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Sample records for electronic structure study

  1. Electronic structure studies of topological materials

    NASA Astrophysics Data System (ADS)

    Zhou, Shuyun

    Three-dimensional (3D) Dirac fermions are a new class of topological quantum materials. In 3D Dirac semimetals, the conduction and valence bands touch each other at discrete points in the momentum space and show linear dispersions along all momentum directions, forming 3D Dirac cones which are protected by the crystal symmetry. Here I will present our recent studies of the electronic structures of novel materials which host 3D Dirac fermions by using angle-resolved photoemission spectroscopy.

  2. Study of electronic structures of solids with strongly interacting electrons

    NASA Astrophysics Data System (ADS)

    Su, Yen-Sheng

    This work contains studies of two classes of perovskite transition metal oxides. The first class is the layered perovskite cuprates and the related nickelate. The second class is the three dimensional perovskite manganites. Both model and ab initio calculations are carried out for the two classes of systems. The dissertation is therefore divided into the following four parts. The first part is about the 3-band Hubbard model. The model is commonly used for describing the electronic properties of the important CuO2 layers in the crystals of high-Tc superconducting cuprates, such as doped La2CuO4 and YBa2Cu3O 7. The straightforward perturbation expansion on the model taking tpd/ɛpd (~0.36 for the cuprates) as the small parameter does not converge. In this work, I show that there exist canonical transformations on the model Hamiltonian such that the perturbation expansion based on the transformed Hamiltonians converges. In the second part, crystal Hartree-Fock calculations are carried out for La2NiO4 and La2CuO4. The results predict correctly that these two materials are antiferromagnetic insulators, in contrast to the wrong predictions made by the density functional calculations using the local spin density approximation (LSDA). The spin form factors of the materials are also calculated. The results agree with previous theoretical works using an embedded cluster model. The calculated spin form factor of La2CuO4 is consistent with the few experimental data currently available, while the results for La2NiO4 show a large discrepancy between theory and experiment. We question the accuracy of the experimental results of La2NiO4 and call for more experiments to settle the issue. In the third part, crystal Hartree-Fock calculations are carried out for LaMnO3. Our main focus is on the magnetic and orbital orderings, the effect of the crystal distortion from the cubic perovskite structure, and the analysis of the projected density of states. In addition, we also find

  3. Electron crystallography for structural and functional studies of membrane proteins.

    PubMed

    Fujiyoshi, Yoshinori

    2011-01-01

    Membrane proteins are important research targets for basic biological sciences and drug design, but studies of their structure and function are considered difficult to perform. Studies of membrane structures have been greatly facilitated by technological and instrumental advancements in electron microscopy together with methodological advancements in biology. Electron crystallography is especially useful in studying the structure and function of membrane proteins. Electron crystallography is now an established method of analyzing the structures of membrane proteins in lipid bilayers, which resembles their natural biological environment. To better understand the neural system function from a structural point of view, we developed the cryo-electron microscope with a helium-cooled specimen stage, which allows for analysis of the structures of membrane proteins at a resolution higher than 3 Å. This review introduces recent instrumental advances in cryo-electron microscopy and presents some examples of structure analyses of membrane proteins, such as bacteriorhodopsin, water channels and gap junction channels. This review has two objectives: first, to provide a personal historical background to describe how we came to develop the cryo-electron microscope and second, to discuss some of the technology required for the structural analysis of membrane proteins based on cryo-electron microscopy.

  4. Studying Atomic Structures by Aberration-Corrected Transmission Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Urban, Knut W.

    2008-07-01

    Seventy-five years after its invention, transmission electron microscopy has taken a great step forward with the introduction of aberration-corrected electron optics. An entirely new generation of instruments enables studies in condensed-matter physics and materials science to be performed at atomic-scale resolution. These new possibilities are meeting the growing demand of nanosciences and nanotechnology for the atomic-scale characterization of materials, nanosynthesized products and devices, and the validation of expected functions. Equipped with electron-energy filters and electron-energy loss spectrometers, the new instruments allow studies not only of structure but also of elemental composition and chemical bonding. The energy resolution is about 100 milli electron volts, and the accuracy of spatial measurements has reached a few picometers. However, understanding the results is generally not straightforward and only possible with extensive quantum-mechanical computer calculations.

  5. Studying atomic structures by aberration-corrected transmission electron microscopy.

    PubMed

    Urban, Knut W

    2008-07-25

    Seventy-five years after its invention, transmission electron microscopy has taken a great step forward with the introduction of aberration-corrected electron optics. An entirely new generation of instruments enables studies in condensed-matter physics and materials science to be performed at atomic-scale resolution. These new possibilities are meeting the growing demand of nanosciences and nanotechnology for the atomic-scale characterization of materials, nanosynthesized products and devices, and the validation of expected functions. Equipped with electron-energy filters and electron-energy-loss spectrometers, the new instruments allow studies not only of structure but also of elemental composition and chemical bonding. The energy resolution is about 100 milli-electron volts, and the accuracy of spatial measurements has reached a few picometers. However, understanding the results is generally not straightforward and only possible with extensive quantum-mechanical computer calculations. PMID:18653874

  6. Theoretical studies of the electronic structure of small metal clusters

    NASA Technical Reports Server (NTRS)

    Jordan, K. D.

    1982-01-01

    Theoretical studies of the electronic structure of metal clusters, in particular clusters of Group IIA and IIB atoms were conducted. Early in the project it became clear that electron correlation involving d orbitals plays a more important role in the binding of these clusters than had been previously anticipated. This necessitated that computer codes for calculating two electron integrals and for constructing the resulting CI Hamiltonions be replaced with newer, more efficient procedures. Program modification, interfacing and testing were performed. Results of both plans are reported.

  7. Electronic structure study of strongly correlated Mott-insulators

    NASA Astrophysics Data System (ADS)

    Yin, Quan

    Strongly correlated electronic systems have presented the most challenging problems to condensed matter theorists for many years and this continues to be the case. They are complicated materials with active d or f orbitals, whose valence electrons are in the intermediate region between itinerant (band-like) and highly localized (atomic-like) limits, which demand genuine many-body treatment. Although dealing with strongly correlated systems is a notorious problem, they have drawn broad interests of both theoretical and experimental condensed matter physicists, with intensive studies carried out in the past and present. This is due to the most exotic properties associated with strongly correlated materials, such as high-temperature superconductivity, metal-insulator transition, volume collapse, Kondo effect, colossal magnetoresistance, and many others. Although density functional theory (DFT) within local density approximation (LDA) is very successful in describing a wide range of materials, it encounters difficulty in predicting strongly correlated systems. Traditionally, they have been studied by model Hamiltonians with empirical parameters. The development of dynamical mean field theory (DMFT) and its marriage to DFT have brought new hope for first-principle study of strongly correlated systems. In this work, electronic structures of select strongly correlated systems are studied using LDA+DMFT. As theoretical backgrounds, reviews of DFT and DMFT are given in the first few chapters, where we also introduce the philosophy and workflow of LDA+DMFT. In the following chapters, applications to transition metal oxides, undoped high-temperature superconductors and actinide oxides are presented, where electronic structures of these materials and other properties derived from electronic structures are calculated and compared with experiments where available. Generally good agreements have been found between theory and experiments.

  8. Electronic Structure Study of Singlet Fission in Tetracene Derivatives.

    PubMed

    Casanova, David

    2014-01-14

    A detailed theoretical study of the singlet fission process in tetracene and two of its derivatives, that is 5,12-diphenyltetracene (DPT) and rubrene, is presented. This work aims to unravel the intricacies and the differences of their singlet fission mechanism by means of electronic structure calculations using molecular and cluster models and a variety of computational tools. Although the electronic structure at the molecular level is very similar for the three compounds, their different crystal packing has important consequences in their ability to produce two triplet states from a single exciton. The results obtained indicate that the lowest singlet is found to delocalize at least over seven molecules. Computed relative energies rule out the presence of charge transfer (CT) states as intermediates in a two-step mechanism in all cases. On the other hand, CT states do play a role as mediators, specially in tetracene. They decisively participate in the coupling between single and multiexcitonic states through second-order contributions. Finally, the present study pinpoints that the transition from the optically allowed exciton to the dark multiexciton state might be facilitated by intramolecular motion toward the lowest excited singlet geometry. PMID:26579913

  9. Oxidation of rubrene thin films: an electronic structure study.

    PubMed

    Sinha, Sumona; Wang, C-H; Mukherjee, M; Mukherjee, T; Yang, Y-W

    2014-12-30

    The performances of organic semiconductor devices are crucially linked with their stability at the ambient atmosphere. The evolution of electronic structures of 20 nm thick rubrene films exposed to ambient environment with time has been studied by UV and X-ray photoemission spectroscopy (UPS and XPS), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and density functional theory (DFT). XPS, NEXAFS data, and DFT calculated values suggest the formation of rubrene-epoxide and rubrene-endoperoxide through reaction of tetracene backbone with oxygen of ambient environment. Angle dependent XPS measurement indicates that the entire probed depth of the films reacts with oxygen by spending only about 120 min in ambient environment. The HOMO peak of pristine rubrene films almost disappears by exposure of 120 min to ambient environment. The evolution of the valence band (occupied states) and NEXAFS (unoccupied states) spectra indicates that the films become more insulating with exposure as the HOMO-LUMO gap increases on oxidation. Oxygen induced chemical reaction completely destroys the delocalized nature of the electron distribution in the tetracene backbone of rubrene. The results are relevant to the performance and reliability of rubrene based devices in the environment. PMID:25383646

  10. Human enamel structure studied by high resolution electron microscopy

    SciTech Connect

    Wen, S.L. )

    1989-01-01

    Human enamel structural features are characterized by high resolution electron microscopy. The human enamel consists of polycrystals with a structure similar to Ca10(PO4)6(OH)2. This article describes the structural features of human enamel crystal at atomic and nanometer level. Besides the structural description, a great number of high resolution images are included. Research into the carious process in human enamel is very important for human beings. This article firstly describes the initiation of caries in enamel crystal at atomic and unit-cell level and secondly describes the further steps of caries with structural and chemical demineralization. The demineralization in fact, is the origin of caries in human enamel. The remineralization of carious areas in human enamel has drawn more and more attention as its potential application is realized. This process has been revealed by high resolution electron microscopy in detail in this article. On the other hand, the radiation effects on the structure of human enamel are also characterized by high resolution electron microscopy. In order to reveal this phenomenon clearly, a great number of electron micrographs have been shown, and a physical mechanism is proposed. 26 references.

  11. Electronic structure study on 2D hydrogenated Icosagens nitride nanosheets

    NASA Astrophysics Data System (ADS)

    Ramesh, S.; Marutheeswaran, S.; Ramaclus, Jerald V.; Paul, Dolon Chapa

    2014-12-01

    Metal nitride nanosheets has attracted remarkable importance in surface catalysis due to its characteristic ionic nature. In this paper, using density functional theory, we investigate geometric stability and electronic properties of hydrogenated Icosagen nitride nanosheets. Binding energy of the sheets reveals hydrogenation is providing more stability. Band structure of the hydrogenated sheets is found to be n-type semiconductor. Partial density of states shows metals (B, Al, Ga and In) and its hydrogens dominating in the Fermi region. Mulliken charge analysis indications that hydrogenated nanosheets are partially hydridic surface nature except boron nitride.

  12. Rf breakdown studies in copper electron linac structures

    SciTech Connect

    Wang, J.W.; Loew, G.A.

    1989-03-01

    This paper presents a summary of rf breakdown-limited electric fields observed in experimental linac structures at SLAC and a discussion of how these experiments can be interpreted against the background of existing, yet incomplete, theories. The motivation of these studies, begun in 1984, is to determine the maximum accelerating field gradients that might be used safely in future e/sup /+-// colliders, to contribute to the basic understanding of the rf breakdown mechanism, and to discover if a special surface treatment might make it possible to supersede the field limits presently reachable in room temperature copper structures. 6 refs., 4 figs., 1 tab.

  13. Electronic structure studies of nanocrystalline diamond grain boundaries

    SciTech Connect

    Zapol, P.; Sternberg, M.; Frauenheim, T.; Gruen, D. M.; Curtiss, L. A.

    1999-11-29

    Diamond growth from hydrogen-poor plasmas results in diamond structures that are profoundly different from conventionally CVD-grown diamond. High concentration of carbon dimers in the microwave plasma results in a high rate of heterogeneous renucleation leading to formation of nanocrystalline diamond with a typical grain size of 3--10 nm. Therefore, up to 10% of carbon atoms are located in the grain boundaries. In this paper the authors report on density-functional based tight-binding molecular dynamics calculations of the structure of a {Sigma}13 twist (100) grain boundary in diamond. Beginning with a coincidence site lattice model, simulated annealing of the initial structure was performed at 1,500 K followed by relaxation toward lower temperatures. About one-half of the carbons in the grain boundary are found to be three-coordinated. Coordination numbers, bond length and bond angle distributions are analyzed and compared to those obtained in previous studies.

  14. Coincidence studies of diffraction structures in binary encounter electron spectra

    SciTech Connect

    Liao, C.; Hagmann, S.; Richard, P.

    1994-12-31

    The authors have measured binary encounter electron (BEe) production in collisions of 0.3 MeV/u Cu{sup q+} (q=4,12) projectiles on H{sub 2} targets from 0 to 70 degrees with respect to the beam direction. Prominent features are the appearance of the BEe peak splitting and a very strong forward peaked angular distribution which are attributed to the diffractive scattering of the quasifree target electrons in the short range potential of the projectile. Using electron-projectile final charge state coincidence techniques, different collision reaction channels can be separated. Measurements of this type are being pursued.

