Antiferromagnetically coupled Mo5+ 4d1 electrons in triply degenerate t2g orbitals are in this material arranged in a geometrically frustrated fcc lattice. Bulk magnetic susceptibility data has previously been interpreted in terms of a freezing to a heterogeneous state with non-magnetic sites where 4d1 electrons have paired in spin-singlets dimers, and residual unpaired Mo5+ 4d1 electron spins. Based on the magnetic heat capacity data it has been suggested that this heterogeneity is the result of kinetic constraints intrinsic to the physics of the pure system (possibly due to topological overprotection) leading to a self-induced glass of valence bonds between neighbouring 4d1 electrons. The muon spin relaxation (μSR) unambiguously points to a heterogeneous state with a static arrangement of unpaired electrons in a background of (valence bond) dimers between the majority of Mo5+ 4d electrons. The ac susceptibility data indicate that the residual magnetic moments freeze into a dilute-spin-glass-like state. This is in apparent contradiction with the muon-spin decoupling at 50 mK in fields up to 200 mT, which indicates that, remarkably, the time scale of the field fluctuations from the residual moments is ∼5 ns. Comparable behaviour has been observed in other geometrically frustrated magnets with spin-liquid-like behaviour and the implications of our observations on Ba2YMoO6 are discussed in this context.

  7. Interacting quasi-band theory for electronic states in compound semiconductor alloys: Wurtzite structure

    NASA Astrophysics Data System (ADS)

    Kishi, Ayaka; Oda, Masato; Shinozuka, Yuzo

    2016-05-01

    This paper reports on the electronic states of compound semiconductor alloys of wurtzite structure calculated by the recently proposed interacting quasi-band (IQB) theory combined with empirical sp3 tight-binding models. Solving derived quasi-Hamiltonian 24 × 24 matrix that is characterized by the crystal parameters of the constituents facilitates the calculation of the conduction and valence bands of wurtzite alloys for arbitrary concentrations under a unified scheme. The theory is applied to III-V and II-VI wurtzite alloys: cation-substituted Al1- x Ga x N and Ga1- x In x N and anion-substituted CdS1- x Se x and ZnO1- x S x . The obtained results agree well with the experimental data, and are discussed in terms of mutual mixing between the quasi-localized states (QLS) and quasi-average bands (QAB): the latter bands are approximately given by the virtual crystal approximation (VCA). The changes in the valence and conduction bands, and the origin of the band gap bowing are discussed on the basis of mixing character.

  8. Smooth Scaling of Valence Electronic Properties in Fullerenes: From One Carbon Atom, to C60, to Graphene

    DTIC Science & Technology

    2012-09-18

    Smooth scaling of valence electronic properties in fullerenes: from one carbon atom , to C60, to graphene Greyson R. Lewis,1 William E. Bunting,1...pacitance scaling lines of the fullerenes. Lastly, it is found that points representing the carbon atom and the graphene limit lie on scaling lines for...icosahedral fullerenes, so their quantum capacitances and their detachment energies scale smoothly from one C atom , through C60, to graphene. I

  9. Micro-Valences: Perceiving Affective Valence in Everyday Objects

    PubMed Central

    Lebrecht, Sophie; Bar, Moshe; Barrett, Lisa Feldman; Tarr, Michael J.

    2012-01-01

    Perceiving the affective valence of objects influences how we think about and react to the world around us. Conversely, the speed and quality with which we visually recognize objects in a visual scene can vary dramatically depending on that scene’s affective content. Although typical visual scenes contain mostly “everyday” objects, the affect perception in visual objects has been studied using somewhat atypical stimuli with strong affective valences (e.g., guns or roses). Here we explore whether affective valence must be strong or overt to exert an effect on our visual perception. We conclude that everyday objects carry subtle affective valences – “micro-valences” – which are intrinsic to their perceptual representation. PMID:22529828

  10. Ultrafast Molecular Three-Electron Auger Decay.

    PubMed

    Feifel, Raimund; Eland, John H D; Squibb, Richard J; Mucke, Melanie; Zagorodskikh, Sergey; Linusson, Per; Tarantelli, Francesco; Kolorenč, Přemysl; Averbukh, Vitali

    2016-02-19

    Three-electron Auger decay is an exotic and elusive process, in which two outer-shell electrons simultaneously refill an inner-shell double vacancy with emission of a single Auger electron. Such transitions are forbidden by the many-electron selection rules, normally making their decay lifetimes orders of magnitude longer than the few-femtosecond lifetimes of normal (two-electron) Auger decay. Here we present theoretical predictions and direct experimental evidence for a few-femtosecond three-electron Auger decay of a double inner-valence-hole state in CH_{3}F. Our analysis shows that in contrast to double core holes, double inner-valence vacancies in molecules can decay exclusively by this ultrafast three-electron Auger process, and we predict that this phenomenon occurs widely.

  11. High pressure and synchrotron radiation studies of solid state electronic instabilities

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

    Pifer, J.H.; Croft, M.C.

    This report discusses Eu and General Valence Instabilities; Ce Problem: L{sub 3} Spectroscopy Emphasis; Bulk Property Emphasis; Transition Metal Compound Electronic Structure; Electronic Structure-Phonon Coupling Studies; High Temperature Superconductivity and Oxide Materials; and Novel Materials Collaboration with Chemistry.

  12. Experimental and computational studies on the electronic excited states of nitrobenzene

    NASA Astrophysics Data System (ADS)

    Krishnakumar, Sunanda; Das, Asim Kumar; Singh, Param Jeet; Shastri, Aparna; Rajasekhar, B. N.

    2016-11-01

    The gas phase electronic absorption spectrum of nitrobenzene (C6H5NO2) in the 4.5-11.2 eV region is recorded using synchrotron radiation with a view to comprehend the nature of the excited states. Electronic excited states of nitrobenzene are mainly classified as local excitations within the benzene ring or nitro group and charge transfer excitations between the benzene and nitro group, with some transitions showing percentage from both. The nature of molecular orbitals, their orderings and energies are obtained from density functional theory calculations which help in assigning partially assigned/unassigned features in earlier photoelectron spectroscopy studies. Optimized geometry of ionic nitrobenzene predicts redistribution of charge density in the benzene ring rather than the nitro group resulting in stabilization of the benzene ring π orbitals in comparison to the neutral molecule. Time dependent density functional theory computations are found to describe the experimental spectra well with respect to energies, relative intensities and nature of the observed transitions in terms of valence, Rydberg or charge transfer type. New insights into the interpretation of 1B2u←1A1g and 1B1u←1A1g shifted benzene transitions in light of the present computational calculations are presented. The first few members of the ns, np and nd type Rydberg series in nitrobenzene, converging to the first six ionization potentials, identified in the spectra as weak but sharp peaks are reported for the first time. In general, transitions to the lowest three unoccupied molecular orbitals 4b1, 3a2 and 5b1 are valence or charge transfer in nature, while excitations to higher orbitals are predominantly Rydberg in nature. This work presents a consolidated experimental study and theoretical interpretation of the electronic absorption spectrum of nitrobenzene.

  13. Interpretation of monoclinic hafnia valence electron energy-loss spectra by time-dependent density functional theory

    NASA Astrophysics Data System (ADS)

    Hung, L.; Guedj, C.; Bernier, N.; Blaise, P.; Olevano, V.; Sottile, F.

    2016-04-01

    We present the valence electron energy-loss spectrum and the dielectric function of monoclinic hafnia (m -HfO2) obtained from time-dependent density-functional theory (TDDFT) predictions and compared to energy-filtered spectroscopic imaging measurements in a high-resolution transmission-electron microscope. Fermi's golden rule density-functional theory (DFT) calculations can capture the qualitative features of the energy-loss spectrum, but we find that TDDFT, which accounts for local-field effects, provides nearly quantitative agreement with experiment. Using the DFT density of states and TDDFT dielectric functions, we characterize the excitations that result in the m -HfO2 energy-loss spectrum. The sole plasmon occurs between 13 and 16 eV, although the peaks ˜28 and above 40 eV are also due to collective excitations. We furthermore elaborate on the first-principles techniques used, their accuracy, and remaining discrepancies among spectra. More specifically, we assess the influence of Hf semicore electrons (5 p and 4 f ) on the energy-loss spectrum, and find that the inclusion of transitions from the 4 f band damps the energy-loss intensity in the region above 13 eV. We study the impact of many-body effects in a DFT framework using the adiabatic local-density approximation (ALDA) exchange-correlation kernel, as well as from a many-body perspective using "scissors operators" matched to an ab initio G W calculation to account for self-energy corrections. These results demonstrate some cancellation of errors between self-energy and excitonic effects, even for excitations from the Hf 4 f shell. We also simulate the dispersion with increasing momentum transfer for plasmon and collective excitation peaks.

  14. Energy shift and conduction-to-valence band transition mediated by a time-dependent potential barrier in graphene

    NASA Astrophysics Data System (ADS)

    Chaves, Andrey; da Costa, D. R.; de Sousa, G. O.; Pereira, J. M.; Farias, G. A.

    2015-09-01

    We investigate the scattering of a wave packet describing low-energy electrons in graphene by a time-dependent finite-step potential barrier. Our results demonstrate that, after Klein tunneling through the barrier, the electron acquires an extra energy which depends on the rate of change of the barrier height with time. If this rate is negative, the electron loses energy and ends up as a valence band state after leaving the barrier, which effectively behaves as a positively charged quasiparticle.

  15. Oxidation States of Grim Glasses in EET79001 Based on Vanadium Valence

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Rao, M. N.; Nyquist, L. E.

    2010-01-01

    Gas-rich impact-melt (GRIM) glasses in SNC meteorites are very rich in Martian atmospheric noble gases and sulfur suggesting a possible occurrence of regolith-derived secondary mineral assemblages in these samples. Previously, we have studied two GRIM glasses, 506 and 507, from EET79001 Lith A and Lith B, respectively, for elemental abundances and spatial distribution of sulfur using EMPA (WDS) and FE-SEM (EDS) techniques and for sulfur-speciation using K-edge XANES techniques. These elemental and FE-SEM micro-graph data at several locations in the GRIM glasses from Shergotty (DBS), Zagami 994 and EET79001, Lith B showed that FeO and SO3 are positively correlated (SO3 represents a mixture of sulfide and sulfate). FE-SEM (EDS) study revealed that the sulfur-rich pockets in these glasses contain numerous micron-sized iron-sulfide (Fe-S) globules sequestered throughout the volume. However, in some areas (though less frequently), we detected significant Fe-S-O signals suggesting the occurrence of iron sulfate. These GRIM glasses were studied by K-edge microXANES techniques for sulfur speciation in association with iron in sulfur-rich areas. In both samples, we found the sulfur speciation dominated by sulfide with minor oxidized sulfur mixed in with various proportions. The abundance of oxidized sulfur was greater in 506 than in 507. Based on these results, we hypothesize that sulfur initially existed as sulfate in the glass precursor materials and, on shock-impact melting of the precursor materials producing these glasses, the oxidized sulfur was reduced to predominately sulfide. In order to further test this hypothesis, we have used microXANES to measure the valence states of vanadium in GRIM glasses from Lith A and Lith B to complement and compare with previous analogous measurements on Lith C (note: 506 and 507 contain the largest amounts of martian atmospheric gases but the gas-contents in Lith C measured by are unknown). Vanadium is ideal for addressing this re

  16. Direct determination of europium valence state by XANES in extraterrestrial merrillite: Implications for REE crystal chemistry and martian magmatism

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

    Shearer, C.K.; Papike, J.J.; Burger, P.V.

    2012-03-15

    The relative proportion of divalent and trivalent Eu has proven to be a useful tool for estimating f{sub O{sub 2}} in various magmatic systems. However, in most cases, direct determination of the Eu valence state has not been made. In this study, direct determination of Eu valence by XANES and REE abundance in merrillite provide insights into the crystal chemistry of these phosphates and their ability to record conditions of magmatism. Merrillite strongly prefers Eu{sup 3+} to Eu{sup 2+}, with the average valence state of Eu ranging between 2.9 and 3 over approximately six orders of magnitude in f{sub O{submore » 2}}. The dramatic shift in the REE patterns of merrillite in martian basaltic magmas, from highly LREE-depleted to LREE-enriched, parallels many other trace element and isotopic variations and reflects the sources for these magmas. The behavior of REE in the merrillite directly reflects the relationship between the eightfold-coordinated Ca1 site and adjacent sixfold Na and tetrahedral P sites that enables charge balancing through coupled substitutions.« less

  17. Bulk and interface quantum states of electrons in multi-layer heterostructures with topological materials.

    PubMed

    Nikolic, Aleksandar; Zhang, Kexin; Barnes, C H W

    2018-06-13

    In this article we describe the bulk and interface quantum states of electrons in multi-layer heterostructures in one dimension, consisting of topological insulators (TIs) and topologically trivial materials. We use and extend an effective four-band continuum Hamiltonian by introducing position dependence to the eight material parameters of the Hamiltonian. We are able to demonstrate complete conduction-valence band mixing in the interface states. We find evidence for topological features of bulk states of multi-layer TI heterostructures, as well as demonstrating both complete and incomplete conduction-valence band inversion at different bulk state energies. We show that the linear k z terms in the low-energy Hamiltonian, arising from overlap of p z orbitals between different atomic layers in the case of chalcogenides, control the amount of tunneling from TIs to trivial insulators. Finally, we show that the same linear k z terms in the low-energy Hamiltonian affect the material's ability to form the localised interface state, and we demonstrate that due to this effect the spin and probability density localisation in a thin film of Sb 2 Te 3 is incomplete. We show that changing the parameter that controls the magnitude of the overlap of p z orbitals affects the transport characteristics of the topologically conducting states, with incomplete topological state localisation resulting in increased backscattering.

  18. Bulk and interface quantum states of electrons in multi-layer heterostructures with topological materials

    NASA Astrophysics Data System (ADS)

    Nikolic, Aleksandar; Zhang, Kexin; Barnes, C. H. W.

    2018-06-01

    In this article we describe the bulk and interface quantum states of electrons in multi-layer heterostructures in one dimension, consisting of topological insulators (TIs) and topologically trivial materials. We use and extend an effective four-band continuum Hamiltonian by introducing position dependence to the eight material parameters of the Hamiltonian. We are able to demonstrate complete conduction-valence band mixing in the interface states. We find evidence for topological features of bulk states of multi-layer TI heterostructures, as well as demonstrating both complete and incomplete conduction-valence band inversion at different bulk state energies. We show that the linear k z terms in the low-energy Hamiltonian, arising from overlap of p z orbitals between different atomic layers in the case of chalcogenides, control the amount of tunneling from TIs to trivial insulators. Finally, we show that the same linear k z terms in the low-energy Hamiltonian affect the material’s ability to form the localised interface state, and we demonstrate that due to this effect the spin and probability density localisation in a thin film of Sb2Te3 is incomplete. We show that changing the parameter that controls the magnitude of the overlap of p z orbitals affects the transport characteristics of the topologically conducting states, with incomplete topological state localisation resulting in increased backscattering.

  19. Spin polarization and magnetic dichroism in photoemission from core and valence states in localized magnetic systems. IV. Core-hole polarization in resonant photoemission

    NASA Astrophysics Data System (ADS)

    van der Laan, Gerrit; Thole, B. T.

    1995-12-01

    A simple theory is presented for core-hole polarization probed by resonant photoemission in a two-steps approximation. After excitation from a core level to the valence shell, the core hole decays into two shallower core holes under emission of an electron. The nonspherical core hole and the final state selected cause a specific angle and spin distribution of the emitted electron. The experiment is characterized by the ground-state moments, the polarization of the light, and the spin and angular distribution of the emitted electron. The intensity is a sum over ground-state expectation values of tensor operators times the probability to create a polarized core hole using polarized light, times the probability for decay of such a core hole into the final state. We give general expressions for the angle- and spin-dependent intensities in various regimes of Coulomb and spin-orbit interaction: LS, LSJ, and jjJ coupling. The core-polarization analysis, which generalizes the use of sum rules in x-ray absorption spectroscopy where the integrated peak intensities give ground-state expectation values of the spin and orbital moment operators, makes it possible to measure different linear combinations of these operators. As an application the 2p3/23p3p decay in ferromagnetic nickel is calculated using Hartree-Fock values for the radial matrix elements and phase factors, and compared with experiment, the dichroism is smaller in the 3P final state but stronger in the 1D, 1S peak.

  20. Barrier-free proton transfer in the valence anion of 2'-deoxyadenosine-5'-monophosphate. II. A computational study

    NASA Astrophysics Data System (ADS)

    Kobyłecka, Monika; Gu, Jiande; Rak, Janusz; Leszczynski, Jerzy

    2008-01-01

    The propensity of four representative conformations of 2'-deoxyadenosine-5'-monophosphate (5'-dAMPH) to bind an excess electron has been studied at the B3LYP /6-31++G(d,p) level. While isolated canonical adenine does not support stable valence anions in the gas phase, all considered neutral conformations of 5'-dAMPH form adiabatically stable anions. The type of an anionic 5'-dAMPH state, i.e., the valence, dipole bound, or mixed (valence/dipole bound), depends on the internal hydrogen bond(s) pattern exhibited by a particular tautomer. The most stable anion results from an electron attachment to the neutral syn-south conformer. The formation of this anion is associated with a barrier-free proton transfer triggered by electron attachment and the internal rotation around the C4'-C5' bond. The adiabatic electron affinity of the a&barbelow;south-syn anion is 1.19eV, while its vertical detachment energy is 1.89eV. Our results are compared with the photoelectron spectrum (PES) of 5'-dAMPH- measured recently by Stokes et al., [J. Chem. Phys. 128, 044314 (2008)]. The computational VDE obtained for the most stable anionic structure matches well with the experimental electron binding energy region of maximum intensity. A further understanding of DNA damage might require experimental and computational studies on the systems in which purine nucleotides are engaged in hydrogen bonding.

  1. Emotional valence and physical space: limits of interaction.

    PubMed

    de la Vega, Irmgard; de Filippis, Mónica; Lachmair, Martin; Dudschig, Carolin; Kaup, Barbara

    2012-04-01

    According to the body-specificity hypothesis, people associate positive things with the side of space that corresponds to their dominant hand and negative things with the side corresponding to their nondominant hand. Our aim was to find out whether this association holds also true for a response time study using linguistic stimuli, and whether such an association is activated automatically. Four experiments explored this association using positive and negative words. In Exp. 1, right-handers made a lexical judgment by pressing a left or right key. Attention was not explicitly drawn to the valence of the stimuli. No valence-by-side interaction emerged. In Exp. 2 and 3, right-handers and left-handers made a valence judgment by pressing a left or a right key. A valence-by-side interaction emerged: For positive words, responses were faster when participants responded with their dominant hand, whereas for negative words, responses were faster for the nondominant hand. Exp. 4 required a valence judgment without stating an explicit mapping of valence and side. No valence-by-side interaction emerged. The experiments provide evidence for an association between response side and valence, which, however, does not seem to be activated automatically but rather requires a task with an explicit response mapping to occur.

  2. Europium mixed-valence, long-range magnetic order, and dynamic magnetic response in EuCu 2 ( Si x Ge 1 - x ) 2

    DOE PAGES

    Nemkovski, Krill S.; Kozlenko, D. P.; Alekseev, Pavel A.; ...

    2016-11-01

    In mixed-valence or heavy-fermion systems, the hybridization between local f orbitals and conduction band states can cause the suppression of long-range magnetic order, which competes with strong spin uctuations. Ce- and Yb-based systems have been found to exhibit fascinating physical properties (heavy-fermion superconductivity, non-Fermi-liquid states, etc.) when tuned to the vicinity of magnetic quantum critical points by use of various external control parameters (temperature, magnetic eld, chemical composition). Recently, similar effects (mixed-valence, Kondo uctuations, heavy Fermi liquid) have been reported to exist in some Eu-based compounds. Unlike Ce (Yb), Eu has a multiple electron (hole) occupancy of its 4f shell,more » and the magnetic Eu 2+ state (4f 7) has no orbital component in the usual LS coupling scheme, which can lead to a quite different and interesting physics. In the EuCu 2(Si xGe 1-x) 2 series, where the valence can be tuned by varying the Si/Ge ratio, it has been reported that a significant valence uctuation can exist even in the magnetic order regime. This paper presents a detailed study of the latter material using different microscopic probes (XANES, Mossbauer spectroscopy, elastic and inelastic neutron scattering), in which the composition dependence of the magnetic order and dynamics across the series is traced back to the change in the Eu valence state. In particular, the results support the persistence of valence uctuations into the antiferromagnetic state over a sizable composition range below the critical Si concentration x c ≈ 0:65. In conclusion, the sequence of magnetic ground states in the series is shown to re ect the evolution of the magnetic spectral response.« less

  3. Ab initio study of the ground and excited electronic states of the methyl radical

    PubMed Central

    Zanchet, A.; Bañares, L.; Senent, M. L.; García-Vela, A.

    2016-01-01

    The ground and some excited electronic states of the methyl radical have been characterized by means of highly correlated ab intio techniques. The specific excited states investigated are those involved in the dissociation of the radical, namely the 3s and 3pz Rydberg states, and the A1 and B1 valence states crossing them, respectively. The C-H dissociative coordinate and the HCH bending angle were considered in order to generate the first two-dimensional ab initio representation of the potential surfaces of the above electronic states of CH3, along with the nonadiabatic couplings between them. Spectroscopic constants and frequencies calculated for the ground and bound excited states agree well with most of the available experimental data. Implications of the shape of the excited potential surfaces and couplings for the dissociation pathways of CH3 are discussed in the light of recent experimental results for dissociation from low-lying vibrational states of CH3. Based on the ab initio data some predictions are made regarding methyl photodissociation from higher initial vibrational states. PMID:27892569

  4. Non-linear valence electron dynamics in metallic clusters

    NASA Astrophysics Data System (ADS)

    Calvayrac, F.

    This work deals with the response of the valence electrons of simple metal clusters to various excitations, in a purely dynamical context. It is related to various recent experiments where the methods based on linear response fail. The electronic motion is solved in direct time, the wavefunctions being discretized on an evenly spaced grid. The theoretical framework is the time dependent density functional theory, restricted to a version local in time and space (LSDA). The other parts of the clusters are either a jellium or an explicit ionic background exerting local or non-local pseudopotentials. The ionic dynamics is discussed, as well as the relevance of various observables. The corresponding numerical techniques are given: either a selfconsistent Crank-Nicholson method is used, approximated by an alternate propagation in every space direction, or a method alternating between direct and Fourier space. The equations suggest a parallel treatment. Several examples of application are given. The case of Na9+ is thoroughly discussed, then the less simple case of Na11+. Spectra obtained for sodium clusters deposited on sodium chlorine surfaces are shown. An example of a simulation with a moving ionic background is handled: the transfer to the ionic degrees of freedom of the energy deposited in a twelve sodium atoms cluster by a femtosecond laser pulse is discussed. The electronic resonance spectrum for a linear carbon cluster C5 is then given. In the conclusion, the work is discussed as well as possible improvements and developments from the theoretical or numerical point of view. Ce travail aborde la réponse des électrons de valence d'agrégats de métaux simples à diverses excitations, dans un contexte purement dynamique, en relation avec diverses expériences récentes que les méthodes fondées sur la réponse linéaire sont incapables d'aborder. Le mouvement de ces électrons est résolu directement en temps, leurs fonctions d'onde étant discrétisées sur une

  5. Imaging ultrafast excited state pathways in transition metal complexes by X-ray transient absorption and scattering using X-ray free electron laser source

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

    Chen, Lin X.; Shelby, Megan L.; Lestrange, Patrick J.

    2016-01-01

    This report will describe our recent studies of transition metal complex structural dynamics on the fs and ps time scales using an X-ray free electron laser source, Linac Coherent Light Source (LCLS). Ultrafast XANES spectra at the Ni K-edge of nickel(II) tetramesitylporphyrin (NiTMP) were successfully measured for optically excited state at a timescale from 100 fs to 50 ps, providing insight into its sub-ps electronic and structural relaxation processes. Importantly, a transient reduced state Ni(I) (π, 3dx2-y2) electronic state is captured through the interpretation of a short-lived excited state absorption on the low-energy shoulder of the edge, which is aidedmore » by the computation of X-ray transitions for postulated excited electronic states. The observed and computed inner shell to valence orbital transition energies demonstrate and quantify the influence of electronic configuration on specific metal orbital energies. A strong influence of the valence orbital occupation on the inner shell orbital energies indicates that one should not use the transition energy from 1s to other orbitals to draw conclusions about the d-orbital energies. For photocatalysis, a transient electronic configuration could influence d-orbital energies up to a few eV and any attempt to steer the reaction pathway should account for this to ensure that external energies can be used optimally in driving desirable processes. NiTMP structural evolution and the influence of the porphyrin macrocycle conformation on relaxation kinetics can be likewise inferred from this study.« less

  6. Ligand-hole localization in oxides with unusual valence Fe

    PubMed Central

    Chen, Wei-Tin; Saito, Takashi; Hayashi, Naoaki; Takano, Mikio; Shimakawa, Yuichi

    2012-01-01

    Unusual high-valence states of iron are stabilized in a few oxides. A-site-ordered perovskite-structure oxides contain such iron cations and exhibit distinct electronic behaviors at low temperatures, e.g. charge disproportionation (4Fe4+ → 2Fe3+ + 2Fe5+) in CaCu3Fe4O12 and intersite charge transfer (3Cu2+ + 4Fe3.75+ → 3Cu3+ + 4Fe3+) in LaCu3Fe4O12. Here we report the synthesis of solid solutions of CaCu3Fe4O12 and LaCu3Fe4O12 and explain how the instabilities of their unusual valence states of iron are relieved. Although these behaviors look completely different from each other in simple ionic models, they can both be explained by the localization of ligand holes, which are produced by the strong hybridization of iron d and oxygen p orbitals in oxides. The localization behavior in the charge disproportionation of CaCu3Fe4O12 is regarded as charge ordering of the ligand holes, and that in the intersite charge transfer of LaCu3Fe4O12 is regarded as a Mott transition of the ligand holes. PMID:22690318

  7. Lattice and Valence Electronic Structures of Crystalline Octahedral Molybdenum Halide Clusters-Based Compounds, Cs2[Mo6X14] (X = Cl, Br, I), Studied by Density Functional Theory Calculations.

    PubMed

    Saito, Norio; Cordier, Stéphane; Lemoine, Pierric; Ohsawa, Takeo; Wada, Yoshiki; Grasset, Fabien; Cross, Jeffrey S; Ohashi, Naoki

    2017-06-05

    The electronic and crystal structures of Cs 2 [Mo 6 X 14 ] (X = Cl, Br, I) cluster-based compounds were investigated by density functional theory (DFT) simulations and experimental methods such as powder X-ray diffraction, ultraviolet-visible spectroscopy, and X-ray photoemission spectroscopy (XPS). The experimentally determined lattice parameters were in good agreement with theoretically optimized ones, indicating the usefulness of DFT calculations for the structural investigation of these clusters. The calculated band gaps of these compounds reproduced those experimentally determined by UV-vis reflectance within an error of a few tenths of an eV. Core-level XPS and effective charge analyses indicated bonding states of the halogens changed according to their sites. The XPS valence spectra were fairly well reproduced by simulations based on the projected electron density of states weighted with cross sections of Al K α , suggesting that DFT calculations can predict the electronic properties of metal-cluster-based crystals with good accuracy.

  8. Characterization of the HSiN HNSi system in its electronic ground state

    NASA Astrophysics Data System (ADS)

    Lind, Maria C.; Pickard, Frank C.; Ingels, Justin B.; Paul, Ankan; Yamaguchi, Yukio; Schaefer, Henry F.

    2009-03-01

    The electronic ground states (X˜Σ+1) of HSiN, HNSi, and the transition state connecting the two isomers were systematically studied using configuration interaction with single and double (CISD) excitations, coupled cluster with single and double (CCSD) excitations, CCSD with perturbative triple corrections [CCSD(T)], multireference complete active space self-consistent field (CASSCF), and internally contracted multireference configuration interaction (ICMRCI) methods. The correlation-consistent polarized valence (cc-pVXZ), augmented correlation-consistent polarized valence (aug-cc-pVXZ) (X=T,Q,5), correlation-consistent polarized core-valence (cc-pCVYZ), and augmented correlation-consistent polarized core-valence (aug-cc-pCVYZ) (Y=T,Q) basis sets were used. Via focal point analyses, we confirmed the HNSi isomer as the global minimum on the ground state HSiN HNSi zero-point vibrational energy corrected surface and is predicted to lie 64.7kcalmol-1 (22640cm-1, 2.81eV) below the HSiN isomer. The barrier height for the forward isomerization reaction (HSiN→HNSi) is predicted to be 9.7kcalmol-1, while the barrier height for the reverse process (HNSi→HSiN) is determined to be 74.4kcalmol-1. The dipole moments of the HSiN and HNSi isomers are predicted to be 4.36 and 0.26D, respectively. The theoretical vibrational isotopic shifts for the HSiN/DSiN and HNSi/DNSi isotopomers are in strong agreement with the available experimental values. The dissociation energy for HSiN [HSiN(X˜Σ+1)→H(S2)+SiN(XΣ+2)] is predicted to be D0=59.6kcalmol-1, whereas the dissociation energy for HNSi [HNSi(X˜Σ+1)→H(S2)+NSi(XΣ+2)] is predicted to be D0=125.0kcalmol-1 at the CCSD(T)/aug-cc-pCVQZ level of theory. Anharmonic vibrational frequencies computed using second order vibrational perturbation theory are in good agreement with available matrix isolation experimental data for both HSiN and HNSi isomers root mean squared derivation (RMSD=9cm-1).

  9. High-Order Coupled Cluster Method (CCM) Calculations for Quantum Magnets with Valence-Bond Ground States

    NASA Astrophysics Data System (ADS)

    Farnell, D. J. J.; Richter, J.; Zinke, R.; Bishop, R. F.

    2009-04-01

    In this article, we prove that exact representations of dimer and plaquette valence-bond ket ground states for quantum Heisenberg antiferromagnets may be formed via the usual coupled cluster method (CCM) from independent-spin product (e.g. Néel) model states. We show that we are able to provide good results for both the ground-state energy and the sublattice magnetization for dimer and plaquette valence-bond phases within the CCM. As a first example, we investigate the spin-half J 1- J 2 model for the linear chain, and we show that we are able to reproduce exactly the dimerized ground (ket) state at J 2/ J 1=0.5. The dimerized phase is stable over a range of values for J 2/ J 1 around 0.5, and results for the ground-state energies are in good agreement with the results of exact diagonalizations of finite-length chains in this regime. We present evidence of symmetry breaking by considering the ket- and bra-state correlation coefficients as a function of J 2/ J 1. A radical change is also observed in the behavior of the CCM sublattice magnetization as we enter the dimerized phase. We then consider the Shastry-Sutherland model and demonstrate that the CCM can span the correct ground states in both the Néel and the dimerized phases. Once again, very good results for the ground-state energies are obtained. We find CCM critical points of the bra-state equations that are in agreement with the known phase transition point for this model. The results for the sublattice magnetization remain near to the "true" value of zero over much of the dimerized regime, although they diverge exactly at the critical point. Finally, we consider a spin-half system with nearest-neighbor bonds for an underlying lattice corresponding to the magnetic material CaV4O9 (CAVO). We show that we are able to provide excellent results for the ground-state energy in each of the plaquette-ordered, Néel-ordered, and dimerized regimes of this model. The exact plaquette and dimer ground states are

  10. Electronic interaction in an outer-sphere mixed-valence double salt: a polarized neutron diffraction study of K(3)(MnO(4))(2).

    PubMed

    Cannon, Roderick D; Jayasooriya, Upali A; Tilford, Claire; Anson, Christopher E; Sowrey, Frank E; Rosseinsky, David R; Stride, John A; Tasset, Francis; Ressouche, Eric; White, Ross P; Ballou, Rafik

    2004-11-01

    The mixed-valence double salt K(3)(MnO(4))(2) crystallizes in space group P2(1)/m with Z = 2. The manganese centers Mn1 and Mn2 constitute discrete "permanganate", [Mn(VII)O(4)](-), and "manganate", [Mn(VI)O(4)](2-), ions, respectively. There is a spin-ordering transition to an antiferromagnetic state at ca. T = 5 K. The spin-density distribution in the paramagnetic phase at T = 10 K has been determined by polarized neutron diffraction, confirming that unpaired spin is largely confined to the nominal manganate ion Mn2. Through use of both Fourier refinement and maximum entropy methods, the spin on Mn1 is estimated as 1.75 +/- 1% of one unpaired electron with an upper limit of 2.5%.

  11. Excitations of one-valence-proton, one-valence-neutron nucleus {sup 210}Bi from cold-neutron capture

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

    Cieplicka-Oryńczak, N.; Institute of Nuclear Physics, Polish Academy of Sciences, PL-31342 Kraków; Fornal, B.

    2015-10-15

    The low-spin structure of one-proton, one-neutron {sup 210}Bi nucleus was investigated in cold-neutron capture reaction on {sup 209}Bi. The γ-coincidence measurements were performed with use of EXILL array consisted of 16 HPGe detectors. The experimental results were compared to shell-model calculations involving valence particles excitations. The {sup 210}Bi nucleus offers the potential to test the effective proton-neutron interactions because most of the states should arise from the proton-neutron excitations. Additionally, it was discovered that a few states should come from the couplings of valence particles to the 3{sup −} octupole vibration in {sup 208}Pb which provides also the possibility ofmore » testing the calculations involving the core excitations.« less

  12. Variation of sigma-hole magnitude with M valence electron population in MX(n)Y(4-n) molecules (n = 1-4; M = C, Si, Ge; X, Y = F, Cl, Br).

    PubMed

    McDowell, Sean A C; Joseph, Jerelle A

    2014-01-14

    Sigma holes are described as electron-deficient regions on atoms, particularly along the extension of covalent bonds, due to non-uniform electron density distribution on the surface of these atoms. A computational study of MX(n)Y(4-n) molecules (n = 1-4; M = C, Si, Ge; X, Y = F, Cl, Br) was undertaken and it is shown that the relative sigma hole potentials on M due to X-M and Y-M can be adequately explained in terms of the variation in the valence electron population of the central M atom. A model is proposed for the depletion of the M valence electron population which explains the trends in sigma hole strengths, especially those that cannot be accounted for solely on the basis of relative electronegativities.

  13. Defect induced electronic states and magnetism in ball-milled graphite.

    PubMed

    Milev, Adriyan; Dissanayake, D M A S; Kannangara, G S K; Kumarasinghe, A R

    2013-10-14

    The electronic structure and magnetism of nanocrystalline graphite prepared by ball milling of graphite in an inert atmosphere have been investigated using valence band spectroscopy (VB), core level near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and magnetic measurements as a function of the milling time. The NEXAFS spectroscopy of graphite milled for 30 hours shows simultaneous evolution of new states at ~284.0 eV and at ~290.5 eV superimposed upon the characteristic transitions at 285.4 eV and 291.6 eV, respectively. The modulation of the density of states is explained by evolution of discontinuities within the sheets and along the fracture lines in the milled graphite. The magnetic measurements in the temperature interval 2-300-2 K at constant magnetic field strength show a correlation between magnetic properties and evolution of the new electronic states. With the reduction of the crystallite sizes of the graphite fragments, the milled material progressively changes its magnetic properties from diamagnetic to paramagnetic with contributions from both Pauli and Curie paramagnetism due to the evolution of new states at ~284 and ~290.5 eV, respectively. These results indicate that the magnetic behaviour of ball-milled graphite can be manipulated by changing the milling conditions.

  14. Valence Band Control of Metal Silicide Films via Stoichiometry.

    PubMed

    Streller, Frank; Qi, Yubo; Yang, Jing; Mangolini, Filippo; Rappe, Andrew M; Carpick, Robert W

    2016-07-07

    The unique electronic and mechanical properties of metal silicide films render them interesting for advanced materials in plasmonic devices, batteries, field-emitters, thermoelectric devices, transistors, and nanoelectromechanical switches. However, enabling their use requires precisely controlling their electronic structure. Using platinum silicide (PtxSi) as a model silicide, we demonstrate that the electronic structure of PtxSi thin films (1 ≤ x ≤ 3) can be tuned between metallic and semimetallic by changing the stoichiometry. Increasing the silicon content in PtxSi decreases the carrier density according to valence band X-ray photoelectron spectroscopy and theoretical density of states (DOS) calculations. Among all PtxSi phases, Pt3Si offers the highest DOS due to the modest shift of the Pt5d manifold away from the Fermi edge by only 0.5 eV compared to Pt, rendering it promising for applications. These results, demonstrating tunability of the electronic structure of thin metal silicide films, suggest that metal silicides can be designed to achieve application-specific electronic properties.

  15. Reactive Force Fields via Explicit Valency

    NASA Astrophysics Data System (ADS)

    Kale, Seyit

    Computational simulations are invaluable in elucidating the dynamics of biological macromolecules. Unfortunately, reactions present a fundamental challenge. Calculations based on quantum mechanics can predict bond formation and rupture; however they suffer from severe length- and time-limitations. At the other extreme, classical approaches provide orders of magnitude faster simulations; however they regard chemical bonds as immutable entities. A few exceptions exist, but these are not always trivial to adopt for routine use. We bridge this gap by providing a novel, pseudo-classical approach, based on explicit valency. We unpack molecules into valence electron pairs and atomic cores. Particles bear ionic charges and interact via pairwise-only potentials. The potentials are informed of quantum effects in the short-range and obey dissociation limits in the long-range. They are trained against a small set of isolated species, including geometries and thermodynamics of small hydrides and of dimers formed by them. The resulting force field captures the essentials of reactivity, polarizability and flexibility in a simple, seamless setting. We call this model LEWIS, after the chemical theory that inspired the use of valence pairs. Following the introduction in Chapter 1, we initially focus on the properties of water. Chapter 2 considers gas phase clusters. To transition to the liquid phase, Chapter 3 describes a novel pairwise long-range compensation that performs comparably to infinite lattice summations. The approach is suited to ionic solutions in general. In Chapters 4 and 5, LEWIS is shown to correctly predict the dipolar and quadrupolar response in bulk liquid, and can accommodate proton transfers in both acid and base. Efficiency permits the study of proton defects at dilutions not accessible to experiment or quantum mechanics. Chapter 6 discusses explicit valency approaches in other hydrides, forming the basis of a reactive organic force field. Examples of simple

  16. Oxygen fugacity of mare basalts and the lunar mantle application of a new microscale oxybarometer based on the valence state of vanadium

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

    Shearer, C.K.; Karner, J.; Papike, J.J.

    2004-05-25

    Using the valence state of vanadium on a microscale in lunar volcanic glasses we have developed another approach to estimating the oxygen fugacity of mare basalts. The ability to estimate oxygen fugacities for mare basalts and to extend these observations to the lunar mantle is limited using bulk analysis techniques based on buffering assemblages or the valence state of iron. These limitations are due to reequilibration of mineral assemblages at subsolidus conditions, deviations of mineral compositions from thermodynamic ideality, size requirements, and the limits of the iron valence at very low fO{sub 2}. Still, these approaches have been helpful andmore » indicate that mare basalts crystallized at fO{sub 2} between the iron-wuestite buffer (IW) and the ilmenite breakdown reaction (ilmenite = rutile + iron). It has also been inferred from these estimates that the lunar mantle is also highly reduced lying at conditions below IW. Generally, these data cannot be used to determine if the mare basalts become increasingly reduced during transport from their mantle source and eruption at the lunar surface and if there are differences in fO{sub 2} among mare basalts or mantle sources. One promising approach to determining the fO2 of mare basalts is using the mean valence of vanadium (2+, 3+, 4+, 5+) determined on spots of a few micrometers in diameter using synchrotron x-ray absorption fine structure (XAFS) spectroscopy. The average valence state of V in basaltic glasses is a function of fO{sub 2}, temperature, V coordination, and melt composition. Here, we report the initial results of this approach applied to lunar pyroclastic glasses.« less

  17. Valence evaluation with approaching or withdrawing cues: directly testing valence-arousal conflict theory.

    PubMed

    Wang, Yan Mei; Li, Ting; Li, Lin

    2017-07-19

    The valence-arousal conflict theory assumes that both valence and arousal will trigger approaching or withdrawing tendencies. It also predicts that the speed of processing emotional stimuli will depend on whether valence and arousal trigger conflicting or congruent motivational tendencies. However, most previous studies have provided evidence of the interaction between valence and arousal only, and have not provided direct proof of the interactive links between valence, arousal and motivational tendencies. The present study provides direct evidence for the relationship between approach-withdrawal tendencies and the valence-arousal conflict. In an empirical test, participants were instructed to judge the valence of emotional words after visual-spatial cues that appeared to be either approaching or withdrawing from participants. A three-way interaction (valence, arousal, and approach-withdrawal tendency) was observed such that the response time was shorter if participants responded to a negative high-arousal stimulus after a withdrawing cue, or to a positive low-arousal stimulus after an approaching cue. These findings suggest that the approach-withdrawal tendency indeed plays a crucial role in valence-arousal conflict, and that the effect depends on the congruency of valence, arousal and tendency at an early stage of processing.

  18. Dynamics in higher lying excited states: Valence to Rydberg transitions in the relaxation paths of pyrrole and methylated derivatives

    NASA Astrophysics Data System (ADS)

    Geng, Ting; Schalk, Oliver; Neville, Simon P.; Hansson, Tony; Thomas, Richard D.

    2017-04-01

    The involvement of intermediate Rydberg states in the relaxation dynamics of small organic molecules which, after excitation to the valence manifold, also return to the valence manifold is rarely observed. We report here that such a transiently populated Rydberg state may offer the possibility to modify the outcome of a photochemical reaction. In a time resolved photoelectron study on pyrrole and its methylated derivatives, N-methyl pyrrole and 2,5-dimethyl pyrrole, 6.2 eV photons (200 nm) are used to excite these molecules into a bright ππ* state. In each case, a π3p-Rydberg state, either the B1(π3py) or the A2(π3pz) state, is populated within 20-50 fs after excitation. The wavepacket then proceeds to the lower lying A2(πσ*) state within a further 20 fs, at which point two competing reaction channels can be accessed: prompt N-H (N-CH3) bond cleavage or return to the ground state via a conical intersection accessed after ring puckering, the latter of which is predicted to require an additional 100-160 fs depending on the molecule.

  19. Can the second order multireference perturbation theory be considered a reliable tool to study mixed-valence compounds?

    PubMed

    Pastore, Mariachiara; Helal, Wissam; Evangelisti, Stefano; Leininger, Thierry; Malrieu, Jean-Paul; Maynau, Daniel; Angeli, Celestino; Cimiraglia, Renzo

    2008-05-07

    In this paper, the problem of the calculation of the electronic structure of mixed-valence compounds is addressed in the frame of multireference perturbation theory (MRPT). Using a simple mixed-valence compound (the 5,5(') (4H,4H('))-spirobi[ciclopenta[c]pyrrole] 2,2('),6,6(') tetrahydro cation), and the n-electron valence state perturbation theory (NEVPT2) and CASPT2 approaches, it is shown that the ground state (GS) energy curve presents an unphysical "well" for nuclear coordinates close to the symmetric case, where a maximum is expected. For NEVPT, the correct shape of the energy curve is retrieved by applying the MPRT at the (computationally expensive) third order. This behavior is rationalized using a simple model (the ionized GS of two weakly interacting identical systems, each neutral system being described by two electrons in two orbitals), showing that the unphysical well is due to the canonical orbital energies which at the symmetric (delocalized) conformation lead to a sudden modification of the denominators in the perturbation expansion. In this model, the bias introduced in the second order correction to the energy is almost entirely removed going to the third order. With the results of the model in mind, one can predict that all MRPT methods in which the zero order Hamiltonian is based on canonical orbital energies are prone to present unreasonable energy profiles close to the symmetric situation. However, the model allows a strategy to be devised which can give a correct behavior even at the second order, by simply averaging the orbital energies of the two charge-localized electronic states. Such a strategy is adopted in a NEVPT2 scheme obtaining a good agreement with the third order results based on the canonical orbital energies. The answer to the question reported in the title (is this theoretical approach a reliable tool for a correct description of these systems?) is therefore positive, but care must be exercised, either in defining the orbital

  20. On Valence-Band Splitting in Layered MoS2.

    PubMed

    Zhang, Youwei; Li, Hui; Wang, Haomin; Liu, Ran; Zhang, Shi-Li; Qiu, Zhi-Jun

    2015-08-25

    As a representative two-dimensional semiconducting transition-metal dichalcogenide (TMD), the electronic structure in layered MoS2 is a collective result of quantum confinement, interlayer interaction, and crystal symmetry. A prominent energy splitting in the valence band gives rise to many intriguing electronic, optical, and magnetic phenomena. Despite numerous studies, an experimental determination of valence-band splitting in few-layer MoS2 is still lacking. Here, we show how the valence-band maximum (VBM) splits for one to five layers of MoS2. Interlayer coupling is found to contribute significantly to phonon energy but weakly to VBM splitting in bilayers, due to a small interlayer hopping energy for holes. Hence, spin-orbit coupling is still predominant in the splitting. A temperature-independent VBM splitting, known for single-layer MoS2, is, thus, observed for bilayers. However, a Bose-Einstein type of temperature dependence of VBM splitting prevails in three to five layers of MoS2. In such few-layer MoS2, interlayer coupling is enhanced with a reduced interlayer distance, but thermal expansion upon temperature increase tends to decouple adjacent layers and therefore decreases the splitting energy. Our findings that shed light on the distinctive behaviors about VBM splitting in layered MoS2 may apply to other hexagonal TMDs as well. They will also be helpful in extending our understanding of the TMD electronic structure for potential applications in electronics and optoelectronics.

  1. Valence, Covalence, Hypervalence, Oxidation State, and Coordination Number

    ERIC Educational Resources Information Center

    Smith, Derek W.

    2005-01-01

    Valence as a numerical measure of an atom's combining power, expressed by the number of bonds it forms in a molecular formulation of the compound in question, was unable to cope with coordination compounds. The covalence of an atom is the nearest model equivalent, but is subject to ambiguity since it often depends on which bonding model is being…

  2. A complete active space valence bond method with nonorthogonal orbitals

    NASA Astrophysics Data System (ADS)

    Hirao, Kimihiko; Nakano, Haruyuki; Nakayama, Kenichi

    1997-12-01

    A complete active space self-consistent field (SCF) wave function is transformed into a valence bond type representation built from nonorthogonal orbitals, each strongly localized on a single atom. Nonorthogonal complete active space SCF orbitals are constructed by Ruedenberg's projected localization procedure so that they have maximal overlaps with the corresponding minimum basis set of atomic orbitals of the free-atoms. The valence bond structures which are composed of such nonorthogonal quasiatomic orbitals constitute the wave function closest to the concept of the oldest and most simple valence bond method. The method is applied to benzene, butadiene, hydrogen, and methane molecules and compared to the previously proposed complete active space valence bond approach with orthogonal orbitals. The results demonstrate the validity of the method as a powerful tool for describing the electronic structure of various molecules.

  3. Evidence of mixed valence states in U M2Al 3 ( M = Ni, Pd) studied by X-ray photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Fujimori, Shin-ichi; Saito, Yasuharu; Sato, Noriaki; Komatsubara, Takemi; Suzuki, Shoji; Sato, Shigeru; Ishii, Takehiko

    1998-01-01

    We have measured the XPS valence band and core-level spectra of U M2Al 3 ( M = Ni and Pd). The results are compared with those of reference materials, dilute alloy U 0.1La 0.9Pd 2Al 3 and itinerant 5 f compound URh 3. The similarity of the core-level spectra between UPd 2Al 3 and U 0.1La 0.9Pd 2Al 3 suggests that their core-level spectra are governed by the interaction between U 5 f and ligand states of neighboring palladium and aluminum sites, with negligible contributions from neighboring uranium states. A complex satellite structure, observed in the core-level spectra of U M2Al 3, suggests that the uranium atoms are in the strong mixed valence states with 5 f2(U 4+) and 5 f3(U 3+).

  4. 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

  5. Non-classical behaviour of higher valence dopants in chromium (III) oxide by a Cr vacancy compensation mechanism

    NASA Astrophysics Data System (ADS)

    Carey, John J.; Nolan, Michael

    2017-10-01

    Modification of metal oxides with dopants that have a stable oxidation in their parent oxides which is higher than the host system is expected to introduce extra electrons into the material to improve carrier mobility. This is essential for applications in catalysis, SOFCs and solar energy materials. Density functional theory calculations are used to investigate the change in electronic and geometric structure of chromium (III) oxide by higher valence dopants, namely; Ce, Ti, V and Zr. For single metal doping, we find that the dopants with variable oxidation states, Ce, Ti and V, adopt a valence state of  +3, while Zr dopant has a  +4 oxidation state and reduces a neighbouring Cr cation. Chromium vacancy formation is greatly enhanced for all dopants, and favoured over oxygen vacancy formation. The Cr vacancies generate holes which oxidise Ce, Ti and V from  +3 to  +4, while also oxidising lattice oxygen sites. For Zr doping, the generated holes oxidise the reduced Cr2+ cation back to Cr3+ and also two lattice oxygen atoms. Three metal atoms in the bulk lattice facilitate spontaneous Cr vacancy from charge compensation. A non-classical compensation mechanism is observed for Ce, Ti and V; all three metals are oxidised from  +3 to  +4, which explains experimental observations that these metals have a  +4 oxidation state in Cr2O3. Charge compensation of the three Zr metals proceeds by a classical higher valence doping mechanism; the three dopants reduce three Cr cations, which are subsequently charge compensated by a Cr vacancy oxidising three Cr2+ to Cr3+. The compensated structures are the correct ground state electronic structure for these doped systems, and used as a platform to investigate cation/anion vacancy formation. Unlike the single metal doped bulks, preference is now given for oxygen vacancy formation over Cr vacancy formation, indicating that the dopants increase the reducibility of Cr2O3 with Ce doping showing the strongest

  6. Core-core and core-valence correlation energy atomic and molecular benchmarks for Li through Ar

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

    Ranasinghe, Duminda S.; Frisch, Michael J.; Petersson, George A., E-mail: gpetersson@wesleyan.edu

    2015-12-07

    We have established benchmark core-core, core-valence, and valence-valence absolute coupled-cluster single double (triple) correlation energies (±0.1%) for 210 species covering the first- and second-rows of the periodic table. These species provide 194 energy differences (±0.03 mE{sub h}) including ionization potentials, electron affinities, and total atomization energies. These results can be used for calibration of less expensive methodologies for practical routine determination of core-core and core-valence correlation energies.

  7. Multireference configuration interaction study of the mixed Valence-Rydberg character of the C2H4 1(π,π*) V state

    NASA Astrophysics Data System (ADS)

    Krebs, Stefan; Buenker, Robert J.

    1997-05-01

    The spatial extension of the C2H41(π,π*) V state is investigated by means of low selection threshold multireference configuration interaction (CI) calculations employing two atomic orbital (AO) basis sets with different numbers of polarization and Rydberg functions. The results are shown to be nearly independent of the choice of one-electron basis (ground N, triplet T, and singlet V self-consistent field molecular orbitals (SCF MOs)) in forming the many-electron basis for the configuration interaction indicating that the AO basis limit has been closely approached in each case. The calculations indicate that the value for the <ΨV|Σxi2|ΨV>≡V matrix element falls in the 18±1 a02 range, 50% larger than the corresponding values computed for N and T, respectively, for the corresponding N and T states. This result is interpreted to be a consequence of the mixing of diabatic 1(π,π*) valence and 1(π,dπ) Rydberg states in the Franck-Condon region of the V-N transition. The corresponding excitation energy is computed to lie in the 7.90-7.95 eV range, indicating that there is a distinct nonverticality in the measured absorption spectrum which is caused in part by nonadiabatic interactions between the V and 1(π,3py) Rydberg states as a result of torsional motion of the C2H4 molecule.

  8. Electron accommodation dynamics in the DNA base thymine

    NASA Astrophysics Data System (ADS)

    King, Sarah B.; Stephansen, Anne B.; Yokoi, Yuki; Yandell, Margaret A.; Kunin, Alice; Takayanagi, Toshiyuki; Neumark, Daniel M.

    2015-07-01

    The dynamics of electron attachment to the DNA base thymine are investigated using femtosecond time-resolved photoelectron imaging of the gas phase iodide-thymine (I-T) complex. An ultraviolet pump pulse ejects an electron from the iodide and prepares an iodine-thymine temporary negative ion that is photodetached with a near-IR probe pulse. The resulting photoelectrons are analyzed with velocity-map imaging. At excitation energies ranging from -120 meV to +90 meV with respect to the vertical detachment energy (VDE) of 4.05 eV for I-T, both the dipole-bound and valence-bound negative ions of thymine are observed. A slightly longer rise time for the valence-bound state than the dipole-bound state suggests that some of the dipole-bound anions convert to valence-bound species. No evidence is seen for a dipole-bound anion of thymine at higher excitation energies, in the range of 0.6 eV above the I-T VDE, which suggests that if the dipole-bound anion acts as a "doorway" to the valence-bound anion, it only does so at excitation energies near the VDE of the complex.

  9. Electron accommodation dynamics in the DNA base thymine.

    PubMed

    King, Sarah B; Stephansen, Anne B; Yokoi, Yuki; Yandell, Margaret A; Kunin, Alice; Takayanagi, Toshiyuki; Neumark, Daniel M

    2015-07-14

    The dynamics of electron attachment to the DNA base thymine are investigated using femtosecond time-resolved photoelectron imaging of the gas phase iodide-thymine (I(-)T) complex. An ultraviolet pump pulse ejects an electron from the iodide and prepares an iodine-thymine temporary negative ion that is photodetached with a near-IR probe pulse. The resulting photoelectrons are analyzed with velocity-map imaging. At excitation energies ranging from -120 meV to +90 meV with respect to the vertical detachment energy (VDE) of 4.05 eV for I(-)T, both the dipole-bound and valence-bound negative ions of thymine are observed. A slightly longer rise time for the valence-bound state than the dipole-bound state suggests that some of the dipole-bound anions convert to valence-bound species. No evidence is seen for a dipole-bound anion of thymine at higher excitation energies, in the range of 0.6 eV above the I(-)T VDE, which suggests that if the dipole-bound anion acts as a "doorway" to the valence-bound anion, it only does so at excitation energies near the VDE of the complex.

  10. Interacting quasi-band model for electronic states in compound semiconductor alloys: Zincblende structure

    NASA Astrophysics Data System (ADS)

    Shinozuka, Yuzo; Oda, Masato

    2015-09-01

    The interacting quasi-band model proposed for electronic states in simple alloys is extended for compound semiconductor alloys with general lattice structures containing several atoms per unit cell. Using a tight-binding model, a variational electronic wave function for quasi-Bloch states yields a non-Hermitian Hamiltonian matrix characterized by matrix elements of constituent crystals and concentration of constituents. Solving secular equations for each k-state yields the alloy’s energy spectrum for any type of randomness and arbitrary concentration. The theory is used to address III-V (II-VI) alloys with a zincblende lattice with crystal band structures well represented by the sp3s* model. Using the resulting 15 × 15 matrix, the concentration dependence of valence and conduction bands is calculated in a unified scheme for typical alloys: Al1-xGaxAs, GaAs1-xPx, and GaSb1-xPx. Results agree well with experiments and are discussed with respect to the concentration dependence, direct-indirect gap transition, and band-gap-bowing origin.

  11. Magnetic-field induced quantum critical points of valence transition in Ce- and Yb-based heavy fermions

    NASA Astrophysics Data System (ADS)

    Watanabe, Shinji; Tsuruta, Atsushi; Miyake, Kazumasa; Flouquet, Jacques

    2009-03-01

    Valence instability and its critical fluctuations have attracted much attention recently in the heavy-electron systems. Valence fluctuations are essentially charge fluctuations, and it is highly non-trivial how the quantum critical point (QCP) as well as the critical end point is controlled by the magnetic field. To clarify this fundamental issue, we have studied the mechanism of how the critical points of the first-order valence transitions are controlled by the magnetic field [1]. We show that the critical temperature is suppressed to be the QCP by the magnetic field and unexpectedly the QCP exhibits nonmonotonic field dependence in the ground-state phase diagram, giving rise to emergence of metamagnetism even in the intermediate valence-crossover regime. The driving force of the field-induced QCP is clarified to be a cooperative phenomenon of Zeeman effect and Kondo effect, which creates a distinct energy scale from the Kondo temperature. This mechanism explains a peculiar magnetic response in CeIrIn5 and metamagnetic transition in YbXCu4 for X=In as well as a sharp contrast between X=Ag and Cd. We present the novel phenomena under the magnetic field to discuss significance of the proximity of the critical points of the first-order valence transition. [1] S. Watanabe et al. PRL100, (2008) 236401.

  12. Electronic structure of germanium selenide investigated using ultra-violet photo-electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Mishra, P.; Lohani, H.; Kundu, A. K.; Patel, R.; Solanki, G. K.; Menon, Krishnakumar S. R.; Sekhar, B. R.

    2015-07-01

    The valence band electronic structure of GeSe single crystals has been investigated using angle resolved photoemission spectroscopy (ARPES) and x-ray photoelectron spectroscopy. The experimentally observed bands from ARPES, match qualitatively with our LDA-based band structure calculations along the Γ-Z, Γ-Y and Γ-T symmetry directions. The valence band maximum occurs nearly midway along the Γ-Z direction, at a binding energy of -0.5 eV, substantiating the indirect band gap of GeSe. Non-dispersive features associated with surface states and indirect transitions have been observed. The difference in hybridization of Se and Ge 4p orbitals leads to the variation of dispersion along the three symmetry directions. The predominance of the Se 4pz orbitals, evidenced from theoretical calculations, may be the cause for highly dispersive bands along the Γ-T direction. Detailed electronic structure analysis reveals the significance of the cation-anion 4p orbitals hybridization in the valence band dispersion of IV-VI semiconductors. This is the first comprehensive report of the electronic structure of a GeSe single crystal using ARPES in conjugation with theoretical band structure analysis.

  13. Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization.

    PubMed

    Lin, Qisheng; Miller, Gordon J

    2018-01-16

    complexity can be realized by small amounts of Li replacing Zn atoms in the parent binary compounds CaZn 2 , CaZn 3 , and CaZn 5 ; their phase formation and bonding schemes can be rationalized by Fermi surface-Brillouin zone interactions between nearly free-electron states. "Cation-rich", electron-poor polar intermetallics have emerged using rare earth metals as the electropositive ("cationic") component together metal/metalloid clusters that mimic the backbones of aromatic hydrocarbon molecules, which give evidence of extensive electronic delocalization and multicenter bonding. Thus, we can identify three distinct, valence electron-poor, polar intermetallic systems that have yielded unprecedented phases adopting novel structures containing complex clusters and intriguing bonding characteristics. In this Account, we summarize our recent specific progress in the developments of novel Au-rich BaAl 4 -type related structures, shown in the "gold-rich grid", lithiation-modulated Ca-Li-Zn phases stabilized by different bonding characteristics, and rare earth-rich polar intermetallics containing unprecedented hydrocarbon-like planar Co-Ge metal clusters and pronounced delocalized multicenter bonding. We will focus mainly on novel structural motifs, bonding analyses, and the role of valence electrons for phase stability.

  14. High-nuclearity mixed-valence clusters and mixed-valence chains: general approach to the calculation of the energy levels and bulk magnetic properties.

    PubMed

    Clemente-Juan, J M; Borrás-Almenar, J J; Coronado, E; Palii, A V; Tsukerblat, B S

    2009-05-18

    A general approach to the problem of electron delocalization in the high-nuclearity mixed-valence (MV) clusters containing an arbitrary number of localized spins and itinerant electrons is developed. Along with the double exchange, we consider the isotropic magnetic exchange between the localized electrons as well as the Coulomb intercenter repulsion. As distinguished from the previous approaches dealing with the MV systems in which itinerant electrons are delocalized over all constituent metal sites, here, we consider a more common case of systems exhibiting partial delocalization and containing several delocalized domains. Taking full advantage of the powerful angular momentum technique, we were able to derive closed form analytical expressions for the matrix elements of the full Hamiltonian. These expressions provide an efficient tool for treating complex mixed-valence systems, because they contain only products of 6j-symbols (that appear while treating the delocalized parts) and 9j-symbols (exchange interactions in localized parts) and do not contain high-order recoupling coefficients and 3j-symbols that essentially constrained all previous theories of mixed valency. The approach developed here is accompanied by an efficient computational procedure that allows us to calculate the bulk thermodynamic properties (magnetic susceptibility, magnetization, and magnetic specific heat) of high-nuclearity MV clusters. Finally, this approach has been used to discuss the magnetic properties of the octanuclear MV cluster [Fe(8)(mu(4)-O)(4)(4-Cl-pz)(12)Cl(4)](-) and the diphthalocyanine chains [YPc(2)].CH(2)Cl(2) and [ScPc(2)].CH(2)Cl(2) composed of MV dimers interacting through the magnetic exchange and Coulomb repulsion.

  15. Excited electronic states of the methyl radical. Ab initio molecular orbital study of geometries, excitation energies and vibronic spectra

    NASA Astrophysics Data System (ADS)

    Mebel, Alexander M.; Lin, Sheng-Hsien

    1997-03-01

    The geometries, vibrational frequencies and vertical and adiabatic excitation energies of the excited valence and Rydberg 3s, 3p, 3d, and 4s electronic states of CH 3 have been studied using ab initio molecular orbital multiconfigurational SCF (CASSCF), internally contracted multireference configuration interaction (MRCI) and equation-of-motion coupled cluster (EOM-CCSD) methods. The vibronic spectra are determined through the calculation of Franck-Condon factors. Close agreement between theory and experiment has been found for the excitation energies, vibrational frequencies and vibronic spectra. The adiabatic excitation energies of the Rydberg 3s B˜ 2A' 1 and 3p 2 2A″ 2 states are calculated to be 46435 and 60065 cm -1 compared to the experimental values of 46300 and 59972 cm -1, respectively. The valence 2A″ excited state of CH 3 has been found to have a pyramidal geometry within C s symmetry and to be adiabatically by 97 kcal/mol higher in energy than the ground state. The 2A″ state is predicted to be stable by 9 and 13 kcal/mol with respect to H 2 and H elimination.

  16. Polarity determination of polar and semipolar (112¯2) InN and GaN layers by valence band photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Skuridina, D.; Dinh, D. V.; Lacroix, B.; Ruterana, P.; Hoffmann, M.; Sitar, Z.; Pristovsek, M.; Kneissl, M.; Vogt, P.

    2013-11-01

    We demonstrate that the polarity of polar (0001), (0001¯) and semipolar (112¯2) InN and GaN thin layers can be determined by valence band X-ray photoemission spectroscopy (XPS). The polarity of the layers has been confirmed by wet etching and convergent beam electron diffraction. Unlike these two techniques, XPS is a non-destructive method and unaffected by surface oxidation or roughness. Different intensities of the valence band states in spectra recorded by using AlKα X-ray radiation are observed for N-polar and group-III-polar layers. The highest intensity of the valence band state at ≈3.5 eV for InN and ≈5.2 eV for GaN correlates with the group-III polarity, while the highest intensity at ≈6.7 eV for InN and ≈9.5 eV for GaN correlates with the N-polarity. The difference between the peaks for the group-III- and N-polar orientations was found to be statistically significant at the 0.05 significance level. The polarity of semipolar (112¯2) InN and GaN layers can be determined by recording valence band photoelectrons emitted along the [000 ± 1] direction.

  17. First determination of the valence band dispersion of CH3NH3PbI3 hybrid organic-inorganic perovskite

    NASA Astrophysics Data System (ADS)

    Lee, Min-I.; Barragán, Ana; Nair, Maya N.; Jacques, Vincent L. R.; Le Bolloc'h, David; Fertey, Pierre; Jemli, Khaoula; Lédée, Ferdinand; Trippé-Allard, Gaëlle; Deleporte, Emmanuelle; Taleb-Ibrahimi, Amina; Tejeda, Antonio

    2017-07-01

    The family of hybrid organic-inorganic halide perovskites is in the limelight because of their recently discovered high photovoltaic efficiency. These materials combine photovoltaic energy conversion efficiencies exceeding 22% and low-temperature and low-cost processing in solution; a breakthrough in the panorama of renewable energy. Solar cell operation relies on the excitation of the valence band electrons to the conduction band by solar photons. One factor strongly impacting the absorption efficiency is the band dispersion. The band dispersion has been extensively studied theoretically, but no experimental information was available. Herein, we present the first experimental determination of the valence band dispersion of methylammonium lead halide in the tetragonal phase. Our results pave the way for contrasting the electronic hopping or the electron effective masses in different theories by comparing to our experimental bands. We also show a significant broadening of the electronic states, promoting relaxed conditions for photon absorption, and demonstrate that the tetragonal structure associated to the octahedra network distortion below 50 °C induces only a minor modification of the electronic bands, with respect to the cubic phase at high temperature, thus minimizing the impact of the cubic-tetragonal transition on solar cell efficiencies.

  18. Metal Oxide Nanoparticles: The Importance of Size, Shape, Chemical Composition, and Valence State in Determining Toxicity

    NASA Astrophysics Data System (ADS)

    Dunnick, Katherine

    Nanoparticles, which are defined as a structure with at least one dimension between 1 and 100 nm, have the potential to be used in a variety of consumer products due to their improved functionality compared to similar particles of larger size. Their small size is associated with increased strength, improved catalytic properties, and increased reactivity; however, their size is also associated with increased toxicity in vitro and in vivo. Numerous toxicological studies have been conducted to determine the properties of nanomaterials that increase their toxicity in order to manufacture new nanomaterials with decreased toxicity. Data indicates that size, shape, chemical composition, and valence state of nanomaterials can dramatically alter their toxicity profile. Therefore, the purpose of this dissertation was to determine how altering the shape, size, and chemical composition of various metal oxide nanoparticles would affect their toxicity. Metal oxides are used in variety of consumer products, from spray-sun screens, to food coloring agents; thus, understanding the toxicity of metal oxides and determining which aspects affect their toxicity may provide safe alternatives nanomaterials for continued use in manufacturing. Tungstate nanoparticles toxicity was assessed in an in vitro model using RAW 264.7 cells. The size, shape, and chemical composition of these nanomaterials were altered and the effect on reactive oxygen species and general cytotoxicity was determined using a variety of techniques. Results demonstrate that shape was important in reactive oxygen species production as wires were able to induce significant reactive oxygen species compared to spheres. Shape, size, and chemical composition did not have much effect on the overall toxicity of these nanoparticles in RAW 264.7 cells over a 72 hour time course, implicating that the base material of the nanoparticles was not toxic in these cells. To further assess how chemical composition can affect toxicity

  19. Valence and lowest Rydberg electronic states of phenol investigated by synchrotron radiation and theoretical methods

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

    Limão-Vieira, P., E-mail: plimaovieira@fct.unl.pt; Ferreira da Silva, F.; Lange, E.

    2016-07-21

    We present the experimental high-resolution vacuum ultraviolet (VUV) photoabsorption spectra of phenol covering for the first time the full 4.3–10.8 eV energy-range, with absolute cross sections determined. Theoretical calculations on the vertical excitation energies and oscillator strengths were performed using time-dependent density functional theory and the equation-of-motion coupled cluster method restricted to single and double excitations level. These have been used in the assignment of valence and Rydberg transitions of the phenol molecule. The VUV spectrum reveals several new features not previously reported in the literature, with particular reference to the 6.401 eV transition, which is here assigned to themore » 3sσ/σ{sup ∗}(OH)←3π(3a″) transition. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of phenol in the earth’s atmosphere (0–50 km).« less

  20. Physics of Resonating Valence Bond Spin Liquids

    NASA Astrophysics Data System (ADS)

    Wildeboer, Julia Saskia

    This thesis will investigate various aspects of the physics of resonating valence bond spin liquids. After giving an introduction to the world that lies beyond Landau's priciple of symmetry breaking, e.g. giving an overview of exotic magnetic phases and how they can be described and (possibly) found, we will study a spin-rotationally invariant model system with a known parent Hamiltonian, and argue its ground state to lie within a highly sought after exotic phase, namely the Z2 quantum spin liquid phase. A newly developed numerical procedure --Pfaffian Monte Carlo-- will be introduced to amass evidence that our model Hamiltonian indeed exhibits a Z2 quantum spin liquid phase. Subsequently, we will prove a useful mathematical property of the resonating valence bond states: these states are shown to be linearly independent. Various lattices are investigated concerning this property, and its applications and usefullness are discussed. Eventually, we present a simplified model system describing the interplay of the well known Heisenberg interaction and the Dzyaloshinskii-Moriya (DM) interaction term acting on a sawtooth chain. The effect of the interplay between the two interaction couplings on the phase diagram is investigated. To do so, we employ modern techniques such as the density matrix renormalization group (DMRG) scheme. We find that for weak DM interaction the system exhibits valence bond order. However, a strong enough DM coupling destroys this order.

  1. Molybdenum Valence in Basaltic Silicate Melts: Effects of Temperature and Pressure

    NASA Technical Reports Server (NTRS)

    Danielson, L. R.; Righter, K.; Newville, M.; Sutton, S.; Choi, Y.; Pando, K.

    2011-01-01

    The metal-silicate partitioning behavior of molybdenum has been used as a test for equilibrium core formation hypotheses [for example, 1-6]. However, current models that apply experimental data to equilibrium core-mantle differentiation infer the oxidation state of molybdenum from solubility data or from multivariable coefficients from metal-silicate partitioning data [1,3,7]. Molybdenum, a multi-valent element with a valence transition near the fO2 of interest for core formation (approx.IW-2) will be sensitive to changes in fO2 of the system and silicate melt structure. In a silicate melt, Mo can occur in either 4+ or 6+ valence state, and Mo(6+) can be either octahedrally or tetrahedrally coordinated. Here we present X-ray absorption near edge structure (XANES) measurements of Mo valence in basaltic run products at a range of P, T, and fO2 and further quantify the valence transition of Mo.

  2. Electronic structure and optical properties of defect chalcopyrite HgGa2Se4

    NASA Astrophysics Data System (ADS)

    Gabrelian, B. V.; Lavrentyev, A. A.; Vu, Tuan V.; Parasyuk, O. V.; Khyzhun, O. Y.

    2018-01-01

    We report on studies from an experimental and theoretical viewpoint of the electronic structure of mercury digallium selenide, HgGa2Se4, a very promising optoelectronic material. In particular, the method of X-ray photoelectron spectroscopy (XPS) was used to evaluate binding energies of the constituent element core electrons and the shape of the valence band for pristine and Ar+-ion bombarded surfaces of HgGa2Se4 single crystal. First principles band-structure calculations were performed in the present work using the augmented plane wave + local orbitals (APW+lo). These calculations indicate that the Se 4p states are the main contributors at the top and in the upper portion of the valence band with slightly smaller contributions of the Ga 4p states in the upper portion of the band as well. Further, the central portion of the valence band is determined mainly by contributions of the Ga 4s states, and the Hg 5d states are the principal contributors to the bottom of the valence band. These theoretical data are in fair agreement when matching on a common energy scale of the X-ray emission bands giving information on the energy distribution of the Se 4p and Ga 4p states and the XPS valence-band spectrum of the HgGa2Se4 crystal. The principal optical constants are elucidated from the DFT calculations.

  3. An adiabatic spectroscopic investigation of the CsRb system in ground and numerous excited states

    NASA Astrophysics Data System (ADS)

    Souissi, Hanen; Jellali, Soulef; Maha, Chaieb; Habli, Héla; Oujia, Brahim; Gadéa, Florent Xavier

    2017-10-01

    Via ab-initio approximations, we investigate the electronic and structural features of the CsRb molecule. Adiabatic potential energy curves of 261,3Σ+, 181,3Π and 61,3Δ electronic states with their derived spectroscopic constants as well as vibrational levels spacing have been carried out and well explained. Our approach is founded on an Effective Core Potential (ECP) describing the valence electrons of the system. Using a large Gaussian basis set, the full valence Configuration Interaction can be applied easily on the two-effective valence electrons of the CsRb system. Furthermore, a detailed analysis of the electric dipolar properties has been made through the investigation of both permanent and transition dipole moments (PDM and TDM). It is significant that the ionic character connected with electron transfer that is linked to Cs+ Rb- state has been clearly illustrated in the adiabatic permanent dipole moment.

  4. On the unusual stability of valence anions of thymine based on very rare tautomers. A computational study

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

    Mazurkiewicz, Kamil; Bachorz, Rafal; Gutowski, Maciej S.

    2006-12-07

    We characterized valence-type and dipole-bound anionic states of thymine using various electronic structure methods, with the most accurate results obtained at the CCSD(T)/aug-cc-pVDZ level of theory followed by extrapolations to complete basis set limits. We found that the most stable anion in the gas phase is related to neither the canonical 2,4-dioxo nor a rare imino-hydroxy tautomer. Instead, it is related to an imino-oxo tautomer, in which the N1H proton is transferred to the C5 atom. This valence anion is characterized by an electron vertical detachment energy (VDE) of 1251 meV and it is adiabatically stable with respect to themore » canonical neutral by 2.4 kcal/mol. It is also more stable than the dipole-bound and valence anion of the canonical tautomer. The latter is adiabatically unbound with respect to by 0.1 kcal/mol and this instability is smaller than the uncertainty of the computational model used. The VDE values for and are 55 and 457 meV, respectively. Another, anionic, low-lying imino-oxo tautomer with a VDE of 2458 meV has a proton transferred from N3H to C5. It is less stable than by 3.2 kcal/mol. The mechanism of formation of anionic tautomers with the carbons C5 or C6 protonated may involve intermolecular proton transfer or dissociative electron attachment to the canonical neutral tautomer followed by a barrier-free attachment of a hydrogen atom to C5. The six-member ring structure of anionic tautomers with carbon atoms protonated might be unstable upon an excess electron detachment. Indeed, the neutral systems resulting from electron detachment from and evolve, along barrier-free decomposition pathways, to a linear or a bicyclo structure, respectively, which might be viewed as lesions to DNA.« less

  5. PROTON GENERATION BY DISSOLUTION OF INTRINSIC OR AUGMENTED ALUMINOSILICATE MINERALS FOR IN SITU CONTAMINANT REMEDIATION BY ZERO-VALENCE-STATE IRON

    EPA Science Inventory

    Metallic, or zero-valence-state, iron is being incorporated into permeable reactive subsurface barriers for remediating a variety of contaminant plume types. The remediation occurs via reductive processes that are associated with surface corrosion of the iron metal. Reaction rate...

  6. Motivation and attention: Incongruent effects of feedback on the processing of valence.

    PubMed

    Rothermund, Klaus

    2003-09-01

    Four experiments investigated the relation between outcome-related motivational states and processes of automatic attention allocation. Experiments 1-3 analyzed influences of feedback on evaluative decisions. Words of opposite valence to the feedback were processed faster, indicating that it is easier to allocate attention to the valence of an affectively incongruent word. Experiment 4 replicated the incongruent effect with interference effects of word valence in a grammatical-categorization task, indicating that the effect reflects automatic attentional capture. In all experiments, incongruent effects of feedback emerged only in a situation involving an attentional shift between words that differed in valence.

  7. The electronic structure of lithium metagallate.

    PubMed

    Johnson, N W; McLeod, J A; Moewes, A

    2011-11-09

    Herein we present a study of the electronic structure of lithium metagallate (LiGaO(2)), a material of interest in the field of optoelectronics. We use soft x-ray spectroscopy to probe the electronic structure of both the valence and conduction bands and compare our measurements to ab initio density functional theory calculations. We use several different exchange-correlation functionals, but find that no single theoretical approach used herein accurately quantifies both the band gap and the Ga 3d(10) states in LiGaO(2). We derive a band gap of 5.6 eV, and characterize electron hybridization in both the valence and conduction bands. Our study of the x-ray spectra may prove useful in analysing spectra from more complicated LiGaO(2) heterostructures. © 2011 IOP Publishing Ltd

  8. Nitrogen-Induced Perturbation of the Valence Band States in GaP1-xNx Alloys

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

    Dudiy, S. V.; Zunger, A.; Felici, M.

    2006-01-01

    The effects of diluted nitrogen impurities on the valence- and conduction-band states of GaP{sub 1-x}N{sub x} have been predicted and measured experimentally. The calculation uses state-of-the-art atomistic modeling: we use large supercells with screened pseudopotentials and consider several random realizations of the nitrogen configurations. These calculations agree with photoluminescence excitation (PLE) measurements performed for nitrogen concentrations x up to 0.035 and photon energies up to 1 eV above the GaP optical-absorption edge, as well as with published ellipsometry data. In particular, a predicted nitrogen-induced buildup of the L character near the valence- and conduction-band edges accounts for the surprising broad-absorptionmore » plateau observed in PLE between the X{sub 1c} and the {Lambda}{sub 1c} critical points of GaP. Moreover, theory accounts quantitatively for the downward bowing of the indirect conduction-band edge and for the upward bowing of the direct transition with increasing nitrogen concentration. We review some of the controversies in the literature regarding the shifts in the conduction band with composition, and conclude that measured results at ultralow N concentration cannot be used to judge behavior at a higher concentration. In particular, we find that at the high concentrations of nitrogen studied here ({approx}1%) the conduction-band edge (CBE) is a hybridized state made from the original GaP X{sub 1c} band-edge state plus all cluster states. In this limit, the CBE plunges down in energy as the N concentration increases, in quantitative agreement with the measurements reported here. However, at ultralow nitrogen concentrations (<0.1%), the CBE is the nearly unperturbed host X{sub 1c}, which does not sense the nitrogen cluster levels. Thus, this state does not move energetically as nitrogen is added and stays pinned in energy, in agreement with experimental results.« less

  9. Dissociating motivational direction and affective valence: specific emotions alter central motor processes.

    PubMed

    Coombes, Stephen A; Cauraugh, James H; Janelle, Christopher M

    2007-11-01

    We aimed to clarify the relation between affective valence and motivational direction by specifying how central and peripheral components of extension movements are altered according to specific unpleasant affective states. As predicted, premotor reaction time was quicker for extension movements initiated during exposure to attack than for extension movements initiated during exposure to all other valence categories (mutilation, erotic couples, opposite-sex nudes, neutral humans, household objects, blank). Exposure to erotic couples and mutilations yielded greater peak force than exposure to images of attack, neutral humans, and household objects. Finally, motor reaction time and peak electromyographic amplitude were not altered by valence. These findings indicate that unpleasant states do not unilaterally prime withdrawal movements, and that the quick execution of extension movements during exposure to threatening images is due to rapid premotor, rather than motor, reaction time. Collectively, our findings support the call for dissociating motivational direction and affective valence.

  10. Oxygen Fugacity of Mare Basalts and the Lunar Mantle Application of a New Microscale Oxybarometer Based on the Valence State of Vanadium

    NASA Technical Reports Server (NTRS)

    Shearer, C. K.; Karner, J.; Papike, J. J.; Sutton, S. R.

    2004-01-01

    The ability to estimate oxygen fugacities for mare basalts and to extend these observations to the lunar mantle is limited using bulk analysis techniques based on buffering assemblages or the valence state of iron. These limitations are due to reequilibration of mineral assemblages at subsolidus conditions, deviations of mineral compositions from thermodynamic ideality, size requirements, and the limits of the iron valence at very low fO2. Still, these approaches have been helpful and indicate that mare basalts crystallized at fO2 between the iron-w stite buffer (IW) and the ilmenite breakdown reaction (ilmenite = rutile + iron). It has also been inferred from these estimates that the lunar mantle is also highly reduced lying at conditions below IW. Generally, these data cannot be used to determine if the mare basalts become increasingly reduced during transport from their mantle source and eruption at the lunar surface and if there are differences in fO2 among mare basalts or mantle sources. One promising approach to determining the fO2 of mare basalts is using the mean valence of vanadium (2+, 3+, 4+, 5+) determined on spots of a few micrometers in diameter using synchrotron x-ray absorption fine structure (XAFS) spectroscopy. The average valence state of V in basaltic glasses is a function of fO2, temperature, V coordination, and melt composition. Here, we report the initial results of this approach applied to lunar pyroclastic glasses.

  11. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    NASA Astrophysics Data System (ADS)

    Egidi, Franco; Segado, Mireia; Koch, Henrik; Cappelli, Chiara; Barone, Vincenzo

    2014-12-01

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π*, π-π*, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  12. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

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

    Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  13. Neural evidence that three dimensions organize mental state representation: Rationality, social impact, and valence

    PubMed Central

    Tamir, Diana I.; Thornton, Mark A.; Contreras, Juan Manuel; Mitchell, Jason P.

    2016-01-01

    How do people understand the minds of others? Existing psychological theories have suggested a number of dimensions that perceivers could use to make sense of others’ internal mental states. However, it remains unclear which of these dimensions, if any, the brain spontaneously uses when we think about others. The present study used multivoxel pattern analysis (MVPA) of neuroimaging data to identify the primary organizing principles of social cognition. We derived four unique dimensions of mental state representation from existing psychological theories and used functional magnetic resonance imaging to test whether these dimensions organize the neural encoding of others’ mental states. MVPA revealed that three such dimensions could predict neural patterns within the medial prefrontal and parietal cortices, temporoparietal junction, and anterior temporal lobes during social thought: rationality, social impact, and valence. These results suggest that these dimensions serve as organizing principles for our understanding of other people. PMID:26621704

  14. The Electronic Structure of the Cs/ n-GaN(0001) Nano-Interface

    NASA Astrophysics Data System (ADS)

    Benemanskaya, G. V.; Lapushkin, M. N.; Marchenko, D. E.; Timoshnev, S. N.

    2018-03-01

    Electronic structures of the n-GaN(0001) surface and Cs/ n-GaN(0001) interface with submonolayer Cs coverages were studied for the first time in situ by the photoelectron spectroscopy (PES) method. The spectra of photoemission from the valence band, surface electron states, and core levels (Ga 3 d, Cs 4 d, Cs 5 p) under synchrotron excitation were measured in a range of photon energies within 50-150 eV. Evolution of the spectrum of surface states near the valence-band maximum was revealed by PES during the adsorption of Cs atoms. A metallic character of the Cs/ n-GaN(0001) nano-interface is demonstrated.

  15. Simulating Ru L3-edge X-ray Absorption Spectroscopy with Time-Dependent Density Functional Theory: Model Complexes and Electron Localization in Mixed-Valence Metal Dimers

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

    Van Kuiken, Benjamin E.; Valiev, Marat; Daifuku, Stephanie L.

    2013-05-01

    Ruthenium L2,3-edge X-ray absorption (XA) spectroscopy probes transitions from core 2p orbitals to the 4d levels of the atom and is a powerful tool for interrogating the local electronic and molecular structure around the metal atom. However, a molecular-level interpretation of the Ru L2,3-edge spectral lineshapes is often complicated by spin–orbit coupling (SOC) and multiplet effects. In this study, we develop spin-free time-dependent density functional theory (TDDFT) as a viable and predictive tool to simulate the Ru L3-edge spectra. We successfully simulate and analyze the ground state Ru L3-edge XA spectra of a series of RuII and RuIII complexes: [Ru(NH3)6]2+/3+,more » [Ru(CN)6]4-/3-, [RuCl6]4-/3-, and the ground (1A1) and photoexcited (3MLCT) transient states of [Ru(bpy)3]2+ and Ru(dcbpy)2(NCS)2 (termed N3). The TDDFT simulations reproduce all the experimentally observed features in Ru L3-edge XA spectra. The advantage of using TDDFT to assign complicated Ru L3-edge spectra is illustrated by its ability to identify ligand specific charge transfer features in complex molecules. We conclude that the B3LYP functional is the most reliable functional for accurately predicting the location of charge transfer features in these spectra. Experimental and simulated Ru L3-edge XA spectra are presented for the transition metal mixed-valence dimers [(NC)5MII-CN-RuIII(NH3)5]- (where M = Fe or Ru) dissolved in water. We explore the spectral signatures of electron delocalization in Ru L3-edge XA spectroscopy and our simulations reveal that the inclusion of explicit solvent molecules is crucial for reproducing the experimentally determined valencies, highlighting the importance of the role of the solvent in transition metal charge transfer chemistry.« less

  16. Impact of Fe doping on the electronic structure of SrTiO3 thin films determined by resonant photoemission

    NASA Astrophysics Data System (ADS)

    Kubacki, J.; Kajewski, D.; Goraus, J.; Szot, K.; Koehl, A.; Lenser, Ch.; Dittmann, R.; Szade, J.

    2018-04-01

    Epitaxial thin films of Fe doped SrTiO3 have been studied by the use of resonant photoemission. This technique allowed us to identify contributions of the Fe and Ti originating electronic states to the valence band. Two valence states of iron Fe2+ and Fe3+, detected on the base of x-ray absorption studies spectra, appeared to form quite different contributions to the valence band of SrTiO3. The electronic states within the in-gap region can be attributed to Fe and Ti ions. The Fe2+ originating states which can be connected to the presence of oxygen vacancies form a broad band reaching binding energies of about 0.5 eV below the conduction band, while Fe3+ states form in the gap a sharp feature localized just above the top of the valence band. These structures were also confirmed by calculations performed with the use of the FP-LAPW/APW+lo method including Coulomb correlations within the d shell. It has been shown that Fe doping induced Ti originating states in the energy gap which can be related to the hybridization of Ti and Fe 3d orbitals.

  17. Core-valence stockholder AIM analysis and its connection to nonadiabatic effects in small molecules.

    PubMed

    Amaral, Paulo H R; Mohallem, José R

    2017-05-21

    A previous theory of separation of motions of core and valence fractions of electrons in a molecule [J. R. Mohallem et al., Chem. Phys. Lett. 501, 575 (2011)] is invoked as basis for the useful concept of Atoms-in-Molecules (AIM) in the stockholder scheme. The output is a new tool for the analysis of the chemical bond that identifies core and valence electron density fractions (core-valence stockholder AIM (CVSAIM)). One-electron effective potentials for each atom are developed, which allow the identification of the parts of the AIM which move along with the nuclei (cores). This procedure results in a general method for obtaining effective masses that yields accurate non-adiabatic corrections to vibrational energies, necessary to attain cm -1 accuracy in molecular spectroscopy. The clear-cut determination of the core masses is exemplified for either homonuclear (H 2 + , H 2 ) or heteronuclear (HeH + , LiH) molecules. The connection of CVSAIM with independent physically meaningful quantities can resume the question of whether they are observable or not.

  18. Core-valence stockholder AIM analysis and its connection to nonadiabatic effects in small molecules

    PubMed Central

    Amaral, Paulo H. R.; Mohallem, José R.

    2017-01-01

    A previous theory of separation of motions of core and valence fractions of electrons in a molecule [J. R. Mohallem et al., Chem. Phys. Lett. 501, 575 (2011)] is invoked as basis for the useful concept of Atoms-in-Molecules (AIM) in the stockholder scheme. The output is a new tool for the analysis of the chemical bond that identifies core and valence electron density fractions (core-valence stockholder AIM (CVSAIM)). One-electron effective potentials for each atom are developed, which allow the identification of the parts of the AIM which move along with the nuclei (cores). This procedure results in a general method for obtaining effective masses that yields accurate non-adiabatic corrections to vibrational energies, necessary to attain cm−1 accuracy in molecular spectroscopy. The clear-cut determination of the core masses is exemplified for either homonuclear (H2+, H2) or heteronuclear (HeH+, LiH) molecules. The connection of CVSAIM with independent physically meaningful quantities can resume the question of whether they are observable or not. PMID:28527456

  19. Pseudo Jahn-Teller coupling in trioxides XO3(0,1,-1) with 22 and 23 valence electrons

    NASA Astrophysics Data System (ADS)

    Grein, Friedrich

    2013-05-01

    D3h and C2v geometries and energies, vertical excitation energies, as well as minimal energy paths as function of the O1(z)-X-O2 angle α were obtained for XO3(0,1,-1) (X = B, Al, Ga; C, Si, Ge; N, P, As; S, Se) molecules and ions with 22 and 23 valence electrons (VE), using density functional theory (DFT), coupled cluster with single and double substitutions with noniterative triple excitations (CCSD(T)), equation of motion (EOM)-CCSD, time-dependent DFT, and multi-reference configuration interaction methods. It is shown that pseudo Jahn-Teller (PJT) coupling increases as the central atom X becomes heavier, due to decreases in excitation energies. As is well known for CO3, the excited 1E' states of the 22 VE systems SiO3, GeO3; NO_3 ^ +, PO3+, AsO3+; BO3-, AlO3-, GaO3- have strong vibronic coupling with the 1A1' ground state via the e' vibrational modes, leading to a C2v minimum around α = 145°. For first and second row X atoms, there is an additional D3h minimum (α = 120°). Interacting excited states have minima around 135°. In the 23 VE systems CO3-, SiO3-; NO3, PO3; SO3+, coupling of the excited 2E' with the 2A2' ground state via the e' mode does not generate a C2v state. Minima of interacting excited states are close to 120°. However, due to very strong PJT coupling, a double-well potential is predicted for GeO3-, AsO3, and SeO3+, with a saddle point at D3h symmetry. Interaction of the b2 highest occupied molecular orbital with the b2 lowest unoccupied molecular orbital, both oxygen lone pair molecular orbitals, is seen as the reason for the C2v stabilization of 22 VE molecules.

  20. Thermal and electron transport studies on the valence fluctuating compound YbNiAl4

    NASA Astrophysics Data System (ADS)

    Falkowski, M.; Kowalczyk, A.

    2018-05-01

    We report the thermoelectric power S and thermal conductivity κ measurements on the valence fluctuating compound YbNiAl4, furthermore taking into account the impact of the applied magnetic field. We discuss our new results with revisiting the magnetic [χ(T)], transport [ρ(T)], and thermodynamic [Cp(T)] properties in order to better understand the phenomenon of thermal and electron transport in this compound. The field dependence of the magnetoresistivity data is also given. The temperature dependence of thermoelectric power S(T) was found to exhibit a similar behaviour as expected for Yb-based compounds with divalent or nearly divalent Yb ions. In addition, the values of total thermal conductivity as a function of temperature κ(T) of YbNiAl4 are fairly low compared to those of pure metals which may be linked to the fact that the conduction band is perturbed by strong hybridization. A deeper analysis of the specific heat revealed the low-T anomaly of the ratio Cp(T)/T3, most likely associated with the localized low-frequency oscillators in this alloy. In addition, the Kadowaki-Woods ratio and the Wilson ratio are discussed with respect to the electronic correlations in YbNiAl4.

  1. Doping induced modifications in the electronic structure and magnetism of ZnO films: Valence band and conduction band studies

    NASA Astrophysics Data System (ADS)

    Katba, Savan; Jethva, Sadaf; Udeshi, Malay; Trivedi, Priyanka; Vagadia, Megha; Shukla, D. K.; Choudhary, R. J.; Phase, D. M.; Kuberkar, D. G.

    2017-11-01

    The electronic structure of Pulsed Laser Deposited (PLD) ZnO, Zn0.95Fe0.05O (ZFO), Zn0.98Al0.02O (ZAO) and Zn0.93Fe0.05Al0.02O (ZFAO) films were investigated by Photoelectron spectroscopy and X-ray absorption spectroscopy. X-ray diffraction and ϕ-scan measurements show epitaxial c-directional growth of the films. Temperature dependent magnetization and M-H loop measurements show the presence of room temperature magnetic ordering in all the films. Fittings of Fe 2p XPS and Fe L3,2 -edge XAS of ZFO and ZFAO films show the presence of Fe, in both, Fe+2 and Fe+3 states in tetrahedral symmetry. Valence band spectra in resonance mode show resonance photon energy at 56 eV showing the presence of Fe2+ state (∼2 eV) near the Fermi level. A significant effect of Fe and Al doping on the spectral shape of O K-edge XAS was observed. Results of the Spectroscopic studies reveal that, ferromagnetism in the films is due to the contribution of oxygen deficiency which increases the number of charge carriers that take part in the exchange interaction. Al co-doping with Fe (in ZFAO) results in the enhancement of saturation magnetization by increase in the carrier-mediated ferromagnetic exchange interaction.

  2. Elucidating ultrafast electron dynamics at surfaces using extreme ultraviolet (XUV) reflection-absorption spectroscopy.

    PubMed

    Biswas, Somnath; Husek, Jakub; Baker, L Robert

    2018-04-24

    Here we review the recent development of extreme ultraviolet reflection-absorption (XUV-RA) spectroscopy. This method combines the benefits of X-ray absorption spectroscopy, such as element, oxidation, and spin state specificity, with surface sensitivity and ultrafast time resolution, having a probe depth of only a few nm and an instrument response less than 100 fs. Using this technique we investigated the ultrafast electron dynamics at a hematite (α-Fe2O3) surface. Surface electron trapping and small polaron formation both occur in 660 fs following photoexcitation. These kinetics are independent of surface morphology indicating that electron trapping is not mediated by defects. Instead, small polaron formation is proposed as the likely driving force for surface electron trapping. We also show that in Fe2O3, Co3O4, and NiO, band gap excitation promotes electron transfer from O 2p valence band states to metal 3d conduction band states. In addition to detecting the photoexcited electron at the metal M2,3-edge, the valence band hole is directly observed as transient signal at the O L1-edge. The size of the resulting charge transfer exciton is on the order of a single metal-oxygen bond length. Spectral shifts at the O L1-edge correlate with metal-oxygen bond covalency, confirming the relationship between valence band hybridization and the overpotential for water oxidation. These examples demonstrate the unique ability to measure ultrafast electron dynamics with element and chemical state resolution using XUV-RA spectroscopy. Accordingly, this method is poised to play an important role to reveal chemical details of previously unseen surface electron dynamics.

  3. SparseMaps—A systematic infrastructure for reduced-scaling electronic structure methods. III. Linear-scaling multireference domain-based pair natural orbital N-electron valence perturbation theory

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

    Guo, Yang; Sivalingam, Kantharuban; Neese, Frank, E-mail: Frank.Neese@cec.mpg.de

    2016-03-07

    Multi-reference (MR) electronic structure methods, such as MR configuration interaction or MR perturbation theory, can provide reliable energies and properties for many molecular phenomena like bond breaking, excited states, transition states or magnetic properties of transition metal complexes and clusters. However, owing to their inherent complexity, most MR methods are still too computationally expensive for large systems. Therefore the development of more computationally attractive MR approaches is necessary to enable routine application for large-scale chemical systems. Among the state-of-the-art MR methods, second-order N-electron valence state perturbation theory (NEVPT2) is an efficient, size-consistent, and intruder-state-free method. However, there are still twomore » important bottlenecks in practical applications of NEVPT2 to large systems: (a) the high computational cost of NEVPT2 for large molecules, even with moderate active spaces and (b) the prohibitive cost for treating large active spaces. In this work, we address problem (a) by developing a linear scaling “partially contracted” NEVPT2 method. This development uses the idea of domain-based local pair natural orbitals (DLPNOs) to form a highly efficient algorithm. As shown previously in the framework of single-reference methods, the DLPNO concept leads to an enormous reduction in computational effort while at the same time providing high accuracy (approaching 99.9% of the correlation energy), robustness, and black-box character. In the DLPNO approach, the virtual space is spanned by pair natural orbitals that are expanded in terms of projected atomic orbitals in large orbital domains, while the inactive space is spanned by localized orbitals. The active orbitals are left untouched. Our implementation features a highly efficient “electron pair prescreening” that skips the negligible inactive pairs. The surviving pairs are treated using the partially contracted NEVPT2 formalism. A detailed

  4. SparseMaps—A systematic infrastructure for reduced-scaling electronic structure methods. III. Linear-scaling multireference domain-based pair natural orbital N-electron valence perturbation theory

    NASA Astrophysics Data System (ADS)

    Guo, Yang; Sivalingam, Kantharuban; Valeev, Edward F.; Neese, Frank

    2016-03-01

    Multi-reference (MR) electronic structure methods, such as MR configuration interaction or MR perturbation theory, can provide reliable energies and properties for many molecular phenomena like bond breaking, excited states, transition states or magnetic properties of transition metal complexes and clusters. However, owing to their inherent complexity, most MR methods are still too computationally expensive for large systems. Therefore the development of more computationally attractive MR approaches is necessary to enable routine application for large-scale chemical systems. Among the state-of-the-art MR methods, second-order N-electron valence state perturbation theory (NEVPT2) is an efficient, size-consistent, and intruder-state-free method. However, there are still two important bottlenecks in practical applications of NEVPT2 to large systems: (a) the high computational cost of NEVPT2 for large molecules, even with moderate active spaces and (b) the prohibitive cost for treating large active spaces. In this work, we address problem (a) by developing a linear scaling "partially contracted" NEVPT2 method. This development uses the idea of domain-based local pair natural orbitals (DLPNOs) to form a highly efficient algorithm. As shown previously in the framework of single-reference methods, the DLPNO concept leads to an enormous reduction in computational effort while at the same time providing high accuracy (approaching 99.9% of the correlation energy), robustness, and black-box character. In the DLPNO approach, the virtual space is spanned by pair natural orbitals that are expanded in terms of projected atomic orbitals in large orbital domains, while the inactive space is spanned by localized orbitals. The active orbitals are left untouched. Our implementation features a highly efficient "electron pair prescreening" that skips the negligible inactive pairs. The surviving pairs are treated using the partially contracted NEVPT2 formalism. A detailed comparison

  5. First-principle calculation of the electronic structure, DOS and effective mass TlInSe2

    NASA Astrophysics Data System (ADS)

    Ismayilova, N. A.; Orudzhev, G. S.; Jabarov, S. H.

    2017-05-01

    The electronic structure, density of states (DOS), effective mass are calculated for tetragonal TlInSe2 from first principle in the framework of density functional theory (DFT). The electronic structure of TlInSe2 has been investigated by Quantum Wise within GGA. The calculated band structure by Hartwigsen-Goedecker-Hutter (HGH) pseudopotentials (psp) shows both the valence band maximum and conduction band minimum located at the T point of the Brillouin zone. Valence band maximum at the T point and the surrounding parts originate mainly from 6s states of univalent Tl ions. Bottom of the conduction band is due to the contribution of 6p-states of Tl and 5s-states of In atoms. Calculated DOS effective mass for holes and electrons are mDOS h∗ = 0.830m e, mDOS h∗ = 0.492m e, respectively. Electron effective masses are fairly isotropic, while the hole effective masses show strong anisotropy. The calculated electronic structure, density of states and DOS effective masses of TlInSe2 are in good agreement with existing theoretical and experimental results.

  6. Microhydration of LiOH: Insight from electronic decays of core-ionized states

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

    Kryzhevoi, Nikolai V., E-mail: nikolai.kryzhevoi@pci.uni-heidelberg.de

    2016-06-28

    We compute and compare the autoionization spectra of a core-ionized LiOH molecule both in its isolated and microhydrated states. Stepwise microhydration of LiOH leads to gradual elongation of the Li–OH bond length and finally to molecular dissociation. The accompanying changes in the local environment of the OH{sup −} and Li{sup +} counterions are reflected in the computed O 1s and Li 1s spectra. The role of solvent water molecules and the counterion in the spectral shape formation is assessed. Electronic decays of the microhydrated LiOH are found to be mostly intermolecular since the majority of the populated final states havemore » at least one outer-valence vacancy outside the initially core-ionized ion, mainly on a neighboring water molecule. The charge delocalization occurs through the intermolecular Coulombic and electron transfer mediated decays. Both mechanisms are highly efficient that is partly attributed to hybridization of molecular orbitals. The computed spectral shapes are sensitive to the counterion separation as well as to the number and arrangement of solvent molecules. These sensitivities can be used for studying the local hydration structure of solvated ions in aqueous solutions.« less

  7. The valence and Rydberg states of difluoromethane: A combined experimental vacuum ultraviolet spectrum absorption and theoretical study by ab initio configuration interaction and density functional computations

    NASA Astrophysics Data System (ADS)

    Palmer, Michael H.; Vrønning Hoffmann, Søren; Jones, Nykola C.; Coreno, Marcello; de Simone, Monica; Grazioli, Cesare

    2018-06-01

    The vacuum ultraviolet (VUV) spectrum for CH2F2 from a new synchrotron study has been combined with earlier data and subjected to detailed scrutiny. The onset of absorption, band I and also band IV, is resolved into broad vibrational peaks, which contrast with the continuous absorption previously claimed. A new theoretical analysis, using a combination of time dependent density functional theory (TDDFT) calculations and complete active space self-consistent field, leads to a major new interpretation. Adiabatic excitation energies (AEEs) and vertical excitation energies, evaluated by these methods, are used to interpret the spectra in unprecedented detail using theoretical vibronic analysis. This includes both Franck-Condon (FC) and Herzberg-Teller (HT) effects on cold and hot bands. These results lead to the re-assignment of several known excited states and the identification of new ones. The lowest calculated AEE sequence for singlet states is 11B1 ˜ 11A2 < 21B1 < 11A1 < 21A1 < 11B2 < 31A1 < 31B1. These, together with calculated higher energy states, give a satisfactory account of the principal maxima observed in the VUV spectrum. Basis sets up to quadruple zeta valence with extensive polarization are used. The diffuse functions within this type of basis generate both valence and low-lying Rydberg excited states. The optimum position for the site of further diffuse functions in the calculations of Rydberg states is shown to lie on the H-atoms. The routine choice on the F-atoms is shown to be inadequate for both CHF3 and CH2F2. The lowest excitation energy region has mixed valence and Rydberg character. TDDFT calculations show that the unusual structure of the onset arises from the near degeneracy of 11B1 and 11A2 valence states, which mix in symmetric and antisymmetric combinations. The absence of fluorescence in the 10.8-11 eV region contrasts with strong absorption. This is interpreted by the 21B1 and 11A1 states where no fluorescence is calculated for these

  8. Generalized valence bond description of the ground states (X(1)Σg(+)) of homonuclear pnictogen diatomic molecules: N2, P2, and As2.

    PubMed

    Xu, Lu T; Dunning, Thom H

    2015-06-09

    The ground state, X1Σg+, of N2 is a textbook example of a molecule with a triple bond consisting of one σ and two π bonds. This assignment, which is usually rationalized using molecular orbital (MO) theory, implicitly assumes that the spins of the three pairs of electrons involved in the bonds are singlet-coupled (perfect pairing). However, for a six-electron singlet state, there are five distinct ways to couple the electron spins. The generalized valence bond (GVB) wave function lifts this restriction, including all of the five spin functions for the six electrons involved in the bond. For N2, we find that the perfect pairing spin function is indeed dominant at Re but that it becomes progressively less so from N2 to P2 and As2. Although the perfect pairing spin function is still the most important spin function in P2, the importance of a quasi-atomic spin function, which singlet couples the spins of the electrons in the σ orbitals while high spin coupling those of the electrons in the π orbitals on each center, has significantly increased relative to N2 and, in As2, the perfect pairing and quasi-atomic spin couplings are on essentially the same footing. This change in the spin coupling of the electrons in the bonding orbitals down the periodic table may contribute to the rather dramatic decrease in the strengths of the Pn2 bonds from N2 to As2 as well as in the increase in their chemical reactivity and should be taken into account in more detailed analyses of the bond energies in these species. We also compare the spin coupling in N2 with that in C2, where the quasi-atomic spin coupling dominants around Re.

  9. High Power Factor and Enhanced Thermoelectric Performance of SnTe-AgInTe2: Synergistic Effect of Resonance Level and Valence Band Convergence.