  15. Studying average electron drift velocity in pHEMT structures

    NASA Astrophysics Data System (ADS)

    Borisov, A. A.; Zhuravlev, K. S.; Zyrin, S. S.; Lapin, V. G.; Lukashin, V. M.; Makovetskaya, A. A.; Novoselets, V. I.; Pashkovskii, A. B.; Toropov, A. I.; Ursulyak, N. D.; Shcherbakov, S. V.

    2016-08-01

    Small-signal characteristics of pseudomorphic high-electron-mobility transistors based on donor-acceptor doped heterostructures (DA-pHEMTs) are compared to those of analogous transistors (pHEMTs) based on traditional heterostructures without acceptor doping. It is established that DA-pHEMTs, under otherwise equal conditions, exhibit (despite lower values of the low-field mobility of electrons) a much higher gain compared to that of usual pHEMTs. This behavior is related to the fact that the average electron drift velocity under the gate in DA-pHEMTs is significantly (1.4-1.6 times) higher than that in pHEMTs. This increase in the electron drift velocity is explained by two main factors of comparable influence: (i) decreasing role of transverse spatial transfer, which is caused by enhanced localization of hot electrons in the channel, and (ii) reduced scattering of hot electrons, which is caused by their strong confinement (dimensional quantization) in the potential well of DA-pHEMT heterostructures.

  16. Structural, optical and electronic structure studies of Al doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Devi, Vanita; Kumar, Manish; Shukla, D. K.; Choudhary, R. J.; Phase, D. M.; Kumar, Ravindra; Joshi, B. C.

    2015-07-01

    Structural, optical and electronic structure of Al doped ZnO thin films grown using pulsed laser deposition on glass substrate are investigated. X-ray diffraction measurements reveal that all the films are textured along the c-axis and have wurtzite structure. Al doping in ZnO films leads to increase in grain size due to relaxation in compressive stress. Enhancement in band gap of ZnO films with the Al doping is also noticed which can be ascribed to the Brustein-Moss shift. The changes in the electronic structure caused by Al in the doped thin film samples are understood through X-ray absorption measurements.

  17. The Electronic Structure of Metals Studied by Auger Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fowles, Paul Stephen

    Available from UMI in association with The British Library. In recent years there has been much study of Auger processes that involve one or more valence electrons. In particular, the degree to which the Auger lineshape reflects the local density of states (DOS) has proved to be of considerable interest and it is often assumed that the Auger profile may be simply obtained by a weighting of the angular components of the local DOS. By using the embedding technique to carry out first principles, self-consistent calculations of the KLV Auger profiles of simple metals, it is possible to investigate the relationship between the Auger profile and the local DOS. Additionally, it is shown that useful approximations can be made which allow the spatial region probed by the Auger process in Mg to be determined. The alloying of Mg with other simple metals causes the Mg KLV spectra to become distorted. The Mg KLV spectra of a LiMg alloy are presented which show considerable modification from the pure metal. Using the embedding technique, these spectra are simulated and the presence of a virtual bound state is predicted around a core-ionized Mg site. High resolution spectra of the KL_ {2,3}-L_{2,3} L_{2,3}V Auger satellite transitions of Mg and Al, which lie to high kinetic energy of the KL_{2,3}V Auger transition, are shown and an attempt made to simulate the profiles of these satellites. This is achieved by determining the intensity and shape of each component by the use of atomic transition rate calculations and lineshapes obtained using the embedding technique. The satellite profile of Al may be explained in this way, however, one feature remains unexplained in the spectrum of Mg. The N_{6,7}O _{4,5}O_ {4,5} and N_{7} O_{4,5}O _{4,5} Auger profiles of Au are presented and the N_{6}O _{4,5}O_ {4,5} profile found by subtraction. By the removal of a background it will be possible to compare these transitions with theoretical calculations. The requirements for subtracting a

  18. Study of electronic structure and spin polarization of dysprosium

    SciTech Connect

    Mund, H. S.

    2015-06-24

    In this paper, I have presented the spin-dependent momentum density of ferromagnetic dysprosium using spin polarized relativistic Korringa-Kohn-Rostoker method. A fully relativistic approach has been used to determine the magnetic Compton profile. The density of state in term of majority-spin and minority-spin of Dy also calculated using SPR-KKR. The magnetic Compton profile discussed in term of 4f and diffused electrons.

  19. The electronic structure of NaCl adlayers on W(110) studied by ionizing radiation

    NASA Astrophysics Data System (ADS)

    Dieckhoff, S.; Müller, H.; Maus-Friedrichs, W.; Brenten, H.; Kempter, V.

    1992-12-01

    The electronic structure of thin NaCl adlayers deposited on W(110) at room temperature is studied with electron energy loss spectroscopy (EELS), ion impact electron spectroscopy (IIES) with He + and He 2+ ions, metastable impact electron spectroscopy (MIES) with He ∗ atoms, ultraviolet photoelectron spectroscopy (UPS), and AES. It is concluded that NaCl adsorbs molecularly under the studied conditions. The transition from the electronic structure of single adsorbed NaCl molecules to the well-known bulk structure could be studied by following the emergence of bulk properties, such as interband transitions and excitonic excitations, as a function of the NaCl exposure. Our results are consistent with lateral growth of two-dimensional islands during the formation of the first adlayer. The electronic transition processes at the surface induced by electrons as well as He projectiles in different excitation and charge states, in particular the vacancy production in the Cl - 3p valence band, are studied. Their relevance for desorption induced by electronic transitions (DIET) is discussed.

  20. Photoemission study of the electronic structure and charge density waves of Na₂Ti₂Sb₂O

    SciTech Connect

    Tan, S. Y.; Jiang, J.; Ye, Z. R.; Niu, X. H.; Song, Y.; Zhang, C. L.; Dai, P. C.; Xie, B. P.; Lai, X. C.; Feng, D. L.

    2015-04-30

    The electronic structure of Na₂Ti₂Sb₂O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calculation of Na₂Ti₂Sb₂O in the non-magnetic state, which indicates that there is no magnetic order in Na₂Ti₂Sb₂O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na₂Ti₂Sb₂O. Photon energy dependent ARPES results suggest that the electronic structure of Na₂Ti₂Sb₂O is rather two-dimensional. Moreover, we find a density wave energy gap forms below the transition temperature and reaches 65 meV at 7 K, indicating that Na₂Ti₂Sb₂O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime. (author)

  1. Ab-initio study of structural, mechanical and electronic properties of functionalized carbon nanotubes

    SciTech Connect

    Milowska, Karolina Z.; Birowska, Magdalena; Majewski, Jacek A.

    2013-12-04

    We present exemplary results of extensive studies of structural, mechanical and electronic properties of covalent functionalization of carbon nanotubes (CNTs). We report new results for metallic (9,0), and semiconducting (10,0) single-wall carbon nanotubes (CNT) functionalized with -COOH, -OH, and both groups with concentration up to 12.5%. Our studies are performed in the framework of the density functional theory (DFT). We discuss here the stability, local and global changes in structure, elastic moduli (Young's, Shear, and Bulk), electronic structure and resulting band gaps, as a function of the density of the adsorbed molecules.

  2. Soft X-ray Studies of Pu Electronic Structure: Past Lessons and Future Directions

    SciTech Connect

    Tobin, J G; Yu, S W

    2008-02-07

    Photoelectron Spectroscopy (PES) and X-ray Absorption Spectroscopy (XAS, Figure 1) have contributed greatly to our improved understanding of Pu electronic structure. From these and related measurements, the following has been determined: (1) The Pu 5f spin-orbit splitting is large; (2) The number of Pu5f electrons is near 5; and (3) The Pu 5f spin-orbit splitting effect dominates 5f itineracy. Significant questions remain concerning the nature of Pu electronic structure. Perhaps the missing piece of the puzzle is the direct experimental determination of the unoccupied electronic structure using high energy inverse photoelectron spectroscopy or Bremstrahlung Isochromat Spectroscopy (BIS). Past BIS studies of Th and U indicate the feasibility and utility of Pu studies.

  3. Pulsed Electron Double Resonance in Structural Studies of Spin-Labeled Nucleic Acids

    PubMed Central

    Fedorova, O. S.; Tsvetkov, Yu. D.

    2013-01-01

    This review deals with the application of the pulsed electron double resonance (PELDOR) method to studies of spin-labeled DNA and RNA with complicated spatial structures, such as tetramers, aptamers, riboswitches, and three- and four-way junctions. The use of this method for studying DNA damage sites is also described. PMID:23556128

  4. Theoretical Studies of the Electronic Structure of the Compounds of the Actinide Elements

    SciTech Connect

    Kaltsoyannis, Nikolas; Hay, P. Jeffrey; Li, Jun; Blaudeau, Jean-Philippe; Bursten, Bruce E.

    2006-02-02

    In this chapter, we will present an overview of the theoretical and computational developments that have increased our understanding of the electronic structure of actinide-containing molecules and ions. The application of modern electronic structure methodologies to actinide systems remains one of the great challenges in quantum chemistry; indeed, as will be discussed below, there is no other portion of the periodic table that leads to the confluence of complexity with respect to the calculation of ground- and excited-state energies, bonding descriptions, and molecular properties. But there is also no place in the periodic table in which effective computational modeling of electronic structure can be more useful. The difficulties in creating, isolating, and handling many of the actinide elements provide an opportunity for computational chemistry to be an unusually important partner in developing the chemistry of these elements. The importance of actinide electronic structure begins with the earliest studies of uranium chemistry and predates the discovery of quantum mechanics. The fluorescence of uranyl compounds was observed as early as 1833 (Jørgensen and Reisfeld, 1983), a presage of the development of actinometry as a tool for measuring photochemical quantum yields. Interest in nuclear fuels has stimulated tremendous interest in understanding the properties, including electronic properties, of small actinide-containing molecules and ions, especially the oxides and halides of uranium and plutonium. The synthesis of uranocene in 1968 (Streitwieser and Mu¨ ller-Westerhoff, 1968) led to the flurry of activity in the organometallic chemistry of the actinides that continues today. Actinide organometallics (or organoactinides) are nearly always molecular systems and are often volatile, which makes them amenable to an arsenal of experimental probes of molecular and electronic structure (Marks and Fischer, 1979). Theoretical and computational studies of the electronic

  5. First-principles study of structural & electronic properties of pyramidal silicon nanowire

    NASA Astrophysics Data System (ADS)

    Jariwala, Pinank; Singh, Deobrat; Sonvane, Y. A.; Gupta, Sanjeev K.; Thakor, P. B.

    2016-05-01

    We have investigated the stable structural and electronic properties of Silicon (Si) nanowires having different cross-sections with 5-7 Si atoms per unit cell. These properties of the studied Si nanowires were significantly changed from those of diamond bulk Si structure. The binding energy increases as increasing atoms number per unit cell in different SiNWs structures. All the nanowires structures are behave like metallic rather than semiconductor in bulk systems. In general, the number of conduction channels increases when the nanowire becomes thicker. The density of charge revealed delocalized metallic bonding for all studied Si nanowires.

  6. Comprehensive studies of the electronic structure of pristine and potassium doped chrysene investigated by electron energy-loss spectroscopy.

    PubMed

    Roth, Friedrich; Mahns, Benjamin; Schönfelder, Ronny; Hampel, Silke; Nohr, Markus; Büchner, Bernd; Knupfer, Martin

    2012-09-21

    We have performed electron energy-loss spectroscopy studies in order to investigate the electronic properties of chrysene molecular solids. The valence band electronic excitation spectra and the C 1s core level excitations have been measured for pristine and potassium doped chrysene. The core level studies show a fine structure which signals the presence of four close lying conduction bands close to the Fermi level. Upon potassium doping, these bands are filled with electrons, and we have reached a doping level of about K(2.7)chrysene. Furthermore, undoped chrysene is characterized by an optical gap of about 3.3 eV and five, relatively weak, excitonic features following the excitation onset. Doping induces major changes in the electronic excitation spectra, with a new, prominent low energy excitation at about 1.3 eV. The results of a Kramers-Kronig analysis indicate that this new feature can be assigned to a charge carrier plasmon in the doped material, and momentum dependent studies reveal a negative plasmon dispersion.

  7. Comprehensive studies of the electronic structure of pristine and potassium doped chrysene investigated by electron energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Roth, Friedrich; Mahns, Benjamin; Schönfelder, Ronny; Hampel, Silke; Nohr, Markus; Büchner, Bernd; Knupfer, Martin

    2012-09-01

    We have performed electron energy-loss spectroscopy studies in order to investigate the electronic properties of chrysene molecular solids. The valence band electronic excitation spectra and the C 1s core level excitations have been measured for pristine and potassium doped chrysene. The core level studies show a fine structure which signals the presence of four close lying conduction bands close to the Fermi level. Upon potassium doping, these bands are filled with electrons, and we have reached a doping level of about K2.7chrysene. Furthermore, undoped chrysene is characterized by an optical gap of about 3.3 eV and five, relatively weak, excitonic features following the excitation onset. Doping induces major changes in the electronic excitation spectra, with a new, prominent low energy excitation at about 1.3 eV. The results of a Kramers-Kronig analysis indicate that this new feature can be assigned to a charge carrier plasmon in the doped material, and momentum dependent studies reveal a negative plasmon dispersion.