    PubMed

    Banik, Ananya; Shenoy, U Sandhya; Saha, Sujoy; Waghmare, Umesh V; Biswas, Kanishka

    2016-10-05

    Understanding the basis of electronic transport and developing ideas to improve thermoelectric power factor are essential for production of efficient thermoelectric materials. Here, we report a significantly large thermoelectric power factor of ∼31.4 μW/cm·K 2 at 856 K in Ag and In co-doped SnTe (i.e., SnAg x In x Te 1+2x ). This is the highest power factor so far reported for SnTe-based material, which arises from the synergistic effects of Ag and In on the electronic structure and the improved electrical transport properties of SnTe. In and Ag play different but complementary roles in modifying the valence band structure of SnTe. In-doping introduces resonance levels inside the valence bands, leading to a significant improvement in the Seebeck coefficient at room temperature. On the other hand, Ag-doping reduces the energy separation between light- and heavy-hole valence bands by widening the principal band gap, which also results in an improved Seebeck coefficient. Additionally, Ag-doping in SnTe enhances the p-type carrier mobility. Co-doping of In and Ag in SnTe yields synergistically enhanced Seebeck coefficient and power factor over a broad temperature range because of the synergy of the introduction of resonance states and convergence of valence bands, which have been confirmed by first-principles density functional theory-based electronic structure calculations. As a consequence, we have achieved an improved thermoelectric figure of merit, zT ≈ 1, in SnAg 0.025 In 0.025 Te 1.05 at 856 K.

  10. Autonomic nervous system reactivity within the valence-arousal affective space: Modulation by sex and age.

    PubMed

    Gomez, Patrick; von Gunten, Armin; Danuser, Brigitta

    2016-11-01

    In the present study, we examined how sex and age shape cardiovascular, electrodermal, and pupillary reactivity to picture series within the valence-arousal affective space in a sample of 176 healthy younger, middle-aged, and older men and women. Across participants, heart rate (HR) decelerated with increasing self-reported unpleasantness, whereas skin conductance level (SCL) and pupil size (PS) increased with increasing self-rated arousal. Systolic (SBP) and diastolic (DBP) blood pressure increased with increasing self-rated arousal when valence was pleasant but much less when valence was unpleasant. Compared to women, men exhibited a stronger correlation between valence and HR and an SBP response characterized by larger increases for pleasant high-arousal states and lower change scores for unpleasant low- and high-arousal and pleasant low-arousal states. Men's largest SCL change scores were for pleasant high-arousal states, whereas women's largest SCL change scores were for unpleasant high-arousal states. The arousal-PS relationship was stronger among women, in particular for unpleasant series. From younger to older age, there were decreases in the strength of the valence-HR, arousal-SCL, and arousal-PS relationships. Older adults had larger overall increases in SBP and DBP than younger adults, but the relationships with self-reported valence and arousal were not age dependent. We discuss how the observed sex and age effects may reflect sex and age differences in emotional processing and in basic autonomic nervous system functioning. Copyright © 2016 Elsevier B.V. All rights reserved.

  11. Total photoelectron yield spectroscopy of energy distribution of electronic states density at GaN surface and SiO2/GaN interface

    NASA Astrophysics Data System (ADS)

    Ohta, Akio; Truyen, Nguyen Xuan; Fujimura, Nobuyuki; Ikeda, Mitsuhisa; Makihara, Katsunori; Miyazaki, Seiichi

    2018-06-01

    The energy distribution of the electronic state density of wet-cleaned epitaxial GaN surfaces and SiO2/GaN structures has been studied by total photoelectron yield spectroscopy (PYS). By X-ray photoelectron spectroscopy (XPS) analysis, the energy band diagram for a wet-cleaned epitaxial GaN surface such as the energy level of the valence band top and electron affinity has been determined to obtain a better understanding of the measured PYS signals. The electronic state density of GaN surface with different carrier concentrations in the energy region corresponding to the GaN bandgap has been evaluated. Also, the interface defect state density of SiO2/GaN structures was also estimated by not only PYS analysis but also capacitance–voltage (C–V) characteristics. We have demonstrated that PYS analysis enables the evaluation of defect state density filled with electrons at the SiO2/GaN interface in the energy region corresponding to the GaN midgap, which is difficult to estimate by C–V measurement of MOS capacitors.

  12. A Multidimensional Measure of Work Valences

    ERIC Educational Resources Information Center

    Porfeli, Erik J.; Lee, Bora; Weigold, Ingrid K.

    2012-01-01

    Work valence is derived from expectancy-valence theory and the literature on children's vocational development and is presumed to be a general appraisal of work that emerges during the childhood period. Work valence serves to promote and inhibit the motivation and tasks associated with vocational development. A measure of work valence, composed of…

  13. Electronic-structure theory of plutonium chalcogenides

    NASA Astrophysics Data System (ADS)

    Shick, Alexander; Havela, Ladislav; Gouder, Thomas; Rebizant, Jean

    2009-03-01

    The correlated band theory methods, the around-mean-field LDA + U and dynamical LDA + HIA (Hubbard-I), are applied to investigate the electronic structure of Pu chalcogenides. The LDA + U calculations for PuX (X = S, Se, Te) provide non-magnetic ground state in agreement with the experimental data. Non-integer filling of 5 f-manifold (from approx. 5.6 in PuS to 5.7 PuTe). indicates a mixed valence ground state which combines f5 and f6 multiplets. Making use of the dynamical LDA+HIA method the photoelectron spectra are calculated in good agreement with experimental data. The three-peak feature near EF attributed to 5 f-manifold is well reproduced by LDA + HIA, and follows from mixed valence character of the ground state.

  14. Intrinsic electronic defects and multiple-atom processes in the oxidic semiconductor Ga2O3

    NASA Astrophysics Data System (ADS)

    Schmeißer, Dieter; Henkel, Karsten

    2018-04-01

    We report on the electronic structure of gallium oxide (Ga2O3) single crystals as studied by resonant photoelectron spectroscopy (resPES). We identify intrinsic electronic defects that are formed by mixed-atomic valence states. We differentiate three coexisting defect states that differ in their electronic correlation energy and their spatial localization lengths. Their relative abundance is described by a fractional ionicity with covalent and ionic bonding contributions. For Ga2O3, our analyses of the resPES data enable us to derive two main aspects: first, experimental access is given to determine the ionicity based on the original concepts of Pauling and Phillips. Second, we report on multi-atomic energy loss processes in the Ga2p core level and X-ray absorption data. The two experimental findings can be explained consistently in the same context of mixed-atomic valence states and intrinsic electronic defects.

  15. High-temperature fcc phase of Pr:  Negative thermal expansion and intermediate valence state

    NASA Astrophysics Data System (ADS)

    Kuznetsov, A. Yu.; Dmitriev, V. P.; Bandilet, O. I.; Weber, H.-P.

    2003-08-01

    A high-temperature angle-dispersive synchrotron radiation diffraction study has revealed the double hexagonal-close-packed-to-face-centered-cubic (dhcp-to-fcc) transformation in the Pr metal occurring martensitically between 575 and 1035 K. The high-temperature fcc phase shows a negative thermal expansion in the range 600 800 K, attributed to the 4f-electron delocalization. A phenomenological theory is developed, which explains consistently the observed effect in terms of the mean valence variation of the metal as a function of temperature; it also predicts the existence of an isostructural phase transition and of a critical end point of a gas-liquid type in compressed Pr. The analysis of published data on P-T variation of conductivity of Pr supports this prediction.

  16. Electron spectroscopy of the diamond surface

    NASA Technical Reports Server (NTRS)

    Pepper, S. V.

    1981-01-01

    The diamond surface is studied by ionization loss spectroscopy and Auger electron spectroscopy. For surfaces heated to temperatures not exceeding 900 C, the band gap was found to be devoid of empty states in the absence of electron beam effects. The incident electron beam generates empty states in the band gap and loss of structure in the valence band for these surfaces. A cross section of 1.4 x 10 to the -19th sq cm was obtained for this effect. For surfaces heated to temperatures exceeding 900 C the spectra were identical to those from surfaces modified by the electron beam. The diamond surface undergoes a thermal conversion in its electronic structure at about 900 C.

  17. Synthesis and spectral characterization of trinuclear, oxo-centered, carboxylate-bridged, mixed-valence iron complexes with Schiff bases.

    PubMed

    Singh, Atresh Kumar; Singh, Alok Kumar

    2012-10-01

    Some novel trinuclear, oxo-centered, carboxylate-bridged, mixed-valence iron complexes of the general formula [Fe(3)O(OOCR)(3)(SB)(3)L(3)] (where R=C(13)H(27), C(15)H(31) or C(17)H(35,) HSB=Schiff bases and L=Ethanol) have been synthesized by the stepwise substitutions of acetate ions from μ(3)-oxo-hexa(acetato)tri(aqua)iron(II)diiron(III), first with straight chain carboxylic acids and then with Schiff bases. The complexes were characterized by elemental analyses, molecular weight determinations and spectral (electronic, infrared, FAB mass, Mössbauer and powder XRD) studies. Molar conductance measurements indicated the complexes to be non-electrolytes in nitrobenzene. Bridging nature of carboxylate and Schiff base anions in the complexes was established by their infrared spectra. Mössbauer spectroscopic studies indicated two quadrupole-split doublets due to Fe(II) and Fe(III) ions at 80, 200 and 295K, confirming the complexes are mixed-valence species. This was also supported by the observed electronic spectra of the complexes. Magnetic susceptibility measurements displayed octahedral geometry around iron in mixed-valence state and a net antiferromagnetic exchange coupling via μ-oxo atom. Trinuclear nature of the complexes was confirmed by their molecular weight determination and FAB mass spectra. A plausible structure for these complexes has been established on the basis of spectral and magnetic moment data. Copyright © 2012 Elsevier B.V. All rights reserved.

  18. Application of Koopmans' theorem for density functional theory to full valence-band photoemission spectroscopy modeling.

    PubMed

    Li, Tsung-Lung; Lu, Wen-Cai

    2015-10-05

    In this work, Koopmans' theorem for Kohn-Sham density functional theory (KS-DFT) is applied to the photoemission spectra (PES) modeling over the entire valence-band. To examine the validity of this application, a PES modeling scheme is developed to facilitate a full valence-band comparison of theoretical PES spectra with experiments. The PES model incorporates the variations of electron ionization cross-sections over atomic orbitals and a linear dispersion of spectral broadening widths. KS-DFT simulations of pristine rubrene (5,6,11,12-tetraphenyltetracene) and potassium-rubrene complex are performed, and the simulation results are used as the input to the PES models. Two conclusions are reached. First, decompositions of the theoretical total spectra show that the dissociated electron of the potassium mainly remains on the backbone and has little effect on the electronic structures of phenyl side groups. This and other electronic-structure results deduced from the spectral decompositions have been qualitatively obtained with the anionic approximation to potassium-rubrene complexes. The qualitative validity of the anionic approximation is thus verified. Second, comparison of the theoretical PES with the experiments shows that the full-scale simulations combined with the PES modeling methods greatly enhance the agreement on spectral shapes over the anionic approximation. This agreement of the theoretical PES spectra with the experiments over the full valence-band can be regarded, to some extent, as a collective validation of the application of Koopmans' theorem for KS-DFT to valence-band PES, at least, for this hydrocarbon and its alkali-adsorbed complex. Copyright © 2015 Elsevier B.V. All rights reserved.

  19. Electronic structure of Ag7GeS5I superionic compound

    NASA Astrophysics Data System (ADS)

    Bletskan, Dmytro; Studenyak, Ihor; Bletskan, Mykhailo; Vakulchak, Vasyl

    2018-05-01

    This paper presents the originally results of ab initio calculations of electronic structure, total and partial densities of electronic states as well as electronic charge density distribution of Ag7GeS5I crystal performed within the density functional theory (DFT) in the local density approximation (LDA) for exchange-correlation potential. According to performed calculations, Ag7GeS5I is the direct-gap semiconductor with the valence band top and the conductivity band bottom in the Γ point of Brillouin zone. The band gap width calculated in the LDA-approximation is Egd = 0.73 eV. The analysis of total and partial densities of electronic states allow us to identify the atomic orbital contributions into the crystal orbitals as well as the formation data of chemical bond in the studied crystal. In the top part of Ag7GeS5I valence band it was revealed the considerable mixing (hybridization) of the occupied d-states of Ag noble metal and the delocalized p-states of sulfur and iodine, which is undoubtedly associated with the covalent character of chemical bond between S, I atoms and noble metal atom.

  20. Adsorbate-induced shifts of electronic surface states: Cs on the (100) faces of tungsten, molybdenum, and tantalum

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

    Soukiassian, P.; Riwan, R.; Lecante, J.

    1985-04-15

    The adsorption of cesium on the (100) faces of W, Mo, and Ta for coverages between 0 and 1 monolayer is studied by angle-resolved ultraviolet photoemission spectroscopy with use of synchro- tron radiation, by electron-energy-loss spectroscopy, and by low-energy electron diffraction. With increasing cesiation, the W(100) surface state at Gamma-bar located 0.3 eV below the Fermi level is shifted by up to 1.0 eV to larger binding energies while remaining sharp and intense. A similar behavior is observed on Ta(100), whereas on Mo(100) the shift of 0.9 eV of this surface state is accompanied by a pronounced attenuation of itsmore » intensity. These experimental shifts are shown to be in excellent agreement with all-electron local-density-functional results obtained with the full-potential linearized augmented-plane-wave method for Cs monolayers on the W(100) and Mo(100) surfaces. Based on these ab initio results, the electronic origin of the shifts is understood by the formation of strongly polarized covalent bonds between the d-like surface states and the Cs 6s--derived valence states. It is argued that even at high Cs coverages, the main electron-energy-loss peaks, which are observed between 1 and 2 eV, could be interpreted as Cs 6s..-->..6p--like interband transitions rather than as surface-plasmon peaks.« less

  1. Automated Construction of Molecular Active Spaces from Atomic Valence Orbitals.

    PubMed

    Sayfutyarova, Elvira R; Sun, Qiming; Chan, Garnet Kin-Lic; Knizia, Gerald

    2017-09-12

    We introduce the atomic valence active space (AVAS), a simple and well-defined automated technique for constructing active orbital spaces for use in multiconfiguration and multireference (MR) electronic structure calculations. Concretely, the technique constructs active molecular orbitals capable of describing all relevant electronic configurations emerging from a targeted set of atomic valence orbitals (e.g., the metal d orbitals in a coordination complex). This is achieved via a linear transformation of the occupied and unoccupied orbital spaces from an easily obtainable single-reference wave function (such as from a Hartree-Fock or Kohn-Sham calculations) based on projectors to targeted atomic valence orbitals. We discuss the premises, theory, and implementation of the idea, and several of its variations are tested. To investigate the performance and accuracy, we calculate the excitation energies for various transition-metal complexes in typical application scenarios. Additionally, we follow the homolytic bond breaking process of a Fenton reaction along its reaction coordinate. While the described AVAS technique is not a universal solution to the active space problem, its premises are fulfilled in many application scenarios of transition-metal chemistry and bond dissociation processes. In these cases the technique makes MR calculations easier to execute, easier to reproduce by any user, and simplifies the determination of the appropriate size of the active space required for accurate results.

  2. Investigations of the valence-shell excitations of molecular ethane by high-energy electron scattering

    NASA Astrophysics Data System (ADS)

    Xu, Wei-Qing; Xu, Long-Quan; Qi, De-Guang; Chen, Tao; Liu, Ya-Wei; Zhu, Lin-Fan

    2018-04-01

    The differential cross sections and generalized oscillator strengths for the low-lying excitations of the valence-shell 1eg orbital electron in ethane have been measured for the first time at a high incident electron energy of 1500 eV and a scattering angular range of 1.5°-10°. A weak feature, termed X here, with a band center of about 7.5 eV has been observed, which was also announced by the previous experimental and theoretical studies. The dynamic behaviors of the generalized oscillator strengths for the 3s (8.7 eV), 3s+3p (9.31 eV, 9.41 eV), and X (˜7.5 eV) transitions on the momentum transfer squared have been obtained. The integral cross sections of these transitions from their thresholds to 5000 eV have been obtained with the aid of the BE-scaling (B is the binding energy and E is the excitation energy) method. The optical oscillator strengths of the above transitions determined by extrapolating their generalized oscillator strengths to the limit of the squared momentum transfer K2 → 0 are in good agreement with the ones from the photoabsorption spectrum [J. W. Au et al., Chem. Phys. 173, 209 (1993)], which indicates that the present differential cross sections, generalized oscillator strengths, and integral cross sections can serve as benchmark data.

  3. Orbital-occupancy versus charge ordering and the strength of electron correlations in electron-doped CaMnO3.

    PubMed

    Luo, Weidong; Franceschetti, Alberto; Varela, Maria; Tao, Jing; Pennycook, Stephen J; Pantelides, Sokrates T

    2007-07-20

    The structural, electronic, and magnetic properties of mixed-valence compounds are believed to be governed by strong electron correlations. Here we report benchmark density-functional calculations in the spin-polarized generalized-gradient approximation (GGA) for the ground-state properties of doped CaMnO(3). We find excellent agreement with all available data, while inclusion of strong correlations in the GGA+U scheme impairs this agreement. We demonstrate that formal oxidation states reflect only orbital occupancies, not charge transfer, and resolve outstanding controversies about charge ordering.

  4. Orbital-Occupancy versus Charge Ordering and the Strength of Electron Correlations in Electron-Doped CaMnO3

    NASA Astrophysics Data System (ADS)

    Luo, Weidong; Franceschetti, Alberto; Varela, Maria; Tao, Jing; Pennycook, Stephen J.; Pantelides, Sokrates T.

    2007-07-01

    The structural, electronic, and magnetic properties of mixed-valence compounds are believed to be governed by strong electron correlations. Here we report benchmark density-functional calculations in the spin-polarized generalized-gradient approximation (GGA) for the ground-state properties of doped CaMnO3. We find excellent agreement with all available data, while inclusion of strong correlations in the GGA+U scheme impairs this agreement. We demonstrate that formal oxidation states reflect only orbital occupancies, not charge transfer, and resolve outstanding controversies about charge ordering.

  5. Ligand Field Strength Mediates Electron Delocalization in Octahedral [((H)L)2Fe6(L')m](n+) Clusters.

    PubMed

    Hernández Sánchez, Raúl; Zheng, Shao-Liang; Betley, Theodore A

    2015-09-02

    To assess the impact of terminal ligand binding on a variety of cluster properties (redox delocalization, ground-state stabilization, and breadth of redox state accessibility), we prepared three electron-transfer series based on the hexanuclear iron cluster [((H)L)2Fe6(L')m](n+) in which the terminal ligand field strength was modulated from weak to strong (L' = DMF, MeCN, CN). The extent of intracore M-M interactions is gauged by M-M distances, spin ground state persistence, and preference for mixed-valence states as determined by electrochemical comproportionation constants. Coordination of DMF to the [((H)L)2Fe6] core leads to weaker Fe-Fe interactions, as manifested by the observation of ground states populated only at lower temperatures (<100 K) and by the greater evidence of valence trapping within the mixed-valence states. Comproportionation constants determined electrochemically (Kc = 10(4)-10(8)) indicate that the redox series exhibits electronic delocalization (class II-III), yet no intervalence charge transfer (IVCT) bands are observable in the near-IR spectra. Ligation of the stronger σ donor acetonitrile results in stabilization of spin ground states to higher temperatures (∼300 K) and a high degree of valence delocalization (Kc = 10(2)-10(8)) with observable IVCT bands. Finally, the anionic cyanide-bound series reveals the highest degree of valence delocalization with the most intense IVCT bands (Kc = 10(12)-10(20)) and spin ground state population beyond room temperature. Across the series, at a given formal oxidation level, the capping ligand on the hexairon cluster dictates the overall properties of the aggregate, modulating the redox delocalization and the persistence of the intracore coupling of the metal sites.

  6. Valence atom with bohmian quantum potential: the golden ratio approach

    PubMed Central

    2012-01-01

    Background The alternative quantum mechanical description of total energy given by Bohmian theory was merged with the concept of the golden ratio and its appearance as the Heisenberg imbalance to provide a new density-based description of the valence atomic state and reactivity charge with the aim of clarifying their features with respect to the so-called DFT ground state and critical charge, respectively. Results The results, based on the so-called double variational algorithm for chemical spaces of reactivity, are fundamental and, among other issues regarding chemical bonding, solve the existing paradox of using a cubic parabola to describe a quadratic charge dependency. Conclusions Overall, the paper provides a qualitative-quantitative explanation of chemical reactivity based on more than half of an electronic pair in bonding, and provide new, more realistic values for the so-called “universal” electronegativity and chemical hardness of atomic systems engaged in reactivity (analogous to the atoms-in-molecules framework). PMID:23146157

  7. A corpuscular picture of electrons in chemical bond

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

    Ando, Koji

    We introduce a theory of chemical bond with a corpuscular picture of electrons. It employs a minimal set of localized electron wave packets with “floating and breathing” degrees of freedom and the spin-coupling of non-orthogonal valence-bond theory. Its accuracy for describing potential energy curves of chemical bonds in ground and excited states of spin singlet and triplet is examined.

  8. Programming interfacial energetic offsets and charge transfer in β-Pb 0.33V 2O 5/quantum-dot heterostructures: Tuning valence-band edges to overlap with midgap states

    DOE PAGES

    Pelcher, Kate E.; Milleville, Christopher C.; Wangoh, Linda; ...

    2016-12-06

    Here, semiconductor heterostructures for solar energy conversion interface light-harvesting semiconductor nanoparticles with wide-band-gap semiconductors that serve as charge acceptors. In such heterostructures, the kinetics of charge separation depend on the thermodynamic driving force, which is dictated by energetic offsets across the interface. A recently developed promising platform interfaces semiconductor quantum dots (QDs) with ternary vanadium oxides that have characteristic midgap states situated between the valence and conduction bands. In this work, we have prepared CdS/β-Pb 0.33V 2O 5 heterostructures by both linker-assisted assembly and surface precipitation and contrasted these materials with CdSe/β-Pb 0.33V 2O 5 heterostructures prepared by the samemore » methods. Increased valence-band (VB) edge onsets in X-ray photoelectron spectra for CdS/β-Pb 0.33V 2O 5 heterostructures relative to CdSe/β-Pb 0.33V 2O 5 heterostructures suggest a positive shift in the VB edge potential and, therefore, an increased driving force for the photoinduced transfer of holes to the midgap state of β-Pb 0.33V 2O 5. This approach facilitates a ca. 0.40 eV decrease in the thermodynamic barrier for hole injection from the VB edge of QDs suggesting an important design parameter. Transient absorption spectroscopy experiments provide direct evidence of hole transfer from photoexcited CdS QDs to the midgap states of β-Pb 0.33V 2O 5 NWs, along with electron transfer into the conduction band of the β-Pb 0.33V 2O 5 NWs. Hole transfer is substantially faster and occurs at <1-ps time scales, whereas completion of electron transfer requires 5—30 ps depending on the nature of the interface. The differentiated time scales of electron and hole transfer, which are furthermore tunable as a function of the mode of attachment of QDs to NWs, provide a vital design tool for designing architectures for solar energy conversion. More generally, the approach developed here suggests that

  9. Programming interfacial energetic offsets and charge transfer in β-Pb 0.33V 2O 5/quantum-dot heterostructures: Tuning valence-band edges to overlap with midgap states

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

    Pelcher, Kate E.; Milleville, Christopher C.; Wangoh, Linda

    Here, semiconductor heterostructures for solar energy conversion interface light-harvesting semiconductor nanoparticles with wide-band-gap semiconductors that serve as charge acceptors. In such heterostructures, the kinetics of charge separation depend on the thermodynamic driving force, which is dictated by energetic offsets across the interface. A recently developed promising platform interfaces semiconductor quantum dots (QDs) with ternary vanadium oxides that have characteristic midgap states situated between the valence and conduction bands. In this work, we have prepared CdS/β-Pb 0.33V 2O 5 heterostructures by both linker-assisted assembly and surface precipitation and contrasted these materials with CdSe/β-Pb 0.33V 2O 5 heterostructures prepared by the samemore » methods. Increased valence-band (VB) edge onsets in X-ray photoelectron spectra for CdS/β-Pb 0.33V 2O 5 heterostructures relative to CdSe/β-Pb 0.33V 2O 5 heterostructures suggest a positive shift in the VB edge potential and, therefore, an increased driving force for the photoinduced transfer of holes to the midgap state of β-Pb 0.33V 2O 5. This approach facilitates a ca. 0.40 eV decrease in the thermodynamic barrier for hole injection from the VB edge of QDs suggesting an important design parameter. Transient absorption spectroscopy experiments provide direct evidence of hole transfer from photoexcited CdS QDs to the midgap states of β-Pb 0.33V 2O 5 NWs, along with electron transfer into the conduction band of the β-Pb 0.33V 2O 5 NWs. Hole transfer is substantially faster and occurs at <1-ps time scales, whereas completion of electron transfer requires 5—30 ps depending on the nature of the interface. The differentiated time scales of electron and hole transfer, which are furthermore tunable as a function of the mode of attachment of QDs to NWs, provide a vital design tool for designing architectures for solar energy conversion. More generally, the approach developed here suggests that

  10. Chromium valences in ureilite olivine and implications for ureilite petrogenesis

    NASA Astrophysics Data System (ADS)

    Goodrich, C. A.; Sutton, S. R.; Wirick, S.; Jercinovic, M. J.

    2013-12-01

    Ureilites are a group of ultramafic achondrites commonly thought to be residues of partial melting on a carbon-rich asteroid. They show a large variation in FeO content (olivine Fo values ranging from ∼74 to 95) that cannot be due to igneous fractionation and suggests instead variation in oxidation state. The presence of chromite in only a few of the most ferroan (Fo 75-76) samples appears to support such a model. MicroXANES analyses were used in this study to determine the valence states of Cr (previously unknown) in olivine cores of 11 main group ureilites. The goal of this work was to use a method that is independent of Fo to determine the oxidation conditions under which ureilites formed, in order to evaluate whether the ureilite FeO-variation is correlated with oxidation state, and whether it is nebular or planetary in origin. Two of the analyzed samples, LEW 88774 (Fo 74.2) and NWA 766 (Fo 76.7) contain primary chromite; two others, LAP 03587 (Fo 74.4) and CMS 04048 (Fo 76.2) contain sub-micrometer-sized exsolutions of chromite + Ca-rich pyroxene in olivine; and one, EET 96328 (Fo 85.2) contains an unusual chromite grain of uncertain origin. No chromite has been observed in the remaining six samples (Fo 77.4-92.3). Chromium in olivine in all eleven samples was found to be dominated by the divalent species, with valences ranging from 2.10 ± 0.02 (1σ) to 2.46 ± 0.04. The non-chromite-bearing ureilites have the most reduced Cr, with a weighted mean valence of 2.12 ± 0.01, i.e., Cr2+/Cr3+ = 7.33. All low-Fo chromite-bearing ureilites have more oxidized Cr, with valences ranging from 2.22 ± 0.03 to 2.46 ± 0.04. EET 96328, whose chromite grain we interpret as a late-crystallizing phase, yielded a reduced Cr valence of 2.15 ± 0.07, similar to the non-chromite-bearing samples. Based on the measured Cr valences, magmatic (1200-1300 °C) oxygen fugacities (fO2) of the non-chromite-bearing samples were estimated to be in the range IW-1.9 to IW-2.8 (assuming

  11. Secondary Electron Emission Spectroscopy of Diamond Surfaces

    NASA Technical Reports Server (NTRS)

    Krainsky, Isay L.; Asnin, Vladimir M.; Petukhov, Andre G.

    1999-01-01

    This report presents the results of the secondary electron emission spectroscopy study of hydrogenated diamond surfaces for single crystals and chemical vapor-deposited polycrystalline films. One-electron calculations of Auger spectra of diamond surfaces having various hydrogen coverages are presented, the major features of the experimental spectra are explained, and a theoretical model for Auger spectra of hydrogenated diamond surfaces is proposed. An energy shift and a change in the line shape of the carbon core-valence-valence (KVV) Auger spectra were observed for diamond surfaces after exposure to an electron beam or by annealing at temperatures higher than 950 C. This change is related to the redistribution of the valence-band local density of states caused by hydrogen desorption from the surface. A strong negative electron affinity (NEA) effect, which appeared as a large, narrow peak in the low-energy portion of the spectrum of the secondary electron energy distribution, was also observed on the diamond surfaces. A fine structure in this peak, which was found for the first time, reflected the energy structure of the bottom of the conduction band. Further, the breakup of the bulk excitons at the surface during secondary electron emission was attributed to one of the features of this structure. The study demonstrated that the NEA type depends on the extent of hydrogen coverage of the diamond surface, changing from the true type for the completely hydrogenated surface to the effective type for the partially hydrogenated surface.

  12. Diamond /111/ studied by electron energy loss spectroscopy in the characteristic loss region

    NASA Technical Reports Server (NTRS)

    Pepper, S. V.

    1982-01-01

    Unoccupied surface states on diamond (111) annealed at greater than 900 C are studied by electron energy loss spectroscopy with valence band excitation. A feature found at 2.1 eV loss energy is attributed to an excitation from occupied surface states into unoccupied surface states of energy within the bulk band gap. A surface band gap of approximately 1 eV is estimated. This result supports a previous suggestion for unoccupied band gap states based on core level energy loss spectroscopy. Using the valence band excitation energy loss spectrosocpy, it is also suggested that hydrogen is removed from the as-polished diamond surface by a Menzel-Gomer-Redhead mechanism.

  13. Eu 2+ –Eu 3+ valence transition in double, Eu-, and Na-doped PbSe from transport, magnetic, and electronic structure studies

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

    Wiendlocha, Bartlomiej; Kim, SunPhil; Lee, Yeseul

    The Eu atoms in Pb 1-xEu xSe have long been assumed to be divalent. We show that p-type doping of this magnetic semiconductor alloy with Na can modify the effective Eu valence: a mixed, Eu 2+–Eu 3+ state appears in Pb 1-x-yEu xNa ySe at particular values of y. Magnetization, carrier concentration, resistivity, and thermopower of Pb 1-x-yEu xNa ySe are reported for a number of samples with different x and y. A pronounced increase in thermopower at a given carrier concentration was identified and attributed to the presence of enhanced ionized impurity scattering. A strong decrease in the holemore » concentration is observed in Pb1-yNaySe when Eu is added to the system, which we attribute to a Eu 2+–Eu 3+ self-ionization process. This is evidenced by magnetization measurements, which reveal a significant reduction of the magnetic moment of Pb 1-xEu xSe upon alloying with Na. Further, a deviation of magnetization from a purely paramagnetic state, described by a Brillouin function, identifies antiferromagnetic interactions between the nearest-neighbor Eu atoms: a value of J ex/k B = -0.35 K was found for the exchange coupling parameter. The conclusion of a Eu 2+–Eu 3+ self-ionization process being in effect is supported further by the electronic structure calculations, which show that an instability of the 4f 7 configuration of the Eu 2+ ion appears with Na doping. In conclusion, schematically, it was found that the Eu 4f levels form states near enough to the Fermi energy that hole doping can lower the Fermi energy and trigger a reconfiguration of a 4f electronic shell.« less

  14. Eu 2+ –Eu 3+ valence transition in double, Eu-, and Na-doped PbSe from transport, magnetic, and electronic structure studies

    DOE PAGES

    Wiendlocha, Bartlomiej; Kim, SunPhil; Lee, Yeseul; ...

    2017-03-27

    The Eu atoms in Pb 1-xEu xSe have long been assumed to be divalent. We show that p-type doping of this magnetic semiconductor alloy with Na can modify the effective Eu valence: a mixed, Eu 2+–Eu 3+ state appears in Pb 1-x-yEu xNa ySe at particular values of y. Magnetization, carrier concentration, resistivity, and thermopower of Pb 1-x-yEu xNa ySe are reported for a number of samples with different x and y. A pronounced increase in thermopower at a given carrier concentration was identified and attributed to the presence of enhanced ionized impurity scattering. A strong decrease in the holemore » concentration is observed in Pb1-yNaySe when Eu is added to the system, which we attribute to a Eu 2+–Eu 3+ self-ionization process. This is evidenced by magnetization measurements, which reveal a significant reduction of the magnetic moment of Pb 1-xEu xSe upon alloying with Na. Further, a deviation of magnetization from a purely paramagnetic state, described by a Brillouin function, identifies antiferromagnetic interactions between the nearest-neighbor Eu atoms: a value of J ex/k B = -0.35 K was found for the exchange coupling parameter. The conclusion of a Eu 2+–Eu 3+ self-ionization process being in effect is supported further by the electronic structure calculations, which show that an instability of the 4f 7 configuration of the Eu 2+ ion appears with Na doping. In conclusion, schematically, it was found that the Eu 4f levels form states near enough to the Fermi energy that hole doping can lower the Fermi energy and trigger a reconfiguration of a 4f electronic shell.« less

  15. Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization

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

    Lin, Qisheng; Miller, Gordon J.

    Intermetallic compounds represent an extensive pool of candidates for energy related applications stemming from magnetic, electric, optic, caloric, and catalytic properties. The discovery of novel intermetallic compounds can enhance understanding of the chemical principles that govern structural stability and chemical bonding as well as finding new applications. Valence electron-poor polar intermetallics with valence electron concentrations (VECs) between 2.0 and 3.0 e –/atom show a plethora of unprecedented and fascinating structural motifs and bonding features. Furthermore, establishing simple structure-bonding-property relationships is especially challenging for this compound class because commonly accepted valence electron counting rules are inappropriate.

  16. Electron-Poor Polar Intermetallics: Complex Structures, Novel Clusters, and Intriguing Bonding with Pronounced Electron Delocalization

    DOE PAGES

    Lin, Qisheng; Miller, Gordon J.

    2017-12-18

    Intermetallic compounds represent an extensive pool of candidates for energy related applications stemming from magnetic, electric, optic, caloric, and catalytic properties. The discovery of novel intermetallic compounds can enhance understanding of the chemical principles that govern structural stability and chemical bonding as well as finding new applications. Valence electron-poor polar intermetallics with valence electron concentrations (VECs) between 2.0 and 3.0 e –/atom show a plethora of unprecedented and fascinating structural motifs and bonding features. Furthermore, establishing simple structure-bonding-property relationships is especially challenging for this compound class because commonly accepted valence electron counting rules are inappropriate.

  17. Subliminal Affect Valence Words Change Conscious Mood Potency but Not Valence: Is This Evidence for Unconscious Valence Affect?

    PubMed Central

    Shevrin, Howard; Panksepp, Jaak; Brakel, Linda A. W.; Snodgrass, Michael

    2012-01-01

    Whether or not affect can be unconscious remains controversial. Research claiming to demonstrate unconscious affect fails to establish clearly unconscious stimulus conditions. The few investigations that have established unconscious conditions fail to rule out conscious affect changes. We report two studies in which unconscious stimulus conditions were met and conscious mood changes measured. The subliminal stimuli were positive and negative affect words presented at the objective detection threshold; conscious mood changes were measured with standard manikin valence, potency, and arousal scales. We found and replicated that unconscious emotional stimuli produced conscious mood changes on the potency scale but not on the valence scale. Were positive and negative affects aroused unconsciously, but reflected consciously in potency changes? Or were the valence words unconscious cognitive causes of conscious mood changes being activated without unconscious affect? A thought experiment is offered as a way to resolve this dilemma. PMID:24961258

  18. From stable divalent to valence-fluctuating behaviour in Eu(Rh1-xIrx)2Si2 single crystals

    NASA Astrophysics Data System (ADS)

    Seiro, Silvia; Geibel, Christoph

    2011-09-01

    We have succeeded in growing high-quality single crystals of the valence-fluctuating system EuIr2Si2, the divalent Eu system EuRh2Si2 and the substitutional alloy Eu(Rh1-xIrx)2Si2 across the range 0 < x < 1, which we characterized by means of x-ray diffraction, energy-dispersive x-ray spectroscopy, specific heat, magnetization and resistivity measurements. On increasing x, the divalent Eu ground state subsists up to x = 0.25 with a slight increase in Néel temperature, while for 0.3≤x < 0.7 a sharp hysteretic change in susceptibility and resistivity marks the first-order valence transition. For x≳0.7 the broad feature observed in the physical properties is characteristic of the continuous valence evolution beyond the critical end point of the valence transition line, and the resistivity is reminiscent of Kondo-like behaviour while the Sommerfeld coefficient indicates a mass renormalization of at least a factor of 8. The resulting phase diagram is similar to those reported for polycrystalline Eu(Pd1-xAux)2Si2 and EuNi2(Si1-xGex)2, confirming its generic character for Eu systems, and markedly different to those of homologue Ce and Yb systems, which present a continuous suppression of the antiferromagnetism accompanied by a very smooth evolution of the valence. We discuss these differences and suggest them to be related to the large polarization energy of the Eu half-filled 4f shell. We further argue that the changes in the rare earth valence between RRh2Si2 and RIr2Si2 (R = Ce, Eu, Yb) are governed by a purely electronic effect and not by a volume effect.

  19. X-Ray Sum Frequency Diffraction for Direct Imaging of Ultrafast Electron Dynamics

    NASA Astrophysics Data System (ADS)

    Rouxel, Jérémy R.; Kowalewski, Markus; Bennett, Kochise; Mukamel, Shaul

    2018-06-01

    X-ray diffraction from molecules in the ground state produces an image of their charge density, and time-resolved x-ray diffraction can thus monitor the motion of the nuclei. However, the density change of excited valence electrons upon optical excitation can barely be monitored with regular diffraction techniques due to the overwhelming background contribution of the core electrons. We present a nonlinear x-ray technique made possible by novel free electron laser sources, which provides a spatial electron density image of valence electron excitations. The technique, sum frequency generation carried out with a visible pump and a broadband x-ray diffraction pulse, yields snapshots of the transition charge densities, which represent the electron density variations upon optical excitation. The technique is illustrated by ab initio simulations of transition charge density imaging for the optically induced electronic dynamics in a donor or acceptor substituted stilbene.

  20. Electronic Structures of Free-Standing Nanowires made from Indirect Bandgap Semiconductor Gallium Phosphide

    PubMed Central

    Liao, Gaohua; Luo, Ning; Chen, Ke-Qiu; Xu, H. Q.

    2016-01-01

    We present a theoretical study of the electronic structures of freestanding nanowires made from gallium phosphide (GaP)—a III-V semiconductor with an indirect bulk bandgap. We consider [001]-oriented GaP nanowires with square and rectangular cross sections, and [111]-oriented GaP nanowires with hexagonal cross sections. Based on tight binding models, both the band structures and wave functions of the nanowires are calculated. For the [001]-oriented GaP nanowires, the bands show anti-crossing structures, while the bands of the [111]-oriented nanowires display crossing structures. Two minima are observed in the conduction bands, while the maximum of the valence bands is always at the Γ-point. Using double group theory, we analyze the symmetry properties of the lowest conduction band states and highest valence band states of GaP nanowires with different sizes and directions. The band state wave functions of the lowest conduction bands and the highest valence bands of the nanowires are evaluated by spatial probability distributions. For practical use, we fit the confinement energies of the electrons and holes in the nanowires to obtain an empirical formula. PMID:27307081

  1. Density of Trap States and Auger-mediated Electron Trapping in CdTe Quantum-Dot Solids.

    PubMed

    Boehme, Simon C; Azpiroz, Jon Mikel; Aulin, Yaroslav V; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Infante, Ivan; Houtepen, Arjan J

    2015-05-13

    Charge trapping is an ubiquitous process in colloidal quantum-dot solids and a major limitation to the efficiency of quantum dot based devices such as solar cells, LEDs, and thermoelectrics. Although empirical approaches led to a reduction of trapping and thereby efficiency enhancements, the exact chemical nature of the trapping mechanism remains largely unidentified. In this study, we determine the density of trap states in CdTe quantum-dot solids both experimentally, using a combination of electrochemical control of the Fermi level with ultrafast transient absorption and time-resolved photoluminescence spectroscopy, and theoretically, via density functional theory calculations. We find a high density of very efficient electron traps centered ∼0.42 eV above the valence band. Electrochemical filling of these traps increases the electron lifetime and the photoluminescence quantum yield by more than an order of magnitude. The trapping rate constant for holes is an order of magnitude lower that for electrons. These observations can be explained by Auger-mediated electron trapping. From density functional theory calculations we infer that the traps are formed by dicoordinated Te atoms at the quantum dot surface. The combination of our unique experimental determination of the density of trap states with the theoretical modeling of the quantum dot surface allows us to identify the trapping mechanism and chemical reaction at play during charge trapping in these quantum dots.

  2. A minimalistic approach to static and dynamic electron correlations: Amending generalized valence bond method with extended random phase approximation correlation correction

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

    Chatterjee, Koushik; Jawulski, Konrad; Pastorczak, Ewa

    A perfect-pairing generalized valence bond (GVB) approximation is known to be one of the simplest approximations, which allows one to capture the essence of static correlation in molecular systems. In spite of its attractive feature of being relatively computationally efficient, this approximation misses a large portion of dynamic correlation and does not offer sufficient accuracy to be generally useful for studying electronic structure of molecules. We propose to correct the GVB model and alleviate some of its deficiencies by amending it with the correlation energy correction derived from the recently formulated extended random phase approximation (ERPA). On the examples ofmore » systems of diverse electronic structures, we show that the resulting ERPA-GVB method greatly improves upon the GVB model. ERPA-GVB recovers most of the electron correlation and it yields energy barrier heights of excellent accuracy. Thanks to a balanced treatment of static and dynamic correlation, ERPA-GVB stays reliable when one moves from systems dominated by dynamic electron correlation to those for which the static correlation comes into play.« less

  3. Valence structures of aromatic bioactive compounds: a combined theoretical and experimental study.

    PubMed

    Wickrama Arachchilage, Anoja Pushpamali; Feyer, Vitaliy; Plekan, Oksana; Iakhnenko, Marianna; Prince, Kevin C; Wang, Feng

    2012-09-01

    Valence electronic structures of three recently isolated aryl bioactive compounds, namely 2-phenylethanol (2PE), p-hydroxyphenylethanol (HPE) and 4-hydroxybenzaldehyde (HBA), are studied using a combined theoretical and experimental method. Density functional theory-based calculations indicate that the side chains cause electron charge redistribution and therefore influence the aromaticity of the benzene derivatives. The simulated IR spectra further reveal features induced by the side chains. Solvent effects on the IR spectra are simulated using the polarizable continuum model, which exhibits enhancement of the O-H stretch vibrations with significant red-shift of 464 cm(-1) in 2PE. A significant spectral peak splitting of 94 cm(-1) between O(4)-H and O(8)-H of HPE is revealed in an aqueous environment. Experimental measurements for valence binding energy spectra for 2PE, HPE and HBA are presented and analyzed using outer-valence Green function calculations. The experimental (predicted) first ionization energies are measured as 9.19 (8.79), 8.47 (8.27) and 8.97 (8.82) eV for 2PE, HPE and HBA, respectively. The frontier orbitals (highest occupied molecular orbitals, HOMOs, and lowest unoccupied molecular orbitals, LUMOs) have similar atomic orbital characters although the HOMO-LUMO energy gaps are quite different.

  4. Wave-function-based approach to quasiparticle bands: Insight into the electronic structure of c-ZnS

    NASA Astrophysics Data System (ADS)

    Stoyanova, A.; Hozoi, L.; Fulde, P.; Stoll, H.

    2011-05-01

    Ab initio wave-function-based methods are employed for the study of quasiparticle energy bands of zinc-blende ZnS, with focus on the Zn 3d “semicore” states. The relative energies of these states with respect to the top of the S 3p valence bands appear to be poorly described as compared to experimental values not only within the local density approximation (LDA), but also when many-body corrections within the GW approximation are applied to the LDA or LDA + U mean-field solutions [T. Miyake, P. Zhang, M. L. Cohen, and S. G. Louie, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.74.245213 74, 245213 (2006)]. In the present study, we show that for the accurate description of the Zn 3d states a correlation treatment based on wave-function methods is needed. Our study rests on a local Hamiltonian approach which rigorously describes the short-range polarization and charge redistribution effects around an extra hole or electron placed into the valence respective conduction bands of semiconductors and insulators. The method also facilitates the computation of electron correlation effects beyond relaxation and polarization. The electron correlation treatment is performed on finite clusters cut off the infinite system. The formalism makes use of localized Wannier functions and embedding potentials derived explicitly from prior periodic Hartree-Fock calculations. The on-site and nearest-neighbor charge relaxation lead to corrections of several eV to the Hartree-Fock band energies and gap. Corrections due to long-range polarization are of the order of 1.0 eV. The dispersion of the Hartree-Fock bands is only slightly affected by electron correlations. We find the Zn 3d “semicore” states to lie ~9.0 eV below the top of the S 3p valence bands, in very good agreement with values from valence-band x-ray photoemission.

  5. Binding patterns of vanadium ions with different valence states to human serum transferrin studied by HPLC/high-resolution ICP-MS.

    PubMed

    Nagaoka, Megumi Hamano; Yamazaki, Takeshi; Maitani, Tamio

    2002-09-06

    Vanadium (V) is an essential metal for mammals and has different valence states. In blood, V is bound to serum transferrin (Tf), a glycoprotein which has two metal-binding sites, and carbonate is generally required for the binding. In this study, the binding patterns of V(III), V(IV), and V(V) to human serum Tf (hTf) were analyzed using an HPLC system equipped with an anion-exchange column and directly connected to a high-resolution inductively coupled plasma-mass spectrometer for metal detection (51V). In affinity to hTf, the three ions were ranked V(III)>V(IV)>V(V) in the presence of bicarbonate and V(III) reverse congruent V(IV)>V(V) in the absence. Intermediates in the "open forms" binding to the respective sites were detected at the initial stage. V(IV) and V(V) were bound to the N-lobe site in the "closed form" and "open form," respectively. In the absence of bicarbonate, V ions with respective valence states were bound to hTf in the "open form." In terms of binding to hTf, tri-valent V was most favorable in the presence of bicarbonate.

  6. Electronic and magnetic properties of epitaxial perovskite SrCrO3(001)

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

    Zhang, Hongliang; Du, Yingge; Sushko, Petr

    2015-06-24

    We have investigated the intrinsic properties of SrCrO3 epitaxial thin films synthesized by molecular beam epitaxy. We find compelling evidence that SrCrO3 is a correlated metal. X-ray photoemission valence band and O K-edge x-ray absorption spectra indicate a strongly hybridized Cr3d-O2p state crossing the Fermi level, leading to metallic behavior. Comparison between valence band spectra near the Fermi level and the densities of states calculated using density functional theory (DFT) also suggests the presence of coherent and incoherent states and points to a strong electron-electron correlation effects. The magnetic susceptibility can be described by Pauli paramagnetism at temperatures above 100more » K, but reveals antiferromagnetic behavior at lower temperatures resulting from orbital ordering as suggested by Ortega-San-Martin et al. [Phys. Rev. Lett. 99, 255701 (2007)].« less

  7. The origin of anisotropy and high density of states in the electronic structure of Cr2GeC by means of polarized soft x-ray spectroscopy and ab initio calculations

    NASA Astrophysics Data System (ADS)

    Magnuson, Martin; Mattesini, Maurizio; Bugnet, Matthieu; Eklund, Per

    2015-10-01

    The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr2GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal differences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr2GeC. The Cr L 2, 3, C K, and Ge M 1, M 2, 3 emission spectra are interpreted with first-principles density-functional theory (DFT) including core-to-valence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should affect the thermal expansion coefficient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.

  8. The origin of anisotropy and high density of states in the electronic structure of Cr2GeC by means of polarized soft x-ray spectroscopy and ab initio calculations.

    PubMed

    Magnuson, Martin; Mattesini, Maurizio; Bugnet, Matthieu; Eklund, Per

    2015-10-21

    The anisotropy in the electronic structure of the inherently nanolaminated ternary phase Cr2GeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal differences between the in-plane and out-of-plane bonding at the (0001) interfaces of Cr2GeC. The Cr L(2, 3), C K, and Ge M1, M(2, 3) emission spectra are interpreted with first-principles density-functional theory (DFT) including core-to-valence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should affect the thermal expansion coefficient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.

  9. NEVER forget: negative emotional valence enhances recapitulation.

    PubMed

    Bowen, Holly J; Kark, Sarah M; Kensinger, Elizabeth A

    2018-06-01

    A hallmark feature of episodic memory is that of "mental time travel," whereby an individual feels they have returned to a prior moment in time. Cognitive and behavioral neuroscience methods have revealed a neurobiological counterpart: Successful retrieval often is associated with reactivation of a prior brain state. We review the emerging literature on memory reactivation and recapitulation, and we describe evidence for the effects of emotion on these processes. Based on this review, we propose a new model: Negative Emotional Valence Enhances Recapitulation (NEVER). This model diverges from existing models of emotional memory in three key ways. First, it underscores the effects of emotion during retrieval. Second, it stresses the importance of sensory processing to emotional memory. Third, it emphasizes how emotional valence - whether an event is negative or positive - affects the way that information is remembered. The model specifically proposes that, as compared to positive events, negative events both trigger increased encoding of sensory detail and elicit a closer resemblance between the sensory encoding signature and the sensory retrieval signature. The model also proposes that negative valence enhances the reactivation and storage of sensory details over offline periods, leading to a greater divergence between the sensory recapitulation of negative and positive memories over time. Importantly, the model proposes that these valence-based differences occur even when events are equated for arousal, thus rendering an exclusively arousal-based theory of emotional memory insufficient. We conclude by discussing implications of the model and suggesting directions for future research to test the tenets of the model.

  10. Composition dependence of electronic, magnetic, transport and morphological properties of mixed valence manganite thin films

    DOE PAGES

    Singh, Surendra; Freeland, J. W.; Fitzsimmons, Michael R.; ...

    2016-07-27

    Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La 1-yPr y) 1-xCaxMnO 3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La 0.4Pr 0.6) 1-xCaxMnO3 films with x = 0.33 and 0.375, across themore » MIT temperature. We combine electrical transport (resistance) measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties.« less

  11. Anomalous Ground State of the Electrons in Nano-confined Water

    DTIC Science & Technology

    2016-06-13

    confined water system, Nafion, is so different from that of bulk water that the weakly electrostatically interacting molecule model of water is clearly...assume that water is made up molecules weakly interacting(on the scale of the zero point bond energy~.2eV) electrostatically with its neighbors2-3. In an...not possible for a collection of molecules interacting weakly electrostatically . These changes in the spatial distribution of valence electrons in

  12. Electronic structure and electron energy-loss spectroscopy of ZrO2 zirconia

    NASA Astrophysics Data System (ADS)

    Dash, L. K.; Vast, Nathalie; Baranek, Philippe; Cheynet, Marie-Claude; Reining, Lucia

    2004-12-01

    The atomic and electronic structures of zirconia are calculated within density functional theory, and their evolution is analyzed as the crystal-field symmetry changes from tetrahedral [cubic (c-ZrO2) and tetragonal (t-ZrO2) phases] to octahedral (hypothetical rutile ZrO2 ), to a mixing of these symmetries (monoclinic phase, m-ZrO2 ). We find that the theoretical bulk modulus in c-ZrO2 is 30% larger than the experimental value, showing that the introduction of yttria in zirconia has a significant effect. Electronic structure fingerprints which characterize each phase from their electronic spectra are identified. We have carried out electron energy-loss spectroscopy experiments at low momentum transfer and compared these results to the theoretical spectra calculated within the random phase approximation. We show a dependence of the valence and 4p ( N2,3 edge) plasmons on the crystal structure, the dependence of the latter being brought into the spectra by local-field effects. Last, we attribute low energy excitations observed in EELS of m-ZrO2 to defect states 2eV above the top of the intrinsic valence band, and the EELS fundamental band gap value is reconciled with the 5.2 or 5.8eV gaps determined by vacuum ultraviolet spectroscopy.

  13. Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

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

    Barnes, J. C.; Fahrenbach, A. C.; Dyar, S. M.

    2012-06-08

    The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylene-bridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquat-p-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ ring encircles the DNP unit. Reduction of the CBPQT4+ leads to the CBPQT2(•+) diradical dication while the P-BIPY2+ unit is reduced to its P-BIPY•+ radical cation. A radical-state co-conformation (RSCC) results from movement of the CBPQT2(•+) ring along the dumbbell to surround the P-BIPY•+ unit.more » This shuttling event induces IET to occur between the pyridinium redox centers of the P-BIPY•+ unit, a property which is absent between these redox centers in the free dumbbell and in the 1:1 complex formed between the CBPQT2(•+) ring and the radical cation of methyl-phenylene-viologen (MPV•+). Using electron paramagnetic resonance (EPR) spectroscopy, the process of IET was investigated by monitoring the line broadening at varying temperatures and determining the rate constant (kET = 1.33 × 107 s-1) and activation energy (ΔG‡ = 1.01 kcal mol-1) for electron transfer. These values were compared to the corresponding values predicted, using the optical absorption spectra and Marcus–Hush theory.« less

  14. A Perfusion MRI Study of Emotional Valence and Arousal in Parkinson's Disease

    PubMed Central

    Limsoontarakul, Sunsern; Campbell, Meghan C.; Black, Kevin J.

    2011-01-01

    Background. Brain regions subserving emotion have mostly been studied using functional magnetic resonance imaging (fMRI) during emotion provocation procedures in healthy participants. Objective. To identify neuroanatomical regions associated with spontaneous changes in emotional state over time. Methods. Self-rated emotional valence and arousal scores, and regional cerebral blood flow (rCBF) measured by perfusion MRI, were measured 4 or 8 times spanning at least 2 weeks in each of 21 subjects with Parkinson's disease (PD). A random-effects SPM analysis, corrected for multiple comparisons, identified significant clusters of contiguous voxels in which rCBF varied with valence or arousal. Results. Emotional valence correlated positively with rCBF in several brain regions, including medial globus pallidus, orbital prefrontal cortex (PFC), and white matter near putamen, thalamus, insula, and medial PFC. Valence correlated negatively with rCBF in striatum, subgenual cingulate cortex, ventrolateral PFC, and precuneus—posterior cingulate cortex (PCC). Arousal correlated positively with rCBF in clusters including claustrum-thalamus-ventral striatum and inferior parietal lobule and correlated negatively in clusters including posterior insula—mediodorsal thalamus and midbrain. Conclusion. This study demonstrates that the temporal stability of perfusion MRI allows within-subject investigations of spontaneous fluctuations in mental state, such as mood, over relatively long-time intervals. PMID:21969917

  15. Determination of a natural valence-band offset - The case of HgTe and CdTe

    NASA Technical Reports Server (NTRS)

    Shih, C. K.; Spicer, W. E.

    1987-01-01

    A method to determine a natural valence-band offset (NVBO), i.e., the change in the valence-band maximum energy which is intrinsic to the bulk band structures of semiconductors is proposed. The HgTe-CdTe system is used as an example in which it is found that the valence-band maximum of HgTe lies 0.35 + or - 0.06 eV above that of CdTe. The NVBO of 0.35 eV is in good agreement with the X-ray photoemission spectroscopy measurement of the heterojunction offset. The procedure to determine the NVBO between semiconductors, and its implication on the heterojunction band lineup and the electronic structures of semiconductor alloys, are discussed.

  16. Optimizing surface defects for atomic-scale electronics: Si dangling bonds

    NASA Astrophysics Data System (ADS)

    Scherpelz, Peter; Galli, Giulia

    2017-07-01

    Surface defects created and probed with scanning tunneling microscopes are a promising platform for atomic-scale electronics and quantum information technology applications. Using first-principles calculations we demonstrate how to engineer dangling bond (DB) defects on hydrogenated Si(100) surfaces, which give rise to isolated impurity states that can be used in atomic-scale devices. In particular, we show that sample thickness and biaxial strain can serve as control parameters to design the electronic properties of DB defects. While in thick Si samples the neutral DB state is resonant with bulk valence bands, ultrathin samples (1-2 nm) lead to an isolated impurity state in the gap; similar behavior is seen for DB pairs and DB wires. Strain further isolates the DB from the valence band, with the response to strain heavily dependent on sample thickness. These findings suggest new methods for tuning the properties of defects on surfaces for electronic and quantum information applications. Finally, we present a consistent and unifying interpretation of many results presented in the literature for DB defects on hydrogenated silicon surfaces, rationalizing apparent discrepancies between different experiments and simulations.

  17. Simultaneous conditioning of valence and arousal.

    PubMed

    Gawronski, Bertram; Mitchell, Derek G V

    2014-01-01

    Evaluative conditioning (EC) refers to the change in the valence of a conditioned stimulus (CS) due to its pairing with a positive or negative unconditioned stimulus (US). To the extent that core affect can be characterised by the two dimensions of valence and arousal, EC has important implications for the origin of affective responses. However, the distinction between valence and arousal is rarely considered in research on EC or conditioned responses more generally. Measuring the subjective feelings elicited by a CS, the results from two experiments showed that (1) repeated pairings of a CS with a positive or negative US of either high or low arousal led to corresponding changes in both CS valence and CS arousal, (2) changes in CS arousal, but not changes in CS valence, were significantly related to recollective memory for CS-US pairings, (3) subsequent presentations of the CS without the US reduced the conditioned valence of the CS, with conditioned arousal being less susceptible to extinction and (4) EC effects were stronger for high arousal than low arousal USs. The results indicate that the conditioning of affective responses can occur simultaneously along two independent dimensions, supporting evidence in related areas that calls for a consideration of both valence and arousal. Implications for research on EC and the acquisition of emotional dispositions are discussed.

  18. Valence change detection in memristive oxide based heterostructure cells by hard X-ray photoelectron emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Kindsmüller, A.; Schmitz, C.; Wiemann, C.; Skaja, K.; Wouters, D. J.; Waser, R.; Schneider, C. M.; Dittmann, R.

    2018-04-01

    The switching mechanism of valence change resistive memory devices is widely accepted to be an ionic movement of oxygen vacancies resulting in a valence change of the metal cations. However, direct experimental proofs of valence changes in memristive devices are scarce. In this work, we have employed hard X-ray photoelectron emission microscopy (PEEM) to probe local valence changes in Pt/ZrOx/Ta memristive devices. The use of hard X-ray radiation increases the information depth, thus providing chemical information from buried layers. By extracting X-ray photoelectron spectra from different locations in the PEEM images, we show that zirconia in the active device area is reduced compared to a neighbouring region, confirming the valence change in the ZrOx film during electroforming. Furthermore, we succeeded in measuring the Ta 4f spectrum for two different resistance states on the same device. In both states, as well as outside the device region, the Ta electrode is composed of different suboxides without any metallic contribution, hinting to the formation of TaOx during the deposition of the Ta thin film. We observed a reduction of the Ta oxidation state in the low resistance state with respect to the high resistive state. This observation is contradictory to the established model, as the internal redistribution of oxygen between ZrOx and the Ta electrode during switching would lead to an oxidation of the Ta layer in the low resistance state. Instead, we have to conclude that the Ta electrode takes an active part in the switching process in our devices and that oxygen is released and reincorporated in the ZrOx/TaOx bilayer during switching. This is confirmed by the degradation of the high resistance state during endurance measurements under vacuum.

  19. Excited State Trends in Bidirectionally Expanded Closed-Shell PAH and PANH Anions

    PubMed Central

    Moore, Megan M.; Lee, Timothy J.

    2018-01-01

    Some anions are known to exhibit excited states independent of external forces such as dipole moments and induced polarizabilities. Such states exist simply as a result of the stabilization of valence accepting orbitals whereby the binding energy of the extra electron is greater than the valence excitation energy. Closed-shell anions are interesting candidates for such transitions since their ground-state, spin-paired nature makes the anions more stable from the beginning. Consequently, this work shows the point beyond which deprotonated, closed-shell polycyclic aromatic hydrocarbons (PAHs) and those PAHs containing nitrogen heteroatoms (PANHs) will exhibit valence excited states. This behavior has already been demonstrated in some PANHs and for anistropically-extended PAHs. This work establishes a general trend for PAHs/PANHs of arbitrary size and directional extension, whether in one dimension or two. Once seven six-membered rings make up a PAH/PANH, valence excited states are present. For most classes of PAHs/PANHs, this number is closer to four. Even though most of these excited states are weak absorbers, the sheer number of PAHs present in various astronomical environments should make them significant contributors to astronomical spectra. PMID:27585793

  20. High pressure and synchrotron radiation studies of solid state electronic instabilities. Final technial report, May 1, 1984--April 1987

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

    Pifer, J.H.; Croft, M.C.

    This report discusses Eu and General Valence Instabilities; Ce Problem: L{sub 3} Spectroscopy Emphasis; Bulk Property Emphasis; Transition Metal Compound Electronic Structure; Electronic Structure-Phonon Coupling Studies; High Temperature Superconductivity and Oxide Materials; and Novel Materials Collaboration with Chemistry.

  1. Feasibility of Valence-to-Core X-ray Emission Spectroscopy for Tracking Transient Species

    DOE PAGES

    March, Anne Marie; Assefa, Tadesse A.; Bressler, Christian; ...

    2015-02-09

    X-ray spectroscopies, when combined in laser-pump, X-ray-probe measurement schemes, can be powerful tools for tracking the electronic and geometric structural changes that occur during the course of a photoinitiated chemical reaction. X-ray absorption spectroscopy (XAS) is considered an established technique for such measurements, and X-ray emission spectroscopy (XES) of the strongest core-to-core emission lines (Kα and Kβ) is now being utilized. Flux demanding valence-to-core XES promises to be an important addition to the time-resolved spectroscopic toolkit. Here In this paper we present measurements and density functional theory calculations on laser-excited, solution-phase ferrocyanide that demonstrate the feasibility of valence-to-core XES formore » time-resolved experiments. Lastly, we discuss technical improvements that will make valence-to-core XES a practical pump–probe technique.« less

  2. First principle investigation of electronic structure, chemical bonding and optical properties of tetrabarium gallium trinitride oxide single crystal

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

    Khan, Saleem Ayaz, E-mail: sayaz_usb@yahoo.com; Azam, Sikander

    The electronic band structure, valence electron charge density and optical susceptibilities of tetrabarium gallium trinitride (TGT) were calculated via first principle study. The electronic band structure calculation describes TGT as semiconductor having direct band gap of 1.38 eV. The valence electronic charge density contour verified the non-polar covalent nature of the bond. The absorption edge and first peak of dielectric tensor components showed electrons transition from N-p state to Ba-d state. The calculated uniaxial anisotropy (0.4842) and birefringence (−0.0061) of present paper is prearranged as follow the spectral components of the dielectric tensor. The first peak in energy loss functionmore » (ELOS) shows the energy loss of fast traveling electrons in the material. The first sharp peak produced in ELOS around 10.5 eV show plasmon loss having plasma frequencies 0.1536, 0.004 and 0.066 of dielectric tensor components. This plasmon loss also cause decrease in reflectivity spectra.« less

  3. Electronic Structures of Purple Bronze KMo6O17 Studied by X-Ray Photoemission Spectra

    NASA Astrophysics Data System (ADS)

    Qin, Xiaokui; Wei, Junyin; Shi, Jing; Tian, Mingliang; Chen, Hong; Tian, Decheng

    X-ray photoemission spectroscopy study has been performed for the purple bronze KMo6O17. The structures of conduction band and valence band are analogous to the results of ultraviolet photoemission spectra and are also consistent with the model of Travaglini et al., but the gap between conduction and valence band is insignificant. The shape of asymmetric and broadening line of O-1s is due to unresolved contributions from the many inequivalent oxygen sites in this crystal structure. Mo 3d core-level spectrum reveals that there are two kinds of valence states of Molybdenum (Mo+5 and Mo+6). The calculated average valence state is about +5.6, which is consistent with the expectation value from the composition of this material. The tail of Mo-3d spectrum toward higher binding energy is the consequence of the excitation of electron-hole pairs with singularity index of 0.21.

  4. Social Annotation Valence: The Impact on Online Informed Consent Beliefs and Behavior.

    PubMed

    Balestra, Martina; Shaer, Orit; Okerlund, Johanna; Westendorf, Lauren; Ball, Madeleine; Nov, Oded

    2016-07-20

    Social media, mobile and wearable technology, and connected devices have significantly expanded the opportunities for conducting biomedical research online. Electronic consent to collecting such data, however, poses new challenges when contrasted to traditional consent processes. It reduces the participant-researcher dialogue but provides an opportunity for the consent deliberation process to move from solitary to social settings. In this research, we propose that social annotations, embedded in the consent form, can help prospective participants deliberate on the research and the organization behind it in ways that traditional consent forms cannot. Furthermore, we examine the role of the comments' valence on prospective participants' beliefs and behavior. This study focuses specifically on the influence of annotations' valence on participants' perceptions and behaviors surrounding online consent for biomedical research. We hope to shed light on how social annotation can be incorporated into digitally mediated consent forms responsibly and effectively. In this controlled between-subjects experiment, participants were presented with an online consent form for a personal genomics study that contained social annotations embedded in its margins. Individuals were randomly assigned to view the consent form with positive-, negative-, or mixed-valence comments beside the text of the consent form. We compared participants' perceptions of being informed and having understood the material, their trust in the organization seeking the consent, and their actual consent across conditions. We find that comment valence has a marginally significant main effect on participants' perception of being informed (F2=2.40, P=.07); specifically, participants in the positive condition (mean 4.17, SD 0.94) felt less informed than those in the mixed condition (mean 4.50, SD 0.69, P=.09). Comment valence also had a marginal main effect on the extent to which participants reported trusting the

  5. On the Highest Oxidation States of Metal Elements in MO4 Molecules (M = Fe, Ru, Os, Hs, Sm, and Pu).

    PubMed

    Huang, Wei; Xu, Wen-Hua; Schwarz, W H E; Li, Jun

    2016-05-02

    Metal tetraoxygen molecules (MO4, M = Fe, Ru, Os, Hs, Sm, Pu) of all metal atoms M with eight valence electrons are theoretically studied using density functional and correlated wave function approaches. The heavier d-block elements Ru, Os, Hs are confirmed to form stable tetraoxides of Td symmetry in (1)A1 electronic states with empty metal d(0) valence shell and closed-shell O(2-) ligands, while the 3d-, 4f-, and 5f-elements Fe, Sm, and Pu prefer partial occupation of their valence shells and peroxide or superoxide ligands at lower symmetry structures with various spin couplings. The different geometric and electronic structures and chemical bonding types of the six iso-stoichiometric species are explained in terms of atomic orbital energies and orbital radii. The variations found here contribute to our general understanding of the periodic trends of oxidation states across the periodic table.

  6. Electronic structure of LiGaS 2

    NASA Astrophysics Data System (ADS)

    Atuchin, V. V.; Isaenko, L. I.; Kesler, V. G.; Lobanov, S.; Huang, H.; Lin, Z. S.

    2009-04-01

    X-ray photoelectron spectroscopy (XPS) measurement has been performed to determine the valence band structure of LiGaS 2 crystals. The experimental measurement is compared with the electronic structure obtained from the density functional calculations. It is found that the Ga 3d states in the XPS spectrum are much higher than the calculated results. In order to eliminate this discrepancy, the LDA+ U method is employed and reasonable agreement is achieved. Further calculations show that the difference of the linear and nonlinear optical coefficients between LDA and LDA+ U calculations is negligibly small, indicating that the Ga 3d states are actually independent of the excited properties of LiGaS 2 crystals since they are located at a very deep position in the valence bands.

  7. Synthesis of a Neutral Mixed-Valence Diferrocenyl Carborane for Molecular Quantum-Dot Cellular Automata Applications.

    PubMed

    Christie, John A; Forrest, Ryan P; Corcelli, Steven A; Wasio, Natalie A; Quardokus, Rebecca C; Brown, Ryan; Kandel, S Alex; Lu, Yuhui; Lent, Craig S; Henderson, Kenneth W

    2015-12-14

    The preparation of 7-Fc(+) -8-Fc-7,8-nido-[C2 B9 H10 ](-) (Fc(+) FcC2 B9 (-) ) demonstrates the successful incorporation of a carborane cage as an internal counteranion bridging between ferrocene and ferrocenium units. This neutral mixed-valence Fe(II) /Fe(III) complex overcomes the proximal electronic bias imposed by external counterions, a practical limitation in the use of molecular switches. A combination of UV/Vis-NIR spectroscopic and TD-DFT computational studies indicate that electron transfer within Fc(+) FcC2 B9 (-) is achieved through a bridge-mediated mechanism. This electronic framework therefore provides the possibility of an all-neutral null state, a key requirement for the implementation of quantum-dot cellular automata (QCA) molecular computing. The adhesion, ordering, and characterization of Fc(+) FcC2 B9 (-) on Au(111) has been observed by scanning tunneling microscopy. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Electron localization in a mixed-valence diniobium benzene complex

    DOE PAGES

    Gianetti, Thomas L.; Nocton, Grégory; Minasian, Stefan G.; ...

    2014-11-11

    Reaction of the neutral diniobium benzene complex {[Nb(BDI)N tBu] 2(μ-C 6H 6)} (BDI = N,N'-diisopropylbenzene-β-diketiminate) with Ag[B(C 6F 5) 4] results in a single electron oxidation to produce a cationic diniobium arene complex, {[Nb(BDI)N tBu] 2(μ-C 6H 6)}{B(C 6F 5) 4}. Investigation of the solid state and solution phase structure using single-crystal X-ray diffraction, cyclic voltammetry, magnetic susceptibility, and multinuclear NMR spectroscopy indicates that the oxidation results in an asymmetric molecule with two chemically inequivalent Nb atoms. Further characterization using density functional theory (DFT) calculations, UV-visible, Nb L 3,2-edge X-ray absorption near-edge structure (XANES), and EPR spectroscopies supports assignment ofmore » a diniobium complex, in which one Nb atom carries a single unpaired electron that is not largely delocalized on the second Nb atom. During the oxidative transformation, one electron is removed from the δ-bonding HOMO, which causes a destabilization of the molecule and formation of an asymmetric product. Subsequent reactivity studies indicate that the oxidized product allows access to metal-based chemistry with substrates that did not exhibit reactivity with the starting neutral complex.« less

  9. Energy-resolved coherent diffraction from laser-driven electronic motion in atoms

    NASA Astrophysics Data System (ADS)

    Shao, Hua-Chieh; Starace, Anthony F.

    2017-10-01

    We investigate theoretically the use of energy-resolved ultrafast electron diffraction to image laser-driven electronic motion in atoms. A chirped laser pulse is used to transfer the valence electron of the lithium atom from the ground state to the first excited state. During this process, the electronic motion is imaged by 100-fs and 1-fs electron pulses in energy-resolved diffraction measurements. Simulations show that the angle-resolved spectra reveal the time evolution of the energy content and symmetry of the electronic state. The time-dependent diffraction patterns are further interpreted in terms of the momentum transfer. For the case of incident 1-fs electron pulses, the rapid 2 s -2 p quantum beat motion of the target electron is imaged as a time-dependent asymmetric oscillation of the diffraction pattern.

  10. The power of emotional valence-from cognitive to affective processes in reading.

    PubMed

    Altmann, Ulrike; Bohrn, Isabel C; Lubrich, Oliver; Menninghaus, Winfried; Jacobs, Arthur M

    2012-01-01

    The comprehension of stories requires the reader to imagine the cognitive and affective states of the characters. The content of many stories is unpleasant, as they often deal with conflict, disturbance or crisis. Nevertheless, unpleasant stories can be liked and enjoyed. In this fMRI study, we used a parametric approach to examine (1) the capacity of increasing negative valence of story contents to activate the mentalizing network (cognitive and affective theory of mind, ToM), and (2) the neural substrate of liking negatively valenced narratives. A set of 80 short narratives was compiled, ranging from neutral to negative emotional valence. For each story mean rating values on valence and liking were obtained from a group of 32 participants in a prestudy, and later included as parametric regressors in the fMRI analysis. Another group of 24 participants passively read the narratives in a three Tesla MRI scanner. Results revealed a stronger engagement of affective ToM-related brain areas with increasingly negative story valence. Stories that were unpleasant, but simultaneously liked, engaged the medial prefrontal cortex (mPFC), which might reflect the moral exploration of the story content. Further analysis showed that the more the mPFC becomes engaged during the reading of negatively valenced stories, the more coactivation can be observed in other brain areas related to the neural processing of affective ToM and empathy.

  11. Bond-valence methods for pKa prediction. II. Bond-valence, electrostatic, molecular geometry, and solvation effects

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

    Bickmore, Barry R.; Rosso, Kevin M.; Tadanier, Christopher J.

    2006-08-15

    In a previous contribution, we outlined a method for predicting (hydr)oxy-acid and oxide surface acidity constants based on three main factors: bond valence, Me?O bond ionicity, and molecular shape. Here electrostatics calculations and ab initio molecular dynamics simulations are used to qualitatively show that Me?O bond ionicity controls the extent to which the electrostatic work of proton removal departs from ideality, bond valence controls the extent of solvation of individual functional groups, and bond valence and molecular shape controls local dielectric response. These results are consistent with our model of acidity, but completely at odds with other methods of predictingmore » acidity constants for use in multisite complexation models. In particular, our ab initio molecular dynamics simulations of solvated monomers clearly indicate that hydrogen bonding between (hydr)oxo-groups and water molecules adjusts to obey the valence sum rule, rather than maintaining a fixed valence based on the coordination of the oxygen atom as predicted by the standard MUSIC model.« less

  12. Voice and Valency in San Luis Potosi Huasteco

    ERIC Educational Resources Information Center

    Munoz Ledo Yanez, Veronica

    2014-01-01

    This thesis presents an analysis of the system of transitivity, voice and valency alternations in Huasteco of San Luis Potosi (Mayan) within a functional-typological framework. The study is based on spoken discourse and elicited data collected in the municipalities of Aquismon and Tancanhuitz de Santos in the state of San Luis Potosi, Mexico. The…

  13. Super heavy element Copernicium: Cohesive and electronic properties revisited

    NASA Astrophysics Data System (ADS)

    Gyanchandani, Jyoti; Mishra, Vinayak; Dey, G. K.; Sikka, S. K.

    2018-01-01

    First principles scalar relativistic (SR) calculations with and without including the spin orbit (SO) interactions have been performed for solid Copernicium (Cn) to determine its ground state equilibrium structure, volume, bulk modulus, pressure derivative of the bulk modulus, density of states and band structure. Both SR and SR+SO calculations have been performed with 6p levels treated as part of core electrons and also as part of valence electrons. These calculations have been performed for the rhombohedral, BCT, FCC, HCP, BCC and SC structures. Results have been compared with the results for Hg which is lighter homologue of Cn in the periodic table. We find hcp to be the stable crystal structure at SR level of theory and also at SR+SO level of theory when the 6p electrons are treated as part of core electrons. With 6p as part of valence electrons, SR+SO level of computations, however, yield bcc structure to be the most stable structure. Equilibrium volume (V0) of the most stable crystal structure at SR level of theory viz. hcp structure is 188.66 a.u.3whereas its value for the bcc structure, the equilibrium ground state structure at SR+SO level of theory is 165.71 a.u.3 i.e a large change due to relativistic effects is seen. The density of states at Fermi level is much smaller in Cn than in Hg, making it a poorer metal than mercury. In addition the cohesive energy of Cn is computed to be almost two times that of Hg for SR+SO case.

  14. Tuning of quantum entanglement in molecular quantum cellular automata based on mixed-valence tetrameric units.

    PubMed

    Palii, Andrew; Tsukerblat, Boris

    2016-10-25

    In this article we consider two coupled tetrameric mixed-valence (MV) units accommodating electron pairs, which play the role of cells in molecular quantum cellular automata. It is supposed that the Coulombic interaction between instantly localized electrons within the cell markedly inhibits the transfer processes between the redox centers. Under this condition, as well as due to the vibronic localization of the electron pair, the cell can encode binary information, which is controlled by neighboring cells. We show that under certain conditions the two low-lying vibronic spin levels of the cell (ground and first excited states) can be regarded as originating from an effective spin-spin interaction. This is shown to depend on the internal parameters of the cell as well as on the induced polarization. Within this simplified two-level picture we evaluate the quantum entanglement in the system represented by the two electrons in the cell and show how the entanglement within the cell and concurrence can be controlled via polarization of the neighboring cells and temperature.

  15. Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study

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

    Alam, Aftab; Johnson, Duane D.

    Cerium and its technologically relevant compounds are examples of anomalous mixed valency, originating from two competing oxidation states—itinerant Ce4+ and localized Ce3+. Under applied stress, anomalous transitions are observed but not well understood. Here we treat mixed valency as an “alloy” problem involving two valences with competing and numerous site-occupancy configurations. We use density-functional theory with Hubbard U (i.e., DFT+U) to evaluate the effective valence and predict properties, including controlling the valence by pseudoternary alloying. For Ce and its compounds, such as (Ce,La)2(Fe,Co)14B permanent magnets, we find a stable mixed-valent α state near the spectroscopic value of νs=3.53. Ce valencymore » in compounds depends on its steric volume and local chemistry. For La doping, Ce valency shifts towards γ-like Ce3+, as expected from steric volume; for Co doping, valency depends on local Ce-site chemistry and steric volume. Our approach captures the key origins of anomalous valency and site-preference chemistry in complex compounds.« less

  16. On the valence fluctuation in the early actinide metals

    DOE PAGES

    Soderlind, P.; Landa, A.; Tobin, J. G.; ...

    2015-12-15

    In this study, recent X-ray measurements suggest a degree of valence fluctuation in plutonium and uranium intermetallics. We are applying a novel scheme, in conjunction with density functional theory, to predict 5f configuration fractions of states with valence fluctuations for the early actinide metals. For this purpose we perform constrained integer f-occupation calculations for the α phases of uranium, neptunium, and plutonium metals. For plutonium we also investigate the δ phase. The model predicts uranium and neptunium to be dominated by the f 3 and f 4 configurations, respectively, with only minor contributions from other configurations. For plutonium (both αmore » and δ phase) the scenario is dramatically different. Here, the calculations predict a relatively even distribution between three valence configurations. The δ phase has a greater configuration fraction of f 6 compared to that of the α phase. The theory is consistent with the interpretations of modern X-ray experiments and we present resonant X-ray emission spectroscopy results for α-uranium.« less

  17. Bulk and surface electronic structures of MgO

    NASA Astrophysics Data System (ADS)

    Schönberger, U.; Aryasetiawan, F.

    1995-09-01

    The bulk electronic structure of MgO is calculated from first principles including correlation effects within the GW approximation. The band gap, the position of the 2s O band, and the valence band width are in good agreement with experiment. From the quasiparticle band structure, optical transitions corresponding to the main optical absorption peaks are identified. The energy-loss spectrum is also calculated and compared with experiment. The surface electronic structure of MgO(100) is calculated self-consistently within the local-density approximation. It is found that states observed in a recent photoemission experiment outside the bulk allowed states are close to surface states.

  18. Social Annotation Valence: The Impact on Online Informed Consent Beliefs and Behavior

    PubMed Central

    Shaer, Orit; Okerlund, Johanna; Westendorf, Lauren; Ball, Madeleine; Nov, Oded

    2016-01-01

    Background Social media, mobile and wearable technology, and connected devices have significantly expanded the opportunities for conducting biomedical research online. Electronic consent to collecting such data, however, poses new challenges when contrasted to traditional consent processes. It reduces the participant-researcher dialogue but provides an opportunity for the consent deliberation process to move from solitary to social settings. In this research, we propose that social annotations, embedded in the consent form, can help prospective participants deliberate on the research and the organization behind it in ways that traditional consent forms cannot. Furthermore, we examine the role of the comments’ valence on prospective participants’ beliefs and behavior. Objective This study focuses specifically on the influence of annotations’ valence on participants’ perceptions and behaviors surrounding online consent for biomedical research. We hope to shed light on how social annotation can be incorporated into digitally mediated consent forms responsibly and effectively. Methods In this controlled between-subjects experiment, participants were presented with an online consent form for a personal genomics study that contained social annotations embedded in its margins. Individuals were randomly assigned to view the consent form with positive-, negative-, or mixed-valence comments beside the text of the consent form. We compared participants’ perceptions of being informed and having understood the material, their trust in the organization seeking the consent, and their actual consent across conditions. Results We find that comment valence has a marginally significant main effect on participants’ perception of being informed (F2=2.40, P=.07); specifically, participants in the positive condition (mean 4.17, SD 0.94) felt less informed than those in the mixed condition (mean 4.50, SD 0.69, P=.09). Comment valence also had a marginal main effect on the

  19. Studies of Copper, Silver, and Gold Cluster Anions: Evidence of Electronic Shell Structure.

    NASA Astrophysics Data System (ADS)

    Pettiette, Claire Lynn

    A new Ultraviolet Magnetic Time-of-Flight Photoelectron Spectrometer (MTOFPES) has been developed for the study of the electronic structure of clusters produced in a pulsed supersonic molecular beam. This is the first technique which has been successful in probing the valence electronic states of metal clusters. The ultraviolet photoelectron spectra of negative cluster ions of the noble metals have been taken at several different photon energies. These are presented along with the electron affinity and HOMO-LUMO gap measurements for Cu_6^- to Cu_ {41}^-, using 4.66 eV and 6.42 eV detachment energies; Ag_3^- to Ag_{21}^-, using 6.42 eV detachment energy; and Au_3^ - to Au_{21}^-, using 6.42 eV and 7.89 eV detachment energies. The spectra provide the first detailed probes of the s valence electrons of the noble metal clusters. In addition, the 6.42 eV and 7.89 eV spectra probe the first one to two electron volts of the molecular orbitals of the d valence electrons of copper and gold clusters. The electron affinity and HOMO-LUMO gap measurements of the noble metal clusters agree with the predictions of the ellipsoidal shell model for mono-valent metal clusters. In particular, cluster numbers 8, 20, and 40--which correspond to the spherical shell closings of this model--have low electron affinities and large HOMO-LUMO gaps. The spectra of the gold cluster ions indicate that the molecular orbital energies of the cluster valence electrons are more widely spaced for gold than for copper or silver. This is to be expected for the heavy atom clusters when relativistic effects are taken into account.

  20. Electronic Properties and Dissociative Photoionization of Thiocyanates, Part III. The Effect of the Group's Electronegativity in the Valence and Shallow-Core (Sulfur and Chlorine 2p) Regions of CCl3SCN and CCl2FSCN.

    PubMed

    Rodríguez Pirani, Lucas S; Della Védova, Carlos O; Geronés, Mariana; Romano, Rosana M; Cavasso-Filho, Reinaldo; Ge, Maofa; Ma, Chunping; Erben, Mauricio F

    2017-12-07

    Both photoelectron spectroscopy (PES) data and PhotoElectron-PhotoIon-Coincidence (PEPICO) spectra obtained from a synchrotron facility have been used to examine the electronic structure and the dissociative ionization of halomethyl thiocyantes in the valence and shallow-core S 2p and Cl 2p regions. Two simple and closely related molecules, namely, CCl 3 SCN and CCl 2 FSCN, have been analyzed to assess the role of halogen substitution in the electronic properties of thiocyanates. The assignment of the He(I) photoelectron spectra has been achieved with the help of quantum chemical calculations at the outer-valence Green's function (OVGF) level of approximation. The first ionization energies observed at 10.55 and 10.78 eV for CCl 3 SCN and CCl 2 FSCN, respectively, are assigned to ionization processes from the sulfur lone pair orbital [n(S)]. When these molecules are compared with CX 3 SCN (X = H, Cl, F) species, a linear relationship between the vertical first ionization energy and electronegativity of CX 3 group is observed. Irradiation of CCl 3 SCN and CCl 2 FSCN with photons in the valence energy regions leads to the formation of CCl 2 X + and CClXSCN + ions (X = Cl or F). Additionally, the achievement of the fragmentation patterns and the total ion yield spectra obtained from the PEPICO data in the S 2p and Cl 2p regions and several dissociation channels can be inferred for the core-excited species by using the triple coincidence PEPIPICO (PhotoElectron-PhotoIon-PhotoIon-Coincidence) spectra.

  1. Electronic structure and magnetic anisotropy of L1{sub 0}-FePt thin film studied by hard x-ray photoemission spectroscopy and first-principles calculations

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

    Ueda, S.; Synchrotron X-ray Station at SPring-8, National Institute for Materials Science, Sayo, Hyogo 679-5148; Mizuguchi, M.

    2016-07-25

    We have studied the electronic structure of the L1{sub 0} ordered FePt thin film by hard x-ray photoemission spectroscopy (HAXPES), cluster model, and first-principles calculations to investigate the relationship between the electronic structure and perpendicular magneto-crystalline anisotropy (MCA). The Fe 2p core-level HAXPES spectrum of the ordered film revealed the strong electron correlation in the Fe 3d states and the hybridization between the Fe 3d and Pt 5d states. By comparing the experimental valence band structure with the theoretical density of states, the strong electron correlation in the Fe 3d states modifies the valence band electronic structure of the L1{submore » 0} ordered FePt thin film through the Fe 3d-Pt 5d hybridization. These results strongly suggest that the strong electron correlation effect in the Fe 3d states and the Fe 3d-Pt 5d hybridization as well as the spin-orbit interaction in the Pt 5d states play important roles in the perpendicular MCA for L1{sub 0}-FePt.« less

  2. Accurate determination of the valence band edge in hard x-ray photoemission spectra using GW theory

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

    Lischner, Johannes, E-mail: jlischner597@gmail.com; Department of Physics and Department of Materials and the Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, London SW7 2AZ; Nemšák, Slavomír

    We introduce a new method for determining accurate values of the valence-band maximum in x-ray photoemission spectra. Specifically, we align the sharpest peak in the valence-band region of the experimental spectrum with the corresponding feature of a theoretical valence-band density of states curve from ab initio GW theory calculations. This method is particularly useful for soft and hard x-ray photoemission studies of materials with a mixture of valence-band characters, where strong matrix element effects can render standard methods for extracting the valence-band maximum unreliable. We apply our method to hydrogen-terminated boron-doped diamond, which is a promising substrate material for novelmore » solar cell devices. By carrying out photoemission experiments with variable light polarizations, we verify the accuracy of our analysis and the general validity of the method.« less

  3. Valence and ionic lowest-lying electronic states of ethyl formate as studied by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy, and ab initio calculations

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

    Śmiałek, M. A., E-mail: smialek@pg.gda.pl; Łabuda, M.; Guthmuller, J.

    2014-09-14

    The highest resolution vacuum ultraviolet photoabsorption spectrum of ethyl formate, C{sub 2}H{sub 5}OCHO, yet reported is presented over the wavelength range 115.0–275.5 nm (10.75–4.5 eV) revealing several new spectral features. Valence and Rydberg transitions and their associated vibronic series, observed in the photoabsorption spectrum, have been assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of ethyl formate and are compared with a newly recorded He(I) photoelectron spectrum (from 10.1 to 16.1 eV). Newmore » vibrational structure is observed in the first photoelectron band. The photoabsorption cross sections have been used to calculate the photolysis lifetime of ethyl formate in the upper stratosphere (20–50 km)« less

  4. Quasi 2D electronic states with high spin-polarization in centrosymmetric MoS2 bulk crystals

    NASA Astrophysics Data System (ADS)

    Gehlmann, Mathias; Aguilera, Irene; Bihlmayer, Gustav; Młyńczak, Ewa; Eschbach, Markus; Döring, Sven; Gospodarič, Pika; Cramm, Stefan; Kardynał, Beata; Plucinski, Lukasz; Blügel, Stefan; Schneider, Claus M.

    2016-06-01

    Time reversal dictates that nonmagnetic, centrosymmetric crystals cannot be spin-polarized as a whole. However, it has been recently shown that the electronic structure in these crystals can in fact show regions of high spin-polarization, as long as it is probed locally in real and in reciprocal space. In this article we present the first observation of this type of compensated polarization in MoS2 bulk crystals. Using spin- and angle-resolved photoemission spectroscopy (ARPES), we directly observed a spin-polarization of more than 65% for distinct valleys in the electronic band structure. By additionally evaluating the probing depth of our method, we find that these valence band states at the point in the Brillouin zone are close to fully polarized for the individual atomic trilayers of MoS2, which is confirmed by our density functional theory calculations. Furthermore, we show that this spin-layer locking leads to the observation of highly spin-polarized bands in ARPES since these states are almost completely confined within two dimensions. Our findings prove that these highly desired properties of MoS2 can be accessed without thinning it down to the monolayer limit.

  5. Electronic structure of the organic semiconductor copper phthalocyanine: experiment and theory.

    PubMed

    Aristov, V Yu; Molodtsova, O V; Maslyuk, V V; Vyalikh, D V; Zhilin, V M; Ossipyan, Yu A; Bredow, T; Mertig, I; Knupfer, M

    2008-01-21

    The electronic structure of the organic semiconductor copper-phthalocyanine (CuPc) has been determined by a combination of conventional and resonant photoemission, near-edge x-ray absorption, as well as by the first-principles calculations. The experimentally obtained electronic valence band structure of CuPc is in very good agreement with the calculated density of states results, allowing the derivation of detailed site specific information.

  6. Human Amygdala Represents the Complete Spectrum of Subjective Valence

    PubMed Central

    Jin, Jingwen; Zelano, Christina; Gottfried, Jay A.

    2015-01-01

    Although the amygdala is a major locus for hedonic processing, how it encodes valence information is poorly understood. Given the hedonic potency of odor stimuli and the amygdala's anatomical proximity to the peripheral olfactory system, we combined high-resolution fMRI with pattern-based multivariate techniques to examine how valence information is encoded in the amygdala. Ten human subjects underwent fMRI scanning while smelling 9 odorants that systematically varied in perceived valence. Representational similarity analyses showed that amygdala codes the entire dimension of valence, ranging from pleasantness to unpleasantness. This unidimensional representation significantly correlated with self-reported valence ratings but not with intensity ratings. Furthermore, within-trial valence representations evolved over time, prioritizing earlier differentiation of unpleasant stimuli. Together, these findings underscore the idea that both spatial and temporal features uniquely encode pleasant and unpleasant odor valence in the amygdala. The availability of a unidimensional valence code in the amygdala, distributed in both space and time, would create greater flexibility in determining the pleasantness or unpleasantness of stimuli, providing a mechanism by which expectation, context, attention, and learning could influence affective boundaries for guiding behavior. SIGNIFICANCE STATEMENT Our findings elucidate the mechanisms of affective processing in the amygdala by demonstrating that this brain region represents the entire valence dimension from pleasant to unpleasant. An important implication of this unidimensional valence code is that pleasant and unpleasant valence cannot coexist in the amygdale because overlap of fMRI ensemble patterns for these two valence extremes obscures their unique content. This functional architecture, whereby subjective valence maps onto a pattern continuum between pleasant and unpleasant poles, offers a robust mechanism by which context

  7. Valence and magnitude ambiguity in feedback processing.

    PubMed

    Gu, Ruolei; Feng, Xue; Broster, Lucas S; Yuan, Lu; Xu, Pengfei; Luo, Yue-Jia

    2017-05-01

    Outcome feedback which indicates behavioral consequences are crucial for reinforcement learning and environmental adaptation. Nevertheless, outcome information in daily life is often totally or partially ambiguous. Studying how people interpret this kind of information would provide important knowledge about the human evaluative system. This study concentrates on the neural processing of partially ambiguous feedback, that is, either its valence or magnitude is unknown to participants. To address this topic, we sequentially presented valence and magnitude information; electroencephalography (EEG) response to each kind of presentation was recorded and analyzed. The event-related potential components feedback-related negativity (FRN) and P3 were used as indices of neural activity. Consistent with previous literature, the FRN elicited by ambiguous valence was not significantly different from that elicited by negative valence. On the other hand, the FRN elicited by ambiguous magnitude was larger than both the large and small magnitude, indicating the motivation to seek unambiguous magnitude information. The P3 elicited by ambiguous valence and ambiguous magnitude was not significantly different from that elicited by negative valence and small magnitude, respectively, indicating the emotional significance of feedback ambiguity. Finally, the aforementioned effects also manifested in the stage of information integration. These findings indicate both similarities and discrepancies between the processing of valence ambiguity and that of magnitude ambiguity, which may help understand the mechanisms of ambiguous information processing.

  8. Oscillator strengths of some Ba lines - A treatment including core-valence correlation and relativistic effects

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.; Jaffe, R. L.; Langhoff, S. R.; Partridge, H.; Mascarello, F. G.

    1985-01-01

    Theoretical calculations of selected excitation energies and oscillator strengths for Ba are presented that overcome the difficulties of previous theoretical treatments. A relativistic effective-core potential treatment is used to account for the relativistic core contraction, but the outermost ten electrons are treated explicitly. Core-valence correlation can be included in this procedure in a rigorous and systematic way through a configuration-interaction calculation. Insight is gained into the importance of relativistic effects by repeating many of the calculations using an all-electron nonrelativistic treatment employing an extended Slater basis set. It is found that the intensity of the intercombination line 3P1-1S0 is accurately determined by accounting for the deviation from LS coupling through spin-orbit mixing with the 1P1 state, and that deviations from the Lande interval rule provide an accurate measure of the degree of mixing.

  9. Electronic structure study of wide band gap magnetic semiconductor (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals in paramagnetic and ferromagnetic phases

    NASA Astrophysics Data System (ADS)

    Dwivedi, G. D.; Joshi, Amish G.; Kumar, Shiv; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L.; Ghosh, A. K.; Chatterjee, Sandip

    2016-04-01

    X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La0.6Pr0.4)0.65Ca0.35MnO3 near Fermi-level. XMCD results indicate that Mn3+ and Mn4+ spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La0.6Pr0.4)0.65Ca0.35MnO3 system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below TC. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

  10. Emotional Valence and the Free-Energy Principle

    PubMed Central

    Joffily, Mateus; Coricelli, Giorgio

    2013-01-01

    The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world. PMID:23785269

  11. Emotional valence and the free-energy principle.

    PubMed

    Joffily, Mateus; Coricelli, Giorgio

    2013-01-01

    The free-energy principle has recently been proposed as a unified Bayesian account of perception, learning and action. Despite the inextricable link between emotion and cognition, emotion has not yet been formulated under this framework. A core concept that permeates many perspectives on emotion is valence, which broadly refers to the positive and negative character of emotion or some of its aspects. In the present paper, we propose a definition of emotional valence in terms of the negative rate of change of free-energy over time. If the second time-derivative of free-energy is taken into account, the dynamics of basic forms of emotion such as happiness, unhappiness, hope, fear, disappointment and relief can be explained. In this formulation, an important function of emotional valence turns out to regulate the learning rate of the causes of sensory inputs. When sensations increasingly violate the agent's expectations, valence is negative and increases the learning rate. Conversely, when sensations increasingly fulfil the agent's expectations, valence is positive and decreases the learning rate. This dynamic interaction between emotional valence and learning rate highlights the crucial role played by emotions in biological agents' adaptation to unexpected changes in their world.

  12. Electronic structure and exchange interactions in diluted semimagnetic semiconductors (Zn,Co)Se and (Zn,Mn)Se

    NASA Astrophysics Data System (ADS)

    Mašek, J.

    1991-05-01

    A comparative study of the electronic structure of (Zn,Co)Se and (Zn,Mn)Se is done by using a tight-binding version of the coherent potential approximation. The densities of states, relevant for a photoemission experiment, are calculated for a magnetically disordered phase. The exchange constant Jpd is obtained from the splitting of the valence band top in the ferromagnetic phase of the mixed crystal; Jdd is estimated from the energy of a spin reversal. We explain the large exchange constant in the Co-based systems as a result of efficient hybridization of the d-states with the valence band.

  13. Role of random magnetic anisotropy on the valence, magnetocaloric and resistivity properties in a hexagonal Sm2Ni0.87Si2.87 compound

    NASA Astrophysics Data System (ADS)

    Pakhira, Santanu; Kundu, Asish K.; Mazumdar, Chandan; Ranganathan, R.

    2018-05-01

    In this work, we report the effect of random magnetic anisotropy (RMA) on the valence, magnetocaloric and resistivity properties in a glassy intermetallic material Sm2Ni0.87Si2.87. On the basis of detailed studies on the valence band and core level electronic structure, we have established that both the Sm3+ and Sm2+ ions are present in the system, suggesting the compound to be of mixed valence in nature. The significant observation of positive magnetic entropy change in zero-field cooled measurement has been argued due to the presence of RMA that develops due to local electronic environmental variations between the rare-earth ions in the system. The quantum interference effect caused by the elastic electron–electron interaction is responsible for the resistivity upturn at low-temperature for this disordered metallic conductor.

  14. Electroencephalography Based Analysis of Working Memory Load and Affective Valence in an N-back Task with Emotional Stimuli

    PubMed Central

    Grissmann, Sebastian; Faller, Josef; Scharinger, Christian; Spüler, Martin; Gerjets, Peter

    2017-01-01

    Most brain-based measures of the electroencephalogram (EEG) are used in highly controlled lab environments and only focus on narrow mental states (e.g., working memory load). However, we assume that outside the lab complex multidimensional mental states are evoked. This could potentially create interference between EEG signatures used for identification of specific mental states. In this study, we aimed to investigate more realistic conditions and therefore induced a combination of working memory load and affective valence to reveal potential interferences in EEG measures. To induce changes in working memory load and affective valence, we used a paradigm which combines an N-back task (for working memory load manipulation) with a standard method to induce affect (affective pictures taken from the International Affective Picture System (IAPS) database). Subjective ratings showed that the experimental task was successful in inducing working memory load as well as affective valence. Additionally, performance measures were analyzed and it was found that behavioral performance decreased with increasing workload as well as negative valence, showing that affective valence can have an effect on cognitive processing. These findings are supported by changes in frontal theta and parietal alpha power, parameters used for measuring of working memory load in the EEG. However, these EEG measures are influenced by the negative valence condition as well and thereby show that detection of working memory load is sensitive to affective contexts. Unexpectedly, we did not find any effects for EEG measures typically used for affective valence detection (Frontal Alpha Asymmetry (FAA)). Therefore we assume that the FAA measure might not be usable if cognitive workload is induced simultaneously. We conclude that future studies should account for potential context-specifity of EEG measures. PMID:29311875

  15. Electroencephalography Based Analysis of Working Memory Load and Affective Valence in an N-back Task with Emotional Stimuli.

    PubMed

    Grissmann, Sebastian; Faller, Josef; Scharinger, Christian; Spüler, Martin; Gerjets, Peter

    2017-01-01

    Most brain-based measures of the electroencephalogram (EEG) are used in highly controlled lab environments and only focus on narrow mental states (e.g., working memory load). However, we assume that outside the lab complex multidimensional mental states are evoked. This could potentially create interference between EEG signatures used for identification of specific mental states. In this study, we aimed to investigate more realistic conditions and therefore induced a combination of working memory load and affective valence to reveal potential interferences in EEG measures. To induce changes in working memory load and affective valence, we used a paradigm which combines an N-back task (for working memory load manipulation) with a standard method to induce affect (affective pictures taken from the International Affective Picture System (IAPS) database). Subjective ratings showed that the experimental task was successful in inducing working memory load as well as affective valence. Additionally, performance measures were analyzed and it was found that behavioral performance decreased with increasing workload as well as negative valence, showing that affective valence can have an effect on cognitive processing. These findings are supported by changes in frontal theta and parietal alpha power, parameters used for measuring of working memory load in the EEG. However, these EEG measures are influenced by the negative valence condition as well and thereby show that detection of working memory load is sensitive to affective contexts. Unexpectedly, we did not find any effects for EEG measures typically used for affective valence detection (Frontal Alpha Asymmetry (FAA)). Therefore we assume that the FAA measure might not be usable if cognitive workload is induced simultaneously. We conclude that future studies should account for potential context-specifity of EEG measures.

  16. Pair natural orbital and canonical coupled cluster reaction enthalpies involving light to heavy alkali and alkaline earth metals: the importance of sub-valence correlation.

    PubMed

    Minenkov, Yury; Bistoni, Giovanni; Riplinger, Christoph; Auer, Alexander A; Neese, Frank; Cavallo, Luigi

    2017-04-05

    In this work, we tested canonical and domain based pair natural orbital coupled cluster methods (CCSD(T) and DLPNO-CCSD(T), respectively) for a set of 32 ligand exchange and association/dissociation reaction enthalpies involving ionic complexes of Li, Be, Na, Mg, Ca, Sr, Ba and Pb(ii). Two strategies were investigated: in the former, only valence electrons were included in the correlation treatment, giving rise to the computationally very efficient FC (frozen core) approach; in the latter, all non-ECP electrons were included in the correlation treatment, giving rise to the AE (all electron) approach. Apart from reactions involving Li and Be, the FC approach resulted in non-homogeneous performance. The FC approach leads to very small errors (<2 kcal mol -1 ) for some reactions of Na, Mg, Ca, Sr, Ba and Pb, while for a few reactions of Ca and Ba deviations up to 40 kcal mol -1 have been obtained. Large errors are both due to artificial mixing of the core (sub-valence) orbitals of metals and the valence orbitals of oxygen and halogens in the molecular orbitals treated as core, and due to neglecting core-core and core-valence correlation effects. These large errors are reduced to a few kcal mol -1 if the AE approach is used or the sub-valence orbitals of metals are included in the correlation treatment. On the technical side, the CCSD(T) and DLPNO-CCSD(T) results differ by a fraction of kcal mol -1 , indicating the latter method as the perfect choice when the CPU efficiency is essential. For completely black-box applications, as requested in catalysis or thermochemical calculations, we recommend the DLPNO-CCSD(T) method with all electrons that are not covered by effective core potentials included in the correlation treatment and correlation-consistent polarized core valence basis sets of cc-pwCVQZ(-PP) quality.

  17. Effect of 3d doping on the electronic structure of BaFe2As2.

    PubMed

    McLeod, J A; Buling, A; Green, R J; Boyko, T D; Skorikov, N A; Kurmaev, E Z; Neumann, M; Finkelstein, L D; Ni, N; Thaler, A; Bud'ko, S L; Canfield, P C; Moewes, A

    2012-05-30

    The electronic structure of BaFe(2)As(2) doped with Co, Ni and Cu has been studied by a variety of experimental and theoretical methods, but a clear picture of the dopant 3d states has not yet emerged. Herein we provide experimental evidence of the distribution of Co, Ni and Cu 3d states in the valence band. We conclude that the Co and Ni 3d states provide additional free carriers to the Fermi level, while the Cu 3d states are found at the bottom of the valence band in a localized 3d(10) shell. These findings help shed light on why superconductivity can occur in BaFe(2)As(2) doped with Co and Ni but not Cu.

  18. [Emotional valence of words in schizophrenia].