  8. Electronic Structures of Uranium Compounds Studied by Soft X-ray Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Fujimori, Shin-ichi; Takeda, Yukiharu; Okane, Tetsuo; Saitoh, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; Ōnuki, Yoshichika

    2016-06-01

    The electronic structures of uranium-based compounds have been studied by photoelectron spectroscopy with soft X-ray synchrotron radiation. Angle-resolved photoelectron spectroscopy with soft X-rays has made it possible to directly observe their bulk band structures and Fermi surfaces. It has been shown that the band structures and Fermi surfaces of itinerant compounds such as UB2, UN, and UFeGa5 are quantitatively described by a band-structure calculation treating all U 5f electrons as itinerant. Furthermore, the overall electronic structures of heavy-fermion compounds such as UPd2Al3, UNi2Al3, and URu2Si2 are also explained by a band-structure calculation, although some disagreements exist, which might originate from the electron correlation effect. This suggests that the itinerant description of U 5f states is an appropriate starting point for the description of their electronic structures. The situation is similar for ferromagnetic superconductors such as UGe2, URhGe, UCoGe, and UIr, although the complications from their low-symmetry crystal structures make it more difficult to describe their detailed electronic structures. The local electronic structures of the uranium site have been probed by core-level photoelectron spectroscopy with soft X-rays. The comparisons of core-level spectra of heavy-fermion compounds with typical itinerant and localized compounds suggest that the local electronic structures of most itinerant and heavy-fermion compounds are close to the U 5f3 configuration except for UPd2Al3 and UPt3. The core-level spectrum of UPd2Al3 has similarities to those of both itinerant and localized compounds, suggesting that it is located at the boundary between the itinerant and localized states. Moreover, the spectrum of UPt3 is very close to that of the localized compound UPd3, suggesting that it is nearly localized, although there are narrow quasi-particle bands in the vicinity of EF.

  9. Structural, ultrastructural, microradiographic, and electron-probe studies of an unusual case of regional odontodysplasia

    SciTech Connect

    Kerebel, B.; Kerebel, L.M.

    1982-09-01

    Structural, ultrastructural, microradiographic, and electron microprobe studies of an unusual case of odontodysplasia were performed. Two cusps were absent from one molar. Normal prismatic enamel and mantle dentin were present on the two others. The dentinal mass resembled osteodentin. The mineral content of enamel and dentin was decreased compared to that of the controls.

  10. Electronic structure dynamics in a low bandgap polymer studied by time-resolved photoelectron spectroscopy.

    PubMed

    Cappel, Ute B; Plogmaker, Stefan; Terschlüsen, Joachim A; Leitner, Torsten; Johansson, Erik M J; Edvinsson, Tomas; Sandell, Anders; Karis, Olof; Siegbahn, Hans; Svensson, Svante; Mårtensson, Nils; Rensmo, Håkan; Söderström, Johan

    2016-08-01

    Means to measure the temporal evolution following a photo-excitation in conjugated polymers are a key for the understanding and optimization of their function in applications such as organic solar cells. In this paper we study the electronic structure dynamics by direct pump-probe measurements of the excited electrons in such materials. Specifically, we carried out a time-resolved photoelectron spectroscopy (TRPES) study of the polymer PCPDTBT by combining an extreme ultraviolet (XUV) high harmonic generation source with a time-of-flight spectrometer. After excitation to either the 1st excited state or to a higher excited state, we follow how the electronic structure develops and relaxes on the electron binding energy scale. Specifically, we follow a less than 50 fs relaxation of the higher exited state and a 10 times slower relaxation of the 1st excited state. We corroborate the results using DFT calculations. Our study demonstrates the power of TRPES for studying photo-excited electron energetics and dynamics of solar cell materials. PMID:27440450

  11. Theoretical studies on the electronic structure and properties of complex ceramic crystals and glasses

    SciTech Connect

    Ching, Wai-Yim.

    1991-01-24

    This progress report summarizes the accomplishment of the DOE-support research program at the University of Missouri-Kansas City for the period July 1, 1991--June 30, 1992. This is the second year of a three-year renewal. The major accomplishments for the year are: (a) Initiation of fundamental studies on the electronic properties of C{sub 60} and related crystals; (b) study of electronic structures and optical properties of several important ceramic crystals, especially on AlN, SiO{sub 2} and Al{sub 2}O{sub 3}; (c) first-principles calculation of total energies and structural phase transitions in oxides, nitrides, and borides; (d) theory of magnetism in Nd{sub 2}Fe{sub 14}B permanent magnetic alloy. The major focus for the next year's effort will be on the following areas: (1) Continuation of the fundamental studies on the buckminsterfullerene system with particular emphasis on the alkali-doped superconducting fullerides. (2) Fundamental studies on the structure and properties of Boron and B-related compounds. (3) Basic studies on the structural and electronic properties of metallic glasses with particular emphasis on the magnetic glasses. (4) Further development of the first-principles OLCAO method for applications to super-complex systems.

  12. Structural and electronic properties of small silver-sulfur clusters: A density functional study

    NASA Astrophysics Data System (ADS)

    Li, Yan-Fang; Li, Yang; Li, Ying; Tan, Jia-Jin; Li, Hui-Li

    2016-10-01

    Density functional theory calculations have been performed to systematically investigate the structural and electronic properties of neutral and anionic AgnSm (2≤n+m≤6) clusters. The results show that the ground-state structures of neutral clusters are different from those of anionic clusters. Theoretical electron detachment energies (both vertical and adiabatic) are compared with the experimental measurements to verify the ground states of silver-sulfur clusters obtained in the present study. For both neutral and anionic systems, the highest occupied-lowest unoccupied molecular orbital energy gaps exhibit an odd-even oscillation as a function of the cluster size. In addition, the natural population analysis reveals that the charges transfer from Ag atoms to S atoms in AgnSm clusters, and the extra electron of AgnSm- clusters is mainly localized on the 3p subshells of S atoms.

  13. Quantum chemical topology study on the electronic structure of cis- and trans-FONO.

    PubMed

    Berski, Slawomir; Latajka, Zdzislaw; Gordon, Agnieszka J

    2010-07-21

    The electronic structure of cis- and trans-FONO has been studied using topological analysis of the electron localization function at the B3LYP/aug-cc-pVTZ computational level. In cis-FONO with "normal" F-O bond length (1.428-1.441 A), a protocovalent F-O bonding has been found. The central N-O bond is "drained off" with the electron density (0.40e and 0.42e) and the terminal N-O bond resembles an electron-rich single bond (2.13e-2.14e). The F...ONO form with a long F...O bond (1.719 and 1.696 A) has a diradical character and consists of F and NO(2) subunits without clear indications of the covalent bond in the F...O region.

  14. [The electron microscopic study of tumour-like structures on the vocal cords].

    PubMed

    Il'inskaia, E V; Stepanova, Iu E; Koren', E E; Kosenko, V A

    2015-01-01

    We have undertaken the electron microscopic investigation into peculiarities of six tumour-like structures on the vocal cords. The study has demonstrated changes in the number and distribution patterns of intercellular junctions, keratin and tonofilament contents in epithelial cells, basal membrane structure, and composition of the basic substance in lamina propria. All the examined tumour-like structures contained bacteria an two of them had viral particles in vacuoles of fibroblasts. Moreover, the bacteria were found on the surface of epithelium, between epithelial cells and in the basic substance in lamina propria. Cytoplasm of epithelial cells and fibroblasts not infrequently contained bacteria in the phase of division.

  15. Photoemission study of the electronic structure and charge density waves of Na₂Ti₂Sb₂O

    DOE PAGES

    Tan, S. Y.; Jiang, J.; Ye, Z. R.; Niu, X. H.; Song, Y.; Zhang, C. L.; Dai, P. C.; Xie, B. P.; Lai, X. C.; Feng, D. L.

    2015-04-30

    The electronic structure of Na₂Ti₂Sb₂O single crystal is studied by photon energy and polarization dependent angle-resolved photoemission spectroscopy (ARPES). The obtained band structure and Fermi surface agree well with the band structure calculation of Na₂Ti₂Sb₂O in the non-magnetic state, which indicates that there is no magnetic order in Na₂Ti₂Sb₂O and the electronic correlation is weak. Polarization dependent ARPES results suggest the multi-band and multi-orbital nature of Na₂Ti₂Sb₂O. Photon energy dependent ARPES results suggest that the electronic structure of Na₂Ti₂Sb₂O is rather two-dimensional. Moreover, we find a density wave energy gap forms below the transition temperature and reaches 65 meV atmore » 7 K, indicating that Na₂Ti₂Sb₂O is likely a weakly correlated CDW material in the strong electron-phonon interaction regime. (author)« less

  16. Lithium halide monolayers: Structural, electronic and optical properties by first principles study

    NASA Astrophysics Data System (ADS)

    Safari, Mandana; Maskaneh, Pegah; Moghadam, Atousa Dashti; Jalilian, Jaafar

    2016-09-01

    Using first principle study, we investigate the structural, electronic and optical properties of lithium halide monolayers (LiF, LiCl, LiBr). In contrast to graphene and other graphene-like structures that form hexagonal rings in plane, these compounds can form and stabilize in cubic shape interestingly. The type of band structure in these insulators is identified as indirect type and ionic nature of their bonds are illustrated as well. The optical properties demonstrate extremely transparent feature for them as a result of wide band gap in the visible range; also their electron transitions are indicated for achieving a better vision on the absorption mechanism in these kinds of monolayers.

  17. Doped penta-graphene and hydrogenation of its related structures: a structural and electronic DFT-D study.

    PubMed

    Quijano-Briones, J J; Fernández-Escamilla, H N; Tlahuice-Flores, A

    2016-06-21

    The structure of penta-graphene (penta-C), an irregular pentagonal two-dimensional (2D) structure, has been predicted recently. In this communication we carried out a dispersion-corrected density functional theory (DFT-D) study of the penta-C doped with Si, Ge and Sn atoms and its related hydrogenated penta-C structures (H-penta-C-X). We predict various new structures as thermally stable based on Born-Oppenheimer molecular dynamics (BOMD) calculations. Moreover, their dynamical stability is attested by phonon dispersions spectra. In general, we found that the bandgap value of doped structures reduces, while H-penta-C-X show large bandgap values. This feature can be exploited for potential uses of hydrogenated doped-penta-C structures as dielectric layers in electronic devices.

  18. Doped penta-graphene and hydrogenation of its related structures: a structural and electronic DFT-D study.

    PubMed

    Quijano-Briones, J J; Fernández-Escamilla, H N; Tlahuice-Flores, A

    2016-06-21

    The structure of penta-graphene (penta-C), an irregular pentagonal two-dimensional (2D) structure, has been predicted recently. In this communication we carried out a dispersion-corrected density functional theory (DFT-D) study of the penta-C doped with Si, Ge and Sn atoms and its related hydrogenated penta-C structures (H-penta-C-X). We predict various new structures as thermally stable based on Born-Oppenheimer molecular dynamics (BOMD) calculations. Moreover, their dynamical stability is attested by phonon dispersions spectra. In general, we found that the bandgap value of doped structures reduces, while H-penta-C-X show large bandgap values. This feature can be exploited for potential uses of hydrogenated doped-penta-C structures as dielectric layers in electronic devices. PMID:27220553

  19. Electronic Structure of EuAl4 Studied by Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kobata, Masaaki; Fujimori, Shin-ichi; Takeda, Yukiharu; Okane, Tetsuo; Saitoh, Yuji; Kobayashi, Keisuke; Yamagami, Hiroshi; Nakamura, Ai; Hedo, Masato; Nakama, Takao; Ōnuki, Yoshichika

    2016-09-01

    The electronic structure of the divalent Eu compound EuAl4, which shows a charge density wave transition at TCDW = 140 K, was studied by hard X-ray angle-integrated photoelectron spectroscopy (HAXPES) and soft X-ray angle-resolved photoelectron spectroscopy (ARPES). The valence band and core-level spectra obtained by HAXPES are consistent with the divalent nature of Eu atoms in EuAl4. From the ARPES results, the Fermi surface as well as band structure in the vicinity of the Fermi energy (EF) of EuAl4 are very similar to those of its isostructural divalent Sr compound SrAl4, which has no 4f electrons. This suggests that the Eu atoms are divalent in EuAl4, and the 4f electrons are localized below 1.8 eV with the Eu 4f7 electronic configuration in the ground state. The ARPES spectra measured along the Γ-(Σ)-Z high-symmetry line did not show significant temperature dependences above and below TCDW within the energy resolution of 80-90 meV. Moreover, the Fermi surface mapping along the kz direction showed that both EuAl4 and SrAl4 have mostly three-dimensional electronic structures, suggesting that the nesting of the Fermi surface is not simple. The Fermi surface and the band structure of EuAl4 were well explained by the band-structure calculation of SrAl4 based on the local density approximation.

  20. Electronic Structure of Fullerene Acceptors in Organic Bulk-Heterojunctions: A Combined EPR and DFT Study.

    PubMed

    Mardis, Kristy L; Webb, Jeremy N; Holloway, Tarita; Niklas, Jens; Poluektov, Oleg G

    2015-12-01

    Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of electron-donating polymers, while electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density functional theory (DFT) calculations characterize the electronic structures of the fullerene radical anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advanced electron paramagnetic resonance (EPR) allows the validation of the DFT calculations. Thus, for the first time, the complete set of magnetic resonance parameters including directions of the principal g-tensor axes were determined. For both molecules, no spin density is present on the PCBM side chain, and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM.

  1. Energetic stability, atomic and electronic structures of extended γ-graphyne: A density functional study.

    PubMed

    Chi, Baoqian; Liu, Yi; Li, Xiaowu; Xu, Jingcheng; Qin, Xuming; Sun, Chen; Bai, Chenghao; Zhao, Xinluo

    2015-06-01

    The energetic stability, atomic and electronic structures of γ-graphyne and its derivatives (γ-GYs) with extended carbon chains were investigated as a function of chain length by density functional calculations in this work. The studied γ-GYs consist of hexagon carbon rings connected by linear chains with C atoms n = 0-22. We predict that the even-numbered C chains of γ-GYs consist of alternating single and triple C-C bonds (polyyne), energetically more stable than the odd-numbered C chains made of continuous C-C double bonds (polycumulene). The calculated electronic structures indicate that γ-GYs can be either metallic (odd n) or semiconductive (even n) depending on the parity of the number of C chain atoms. The semiconducting γ-GYs are predicted to have ~1.2 eV direct band gaps and 0.1-0.2 effective electron masses independent of the chain length. Thus introducing sp carbon atoms into sp (2)-based graphene provides a novel way to open up band gaps without doping and defects while maintaining small electron masses critical to good transport properties. Graphical Abstract The typical atomic model of graphyne (middle) as well as their band gaps (left) and electron density (right).