    PubMed

    Jalenques, I; Enjolras, J; Izaute, M

    2013-06-01

    Emotion recognition is a domain in which deficits have been reported in schizophrenia. A number of emotion classification studies have indicated that emotion processing deficits in schizophrenia are more pronounced for negative affects. Given the difficulty of developing material suitable for the study of these emotional deficits, it would be interesting to examine whether patients suffering from schizophrenia are responsive to positively and negatively charged emotion-related words that could be used within the context of remediation strategies. The emotional perception of words was examined in a clinical experiment involving schizophrenia patients. This emotional perception was expressed by the patients in terms of the valence associated with the words. In the present study, we investigated whether schizophrenia patients would assign the same negative and positive valences to words as healthy individuals. Twenty volunteer, clinically stable, outpatients from the Psychiatric Service of the University Hospital of Clermont-Ferrand were recruited. Diagnoses were based on DSM-IV criteria. Global psychiatric symptoms were assessed using the Positive and Negative Symptoms Scale (PANSS). The patients had to evaluate the emotional valence of a set of 300 words on a 5-point scale ranging from "very unpleasant" to "very pleasant". . The collected results were compared with those obtained by Bonin et al. (2003) [13] from 97 University students. Correlational analyses of the two studies revealed that the emotional valences were highly correlated, i.e. the schizophrenia patients estimated very similar emotional valences. More precisely, it was possible to examine three separate sets of 100 words each (positive words, neutral words and negative words). The positive words that were evaluated were the more positive words from the norms collected by Bonin et al. (2003) [13], and the negative words were the more negative examples taken from these norms. The neutral words

  19. On the correlations between the polyhedron eccentricity parameters and the bond-valence sums for the cations with one lone electron pair. Addendum.

    PubMed

    Sidey, Vasyl

    2009-06-01

    Systematic variations of the bond-valence sums calculated from the poorly determined bond-valence parameters [Sidey (2008), Acta Cryst. B64, 515-518] have been illustrated using a simple graphical scheme.

  20. Electronic Structure of HgBa2CaCu2O(6+delta) Epitaxial films measured by x-ray Photoemission

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Rupp, M.; Gupta, A.; Tsuei, C. C.

    1995-01-01

    The electronic structure and chemical states of HgBa2CaCu20(sub 6 + delta), epitaxial films have been studied with x-ray photelectron spectroscopy. Signals from the superconducting phase dominate all the core-level spectra, and a clear Fermi edge is observed in the valence-band region. The Ba, Ca, Cu, and O core levels are similar to those of Tl2Ba2CaCu208(+)O(sub 6 + delta), but distinct differences are observed in the valence bands which are consistent with differences in the calculated densities of states.

  1. The role of valence focus and appraisal overlap in emotion differentiation.

    PubMed

    Erbas, Yasemin; Ceulemans, Eva; Koval, Peter; Kuppens, Peter

    2015-06-01

    Emotion differentiation refers to the level of specificity with which people distinguish between their emotional states and is considered to play an important role for psychological well-being. Yet, not much is known about what characterizes people high or low in emotion differentiation and what underlies these differences. In 2 studies involving experience sampling (Studies 1-2) and lab based (Study 2) methods, we investigated how emotion differentiation is related to individual differences in valence focus and the overlap in appraisal patterns between emotions. In line with expectations, results showed that high levels of both positive and negative emotion differentiation are related to lower levels of valence focus and lower levels of appraisal overlap between emotions. These findings suggest that individuals who are low in emotion differentiation mainly emphasize the valence aspect of emotions while individuals who are high in emotion differentiation make stronger distinctions between emotions in terms of their underlying appraisal profiles. (c) 2015 APA, all rights reserved).

  2. Neurons for hunger and thirst transmit a negative-valence teaching signal

    PubMed Central

    Gong, Rong; Magnus, Christopher J.; Yu, Yang; Sternson, Scott M.

    2015-01-01

    Homeostasis is a biological principle for regulation of essential physiological parameters within a set range. Behavioural responses due to deviation from homeostasis are critical for survival, but motivational processes engaged by physiological need states are incompletely understood. We examined motivational characteristics and dynamics of two separate neuron populations that regulate energy and fluid homeostasis by using cell type-specific activity manipulations in mice. We found that starvation-sensitive AGRP neurons exhibit properties consistent with a negative-valence teaching signal. Mice avoided activation of AGRP neurons, indicating that AGRP neuron activity has negative valence. AGRP neuron inhibition conditioned preference for flavours and places. Correspondingly, deep-brain calcium imaging revealed that AGRP neuron activity rapidly reduced in response to food-related cues. Complementary experiments activating thirst-promoting neurons also conditioned avoidance. Therefore, these need-sensing neurons condition preference for environmental cues associated with nutrient or water ingestion, which is learned through reduction of negative-valence signals during restoration of homeostasis. PMID:25915020

  3. Neurons for hunger and thirst transmit a negative-valence teaching signal.

    PubMed

    Betley, J Nicholas; Xu, Shengjin; Cao, Zhen Fang Huang; Gong, Rong; Magnus, Christopher J; Yu, Yang; Sternson, Scott M

    2015-05-14

    Homeostasis is a biological principle for regulation of essential physiological parameters within a set range. Behavioural responses due to deviation from homeostasis are critical for survival, but motivational processes engaged by physiological need states are incompletely understood. We examined motivational characteristics of two separate neuron populations that regulate energy and fluid homeostasis by using cell-type-specific activity manipulations in mice. We found that starvation-sensitive AGRP neurons exhibit properties consistent with a negative-valence teaching signal. Mice avoided activation of AGRP neurons, indicating that AGRP neuron activity has negative valence. AGRP neuron inhibition conditioned preference for flavours and places. Correspondingly, deep-brain calcium imaging revealed that AGRP neuron activity rapidly reduced in response to food-related cues. Complementary experiments activating thirst-promoting neurons also conditioned avoidance. Therefore, these need-sensing neurons condition preference for environmental cues associated with nutrient or water ingestion, which is learned through reduction of negative-valence signals during restoration of homeostasis.

  4. Theory of electron transfer and molecular state in DNA

    NASA Astrophysics Data System (ADS)

    Endres, Robert Gunter

    2002-09-01

    In this thesis, a mechanism for long-range electron transfer in DNA and a systematic search for high conductance DNA are developed. DNA is well known for containing the genetic code of all living species. On the other hand, there are some experimental indications that DNA can mediate effectively long-range electron transfer leading to the concept of chemistry at a distance. This can be important for DNA damage and healing. In the first part of the thesis, a possible mechanism for long-range electron transfer is introduced. The weak distance dependent electron transfer was experimentally observed using transition metal intercalators for donor and acceptor. In our model calculations, the transfer is mediated by the molecular analogue of a Kondo bound state well known from solid state physics of mixed-valence rare-earth compounds. We believe this is quite realistic, since localized d orbitals of the transition metal ions could function as an Anderson impurity embedded in a reservoir of rather delocalized molecular orbitals of the intercalator ligands and DNA pi orbitals. The effective Anderson model is solved with a physically intuitive variational ansatz as well as with the essentially exact DMRG method. The electronic transition matrix element, which is important because it contains the donor-acceptor distance dependence, is obtained with the Mulliken-Hush algorithm as well as from Born-Oppenheimer potential energy surfaces. Our possible explanation of long-range electron transfer is put in context to other more conventional mechanisms which also could lead to similar behavior. Another important issue of DNA is its possible use for nano-technology. Although DNA's mechanical properties are excellent, the question whether it can be conducting and be used for nano-wires is highly controversial. Experimentally, DNA shows conducting, semi-conducting and insulating properties. Motivated by these wide ranging experimental results on the conductivity of DNA, we have

  5. Effect of Pr Valence State on Interfacial Structure and Electrical Properties of Pr Oxide/PrON/Ge Gate Stack Structure

    NASA Astrophysics Data System (ADS)

    Kato, Kimihiko; Sakashita, Mitsuo; Takeuchi, Wakana; Kondo, Hiroki; Nakatsuka, Osamu; Zaima, Shigeaki

    2011-04-01

    In this study, we investigated the valence state and chemical bonding state of Pr in a Pr oxide/PrON/Ge structure. We clarified the relationship between the valence state of Pr and the Pr oxide/Ge interfacial reaction using Pr oxide/Ge and Pr oxide/PrON/Ge samples. We found the formation of three Pr oxide phases in Pr oxide films; hexagonal Pr2O3 (h-Pr2O3) (Pr3+), cubic Pr2O3 (c-Pr2O3) (Pr3+), and c-PrO2 (Pr4+). We also investigated the effect of a nitride interlayer on the interfacial reaction in Pr oxide/Ge gate stacks. In a sample with a nitride interlayer (Pr oxide/PrON/Ge), metallic Pr-Pr bonds are also formed in the c-Pr2O3 film. After annealing in H2 ambient, the diffusion of Ge into Pr oxide is not observed in this sample. Pr-Pr bonds probably prevent the interfacial reaction and Ge oxide formation, considering that the oxygen chemical potential of this film is lower than that of a GeO2/Ge system. On the other hand, the rapid thermal oxidation (RTO) treatment terminates the O vacancies and defects in c-Pr2O3. As a result, c-PrO2 with tetravalent Pr is formed in the Pr oxide/PrON/Ge sample with RTO. In this sample, the leakage current density is effectively decreased in comparison with the sample without RTO. Hydrogen termination works effectively in Pr oxide/PrON/Ge samples with and without RTO, and we can achieve an interface state density of as low as 4 ×1011 eV-1·cm-2.

  6. Stabilization of very rare tautomers of uracil by an excess electron.

    PubMed

    Bachorz, Rafał A; Rak, Janusz; Gutowski, Maciej

    2005-05-21

    We characterized valence-type and dipole-bound anionic states of uracil using various electronic structure methods. We found that the most stable anion is related to neither the canonical 2,4-dioxo nor a rare imino-hydroxy tautomer. Instead, it is related to an imino-oxo tautomer, in which the N1H proton is transferred to the C5 atom. This valence anion is characterized by an electron vertical detachment energy (VDE) of 1267 meV and it is adiabatically stable with respect to the canonical neutral by 3.93 kcal mol(-1). It is also more stable by 2.32 and 5.10 kcal mol(-1) than the dipole-bound and valence anion, respectively, of the canonical tautomer. The VDE values for the former and the latter are 73 and 506 meV, respectively. Another, anionic, low-lying imino-oxo tautomer with a VDE of 2499 meV has a proton transferred from N3H to C5. It is less stable than the neutral canonical tautomer by 1.38 kcal mol(-1). The mechanism of formation of anionic tautomers with the carbon C5 protonated may involve intermolecular proton transfer or dissociative electron attachment to the canonical neutral tautomer followed by a barrier-free attachment of a hydrogen atom to C5. The six-member ring structure of anionic tautomers with carbon atoms protonated might be unstable upon an excess electron detachment. Indeed, the neutral systems resulting from electron detachment from anionic tautomers with carbon atoms protonated evolve along barrier-free decomposition pathways to a linear or a bicyclo structure, which might be viewed as lesions to RNA. Within the PCM hydration model, the low-lying valence anions become adiabatically bound with respect to the canonical neutral and the two most stable tautomers have carbon atoms protonated.

  7. Cs(2)K(UO)(2)Si(4)O(12): a mixed-valence uranium(IV,V) silicate.

    PubMed

    Lee, Cheng-Shiuan; Wang, Sue-Lein; Lii, Kwang-Hwa

    2009-10-28

    The first mixed-valence uranium(IV,V) silicate is synthesized under high-temperature, high-pressure hydrothermal conditions. The structure contains chains of corner-sharing U(IV,V)O(6) octahedra which are interconnected by Si(4)O(12) four-membered rings to form a 3-D framework. XPS and XANES spectra were measured to identify the valence state of uranium.

  8. Structure and Magnetic Properties of a Mixed-Valence Heptanuclear Manganese Cluster.

    PubMed

    Abbati, Gian Luca; Cornia, Andrea; Fabretti, Antonio C.; Caneschi, Andrea; Gatteschi, Dante

    1998-07-27

    Two novel polynuclear manganese(II,III) complexes have been synthesized by exploiting controlled methanolysis. A one-pot reaction of MnCl(2), NaOMe, dibenzoylmethane (Hdbm), and O(2) in anhydrous methanol, followed by recrystallization from MeOH/CHCl(3) mixtures, afforded the alkoxomanganese complexes [Mn(7)(OMe)(12)(dbm)(6)].CHCl(3).14MeOH (2) and [Mn(2)(OMe)(2)(dbm)(4)] (3). Complex 2 crystallizes in trigonal space group R&thremacr; with a = 14.439(2) Å, alpha = 86.34(1) degrees, and Z = 1. Complex 3 crystallizes in triclinic space group P&onemacr; with a = 9.612(1) Å, b = 10.740(1) Å, c = 13.168(1) Å, alpha = 80.39(1) degrees, beta = 87.66(1) degrees, gamma = 83.57(1) degrees, and Z = 1. The solid-state structure of 2 comprises a [Mn(6)(OMe)(12)(dbm)(6)] "crown" with crystallographically imposed 6-fold symmetry plus a central manganese ion. The layered Mn/O core mimics a fragment of the manganese oxide mineral lithiophorite. Conductivity measurements confirmed the nonionic character of 2 and suggested a mixed-valence Mn(II)(3)Mn(III)(4) formulation. The metrical parameters of the core were analyzed with the aid of bond-valence sum calculations. The central ion is essentially a valence-trapped Mn(II) ion, whereas the average Mn-O distances for the manganese ions of the "crown" are consistent with the presence of two Mn(II) and four Mn(III) ions. However, (1)H NMR spectra in solution strongly support valence localization and suggest that the observed solid-state structure may be a result of static disorder effects. Magnetic susceptibility vs T and magnetization vs field data at low temperature are consistent with an S = (17)/(2) ground state. Complex 3 is a symmetric alkoxo-bridged dimer. The two high-spin Mn(III) ions are antiferromagnetically coupled with J = 0.28(4) cm(-)(1), g = 1.983(2), and D = -2.5(4) cm(-)(1).

  9. Exact solution of the PPP model for correlated electronic states of tetracene and substituted tetracene.

    PubMed

    Pati, Y Anusooya; Ramasesha, S

    2014-06-12

    Tetracene is an important conjugated molecule for device applications. We have used the diagrammatic valence bond method to obtain the desired states, in a Hilbert space of about 450 million singlets and 902 million triplets. We have also studied the donor/acceptor (D/A)-substituted tetracenes with D and A groups placed symmetrically about the long axis of the molecule. In these cases, by exploiting a new symmetry, which is a combination of C2 symmetry and electron-hole symmetry, we are able to obtain their low-lying states. In the case of substituted tetracene, we find that optically allowed one-photon excitation gaps reduce with increasing D/A strength, while the lowest singlet-triplet gap is only weakly affected. In all the systems we have studied, the excited singlet state, S1, is at more than twice the energy of the lowest triplet state and the second triplet is very close to the S1 state. Thus, donor-acceptor-substituted tetracene could be a good candidate in photovoltaic device application as it satisfies energy criteria for singlet fission. We have also obtained the model exact second harmonic generation (SHG) coefficients using the correction vector method, and we find that the SHG responses increase with the increase in D/A strength.

  10. Optical and electronic properties of doped p -type CuI: Explanation of transparent conductivity from first principles

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

    Li, Yuwei; Sun, Jifeng; Singh, David J.

    In this paper, we report the properties of the reported transparent conductor CuI, including the effect of heavy p-type doping. The results, based on first-principles calculations, include an analysis of the electronic structure and calculations of optical and dielectric properties. We find that the origin of the favorable transparent conducting behavior lies in the absence in the visible of strong interband transitions between deeper valence bands and states at the valence-band maximum that become empty with p-type doping. Instead, strong interband transitions to the valence-band maximum are concentrated in the infrared with energies below 1.3 eV. This is contrast tomore » the valence bands of many wide-band-gapmaterials. Turning to the mobility,we find that the states at the valence-band maximum are relatively dispersive. This originates from their antibonding Cu d–I p character. We find a modest enhancement of the Born effective charges relative to nominal values, leading to a dielectric constant ε(0) = 6.3. This is sufficiently large to reduce ionized impurity scattering, leading to the expectation that the properties of CuI can still be significantly improved through sample quality.« less

  11. Optical and electronic properties of doped p -type CuI: Explanation of transparent conductivity from first principles

    DOE PAGES

    Li, Yuwei; Sun, Jifeng; Singh, David J.

    2018-03-26

    In this paper, we report the properties of the reported transparent conductor CuI, including the effect of heavy p-type doping. The results, based on first-principles calculations, include an analysis of the electronic structure and calculations of optical and dielectric properties. We find that the origin of the favorable transparent conducting behavior lies in the absence in the visible of strong interband transitions between deeper valence bands and states at the valence-band maximum that become empty with p-type doping. Instead, strong interband transitions to the valence-band maximum are concentrated in the infrared with energies below 1.3 eV. This is contrast tomore » the valence bands of many wide-band-gapmaterials. Turning to the mobility,we find that the states at the valence-band maximum are relatively dispersive. This originates from their antibonding Cu d–I p character. We find a modest enhancement of the Born effective charges relative to nominal values, leading to a dielectric constant ε(0) = 6.3. This is sufficiently large to reduce ionized impurity scattering, leading to the expectation that the properties of CuI can still be significantly improved through sample quality.« less

  12. Electron-impact electronic-state excitation of para-benzoquinone

    NASA Astrophysics Data System (ADS)

    Jones, D. B.; da Costa, R. F.; Kossoski, F.; Varella, M. T. do N.; Bettega, M. H. F.; Ferreira da Silva, F.; Limão-Vieira, P.; García, G.; Lima, M. A. P.; White, R. D.; Brunger, M. J.

    2018-03-01

    Angle resolved electron energy loss spectra (EELS) for para-benzoquinone (C6H4O2) have been recorded for incident electron energies of 20, 30, and 40 eV. Measured differential cross sections (DCSs) for electronic band features, composed of a combination of energetically unresolved electronic states, are subsequently derived from those EELS. Where possible, the obtained DCSs are compared with those calculated using the Schwinger multichannel method with pseudopotentials. These calculations were performed using a minimum orbital basis single configuration interaction framework at the static exchange plus polarisation level. Here, quite reasonable agreement between the experimental cross sections and the theoretical cross sections for the summation of unresolved states was observed.

  13. Effects of crystalline electronic field and onsite interorbital interaction in Yb-based quasicrystal and approximant crystal.

    PubMed

    Watanabe, Shinji; Miyake, Kazumasa

    2018-05-10

    To get an insight into a new type of quantum critical phenomena recently discovered in the quasicrystal Yb 15 Al 34 Au 51 and approximant crystal (AC) Yb 14 Al 35 Au 51 under pressure, we discuss the property of the crystalline electronic field (CEF) at Yb in the AC and show that uneven CEF levels at each Yb site can appear because of the Al/Au mixed sites. Then we construct the minimal model for the electronic state on the AC by introducing the onsite Coulomb repulsion between the 4f and 5d orbitals at Yb. Numerical calculations for the ground state shows that the lattice constant dependence of the Yb valence well explains the recent measurement done by systematic substitution of elements of Al and Au in the quasicrystal and AC, where the quasicrystal Yb 15 Al 34 Au 51 is just located at the point from where the Yb-valence starts to change drastically. Our calculation convincingly demonstrates that this is indeed the evidence that this material is just located at the quantum critical point of the Yb-valence transition.

  14. Effects of crystalline electronic field and onsite interorbital interaction in Yb-based quasicrystal and approximant crystal

    NASA Astrophysics Data System (ADS)

    Watanabe, Shinji; Miyake, Kazumasa

    2018-05-01

    To get an insight into a new type of quantum critical phenomena recently discovered in the quasicrystal Yb15Al34Au51 and approximant crystal (AC) Yb14Al35Au51 under pressure, we discuss the property of the crystalline electronic field (CEF) at Yb in the AC and show that uneven CEF levels at each Yb site can appear because of the Al/Au mixed sites. Then we construct the minimal model for the electronic state on the AC by introducing the onsite Coulomb repulsion between the 4f and 5d orbitals at Yb. Numerical calculations for the ground state shows that the lattice constant dependence of the Yb valence well explains the recent measurement done by systematic substitution of elements of Al and Au in the quasicrystal and AC, where the quasicrystal Yb15Al34Au51 is just located at the point from where the Yb-valence starts to change drastically. Our calculation convincingly demonstrates that this is indeed the evidence that this material is just located at the quantum critical point of the Yb-valence transition.

  15. Electron energy-loss spectra in molecular fluorine

    NASA Technical Reports Server (NTRS)

    Nishimura, H.; Cartwright, D. C.; Trajmar, S.

    1979-01-01

    Electron energy-loss spectra in molecular fluorine, for energy losses from 0 to 17.0 eV, have been taken at incident electron energies of 30, 50, and 90 eV and scattering angles from 5 to 140 deg. Features in the spectra above 11.5 eV energy loss agree well with the assignments recently made from optical spectroscopy. Excitations of many of the eleven repulsive valence excited electronic states are observed and their location correlates reasonably well with recent theoretical results. Several of these excitations have been observed for the first time and four features, for which there are no identifications, appear in the spectra.

  16. Positive valence music restores executive control over sustained attention

    PubMed Central

    Lewis, Bridget A.

    2017-01-01

    Music sometimes improves performance in sustained attention tasks. But the type of music employed in previous investigations has varied considerably, which can account for equivocal results. Progress has been hampered by lack of a systematic database of music varying in key characteristics like tempo and valence. The aims of this study were to establish a database of popular music varying along the dimensions of tempo and valence and to examine the impact of music varying along these dimensions on restoring attentional resources following performance of a sustained attention to response task (SART) vigil. Sixty-nine participants rated popular musical selections that varied in valence and tempo to establish a database of four musical types: fast tempo positive valence, fast tempo negative valence, slow tempo positive valence, and slow tempo negative valence. A second group of 89 participants performed two blocks of the SART task interspersed with either no break or a rest break consisting of 1 of the 4 types of music or silence. Presenting positive valence music (particularly of slow tempo) during an intermission between two successive blocks of the SART significantly decreased miss rates relative to negative valence music or silence. Results support an attentional restoration theory of the impact of music on sustained attention, rather than arousal theory and demonstrate a means of restoring sustained attention. Further, the results establish the validity of a music database that will facilitate further investigations of the impact of music on performance. PMID:29145395

  17. Positive valence music restores executive control over sustained attention.

    PubMed

    Baldwin, Carryl L; Lewis, Bridget A

    2017-01-01

    Music sometimes improves performance in sustained attention tasks. But the type of music employed in previous investigations has varied considerably, which can account for equivocal results. Progress has been hampered by lack of a systematic database of music varying in key characteristics like tempo and valence. The aims of this study were to establish a database of popular music varying along the dimensions of tempo and valence and to examine the impact of music varying along these dimensions on restoring attentional resources following performance of a sustained attention to response task (SART) vigil. Sixty-nine participants rated popular musical selections that varied in valence and tempo to establish a database of four musical types: fast tempo positive valence, fast tempo negative valence, slow tempo positive valence, and slow tempo negative valence. A second group of 89 participants performed two blocks of the SART task interspersed with either no break or a rest break consisting of 1 of the 4 types of music or silence. Presenting positive valence music (particularly of slow tempo) during an intermission between two successive blocks of the SART significantly decreased miss rates relative to negative valence music or silence. Results support an attentional restoration theory of the impact of music on sustained attention, rather than arousal theory and demonstrate a means of restoring sustained attention. Further, the results establish the validity of a music database that will facilitate further investigations of the impact of music on performance.

  18. Location of the valence band maximum in the band structure of anisotropic 1 T'-ReSe2

    NASA Astrophysics Data System (ADS)

    Eickholt, P.; Noky, J.; Schwier, E. F.; Shimada, K.; Miyamoto, K.; Okuda, T.; Datzer, C.; Drüppel, M.; Krüger, P.; Rohlfing, M.; Donath, M.

    2018-04-01

    Transition-metal dichalcogenides (TMDCs) are a focus of current research due to their fascinating optical and electronic properties with possible technical applications. ReSe2 is an interesting material of the TMDC family, with unique anisotropic properties originating from its distorted 1 T structure (1 T '). To develop a fundamental understanding of the optical and electric properties, we studied the underlying electronic structure with angle-resolved photoemission (ARPES) as well as band-structure calculations within the density functional theory (DFT)-local density approximation (LDA) and GdW approximations. We identified the Γ ¯M¯1 direction, which is perpendicular to the a axis, as a distinct direction in k space with the smallest bandwidth of the highest valence band. Using photon-energy-dependent ARPES, two valence band maxima are identified within experimental limits of about 50 meV: one at the high-symmetry point Z , and a second one at a non-high-symmetry point in the Brillouin zone. Thus, the position in k space of the global valence band maximum is undecided experimentally. Theoretically, an indirect band gap is predicted on a DFT-LDA level, while quasiparticle corrections lead to a direct band gap at the Z point.

  19. Influence of valence electron concentration on Laves phases: Structures and phase stability of pseudo-binary MgZn 2-xPd x

    DOE PAGES

    Thimmaiah, Srinivasa; Miller, Gordon J.

    2015-06-03

    A series of pseudo-binary compounds MgZn 2-xPd x (0.15 ≤ x ≤ 1.0) were synthesized and structurally characterized to understand the role of valence electron concentration (vec) on the prototype Laves phase MgZn 2 with Pd-substitution. Three distinctive phase regions were observed with respect to Pd content, all exhibiting fundamental Laves phase structures: 0.1 ≤ x ≤ 0.3 (MgNi 2-type, hP24; MgZn 1.80Pd 0.20(2)), 0.4 ≤ x ≤ 0.6 (MgCu 2-type, cF24; MgZn 1.59Pd 0.41(2)), and 0.62 ≤ x ≤ 0.8 (MgZn 2-type, hP12: MgZn 1.37Pd 0.63(2)). Refinements from single-crystal X-ray diffraction indicated nearly statistical distributions of Pd and Znmore » atoms among the majority atom sites in these structures. Interestingly, the MgZn 2-type structure re-emerges in MgZn 2–xPd x at x ≈ 0.7 with the refined composition MgZn 1.37(2)Pd 0.63 and a c/a ratio of 1.59 compared to 1.64 for binary MgZn 2. Electronic structure calculations on a model “MgZn 1.25Pd 0.75” yielded a density of states (DOS) curve showing enhancement of a pseudogap at the Fermi level as a result of electronic stabilization due to the Pd addition. Moreover, integrated crystal orbital Hamilton population values show significant increases of orbital interactions for (Zn,Pd)–(Zn,Pd) atom pairs within the majority atom substructure, i.e., within the Kagomé nets as well as between a Kagomé net and an apical site, from binary MgZn 2 to the ternary “MgZn 1.25Pd 0.75”. Multi-centered bonding is evident from electron localization function plots for “MgZn 1.25Pd 0.75”, an outcome which is in accordance with analysis of other Laves phases.« less

  20. First-principle simulations of electronic structure in semicrystalline polyethylene

    NASA Astrophysics Data System (ADS)

    Moyassari, A.; Unge, M.; Hedenqvist, M. S.; Gedde, U. W.; Nilsson, F.

    2017-05-01

    In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed. The modeled PE had a structure in agreement with established experimental data. Linear-scaling density functional theory (LS-DFT) was used to examine the electronic structure (e.g., spatial distribution of molecular orbitals, bandgaps and mobility edges) on all the materials, whereas conventional DFT was used to validate the LS-DFT results on small systems. When hybrid functionals were used, the simulated bandgaps were close to the experimental values. The localization of valence and conduction band states was demonstrated. The localized states in the conduction band were primarily found in the free volume (result of gauche conformations) present in the amorphous regions. For branched and crosslinked structures, the localized electronic states closest to the valence band edge were positioned at branches and crosslinks, respectively. At 0 K, the activation energy for transport was lower for holes than for electrons. However, at room temperature, the effective activation energy was very low (˜0.1 eV) for both holes and electrons, which indicates that the mobility will be relatively high even below the mobility edges and suggests that charge carriers can be hot carriers above the mobility edges in the presence of a high electrical field.

  1. Singular Valence Fluctuations at a Kondo Destroyed Quantum Critical Point

    NASA Astrophysics Data System (ADS)

    Pixley, Jedediah; Kirchner, Stefan; Ingersent, Kevin; Si, Qimiao

    2012-02-01

    Recent experiments on the heavy fermion superconductor beta-YbAlB4 have indicated that this compound satisfies quantum critical scaling [1]. Motivated by the observation of mixed valency in this material [2], we study the Kondo destruction physics in the mixed-valence regime [3] of a particle-hole asymmetric Anderson impurity model with a pseudogapped density of states. In the vicinity of the quantum critical point we determine the finite temperature spin and charge susceptibilities by utilizing a continuous time quantum Monte Carlo method [4] and the numerical renormalization group. We show that this mixed-valence quantum critical point displays a Kondo breakdown effect. Furthermore, we find that both dynamic spin and charge susceptibilities obey frequency over temperature scaling, and that the static charge susceptibility diverges with a universal exponent. Possible implications of our results for beta-YbAlB4 are discussed. [1] Matsumoto et al, Science 331, 316 (2011). [2] Okawaet al, Physical Review Letters 104, 247201 (2010). [3] J. H. Pixley, S. Kirchner, Kevin Ingersent and Q. Si, arXiv:1108.5227v1 (2011). [4] M. Glossop, S. Kirchner, J. H. Pixley and Q. Si, Phys. Rev. Lett. 107, 076404 (2011).

  2. The Full Story of the Electron Configurations of the Transition Elements

    ERIC Educational Resources Information Center

    Schwarz, W. H. Eugen

    2010-01-01

    The dominant electronic valence configurations of atoms in chemical substances of a transition element of group "G" in period "n" is ("n" - 1)d[superscript "G"]"n"s[superscript 0]. Transition-metal chemistry is d orbital chemistry. In contrast, the ground states of free, unbound atoms derive, in most cases, from configurations ("n" -…

  3. Exact valence bond entanglement entropy and probability distribution in the XXX spin chain and the potts model.

    PubMed

    Jacobsen, J L; Saleur, H

    2008-02-29

    We determine exactly the probability distribution of the number N_(c) of valence bonds connecting a subsystem of length L>1 to the rest of the system in the ground state of the XXX antiferromagnetic spin chain. This provides, in particular, the asymptotic behavior of the valence-bond entanglement entropy S_(VB)=N_(c)ln2=4ln2/pi(2)lnL disproving a recent conjecture that this should be related with the von Neumann entropy, and thus equal to 1/3lnL. Our results generalize to the Q-state Potts model.

  4. Architectural Representation of Valence in the Limbic System

    PubMed Central

    Namburi, Praneeth; Al-Hasani, Ream; Calhoon, Gwendolyn G; Bruchas, Michael R; Tye, Kay M

    2016-01-01

    In order to thrive, animals must be able to recognize aversive and appetitive stimuli within the environment and subsequently initiate appropriate behavioral responses. This assignment of positive or negative valence to a stimulus is a key feature of emotional processing, the neural substrates of which have been a topic of study for several decades. Until recently, the result of this work has been the identification of specific brain regions, such as the basolateral amygdala (BLA) and nucleus accumbens (NAc), as important to valence encoding. The advent of modern tools in neuroscience has allowed further dissection of these regions to identify specific populations of neurons signaling the valence of environmental stimuli. In this review, we focus upon recent work examining the mechanisms of valence encoding, and provide a model for the systematic investigation of valence within anatomically-, genetically-, and functionally defined populations of neurons. PMID:26647973

  5. First principle study of electronic structures and optical properties of Ce-doped SiO2

    NASA Astrophysics Data System (ADS)

    Cong, Wei-Yan; Lu, Ying-Bo; Zhang, Peng; Guan, Cheng-Bo

    2018-05-01

    Electronic structures and optical properties of Silicon dioxide (SiO2) systems with and without cerium(Ce) dopant were calculated using the density functional theory. We find that after the Ce incorporation, a new localized impurity band appears between the valance band maximum (VBM) and the conduction band minimum (CBM) of SiO2 system, which is induced mainly by the Ce-4f orbitals. The localized impurity band constructs a bridge between the valence band and the conduction band, making the electronic transition much easier. The calculated optical properties show that in contrast from the pure SiO2 sample, absorption in the visible-light region is found in Ce-doped SiO2 system, which originates from the transition between the valence band and Ce-4f dominated impurity band, as well as the electronic transition from Ce-4f states to Ce-5d states. All calculated results indicate that Ce doping is an effective strategy to improve the optical performance of SiO2 sample, which is in agreement with the experimental results.

  6. Pressure dependence of Ce valence in CeRhIn 5

    DOE PAGES

    Brubaker, Z. E.; Stillwell, R. L.; Chow, P.; ...

    2017-12-14

    We have studied the Ce valence as a function of pressure in CeRhIn5 at 300 K and at 22 K using x-ray absorption spectroscopy in partial fluorescent yield mode. At room temperature, we found no detectable change in Ce valence greater than 0.01 up to a pressure of 5.5 GPa. At 22 K, the valence remains robust against pressure below 6 GPa, in contrast to the predicted valence crossover at P = 2.35 GPa. In conclusion, this work yields an upper limit for the change in Ce-valence and suggests that the critical valence fluctuation scenario, in its current form, ismore » unlikely.« less

  7. Difference between resistance degradation of fixed valence acceptor (Mg) and variable valence acceptor (Mn)-doped BaTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Yoon, Seok-Hyun; Randall, Clive A.; Hur, Kang-Heon

    2010-09-01

    The difference in the resistance degradation behavior was investigated between fixed valence acceptor (Mg) and the variable valence acceptor (Mn)-doped BaTiO3 ceramics with an increase of each acceptor concentration. Coarse-grained specimens with uniform grain sizes and different acceptor concentrations were prepared. In the case of Mg-doped BaTiO3, the time to degradation systematically decreased with the increase in Mg concentration. In contrast, there is a systematically increased time to degradation with the increase in Mn concentration in Mn-doped BaTiO3. The fast degradation by the increase in Mg concentration directly corresponded to an increase in the Warburg impedance and ionic transference number (tion) associated with an increase in oxygen vacancy concentration ([VO••]). On the other hand, no distinct Warburg impedance or ionic conduction contribution could be observed with the increase in Mn concentration. It is supposed that the increase in [VO••] is negligible in spite of the increase in acceptor Mn concentration, when it is compared to Mg-doped BaTiO3. The much lower [VO••] and more dominant electron/hole trapping effect due to multivalence nature of Mn are supposed to cause such a contrary degradation behavior between Mg and Mn-doped BaTiO3. Reoxidation in a slightly reducing atmosphere (N2) showed better resistance to degradation behavior than in a oxidizing air atmosphere in both Mg and Mn-doped BaTiO3, which is anticipated to be an increase in the electron/hole trapping sites. All these behaviors could be explained by the low temperature defect chemical model that shows difference in the defect structure between Mg and Mn-doped BaTiO3, and its dependence on the oxygen partial pressure (pO2) during reoxidation and cooling. Not only the [VO••], but also the density of electron/hole trap sites, are believed to be crucial in controlling resistance degradation.

  8. Social learning modulates the lateralization of emotional valence.

    PubMed

    Shamay-Tsoory, Simone G; Lavidor, Michal; Aharon-Peretz, Judith

    2008-08-01

    Although neuropsychological studies of lateralization of emotion have emphasized valence (positive vs. negative) or type (basic vs. complex) dimensions, the interaction between the two dimensions has yet to be elucidated. The purpose of the current study was to test the hypothesis that recognition of basic emotions is processed preferentially by the right prefrontal cortex (PFC), whereas recognition of complex social emotions is processed preferentially by the left PFC. Experiment 1 assessed the ability of healthy controls and patients with right and left PFC lesions to recognize basic and complex emotions. Experiment 2 modeled the patient's data of Experiment 1 on healthy participants under lateralized displays of the emotional stimuli. Both experiments support the Type as well as the Valence Hypotheses. However, our findings indicate that the Valence Hypothesis holds for basic but less so for complex emotions. It is suggested that, since social learning overrules the basic preference of valence in the hemispheres, the processing of complex emotions in the hemispheres is less affected by valence.

  9. Affective valence signals agency within and between individuals.

    PubMed

    Chang, Yen-Ping; Algoe, Sara B; Chen, Lung Hung

    2017-03-01

    Affective valence is a core component of all emotional experiences. Building on recent evidence and theory, we reason that valence informs individuals about their agency-the mental capability of doing and intending. Expressed affect may also lead to perceptions of agency by others. Supporting the hypothesis that valence influences self- and other-perception of agency, across 5 studies, we showed that participants perceived more agency in themselves in positive versus neutral and negative personal (Study 1) and interpersonal (Study 2) events. Participants also perceived more agency in fictional characters showing positive versus negative affect, regardless of how acceptable the characters' behavior was (Studies 3 and 4). Finally, we had participants personify 24 specific emotions across the valence dimension, and found that the more positive and less negative an emotion was, the more agency participants ascribed to the "person" (Study 5). We discuss the results in terms of how valence may help with human self- and social regulation. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

  10. MgH Rydberg series: Transition energies from electron propagator theory and oscillator strengths from the molecular quantum defect orbital method

    NASA Astrophysics Data System (ADS)

    Corzo, H. H.; Velasco, A. M.; Lavín, C.; Ortiz, J. V.

    2018-02-01

    Vertical excitation energies belonging to several Rydberg series of MgH have been inferred from 3+ electron-propagator calculations of the electron affinities of MgH+ and are in close agreement with experiment. Many electronically excited states with n > 3 are reported for the first time and new insight is given on the assignment of several Rydberg series. Valence and Rydberg excited states of MgH are distinguished respectively by high and low pole strengths corresponding to Dyson orbitals of electron attachment to the cation. By applying the Molecular Quantum Defect Orbital method, oscillator strengths for electronic transitions involving Rydberg states also have been determined.

  11. The influence of coordination geometry and valency on the K-edge absorption near edge spectra of selected chromium compounds

    NASA Astrophysics Data System (ADS)

    Pantelouris, A.; Modrow, H.; Pantelouris, M.; Hormes, J.; Reinen, D.

    2004-05-01

    X-ray absorption spectra at the chromium K-edge are reported for a number of selected chromium compounds of known chemical structure. The spectra were obtained with use of synchrotron radiation available at the ELectron Stretcher Accelerator ELSA in Bonn. The compounds studied include the tetrahedrally coordinated compounds Ca 2Ge 0.8Cr 0.2O 4, Ba 2Ge 0.1Cr 0.9O 4, Sr 2CrO 4, Ca 2(PO 4) x(CrO 4) 1- xCl ( x=0.25,0.5), Ca 5(CrO 4) 3Cl, CrO 3, the octahedrally coordinated compounds Cr(II)-acetate, CrCl 3, CrF 3, Cr 2O 3, KCr(SO 4) 2 · 12H 2O, CrO 2 and cubic coordinated metallic chromium. In these compounds chromium exhibits a wide range of formal oxidation states (0 to VI). The absorption features in the near edge region are shown to be characteristic of the spatial environment of the absorbing atom. The occurrence of a single pre-edge line easily allows one to distinguish between tetrahedral and octahedral coordination geometry, whereas the energy position of the absorption edge is found to be very sensitive to the valency of the excited chromium atom. Calculations of the ionisation potential of Cr in different oxidation states using the non-relativistic Hartree-Fock method (Froese-Fischer) confirm that the ionisation limit shifts to higher energy with increasing Cr valency. More detailed information on the electronic structure of the different compounds is gained by real-space full multiple scattering calculations using the FEFF8 code.

  12. Thermoelectric power as a probe of density of states in correlated actinide materials: The case of PuCoGa 5 superconductor

    DOE PAGES

    Gofryk, K.; Griveau, J. -C.; Riseborough, P. S.; ...

    2016-11-09

    We present measurements of the thermoelectric power of the plutonium-based unconventional superconductor PuCoGa 5. The data is interpreted within a phenomenological model for the quasiparticle density of states of intermediate valence systems and the results are compared with results obtained from photoemission spectroscopy. The results are consistent with intermediate valence nature of 5f-electrons, furthermore, we propose that measurements of the Seebeck coefficient can be used as a probe of density of states in this material, thereby providing a link between transport measurements and photoemission in strongly correlated materials. Here, we discuss these results and their implications for the electronic structuremore » determination of other strongly correlated systems, especially nuclear materials.« less

  13. Photoemission and Photoabsorption Investigation of the Electronic Structure of Ytterbium Doped Strontium Fluoroapatite

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

    Nelson, A J; van Buuren, T; Bostedt, C

    X-ray photoemission and x-ray photoabsorption were used to study the composition and the electronic structure of ytterbium doped strontium fluoroapatite (Yb:S-FAP). High resolution photoemission measurements on the valence band electronic structure was used to evaluate the density of occupied states of this fluoroapatite. Element specific density of unoccupied electronic states in Yb:S-FAP were probed by x-ray absorption spectroscopy (XAS) at the Yb 4d (N{sub 4,5}-edge), Sr 3d (M{sub 4,5}-edge), P 2p (L{sub 2,3}-edge), F 1s and O 1s (K-edges) absorption edges. These results provide the first measurements of the electronic structure and surface chemistry of this material.

  14. Polarization Dependent Bulk-sensitive Valence Band Photoemission Spectroscopy and Density Functional Theory Calculations: Part I. 3d Transition Metals

    NASA Astrophysics Data System (ADS)

    Ueda, Shigenori; Hamada, Ikutaro

    2017-12-01

    The X-ray polarization dependent valence band HAXPES spectra of 3d transition metals (TMs) of Ti-Zn were measured to investigate the orbital resolved electronic structures by utilizing that the fact the photoionization cross-section of the atomic orbitals strongly depends on the experimental geometry. We have calculated the HAXPES spectra, which correspond to the cross-section weighted densities of states (CSW-DOSs), where the DOSs were obtained by the density functional theory calculations, and we have determined the relative photoionization cross-sections of the 4s and 4p orbitals to the 3d orbital in the 3d TMs. The experimentally obtained bulk-sensitive 3d and 4s DOSs were good agreement with the calculated DOSs in Ti, V, Cr, and Cu. In contrast, the deviations between the experimental and calculated 3d DOSs for Mn, Fe, Co, Ni were found, suggesting that the electron correlation plays an important role in the electronic structures for these materials.

  15. Electronic structure of ZrX2 (X = Se, Te)

    NASA Astrophysics Data System (ADS)

    Shkvarin, A. S.; Merentsov, A. I.; Shkvarina, E. G.; Yarmoshenko, Yu. M.; Píš, I.; Nappini, S.; Titov, A. N.

    2018-03-01

    The electronic structure of the ZrX2 (X = Se, Te) compounds has been studied using photoelectron, resonant photoelectron and X-ray absorption spectroscopy, theoretical calculations of the X-ray absorption spectra, and density of electronic states. It was found that the absorption spectra and valence band spectra are influenced by the chalcogen type. The results of the multiplet calculation of the Zr4+ atom show that the change in the splitting in the crystal field, which is described by the 10Dq parameter, is due to the change in the ratio of covalent and ionic contributions to the chemical bond. The resonance band near the Fermi level in the valence band spectra is observed for ZrTe2 in the Zr 3p-4d resonant excitation mode. The extent of photon energy indicates the charge localization on the Zr atom. Similar resonance band for ZrSe2 is absent; it indicates the presence of a gap at the Fermi level.

  16. Site-specific intermolecular valence-band dispersion in α-phase crystalline films of cobalt phthalocyanine studied by angle-resolved photoemission spectroscopy

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

    Yamane, Hiroyuki; Kosugi, Nobuhiro; The Graduate University for Advanced Studies, Okazaki 444-8585

    2014-12-14

    The valence band structure of α-phase crystalline films of cobalt phthalocyanine (CoPc) grown on Au(111) is investigated by using angle-resolved photoemission spectroscopy (ARPES) with synchrotron radiation. The photo-induced change in the ARPES peaks is noticed in shape and energy of the highest occupied molecular orbital (HOMO, C 2p) and HOMO-1 (Co 3d) of CoPc, and is misleading the interpretation of the electronic properties of CoPc films. From the damage-free normal-emission ARPES measurement, the clear valence-band dispersion has been first observed, showing that orbital-specific behaviors are attributable to the interplay of the intermolecular π-π and π-d interactions. The HOMO band dispersionmore » of 0.1 eV gives the lower limit of the hole mobility for α-CoPc of 28.9 cm{sup 2} V{sup −1} s{sup −1} at 15 K. The non-dispersive character of the split HOMO-1 bands indicates that the localization of the spin state is a possible origin of the antiferromagnetism.« less

  17. The localized effect of the Bi level on the valence band in the dilute bismuth GaBixAs1-x alloy

    NASA Astrophysics Data System (ADS)

    Zhao, Chuan-Zhen; Zhu, Min-Min; Wang, Jun; Wang, Sha-Sha; Lu, Ke-Qing

    2018-05-01

    The research on the temperature dependence of the band gap energy of the dilute bismuth GaBixAs1-x alloy has been done. It is found that its temperature insensitiveness is due to the enhanced localized character of the valence band state and the small decrease of the temperature coefficient for the conduction band minimum (CBM). The enhanced localized character of the valence band state is the main factor. In order to describe the localized effect of the Bi levels on the valence band, the localized energy is introduced into the Varshni's equation. It is found that the effect of the localized Bi level on the valence band becomes strong with increasing Bi content. In addition, it is found that the pressure dependence of the band gap energy of GaBixAs1-x does not seem to be influenced by the localized Bi levels. It is due to two factors. One is that the pressure dependence of the band gap energy is mainly determined by the D CBM of GaBixAs1-x. The D CBM of GaBixAs1-x is not influenced by the localized Bi levels. The other is that the small variation of the pressure coefficient for the D valence band maximum (VBM) state of GaBixAs1-x can be cancelled by the variation of the pressure coefficient for the D CBM state of GaBixAs1-x.

  18. Theoretical studies of electronically excited states

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

    Besley, Nicholas A.

    2014-10-06

    Time-dependent density functional theory is the most widely used quantum chemical method for studying molecules in electronically excited states. However, excited states can also be computed within Kohn-Sham density functional theory by exploiting methods that converge the self-consistent field equations to give excited state solutions. The usefulness of single reference self-consistent field based approaches for studying excited states is demonstrated by considering the calculation of several types of spectroscopy including the infrared spectroscopy of molecules in an electronically excited state, the rovibrational spectrum of the NO-Ar complex, core electron binding energies and the emission spectroscopy of BODIPY in water.

  19. Structural and magnetic characterization of mixed valence Co(II, III)xZn1-xO epitaxial thin films

    NASA Astrophysics Data System (ADS)

    Negi, D. S.; Loukya, B.; Dileep, K.; Sahu, R.; Shetty, S.; Kumar, N.; Ghatak, J.; Pachauri, N.; Gupta, A.; Datta, R.

    2014-03-01

    In this article, we report on the Co atom incorporation, secondary phase formation and composition-dependent magnetic and optical properties of mixed valence Co(II, III)xZn1-xO epitaxial thin films grown by pulsed laser deposition. The intended total Co concentration is varied between ~6-60 at.% with relatively higher concentration of +3 over +2 charge state. Mixed valence Co(II, III) shows high solubility in ZnO (up to 38 at.%) and ferromagnetism is observed in samples with total Co incorporation of ~29 and 38 at.%. Electron diffraction pattern and high resolution transmission electron microscopy images reveal single crystalline nature of the thin films with wurtzite structure. Co oxide interlayer, with both rock salt and spinel structure, are observed to be formed between the substrate and wurtzite film for total Co concentration at ~17 at.% and above. Magnetization shows composition dependence with a saturation moment value of ~93 emu cm-3 and a coercive field of ~285 Oe observed for ~38 at.% Co:ZnO films. Ferromagnetism was not observed for films with Co concentration 17 and 9 at.%. The Co oxide interlayer does not show any ferromagnetism. All the films are n-type with carrier concentration ~1019 cm-3. The observed magnetism is probably resulting from direct antiferromagntic exchange interaction between Co2+ and Co3+ ions favored by heavy Co alloying giving rise to ferrimagnetism in the system.

  20. Taboo, emotionally valenced, and emotionally neutral word norms.

    PubMed

    Janschewitz, Kristin

    2008-11-01

    Although taboo words are used to study emotional memory and attention, no easily accessible normative data are available that compare taboo, emotionally valenced, and emotionally neutral words on the same scales. Frequency, inappropriateness, valence, arousal, and imageability ratings for taboo, emotionally valenced, and emotionally neutral words were made by 78 native-English-speaking college students from a large metropolitan university. The valenced set comprised both positive and negative words, and the emotionally neutral set comprised category-related and category-unrelated words. To account for influences of demand characteristics and personality factors on the ratings, frequency and inappropriateness measures were decomposed into raters' personal reactions to the words versus raters' perceptions of societal reactions to the words (personal use vs. familiarity and offensiveness vs. tabooness, respectively). Although all word sets were rated higher in familiarity and tabooness than in personal use and offensiveness, these differences were most pronounced for the taboo set. In terms of valence, the taboo set was most similar to the negative set, although it yielded higher arousal ratings than did either valenced set. Imageability for the taboo set was comparable to that of both valenced sets. The ratings of each word are presented for all participants as well as for single-sex groups. The inadequacies of the application of normative data to research that uses emotional words and the conceptualization of taboo words as a coherent category are discussed. Materials associated with this article may be accessed at the Psychonomic Society's Archive of Norms, Stimuli, and Data, www.psychonomic.org/archive.

  1. NiMn layered double hydroxide nanosheets/NiCo2O4 nanowires with surface rich high valence state metal oxide as an efficient electrocatalyst for oxygen evolution reaction

    NASA Astrophysics Data System (ADS)

    Yang, Liting; Chen, Lin; Yang, Dawen; Yu, Xu; Xue, Huaiguo; Feng, Ligang

    2018-07-01

    High valence transition metal oxide is significant for anode catalyst of proton membrane water electrolysis technique. Herein, we demonstrate NiMn layered double hydroxide nanosheets/NiCo2O4 nanowires hierarchical nanocomposite catalyst with surface rich high valence metal oxide as an efficient catalyst for oxygen evolution reaction. A low overpotential of 310 mV is needed to drive a 10 mA cm-2 with a Tafel slope of 99 mV dec-1, and a remarkable stability during 8 h is demonstrated in a chronoamperometry test. Theoretical calculation displays the change in the rate-determining step on the nanocomposite electrode in comparison to NiCo2O4 nanowires alone. It is found high valence Ni and Mn oxide in the catalyst system can efficiently facilitate the charge transport across the electrode/electrolyte interface. The enhanced electrical conductivity, more accessible active sites and synergistic effects between NiMn layered double hydroxide nanosheets and NiCo2O4 nanowires can account for the excellent oxygen evolution reaction. The catalytic performance is comparable to most of the best non-noble catalysts and IrO2 noble catalyst, indicating the promising applications in water-splitting technology. It is an important step in the development of hierarchical nanocomposites by surface valence state tuning as an alternative to noble metals for oxygen evolution reaction.

  2. Neural mechanisms underlying valence inferences to sound: The role of the right angular gyrus.

    PubMed

    Bravo, Fernando; Cross, Ian; Hawkins, Sarah; Gonzalez, Nadia; Docampo, Jorge; Bruno, Claudio; Stamatakis, Emmanuel Andreas

    2017-07-28

    We frequently infer others' intentions based on non-verbal auditory cues. Although the brain underpinnings of social cognition have been extensively studied, no empirical work has yet examined the impact of musical structure manipulation on the neural processing of emotional valence during mental state inferences. We used a novel sound-based theory-of-mind paradigm in which participants categorized stimuli of different sensory dissonance level in terms of positive/negative valence. Whilst consistent with previous studies which propose facilitated encoding of consonances, our results demonstrated that distinct levels of consonance/dissonance elicited differential influences on the right angular gyrus, an area implicated in mental state attribution and attention reorienting processes. Functional and effective connectivity analyses further showed that consonances modulated a specific inhibitory interaction from associative memory to mental state attribution substrates. Following evidence suggesting that individuals with autism may process social affective cues differently, we assessed the relationship between participants' task performance and self-reported autistic traits in clinically typical adults. Higher scores on the social cognition scales of the AQ were associated with deficits in recognising positive valence in consonant sound cues. These findings are discussed with respect to Bayesian perspectives on autistic perception, which highlight a functional failure to optimize precision in relation to prior beliefs. Copyright © 2017 Elsevier Ltd. All rights reserved.

  3. Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Addition of Hydrogen Atoms.

    PubMed

    Lindquist, Beth A; Takeshita, Tyler Y; Dunning, Thom H

    2016-05-05

    Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species.