  2. Study on the electronic structure and hydrogen adsorption by transition metal decorated single wall carbon nanotubes.

    PubMed

    Modak, P; Chakraborty, Brahmananda; Banerjee, S

    2012-05-01

    The ground state geometry and electronic structure of various 4d transition metal (TM) atom (Y, Zr, Nb and Mo) decorated single wall carbon nanotubes (SWCNTs) are obtained using density functional theory and the projector augmented wave (PAW) method. We found a systematic change in the adsorption site of the transition metal atom with increasing number of d electrons. We also predicted that Y and Zr decorated SWCNTs are metallic whereas Nb and Mo decorated SWCNTs are semiconducting. From detailed electronic structure and Bader charge analysis we found that the systematic variation of the adsorption site with the number of d electrons is related to the decreasing amount of charge transfer from the TM atom to the SWCNT along the 4d series. We have also studied the hydrogen adsorption capabilities of these decorated SWCNTs to understand the role of transition metal d electrons in binding the hydrogen molecules to the system. We found that metallic SWCNT + TM systems are better hydrogen adsorbers. We showed that the hydrogen adsorption by a TM decorated SWCNT will be maximum when all the adsorptions are physisorption and that the retention of magnetism by the system is crucial for physisorption.

  3. Electronic Structure of Fullerene Acceptors in Organic Bulk-Heterojunctions. A Combined EPR and DFT Study

    SciTech Connect

    Mardis, Kristy L.; Webb, J.; Holloway, Tarita; Niklas, Jens; Poluektov, Oleg G.

    2015-11-16

    Organic photovoltaic (OPV) devices are a promising alternative energy source. Attempts to improve their performance have focused on the optimization of electron-donating polymers, while electron-accepting fullerenes have received less attention. Here, we report an electronic structure study of the widely used soluble fullerene derivatives PC61BM and PC71BM in their singly reduced state, that are generated in the polymer:fullerene blends upon light-induced charge separation. Density functional theory (DFT) calculations characterize the electronic structures of the fullerene radical anions through spin density distributions and magnetic resonance parameters. The good agreement of the calculated magnetic resonance parameters with those determined experimentally by advanced electron paramagnetic resonance (EPR) allows the validation of the DFT calculations. Thus, for the first time, the complete set of magnetic resonance parameters including directions of the principal g-tensor axes were determined. For both molecules, no spin density is present on the PCBM side chain, and the axis of the largest g-value lies along the PCBM molecular axis. While the spin density distribution is largely uniform for PC61BM, it is not evenly distributed for PC71BM.

  4. First principle study of structural, electronic and magnetic properties of zigzag boron nitride nanoribbon: Role of vacancies

    SciTech Connect

    Kumar, Arun; Bahadur, Amar; Mishra, Madhukar; Vasudeva, Neena

    2015-05-15

    We study the effect of vacancies on the structural, electronic and magnetic properties of zigzag boron nitride nanoribbon (ZBNNR) by using first principle calculations. We find that the shift of the vacancies with respect to the ribbon edges causes change in the structural geometry, electronic structure and magnetization of ZBNNR. These vacancies also produce band gap modulation and consequently results the magnetization of ZBNNR.

  5. Structural, electronic and magnetic properties of pure metallic and bimetallic nanoclusters: Empirical and density functional studies

    NASA Astrophysics Data System (ADS)

    Hijazi, Iyad Ahmed

    This thesis is aimed at investigating structural, electronic and magnetic properties of metallic/bimetallic nanoclusters. First, a simple empirical embedded-atom potential (EAM) that includes a long range force is developed for FCC metals and alloys. The proposed potential for pure metals does not require modification of the initial function form when being applied to alloy systems. The potential parameters are determined by fitting lattice constant, three elastic constants, cohesive energy, and vacancy formation energies of the pure metals, and the heats of solution of the binary alloys via an optimization technique. Parameters for Ag, Al, Au, Cu, Ni, Pd and Pt have been obtained and used to calculate the bulk modulus, divacancy formation energy, crystal stability, stacking fault energy, vacancy migration energy, and melting point for each pure metal and the heats of formation and lattice constants for binary alloys. The predicted values are in good agreement with experimental results. Structural stabilities and energetics for Cu and Au clusters with up to 56 atoms were also studied using a hierarchical search method. The method employed an effective Monte Carlo (MC) simulated annealing method, utilizing our EAM potential, to identify low-lying structures. In general agreement with previous empirical studies, the lowest-energy copper structures adapt a single icosahedral structural motif. However, contrary to studies that describe gold as less symmetric, this work demonstrates that gold clusters adapt both an icosahedral and icositetrahedral structural motifs with many clusters having symmetric geometries. The structures of the lowest-energy isomers were later optimized using Density Functional Theory (DFT) simulations, and compared to those of available clusters from previous studies. Their lowest-energy structures are mostly found in our pool of isomers, identified by the present method. Our results are in agreement with or lower in energy than existing ab

  6. First-principles study of structural, elastic, electronic, vibrational and thermodynamic properties of UN

    NASA Astrophysics Data System (ADS)

    Mei, Zhi-Gang; Stan, Marius; Pichler, Benjamin

    2013-09-01

    The structural, elastic, electronic, phonon and thermodynamic properties of UN are studied by density functional theory (DFT) within local-density approximation (LDA) and generalized gradient approximation (GGA), and GGA + U. The GGA calculations of the ground state structural and elastic properties of UN show an overall better agreement with experimental data compared to LDA or GGA + U. The melting temperature of UN (Tm) is estimated from the calculated elastic constant, with GGA predicting Tm = 2944 ± 300 K, in excellent agreement with experimental data. The calculated phonon dispersions of UN agree well with the low temperature measurements. Furthermore, the thermodynamic properties of UN are studied using quasiharmonic approximation by including both lattice vibrational and thermal electronic contributions. The predicted thermodynamic properties, such as enthalpy, entropy, Gibbs energy, heat capacity and thermal expansion coefficient, agree well with experimental data. The derived thermodynamic functions of UN are useful to the thermodynamic modeling of phase stabilities in UN-based materials. This study shows that the thermal electronic energy and entropy due to U 5f electrons are important to describe the free energy of UN, due to the metallic character of UN. The calculated thermodynamic properties also suggest that the anharmonic effects are less important in UN even at high-temperature.

  7. Ab initio studies of electronic and structural transitions in low-Z liquids under extreme conditions

    NASA Astrophysics Data System (ADS)

    Bonev, Stanimir

    2007-06-01

    The liquids of group I elements (H, Li, Na, and K) are studied using first principles theory. It will be shown that they undergo electronic and structural transitions analogous to that observed in their solids, but commencing at much lower pressure in the presence of disorder. These changes result in exotic melting behavior and in molten phases with unusual properties. The theoretical predictions will be compared with experimental data and ways for further experimental verification of the theoretical results will be suggested.

  8. A structural study of cyanotrichite from Dachang by conventional and automated electron diffraction

    NASA Astrophysics Data System (ADS)

    Ventruti, Gennaro; Mugnaioli, Enrico; Capitani, Giancarlo; Scordari, Fernando; Pinto, Daniela; Lausi, Andrea

    2015-09-01

    The crystal structure of cyanotrichite, having general formula Cu4Al2(SO4)(OH)12·2H2O, from the Dachang deposit (China) was studied by means of conventional transmission electron microscopy, automated electron diffraction tomography (ADT) and synchrotron X-ray powder diffraction (XRPD). ADT revealed the presence of two different cyanotrichite-like phases. The same phases were also recognized in the XRPD pattern, allowing the perfect indexing of all peaks leading, after refinement to the following cell parameters: (1) a = 12.417(2) Å, b = 2.907(1) Å, c = 10.157(1) Å and β = 98.12(1); (2) a = 12.660(2) Å, b = 2.897(1) Å, c = 10.162(1) Å and β = 92.42(1)°. Only for the former phase, labeled cyanotrichite-98, a partial structure, corresponding to the [Cu4Al2(OH){12/2+}] cluster, was obtained ab initio by direct methods in space group C2/ m on the basis of electron diffraction data. Geometric and charge-balance considerations allowed to reach the whole structure model for the cyanotrichite-98 phase. The sulfate group and water molecule result to be statistically disordered over two possible positions, but keeping the average structure consistent with the C-centering symmetry, in agreement with ADT results.

  9. Structural and electronic properties of BxCyNz nanoribbons: A first principles study

    NASA Astrophysics Data System (ADS)

    Gonçalves, R. D.; Azevedo, S.; Machado, M.

    2013-12-01

    We have performed an extensive ab initio study on the energetic stability of hydrogen passivated BxCyNz nanoribbons and at the electronic structure and magnetic properties of BC2N ribbons with different widths and configurations. In particular, it was investigated that BC2N ribbons composed of boron-nitride clusters surrounded by carbon atoms are showing armchair and zigzag edges. It was seen that the zigzag and armchair BC2N ribbons can be small gap semiconductors or metallic according to the ribbons width. Also, magnetic behavior is observed for these structures, for all the considered widths, while the armchair ones do not show any magnetization.

  10. Electronic structure and elastic properties of scandium carbide and yttrium carbide: A first principles study

    NASA Astrophysics Data System (ADS)

    Maibam, Jameson; Indrajit Sharma, B.; Bhattacharjee, Ramendu; Thapa, R. K.; Brojen Singh, R. K.

    2011-11-01

    We have studied the electronic, structural, and elastic properties of scandium carbide and yttrium carbide by means of accurate first principles total energy calculations using the full-potential linearized plane wave method (FP-LAPW). We have used the generalized gradient approximation (GGA) for the exchange and correlation potential. Volume optimization, energy band structure, and density of states (DOS) of the systems are presented. The second order elastic constants have been calculated and other related quantities such as the Zener anisotropy factor, Poisson's ratio, Young's modulus, Kleinman parameter, Debye temperature, and sound velocities have been determined. The band gap calculation shows that YC is relatively more ionic than ScC.

  11. SPE-LEEM Studies on the Surface and Electronic Structure of 2-D Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Yeh, Po-Chun; Jin, Wencan; Zaki, Nader; Zhang, Datong; Sadowski, Jerzy; Al-Mahboob, Abdullah; van de Zande, Arend; Chenet, Daniel; Dadap, Jerry; Herman, Irving; Sutter, Petter; Hone, James; Osgood, Richard

    2014-03-01

    In this work, we studied the surface and electronic structure of monolayer and few-layer exfoliated MoS2 and WSe2, as well as chemical-vapor-deposition (CVD) grown MoS2, using Spectroscopic Photoemission and Low Energy Electron Microscope (SPE-LEEM). LEEM measurements reveal that, unlike exfoliated MoS2, CVD-grown MoS2 exhibits grain-boundary alterations due to surface strain. However, LEEM and micro-probe low energy electron diffraction show that the quality of CVD-grown MoS2 is comparable to that of exfoliated MoS2. Micrometer-scale angle-resolved photoemission spectroscopy (ARPES) measurement on exfoliated MoS2 and WSe2 single-crystals provides direct evidence for the shifting of the valence band maximum from Γ to K, when the layer number is thinned down to one, as predicted by density functional theory. Our measurements of the k-space resolved electronic structure allow for further comparison with other theoretical predictions and with transport measurements. Session I and II

  12. Stability and electronic structures of isoelectronic impurity complexes in Si: First-principles study

    NASA Astrophysics Data System (ADS)

    Iizuka, Shota; Nakayama, Takashi

    2016-10-01

    The stability and electronic structures of various isoelectronic cation+anion pairs in Si were studied by first-principles calculations. It was shown that the nearest-neighboring substitutional configuration is the most stable structure for most cation+anion pairs, while B+N, Mg+O, and Be+O pairs preferentially occupy a single Si site owing to the small atomic radii of B, N, and O atoms. We found that only Al+N, Ga+N, and In+N pairs produce electron-unoccupied weakly localized states in the band gap of Si, reflecting the large negativity of N atoms. We also showed that single N doping produces N+N pairs and that such pairs induce no electronic states in the band gap of Si. Therefore, the codoping of Al and N atoms is essential to produce an electronic state in the Si band gap and increase the tunneling current in Si tunneling field-effect transistors.

  13. First-principles study of structural, elastic, and electronic properties of chromium carbides

    NASA Astrophysics Data System (ADS)

    Jiang, Chao

    2008-01-01

    Using first-principles calculations, we systematically studied the structural, elastic, and electronic properties of the technologically important chromium carbides: Cr3C2, Cr7C3, Cr23C6, Cr3C, and CrC. Our calculations show that the ground state structure for Cr7C3 is hexagonal, not orthorhombic. We further predict WC to be the energetically most stable structure for CrC. Our results indicate that all chromium carbides considered in this study are metallic and mechanically stable under the ambient condition. Among all chromium carbides, WC-type CrC exhibits the highest bulk and shear moduli and the lowest Poisson's ratio, and is a potential low-compressibility and hard material.

  14. Comparisons of electron acceleration efficiency among different structures during magnetic reconnection: a Cluster multicase study

    NASA Astrophysics Data System (ADS)

    Zhou, M.; Li, T.; Deng, X.; Huang, S.; Li, H.

    2015-12-01

    Magnetic reconnection has long been believed to be an efficient engine for energetic electrons production. Four different structures have been proposed for electrons being energized: flux pileup region, density cavity located around the separatrix, magnetic island and thin current sheet. In this paper, we compare the electron acceleration efficiency among these structures based on 12 magnetotail reconnection events observed by the Cluster spacecraft in 2001-2006. We used the flux ratio between the energetic electrons (> 50 keV) and lower energy electrons (< 26 keV) to quantify the electron acceleration efficiency. We do not find any specific sequence in which electrons are accelerated within these structures, though the flux pileup region, magnetic island and thin current sheet have higher probabilities to reach the maximum efficiency among the four structures than the density cavity. However, the most efficient electron energization usually occurs outside these structures. We suggest that other structures may also play important roles in energizing electrons. Our results could provide important constraints for the further modeling of electron acceleration during magnetic reconnection.