  4. Ultrafast Charge Transfer of a Valence Double Hole in Glycine Driven Exclusively by Nuclear Motion

    NASA Astrophysics Data System (ADS)

    Li, Zheng; Vendrell, Oriol; Santra, Robin

    2015-10-01

    We explore theoretically the ultrafast transfer of a double electron hole between the functional groups of glycine after K -shell ionization and subsequent Auger decay. Although a large energy gap of about 15 eV initially exists between the two electronic states involved and coherent electronic dynamics play no role in the hole transfer, we find that the double hole is transferred within 3 to 4 fs between both functional ends of the glycine molecule driven solely by specific nuclear displacements and non-Born-Oppenheimer effects. The nuclear displacements along specific vibrational modes are of the order of 15% of a typical chemical bond between carbon, oxygen, and nitrogen atoms and about 30% for bonds involving hydrogen atoms. The time required for the hole transfer corresponds to less than half a vibrational period of the involved nuclear modes. This finding challenges the common wisdom that nuclear dynamics of the molecular skeleton are unimportant for charge transfer processes at the few-femtosecond time scale and shows that they can even play a prominent role. It also indicates that in x-ray imaging experiments, in which ionization is unavoidable, valence electron redistribution caused by nuclear dynamics might be much faster than previously anticipated. Thus, non-Born-Oppenheimer effects may affect the apparent electron densities extracted from such measurements.

  5. Ultrafast Charge Transfer of a Valence Double Hole in Glycine Driven Exclusively by Nuclear Motion.

    PubMed

    Li, Zheng; Vendrell, Oriol; Santra, Robin

    2015-10-02

    We explore theoretically the ultrafast transfer of a double electron hole between the functional groups of glycine after K-shell ionization and subsequent Auger decay. Although a large energy gap of about 15 eV initially exists between the two electronic states involved and coherent electronic dynamics play no role in the hole transfer, we find that the double hole is transferred within 3 to 4 fs between both functional ends of the glycine molecule driven solely by specific nuclear displacements and non-Born-Oppenheimer effects. The nuclear displacements along specific vibrational modes are of the order of 15% of a typical chemical bond between carbon, oxygen, and nitrogen atoms and about 30% for bonds involving hydrogen atoms. The time required for the hole transfer corresponds to less than half a vibrational period of the involved nuclear modes. This finding challenges the common wisdom that nuclear dynamics of the molecular skeleton are unimportant for charge transfer processes at the few-femtosecond time scale and shows that they can even play a prominent role. It also indicates that in x-ray imaging experiments, in which ionization is unavoidable, valence electron redistribution caused by nuclear dynamics might be much faster than previously anticipated. Thus, non-Born-Oppenheimer effects may affect the apparent electron densities extracted from such measurements.

  6. Stabilization of very rare tautomers of 1-methylcytosine by an excess electron.

    PubMed

    Harańczyk, Maciej; Rak, Janusz; Gutowski, Maciej

    2005-12-22

    We characterized valence anionic states of 1-methylcytosine using various electronic structure methods. We found that the most stable valence anion is related to neither the canonical amino-oxo nor a rare imino-oxo tautomer, in which a proton is transferred from the N4 to N3 atom. Instead, it is related to an imino-oxo tautomer, in which the C5 atom is protonated. This anion is characterized by an electron vertical detachment energy (VDE) of 2.12 eV and it is more stable than the anion based on the canonical tautomer by 1.0 kcal/mol. The latter is characterized by a VDE of 0.31 eV. Another unusual low-lying imino-oxo tautomer with a VDE of 3.60 eV has the C6 atom protonated and is 3.6 kcal/mol less stable than the anion of the canonical tautomer. All these anionic states are adiabatically unbound with respect to the canonical amino-oxo neutral, with the instability of 5.8 kcal/mol for the most stable valence anion. The mechanism of formation of anionic tautomers with carbon atoms protonated may involve intermolecular proton transfer or dissociative electron attachment to the canonical neutral tautomer followed by a barrier-free attachment of a hydrogen atom to the C5 or C6 atom. The six-member ring structure of anionic tautomers with carbon atoms protonated is unstable upon an excess electron detachment. Indeed the neutral systems collapse without a barrier to a linear or a bicyclo structure, which might be viewed as lesions to DNA or RNA. Within the PCM hydration model, the anions become adiabatically bound with respect to the corresponding neutrals, and the two most stable tautomers have a carbon atom protonated.

  7. Nature of the magnetic ground state in the mixed valence compound CeRuSn: a single-crystal study.

    PubMed

    Fikáček, J; Prokleška, J; Prchal, J; Custers, J; Sechovský, V

    2013-10-16

    We report on detailed low-temperature measurements of the magnetization, the specific heat and the electrical resistivity on high-quality CeRuSn single crystals. The compound orders antiferromagnetically at T(N) = 2.8 K with the Ce(3+) ions locked within the a-c plane of the monoclinic structure. Magnetization shows that below T(N) CeRuSn undergoes a metamagnetic transition when applying a magnetic field of 1.5 and 0.8 T along the a- and c-axis, respectively. This transition manifests in a tremendous negative jump of ~25% in the magnetoresistance. The value of the saturated magnetization along the easy magnetization direction (c-axis) and the magnetic entropy above T(N) derived from specific heat data correspond to the scenario of only one third of the Ce ions in the compound being trivalent and carrying a stable Ce(3+) magnetic moment, whereas the other two thirds of the Ce ions are in a nonmagnetic tetravalent and/or mixed valence state. This is consistent with the low-temperature CeRuSn crystal structure i.e., a superstructure consisting of three unit cells of the CeCoAl type piled up along the c-axis, and in which the Ce(3+) ions are characterized by large distances from the Ru ligands while the Ce-Ru distances of the other Ce ions are much shorter causing a strong 4f-ligand hybridization and hence leading to tetravalent and/or mixed valence Ce ions.

  8. Effects of Emotional Valence and Arousal on Time Perception

    PubMed Central

    Van Volkinburg, Heather; Balsam, Peter

    2016-01-01

    We examined the influence of emotional arousal and valence on estimating time intervals. A reproduction task was used in which images from the International Affective Picture System served as the stimuli to be timed. Experiment 1 assessed the effects of positive and negative valence at a moderate arousal level and Experiment 2 replicated Experiment 1 with the addition of a high arousal condition. Overestimation increased as a function of arousal during encoding of times regardless of valence. For images presented during reproduction, overestimation occurred at the moderate arousal level for positive and negative valence but underestimation occurred in the negative valence high arousal condition. The overestimation of time intervals produced by emotional arousal during encoding and during reproduction suggests that emotional stimuli affect temporal information processing in a qualitatively different way during different phases of temporal information processing. PMID:27110491

  9. Bistable mixed-valence molecular architectures for bit storage

    NASA Astrophysics Data System (ADS)

    Guihery, Nathalie; Durand, Gérard; Lepetit, Marie-Bernadette

    1994-05-01

    The work examines the possible realization of bit storage at the molecular scale using mixed valence compounds i.e. the existence of two stable and degenerate forms associated with the 0 and 1 positions of the bit. The proposed systems are constituted of two donors (D) and acceptor (A), or one donor and two acceptors, juxtaposed in DAD or ADA architectures. Our proposals take advantage of the possibility of donor—acceptor complexes to exhibit either complete or partial charge transfer. The first system we propose has an essentially neutral ground state. However, the potential energy surface (PES) presents two degenerated minima associated with a partial charge transfer between the donor and one of the two acceptor molecules (A δ-D δ+1 A and AD δ+ A δ-). Systems presenting a complete charge transfer give rise to two stable, weakly coupled, and degenerate ionic electronic states, A - A + A and AD + A - for an ADA architecture and D + A -D and DA -D + for a DAD In these cases, the two forms differ by both their intramolecular geometries and the relative positions of their constituents. It seems rather difficult to conceive such bistable molecular systems using closed-shell molecules, while a donor radical and a closed-shell acceptor or an acceptor radical and closed-shell donor can generate very stable ionic states. It is assumed that the relative positions of the donor and acceptor molecules can be fixed using chemical bridges constituted of rigid or flexible ligands. The writing and reading processes are discussed for each system as well as the information stability when a large number of bits are juxtaposed on a surface.

  10. Electronic Structure of Small Lanthanide Containing Molecules

    NASA Astrophysics Data System (ADS)

    Kafader, Jared O.; Ray, Manisha; Topolski, Josey E.; Chick Jarrold, Caroline

    2016-06-01

    Lanthanide-based materials have unusual electronic properties because of the high number of electronic degrees of freedom arising from partial occupation of 4f orbitals, which make these materials optimal for their utilization in many applications including electronics and catalysis. Electronic spectroscopy of small lanthanide molecules helps us understand the role of these 4f electrons, which are generally considered core-like because of orbital contraction, but are energetically similar to valence electrons. The spectroscopy of small lanthanide-containing molecules is relatively unexplored and to broaden this understanding we have completed the characterization of small cerium, praseodymium, and europium molecules using photoelectron spectroscopy coupled with DFT calculations. The characterization of PrO, EuH, EuO/EuOH, and CexOy molecules have allowed for the determination of their electron affinity, the assignment of numerous anion to neutral state transitions, modeling of anion/neutral structures and electron orbital occupation.

  11. Measurement of the low energy spectral contribution in coincidence with valence band (VB) energy levels of Ag(100) using VB-VB coincidence spectroscopy

    NASA Astrophysics Data System (ADS)

    Gladen, R. W.; Joglekar, P. V.; Lim, Z. H.; Shastry, K.; Hulbert, S. L.; Weiss, A. H.

    A set of coincidence measurements were obtained for the study and measurement of the electron contribution arising from the inter-valence band (VB) transitions along with the inelastically scattered VB electron contribution. These Auger-unrelated contributions arise in the Auger spectrum (Ag 4p NVV) obtained using Auger Photoelectron Coincidence Spectroscopy (APECS). The measured Auger-unrelated contribution can be eliminated from Auger spectrum to obtain the spectrum related to Auger. In our VB-VB coincidence measurement, a photon beam of energy 180eV was used to probe the Ag(100) sample. The coincidence spectrum was obtained using two Cylindrical Mirror Analyzers (CMA's). The scan CMA measured the low energy electron contribution in the energy range 0-70eV in coincidence with VB electrons measured by the fixed CMA. In this talk, we present the data obtained for VB-VB coincidence at the valence band energy of 171eV along with the coincidence measurements in the energy range of 4p core and valence band. NSF DMR 0907679, NSF Award Number: 1213727. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, under Contract No. DEAC02-98CH10886.

  12. Measurement of the low energy spectral contribution in coincidence with valence band (VB) energy levels of Ag(100) using VB-VB coincidence spectroscopy

    NASA Astrophysics Data System (ADS)

    Joglekar, P. V.; Gladen, R.; Lim, Z. H.; Shastry, K.; Hulbert, S. L.; Weiss, A. H.

    2015-03-01

    A set of coincidence measurements were obtained for the study and measurement of the electron contribution arising from the inter-valence band (VB) transitions along with the inelastically scattered VB electron contribution. These Auger-unrelated contributions arise in the Auger spectrum (Ag 4p NVV) obtained using Auger Photoelectron Coincidence Spectroscopy (APECS). The measured Auger-unrelated contribution can be eliminated from Auger spectrum to obtain the spectrum related to Auger. In our VB-VB coincidence measurement, a photon beam of energy 180eV was used to probe the Ag(100) sample. The coincidence spectrum was obtained using two Cylindrical Mirror Analyzers (CMA's). The scan CMA measured the low energy electron contribution in the energy range 0-70eV in coincidence with VB electrons measured by the fixed CMA. In this talk, we present the data obtained for VB-VB coincidence at the valence band energy of 171eV along with the coincidence measurements in the energy range of 4p core and valence band. NSF DMR 0907679, NSF Award Number: 1213727. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. DOE, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

  13. Targeting excited states in all-trans polyenes with electron-pair states.

    PubMed

    Boguslawski, Katharina

    2016-12-21

    Wavefunctions restricted to electron pair states are promising models for strongly correlated systems. Specifically, the pair Coupled Cluster Doubles (pCCD) ansatz allows us to accurately describe bond dissociation processes and heavy-element containing compounds with multiple quasi-degenerate single-particle states. Here, we extend the pCCD method to model excited states using the equation of motion (EOM) formalism. As the cluster operator of pCCD is restricted to electron-pair excitations, EOM-pCCD allows us to target excited electron-pair states only. To model singly excited states within EOM-pCCD, we modify the configuration interaction ansatz of EOM-pCCD to contain also single excitations. Our proposed model represents a simple and cost-effective alternative to conventional EOM-CC methods to study singly excited electronic states. The performance of the excited state models is assessed against the lowest-lying excited states of the uranyl cation and the two lowest-lying excited states of all-trans polyenes. Our numerical results suggest that EOM-pCCD including single excitations is a good starting point to target singly excited states.

  14. Spectroscopic evidence for temperature dependent relative movement of light and heavy hole valence bands of PbQ (Q=Te,Se,S)

    NASA Astrophysics Data System (ADS)

    Chatterjee, Utpal; Zhao, Junjing; Kanatzidis, Mercouri; Malliakas, Christos

    We have conducted temperature dependent Angle Resolved Photoemission Spectroscopy (ARPES) studies of the electronic structures of PbTe, PbSe and PbS. Our ARPES measurements provide direct evidences for the light hole upper valence bands (UVBs) and the so-called heavy hole lower valence bands (LVBs), and an unusual temperature dependent relative movement between their band maxima leading to a monotonic decrease in the energy separation between LVBs and UVBs with increase in temperature. This enables convergence of these valence bands and consequently an effective increase in the valley degeneracy in PbQ at higher temperatures, which has long been believed to be the driving factor behind their extraordinary thermoelectric performance.

  15. Electron doped layered nickelates: Spanning the phase diagram of the cuprates

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

    Botana, Antia S.; Pardo, Victor; Norman, Michael R.

    2017-07-01

    Pr4Ni3O8 is an overdoped analog of hole-doped layered cuprates. Here we show via ab initio calculations that Ce-doped Pr4Ni3O8 (Pr3CeNi3O8) has the same electronic structure as the antiferromagnetic insulating phase of parent cuprates.We find that substantial Ce doping should be thermodynamically stable and that other 4+ cations would yield a similar antiferromagnetic insulating state, arguing this configuration is robust for layered nickelates of low-enough valence. The analogies with cuprates at different d fillings suggest that intermediate Ce-doping concentrations near 1/8 should be an appropriate place to search for superconductivity in these low-valence Ni oxides.

  16. Electronic structure and shearing in nanolaminated ternary carbides

    NASA Astrophysics Data System (ADS)

    Music, Denis; Sun, Zhimei; Voevodin, Andrey A.; Schneider, Jochen M.

    2006-07-01

    We have studied shearing in M 2AlC phases (M=Sc,Y,La,Ti,Zr,Hf,V,Nb,Ta,Cr,Mo,W) using ab initio calculations. We propose that these phases can be classified into two groups based on the valence electron concentration induced changes in C 44. One group comprises M=V B and VIB, where the C 44 values are approximately 170 GPa and independent of the corresponding MC. The other group includes M=IIIB and IVB, where the C 44 shows a linear dependency with the corresponding MC. This may be understood based on the electronic structure: shear resistant bands are filled in M 2AlC phases with M=V B and VIB, while they are not completely filled when M=IIIB and IVB. This notion is also consistent with our stress-strain analysis. These valence electron concentration induced changes in shear behaviour were compared to previously published valence electron concentration induced changes in compression behaviour [Z. Sun, D. Music, R. Ahuja, S. Li, J.M. Schneider, Phys. Rev. B 70 (2004) 092102]. These classification proposals exhibit identical critical valence electron concentration values for the group boundary. However, the physical mechanisms are not identical: the classification proposal for the bulk modulus is based on MC-A coupling, while shearing is based on MC-MC coupling.

  17. The allocation of valenced concepts onto 3D space.

    PubMed

    Marmolejo-Ramos, Fernando; Tirado, Carlos; Arshamian, Edward; Vélez, Jorge Iván; Arshamian, Artin

    2018-06-01

    The valence-space metaphor research area investigates the metaphorical mapping of valenced concepts onto space. Research findings from this area indicate that positive, neutral, and negative concepts are associated with upward, midward, and downward locations, respectively, in the vertical plane. The same research area has also indicated that such concepts seem to have no preferential location on the horizontal plane. The approach-avoidance effect consists in decreasing the distance between positive stimuli and the body (i.e. approach) and increasing the distance between negative stimuli and the body (i.e. avoid). Thus, the valence-space metaphor accounts for the mapping of valenced concepts onto the vertical and horizontal planes, and the approach-avoidance effect accounts for the mapping of valenced concepts onto the "depth" plane. By using a cube conceived for the study of allocation of valenced concepts onto 3D space, we show in three studies that positive concepts are placed in upward locations and near the participants' body, negative concepts are placed in downward locations and far from the participants' body, and neutral concepts are placed in between these concepts in both planes.

  18. Electronic structure and dynamics of thin Ge/GaAs(110) heterostructures

    NASA Astrophysics Data System (ADS)

    Haight, R.; Silberman, J. A.

    1990-10-01

    Using angle-resolved picosecond laser photoemission we have investigated both occupied and transiently excited empty states at the surface of Ge grown epitaxially on GaAs(110). We observe a normally unoccupied, Ge layer derived state whose separation from the valence-band maximum of the system is 700±50 meV at six monolayers Ge coverage. The evolution of the electronic structure is followed as a function of coverage and correlated with low-energy electron diffraction. The time dependence of the transiently occupied Ge signal is compared with that of the clean GaAs(110) surface and shows that electrons are prevented from diffusing into the GaAs bulk by the conduction-band offset of 330±40 meV.

  19. Attosecond electron pulse trains and quantum state reconstruction in ultrafast transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Priebe, Katharina E.; Rathje, Christopher; Yalunin, Sergey V.; Hohage, Thorsten; Feist, Armin; Schäfer, Sascha; Ropers, Claus

    2017-12-01

    Ultrafast electron and X-ray imaging and spectroscopy are the basis for an ongoing revolution in the understanding of dynamical atomic-scale processes in matter. The underlying technology relies heavily on laser science for the generation and characterization of ever shorter pulses. Recent findings suggest that ultrafast electron microscopy with attosecond-structured wavefunctions may be feasible. However, such future technologies call for means to both prepare and fully analyse the corresponding free-electron quantum states. Here, we introduce a framework for the preparation, coherent manipulation and characterization of free-electron quantum states, experimentally demonstrating attosecond electron pulse trains. Phase-locked optical fields coherently control the electron wavefunction along the beam direction. We establish a new variant of quantum state tomography—`SQUIRRELS'—for free-electron ensembles. The ability to tailor and quantitatively map electron quantum states will promote the nanoscale study of electron-matter entanglement and new forms of ultrafast electron microscopy down to the attosecond regime.

  20. Electron affinities of the alkali dimers - Na2, K2, and Rb2

    NASA Technical Reports Server (NTRS)

    Partridge, H.; Dixon, D. A.; Walch, S. P.; Bauschlicher, C. W., Jr.; Gole, J. L.

    1983-01-01

    Ab initio calculations on the ground states of the alkali dimers, Na2, K2, and Rb2, and their anions are reported. The calculations employ large Gaussian basis sets and account for nearly all of the valence correlation energy. The calculated atomic electron affinities are within 0.02 eV of experiment and the calculated adiabatic electron affinities for Na2, K2, and Rb2 are, respectively, 0.470, 0.512, and 0.513 eV.

  1. Electron core ionization in compressed alkali metal cesium

    NASA Astrophysics Data System (ADS)

    Degtyareva, V. F.

    2018-01-01

    Elements of groups I and II in the periodic table have valence electrons of s-type and are usually considered as simple metals. Crystal structures of these elements at ambient pressure are close-packed and high-symmetry of bcc and fcc-types, defined by electrostatic (Madelung) energy. Diverse structures were found under high pressure with decrease of the coordination number, packing fraction and symmetry. Formation of complex structures can be understood within the model of Fermi sphere-Brillouin zone interactions and supported by Hume-Rothery arguments. With the volume decrease there is a gain of band structure energy accompanied by a formation of many-faced Brillouin zone polyhedra. Under compression to less than a half of the initial volume the interatomic distances become close to or smaller than the ionic radius which should lead to the electron core ionization. At strong compression it is necessary to assume that for alkali metals the valence electron band overlaps with the upper core electrons, which increases the valence electron count under compression.

  2. Valence-Dependent Belief Updating: Computational Validation.

    PubMed

    Kuzmanovic, Bojana; Rigoux, Lionel

    2017-01-01

    People tend to update beliefs about their future outcomes in a valence-dependent way: they are likely to incorporate good news and to neglect bad news. However, belief formation is a complex process which depends not only on motivational factors such as the desire for favorable conclusions, but also on multiple cognitive variables such as prior beliefs, knowledge about personal vulnerabilities and resources, and the size of the probabilities and estimation errors. Thus, we applied computational modeling in order to test for valence-induced biases in updating while formally controlling for relevant cognitive factors. We compared biased and unbiased Bayesian models of belief updating, and specified alternative models based on reinforcement learning. The experiment consisted of 80 trials with 80 different adverse future life events. In each trial, participants estimated the base rate of one of these events and estimated their own risk of experiencing the event before and after being confronted with the actual base rate. Belief updates corresponded to the difference between the two self-risk estimates. Valence-dependent updating was assessed by comparing trials with good news (better-than-expected base rates) with trials with bad news (worse-than-expected base rates). After receiving bad relative to good news, participants' updates were smaller and deviated more strongly from rational Bayesian predictions, indicating a valence-induced bias. Model comparison revealed that the biased (i.e., optimistic) Bayesian model of belief updating better accounted for data than the unbiased (i.e., rational) Bayesian model, confirming that the valence of the new information influenced the amount of updating. Moreover, alternative computational modeling based on reinforcement learning demonstrated higher learning rates for good than for bad news, as well as a moderating role of personal knowledge. Finally, in this specific experimental context, the approach based on reinforcement

  3. Valence-Dependent Belief Updating: Computational Validation

    PubMed Central

    Kuzmanovic, Bojana; Rigoux, Lionel

    2017-01-01

    People tend to update beliefs about their future outcomes in a valence-dependent way: they are likely to incorporate good news and to neglect bad news. However, belief formation is a complex process which depends not only on motivational factors such as the desire for favorable conclusions, but also on multiple cognitive variables such as prior beliefs, knowledge about personal vulnerabilities and resources, and the size of the probabilities and estimation errors. Thus, we applied computational modeling in order to test for valence-induced biases in updating while formally controlling for relevant cognitive factors. We compared biased and unbiased Bayesian models of belief updating, and specified alternative models based on reinforcement learning. The experiment consisted of 80 trials with 80 different adverse future life events. In each trial, participants estimated the base rate of one of these events and estimated their own risk of experiencing the event before and after being confronted with the actual base rate. Belief updates corresponded to the difference between the two self-risk estimates. Valence-dependent updating was assessed by comparing trials with good news (better-than-expected base rates) with trials with bad news (worse-than-expected base rates). After receiving bad relative to good news, participants' updates were smaller and deviated more strongly from rational Bayesian predictions, indicating a valence-induced bias. Model comparison revealed that the biased (i.e., optimistic) Bayesian model of belief updating better accounted for data than the unbiased (i.e., rational) Bayesian model, confirming that the valence of the new information influenced the amount of updating. Moreover, alternative computational modeling based on reinforcement learning demonstrated higher learning rates for good than for bad news, as well as a moderating role of personal knowledge. Finally, in this specific experimental context, the approach based on reinforcement

  4. Emotion and language: Valence and arousal affect word recognition

    PubMed Central

    Brysbaert, Marc; Warriner, Amy Beth

    2014-01-01

    Emotion influences most aspects of cognition and behavior, but emotional factors are conspicuously absent from current models of word recognition. The influence of emotion on word recognition has mostly been reported in prior studies on the automatic vigilance for negative stimuli, but the precise nature of this relationship is unclear. Various models of automatic vigilance have claimed that the effect of valence on response times is categorical, an inverted-U, or interactive with arousal. The present study used a sample of 12,658 words, and included many lexical and semantic control factors, to determine the precise nature of the effects of arousal and valence on word recognition. Converging empirical patterns observed in word-level and trial-level data from lexical decision and naming indicate that valence and arousal exert independent monotonic effects: Negative words are recognized more slowly than positive words, and arousing words are recognized more slowly than calming words. Valence explained about 2% of the variance in word recognition latencies, whereas the effect of arousal was smaller. Valence and arousal do not interact, but both interact with word frequency, such that valence and arousal exert larger effects among low-frequency words than among high-frequency words. These results necessitate a new model of affective word processing whereby the degree of negativity monotonically and independently predicts the speed of responding. This research also demonstrates that incorporating emotional factors, especially valence, improves the performance of models of word recognition. PMID:24490848

  5. Boron difluoride dibenzoylmethane derivatives: Electronic structure and luminescence

    NASA Astrophysics Data System (ADS)

    Tikhonov, Sergey A.; Vovna, Vitaliy I.; Osmushko, Ivan S.; Fedorenko, Elena V.; Mirochnik, Anatoliy G.

    2018-01-01

    Electronic structure and optical properties of boron difluoride dibenzoylmethanate and four of its derivatives have been studied by X-ray photoelectron spectroscopy, absorption and luminescence spectroscopy and quantum chemistry (DFT, TDDFT). The relative quantum luminescence yields have been revealed to correlate with charge transfers of HOMO-LUMO transitions, energy barriers of aromatic substituents rotation and the lifetime of excited states in the investigated complexes. The bathochromic shift of intensive bands in the optical spectra has been observed to occur when the functional groups are introduced into p-positions of phenyl cycles due to destabilizing HOMO levels. Calculated energy intervals between electronic levels correlate well with XPS spectra structure of valence and core electrons.

  6. Electronic structure and optical properties of noncentrosymmetric LiGaGe2Se6, a promising nonlinear optical material

    NASA Astrophysics Data System (ADS)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Ananchenko, L. N.; Isaenko, L. I.; Yelisseyev, A.; Krinitsin, P. G.; Khyzhun, O. Y.

    2016-11-01

    X-ray photoelectron core-level and valence-band spectra are measured for pristine and Ar+ ion-bombarded surfaces of LiGaGe2Se6 single crystal grown by Bridgman-Stockbarger technique. Further, electronic structure of LiGaGe2Se6 is elucidated from both theoretical and experimental viewpoints. Density functional theory (DFT) calculations are made using the augmented plane wave +local orbitals (APW+lo) method to study total and partial densities of states in the LiGaGe2Se6 compound. The present calculations indicate that the principal contributors to the valence band are the Se 4p states: they contribute mainly at the top and in the central portion of the valence band of LiGaGe2Se6, with also their significant contributions in its lower portion. The Ge 4s and Ge 4p states are among other significant contributors to the valence band of LiGaGe2Se6, contributing mainly at the bottom and in the central portion, respectively. In addition, the calculations indicate that the bottom of the conduction band is composed mainly from the unoccupied Ge s and Se p states. The present DFT calculations are supported experimentally by comparison on a common energy scale of the X-ray emission bands representing the energy distribution of the 4p states associated with Ga, Ge and Se and the XPS valence-band spectrum of the LiGaGe2Se6 single crystal. The main optical characteristics of the LiGaGe2Se6 compound are elucidated by the first-principles calculations.

  7. Ab initio investigation of sulfur monofluoride and its singly charged cation and anion in their ground electronic state

    NASA Astrophysics Data System (ADS)

    Song, Li; Shan-Jun, Chen; Yan, Chen; Peng, Chen

    2016-03-01

    The SF radical and its singly charged cation and anion, SF+ and SF-, have been investigated on the MRCI/aug-cc-pVXZ (X = Q, 5, 6) levels of theory with Davidson correction. Both the core-valence correlation and the relativistic effect are considered. The extrapolating to the complete basis set (CBS) limit is adopted to remove the basis set truncation error. Geometrical parameters, potential energy curves (PECs), vibrational energy levels, spectroscopic constants, ionization potentials, and electron affinities of the ground electronic state for all these species are obtained. The information with respect to molecular characteristics of the SFn (n = -1, 0, +1) systems derived in this work will help to extend our knowledge and to guide further experimental or theoretical researches. Project supported by the National Natural Science Foundation of China (Grant Nos. 11304023 and 11447172), the Young and Middle-Aged Talent of Education Burea of Hubei Province, China (Grant No. Q20151307), and the Yangtze Youth Talents Fund of Yangtze University, China (Grant No. 2015cqr21).

  8. Electronic structure of β-Ga2O3 single crystals investigated by hard X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Li, Guo-Ling; Zhang, Fabi; Cui, Yi-Tao; Oji, Hiroshi; Son, Jin-Young; Guo, Qixin

    2015-07-01

    By combination of hard X-ray photoelectron spectroscopy (HAXPES) and first-principles band structure calculations, the electronic states of β-Ga2O3 were investigated to deepen the understanding of bulk information for this compound. The valence band spectra of HAXPES presented the main contribution from Ga 4sp, which are well represented by photoionization cross section weighted partial density of states. The experimental data complemented with the theoretical study yield a realistic picture of the electronic structure for β-Ga2O3.

  9. Systematic study of electronic and magnetic properties for Cu{sub 12–x}TM{sub x}Sb{sub 4}S{sub 13} (TM = Mn, Fe, Co, Ni, and Zn) tetrahedrite

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

    Suekuni, K., E-mail: ksuekuni@hiroshima-u.ac.jp; Tomizawa, Y.; Ozaki, T.

    2014-04-14

    Substitution effects of 3d transition metal (TM) impurities on electronic and magnetic properties for Cu{sub 12}Sb{sub 4}S{sub 13} tetrahedrite are investigated by the combination of low-temperature experiments and first-principles electronic-structure calculations. The electrical resistivity for the cubic phase of Cu{sub 12}Sb{sub 4}S{sub 13} exhibits metallic behavior due to an electron-deficient character of the compound. Whereas that for 0.5 ≤ x ≤ 2.0 of Cu{sub 12−x}Ni{sub x}Sb{sub 4}S{sub 13} exhibits semiconducting behavior. The substituted Ni for Cu is in the divalent ionic state with a spin magnetic moment and creates impurity bands just above the Fermi level at the top of the valence band. Therefore,more » the semiconducting behavior of the electrical resistivity is attributed to the thermal excitation of electrons from the valence band to the impurity band. The substitution effect of TM on the electronic structure and the valency of TM for Cu{sub 11.0}TM{sub 1.0}Sb{sub 4}S{sub 13} are systematically studied by the calculation. The substituted Mn, Fe, and Co for Cu are found to be in the ionic states with the spin magnetic moments due to the large exchange splitting of the 3d bands between the minority- and majority-spin states.« less

  10. Combining state-of-the-art experiment and ab initio calculations for a better understanding of the interplay between valence, magnetism and structure in Eu compounds at high pressure

    DOE PAGES

    Souza-Neto, N. M.; Haskel, D.; dos Reis, R. D.; ...

    2016-07-26

    Here, we describe how first principle calculations can play a key role in the interpretation of X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectra for a better understanding of emergent phenomena in condensed matter physics at high applied pressure. Eu compounds are used as case study to illustrate the advantages of this methodology, ranging from studies of electronic charge transfer probed by quadrupolar and dipolar contributions, to accurately determining electronic valence, and to inform about the influence of pressure on RKKY interactions and magnetism. This description should help advance studies where the pressure dependence of XANESmore » and XMCD data must be tackled with the support of theoretical calculations for a proper understanding of the electronic properties of materials.« less

  11. Electronic and Vibrational Coherence in Charge-Transfer Reactions

    NASA Astrophysics Data System (ADS)

    Scherer, Norbert

    1996-03-01

    The ultrafast dynamics associated with optically-induced intervalence charge-transfer reactions in solution and protein environments are reported. These studies include the Fe^(II)-Fe^(III) MMCT complex Prussian blue and the mixed valence dimer (CN)_5Ru^(II)CNRuRu^(III)(NH_3)_5. The protein systems include blue copper proteins and the bacterial photosynthetic reaction center. The experimental approaches include photon echo, wavelength-resolved pump-probe and anisotropy measurements performed with 12-16fs duration optical pulses. Complicated time-domain waveforms reflect the several different p[rocesses and time scales for relaxation of coherences (both electronic and vibrational) and populations within these systems. The photon echo and anisotropy results probe electronic coherence and dephasing prior to back electron transfer. Wavelength-resolved pump-probe results reveal vibrational modes coupled to the CT-coordinate as well as formation of new product states or vibrational cooling in the ground state following back electron transfer.

  12. Measurement of Electronic States of PbS Nanocrystal Quantum Dots Using Scanning Tunneling Spectroscopy: The Role of Parity Selection Rules in Optical Absorption

    NASA Astrophysics Data System (ADS)

    Diaconescu, Bogdan; Padilha, Lazaro A.; Nagpal, Prashant; Swartzentruber, Brian S.; Klimov, Victor I.

    2013-03-01

    We study the structure of electronic states in individual PbS nanocrystal quantum dots by scanning tunneling spectroscopy (STS) using one-to-two monolayer nanocrystal films treated with 1, 2-ethanedithiols (EDT). Up to six individual valence and conduction band states are resolved for a range of quantum dot sizes. The measured states’ energies are in good agreement with calculations using the k·p four-band envelope function formalism. A comparison of STS and optical absorption spectra indicates that some of the absorption features can only be explained by asymmetric transitions involving the states of different symmetries (e.g., S and P or P and D), which points towards the relaxation of the parity selection rules in these nanostructures. STS measurements also reveal a midgap feature, which is likely similar to one observed in previous charge transport studies of EDT-treated quantum dot films.

  13. Valenced cues and contexts have different effects on event-based prospective memory.

    PubMed

    Graf, Peter; Yu, Martin

    2015-01-01

    This study examined the separate influence and joint influences on event-based prospective memory task performance due to the valence of cues and the valence of contexts. We manipulated the valence of cues and contexts with pictures from the International Affective Picture System. The participants, undergraduate students, showed higher performance when neutral compared to valenced pictures were used for cueing prospective memory. In addition, neutral pictures were more effective as cues when they occurred in a valenced context than in the context of neutral pictures, but the effectiveness of valenced cues did not vary across contexts that differed in valence. The finding of an interaction between cue and context valence indicates that their respective influence on event-based prospective memory task performance cannot be understood in isolation from each other. Our findings are not consistent with by the prevailing view which holds that the scope of attention is broadened and narrowed, respectively, by positively and negatively valenced stimuli. Instead, our findings are more supportive of the recent proposal that the scope of attention is determined by the motivational intensity associated with valenced stimuli. Consistent with this proposal, we speculate that the motivational intensity associated with different retrieval cues determines the scope of attention, that contexts with different valence values determine participants' task engagement, and that prospective memory task performance is determined jointly by attention scope and task engagement.

  14. Valenced Cues and Contexts Have Different Effects on Event-Based Prospective Memory

    PubMed Central

    Graf, Peter; Yu, Martin

    2015-01-01

    This study examined the separate influence and joint influences on event-based prospective memory task performance due to the valence of cues and the valence of contexts. We manipulated the valence of cues and contexts with pictures from the International Affective Picture System. The participants, undergraduate students, showed higher performance when neutral compared to valenced pictures were used for cueing prospective memory. In addition, neutral pictures were more effective as cues when they occurred in a valenced context than in the context of neutral pictures, but the effectiveness of valenced cues did not vary across contexts that differed in valence. The finding of an interaction between cue and context valence indicates that their respective influence on event-based prospective memory task performance cannot be understood in isolation from each other. Our findings are not consistent with by the prevailing view which holds that the scope of attention is broadened and narrowed, respectively, by positively and negatively valenced stimuli. Instead, our findings are more supportive of the recent proposal that the scope of attention is determined by the motivational intensity associated with valenced stimuli. Consistent with this proposal, we speculate that the motivational intensity associated with different retrieval cues determines the scope of attention, that contexts with different valence values determine participants’ task engagement, and that prospective memory task performance is determined jointly by attention scope and task engagement. PMID:25647484

  15. Correlation of molecular valence- and K-shell photoionization resonances with bond lengths

    NASA Technical Reports Server (NTRS)

    Sheehy, J. A.; Gil, T. J.; Winstead, C. L.; Farren, R. E.; Langhoff, P. W.

    1989-01-01

    The relationship between the interatomic distance and the positions of valence-shell and K-shell sigma(asterisk) photoionization resonances is investigated theoretically for the molecules C2, F2, N2, O2, CO, NO, C2H2, C2H4, C2H6, HCN, H2CO, N20, CO2, and C2N2. The results of molecular-orbital computations are presented in three-dimensional diagrams, which are shown to be similar to the wave functions of a particle in a cylindrical well, confirming the validity of free-electron molecular-orbital (FEMO) approximations for modeling the potential along the symmetry axis. FEMO orbital energies and resonance positions are found to be in good agreement with previous theoretical and experimental results. Also included is a Feshbach-Fano analysis of the relevance of virtual-valence orbitals to the appearance of single-channel resonances in molecular photoionization cross sections.

  16. Experimental Constraints on the Partitioning and Valence of V and Cr in Garnet and Coexisting Glass

    NASA Technical Reports Server (NTRS)

    Righter, K.; Sutton, S.; Berthet, S.; Newville, M.

    2008-01-01

    A series of experiments with garnet and coexisting melt have been carried out across a range of oxygen fugacities (near hematite-magnetite (HM) to below the iron-wustite (IW) buffers) at 1.7 GPa to study the partitioning and valence of Cr and V in both phases. Experiments were carried out in a non end loaded piston cylinder apparatus, and the run products were analyzed with electron microprobe and xray absorption near edge structure (XANES) analysis at beamline 13-ID at the Advanced Photon Source of Argonne National Lab. The valence of vanadium and chromium were determined using the position and intensity of the Ka pre-edge peaks, calibrated on a series of Cr and Vbearing standard glasses. This technique has been applied to V and Cr in glasses and V in spinels previously, and in these isotropic phases there are no orientational effects on the XANES spectra (Righter et al., 2006, Amer. Mineral. 91, 1643-1656). We also now demonstrate this to be true for V and Cr in garnet. Also, previous work has shown that V has a higher valence in the glass (or melt) than in the coexisting spinel. This is also true for V in garnet-glass pairs in this study. Vanadium valence in garnets varies from 2.7 below the IW buffer to 3.7 near HM, and for coexisting glass it varies from 3.2 to 4.3. Vanadium valence measured in some natural garnets from mantle localities indicates V in the more reduced range at 2.5. Comparisons will be made between fO2 estimated from V valence and other methods for garnet-bearing mantle samples. In contrast, Cr valence measured in garnet and coexisting glass for all experimental and natural samples is 2.9- 3.0, suggesting that the valence of Cr does not vary within either phase across a large fO2 range. These results demonstrate that while V varies from 2+ to 3+ to 4+ in garnet-melt systems, Cr does not, and this will ultimately affect the partitioning behavior of these two elements in natural systems. Garnet/melt D(Cr) are between 12 and 17 across this range

  17. Electron localization of anions probed by nitrile vibrations

    DOE PAGES

    Mani, Tomoyasu; Grills, David C.; Newton, Marshall D.; ...

    2015-08-02

    Localization and delocalization of electrons is a key concept in chemistry, and is one of the important factors determining the efficiency of electron transport through organic conjugated molecules, which have potential to act as “molecular wires”. This, in turn, substantially influences the efficiencies of organic solar cells and other molecular electronic devices. It is also necessary to understand the electronic energy landscape and the dynamics of electrons through molecular chain that govern their transport capabilities in one-dimensional conjugated chains so that we can better define the design principles of conjugated molecules for their applications. We show that nitrile ν(C≡N) vibrationsmore » respond to the degree of electron localization in nitrile-substituted organic anions by utilizing time-resolved infrared (TRIR) detection combined with pulse radiolysis. Measurements of a series of aryl nitrile anions allow us to construct a semi-empirical calibration curve between the changes in the ν(C≡N) IR shifts and the changes in the electronic charges from the neutral to the anion states in the nitriles; more electron localization in the nitrile anion results in larger IR shifts. Furthermore, the IR linewidth in anions can report a structural change accompanying changes in the electronic density distribution. Probing the shift of the nitrile ν(C≡N) IR vibrational bands enables us to determine how the electron is localized in anions of nitrile-functionalized oligofluorenes, considered as organic mixed-valence compounds. We estimate the diabatic electron transfer distance, electronic coupling strengths, and energy barriers in these organic mixed-valence compounds. The analysis reveals a dynamic picture, showing that the electron is moving back and forth within the oligomers with a small activation energy of ≤ k BT, likely controlled by the movement of dihedral angles between monomer units. Thus, implications for the electron transport capability

  18. Decoding emotional valence from electroencephalographic rhythmic activity.

    PubMed

    Celikkanat, Hande; Moriya, Hiroki; Ogawa, Takeshi; Kauppi, Jukka-Pekka; Kawanabe, Motoaki; Hyvarinen, Aapo

    2017-07-01

    We attempt to decode emotional valence from electroencephalographic rhythmic activity in a naturalistic setting. We employ a data-driven method developed in a previous study, Spectral Linear Discriminant Analysis, to discover the relationships between the classification task and independent neuronal sources, optimally utilizing multiple frequency bands. A detailed investigation of the classifier provides insight into the neuronal sources related with emotional valence, and the individual differences of the subjects in processing emotions. Our findings show: (1) sources whose locations are similar across subjects are consistently involved in emotional responses, with the involvement of parietal sources being especially significant, and (2) even though the locations of the involved neuronal sources are consistent, subjects can display highly varying degrees of valence-related EEG activity in the sources.

  19. Electronic structure and optical properties of noncentrosymmetric LiGaSe2: Experimental measurements and DFT band structure calculations

    NASA Astrophysics Data System (ADS)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Ananchenko, L. N.; Isaenko, L. I.; Yelisseyev, A. P.; Khyzhun, O. Y.

    2017-04-01

    We report on measurements of X-ray photoelectron (XP) spectra for pristine and Ar+ ion-irradiated surfaces of LiGaSe2 single crystal grown by Bridgman-Stockbarger method. Electronic structure of the LiGaSe2 compound is studied from a theoretical and experimental viewpoint. In particular, total and partial densities of states of LiGaSe2 are investigated by density functional theory (DFT) calculations employing the augmented plane wave + local orbitals (APW + lo) method and they are verified by data of X-ray spectroscopy measurements. The DFT calculations indicate that the main contributors to the valence band of LiGaSe2 are the Se 4p states, which contribute mainly at the top and in the upper portion of the valence band, with also essential contributions of these states in the lower portion of the band. Other substantial contributions to the valence band of LiGaSe2 emerge from the Ga 4s and Ga 4p states contributing mainly at the lower ant upper portions of the valence band, respectively. With respect to the conduction band, the calculations indicate that its bottom is composed mainly from contributions of the unoccupied Ga s and Se p states. The present calculations are confirmed experimentally when comparing the XP valence-band spectrum of the LiGaS2 single crystal on a common energy scale with the X-ray emission bands representing the energy distribution of the Ga 4p and Se 4p states. Measurements of the fundamental absorption edges at room temperature reveal that bandgap value, Eg, of LiGaSe2 is equal to 3.47 eV and the Eg value increases up to 3.66 eV when decreasing temperature to 80 K. The main optical characteristics of the LiGaSe2 compound are clarified by the DFT calculations.

  20. Core-core and core-valence correlation

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.

    1988-01-01

    The effect of (1s) core correlation on properties and energy separations was analyzed using full configuration-interaction (FCI) calculations. The Be 1 S - 1 P, the C 3 P - 5 S and CH+ 1 Sigma + or - 1 Pi separations, and CH+ spectroscopic constants, dipole moment and 1 Sigma + - 1 Pi transition dipole moment were studied. The results of the FCI calculations are compared to those obtained using approximate methods. In addition, the generation of atomic natural orbital (ANO) basis sets, as a method for contracting a primitive basis set for both valence and core correlation, is discussed. When both core-core and core-valence correlation are included in the calculation, no suitable truncated CI approach consistently reproduces the FCI, and contraction of the basis set is very difficult. If the (nearly constant) core-core correlation is eliminated, and only the core-valence correlation is included, CASSCF/MRCI approached reproduce the FCI results and basis set contraction is significantly easier.

  1. Space-valence priming with subliminal and supraliminal words.

    PubMed

    Ansorge, Ulrich; Khalid, Shah; König, Peter

    2013-01-01

    To date it is unclear whether (1) awareness-independent non-evaluative semantic processes influence affective semantics and whether (2) awareness-independent affective semantics influence non-evaluative semantic processing. In the current study, we investigated these questions with the help of subliminal (masked) primes and visible targets in a space-valence across-category congruence effect. In line with (1), we found that subliminal space prime words influenced valence classification of supraliminal target words (Experiment 1): classifications were faster with a congruent prime (e.g., the prime "up" before the target "happy") than with an incongruent prime (e.g., the prime "up" before the target "sad"). In contrast to (2), no influence of subliminal valence primes on the classification of supraliminal space targets into up- and down-words was found (Experiment 2). Control conditions showed that standard masked response priming effects were found with both subliminal prime types, and that an across-category congruence effect was also found with supraliminal valence primes and spatial target words. The final Experiment 3 confirmed that the across-category congruence effect indeed reflected priming of target categorization of a relevant meaning category. Together, the data jointly confirmed prediction (1) that awareness-independent non-evaluative semantic priming influences valence judgments.

  2. Space-Valence Priming with Subliminal and Supraliminal Words

    PubMed Central

    Ansorge, Ulrich; Khalid, Shah; König, Peter

    2013-01-01

    To date it is unclear whether (1) awareness-independent non-evaluative semantic processes influence affective semantics and whether (2) awareness-independent affective semantics influence non-evaluative semantic processing. In the current study, we investigated these questions with the help of subliminal (masked) primes and visible targets in a space-valence across-category congruence effect. In line with (1), we found that subliminal space prime words influenced valence classification of supraliminal target words (Experiment 1): classifications were faster with a congruent prime (e.g., the prime “up” before the target “happy”) than with an incongruent prime (e.g., the prime “up” before the target “sad”). In contrast to (2), no influence of subliminal valence primes on the classification of supraliminal space targets into up- and down-words was found (Experiment 2). Control conditions showed that standard masked response priming effects were found with both subliminal prime types, and that an across-category congruence effect was also found with supraliminal valence primes and spatial target words. The final Experiment 3 confirmed that the across-category congruence effect indeed reflected priming of target categorization of a relevant meaning category. Together, the data jointly confirmed prediction (1) that awareness-independent non-evaluative semantic priming influences valence judgments. PMID:23439863

  3. Comparative study of inelastic squared form factors of the vibronic states of B 1Σu+ , C 1Πu , and E F 1Σg+ for molecular hydrogen: Inelastic x-ray and electron scattering

    NASA Astrophysics Data System (ADS)

    Xu, Long-Quan; Kang, Xu; Peng, Yi-Geng; Xu, Xin; Liu, Ya-Wei; Wu, Yong; Yang, Ke; Hiraoka, Nozomu; Tsuei, Ku-Ding; Wang, Jian-Guo; Zhu, Lin-Fan

    2018-03-01

    A joint experimental and theoretical investigation of the valence-shell excitations of hydrogen has been performed by the high-resolution inelastic x-ray scattering and electron scattering as well as the multireference single- and double-excitation configuration-interaction method. Momentum-transfer-dependent inelastic squared form factors for the vibronic series belonging to the B 1Σu+ ,C 1Πu , and E F 1Σg+ electronic states of molecular hydrogen have been derived from the inelastic x-ray scattering method at an impact photon energy around 10 keV, and the electron energy-loss spectra measured at an incident electron energy of 1500 eV. It is found that both the present and the previous calculations cannot satisfactorily reproduce the inelastic squared form-factor profiles for the higher vibronic transitions of the B 1Σu+ state of molecular hydrogen, which may be due to the electronic-vibrational coupling for the higher vibronic states. For the C 1Πu state and some vibronic excitations of E F 1Σg+ state, the present experimental results are in good agreement with the present and previous calculations, while the slight differences between the inelastic x-ray scattering and electron energy-loss spectroscopy results in the larger squared momentum-transfer region may be attributed to the increasing role of the higher-order Born terms in the electron-scattering process.

  4. Valence-band and core-level photoemission study of single-crystal Bi2CaSr2Cu2O8 superconductors

    NASA Astrophysics Data System (ADS)

    Shen, Z.-X.; Lindberg, P. A. P.; Wells, B. O.; Mitzi, D. B.; Lindau, I.; Spicer, W. E.; Kapitulnik, A.

    1988-12-01

    High-quality single crystals of Bi2CaSr2Cu2O8 superconductors have been prepared and cleaved in ultrahigh vacuum. Low-energy electron diffraction measurements show that the surface structure is consistent with the bulk crystal structure. Ultraviolet photoemission and x-ray photoemission experiments were performed on these well-characterized sample surfaces. The valence-band and the core-level spectra obtained from the single-crystal surfaces are in agreement with spectra recorded from polycrystalline samples, justifying earlier results from polycrystalline samples. Cu satellites are observed both in the valence band and Cu 2p core level, signaling the strong correlation among the Cu 3d electrons. The O 1s core-level data exhibit a sharp, single peak at 529-eV binding energy without any clear satellite structures.

  5. Probing the Electronic Structure of - and Electron-Doped High-Temperature Superconductors with Photoemission and X-Ray Absorption Spectroscopies

    NASA Astrophysics Data System (ADS)

    Lederman, Eli R.

    1990-01-01

    The electronic structures of hole- and electron -doped high temperature superconductors have been probed using x-ray absorption near-edge spectroscopy (XANES) and photoelectron emission spectroscopy (PES). These measurements have been performed on RBa_2Cu _3O_{rm 7-y} , La_{rm 2-x}Sr _{rm x}CuO _4 and Ln_{rm 2 -x}Ce_{rm x} CuO_{rm 4} for R = Y, Eu and Ln = Nd, Pr and Sm. The parameters x and y have been varied to include a range of hole and electron carrier densities and the undoped parent compounds. Previous XANES and PES results have indicated that unoccupied states of O 2p character can be associated with the carriers in the materials RBa_2 Cu_3O_{ rm 7-y} and La_{ rm 2-x}Sr_{rm x}CuO_4 and that the density of holes increases with O and Sr content, respectively. Conduction was hole-based in all known high-T_{ rm c} cuprates until the recent discovery of superconductivity in Ln_{rm 2-x}Ce_{rm x} CuO_4. Hall coefficient measurements have suggested that the carriers in this system are electrons added with Ce doping. It has been anticipated that these electron-doped materials will provide an important test for models of high temperature superconductivity. PES measurements are presented that show significant Cu 3d character in the valence band of these electron-based materials, but that the Cu^{2+} /Cu^{1+} ratio is unchanged by the level of Ce doping, indicating that doped electrons are itinerant rather than highly correlated. Resonant photoemission from the valence band indicates the presence of unoccupied O 2p states, but these holes are less abundant than in the hole-doped materials. Measurements of XANES at the O 1s edge suggest that unoccupied states of O 2p character in the electron -doped materials are not related to conduction in a simple way. The density of these holes is shown to decrease upon Ce doping and the process of reduction, despite the fact that both are necessary of superconductivity. Furthermore, whereas the O 2p holes are at E_{rm F} in the

  6. Electronic and spectroscopic characterizations of SNP isomers

    NASA Astrophysics Data System (ADS)

    Trabelsi, Tarek; Al Mogren, Muneerah Mogren; Hochlaf, Majdi; Francisco, Joseph S.

    2018-02-01

    High-level ab initio electronic structure calculations were performed to characterize SNP isomers. In addition to the known linear SNP, cyc-PSN, and linear SPN isomers, we identified a fourth isomer, linear PSN, which is located ˜2.4 eV above the linear SNP isomer. The low-lying singlet and triplet electronic states of the linear SNP and SPN isomers were investigated using a multi-reference configuration interaction method and large basis set. Several bound electronic states were identified. However, their upper rovibrational levels were predicted to pre-dissociate, leading to S + PN, P + NS products, and multi-step pathways were discovered. For the ground states, a set of spectroscopic parameters were derived using standard and explicitly correlated coupled-cluster methods in conjunction with augmented correlation-consistent basis sets extrapolated to the complete basis set limit. We also considered scalar and core-valence effects. For linear isomers, the rovibrational spectra were deduced after generation of their 3D-potential energy surfaces along the stretching and bending coordinates and variational treatments of the nuclear motions.

  7. Designing Semiconductor Heterostructures Using Digitally Accessible Electronic-Structure Data

    NASA Astrophysics Data System (ADS)

    Shapera, Ethan; Schleife, Andre

    Semiconductor sandwich structures, so-called heterojunctions, are at the heart of modern applications with tremendous societal impact: Light-emitting diodes shape the future of lighting and solar cells are promising for renewable energy. However, their computer-based design is hampered by the high cost of electronic structure techniques used to select materials based on alignment of valence and conduction bands and to evaluate excited state properties. We describe, validate, and demonstrate an open source Python framework which rapidly screens existing online databases and user-provided data to find combinations of suitable, previously fabricated materials for optoelectronic applications. The branch point energy aligns valence and conduction bands of different materials, requiring only the bulk density functional theory band structure. We train machine learning algorithms to predict the dielectric constant, electron mobility, and hole mobility with material descriptors available in online databases. Using CdSe and InP as emitting layers for LEDs and CH3NH3PbI3 and nanoparticle PbS as absorbers for solar cells, we demonstrate our broadly applicable, automated method.

  8. Developmental reversals in false memory: Effects of emotional valence and arousal.

    PubMed

    Brainerd, C J; Holliday, R E; Reyna, V F; Yang, Y; Toglia, M P

    2010-10-01

    Do the emotional valence and arousal of events distort children's memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can be manipulated factorially. False memories increased with age for unpresented semantic associates of word lists, and net accuracy (the ratio of true memory to total memory) decreased with age. These surprising developmental trends were more pronounced for negatively valenced materials than for positively valenced materials, they were more pronounced for high-arousal materials than for low-arousal materials, and developmental increases in the effects of arousal were small in comparison with developmental increases in the effects of valence. These findings have ramifications for legal applications of false memory research; materials that share the emotional hallmark of crimes (events that are negatively valenced and arousing) produced the largest age increases in false memory and the largest age declines in net accuracy. Copyright 2010 Elsevier Inc. All rights reserved.

  9. Cooperative magnetic behaviour in the new valence fluctuating compound Ce2Rh3Ge

    NASA Astrophysics Data System (ADS)

    Falkowski, M.; Strydom, A. M.

    2015-10-01

    In this study we report the physical properties of the new ternary compound Ce2Rh3Ge that crystallizes in the rhombohedral, triple hexagonal MgCu2-type of structure. The electronic ground state properties of Ce2Rh3Ge were characterized by magnetic susceptibility, specific heat, electrical resistivity and thermal transport measurements. The results indicate the presence of short range magnetic interaction, probably of ferromagnetic origin below T C  =  4 K. The shape of χ -1(T) deviates from the Curie-Weiss behavior with a broad minimum at about T\\min{{χ-1}}   =  450 K reminiscent of valence fluctuating cerium systems. At T  =  10 K, the magnetic part of the resistivity ρ 4 f (T) exhibits a shallow minimum followed by increase of resistivity ρ(T) \\propto   -lnT, which hints at a substantial Kondo screening effect. Ce2Rh3Ge belongs to a small group of strongly correlated cerium compounds in which the two competing effects of Kondo and RKKY interactions produce long-range magnetic order from strongly hybridized and intermediate-valent 4 f spins. At sufficiently low temperatures Ce2Rh3Ge scales well with the Kadowaki-Woods ratio A/γ 2 and the value of the Wilson ratio χ(T  →  0)/γ found for this compound classifies it as a mixed-valence compound. The presence of valence fluctuation and magnetic order it is rare for these attributes to be found simultaneously in same compound, in same temperature range. In our opinion a novelty of presented results of Ce2Rh3Ge is that this compound adds a new member to a small but growing class of systems bearing a strongly mixed- or intermediate-valent 4 f magnetic moment, but in which the lattice of spins nevertheless end up finding it possible to order magnetically.

  10. Local electronic structure and ferromagnetic interaction in La(Co,Ni)O3

    NASA Astrophysics Data System (ADS)

    Schuppler, S.; Nagel, P.; Fuchs, D.; Löhneysen, H. V.; Merz, M.; Huang, M.-J.

    Perovskite-related transition-metal oxides exhibit properties ranging from insulating to superconducting as well as unusual magnetic phases, and cobaltates, in particular, have been known for their propensity for spin-state transitions. Nonmagnetic LaCoO3 and paramagnetic LaNiO3 are parent compounds for the La(Co1-xNix) O3 (LCNO) family, which, for intermediate Ni content x, exhibits ferromagnetism. The local electronic structure and the ferromagnetic interaction in LCNO have been studied by x-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD). XAS indicates a mixed-valence state for both Co and Ni, with both valences changing systematically with increasing x. Simultaneously, a spin-state redistribution towards HS (Co site) and LS (Ni site) occurs, and temperature-dependent spin-state transitions are increasingly suppressed. XMCD identifies the element-specific contributions to the magnetic moment and interactions. A simple model based on a double-exchange-like mechanism between Co3+ HS and Ni3+HS can qualitatively account for the evolution of ferromagnetism in the LCNO series.

  11. Inhibition of unintentional extra carriers by Mn valence change for high insulating devices

    PubMed Central

    Guo, Daoyou; Li, Peigang; Wu, Zhenping; Cui, Wei; Zhao, Xiaolong; Lei, Ming; Li, Linghong; Tang, Weihua

    2016-01-01

    For intrinsic oxide semiconductors, oxygen vacancies served as the electron donors have long been, and inevitably still are, attributed as the primary cause of conductivity, making oxide semiconductors seem hard to act as high insulating materials. Meanwhile, the presence of oxygen vacancies often leads to a persistent photoconductivity phenomenon which is not conducive to the practical use in the fast photoelectric response devices. Herein, we propose a possible way to reduce the influence of oxygen vacancies by introducing a valence change doping in the monoclinic β-Ga2O3 epitaxial thin film. The unintentional extra electrons induced by oxygen vacancies can be strongly suppressed by the change valence of the doped Mn ions from +3 to +2. The resistance for the Mn-doped Ga2O3 increases two orders of magnitude in compared with the pure Ga2O3. As a result, photodetector based on Mn-doped Ga2O3 thin films takes on a lower dark current, a higher sensitivity, and a faster photoresponse time, exhibiting a promising candidate using in high performance solar-blind photodetector. The study presents that the intentional doping of Mn may provide a convenient and reliable method of obtaining high insulating thin film in oxide semiconductor for the application of specific device. PMID:27068227

  12. The acoustic correlates of valence depend on emotion family.

    PubMed

    Belyk, Michel; Brown, Steven

    2014-07-01

    The voice expresses a wide range of emotions through modulations of acoustic parameters such as frequency and amplitude. Although the acoustics of individual emotions are well understood, attempts to describe the acoustic correlates of broad emotional categories such as valence have yielded mixed results. In the present study, we analyzed the acoustics of emotional valence for different families of emotion. We divided emotional vocalizations into "motivational," "moral," and "aesthetic" families as defined by the OCC (Ortony, Clore, and Collins) model of emotion. Subjects viewed emotional scenarios and were cued to vocalize congruent exclamations in response to them, for example, "Yay!" and "Damn!". Positive valence was weakly associated with high-pitched and loud vocalizations. However, valence interacted with emotion family for both pitch and amplitude. A general acoustic code for valence does not hold across families of emotion, whereas family-specific codes provide a more accurate description of vocal emotions. These findings are consolidated into a set of "rules of expression" relating vocal dimensions to emotion dimensions. Copyright © 2014 The Voice Foundation. Published by Mosby, Inc. All rights reserved.

  13. Electronic structure study of wide band gap magnetic semiconductor (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} nanocrystals in paramagnetic and ferromagnetic phases

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

    Dwivedi, G. D.; Chou, H.; Yang, K. S.

    2016-04-25

    X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} near Fermi-level. XMCD results indicate that Mn{sup 3+} and Mn{sup 4+} spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La{sub 0.6}Pr{sub 0.4}){sub 0.65}Ca{sub 0.35}MnO{sub 3} system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below T{sub C}. The valence bandmore » UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.« less

  14. Sex, Age, and Emotional Valence: Revealing Possible Biases in the 'Reading the Mind in the Eyes' Task.

    PubMed

    Kynast, Jana; Schroeter, Matthias L

    2018-01-01

    The 'Reading the Mind in the Eyes' test (RMET) assesses a specific socio-cognitive ability, i.e., the ability to identify mental states from gaze. The development of this ability in a lifespan perspective is of special interest. Whereas former investigations were limited mainly to childhood and adolescence, the focus has been shifted towards aging, and psychiatric and neurodegenerative diseases recently. Although the RMET is frequently applied in developmental psychology and clinical settings, stimulus characteristics have never been investigated with respect to potential effects on test performance. Here, we analyzed the RMET stimulus set with a special focus on interrelations between sex, age and emotional valence. Forty-three persons rated age and emotional valence of the RMET picture set. Differences in emotional valence and age ratings between male and female items were analyzed. The linear relation between age and emotional valence was tested over all items, and separately for male and female items. Male items were rated older and more negative than female stimuli. Regarding male RMET items, age predicted emotional valence: older age was associated with negative emotions. Contrary, age and valence were not linearly related in female pictures. All ratings were independent of rater characteristics. Our results demonstrate a strong confound between sex, age, and emotional valence in the RMET. Male items presented a greater variability in age ratings compared to female items. Age and emotional valence were negatively associated among male items, but no significant association was found among female stimuli. As personal attributes impact social information processing, our results may add a new perspective on the interpretation of previous findings on interindividual differences in RMET accuracy, particularly in the field of developmental psychology, and age-associated neuropsychiatric diseases. A revision of the RMET might be afforded to overcome confounds

  15. Evidence for anisotropic dielectric properties of monoclinic hafnia using valence electron energy-loss spectroscopy in high-resolution transmission electron microscopy and ab initio time-dependent density-functional theory

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

    Guedj, C.; CEA, LETI, MINATEC Campus, F-38054 Grenoble; Hung, L.

    2014-12-01

    The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO{sub 2}) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO{sub 2}, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO{sub 2} may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectricmore » permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.« less

  16. Processing negative valence of word pairs that include a positive word.

    PubMed

    Itkes, Oksana; Mashal, Nira

    2016-09-01

    Previous research has suggested that cognitive performance is interrupted by negative relative to neutral or positive stimuli. We examined whether negative valence affects performance at the word or phrase level. Participants performed a semantic decision task on word pairs that included either a negative or a positive target word. In Experiment 1, the valence of the target word was congruent with the overall valence conveyed by the word pair (e.g., fat kid). As expected, response times were slower in the negative condition relative to the positive condition. Experiment 2 included target words that were incongruent with the overall valence of the word pair (e.g., fat salary). Response times were longer for word pairs whose overall valence was negative relative to positive, even though these word pairs included a positive word. Our findings support the Cognitive Primacy Hypothesis, according to which emotional valence is extracted after conceptual processing is complete.

  17. Electronic Properties, Screening, and Efficient Carrier Transport in NaSbS 2

    DOE PAGES

    Sun, Jifeng; Singh, David J.

    2017-02-13

    NaSbS 2 is a semiconductor that was recently shown to have remarkable efficacy as a solar absorber indicating efficient charge collection even in material containing defects. We report first-principles calculations of properties that show (1) an indirect gap only slightly smaller than the direct gap, which may impede the recombination of photoexcited carriers, (2) highly anisotropic electronic and optical properties reflecting a layered crystal structure, (3) a pushed-up valence-band maximum due to repulsion from the Sb 5s states, and (4) cross-gap hybridization between the S p—derived valence bands and the Sb 5p states. This latter feature leads to enhanced Bornmore » effective charges that can provide local screening and, therefore, defect tolerance. Finally, these features are discussed in relation to the performance of the compound as a semiconductor with efficient charge collection.« less

  18. The electronic structure of vanadium monochloride cation (VCl+): Tackling the complexities of transition metal species

    NASA Astrophysics Data System (ADS)

    DeYonker, Nathan J.; Halfen, DeWayne T.; Allen, Wesley D.; Ziurys, Lucy M.

    2014-11-01

    Six electronic states (X 4Σ-, A 4Π, B 4Δ, 2Φ, 2Δ, 2Σ+) of the vanadium monochloride cation (VCl+) are described using large basis set coupled cluster theory. For the two lowest quartet states (X 4Σ- and A 4Π), a focal point analysis (FPA) approach was used that conjoined a correlation-consistent family of basis sets up to aug-cc-pwCV5Z-DK with high-order coupled cluster theory through pentuple (CCSDTQP) excitations. FPA adiabatic excitation energies (T0) and spectroscopic constants (re, r0, Be, B0, bar De, He, ωe, v0, αe, ωexe) were extrapolated to the valence complete basis set Douglas-Kroll (DK) aug-cc-pV∞Z-DK CCSDT level of theory, and additional treatments accounted for higher-order valence electron correlation, core correlation, and spin-orbit coupling. Due to the delicate interplay between dynamical and static electronic correlation, single reference coupled cluster theory is able to provide the correct ground electronic state (X 4Σ-), while multireference configuration interaction theory cannot. Perturbations from the first- and second-order spin orbit coupling of low-lying states with quartet spin multiplicity reveal an immensely complex rotational spectrum relative to the isovalent species VO, VS, and TiCl. Computational data on the doublet manifold suggest that the lowest-lying doublet state (2Γ) has a Te of ˜11 200 cm-1. Overall, this study shows that laboratory and theoretical rotational spectroscopists must work more closely in tandem to better understand the bonding and structure of molecules containing transition metals.

  19. Plasmon satellites in valence-band photoemission spectroscopy. Ab initio study of the photon-energy dependence in semiconductors

    NASA Astrophysics Data System (ADS)

    Guzzo, M.; Kas, J. J.; Sottile, F.; Silly, M. G.; Sirotti, F.; Rehr, J. J.; Reining, L.

    2012-09-01

    We present experimental data and theoretical results for valence-band satellites in semiconductors, using the prototypical example of bulk silicon. In a previous publication we introduced a new approach that allows us to describe satellites in valence photoemission spectroscopy, in good agreement with experiment. Here we give more details; we show how the the spectra change with photon energy, and how the theory explains this behaviour. We also describe how we include several effects which are important to obtain a correct comparison between theory and experiment, such as secondary electrons and photon cross sections. In particular the inclusion of extrinsic losses and their dependence on the photon energy are key to the description of the energy dependence of spectra.

  20. The Eighteen-Electron Rule

    ERIC Educational Resources Information Center

    Mitchell, P. R.; Parish, R. V.

    1969-01-01

    Discusses the stability of the structures of transition metal complexes (primarily carbonyls and organometallic compounds) having 18 electrons or less in their valence shell. Presents molecular orbital diagrams for various structures involving alpha and pi bonding and describes the conditions under which the 18 electron rule applies. (RR)

  1. Excited-state relaxation in PbSe quantum dots

    NASA Astrophysics Data System (ADS)

    An, Joonhee M.; Califano, Marco; Franceschetti, Alberto; Zunger, Alex

    2008-04-01

    In solids the phonon-assisted, nonradiative decay from high-energy electronic excited states to low-energy electronic excited states is picosecond fast. It was hoped that electron and hole relaxation could be slowed down in quantum dots, due to the unavailability of phonons energy matched to the large energy-level spacings ("phonon-bottleneck"). However, excited-state relaxation was observed to be rather fast (⩽1ps) in InP, CdSe, and ZnO dots, and explained by an efficient Auger mechanism, whereby the excess energy of electrons is nonradiatively transferred to holes, which can then rapidly decay by phonon emission, by virtue of the densely spaced valence-band levels. The recent emergence of PbSe as a novel quantum-dot material has rekindled the hope for a slow down of excited-state relaxation because hole relaxation was deemed to be ineffective on account of the widely spaced hole levels. The assumption of sparse hole energy levels in PbSe was based on an effective-mass argument based on the light effective mass of the hole. Surprisingly, fast intraband relaxation times of 1-7ps were observed in PbSe quantum dots and have been considered contradictory with the Auger cooling mechanism because of the assumed sparsity of the hole energy levels. Our pseudopotential calculations, however, do not support the scenario of sparse hole levels in PbSe: Because of the existence of three valence-band maxima in the bulk PbSe band structure, hole energy levels are densely spaced, in contradiction with simple effective-mass models. The remaining question is whether the Auger decay channel is sufficiently fast to account for the fast intraband relaxation. Using the atomistic pseudopotential wave functions of Pb2046Se2117 and Pb260Se249 quantum dots, we explicitly calculated the electron-hole Coulomb integrals and the P →S electron Auger relaxation rate. We find that the Auger mechanism can explain the experimentally observed P →S intraband decay time scale without the need to

  2. Ultra-bright pulsed electron beam with low longitudinal emittance

    DOEpatents

    Zolotorev, Max

    2010-07-13

    A high-brightness pulsed electron source, which has the potential for many useful applications in electron microscopy, inverse photo-emission, low energy electron scattering experiments, and electron holography has been described. The source makes use of Cs atoms in an atomic beam. The source is cycled beginning with a laser pulse that excites a single Cs atom on average to a band of high-lying Rydberg nP states. The resulting valence electron Rydberg wave packet evolves in a nearly classical Kepler orbit. When the electron reaches apogee, an electric field pulse is applied that ionizes the atom and accelerates the electron away from its parent ion. The collection of electron wave packets thus generated in a series of cycles can occupy a phase volume near the quantum limit and it can possess very high brightness. Each wave packet can exhibit a considerable degree of coherence.

  3. Effect of magnetic exchange, double exchange, vibronic coupling, and asymmetry on magnetic properties in d2-d3 mixed-valence dimers

    NASA Astrophysics Data System (ADS)

    Yang, Xiaohua; Hu, Haiquan; Chen, Zhida

    The effect of magnetic exchange, double exchange, vibronic coupling, and asymmetry on magnetic properties of d2-d3 systems is discussed. The temperature-dependent magnetic moment was calculated with the semiclassical adiabatic approach. The results show that the vibronic coupling from the out-of-phase breathing vibration on the metal sites (Piepho, Krausz, and Schatz [PKS] model) and the vibronic coupling from the stretching vibration between the metal sites (P model) favor the localization and delocalization of the "extra" electron in mixed-valence dimers, respectively. The magnetic properties are determined by the interplay among magnetic exchange, double exchange, and vibronic coupling. The results obtained by analyzing d2-d3 systems can be generalized to other full delocalized dinuclear mixed valence systems with a unique transferable electron.

  4. X-ray spectroscopy study of electronic structure of laser-irradiated Au nanoparticles in a silica film

    NASA Astrophysics Data System (ADS)

    Jonnard, P.; Bercegol, H.; Lamaignère, L.; Morreeuw, J.-P.; Rullier, J.-L.; Cottancin, E.; Pellarin, M.

    2005-03-01

    The electronic structure of gold nanoparticles embedded in a silica film is studied, both before and after irradiation at 355nm by a laser. The Au 5d occupied valence states are observed by x-ray emission spectroscopy. They show that before irradiation the gold atoms are in metallic states within the nanoparticles. After irradiation with a fluence of 0.5J/cm2, it is found that gold valence states are close to those of a metal-poor gold silicide; thanks to a comparison of the experimental Au 5d states with the calculated ones for gold silicides using the density-functional theory. The formation of such a compound is driven by the diffusion of the gold atoms into the silica film upon the laser irradiation. At higher fluence, 1J/cm2, we find a higher percentage of metallic gold that could be attributed to annealing in the silica matrix.

  5. Explaining the effect of event valence on unrealistic optimism.

    PubMed

    Gold, Ron S; Brown, Mark G

    2009-05-01

    People typically exhibit 'unrealistic optimism' (UO): they believe they have a lower chance of experiencing negative events and a higher chance of experiencing positive events than does the average person. UO has been found to be greater for negative than positive events. This 'valence effect' has been explained in terms of motivational processes. An alternative explanation is provided by the 'numerosity model', which views the valence effect simply as a by-product of a tendency for likelihood estimates pertaining to the average member of a group to increase with the size of the group. Predictions made by the numerosity model were tested in two studies. In each, UO for a single event was assessed. In Study 1 (n = 115 students), valence was manipulated by framing the event either negatively or positively, and participants estimated their own likelihood and that of the average student at their university. In Study 2 (n = 139 students), valence was again manipulated and participants again estimated their own likelihood; additionally, group size was manipulated by having participants estimate the likelihood of the average student in a small, medium-sized, or large group. In each study, the valence effect was found, but was due to an effect on estimates of own likelihood, not the average person's likelihood. In Study 2, valence did not interact with group size. The findings contradict the numerosity model, but are in accord with the motivational explanation. Implications for health education are discussed.

  6. Density-Pressure Profiles of Fe-Bearing MgSiO3 Liquid: Effects of Valence and Spin States, and Implications for the Chemical Evolution of the Lower Mantle

    NASA Astrophysics Data System (ADS)

    Karki, Bijaya B.; Ghosh, Dipta B.; Maharjan, Charitra; Karato, Shun-ichiro; Park, Jeffrey

    2018-05-01

    Density is a key property controlling the chemical state of Earth's interior. Our knowledge about the density of relevant melt compositions is currently poor at deep-mantle conditions. Here we report results from first-principles molecular-dynamics simulations of Fe-bearing MgSiO3 liquids considering different valence and spin states of iron over the whole mantle pressure conditions. Our simulations predict the high-spin to low-spin transition in both ferrous and ferric iron in the silicate liquid to occur gradually at pressures around 100 GPa. The calculated iron-induced changes in the melt density (about 8% increase for 25% iron content) are primarily due to the difference in atomic mass between Mg and Fe, with smaller contributions (<2%) from the valence and spin states. A comparison of the predicted density of mixtures of (Mg,Fe)(Si,Fe)O3 and (Mg,Fe)O liquids with the mantle density indicates that the density contrast between the melt and residual-solid depends strongly on pressure (depth): in the shallow lower mantle (depths < 1,000 km), the melt is lighter than the solids, whereas in the deep lower mantle (e.g., the D″ layer), the melt density exceeds the mantle density when iron content is relatively high and/or melt is enriched with Fe-rich ferropericlase.

  7. Electron-electron interaction in ion-atom collisions studied by projectile state-resolved Auger-electron spectroscopy

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

    Dohyung Lee.

    This dissertation addresses the problem of dynamic electron-electron interactions in fast ion-atom collisions using projectile Auger electron spectroscopy. The study was carried out by measuring high-resolution projectile KKL Auger electron spectra as a function of projectile energy for the various collision systems of 0.25-2 MeV/u O{sup q+} and F{sup q+} incident on H{sub 2} and He targets. The electrons were detected in the beam direction, where the kinematic broadening is minimized. A zero-degree tandem electron spectrometer system, was developed and showed the versatility of zero-degree measurements of collisionally-produced atomic states. The zero-degree binary encounter electrons (BEe), quasifree target electrons ionizedmore » by the projectiles in head-on collisions, were observed as a strong background in the KLL Auger electron spectrum. They were studied by treating the target ionization as 180{degree} Rutherford elastic scattering in the projectile frame, and resulted in a validity test of the impulse approximation (IA) and a way to determine the spectrometer efficiency. An anomalous q-dependence, in which the zero-degree BEe yields increase with decreasing projectile charge state (q), was observed. State-resolved KLL Auger cross sections were determined by using the BEe normalization and thus the cross section of the electron-electron interactions such as resonant transfer-excitation (RTE), electron-electron excitation (eeE), and electron-electron ionization (eeI) were determined. Projectile 2l capture with 1s {yields} 2p excitation by the captured target electron was observed as an RTE process with Li-like and He-like projectiles and the measured RTEA (RTE followed by Auger decay) cross sections showed good agreement with an RTE-IA treatment and RTE alignment theory.« less

  8. Electron Source in Photoinduced Hydrogen Production on Pt-supported TiO Particles

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

    Perkins, Craig L.; Henderson, Michael A.; McCready, David E.

    2001-01-18

    Abe et al. illuminated an aqueous suspension of TiO/Pt with a Hg arc lamp and observed H production in the absence of O production. An unspecified elemental analysis excluded carbonaceous contaminants, and the source of the electron donor was concluded to be Ti+ cations. We can suggest at least three more likely (than Ti) sources for their mysterious electron donor: (1)an overlooked inorganic species, (2) Ti, and/or (3)organic impurities. The authors excluded the latter in their paper, but we view this conclusion as suspect given the lack of information on the limits of detection of the carbon assay, and themore » fact that the choice of argon(thermal conductivity= 41.33 x 10-6 cal cm-2s-1 (C cm-1)-1)3 as a carrier gas in their thermal conductivity detector4 probably precluded the observation of CO (thermal conductivity= 37.61 x 10-6 cal cm-2s-1 (C cm-1)-1)3, which is a common product of organic photochemical oxidations. No mention is made of an analysis for inorganic impurities. It is widely accepted that nanometer scale TiO particles can have significant fractions of undercoordinated Ti sites which can be easily oxidized to Ti, the highest valence of Ti observed in condensed phases. Here we point out that oxidation of Ti to Ti is much more physically realistic than oxidation of Ti to Ti. Removal of a fifth electron from titanium requires {approx}56 eV5.Ti, if it were to be generated in a solid oxide, would extract an electron from the valence band composed mainly of oxygen 2s and 2p states rather than remain in the 5 valence state. This unrealistically high oxidation state seems even more unlikely given the fact that at the room temperatures used in the authors' reactions Ti would have been generated and remained at the surface (at room temperature the diffusion of Ti cations in TiO is minimal), and the fact that the surface Madelung potential is smaller than that of the bulk6.« less

  9. Spectroscopic evidence for temperature-dependent convergence of light- and heavy-hole valence bands of PbQ (Q = Te, Se, S)

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

    Zhao, J.; Malliakas, C. D.; Wijayaratne, K.

    2017-01-01

    We have conducted a temperature- dependent angle-resolved photoemission spectroscopy (ARPES) study of the electronic structures of PbTe, PbSe and PbS. Our ARPES data provide direct evidence for the light-hole upper valence bands (UVBs) and hitherto undetected heavy-hole lower valence bands (LVBs) in these materials. An unusual temperature-dependent relative movement between these bands leads to a monotonic decrease in the energy separation between their maxima with increasing temperature, which is known as band convergence and has long been believed to be the driving factor behind extraordinary thermoelectric performances of these compounds at elevated temperatures.

  10. Spectroscopic evidence for temperature-dependent convergence of light- and heavy-hole valence bands of PbQ (Q = Te, Se, S)

    NASA Astrophysics Data System (ADS)

    Zhao, J.; Malliakas, C. D.; Wijayaratne, K.; Karlapati, V.; Appathurai, N.; Chung, D. Y.; Rosenkranz, S.; Kanatzidis, M. G.; Chatterjee, U.

    2017-01-01

    We have conducted a temperature-dependent angle-resolved photoemission spectroscopy (ARPES) study of the electronic structures of PbTe, PbSe and PbS. Our ARPES data provide direct evidence for the light-hole upper valence bands (UVBs) and hitherto undetected heavy-hole lower valence bands (LVBs) in these materials. An unusual temperature-dependent relative movement between these bands leads to a monotonic decrease in the energy separation between their maxima with increasing temperature, which is known as band convergence and has long been believed to be the driving factor behind extraordinary thermoelectric performances of these compounds at elevated temperatures.

  11. Finding the hidden valence band of N  =  7 armchair graphene nanoribbons with angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Senkovskiy, Boris V.; Usachov, Dmitry Yu; Fedorov, Alexander V.; Haberer, Danny; Ehlen, Niels; Fischer, Felix R.; Grüneis, Alexander

    2018-07-01

    To understand the optical and transport properties of graphene nanoribbons, an unambiguous determination of their electronic band structure is needed. In this work we demonstrate that the photoemission intensity of each valence sub-band, formed due to the quantum confinement in quasi-one-dimensional (1D) graphene nanoribbons, is a peaked function of the two-dimensional (2D) momentum. We resolve the long-standing discrepancy regarding the valence band effective mass () of armchair graphene nanoribbons with a width of N  =  7 carbon atoms (7-AGNRs). In particular, angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy report   ≈0.2 and  ≈0.4 of the free electron mass (m e ), respectively. ARPES mapping in the full 2D momentum space identifies the experimental conditions for obtaining a large intensity for each of the three highest valence 1D sub-bands. Our detail map reveals that previous ARPES experiments have incorrectly assigned the second sub-band as the frontier one. The correct frontier valence sub-band for 7-AGNRs is only visible in a narrow range of emission angles. For this band we obtain an ARPES derived effective mass of 0.4 m e , a charge carrier velocity in the linear part of the band of 0.63  ×  106 m s‑1 and an energy separation of only  ≈60 meV to the second sub-band. Our results are of importance not only for the growing research field of graphene nanoribbons but also for the community, which studies quantum confined systems.

  12. Sex, Age, and Emotional Valence: Revealing Possible Biases in the ‘Reading the Mind in the Eyes’ Task

    PubMed Central

    Kynast, Jana; Schroeter, Matthias L.

    2018-01-01

    The ‘Reading the Mind in the Eyes’ test (RMET) assesses a specific socio-cognitive ability, i.e., the ability to identify mental states from gaze. The development of this ability in a lifespan perspective is of special interest. Whereas former investigations were limited mainly to childhood and adolescence, the focus has been shifted towards aging, and psychiatric and neurodegenerative diseases recently. Although the RMET is frequently applied in developmental psychology and clinical settings, stimulus characteristics have never been investigated with respect to potential effects on test performance. Here, we analyzed the RMET stimulus set with a special focus on interrelations between sex, age and emotional valence. Forty-three persons rated age and emotional valence of the RMET picture set. Differences in emotional valence and age ratings between male and female items were analyzed. The linear relation between age and emotional valence was tested over all items, and separately for male and female items. Male items were rated older and more negative than female stimuli. Regarding male RMET items, age predicted emotional valence: older age was associated with negative emotions. Contrary, age and valence were not linearly related in female pictures. All ratings were independent of rater characteristics. Our results demonstrate a strong confound between sex, age, and emotional valence in the RMET. Male items presented a greater variability in age ratings compared to female items. Age and emotional valence were negatively associated among male items, but no significant association was found among female stimuli. As personal attributes impact social information processing, our results may add a new perspective on the interpretation of previous findings on interindividual differences in RMET accuracy, particularly in the field of developmental psychology, and age-associated neuropsychiatric diseases. A revision of the RMET might be afforded to overcome confounds

  13. Lying about the valence of affective pictures: an fMRI study.

    PubMed

    Lee, Tatia M C; Lee, Tiffany M Y; Raine, Adrian; Chan, Chetwyn C H

    2010-08-25

    The neural correlates of lying about affective information were studied using a functional magnetic resonance imaging (fMRI) methodology. Specifically, 13 healthy right-handed Chinese men were instructed to lie about the valence, positive or negative, of pictures selected from the International Affective Picture System (IAPS) while their brain activity was scanned by a 3T Philip Achieva scanner. The key finding is that the neural activity associated with deception is valence-related. Comparing to telling the truth, deception about the valence of the affectively positive pictures was associated with activity in the inferior frontal, cingulate, inferior parietal, precuneus, and middle temporal regions. Lying about the valence of the affectively negative pictures, on the other hand, was associated with activity in the orbital and medial frontal regions. While a clear valence-related effect on deception was observed, common neural regions were also recruited for the process of deception about the valence of the affective pictures. These regions included the lateral prefrontal and inferior parietal regions. Activity in these regions has been widely reported in fMRI studies on deception using affectively-neutral stimuli. The findings of this study reveal the effect of valence on the neural activity associated with deception. Furthermore, the data also help to illustrate the complexity of the neural mechanisms underlying deception.

  14. High Resolution UV Emission Spectroscopy of Molecules Excited by Electron Impact

    NASA Technical Reports Server (NTRS)

    James, G. K.; Ajello, J. M.; Beegle, L.; Ciocca, M.; Dziczek, D.; Kanik, I.; Noren, C.; Jonin, C.; Hansen, D.

    1999-01-01

    Photodissociation via discrete line absorption into predissociating Rydberg and valence states is the dominant destruction mechanism of CO and other molecules in the interstellar medium and molecular clouds. Accurate values for the rovibronic oscillator strengths of these transitions and predissociation yields of the excited states are required for input into the photochemical models that attempt to reproduce observed abundances. We report here on our latest experimental results of the electron collisional properties of CO and N2 obtained using the 3-meter high resolution single-scattering spectroscopic facility at JPL.

  15. Developmental Reversals in False Memory: Effects of Emotional Valence and Arousal

    ERIC Educational Resources Information Center

    Brainerd, C. J.; Holliday, R. E.; Reyna, V. F.; Yang, Y.; Toglia, M. P.

    2010-01-01

    Do the emotional valence and arousal of events distort children's memories? Do valence and arousal modulate counterintuitive age increases in false memory? We investigated those questions in children, adolescents, and adults using the Cornell/Cortland Emotion Lists, a word list pool that induces false memories and in which valence and arousal can…

  16. Temperature-dependent electron paramagnetic resonance detect oxygen vacancy defects and Cr valence of tetragonal Ba(Ti1-xCrx)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Han, Dan-Dan; Lu, Da-Yong; Meng, Fan-Ling; Yu, Xin-Yu

    2018-03-01

    Temperature-dependent electron paramagnetic resonance (EPR) study was employed to detect oxygen vacancy defects in the tetragonal Ba(Ti1-xCrx)O3 (x = 5%) ceramic for the first time. In the rhombohedral phase below -150 °C, an EPR signal at g = 1.955 appeared in the insulating Ba(Ti1-xCrx)O3 (x = 5%) ceramic with an electrical resistivity of 108 Ω cm and was assigned to ionized oxygen vacancy defects. Ba(Ti1-xCrx)O3 ceramics exhibited a tetragonal structure except Ba(Ti1-xCrx)O3 (x = 10%) with a tetragonal-hexagonal mixed phase and a first-order phase transition dielectric behavior (ε‧m > 11,000). Mixed valence Cr ions could coexist in ceramics, form CrTi‧-VOrad rad or CrTirad-TiTi‧ defect complexes and make no contribution to a dielectric peak shift towards low temperature.

  17. An incompressible state of a photo-excited electron gas

    PubMed Central

    Chepelianskii, Alexei D.; Watanabe, Masamitsu; Nasyedkin, Kostyantyn; Kono, Kimitoshi; Konstantinov, Denis

    2015-01-01

    Two-dimensional electrons in a magnetic field can form new states of matter characterized by topological properties and strong electronic correlations as displayed in the integer and fractional quantum Hall states. In these states, the electron liquid displays several spectacular characteristics, which manifest themselves in transport experiments with the quantization of the Hall resistance and a vanishing longitudinal conductivity or in thermodynamic equilibrium when the electron fluid becomes incompressible. Several experiments have reported that dissipationless transport can be achieved even at weak, non-quantizing magnetic fields when the electrons absorb photons at specific energies related to their cyclotron frequency. Here we perform compressibility measurements on electrons on liquid helium demonstrating the formation of an incompressible electronic state under these resonant excitation conditions. This new state provides a striking example of irradiation-induced self-organization in a quantum system. PMID:26007282

  18. Tunability of the fractional quantum Hall states in buckled Dirac materials

    NASA Astrophysics Data System (ADS)

    Apalkov, Vadym M.; Chakraborty, Tapash

    2014-12-01

    We report on the fractional quantum Hall states of germanene and silicene where one expects a strong spin-orbit interaction. This interaction causes an enhancement of the electron-electron interaction strength in one of the Landau levels corresponding to the valence band of the system. This enhancement manifests itself as an increase of the fractional quantum Hall effect gaps compared to that in graphene and is due to the spin-orbit induced coupling of the Landau levels of the conduction and valence bands, which modifies the corresponding wave functions and the interaction within a single level. Due to the buckled structure, a perpendicular electric field lifts the valley degeneracy and strongly modifies the interaction effects within a single Landau level: in one valley the perpendicular electric field enhances the interaction strength in the conduction band Landau level, while in another valley, the electric field strongly suppresses the interaction effects.

  19. Character Disposition and Behavior Type: Influences of Valence on Preschool Children's Social Judgments

    ERIC Educational Resources Information Center

    Jones, Elaine F.; Tobias, Marvin; Pauley, Danielle; Thomson, Nicole Renick; Johnson, Shawana Lewis

    2009-01-01

    The authors studied the influences of valence information on preschool children's (n = 47) moral (good or bad), liking (liked or disliked by a friend), and consequence-of-behavior (reward or punishment) judgments. The authors presented 8 scenarios describing the behavior valence, positive valence (help, share), negative valence (verbal insult,…

  20. Motivation but not valence modulates neuroticism-dependent cingulate cortex and insula activity.

    PubMed

    Deng, Yaling; Li, Shijia; Zhou, Renlai; Walter, Martin

    2018-04-01

    Neuroticism has been found to specifically modulate amygdala activations during differential processing of valence and motivation while other brain networks yet are unexplored for associated effects. The main purpose of this study was to investigate whether neural mechanisms processing valence or motivation are prone to neuroticism in the salience network (SN), a network that is anchored in the anterior cingulate cortex (ACC) and the anterior insula. This study used functional magnetic resonance imaging (fMRI) and an approach/avoid emotional pictures task to investigate brain activations modulated by pictures' valence or motivational status between high and low neurotic individuals. We found that neuroticism-dependent SN and the parahippocampal-fusiform area activations were modulated by motivation but not valence. Valence in contrast interacted with neuroticism in the lateral orbitofrontal cortex. We suggested that neuroticism modulated valence and motivation processing, however, under the influence of the two distinct networks. Neuroticism modulated the motivation through the SN while it modulated the valence through the orbitofrontal networks. © 2018 Wiley Periodicals, Inc.

  1. Chemical and valence reconstruction at the surface of SmB6 revealed by means of resonant soft x-ray reflectometry

    NASA Astrophysics Data System (ADS)

    Zabolotnyy, V. B.; Fürsich, K.; Green, R. J.; Lutz, P.; Treiber, K.; Min, Chul-Hee; Dukhnenko, A. V.; Shitsevalova, N. Y.; Filipov, V. B.; Kang, B. Y.; Cho, B. K.; Sutarto, R.; He, Feizhou; Reinert, F.; Inosov, D. S.; Hinkov, V.

    2018-05-01

    Samarium hexaboride (SmB6), a Kondo insulator with mixed valence, has recently attracted much attention as a possible host for correlated topological surface states. Here, we use a combination of x-ray absorption and reflectometry techniques, backed up with a theoretical model for the resonant M4 ,5 absorption edge of Sm and photoemission data, to establish laterally averaged chemical and valence depth profiles at the surface of SmB6. We show that upon cleaving, the highly polar (001) surface of SmB6 undergoes substantial chemical and valence reconstruction, resulting in boron termination and a Sm3 + dominated subsurface region. Whereas at room temperature, the reconstruction occurs on a timescale of less than 2 h, it takes about 24 h below 50 K. The boron termination is eventually established, irrespective of the initial termination. Our findings reconcile earlier depth resolved photoemission and scanning tunneling spectroscopy studies performed at different temperatures and are important for better control of surface states in this system.

  2. Electronic structures of GaAs/AlxGa1-xAs quantum double rings

    PubMed Central

    Xia, Jian-Bai

    2006-01-01

    In the framework of effective mass envelope function theory, the electronic structures of GaAs/AlxGa1-xAs quantum double rings (QDRs) are studied. Our model can be used to calculate the electronic structures of quantum wells, wires, dots, and the single ring. In calculations, the effects due to the different effective masses of electrons and holes in GaAs and AlxGa1-xAs and the valence band mixing are considered. The energy levels of electrons and holes are calculated for different shapes of QDRs. The calculated results are useful in designing and fabricating the interrelated photoelectric devices. The single electron states presented here are useful for the study of the electron correlations and the effects of magnetic fields in QDRs.

  3. Startle modulation and explicit valence evaluations dissociate during backward fear conditioning.

    PubMed

    Luck, Camilla C; Lipp, Ottmar V

    2017-05-01

    Blink startle magnitude is linearly modulated by affect such that, relative to neutral stimuli, startle magnitude is inhibited during pleasant stimuli and potentiated during unpleasant stimuli. Andreatta, Mühlberger, Yarali, Gerber, and Pauli (2010), however, report a dissociation between startle modulation and explicit valence evaluations during backward conditioning, a procedure in which the unconditional stimulus precedes the conditional stimulus (CS). Relative to controls, startles elicited during the CS were inhibited, suggesting that the CS had acquired positive valence, but participants still evaluated the CS as unpleasant after the experiment. In Experiment 1, we aimed to replicate this dissociation using a trial-by-trial measure of CS valence to measure startle modulation and CS valence simultaneously during forward and backward differential fear conditioning. In Experiment 2, we examined whether early and late portions of the CS could acquire differential valence by presenting startle probes at early and late probe positions during the CS. In both experiments, the dissociation between startle modulation and explicit valence evaluations in backward conditioning replicated, with CS+ evaluated as less pleasant than CS-, but startles elicited during CS+ inhibited relative to CS-. In Experiment 2, we provide preliminary evidence that this inhibition was present early, but not late, during the CS+. The results replicate the dissociation between implicit and explicit CS valence reported by Andreatta et al. (2010) using a trial-by-trial measure of valence. We also provide preliminary evidence that this dissociation may occur because the implicit and explicit measures are recorded at different times during the CS presentation. © 2017 Society for Psychophysiological Research.

  4. Magnetic and electronic properties of SrMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Mandal, Arup Kumar; Panchal, Gyanendra; Choudhary, R. J.; Phase, D. M.

    2018-05-01

    Single phase hexagonal bulk SrMnO3 (SMO) was prepared by solid state route and it was used for depositing thin films by pulsed laser deposition (PLD) technique on single crystalline (100) oriented SrTiO3 (STO) substrate. X-ray diffraction shows that the thin film is deposited in cubic SrMnO3 phase. From X-ray absorption at the Mn L edge we observed the mixed valency of Mn (Mn3+& Mn4+) due to strain induced by the lattice mismatching between SMO and STO. Due to this mixed valency of Mn ion in SMO film, the ferromagnetic nature is observed at lower temperature because of double exchange. After post annealing with very low oxygen partial pressure, magnetic and electronic property of SMO films are effectively modified.

  5. Intramolecular interactions of L-phenylalanine: Valence ionization spectra and orbital momentum distributions of its fragment molecules.

    PubMed

    Ganesan, Aravindhan; Wang, Feng; Falzon, Chantal

    2011-02-01

    Intramolecular interactions between fragments of L-phenylalanine, i.e., phenyl and alaninyl, have been investigated using dual space analysis (DSA) quantum mechanically. Valence space photoelectron spectra (PES), orbital energy topology and correlation diagram, as well as orbital momentum distributions (MDs) of L-phenylalanine, benzene and L-alanine are studied using density functional theory methods. While fully resolved experimental PES of L-phenylalanine is not yet available, our simulated PES reproduces major features of the experimental measurement. For benzene, the simulated orbital MDs for 1e(1g) and 1a(2u) orbitals also agree well with those measured using electron momentum spectra. Our theoretical models are then applied to reveal intramolecular interactions of the species on an orbital base, using DSA. Valence orbitals of L-phenylalanine can be essentially deduced into contributions from its fragments such as phenyl and alaninyl as well as their interactions. The fragment orbitals inherit properties of their parent species in energy and shape (ie., MDs). Phenylalanine orbitals show strong bonding in the energy range of 14-20 eV, rather than outside of this region. This study presents a competent orbital based fragments-in-molecules picture in the valence space, which supports the fragment molecular orbital picture and building block principle in valence space. The optimized structures of the molecules are represented using the recently developed interactive 3D-PDF technique. Copyright © 2010 Wiley Periodicals, Inc.

  6. Electron beams in research and technology

    NASA Astrophysics Data System (ADS)

    Mehnert, R.

    1995-11-01

    Fast electrons lose their energy by inelastic collisions with electrons of target molecules forming secondary electrons and excited molecules. Coulomb interaction of secondary electrons with valence electrons of neighboring molecules leads to the formation of radical cations, thermalized electrons, excited molecular states and radicals. The primary reactive species initiate chemical reactions in the materials irradiated. Polymer modifications using accelerated electrons such as cross-linking of cable insulation, tubes, pipes and moldings, vulcanization of elastomers, grafting of polymer surfaces, processing of foamed plastics and heat shrinkable materials have gained wide industrial acceptance. A steadily growing electron beam technology is curing of paints, lacquers, printing inks and functional coatings. Electron beam processing offers high productivity, the possibility to treat the materials at normal temperature and pressure, excellent process control and clean production conditions. On an industrial scale the most important application of fast electrons is curing of 100% reactive monomer/prepolymer systems. Mainly acrylates and epoxides are used to formulate functional coatings on substrates such as paper, foil, wood, fibre board and high pressure laminates. A survey is given about the reaction mechanism of curing, the characterization of cured coatings, and of some industrial application.

  7. Revealing the electronic ground state of ReNiO3 combining Ni-L3 x-ray absorption and resonant inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Bisogni, Valentina; Catalano, Sara; Green, Robert; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Balandesh, Shadi; Strocov, Vladimir N.; Zubko, Pavlo; Sawatzky, George; Triscone, Jean-Marc; Schmitt, Thorsten

    Rare-earth nickelates ReNiO3 attract a lot of interest thanks to their intriguing physical properties like sharp metal to insulator transition, unusual magnetic order and expected superconductivity in nickelate-based heterostructures. Full understanding of these materials, however, is hampered by the difficulties in describing their electronic ground state (GS). Taking a NdNiO3 thin film as a representative example, we reveal with x-ray absorption and resonant inelastic x-ray scattering unusual coexistence of bound and continuum excitations, providing strong evidence for abundant O 2p holes in the GS of these materials. Using an Anderson impurity model interpretation, we show that these distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the O 2p valence band, confirming suggestions that these materials exhibit a negative charge-transfer energy, with O 2p states extending across the Fermi level.

  8. Effects of Emotion on Associative Recognition: Valence and Retention Interval Matter

    PubMed Central

    Pierce, Benton H.; Kensinger, Elizabeth A.

    2011-01-01

    In two experiments, we examined the effects of emotional valence and arousal on associative binding. Participants studied negative, positive, and neutral word pairs, followed by an associative recognition test. In Experiment 1, with a short-delayed test, accuracy for intact pairs was equivalent across valences, whereas accuracy for rearranged pairs was lower for negative than for positive and neutral pairs. In Experiment 2, we tested participants after a one-week delay and found that accuracy was greater for intact negative than for intact neutral pairs, whereas rearranged pair accuracy was equivalent across valences. These results suggest that, although negative emotional valence impairs associative binding after a short delay, it may improve binding after a longer delay. The results also suggest that valence, as well as arousal, needs to be considered when examining the effects of emotion on associative memory. PMID:21401233

  9. Transferable pseudoclassical electrons for aufbau of atomic ions.

    PubMed

    Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

    2014-06-05

    Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. Copyright © 2014 Wiley Periodicals, Inc.

  10. Reconfiguring crystal and electronic structures of MoS 2 by substitutional doping

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

    Suh, Joonki; Tan, Teck Leong; Zhao, Weijie

    Doping of traditional semiconductors has enabled technological applications in modern electronics by tailoring their chemical, optical and electronic properties. However, substitutional doping in two-dimensional semiconductors is at a comparatively early stage, and the resultant effects are less explored. In this work, we report unusual effects of degenerate doping with Nb on structural, electronic and optical characteristics of MoS 2 crystals. The doping readily induces a structural transformation from naturally occurring 2H stacking to 3R stacking. Electronically, a strong interaction of the Nb impurity states with the host valence bands drastically and nonlinearly modifies the electronic band structure with the valencemore » band maximum of multilayer MoS 2 at the Γ point pushed upward by hybridization with the Nb states. Finally, when thinned down to monolayers, in stark contrast, such significant nonlinear effect vanishes, instead resulting in strong and broadband photoluminescence via the formation of exciton complexes tightly bound to neutral acceptors.« less

  11. Reconfiguring crystal and electronic structures of MoS 2 by substitutional doping

    DOE PAGES

    Suh, Joonki; Tan, Teck Leong; Zhao, Weijie; ...

    2018-01-15

    Doping of traditional semiconductors has enabled technological applications in modern electronics by tailoring their chemical, optical and electronic properties. However, substitutional doping in two-dimensional semiconductors is at a comparatively early stage, and the resultant effects are less explored. In this work, we report unusual effects of degenerate doping with Nb on structural, electronic and optical characteristics of MoS 2 crystals. The doping readily induces a structural transformation from naturally occurring 2H stacking to 3R stacking. Electronically, a strong interaction of the Nb impurity states with the host valence bands drastically and nonlinearly modifies the electronic band structure with the valencemore » band maximum of multilayer MoS 2 at the Γ point pushed upward by hybridization with the Nb states. Finally, when thinned down to monolayers, in stark contrast, such significant nonlinear effect vanishes, instead resulting in strong and broadband photoluminescence via the formation of exciton complexes tightly bound to neutral acceptors.« less

  12. What is the valence of Mn in GaMnN?

    NASA Astrophysics Data System (ADS)

    Nelson, Ryky; Berlijn, Tom; Moreno, Juana; Jarrell, Mark; Ku, Wei

    2014-03-01

    Motivated by the potential high Curie temperature of GaMnN, we investigate the controversial Mn-valence in this diluted magnetic semiconductor. From a first-principles Wannier functions analysis of the high energy Hilbert space we find unambiguously the charge state of Mn to be close to 2 + (d5), but in a mixed spin configuration with average magnetic moments of 4 μB. Using more extended Wannier orbitals to capture the lower-energy physics, we further demonstrate the feasibility of both the effective d4 description (appropriate to deal with the local magnetic moment and Jahn-Teller distortion), and the effective d5 description (relevant to study long-range magnetic order). Our derivation highlights the general richness of low-energy sectors in interacting many-body systems and the generic need for multiple effective descriptions, and advocates for a diminished relevance of atomic valence measured by various experimental probes. This research is supported in part by LA-SiGMA, NSF Award Number #EPS-1003897. TB was supported by DOE CMCSN and as a Wigner Fellow at the Oak Ridge National Laboratory.

  13. Effects of emotionally valenced working memory taxation on negative memories.

    PubMed

    Tsai, Cynthia; McNally, Richard J

    2014-03-01

    Memories enter a labile state during recollection. Thus, memory changes that occur during recollection can affect future instances of its activation. Having subjects perform a secondary task that taxes working memory while they recall a negative emotional memory often reduces its vividness and emotional intensity during subsequent recollections. However, researchers have not manipulated the emotional valence of the secondary task itself. Subjects viewed a video depicting the aftermath of three fatal road traffic accidents, establishing the same negative emotional memory for all subjects. We then tested their memory for the video after randomly assigning them to no secondary task or a delayed match-to-sample secondary task involving photographs of positive, negative, or neutral emotional valence. The positive secondary task reduced memory for details about the video, whereas negative and neutral tasks did not. We did not assess the vividness and emotionality of the subjects' memory of the video. Having subjects recall a stressful experience while performing a positively valent secondary task can decrement details of the memory and perhaps its emotionality. Copyright © 2013 Elsevier Ltd. All rights reserved.