  15. First principles study of the structural, electronic, and transport properties of triarylamine-based nanowires

    NASA Astrophysics Data System (ADS)

    Akande, Akinlolu; Bhattacharya, Sandip; Cathcart, Thomas; Sanvito, Stefano

    2014-02-01

    We investigate with state of the art density functional theory the structural, electronic, and transport properties of a class of recently synthesized nanostructures based on triarylamine derivatives. First, we consider the single molecule precursors in the gas phase and calculate their static properties, namely (i) the geometrical structure of the neutral and cationic ions, (ii) the electronic structure of the frontier molecular orbitals, and (iii) the ionization potential, hole extraction potential, and internal reorganization energy. This initial study does not evidence any direct correlation between the properties of the individual molecules and their tendency to self-assembly. Subsequently, we investigate the charge transport characteristics of the triarylamine derivatives nanowires, by using Marcus theory. For one derivative we further construct an effective Hamiltonian including intermolecular vibrations and evaluate the mobility from the Kubo formula implemented with Monte Carlo sampling. These two methods, valid respectively in the sequential hopping and polaronic band limit, give us values for the room-temperature mobility in the range 0.1-12 cm2/Vs. Such estimate confirms the superior transport properties of triarylamine-based nanowires, and make them an attracting materials platform for organic electronics.

  16. Electron Structure of Francium

    NASA Astrophysics Data System (ADS)

    Koufos, Alexander

    2012-02-01

    This talk presents the first calculations of the electronic structure of francium for the bcc, fcc and hcp structures, using the Augmented Plane Wave (APW) method in its muffin-tin and linearized general potential forms. Both the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA), were used to calculate the electronic structure and total energy of francium (Fr). The GGA and LDA both found the total energy of the hcp structure slightly below that of the fcc and bcc structure, respectively. This is in agreement with similar results for the other alkali metals using the same methodology. The equilibrium lattice constant, bulk modulus and superconductivity parameters were calculated. We found that under pressures, in the range of 1-5 GPa, Fr could be a superconductor at a critical temperature of about 4K.

  17. Electronic Structures of Anti-Ferromagnetic Tetraradicals: Ab Initio and Semi-Empirical Studies.

    PubMed

    Zhang, Dawei; Liu, Chungen

    2016-04-12

    The energy relationships and electronic structures of the lowest-lying spin states in several anti-ferromagnetic tetraradical model systems are studied with high-level ab initio and semi-empirical methods. The Full-CI method (FCI), the complete active space second-order perturbation theory (CASPT2), and the n-electron valence state perturbation theory (NEVPT2) are employed to obtain reference results. By comparing the energy relationships predicted from the Heisenberg and Hubbard models with ab initio benchmarks, the accuracy of the widely used Heisenberg model for anti-ferromagnetic spin-coupling in low-spin polyradicals is cautiously tested in this work. It is found that the strength of electron correlation (|U/t|) concerning anti-ferromagnetically coupled radical centers could range widely from strong to moderate correlation regimes and could become another degree of freedom besides the spin multiplicity. Accordingly, the Heisenberg-type model works well in the regime of strong correlation, which reproduces well the energy relationships along with the wave functions of all the spin states. In moderately spin-correlated tetraradicals, the results of the prototype Heisenberg model deviate severely from those of multi-reference electron correlation ab initio methods, while the extended Heisenberg model, containing four-body terms, can introduce reasonable corrections and maintains its accuracy in this condition. In the weak correlation regime, both the prototype Heisenberg model and its extended forms containing higher-order correction terms will encounter difficulties. Meanwhile, the Hubbard model shows balanced accuracy from strong to weak correlation cases and can reproduce qualitatively correct electronic structures, which makes it more suitable for the study of anti-ferromagnetic coupling in polyradical systems. PMID:26963572

  18. A molecular dynamics study on the structural and electronic properties of two-dimensional icosahedral B12 cluster based structures

    NASA Astrophysics Data System (ADS)

    Kah, Cherno Baba; Yu, M.; Jayanthi, C. S.; Wu, S. Y.

    2014-03-01

    Our previous study on one-dimensional icosahedral B12 cluster (α-B12) based chain [Bulletin of APS Annual Meeting, p265 (2013)] and ring structures has prompted us to study the two-dimensional (2D) α-B12 based structures. Recently, we have carried out a systematic molecular dynamics study on the structural stabilities and electronic properties of the 2D α-B12 based structures using the SCED-LCAO method [PRB 74, 15540 (2006)]. We have considered several types of symmetry for these 2D structures such as δ3, δ4, δ6 (flat triangular), and α' types. We have found that the optimized structures are energetically in the order of δ6 < α' < δ3 < δ4 which is different from the energy order of α'< δ6 < δ4 < δ3 found in the 2D boron monolayer sheets [ACS Nano 6, 7443 (2012)]. A detailed discussion of this study will be presented. The first author acknowledges the McSweeny Fellowship for supporting his research in this work.

  19. A first-principle study of Os-based compounds: Electronic structure and vibrational properties

    NASA Astrophysics Data System (ADS)

    Arıkan, N.; Örnek, O.; Charifi, Z.; Baaziz, H.; Uğur, Ş.; Uğur, G.

    2016-09-01

    The electronic structure, elastic, and phonon properties of OsM (M=Hf, Ti, Y and Zr) compounds are studied using first-principles calculations. Elastic constants of OsY and specific heat capacity of OsM (M=Hf, Ti, Y, and Zr) are reported for the first time. The predicted equilibrium lattice constants are in excellent agreement with experiment. The calculated values of bulk moduli are considerably high but are much smaller than that of Osmium, which is around 400 GPa. The phase stability of the OsM (M=Hf, Ti, Y and Zr) compounds were studied by DOS calculations and the results suggest that OsY is unstable in the B2 phase. The brittleness and ductility properties of OsM (M=Hf, Ti, Y and Zr) are determined. OsM (M=Hf, Ti, Y and Zr) compounds are predicted to be ductile materials. The electronic structure and phonon frequency curves of OsM (M=Hf, Ti, Y and Zr) compounds are obtained. The position of Fermi level of these systems was calculated and discussed in terms of the pseudo gaps. The finite and small DOS at the Fermi level 0.335, 0.375, 1.063, and 0.383 electrons/eV for OsHf, OsTi, OsY, and OsZr, respectively, suggest that OsM (M=Hf, Ti, Y and Zr) compounds are weak metals.

  20. Cryogenic Electron Microscopy Studies: Structure and Formation of Self-assembled Nanostructures in Solution

    NASA Astrophysics Data System (ADS)

    Lee, Han Seung

    Cryogenic electron microscopy (Cryo-EM) techniques are among the most powerful to characterize self-assembling soft materials (colloids, polymers, and microemulsions, etc.) at the nanometer scale, without any need for implicit models or assumptions about the structure. We can even visualize structure under dynamic conditions, capturing each stage of development. In this thesis, cryo-EM has been used to investigate the formation and structure of a variety of self-assembling soft materials. Visualization is complemented by small angle X-ray scattering (SAXS), dynamic light scattering, and conductivity measurements. In each case, cryo-EM provides new insights, not otherwise available, into the nanostructure development. Self-assembly phenomena at the molecular level are critical to the performance of tremendous number of applied systems ranging from personal care products to industrial products. To evaluate these self-assembled materials, multiple characterization techniques are required. We investigated aggregation behavior of cesium dodecyl sulfate (CsDS) ionic surfactant in aqueous solution. Coupled with the real space data from cryogenic transmission electron microscopy (Cryo-TEM) and the inverse space data from SAXS, the experimental result of CsDS in aqueous solution gave a new insight in CsDS micellar structures and their development as a function of concentration. Cryo-TEM showed the presence of the liquid-like hydrocarbon core in the CsDS micelles and relatively thick shell structures at a low CsDS concentration. The core-shell sphere structure micelle shifted to core-shell cylindrical micelle structure at high concentration. The morphology and structure of paclitaxel silicate (PTX) prodrug, encapsulated with amphiphilic poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) diblock copolymers were studied. The six different silicate PTX prodrug candidates were characterized with cryo-TEM. Direct imaging with cryo-TEM illustrated structure of prodrug

  1. The structural, electronic and phonon behavior of CsPbI3: A first principles study

    NASA Astrophysics Data System (ADS)

    Bano, Amreen; Khare, Preeti; Parey, Vanshree; Shukla, Aarti; Gaur, N. K.

    2016-05-01

    Metal halide perovskites are optoelectronic materials that have attracted enormous attention as solar cells with power conversion efficiencies reaching 20%. The benefit of using hybrid compounds resides in their ability to combine the advantage of these two classes of compounds: the high mobility of inorganic materials and the ease of processing of organic materials. In spite of the growing attention of this new material, very little is known about the electronic and phonon properties of the inorganic part of this compounds. A theoretical study of structural, electronic and phonon properties of metal-halide cubic perovskite, CsPbI3 is presented, using first-principles calculations with planewave pseudopotential method as personified in PWSCF code. In this approach local density approximation (LDA) is used for exchange-correlation potential.

  2. X-ray absorption study of the electronic structure of Mn-doped amorphous Si

    SciTech Connect

    Arenholz, Elke; Zeng, Li; Huegel, A.; Helgren, E.; Hellman, F.; Piamonteze, C.; Arenholz, E.

    2008-03-08

    The electronic structure of Mn in amorphous Si (a-Mn{sub x}Si{sub 1?x}) is studied by X-ray absorption spectroscopy at the Mn L{sub 3,2} edges for x = 0.005-0.18. Except the x = 0.005 sample, which shows a slight signature of Mn{sup 2+} atomic multiplets associated with a local Mn moment, all samples have broad and featureless L{sub 3,2} absorption peaks, corresponding to an itinerant state for all 3d electrons. The broad X-ray absorption spectra exclude the possibility of a localized 3d moment and explain the unexpectedly quenched Mn moment in this magnetically-doped amorphous semiconductor. Such a fully delocalized d state of Mn dopant in Si has not been previously suggested.

  3. Synchrotron-Radiation Photoemission Study of Electronic Structures of a Cs-Doped Rubrene Surface

    NASA Astrophysics Data System (ADS)

    Cheng, Chiu-Ping; Lu, Meng-Han; Chu, Yu-Ya; Pi, Tun-Wen

    Using synchrotron-radiation photoemission spectroscopy, we have studied the electronic structure of a cesium-doped rubrene thin film. The addition of cesium atoms causes the movement of the valence-band spectra and the change in line shapes at different concentration that can be separated into four different stages. In the first stage, the cesium atoms continuously diffuse into the substrate, and the Fermi level moves in the energy gap as a result of an electron transferred from the cesium to the rubrene. The second stage, in which the shifts of the spectra are interrupted, is characterized by the introduction of two in-gap states. When increasing doping of cesium into the third stage, the spectra move again; whereas, the line shapes maintain at the stoichiometric ratio of one. In the fourth stage, new in-gap states appear, which are the highest occupied molecular orbital (HOMO) and HOMO+1 states of (rubrene)2- anion.

  4. A comparative study about electronic structures at rubrene/Ag and Ag/rubrene interfaces

    SciTech Connect

    Sinha, Sumona Mukherjee, M.

    2015-10-15

    The contact between the electrode and the organic semiconductor is one of the most crucial factors in determining the organic device performance. The development and production technology of different organic devices require the understanding of different types of metal/organic semiconducting thin film interfaces. Comparisons about the electronic structures at Rubrene/Ag and Ag/Rubrene interfaces have been studied using photoemission spectroscopy. The Ag on rubrene interfaces is found to show more interesting and complex natures than its counterpart. The vacuum level (VL) was shifted about 0.51 eV from push back effect for deposition of 5 Å rubrene onto Ag film whereas the electronic features of silver was only suppressed and no energy shift was resulted. While the deposition of 5 Å Ag onto rubrene film leads to the diffusion of the Ag atoms, as a cluster with quantum size effect, inside the film. Angle dependent XPS measurement indicates that diffused metal clusters were present at entire probed depth of the film. Moreover these clusters dope the uppermost surface of the rubrene film which consequences a shift of the electronic states of thick organic film towards higher binding energy. The VL was found to shift about 0.31 eV toward higher binding energy whereas the shift was around 0.21 eV for the electronic states of rubrene layer.

  5. A comparative study about electronic structures at rubrene/Ag and Ag/rubrene interfaces

    NASA Astrophysics Data System (ADS)

    Sinha, Sumona; Mukherjee, M.

    2015-10-01

    The contact between the electrode and the organic semiconductor is one of the most crucial factors in determining the organic device performance. The development and production technology of different organic devices require the understanding of different types of metal/organic semiconducting thin film interfaces. Comparisons about the electronic structures at Rubrene/Ag and Ag/Rubrene interfaces have been studied using photoemission spectroscopy. The Ag on rubrene interfaces is found to show more interesting and complex natures than its counterpart. The vacuum level (VL) was shifted about 0.51 eV from push back effect for deposition of 5 Å rubrene onto Ag film whereas the electronic features of silver was only suppressed and no energy shift was resulted. While the deposition of 5 Å Ag onto rubrene film leads to the diffusion of the Ag atoms, as a cluster with quantum size effect, inside the film. Angle dependent XPS measurement indicates that diffused metal clusters were present at entire probed depth of the film. Moreover these clusters dope the uppermost surface of the rubrene film which consequences a shift of the electronic states of thick organic film towards higher binding energy. The VL was found to shift about 0.31 eV toward higher binding energy whereas the shift was around 0.21 eV for the electronic states of rubrene layer.

  6. Electronic structure of copper phthalocyanine: an experimental and theoretical study of occupied and unoccupied levels.

    PubMed

    Evangelista, Fabrizio; Carravetta, Vincenzo; Stefani, Giovanni; Jansik, Branislav; Alagia, Michele; Stranges, Stefano; Ruocco, Alessandro

    2007-03-28

    An experimental and theoretical study of the electronic structure of copper phthalocyanine (CuPc) molecule is presented. We performed x-ray photoemission spectroscopy (XPS) and photoabsorption [x-ray absorption near-edge structure (XANES)] gas phase experiments and we compared the results with self-consistent field, density functional theory (DFT), and static-exchange theoretical calculations. In addition, ultraviolet photoelectron spectra (UPS) allowed disentangling several outer molecular orbitals. A detailed study of the two highest occupied orbitals (having a(1u) and b(1g) symmetries) is presented: the high energy resolution available for UPS measurements allowed resolving an extra feature assigned to vibrational stretching in the pyrrole rings. This observation, together with the computed DFT electron density distributions of the outer valence orbitals, suggests that the a(1u) orbital (the highest occupied molecular orbital) is mainly localized on the carbon atoms of pyrrole rings and it is doubly occupied, while the b(1g) orbital, singly occupied, is mainly localized on the Cu atom. Ab initio calculations of XPS and XANES spectra at carbon K edge of CuPc are also presented. The comparison between experiment and theory revealed that, in spite of being formally not equivalent, carbon atoms of the benzene rings experience a similar electronic environment. Carbon K-edge absorption spectra were interpreted in terms of different contributions coming from chemically shifted C 1s orbitals of the nonequivalent carbon atoms on the inner ring of the molecule formed by the sequence of CN bonds and on the benzene rings, respectively, and also in terms of different electronic distributions of the excited lowest unoccupied molecular orbital (LUMO) and LUMO+1. In particular, the degenerate LUMO appears to be mostly localized on the inner pyrrole ring.

  7. Electronic structure of copper phthalocyanine: An experimental and theoretical study of occupied and unoccupied levels

    SciTech Connect

    Evangelista, Fabrizio; Carravetta, Vincenzo; Stefani, Giovanni; Jansik, Branislav; Alagia, Michele; Stranges, Stefano; Ruocco, Alessandro

    2007-03-28

    An experimental and theoretical study of the electronic structure of copper phthalocyanine (CuPc) molecule is presented. We performed x-ray photoemission spectroscopy (XPS) and photoabsorption [x-ray absorption near-edge structure (XANES)] gas phase experiments and we compared the results with self-consistent field, density functional theory (DFT), and static-exchange theoretical calculations. In addition, ultraviolet photoelectron spectra (UPS) allowed disentangling several outer molecular orbitals. A detailed study of the two highest occupied orbitals (having a{sub 1u} and b{sub 1g} symmetries) is presented: the high energy resolution available for UPS measurements allowed resolving an extra feature assigned to vibrational stretching in the pyrrole rings. This observation, together with the computed DFT electron density distributions of the outer valence orbitals, suggests that the a{sub 1u} orbital (the highest occupied molecular orbital) is mainly localized on the carbon atoms of pyrrole rings and it is doubly occupied, while the b{sub 1g} orbital, singly occupied, is mainly localized on the Cu atom. Ab initio calculations of XPS and XANES spectra at carbon K edge of CuPc are also presented. The comparison between experiment and theory revealed that, in spite of being formally not equivalent, carbon atoms of the benzene rings experience a similar electronic environment. Carbon K-edge absorption spectra were interpreted in terms of different contributions coming from chemically shifted C 1s orbitals of the nonequivalent carbon atoms on the inner ring of the molecule formed by the sequence of CN bonds and on the benzene rings, respectively, and also in terms of different electronic distributions of the excited lowest unoccupied molecular orbital (LUMO) and LUMO+1. In particular, the degenerate LUMO appears to be mostly localized on the inner pyrrole ring.

  8. Interfacial electronic structure of Na deposited on rubrene thin film studied by synchrotron radiation photoemission

    NASA Astrophysics Data System (ADS)

    Wei, Ching-Hsuan; Cheng, Chiu-Ping; Lin, Hong-Cheu; Pi, Tun-Wen

    2015-12-01

    The electronic structure of rubrene doped with various concentrations of Na was studied by synchrotron-radiation photoemission. Three stages of development were found with increasing Na concentration; Na penetrating deep into the organic film, followed by development of gap states, and ended with a metallic Na film. The charge transfer from Na to rubrene resulted in a vacuum-level shift. By doping Na into rubrene, we could control the IP of the organic molecule, which is favorable for application in organic semiconductor devices.

  9. Structural, electronic and phase transition properties of ytterbium monopnictides under high pressure: A LSDA +U study

    NASA Astrophysics Data System (ADS)

    Kumar Singh, Sanjay; Rana, P.; Verma, U.

    2013-06-01

    In present paper, we have investigated the structural, electronic properties of ytterbium monopnictides (YbX = N, P) and its phase transition behaviour under high pressure by using the full potential linear augmented plane wave plus local orbitals approach within the framework of density functional theory. In the study the generalized gradient approximation (GGA) is chosen for the exchange-correlation functional energy. The equilibrium properties viz., equilibrium lattice constants, bulk modulus, its pressure derivative and total energy are calculated in four different phases i . e . B1, B2, B3 (zinc blende), and BCT phases and compared with previous calculations and available experimental data. The local spin-density approximation along with Hubbard-U corrections and spin-orbit coupling has been used for correct prediction of electronic properties. The LSDA + U strategy shows significant impact on the energy levels of the occupied and unoccupied 4 fstates in the electronic structure of both the compounds. The calculation shows YbX to be semi-metallic. The LSDA + U method provides better description of crystal properties of present system. At ambient conditions YbX (X = N, P) stabilize in NaCl (B1) structure characterized by the space group Fm-3m. Under compression, both YbN and YbP undergo first-order structural transition from Fm-3m (B1) to Pm-3m (B2) at 164.0 and 31.0 GPa, respectively. The One of the authors (UPV) acknowledges the financial assistance provided by UGC, New Delhi F. no. 36-124/2008(SR), India.

  10. A scanning electron microscopy study of the macro-crystalline structure of 2-(2,4-dinitrobenzyl) pyridine

    NASA Technical Reports Server (NTRS)

    Ware, Jacqueline; Hammond, Ernest C., Jr.

    1989-01-01

    The compound, 2-(2,4-dinitrobenzyl) pyridine, was synthesized in the laboratory; an introductory level electron microscopy study of the macro-crystalline structure was conducted using the scanning electron microscope (SEM). The structure of these crystals was compared with the macrostructure of the crystal of 2-(2,4-dinitrobenzyl) pyridinium bromide, the hydrobromic salt of the compound which was also synthesized in the laboratory. A scanning electron microscopy crystal study was combined with a study of the principle of the electron microscope.

  11. Impact of potassium doping on the electronic structure of tetracene and pentacene: An electron energy-loss study

    SciTech Connect

    Roth, Friedrich

    2015-10-21

    We report the doping induced changes of the electronic structure of tetracene and pentacene probed by electron energy-loss spectroscopy in transmission. A comparison between the dynamic response of undoped and potassium-intercalated tetracene and pentacene emphasizes the appearance of a new excitation feature in the former gap upon potassium addition. Interestingly, the momentum dependency of this new excitation shows a negative dispersion. Moreover, the analysis of the C 1s and K 2p core-level excitation results in a significantly lower doping level compared to potassium doped picene, a recently discovered superconductor. Therefore, the present electronic structure investigations open a new pathway to better understand the exceptional differences between acenes and phenacene and their divergent behavior upon alkali doping.

  12. Structural, electronic and magnetic effects of Al-doped niobium clusters: a density functional theory study.

    PubMed

    Wang, Huai-Qian; Li, Hui-Fang; Wang, Jia-Xian; Kuang, Xiao-Yu

    2012-07-01

    The application of the ab initio stochastic search procedure with Saunders "kick" method has been carried out for the elucidation of global minimum structures of a series of Al-doped clusters, Nb(n)Al (1 ≤ n ≤ 10). We have studied the structural characters, growth behaviors, electronic and magnetic properties of Nb(n)Al by the density functional theory calculations. Unlike the previous literature reported on Al-doped systems where ground state structures undergo a structural transition from the Al-capped frame to Al-encapsulated structure, we found that Al atom always occupies the surface of Nb(n)Al clusters and structural transition does not take place until n = 10. Note that the fragmentation proceeds preferably by the ejection of an aluminum atom other than niobium atom. According to the natural population analysis, charges always transfer from aluminum to niobium atoms. Furthermore, the magnetic moments of the Nb(n)Al clusters are mainly located on the 4d orbital of niobium atoms, and aluminum atom possesses very small magnetic moments.

  13. Structural, electronic and magnetic properties of Fe2-based full Heusler alloys: A first principle study

    NASA Astrophysics Data System (ADS)

    Dahmane, F.; Mogulkoc, Y.; Doumi, B.; Tadjer, A.; Khenata, R.; Bin Omran, S.; Rai, D. P.; Murtaza, G.; Varshney, Dinesh

    2016-06-01

    Using the first-principles density functional calculations, the structural, electronic and magnetic properties of the Fe2XAl (X=Cr, Mn, Ni) compounds in both the Hg2CuTi and Cu2MnAl-type structures were studied by the full-potential linearized augmented plane waves (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) where the results show that the Cu2MnAl-type structure is energetically more stable than the Hg2CuTi-type structure for the Fe2CrAl and Fe2MnAl compounds at the equilibrium volume. The full Heusler compounds Fe2XAl (X=Cr, Mn) are half-metallic in the Cu2MnAl-type structure. Fe2NiAl has a metallic character in both CuHg2Ti and AlCu2Mn-type structures. The total magnetic moments of the Fe2CrAl and Fe2MnAl compounds are 1.0 and 2.0 μB, respectively, which are in agreement with the Slater-Pauling rule Mtot=Ztot- 24.

  14. First-principles study of crystal and electronic structure of rare-earth cobaltites

    NASA Astrophysics Data System (ADS)

    Topsakal, M.; Leighton, C.; Wentzcovitch, R. M.

    2016-06-01

    Using density functional theory plus self-consistent Hubbard U (DFT + Usc) calculations, we have investigated the structural and electronic properties of the rare-earth cobaltites RCoO3 (R = Pr - Lu). Our calculations show the evolution of crystal and electronic structure of the insulating low-spin RCoO3 with increasing rare-earth atomic number (decreasing ionic radius), including the invariance of the Co-O bond distance (dCo-O), the decrease of the Co-O-Co bond angle (Θ), and the increase of the crystal field splitting (ΔCF) and band gap energy (Eg). Agreement with experiment for the latter improves considerably with the use of DFT + Usc and all trends are in good agreement with the experimental data. These trends enable a direct test of prior rationalizations of the trend in spin-gap associated with the spin crossover in this series, which is found to expose significant issues with simple band based arguments. We also examine the effect of placing the rare-earth f-electrons in the core region of the pseudopotential. The effect on lattice parameters and band structure is found to be small, but distinct for the special case of PrCoO3 where some f-states populate the middle of the gap, consistent with the recent reports of unique behavior in Pr-containing cobaltites. Overall, this study establishes a foundation for future predictive studies of thermally induced spin excitations in rare-earth cobaltites and similar systems.

  15. Theoretical studies on the electronic structure and properties of complex ceramic crystals and glasses

    SciTech Connect

    Ching, Wai-Yim.

    1991-01-10

    This progress report summarizes the research activities for the period July 1, 1990--June 30, 1991, the first year of a three-year renewal. The major accomplishments for the current year are: study of electronic structures and optical properties of several important ceramic crystals such as Y{sub 2}O{sub 3}, Al{sub 2}O{sub 3}, MgO, MgAl{sub 2}O{sub 4}, ZrO{sub 2},V{sub 2}O{sub 3}, V{sub 2}O{sub 5} and all polycrystalline forms of SiO{sub 2}; theoretical study on superconducting oxides; first-principles calculation of total energies and structural phase transitions in oxides and nitrides; basic study on metallic glasses including calculation of transport properties; and theory of rare-earth and transition metal compounds. The major thrust for the next year's effort will be concentrating on the following: continuation of electronic and optical studies of important ceramic systems. Particular emphasis will be on the total energy calculations on complex crystals such as various polymorphic forms of SiO{sub 2}, ZrO{sub 2}, and Si{sub 3}N{sub 4}; fundamental studies on the structure and properties of different phases of Boron and B-related compounds; and further development of the OLCAO method such as application of self-interaction correction to wide gap insulators, spin-polarized calculations on the magnetic glasses and extraction of effective interatomic pair potentials for simulational studies.

  16. Structural stability and electronic properties of β-tetragonal boron: A first-principles study

    SciTech Connect

    Hayami, Wataru

    2015-01-15

    It is known that elemental boron has five polymorphs: α- and β-rhombohedral, α- and β-tetragonal, and the high-pressure γ phase. β-tetragonal (β-t) boron was first discovered in 1960, but there have been only a few studies since then. We have thoroughly investigated, using first-principles calculations, the atomic and electronic structures of β-t boron, the details of which were not known previously. The difficulty of calculation arises from the fact that β-t boron has a large unit cell that contains between 184 and 196 atoms, with 12 partially-occupied interstitial sites. This makes the number of configurations of interstitial atoms too great to calculate them all. By introducing assumptions based on symmetry and preliminary calculations, the number of configurations to calculate can be greatly reduced. It was eventually found that β-t boron has the lowest total energy, with 192 atoms (8 interstitial atoms) in an orthorhombic lattice. The total energy per atom was between those of α- and β-rhombohedral boron. Another tetragonal structure with 192 atoms was found to have a very close energy. The valence bands were fully filled and the gaps were about 1.16 to 1.54 eV, making it comparable to that of β-rhombohedral boron. - Graphical abstract: Electronic density distribution for the lowest-energy configuration (N=192) viewed from the 〈1 0 0〉 direction. Left: isosurface (yellow) at d=0.09 electrons/a.u.{sup 3} Right: isosurface (orange) at d=0.12 electrons/a.u.{sup 3}. - Highlights: • β-tetragonal boron was thoroughly investigated using first-principles calculations. • The lowest energy structure contains 192 atoms in an orthorhombic lattice. • Another tetragonal structure with 192 atoms has a very close energy. • The total energy per atom is between those of α- and β-rhombohedral boron. • The band gap of the lowest energy structure is about 1.16 to 1.54 eV.