  14. Quasi-degenerate perturbation theory using matrix product states

    NASA Astrophysics Data System (ADS)

    Sharma, Sandeep; Jeanmairet, Guillaume; Alavi, Ali

    2016-01-01

    In this work, we generalize the recently proposed matrix product state perturbation theory (MPSPT) for calculating energies of excited states using quasi-degenerate (QD) perturbation theory. Our formulation uses the Kirtman-Certain-Hirschfelder canonical Van Vleck perturbation theory, which gives Hermitian effective Hamiltonians at each order, and also allows one to make use of Wigner's 2n + 1 rule. Further, our formulation satisfies Granovsky's requirement of model space invariance which is important for obtaining smooth potential energy curves. Thus, when we use MPSPT with the Dyall Hamiltonian, we obtain a model space invariant version of quasi-degenerate n-electron valence state perturbation theory (NEVPT), a property that the usual formulation of QD-NEVPT2 based on a multipartitioning technique lacked. We use our method on the benchmark problems of bond breaking of LiF which shows ionic to covalent curve crossing and the twist around the double bond of ethylene where significant valence-Rydberg mixing occurs in the excited states. In accordance with our previous work, we find that multi-reference linearized coupled cluster theory is more accurate than other multi-reference theories of similar cost.

  15. The electronic and optical properties of amorphous silica with hydrogen defects by ab initio calculations

    NASA Astrophysics Data System (ADS)

    Ren, Dahua; Xiang, Baoyan; Hu, Cheng; Qian, Kai; Cheng, Xinlu

    2018-04-01

    Hydrogen can be trapped in the bulk materials in four forms: interstitial molecular H2, interstitial atom H, O‑H+(2Si=O–H)+, Si‑H‑( {{4O}}\\bar \\equiv {{Si&x2212H}})‑ to affect the electronic and optical properties of amorphous silica. Therefore, the electronic and optical properties of defect-free and hydrogen defects in amorphous silica were performed within the scheme of density functional theory. Initially, the negative charged states hydrogen defects introduced new defect level between the valence band top and conduction band bottom. However, the neutral and positive charged state hydrogen defects made both the valence band and conduction band transfer to the lower energy. Subsequently, the optical properties such as absorption spectra, conductivity and loss functions were analyzed. It is indicated that the negative hydrogen defects caused the absorption peak ranging from 0 to 2.0 eV while the positive states produced absorption peaks at lower energy and two strong absorption peaks arose at 6.9 and 9.0 eV. However, the neutral hydrogen defects just improved the intensity of absorption spectrum. This may give insights into understanding the mechanism of laser-induced damage for optical materials. Project supported by the Science and Technology of Hubei Provincial Department of Education (No. B2017098).

  16. Magnetic properties and core electron binding energies of liquid water

    NASA Astrophysics Data System (ADS)

    Galamba, N.; Cabral, Benedito J. C.

    2018-01-01

    The magnetic properties and the core and inner valence electron binding energies of liquid water are investigated. The adopted methodology relies on the combination of molecular dynamics and electronic structure calculations. Born-Oppenheimer molecular dynamics with the Becke and Lee-Yang-Parr functionals for exchange and correlation, respectively, and includes an empirical correction (BLYP-D3) functional and classical molecular dynamics with the TIP4P/2005-F model were carried out. The Keal-Tozer functional was applied for predicting magnetic shielding and spin-spin coupling constants. Core and inner valence electron binding energies in liquid water were calculated with symmetry adapted cluster-configuration interaction. The relationship between the magnetic shielding constant σ(17O), the role played by the oxygen atom as a proton acceptor and donor, and the tetrahedral organisation of liquid water are investigated. The results indicate that the deshielding of the oxygen atom in water is very dependent on the order parameter (q) describing the tetrahedral organisation of the hydrogen bond network. The strong sensitivity of magnetic properties on changes of the electronic density in the nuclei environment is illustrated by a correlation between σ(17O) and the energy gap between the 1a1[O1s] (core) and the 2a1 (inner valence) orbitals of water. Although several studies discussed the eventual connection between magnetic properties and core electron binding energies, such a correlation could not be clearly established. Here, we demonstrate that for liquid water this correlation exists although involving the gap between electron binding energies of core and inner valence orbitals.

  17. High-Harmonic Generation in Solids with and without Topological Edge States

    NASA Astrophysics Data System (ADS)

    Bauer, Dieter; Hansen, Kenneth K.

    2018-04-01

    High-harmonic generation in the two topological phases of a finite, one-dimensional, periodic structure is investigated using a self-consistent time-dependent density functional theory approach. For harmonic photon energies smaller than the band gap, the harmonic yield is found to differ by up to 14 orders of magnitude for the two topological phases. This giant topological effect is explained by the degree of destructive interference in the harmonic emission of all valence-band (and edge-state) electrons, which strongly depends on whether or not topological edge states are present. The combination of strong-field laser physics with topological condensed matter opens up new possibilities to electronically control strong-field-based light or particle sources or—conversely—to steer by all optical means topological electronics.

  18. Structural, optical and electronic properties of K2Ba(NO3)4 crystal

    NASA Astrophysics Data System (ADS)

    Isaenko, L. I.; Korzhneva, K. E.; Goryainov, S. V.; Goloshumova, A. A.; Sheludyakova, L. A.; Bekenev, V. L.; Khyzhun, O. Y.

    2018-02-01

    Nitrate crystals reveal nonlinear optical properties and could be considered as converters of laser radiation in the short-wave region. The conditions for obtaining and basic properties of K2Ba(NO3)4 double nitrate crystals were investigated. Crystal growth was implemented by slow cooling in the temperature range of 72-49 °C and low rate evaporation. The structural analysis of K2Ba(NO3)4 formation on the basis of two mixed simple nitrate structures is discussed. The main groups of oscillations in K2Ba(NO3)4 crystal were revealed using Raman and IR spectroscopy, and the table of vibrations for this compound was compiled. The electronic structure of K2Ba(NO3)4 was elucidated in the present work from both experimental and theoretical viewpoints. In particular, X-ray photoelectron spectroscopy (XPS) was employed in the present work to measure binding energies of the atoms constituting the titled compound and its XPS valence-band spectrum for both pristine and Ar+ ion-bombarded surfaces. Further, total and partial densities of states of constituent atoms of K2Ba(NO3)4 have been calculated. The calculations reveal that the O 2p states dominate in the total valence-band region of K2Ba(NO3)4 except of its bottom, where K 3p and Ba 5p states are the principal contributors, while the bottom of the conduction band is composed mainly of the unoccupied O 2p states, with somewhat smaller contributions of the N 2p∗ states as well. With respect to the occupation of the valence band by the O 2p states, the present band-structure calculations are confirmed by comparison on a common energy scale of the XPS valence-band spectrum and the X-ray emission O Kα band for the K2Ba(NO3)4 crystal under study. Furthermore, the present calculations indicate that the K2Ba(NO3)4 compound is a direct-gap material.

  19. Electronic structure of LiCoO2 thin films: A combined photoemission spectroscopy and density functional theory study

    NASA Astrophysics Data System (ADS)

    Ensling, David; Thissen, Andreas; Laubach, Stefan; Schmidt, Peter C.; Jaegermann, Wolfram

    2010-11-01

    The electronic properties of LiCoO2 have been studied by theoretical band-structure calculations (using density functional theory) and experimental methods (photoemission). Synchrotron-induced photoelectron spectroscopy, resonant photoemission spectroscopy (ResPES), and soft x-ray absorption (XAS) have been applied to investigate the electronic structure of both occupied and unoccupied states. High-quality PES spectra were obtained from stoichiometric and highly crystalline LiCoO2 thin films deposited “in situ” by rf magnetron sputtering. An experimental approach of separating oxygen- and cobalt-derived (final) states by ResPES in the valence-band region is presented. The procedure takes advantage of an antiresonant behavior of cobalt-derived states at the 3p-3d excitation threshold. Information about the unoccupied density of states has been obtained by OK XAS. The structure of the CoL absorption edge is compared to semiempirical charge-transfer multiplet calculations. The experimental results are furthermore compared with band-structure calculations considering three different exchange potentials [generalized gradient approximation (GGA), using a nonlocal Hubbard U (GGA+U) and using a hybrid functional (Becke, three-parameter, Lee-Yang-Parr [B3LYP])]. For these different approaches total density of states and partial valence-band density of states have been investigated. The best qualitative agreement with experimental results has been obtained by using a GGA+U functional with U=2.9eV .

  20. Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations

    NASA Astrophysics Data System (ADS)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.

    2015-04-01

    High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

  1. Electron exchange between tin impurity U{sup –} centers in PbS{sub z}Se{sub 1–z} alloys

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

    Marchenko, A. V.; Terukov, E. I.; Seregin, P. P., E-mail: ppseregin@mail.ru

    2016-07-15

    Using emission {sup 119mm}Sn({sup 119m}Sn) and {sup 119}Sb({sup 119m}Sn) Mössbauer spectroscopy, it is shown that impurity tin atoms in PbS{sub z}Se{sub 1–z} alloys substitute lead atoms and are two-electron donors with negative correlation energy (U{sup –} centers). It is found that the energy levels related to impurity tin atoms are in the lower half of the band gap at z ≥ 0.5 against the background of allowed valence-band states at z ≤ 0.4. The electron exchange between neutral and doubly ionized tin U{sup –} centers in partially compensated Pb{sub 0.99}Sn{sub 0.005}Na{sub 0.005}S{sub z}Se{sub 1–z} alloys is studied. The activation energymore » of this process decreases from 0.111(5) eV for a composition with z = 1 to 0.049(5) eV for compositions with c ≤ 0. For all z, the exchange is implemented via the simultaneous transfer of two electrons using delocalized valence-band states.« less

  2. Work Valence as a Predictor of Academic Achievement in the Family Context

    ERIC Educational Resources Information Center

    Porfeli, Erik; Ferrari, Lea; Nota, Laura

    2013-01-01

    This study asserts a theoretical model of academic and work socialization within the family setting. The presumed associations between parents' work valences, children's work valences and valence perceptions, and children's academic interest and achievement are tested. The results suggest that children's perceptions of parents mediate the…

  3. Valence and L-shell photoionization of Cl-like argon using R-matrix techniques

    NASA Astrophysics Data System (ADS)

    Tyndall, N. B.; Ramsbottom, C. A.; Ballance, C. P.; Hibbert, A.

    2016-02-01

    Photoionization cross-sections are obtained using the relativistic Dirac Atomic R-matrix Codes (DARC) for all valence and L-shell energy ranges between 27 and 270 eV. A total of 557 levels arising from the dominant configurations 3s23p4, 3s3p5, 3p6, 3s23p3[3d, 4s, 4p], 3p53d, 3s23p23d2, 3s3p43d, 3s3p33d2 and 2s22p53s23p5 have been included in the target wavefunction representation of the Ar III ion, including up to 4p in the orbital basis. We also performed a smaller Breit-Pauli (BP) calculation containing the lowest 124 levels. Direct comparisons are made with previous theoretical and experimental work for both valence shell and L-shell photoionization. Excellent agreement was found for transitions involving the 2Po initial state to all allowed final states for both calculations across a range of photon energies. A number of resonant states have been identified to help analyse and explain the nature of the spectra at photon energies between 250 and 270 eV.

  4. Resonant electron capture by orotic acid molecules

    NASA Astrophysics Data System (ADS)

    Muftakhov, M. V.; Shchukin, P. V.; Khatymov, R. V.

    2017-09-01

    Resonant electron attachment by orotic acid molecules (6-COOH-uracil) are studied in the energy range of 0-14 eV via negative ion mass spectrometry. Molecular ions, whose lifetimes relative to electron autodetachment are found to be 300 μs are recorded in the region of thermal electron energies; they form in the valence state through a vibration-excited resonance mechanism. Unlike unsubstituted uracil, most dissociative processes occur in the low-energy region of <4 eV and are due to carboxylic anions. An absolute cross section of 2.4 × 10-17 cm2 is found for the most intense fragment ions [M-H]- at an output energy of 1.33 eV. The kinetics of decarboxylation is considered for these ions. This could be a model reaction for the last stage of uridine monophosphate biosynthesis.

  5. Spectroscopic and theoretical investigation of the electronic states of layered perovskite oxyfluoride S r2Ru O3F2 thin films

    NASA Astrophysics Data System (ADS)

    Chikamatsu, Akira; Kurauchi, Yuji; Kawahara, Keisuke; Onozuka, Tomoya; Minohara, Makoto; Kumigashira, Hiroshi; Ikenaga, Eiji; Hasegawa, Tetsuya

    2018-06-01

    We investigated the electronic structure of a layered perovskite oxyfluoride S r2Ru O3F2 thin film by hard x-ray photoemission spectroscopy (HAXPES) and soft x-ray absorption spectroscopy (XAS) as well as density functional theory (DFT)-based calculations. The core-level HAXPES spectra suggested that S r2Ru O3F2 is a Mott insulator. The DFT calculations described the total and site-projected density of states and the band dispersion for the optimized crystal structure of S r2Ru O3F2 , predicting that R u4 + takes a high-spin configuration of (xy ) ↑(yz ,z x ) ↑↑(3z2-r2 ) ↑ and that S r2Ru O3F2 has an indirect band gap of 0.7 eV with minima at the M ,A and X ,R points. HAXPES spectra near the Fermi level and the angular-dependent O 1 s XAS spectra of the S r2Ru O3F2 thin film, corresponding to the valence band and conduction band density of states, respectively, were drastically different compared to those of the S r2Ru O4 film, suggesting that the changes in the electronic states were mainly driven by the substitution of an oxygen atom coordinated to Ru by fluorine and subsequent modification of the crystal field.

  6. Vibrational treatment of the formic acid double minimum case in valence coordinates

    NASA Astrophysics Data System (ADS)

    Richter, Falk; Carbonnière, P.

    2018-02-01

    One single full dimensional valence coordinate HCOOH ground state potential energy surface accurate for both cis and trans conformers for all levels up to 6000 cm-1 relative to trans zero point energy has been generated at CCSD(T)-F12a/aug-cc-pVTZ level. The fundamentals and a set of eigenfunctions complete up to about 3120 and 2660 cm-1 for trans- and cis-HCOOH, respectively, have been calculated and assigned using the improved relaxation method of the Heidelberg multi-configuration time-dependent Hartree package and an exact expression for the kinetic energy in valence coordinates generated by the TANA program. The calculated trans fundamental transition frequencies agree with experiment to within 5 cm-1. A few reassignments are suggested. Our results discard any cis trans delocalization effects for vibrational eigenfunctions up to 3640 cm-1 relative to trans zero point energy.

  7. Chemical Bonding: The Orthogonal Valence-Bond View

    PubMed Central

    Sax, Alexander F.

    2015-01-01

    Chemical bonding is the stabilization of a molecular system by charge- and spin-reorganization processes in chemical reactions. These processes are said to be local, because the number of atoms involved is very small. With multi-configurational self-consistent field (MCSCF) wave functions, these processes can be calculated, but the local information is hidden by the delocalized molecular orbitals (MO) used to construct the wave functions. The transformation of such wave functions into valence bond (VB) wave functions, which are based on localized orbitals, reveals the hidden information; this transformation is called a VB reading of MCSCF wave functions. The two-electron VB wave functions describing the Lewis electron pair that connects two atoms are frequently called covalent or neutral, suggesting that these wave functions describe an electronic situation where two electrons are never located at the same atom; such electronic situations and the wave functions describing them are called ionic. When the distance between two atoms decreases, however, every covalent VB wave function composed of non-orthogonal atomic orbitals changes its character from neutral to ionic. However, this change in the character of conventional VB wave functions is hidden by its mathematical form. Orthogonal VB wave functions composed of orthonormalized orbitals never change their character. When localized fragment orbitals are used instead of atomic orbitals, one can decide which local information is revealed and which remains hidden. In this paper, we analyze four chemical reactions by transforming the MCSCF wave functions into orthogonal VB wave functions; we show how the reactions are influenced by changing the atoms involved or by changing their local symmetry. Using orthogonal instead of non-orthogonal orbitals is not just a technical issue; it also changes the interpretation, revealing the properties of wave functions that remain otherwise undetected. PMID:25906476

  8. Electron momentum density and Compton profile by a semi-empirical approach

    NASA Astrophysics Data System (ADS)

    Aguiar, Julio C.; Mitnik, Darío; Di Rocco, Héctor O.

    2015-08-01

    Here we propose a semi-empirical approach to describe with good accuracy the electron momentum densities and Compton profiles for a wide range of pure crystalline metals. In the present approach, we use an experimental Compton profile to fit an analytical expression for the momentum densities of the valence electrons. This expression is similar to a Fermi-Dirac distribution function with two parameters, one of which coincides with the ground state kinetic energy of the free-electron gas and the other resembles the electron-electron interaction energy. In the proposed scheme conduction electrons are neither completely free nor completely bound to the atomic nucleus. This procedure allows us to include correlation effects. We tested the approach for all metals with Z=3-50 and showed the results for three representative elements: Li, Be and Al from high-resolution experiments.

  9. Emotions and false memories: valence or arousal?

    PubMed

    Corson, Yves; Verrier, Nadège

    2007-03-01

    The effects of mood on false memories have not been studied systematically until recently. Some results seem to indicate that negative mood may reduce false recall and thus suggest an influence of emotional valence on false memory. The present research tested the effects of both valence and arousal on recall and recognition and indicates that the effect is actually due to arousal. In fact, whether participants' mood is positive, negative, or neutral, false memories are significantly more frequent under conditions of high arousal than under conditions of low arousal.

  10. Excitation of lowest electronic states of the uracil molecule by slow electrons

    NASA Astrophysics Data System (ADS)

    Chernyshova, I. V.; Kontros, J. E.; Markush, P. P.; Shpenik, O. B.

    2012-07-01

    The excitation of lowest electronic states of the uracil molecule in the gas phase has been studied by electron energy loss spectroscopy. Along with excitation of lowest singlet states, excitation of two lowest triplet states at 3.75 and 4.76 eV (±0.05 eV) and vibrational excitation of the molecule in two resonant ranges (1-2 and 3-4 eV) have been observed for the first time. The peak of the excitation band related to the lowest singlet state (5.50 eV) is found to be blueshifted by 0.4 eV in comparison with the optical absorption spectroscopy data. The threshold excitation spectra have been measured for the first time, with detection of electrons inelastically scattered by an angle of 180°. These spectra exhibit clear separation of the 5.50-eV-wide band into two bands, which are due to the excitation of the triplet 13 A″ and singlet 11 A' states.

  11. Identification of metal s states in Sn-doped anatase by polarisation dependent hard X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Regoutz, A.; Oropeza, F. E.; Poll, C. G.; Payne, D. J.; Palgrave, R. G.; Panaccione, G.; Borgatti, F.; Agrestini, S.; Utsumi, Y.; Tsuei, K. D.; Liao, Y. F.; Watson, G. W.; Egdell, R. G.

    2016-03-01

    The contributions of Sn 5s and Ti 4s states to the valence band electronic structure of Sn-doped anatase have been identified by hard X-ray photoelectron spectroscopy. The metal s state intensity is strongly enhanced relative to that of O 2p states at high photon energies due to matrix element effects when electrons are detected parallel to the direction of the polarisation vector of the synchrotron beam, but becomes negligible in the perpendicular direction. The experimental spectra in both polarisations are in good agreement with cross section and asymmetry parameter weighted partial densities of states derived from density functional theory calculations.

  12. A revised MRCI-algorithm. I. Efficient combination of spin adaptation with individual configuration selection coupled to an effective valence-shell Hamiltonian

    NASA Astrophysics Data System (ADS)

    Strodel, Paul; Tavan, Paul

    2002-09-01

    We present a revised multi-reference configuration interaction (MRCI) algorithm for balanced and efficient calculation of electronic excitations in molecules. The revision takes up an earlier method, which had been designed for flexible, state-specific, and individual selection (IS) of MRCI expansions, included perturbational corrections (PERT), and used the spin-coupled hole-particle formalism of Tavan and Schulten (1980) for matrix-element evaluation. It removes the deficiencies of this method by introducing tree structures, which code the CI bases and allow us to efficiently exploit the sparseness of the Hamiltonian matrices. The algorithmic complexity is shown to be optimal for IS/MRCI applications. The revised IS/MRCI/PERT module is combined with the effective valence shell Hamiltonian OM2 suggested by Weber and Thiel (2000). This coupling serves the purpose of making excited state surfaces of organic dye molecules accessible to relatively cheap and sufficiently precise descriptions.

  13. Electronic structures and chemical states of methylammonium lead triiodide thin films and the impact of annealing and moisture exposure

    NASA Astrophysics Data System (ADS)

    Yamanaka, Soichiro; Hayakawa, Kei; Cojocaru, Ludmila; Tsuruta, Ryohei; Sato, Tomoya; Mase, Kazuhiko; Uchida, Satoshi; Nakayama, Yasuo

    2018-04-01

    Methylammonium lead triiodide (CH3NH3PbI3) is the fundamental material used in perovskite solar cells, and its electronic properties have, therefore, attracted a great deal of attention as a potential key to highly efficient solar cell performance. However, the deterioration of perovskite solar cells when exposed to high temperature and humidity remains a serious obstacle to the material's use, and the clarification of the degradation mechanisms has been keenly anticipated. In this study, the valence electronic structures and depth-dependence of the chemical states of CH3NH3PbI3 thin films are investigated using ultraviolet photoelectron spectroscopy and excitation energy dependent X-ray photoelectron spectroscopy. Additionally, the effects of high temperature and a moisture rich atmosphere on the CH3NH3PbI3 thin films are examined. It is confirmed that the high temperature and moist atmosphere facilitate the oxidation of CH3NH3PbI3, whereas the Pb:I stoichiometry of the CH3NH3PbI3 thin films is found to be preserved at its original ratio (1:3) after thermal annealing and exposure to a moist atmosphere.

  14. Electronic properties of graphene and effect of doping on the same

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

    Nag, Abhinav, E-mail: abhinavn76@gmail.com; Kumar, Jagdish, E-mail: jagdishphysicist@gmail.com; Sastri, O. S. K. S., E-mail: sastri.osks@gmail.com

    2015-05-15

    The electronic structure of pure and doped two dimensional crystalline material graphene have been computed and analyzed. Density functional theory has been employed to perform calculations. The electronic exchange and correlations are considered using local density approximation (LDA). The doped material is studied within virtual crystal approximation (VCA) upto 0.15e excess as well as deficient charge per unit cell. Full Potential Linear Augmented Plane Wave basis as implemented in ELK code has been used to perform the calculations. To ensures the monolayer of graphene, distance after which energy is almost constant when interlayer seperation is varied, is taken as separatingmore » distance between the layers. The obtained density of states and band structure is analyzed. Results show that there is zero band gap in undoped graphene and conduction and valence band meets at fermi level at symmetry point K. PDOS graph shows that near the fermi level the main contribution is due to 2p{sub z} electrons. By using VCA, calculations for doped graphene are done and the results for doped graphene are compared with undoped graphene. We found that by electron or hole doping, the point where conduction and valence bands meet can shift below or above the fermi level. The shift in bands seems almost as per rigid band model upto doping concentration studied.« less

  15. Transferable Pseudo-Classical Electrons for Aufbau of Atomic Ions

    PubMed Central

    Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

    2014-01-01

    Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. PMID:24752384

  16. STEADY-STATE MODEL OF SOLAR WIND ELECTRONS REVISITED

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

    Yoon, Peter H.; Kim, Sunjung; Choe, G. S., E-mail: yoonp@umd.edu

    2015-10-20

    In a recent paper, Kim et al. put forth a steady-state model for the solar wind electrons. The model assumed local equilibrium between the halo electrons, characterized by an intermediate energy range, and the whistler-range fluctuations. The basic wave–particle interaction is assumed to be the cyclotron resonance. Similarly, it was assumed that a dynamical steady state is established between the highly energetic superhalo electrons and high-frequency Langmuir fluctuations. Comparisons with the measured solar wind electron velocity distribution function (VDF) during quiet times were also made, and reasonable agreements were obtained. In such a model, however, only the steady-state solution for themore » Fokker–Planck type of electron particle kinetic equation was considered. The present paper complements the previous analysis by considering both the steady-state particle and wave kinetic equations. It is shown that the model halo and superhalo electron VDFs, as well as the assumed wave intensity spectra for the whistler and Langmuir fluctuations, approximately satisfy the quasi-linear wave kinetic equations in an approximate sense, thus further validating the local equilibrium model constructed in the paper by Kim et al.« less

  17. Electronic structure of the dilute magnetic semiconductor G a1 -xM nxP from hard x-ray photoelectron spectroscopy and angle-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Keqi, A.; Gehlmann, M.; Conti, G.; Nemšák, S.; Rattanachata, A.; Minár, J.; Plucinski, L.; Rault, J. E.; Rueff, J. P.; Scarpulla, M.; Hategan, M.; Pálsson, G. K.; Conlon, C.; Eiteneer, D.; Saw, A. Y.; Gray, A. X.; Kobayashi, K.; Ueda, S.; Dubon, O. D.; Schneider, C. M.; Fadley, C. S.

    2018-04-01

    We have investigated the electronic structure of the dilute magnetic semiconductor (DMS) G a0.98M n0.02P and compared it to that of an undoped GaP reference sample, using hard x-ray photoelectron spectroscopy (HXPS) and hard x-ray angle-resolved photoemission spectroscopy (HARPES) at energies of about 3 keV. We present experimental data, as well as theoretical calculations, to understand the role of the Mn dopant in the emergence of ferromagnetism in this material. Both core-level spectra and angle-resolved or angle-integrated valence spectra are discussed. In particular, the HARPES experimental data are compared to free-electron final-state model calculations and to more accurate one-step photoemission theory. The experimental results show differences between G a0.98M n0.02P and GaP in both angle-resolved and angle-integrated valence spectra. The G a0.98M n0.02P bands are broadened due to the presence of Mn impurities that disturb the long-range translational order of the host GaP crystal. Mn-induced changes of the electronic structure are observed over the entire valence band range, including the presence of a distinct impurity band close to the valence-band maximum of the DMS. These experimental results are in good agreement with the one-step photoemission calculations and a prior HARPES study of G a0.97M n0.03As and GaAs [Gray et al., Nat. Mater. 11, 957 (2012), 10.1038/nmat3450], demonstrating the strong similarity between these two materials. The Mn 2 p and 3 s core-level spectra also reveal an essentially identical state in doping both GaAs and GaP.

  18. Aesthetic valence of visual illusions

    PubMed Central

    Stevanov, Jasmina; Marković, Slobodan; Kitaoka, Akiyoshi

    2012-01-01

    Visual illusions constitute an interesting perceptual phenomenon, but they also have an aesthetic and affective dimension. We hypothesized that the illusive nature itself causes the increased aesthetic and affective valence of illusions compared with their non-illusory counterparts. We created pairs of stimuli. One qualified as a standard visual illusion whereas the other one did not, although they were matched in as many perceptual dimensions as possible. The phenomenal quality of being an illusion had significant effects on “Aesthetic Experience” (fascinating, irresistible, exceptional, etc), “Evaluation” (pleasant, cheerful, clear, bright, etc), “Arousal” (interesting, imaginative, complex, diverse, etc), and “Regularity” (balanced, coherent, clear, realistic, etc). A subsequent multiple regression analysis suggested that Arousal was a better predictor of Aesthetic Experience than Evaluation. The findings of this study demonstrate that illusion is a phenomenal quality of the percept which has measurable aesthetic and affective valence. PMID:23145272

  19. Valence-band-edge shift due to doping in p + GaAs

    NASA Astrophysics Data System (ADS)

    Silberman, J. A.; de Lyon, T. J.; Woodall, J. M.

    1991-05-01

    Accurate knowledge of the shifts in valence- and conduction-band edges due to heavy doping effects is crucial in modeling GaAs device structures that utilize heavily doped layers. X-ray photoemission spectroscopy was used to deduce the shift in the valence-band-edge induced by carbon (p type) doping to a carrier density of 1×1020 cm-3 based on a determination of the bulk binding energy of the Ga and As core levels in this material. Analysis of the data indicates that the shift of the valence-band maximum into the gap and the penetration of the Fermi level into the valence bands exactly compensate at this degenerate carrier concentration, to give ΔEv =0.12±0.05 eV.

  20. Electronic Structure of ABC-stacked Multilayer Graphene and Trigonal Warping:A First Principles Calculation

    NASA Astrophysics Data System (ADS)

    Yelgel, Celal

    2016-04-01

    We present an extensive density functional theory (DFT) based investigation of the electronic structures of ABC-stacked N-layer graphene. It is found that for such systems the dispersion relations of the highest valence and the lowest conduction bands near the K point in the Brillouin zone are characterised by a mixture of cubic, parabolic, and linear behaviours. When the number of graphene layers is increased to more than three, the separation between the valence and conduction bands decreases up until they touch each other. For five and six layer samples these bands show flat behaviour close to the K point. We note that all states in the vicinity of the Fermi energy are surface states originated from the top and/or bottom surface of all the systems considered. For the trilayer system, N = 3, pronounced trigonal warping of the bands slightly above the Fermi level is directly obtained from DFT calculations.

  1. Beyond valence in the perception of likelihood: the role of emotion specificity.

    PubMed

    DeSteno, D; Petty, R E; Wegener, D T; Rucker, D D

    2000-03-01

    Positive and negative moods have been shown to increase likelihood estimates of future events matching these states in valence (e.g., E. J. Johnson & A. Tversky, 1983). In the present article, 4 studies provide evidence that this congruency bias (a) is not limited to valence but functions in an emotion-specific manner, (b) derives from the informational value of emotions, and (c) is not the inevitable outcome of likelihood assessment under heightened emotion. Specifically, Study 1 demonstrates that sadness and anger, 2 distinct, negative emotions, differentially bias likelihood estimates of sad and angering events. Studies 2 and 3 replicate this finding in addition to supporting an emotion-as-information (cf. N. Schwarz & G. L. Clore, 1983), as opposed to a memory-based, mediating process for the bias. Finally, Study 4 shows that when the source of the emotion is salient, a reversal of the bias can occur given greater cognitive effort aimed at accuracy.

  2. Trait valence and the better-than-average effect.

    PubMed

    Gold, Ron S; Brown, Mark G

    2011-12-01

    People tend to regard themselves as having superior personality traits compared to their average peer. To test whether this "better-than-average effect" varies with trait valence, participants (N = 154 students) rated both themselves and the average student on traits constituting either positive or negative poles of five trait dimensions. In each case, the better-than-average effect was found, but trait valence had no effect. Results were discussed in terms of Kahneman and Tversky's prospect theory.

  3. Electronic structure and properties of unsubstituted rhodamine in different electron states

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

    Artyukhov, V.Ya.

    1988-04-01

    An analysis is given of the electron density distribution, dipole moment variation, and proton acceptor properties of unsubstituted rhodamine molecules in different electron states. It is shown that the electron density redistribution between the pyronine and benzoin parts of rhodamine may be large and strongly affect the molecular properties. In one of the electron transitions (S/sub 4/) producing the third absorption band the proton acceptor power markedly increases, giving rise to a protonated form under suitable conditions.

  4. Electronic structure and properties of unsubstituted rhodamine in different electron states

    NASA Astrophysics Data System (ADS)

    Artyukhov, V. Ya.

    1987-10-01

    An analysis is given of the electron density distribution, dipole moment variation, and proton acceptor properties of unsubstituted rhodamine molecules in different electron states. It is shown that the electron density redistribution between the pyronine and benzoin parts of rhodamine may be large and strongly affect the molecular properties. In one of the electron transitions (S4) producing the third absorption band the proton acceptor power markedly increases, giving rise to a protonated form under suitable conditions.

  5. Valence bond and von Neumann entanglement entropy in Heisenberg ladders.

    PubMed

    Kallin, Ann B; González, Iván; Hastings, Matthew B; Melko, Roger G

    2009-09-11

    We present a direct comparison of the recently proposed valence bond entanglement entropy and the von Neumann entanglement entropy on spin-1/2 Heisenberg systems using quantum Monte Carlo and density-matrix renormalization group simulations. For one-dimensional chains we show that the valence bond entropy can be either less or greater than the von Neumann entropy; hence, it cannot provide a bound on the latter. On ladder geometries, simulations with up to seven legs are sufficient to indicate that the von Neumann entropy in two dimensions obeys an area law, even though the valence bond entanglement entropy has a multiplicative logarithmic correction.

  6. Chalcogen doping at anionic site: A scheme towards more dispersive valence band in CuAlO2

    NASA Astrophysics Data System (ADS)

    Mazumder, Nilesh; Sen, Dipayan; Chattopadhyay, Kalyan Kumar

    2013-02-01

    Using first-principles calculations, we propose to enhance the dispersion of the top of valence band at high-symmetry points by selective introduction of chalcogen (Ch) impurities at oxygen site. As ab-plane hole mobility of CuAlO2 is large enough to support a band-conduction model over a polaronic one at room temperature [M. S. Lee et al. Appl. Phys. Lett. 79, 2029, (2001); J. Tate et al. Phys. Rev. B 80, 165206, (2009)], we examine its electronic and optical properties normal to c-axis. Intrinsic indirectness of energy-gap at Γ-point can be effectively removed along with substantial increase in density of states near Fermi level (EF) upon Ch addition. This can be attributed to S 2p-Cu 3d interaction just at or below EF, which should result in significantly improved carrier mobility and conductivity profile for this important p-type TCO.

  7. Human Amygdala Tracks a Feature-Based Valence Signal Embedded within the Facial Expression of Surprise.

    PubMed

    Kim, M Justin; Mattek, Alison M; Bennett, Randi H; Solomon, Kimberly M; Shin, Jin; Whalen, Paul J

    2017-09-27

    Human amygdala function has been traditionally associated with processing the affective valence (negative vs positive) of an emotionally charged event, especially those that signal fear or threat. However, this account of human amygdala function can be explained by alternative views, which posit that the amygdala might be tuned to either (1) general emotional arousal (activation vs deactivation) or (2) specific emotion categories (fear vs happy). Delineating the pure effects of valence independent of arousal or emotion category is a challenging task, given that these variables naturally covary under many circumstances. To circumvent this issue and test the sensitivity of the human amygdala to valence values specifically, we measured the dimension of valence within the single facial expression category of surprise. Given the inherent valence ambiguity of this category, we show that surprised expression exemplars are attributed valence and arousal values that are uniquely and naturally uncorrelated. We then present fMRI data from both sexes, showing that the amygdala tracks these consensus valence values. Finally, we provide evidence that these valence values are linked to specific visual features of the mouth region, isolating the signal by which the amygdala detects this valence information. SIGNIFICANCE STATEMENT There is an open question as to whether human amygdala function tracks the valence value of cues in the environment, as opposed to either a more general emotional arousal value or a more specific emotion category distinction. Here, we demonstrate the utility of surprised facial expressions because exemplars within this emotion category take on valence values spanning the dimension of bipolar valence (positive to negative) at a consistent level of emotional arousal. Functional neuroimaging data showed that amygdala responses tracked the valence of surprised facial expressions, unconfounded by arousal. Furthermore, a machine learning classifier identified

  8. Effects of valence and divided attention on cognitive reappraisal processes

    PubMed Central

    Leclerc, Christina M.; Kensinger, Elizabeth A.

    2014-01-01

    Numerous studies have investigated the neural substrates supporting cognitive reappraisal, identifying the importance of cognitive control processes implemented by prefrontal cortex (PFC). This study examined how valence and attention affect the processes used for cognitive reappraisal by asking participants to passively view or to cognitively reappraise positive and negative images with full or divided attention. When participants simply viewed these images, results revealed few effects of valence or attention. However, when participants engaged in reappraisal, there was a robust effect of valence, with the reappraisal of negative relative to positive images associated with more widespread activation, including within regions of medial and lateral PFC. There also was an effect of attention, with more lateral PFC recruitment when regulating with full attention and more medial PFC recruitment when regulating with divided attention. Within two regions of medial PFC and one region of ventrolateral PFC, there was an interaction between valence and attention: in these regions, divided attention reduced activity during reappraisal of positive but not negative images. Critically, participants continued to report reappraisal success even during the Divided Attention condition. These results suggest multiple routes to successful cognitive reappraisal, depending upon image valence and the availability of attentional resources. PMID:24493837

  9. Effects of valence and divided attention on cognitive reappraisal processes.

    PubMed

    Morris, John A; Leclerc, Christina M; Kensinger, Elizabeth A

    2014-12-01

    Numerous studies have investigated the neural substrates supporting cognitive reappraisal, identifying the importance of cognitive control processes implemented by prefrontal cortex (PFC). This study examined how valence and attention affect the processes used for cognitive reappraisal by asking participants to passively view or to cognitively reappraise positive and negative images with full or divided attention. When participants simply viewed these images, results revealed few effects of valence or attention. However, when participants engaged in reappraisal, there was a robust effect of valence, with the reappraisal of negative relative to positive images associated with more widespread activation, including within regions of medial and lateral PFC. There also was an effect of attention, with more lateral PFC recruitment when regulating with full attention and more medial PFC recruitment when regulating with divided attention. Within two regions of medial PFC and one region of ventrolateral PFC, there was an interaction between valence and attention: in these regions, divided attention reduced activity during reappraisal of positive but not negative images. Critically, participants continued to report reappraisal success even during the Divided Attention condition. These results suggest multiple routes to successful cognitive reappraisal, depending upon image valence and the availability of attentional resources. © The Author (2014). Published by Oxford University Press. For Permissions, please email: journals.permissions@oup.com.

  10. Metallic surface states in elemental electrides

    NASA Astrophysics Data System (ADS)

    Naumov, Ivan I.; Hemley, Russell J.

    2017-07-01

    Recent high-pressure studies have uncovered an alternative class of materials, insulating electride phases created by compression of simple metals. These exotic insulating phases develop an unusual electronic structure: the valence electrons move away from the nuclei and condense at interstitial sites, thereby acquiring the role of atomic anions or even molecules. We show that they are also topological phases as they exhibit a wide diversity of metallic surface states (SSs) that are controlled by the bulk electronic structure. The electronic reconstruction occurs that involves charge transfer between the surfaces of opposite polarity making both of them metallic, resembling the appearance of the two-dimensional gas at the renowned SrTi O3 /LaAl O3 interface. Remarkably, these materials thus embody seemingly disparate physical concepts—chemical electron localization, topological control of bulk-surface conductivity, and the two-dimensional electron gas. Such metallic SSs could be probed by direct electrical resistance or by standard photoemission measurements on recovery to ambient conditions.

  11. Examination of U valence states in the brannerite structure by near-infrared diffuse reflectance and X-ray photoelectron spectroscopies

    NASA Astrophysics Data System (ADS)

    Finnie, Kim S.; Zhang, Zhaoming; Vance, Eric R.; Carter, Melody L.

    2003-04-01

    The valence state of uranium doped into a f 0 thorium analog of brannerite (i.e., thorutite) has been examined using near-infrared (NIR) diffuse reflectance (DRS) and X-ray photoelectron (XPS) spectroscopies. NIR transitions of U 4+, which are not observed in spectra of brannerite, have been detected in the samples of U xTh 1- xTi 2O 6, and we propose that strong specular reflectance is responsible for the lack of U 4+ features in UTi 2O 6. Characteristic U 5+ bands have been identified in samples in which sufficient Ca 2+ has been added to nominally effect complete oxidation to U 5+. XPS results support the assignments of U 4+ and U 5+ by DRS. The presence of residual U 4+ bands in the spectra of the Ca-doped samples is consistent with segregation of Ca 2+ to the grain boundaries during high temperature sintering.

  12. Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Bonding in O3 and SO2.

    PubMed

    Takeshita, Tyler Y; Lindquist, Beth A; Dunning, Thom H

    2015-07-16

    There are many well-known differences in the physical and chemical properties of ozone (O3) and sulfur dioxide (SO2). O3 has longer and weaker bonds than O2, whereas SO2 has shorter and stronger bonds than SO. The O-O2 bond is dramatically weaker than the O-SO bond, and the singlet-triplet gap in SO2 is more than double that in O3. In addition, O3 is a very reactive species, while SO2 is far less so. These disparities have been attributed to variations in the amount of diradical character in the two molecules. In this work, we use generalized valence bond (GVB) theory to characterize the electronic structure of ozone and sulfur dioxide, showing O3 does indeed possess significant diradical character, whereas SO2 is effectively a closed shell molecule. The GVB results provide critical insights into the genesis of the observed difference in these two isoelectronic species. SO2 possesses a recoupled pair bond dyad in the a"(π) system, resulting in SO double bonds. The π system of O3, on the other hand, has a lone pair on the central oxygen atom plus a pair of electrons in orbitals on the terminal oxygen atoms that give rise to a relatively weak π interaction.

  13. A low-temperature study of manganese-induced ferromagnetism and valence band convergence in tin telluride

    DOE PAGES

    Chi, Hang; Tan, Gangjian; Kanatzidis, Mercouri G.; ...

    2016-05-02

    In this study, SnTe is renowned for its promise in advancing energy-related technologies based on thermoelectricity and for its topological crystalline insulator character. Here, we demonstrate that each Mn atom introduces ~4 μ B (Bohr magneton) of magnetic moment to Sn 1–xMn xTe. The Curie temperatureTC reaches ~14K for x = 0.12, as observed in the field dependent hysteresis of magnetization and the anomalous Hall effect. In accordance with a modified two-band electronic Kane model, the light L-valence-band and the heavy Σ-valence-band gradually converge in energy with increasing Mn concentration, leading to a decreasing ordinary Hall coefficient R H andmore » a favorably enhanced Seebeck coefficient S at the same time. With the thermal conductivityκ lowered chiefly via point defects associated with the incorporation of Mn, the strategy of Mn doping also bodes well for efficient thermoelectric applications at elevated temperatures.« less

  14. Imaging the photodissociation dynamics of the methyl radical from the 3s and 3pz Rydberg states

    PubMed Central

    Marggi Poullain, Sonia; Chicharro, David V.; Zanchet, Alexandre; González, Marta G.; Rubio-Lago, Luis; Senent, María L.; García-Vela, Alberto; Bañares, Luis

    2016-01-01

    The photodissociation dynamics of the methyl radical from the 3s and 3pz Rydberg states have been studied using velocity map and slice ion imaging in combination with pump-probe nanosecond laser pulses. The reported translational energy and angular distributions of the H(2S) photofragment detected by (2+1) REMPI highlight different dissociation mechanisms for the 3s and 3pz Rydberg states. A narrow peak in the translational energy distribution and an anisotropic angular distribution characterizes the fast 3s photodissociation, while for the 3pz state Boltzmann-type translational energy and isotropic angular distributions are found. High level ab initio calculations have been performed in order to elucidate the photodissociation mechanisms from the two Rydberg states and to rationalize the experimental results. The calculated potential energy curves highlight a typical predissociation mechanism for the 3s state, characterized by the coupling between the 3s Rydberg state and a valence repulsive state. On the other hand, the photodissociation on the 3pz state is initiated by a predissociation process due to the coupling between the 3pz Rydberg state and a valence repulsive state and constrained, later on, by two conical intersections that allow the system to relax to lower electronic states. Such mechanism opens different reaction pathways leading to CH2 photofragments in different electronic states and inducing a transfer of energy between translational and internal modes. PMID:27296907

  15. OPTOELECTRONIC PROPERTIES AND THE GAP STATE DISTRIBUTION IN a-Si, Ge ALLOYS

    NASA Astrophysics Data System (ADS)

    Aljishi, S.; Smith, Z. E.; Wagner, S.

    In this article we review optical and electronic transport data measured in amorphous silicon-germanium alloys with the goal of identifying the density of states as a function of alloy composition. The results show that while alloying a-Si:H with germanium has little effect on the valence band tail, the conduction band tail density of states is increased dramatically. Defect distributions both above and below midgap are detected and identified with the dangling bond D+/° and D°/- states. The density of deep defects below midgap increases exponentially with germanium content. Above midgap, a large concentration of defects lying between 0.3 and 0.5 eV below the conduction band edge has a strong effect on transient electron transport.

  16. Relationship Between Iron Valence States of Serpentine in CM Chondrites and Their Aqueous Alteration Degrees

    NASA Technical Reports Server (NTRS)

    Mikouchi, T.; Zolensky, M.; Satake, W.; Le, L.

    2012-01-01

    The 0.6-0.7 micron absorption band observed for C-type asteroids is caused by the presence of Fe(3+) in phyllosilicates . Because Fe-bearing phyllosilicates, especially serpentine, are the most dominant product of aqueous alteration in the most abundant carbonaceous chondrites, CM chondrites, it is important to understand the crystal chemistry of serpentine in CM chondrites to better understand spectral features of C-type asteroids. CM chondrites show variable degrees of aqueous alteration, which should be related to iron valences in serpentine. It is predicted that the Fe(3+)/Sum of (Fe) ratios of serpentine in CM chondrites decrease as alteration proceeds by Si and Fe(3+) substitutions from end-member cronstedtite to serpentine, which should be apparent in the absorption intensity of the 0.6-0.7 micron band from C-type asteroids. In fact, the JAXA Hayabusa 2 target (C-type asteroid: 1993 JU3) exhibits heterogeneous spectral features (0.7 micron absorption band disappears by rotation). From these points of view, we have analyzed iron valences of matrix serpentine in several CM chondrites which span the entire observed range of aqueous alteration using Synchrotron Radiation X-ray Absorption Near-Edge Structure (SR-XANES). In this abstract we discuss the relationship between obtained Fe(3+)/Sum of (Fe) ratios and alteration degrees by adding new data to our previous studies

  17. Connecting [NiFe]- and [FeFe]-Hydrogenases: Mixed-Valence Nickel-Iron Dithiolates With Rotated Structures

    PubMed Central

    Schilter, David; Rauchfuss, Thomas B.; Stein, Matthias

    2012-01-01

    A series of mixed-valence iron-nickel dithiolates is described that exhibits structures similar to those of mixed-valence diiron dithiolates. Interaction of tricarbonyl salt [(dppe)Ni(pdt)Fe(CO)3]BF4 ([1]BF4, dppe = Ph2PCH2CH2PPh2, pdtH2 = HSCH2CH2CH2SH) with P-donor ligands (L) afforded the substituted derivatives [(dppe)Ni(pdt)Fe(CO)2L]BF4 incorporating L = PHCy2 ([1a]BF4), PPh(NEt2)2 ([1b]BF4), P(NMe2)3 ([1c]BF4), P(i-Pr)3 ([1d]BF4) and PCy3 ([1e]BF4). The related precursor [(dcpe)Ni(pdt)Fe(CO)3]BF4 ([2]BF4, dcpe = Cy2PCH2CH2PCy2) gave the more electron-rich family of compounds [(dcpe)Ni(pdt)Fe(CO)2L]BF4 for L = PPh2(2-pyridyl) ([2a]BF4), PPh3 ([2b]BF4) and PCy3 ([2c]BF4). For bulky and strongly basic monophosphorus ligands, the salts feature distorted Fe coordination geometries: crystallographic analyses of [1e]BF4 and [2c]BF4 showed they adopt ‘rotated’ Fe(I) centers, in which PCy3 occupies a basal site and one CO ligand partially bridges the Ni and Fe centers. Like the undistorted mixed-valence derivatives, the new class of complexes are described as Ni(II)Fe(I) (S = ½) systems according to EPR spectroscopy, although with attenuated 31P hyperfine interactions. DFT calculations using the BP86, B3LYP, and PBE0 exchange-correlation functionals agree with the structural and spectroscopic data, suggesting that the spin for [1e]+ is localized in a Fe(I)-centered d(z2) orbital, orthogonal to the Fe-P bond. The PCy3 complexes, rare examples of species featuring ‘rotated’ Fe centers, both structurally and spectroscopically resemble mixed-valence diiron dithiolates. Also reproducing the NiS2Fe core of the [NiFe]-H2ase active site, the hybrid models incorporate key features of the two major classes of H2ase. Furthermore, cyclic voltammetry experiments suggest that the highly basic phosphine ligands enable a second oxidation corresponding to the couple [(dxpe)Ni(pdt)Fe(CO)2L]+/2+. The resulting unsaturated 32e− dications represent the closest approach to

  18. Mulliken-Hush analysis of a bis(triarylamine) mixed-valence system with a N...N distance of 28.7 A.

    PubMed

    Heckmann, Alexander; Amthor, Stephan; Lambert, Christoph

    2006-07-28

    An organic mixed valence compound with a spacer length of 25 unsaturated bonds separating two amine redox centres was synthesised and the electron transfer behaviour was investigated in the context of a Mulliken-Hush analysis in order to estimate the longest redox centre separation for which an intervalence charge transfer band can be observed.

  19. Memory effects of sleep, emotional valence, arousal and novelty in children.

    PubMed

    Vermeulen, Marije C M; van der Heijden, Kristiaan B; Benjamins, Jeroen S; Swaab, Hanna; van Someren, Eus J W

    2017-06-01

    Effectiveness of memory consolidation is determined by multiple factors, including sleep after learning, emotional valence, arousal and novelty. Few studies investigated how the effect of sleep compares with (and interacts with) these other factors, of which virtually none are in children. The present study did so by repeated assessment of declarative memory in 386 children (45% boys) aged 9-11 years through an online word-pair task. Children were randomly assigned to either a morning or evening learning session of 30 unrelated word-pairs with positive, neutral or negative valenced cues and neutral targets. After immediately assessing baseline recognition, delayed recognition was recorded either 12 or 24 h later, resulting in four different assessment schedules. One week later, the procedure was repeated with exactly the same word-pairs to evaluate whether effects differed for relearning versus original novel learning. Mixed-effect logistic regression models were used to evaluate how the probability of correct recognition was affected by sleep, valence, arousal, novelty and their interactions. Both immediate and delayed recognition were worse for pairs with negatively valenced or less arousing cue words. Relearning improved immediate and delayed word-pair recognition. In contrast to these effects, sleep did not affect recognition, nor did sleep moderate the effects of arousal, valence and novelty. The findings suggest a robust inclination of children to specifically forget the pairing of words to negatively valenced cue words. In agreement with a recent meta-analysis, children seem to depend less on sleep for the consolidation of information than has been reported for adults, irrespective of the emotional valence, arousal and novelty of word-pairs. © 2017 European Sleep Research Society.

  20. The 3d Rydberg (3A2) electronic state observed by Herzberg and Shoosmith for methylene

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Yukio; Schaefer, Henry F., III

    1997-06-01

    In 1959 and 1961 Herzberg and Shoosmith reported the vacuum ultraviolet spectrum of the triplet state of CH2. The present study focuses on a characterization of the upper state, the 3d Rydberg (3A2) state, observed at 1415 Å. The theoretical interpretation of these experiments is greatly complicated by the presence of a lower-lying 3A2 valence state with a very small equilibrium bond angle. Ab initio electronic structure methods involving self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), complete active space (CAS) SCF, state-averaged (SA) CASSCF, coupled cluster with single and double excitations (CCSD), CCSD with perturbative triple excitations [CCSD(T)], CASSCF second-order (SO) CI, and SACASSCF-SOCI have been employed with six distinct basis sets. With the largest basis set, triple zeta plus triple polarization with two sets of higher angular momentum functions and three sets of diffuse functions TZ3P(2 f,2d)+3diff, the CISD level of theory predicts the equilibrium geometry of the 3d Rydberg (3A2) state to be re=1.093 Å and θe=141.3 deg. With the same basis set the energy (Te value) of the 3d Rydberg state relative to the ground (X˜ 3B1) state has been determined to be 201.6 kcal mol-1 (70 500 cm-1) at the CCSD (T) level, 200.92kcal mol-1 (70 270 cm-1) at the CASSCF-SOCI level, and 200.89kcal mol-1 (70 260 cm-1) at the SACASSCF-SOCI level of theory. These predictions are in excellent agreement with the experimental T0 value of 201.95 kcalmol-1 (70 634 cm-1) reported by Herzberg.