  17. Electronic structure of Sc C[sub 60]. An ab initio theoretical study

    SciTech Connect

    Guo, T.; Odom, G.K.; Scuseria, G.E. )

    1994-08-11

    We have studied the electronic structure of Sc C[sub 60] at the self-consistent-field Hartree-Fock (SCF-HF) level of theory employing a double-zeta (DZ) basis set. Binding energies have also been calculated employing a hybrid of HF and density functional theory (herein denoted as HF-BLYP). Several electronic states in C[sub 50] and C[sub 30] symmetry were considered. A double-minimum configuration is found for the open-shell [sup 4]A[sub 2] electronic ground state in C[sub 50] symmetry. The lowest energy minimum has Sc located 1.175 [angstrom] away from the center of the cage, approaching a C[sub 60] pentagon along a C[sub 5] axis. Bonding between the Sc atom and the cage occurs by donation of the 4s electrons to the lowest unoccupied orbital of C[sub 60] and by 3d electron interaction with the antibonding orbital associated with the five double bonds radiating from the pentagon closest to Sc ([approximately] 2.5 [angstrom]). The other local minimum has Sc located at the center of the cage and is predicted to be 1.2 eV higher in energy at the highest level of theory employed in this work (DZ/HF-BLYP). The energy barrier for moving Sc from the center of the cage to the lowest energy position is predicted to be 0.1 eV at the same level of theory. 33 refs., 2 figs., 2 tabs.

  18. First principles study of structural, electronic and mechanical properties of alkali nitride-KN

    SciTech Connect

    Murugan, A.; Rajeswarapalanichamy, R. Santhosh, M.; Iyakutti, K.

    2015-06-24

    The structural, electronic and elastic properties of alkali- metal nitride (KN) is investigated by the first principles calculations based on density functional theory as implemented in Vienna ab-initio simulation package. At ambient pressure KN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that the KN is half metallic ferromagnet at normal pressure. A pressure-induced structural phase transition from NaCl to ZB phase is observed in KN. Half metallicity and ferromagnetism is maintained at all pressures.

  19. Electronic structure effects in liquid water studied by photoelectron spectroscopy and density functional theory

    SciTech Connect

    Nordlund, Dennis; Odelius, Michael; Bluhm, Hendrik; Ogasawara, Hirohito; Pettersson, Lars G.M.; Nilsson, Anders

    2008-04-29

    We present valence photoelectron emission spectra of liquid water in comparison with gas-phase water, ice close to the melting point, low temperature amorphous and crystalline ice. All aggregation states have major electronic structure changes relative to the free molecule, with rehybridization and development of bonding and anti-bonding states accompanying the hydrogen bond formation. Sensitivity to the local structural order, most prominent in the shape and splitting of the occupied 3a{sub 1} orbital, is understood from the electronic structure averaging over various geometrical structures, and reflects the local nature of the orbital interaction.

  20. Electronic structure of the sulfonyl and phosphonyl groups: a computational and crystallographic study.

    PubMed

    Denehy, Emma; White, Jonathan M; Williams, Spencer J

    2007-10-15

    A computational and X-ray crystallographic investigation of the electronic and geometric structures of a range of sulfonyl (-SO(2)-) and phosphonyl (-PO(2)--) containing species was undertaken to investigate the nature of valency and bonding in these functional groups. The traditional representation of sulfonyl and phosphonyl species is with octet-violating Lewis structures, which require d-orbital participation at the central atom. However, computational studies cast serious doubt upon this bonding model. In this work, we have employed NBO/NRT analysis to investigate hybridization, atomic formal charges, donor-acceptor interactions, and resonance structure contributions. Our results predict that within sulfonyl and phosphonyl systems, bonding interactions are highly polarized, of the form X+-Y- (X = P, S), and possess additional contributions from reciprocal n --> sigma* interactions where substituents off sulfur or phosphorus simultaneously act as donors and acceptors. Experimental evidence for the proposed bonding arrangement is provided for the sulfonyl functional group through a series of low-temperature X-ray structure correlations for sulfate monoesters, sulfamates, and methanesulfonates. Examination of changes to bond lengths and geometries upon substituent variation support the computational results. Together, our studies lend support for a bonding network in sulfonyl and phosphonyl groups composed of polar interactions augmented with reciprocal hyperconjugative bonding, which does not necessitate significant d-orbital participation nor formal octet violation at the central sulfur or phosphorus. PMID:17880060

  1. Theoretical Studies on the Electronic Structures and Properties of Complex Ceramic Crystals and Novel Materials

    SciTech Connect

    Ching, Wai-Yim

    2012-01-14

    This project is a continuation of a long program supported by the Office of Basic Energy Science in the Office of Science of DOE for many years. The final three-year continuation started on November 1, 2005 with additional 1 year extension to October 30, 2009. The project was then granted a two-year No Cost Extension which officially ended on October 30, 2011. This report covers the activities within this six year period with emphasis on the work completed within the last 3 years. A total of 44 papers with acknowledgement to this grant were published or submitted. The overall objectives of this project are as follows. These objectives have been evolved over the six year period: (1) To use the state-of-the-art computational methods to investigate the electronic structures of complex ceramics and other novel crystals. (2) To further investigate the defects, surfaces/interfaces and microstructures in complex materials using large scale modeling. (3) To extend the study on ceramic materials to more complex bioceramic crystals. (4) To initiate the study on soft condensed matters including water and biomolecules. (5) To focus on the spectroscopic studies of different materials especially on the ELNES and XANES spectral calculations and their applications related to experimental techniques. (6) To develop and refine computational methods to be effectively executed on DOE supercomputers. (7) To evaluate mechanical properties of different crystals and those containing defects and relate them to the fundamental electronic structures. (8) To promote and publicize the first-principles OLCAO method developed by the PI (under DOE support for many years) for applications to large complex material systems. (9) To train a new generation of graduate students and postdoctoral fellows in modern computational materials science and condensed matter physics. (10) To establish effective international and domestic collaborations with both experimentalists and theorists in materials

  2. Change in electronic structure upon optical excitation of 8-vinyladenosine: an experimental and theoretical study.

    PubMed

    Kodali, Goutham; Kistler, Kurt A; Narayanan, Madhavan; Matsika, Spiridoula; Stanley, Robert J

    2010-01-14

    8-Vinyladenosine (8VA) is an adenosine analog, like 2-aminopurine (2AP), that has a red-shifted absorption and high fluorescence quantum yield. When introduced into double-stranded DNA (dsDNA), its base-pairing and base-stacking properties are similar to those of adenine. Of particular interest, the fluorescence quantum yield of 8VA is sensitive to base stacking, making it a very useful real-time probe of DNA structure. The fundamental photophysics underlying this fluorescence quenching by base stacking is not well understood, and thus exploring the excited state electronic structure of the analog is warranted. In this study, we report on changes in the electronic structure of 8VA upon optical excitation. Stark spectroscopy was performed on 8VA monomer in frozen ethanol glass at 77 K to obtain the direction and degree of charge redistribution in the form of the difference dipole moment, Deltamu(01) = 4.7 +/- 0.3 D, and difference static polarizability, tr(Delta(alpha)01) = 21 +/- 11 A(3), for the S(0)-->S(1) transition. In addition, solvatochromism experiments were performed on 8VA in various solvents and analyzed using Bakhshiev's model. High level ab initio methods were employed to calculate transition energies, oscillator strengths, and dipole moments of the ground and excited states of 8VA. The direction of Deltamu(01) was assigned in the molecular frame for the lowest optically accessible state. Our study shows that the angle between ground and excited state dipole moment plays a critical role in understanding the change in electronic structure upon optical excitation. Compared to 2AP, 8VA has a larger difference dipole moment which, with twice the extinction coefficient, suggests that 8VA is superior as a two-photon probe for microscopy studies. To this end, we have measured the ratio of the two-photon fluorescence yields of the two analogs by excitation at the respective monomer absorption maxima. We show that 8VA is indeed a significantly brighter two

  3. Size effects on the structural, electronic, and optical properties of (5,0) finite-length carbon nanotube: An ab-initio electronic structure study

    NASA Astrophysics Data System (ADS)

    Tarighi Ahmadpour, Mahdi; Hashemifar, S. Javad; Rostamnejadi, Ali

    2016-07-01

    We use density functional computations to study the zero temperature structural, electronic, magnetic, and optical properties of (5,0) finite carbon nanotubes (FCNT), with length in the range of 4-44 Å. It is found that the structural and electronic properties of (5,0) FCNTs, in the ground state, converge at a length of about 30 Å, while the excited state properties exhibit long-range edge effects. We discuss that curvature effects enhance energy gap of FCNTs, in contrast to the known trend in the periodic limit. It is seen that compensation of curvature effects in two special small sizes may give rise to spontaneous magnetization. The obtained cohesive energies provide some insights into the effects of environment on the growth of FCNTs. The second-order difference of the total energies reveals an important magic size of about 15 Å. The optical and dynamical magnetic responses of the FCNTs to polarized electromagnetic pulses are studied by time dependent density functional theory. The results show that the static and dynamic magnetic properties mainly come from the edge carbon atoms. The optical absorption properties are described in terms of local field effects and characterized by Casida linear response method.

  4. Combined First Principles Electronic Structure Calculations and Thermodynamic Study of Binary Alloys

    NASA Astrophysics Data System (ADS)

    Guo, Xiaoqing

    In the past decade, density functional theory (DFT), combined with the highly precise computational methods and the increasing computer power, has become a most successful tool to study the physical properties of atoms, molecules, solids, surfaces and disordered systems. In this dissertation, we present a common framework, based on the density functional theory, to study the electronic structure, structural stability and the phase equilibria of both ordered compounds and solid solution of the binary alloys which usually have very small energy differences. As an illustrative example, we have made a systematic study on the Al-Li alloys which have become promising low density, high strength aerospace materials. The Al-Li ordered compounds are calculated by the all electron self-consistent, full potential linearized augmented plane wave (FLAPW) method within the local density approximation. All the stable and metastable phases are correctly predicted due to the high precision of the method. The phase stability in Al-Li alloys can be understood by our assumption that the Li atoms basically transfer their valence electrons in between the Al bonds and the resultant strengthened bonds stabilize the Al-Li compounds. The unusually high elastic modulus of the Al-Li alloys is due to the increased anisotropic Al bonding (decrease of the Poisson's ratio) with increasing Li content. Very good agreement with experiment is obtained. To utilize the existing highly precise band calculation method, we describe the Al-Li solid solution by a supercell method based on the "theory of locality". The relatively small size of a supercell is shown to give a very good description of Al-rich Al-Li solid solution. A thermodynamic model is proposed, as a first step, to calculate the phase diagrams of the binary alloys. The grand partition function, constructed from volume-dependent internal energies obtained from local-density total-energy supercell calculations, permits the determination of the

  5. Electronic Structure of Few-Electron Quantum Dot Molecules

    NASA Astrophysics Data System (ADS)

    Popsueva, V.; Hansen, J. P.; Caillat, J.

    2007-12-01

    We present a study of strongly correlated few-electron quantum dots, exploring the spectra of various few-electron quantum dot molecules: a double (diatomic) structure a quadruple two-electron quantum dot, and a three-electron double dot. Electron energy spectra are computed for different values of dot separation. All spectra show clear band structures and can be understood from asymptotical properties of the system.

  6. Characterization of electronic structure and physicochemical properties of antiparasitic nifurtimox analogues: A theoretical study

    NASA Astrophysics Data System (ADS)

    Soriano-Correa, Catalina; Raya, A.; Esquivel, Rodolfo O.

    American trypanosomiasis, also known as Chagas' disease, is caused by Trypanosoma cruzi (T. cruzi). It is well known that trypanosomes, and particularly T. cruzi, are highly sensitive towards oxidative stress, i.e., to compounds than are able to produce free radicals. Generally, nifurtimox (NFX) and benznidazol are most effective in the acute phase of the disease; therefore, nitroheterocycles constitute good models to design other nitrocompounds with specific biological characteristics. Thus, we have performed an ab initio study at the Hartree-Fock and Density Functional Theory levels of theory of several NFX analogues recently synthesized, to characterize them by obtaining their electronic, structural, and physicochemical properties, which might be linked to the observed antichagasic activity. The antitrypanosomal activity scale previously reported for the NFX analogues studied in this work is in good agreement with our theoretical results, from which we can conclude that the activity seems to be related to the reactivity along with the acidity observed for the most active molecules.

  7. Electronic structure and photoluminescence study of silicon doped diamond like carbon (Si:DLC) thin films

    SciTech Connect

    Ray, S.C. . E-mail: raysekhar@rediffmail.com; Okpalugo, T.I.T.; Pao, C.W.; Tsai, H.M.; Chiou, J.W.; Jan, J.C.; Pong, W.F.; Papakonstantinou, P.; McLaughlin, J.A.; Wang, W.J.

    2005-10-06

    We have investigated the electronic and bonding structure using Fourier-transform infra-red (FT-IR) spectra and studied photoluminescence (PL) from micro-Raman spectra analysis of a-C:H:Si (Si:DLC) thin films deposited by plasma enhanced chemical vapour deposition (PECVD) method. Tetramethylsilane [Si(CH{sub 3}){sub 4}, TMS] vapour was used as Silicon precursor and a bias voltage of 400 V was applied during deposition. It is observed from FT-IR spectra that with increasing TMS flow rate, the intensity of Si-H {sub n} and C-H {sub n} modes is increased significantly. PL study indicates that the PL is increased and that the PL peak position is shifted towards lower energy when the TMS flow rate increases gradually during deposition.

  8. Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

    NASA Astrophysics Data System (ADS)

    Dabhi, Shweta D.; Gupta, Sanjay D.; Jha, Prafulla K.

    2014-05-01

    We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

  9. Structural, electronic, mechanical, and dynamical properties of graphene oxides: A first principles study

    SciTech Connect

    Dabhi, Shweta D.; Gupta, Sanjay D.; Jha, Prafulla K.

    2014-05-28

    We report the results of a theoretical study on the structural, electronic, mechanical, and vibrational properties of some graphene oxide models (GDO, a-GMO, z-GMO, ep-GMO and mix-GMO) at ambient pressure. The calculations are based on the ab-initio plane-wave pseudo potential density functional theory, within the generalized gradient approximations for the exchange and correlation functional. The calculated values of lattice parameters, bulk modulus, and its first order pressure derivative are in good agreement with other reports. A linear response approach to the density functional theory is used to derive the phonon frequencies. We discuss the contribution of the phonons in the dynamical stability of graphene oxides and detailed analysis of zone centre phonon modes in all the above mentioned models. Our study demonstrates a wide range of energy gap available in the considered models of graphene oxide and hence the possibility of their use in nanodevices.

  10. Electron nanodiffraction and high-resolution electron microscopy studies of the structure and composition of physiological and pathological ferritin.

    PubMed

    Quintana, C; Cowley, J M; Marhic, C

    2004-08-01

    Structures of core nanocrystals of physiological (horse spleen, human liver, and brain) and pathological human brain of patients with progressive supranuclear palsy (PSP) and Alzheimer's disease (AD) ferritin molecules were determined using electron nanodiffraction and high-resolution transmission electron microscopy. The poly-phasic structure of the ferritin cores is confirmed. There are significant differences in the mineral composition between the physiological and pathological ferritins. The physiological ferritin cores mainly consist of single nanocrystals containing hexagonal ferrihydrite (Fh) and hematite (Hm) and some cubic magnetite/maghemite phase. In the pathological cores, Fh is present but only as a minor phase and Hm is absent. The major phases are a face-centered-cubic (fcc) structure with a = 0.43 nm and a high degree of disorder, related to wustite, and a cubic magnetite-like structure. These two cubic phases are also present in human aged normal brain. Evidence for the presence of hemosiderin together with ferritin in the pathological brains is deduced from the similarities of the diffraction patterns with those from patients with primary hemochromatosis, and differences in the shapes and protein composition of the protein shell. These findings suggest a disfunction of the ferritin associated with PSP and AD, associated with an increase in the concentration of brain ferrous toxic iron.

  11. Ab initio electronic structure study of a model water splitting dimer complex.

    PubMed

    Fernando, Amendra; Aikens, Christine M

    2015-12-28

    A model manganese dimer electrocatalyst bridged by μ-OH ligands is used to investigate changes in spin states that may occur during water oxidation. We have employed restricted open-shell Hartree-Fock (ROHF), second-order Møller-Plesset perturbation theory (MP2), complete active space self-consistent field (CASSCF), and multireference second-order Møller-Plesset perturbation theory (MRMP2) calculations to investigate this system. Multiconfigurational methods like CASSCF and MRMP2 are appropriate methods to study these systems with antiferromagnetically-coupled electrons. Orbital occupations and distributions have been closely analyzed to understand the electronic details and contributions to the water splitting from manganese and oxygen atoms. The presence of Mn(IV)O˙ radical moieties has been observed in this catalytic pathway. Multiple nearly degenerate excited states were found close to the ground state in all structures. This suggests competing potential energy landscapes near the ground state may influence the reactivity of manganese complexes such as the dimers studied in this work.

  12. First-principles study on oxidation of Ge and its interface electronic structures

    NASA Astrophysics Data System (ADS)

    Ono, Tomoya; Saito, Shoichiro; Iwase, Shigeru

    2016-08-01

    We review a series of first-principles studies on the defect generation mechanism and electronic structures of the Ge/GeO2 interface. Several experimental and theoretical studies proved that Si atoms at the Si/SiO2 interface are emitted to release interface stress. In contrast, total-energy calculation reveals that Ge atoms at the Ge/GeO2 interface are hardly emitted, resulting in the low trap density. Even if defects are generated, those at the Ge/GeO2 interface are found to behave differently from those at the Si/SiO2 interface. The states attributed to the dangling bonds at the Ge/GeO2 interface lie below the valence-band maximum of Ge, while those at the Si/SiO2 interface generate the defect state within the band gap of Si. First-principles electron-transport calculation elucidates that this characteristic behavior of the defect states is relevant to the difference in the leakage current through the Si/SiO2 and Ge/GeO2 interfaces.

  13. First-principles study of the structural, energetic and electronic properties of C20-carbon nanobuds

    NASA Astrophysics Data System (ADS)

    Wen, Y. W.; Liu, Xiao; Duan, Xianbao; Chen, Rong; Shan, Bin

    2013-04-01

    The structural, energetic and electronic properties of carbon nanobuds (CNBs) with the smallest fullerene C20 covalently attached to the sidewall of single-walled carbon nanotubes (SWNTs) are studied by first-principles calculations. Due to the high curvature of C20 and the resulting chemical activity, the binding between C20 and SWNTs is quite strong. Among different CNB configurations, bond cycloaddition is energetically most favorable. The activation barrier for C20-CNB formation is only one-fourth that of C60 and it would maintain good stability once formed. Our results also reveal that C20-CNB stability depends on the chirality of the SWNTs, and they exhibit tunable band gaps that can be modulated by the density of C20 attached to the SWNTs.

  14. Structure, vibrational analysis, electronic properties and chemical reactivity of two benzoxazole derivatives: Functional density theory study

    NASA Astrophysics Data System (ADS)

    Zaater, Sihem; Bouchoucha, Afaf; Djebbar, Safia; Brahimi, Meziane

    2016-11-01

    In the present work we calculate structural parameters, vibrational spectra (IR, 1H NMR and UV-Visible Absorption) and corresponding mode of vibrational assignments of two ligands derived from benzoxazole; L1: 2-(5-(trifluoromethylpyridin-2-yl)-benzoxazole and L2: 2-(5-methylpyridin-2-yl)-benzoxazole at B3LYP/6-311++G** level, in the gas phase. The HOMO and LUMO study is used to determine the charge transfer within the molecules. Reactivity descriptors such as ionization energy, electronic affinity, global hardness, global softness, electrophilicity, nucleophilicity and condensed Fukui functions using NBO population analysis are also determined to predict the reactivity of L1 and L2. The calculated geometrical parameters are in good agreement with those of similar benzoxazole derivatives. Theoretical frequencies assignments confirmed the experimental ones of these benzoxazole derivatives.

  15. Structure, electronic and electrochemical properties of Li-rich metal phosphate by first-principles study

    NASA Astrophysics Data System (ADS)

    Lin, Zhiping; Zhao, Yu-Jun; Zhao, Yanming; Xu, Jiantie

    2014-01-01

    We present a first-principles investigation for the structure, electronic properties, and average potentials of Li9M3(P2O7)3(PO4)2 (M = V, Fe, Cr) compounds. The calculated Wyckoff coordinates are in good agreement with experimental observations. All the studied compounds show semiconductor characteristics, with band gaps between 1.89 eV and 2.55 eV. It is found that the Li-ion extraction is in the order of Li1(2b), Li2(12g), and Li3(4d) based on the calculated formation enthalpies of Li vacancies. Consequently, the calculated average potentials versus the number of Li ions are in good agreement with experiment.

  16. Density functional theory studies on molecular structure, vibrational spectra and electronic properties of cyanuric acid.

    PubMed

    Prabhaharan, M; Prabakaran, A R; Srinivasan, S; Gunasekaran, S

    2015-03-01

    The present work has been carried out a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid. The FT-IR (100-4000cm(-1)) and FT-Raman spectra (400-4000cm(-1)) of cyanuric acid were recorded. In DFT methods, Becke's three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) by implementing the split-valence polarized 6-31G(d,p) and 6-31++G(d,p) basis sets have been considered for the computation of the molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The density functional theory (DFT) result complements the experimental findings. The electronic properties, such as HOMO-LUMO energies and molecular electrostatic potential (MESP) are also performed. Mulliken population analysis on atomic charges is also calculated. The first order hyperpolarizability (βtotal) of this molecular system and related properties (β, μ and Δα) are calculated using DFT/B3LYP/6-31G (d,p) and B3LYP/6-311++G(d,p) methods. The thermodynamic functions (heat capacity, entropy and enthalpy) from spectroscopic data by statistical methods were also obtained for the range of temperature 50-1000K.

  17. Density functional theory studies on molecular structure, vibrational spectra and electronic properties of cyanuric acid

    NASA Astrophysics Data System (ADS)

    Prabhaharan, M.; Prabakaran, A. R.; Srinivasan, S.; Gunasekaran, S.

    2015-03-01

    The present work has been carried out a combined experimental and theoretical study on molecular structure, vibrational spectra and NBO analysis of cyanuric acid. The FT-IR (100-4000 cm-1) and FT-Raman spectra (400-4000 cm-1) of cyanuric acid were recorded. In DFT methods, Becke's three parameter exchange-functional (B3) combined with gradient-corrected correlation functional of Lee, Yang and Parr (LYP) by implementing the split-valence polarized 6-31G(d,p) and 6-31++G(d,p) basis sets have been considered for the computation of the molecular structure optimization, vibrational frequencies, thermodynamic properties and energies of the optimized structures. The density functional theory (DFT) result complements the experimental findings. The electronic properties, such as HOMO-LUMO energies and molecular electrostatic potential (MESP) are also performed. Mulliken population analysis on atomic charges is also calculated. The first order hyperpolarizability (βtotal) of this molecular system and related properties (β, μ and Δα) are calculated using DFT/B3LYP/6-31G (d,p) and B3LYP/6-311++G(d,p) methods. The thermodynamic functions (heat capacity, entropy and enthalpy) from spectroscopic data by statistical methods were also obtained for the range of temperature 50-1000 K.

  18. The structure of oxotitanium phthalocyanine: a gas-phase electron diffraction and computational study.

    PubMed

    Zakharov, Alexander V; Shlykov, Sergei A; Zhabanov, Yuriy A; Girichev, Georgy V

    2009-05-14

    The gas-phase molecular structure of oxotitanium phthalocyanine (TiOPc) has been studied by a synchronous gas electron diffraction and mass spectrometric experiment, and density functional theory calculations using the B3LYP hybrid method and cc-pVTZ basis sets. The molecule has an equilibrium structure of C4v symmetry with a convex macrocycle. The titanium atom is out-of-the-plane of the four central nitrogen atoms and forms a square pyramid with them, with the following parameters: r(Ti-N)=2.090(5) A, r(NN)=2.813(9) A (the side of the pyramid base), z(Ti)-z(N)=0.614 A (the height of the pyramid). Compared to solid-state crystal structures, the Ti-O distance in gas-phase TiOPc is shortened and the Ti-N distance is elongated, which can be attributed to significant intermolecular interaction in the crystals. PMID:19421550

  19. Structural and electronic properties of V2O3 ultrathin film on Ag(001): LEED and photoemission study

    NASA Astrophysics Data System (ADS)

    Kundu, Asish K.; Menon, Krishnakumar S. R.

    2016-05-01

    V2O3 ultrathin films were grown on Ag(001) substrate by reactive evaporation of vanadium (V) metal in presence of oxygen and their structural and electronic properties were studied by Low Energy Electron Diffraction (LEED), X-ray Photo Electron Spectroscopy (XPS) and Angle Resolved Photoemission Spectroscopic (ARPES) techniques, respectively. On top of square symmetry substrate Ag(001), hexagonal surface of V2O3 (0001) is stabilized in the form of two domain structure, rotated by 30°(or 90°)to each other, has been observed by LEED. Rather than epitaxial flat monolayer, formation of well-ordered V2O3 (0001) island has been confirmed from the LEED and the Photoemission Spectroscopic (PES) study. Stoichiometry of the grown film was confirmed by the XPS study. Evolution of valance band electronic structure of V2O3 (0001) surface has been studied as a function of film thickness by ARPES.

  20. Electronic structure and orientation of NO on Ni(111) studied by arups using synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Steinrück, H.-P.; Schneider, C.; Heimann, P. A.; Pache, T.; Umbach, E.; Menzel, D.

    1989-01-01

    The electronic structure and the orientation of NO adsorbed on Ni(111) at 120 K was studied by angle resolved UPS using linearly polarized synchrotron radiation and a multichannel angle resolving electron analyzer. The layer investigated corresponds to a coverage of 0.5 ML and exhibits a c(4 × 2) LEED pattern with only twofold bridging sites being occupied. The binding energies for 4 ˜gs, 5 ˜gs and 1 ˜gP at the ḡG point are 15.1, 9.3 and 7.5 eV, respectively; the 1 ˜gP level is very broad which may be due to splitting. The 2D band structure shows a dispersion of 0.3 eV for the 4 ˜gs and 0.6 eV for the 5 ˜gs level, indicative of lateral interactions within the adsorbed NO layer. The photon energy dependence of the photoionization cross sections of the 4 ˜gs, 5 ˜gs and 1 ˜gP NO molecular orbitais has been studied in the energy range 26 eV ⩽ ℏ gw ⩽ 60 eV. The 4 ˜gs level shows a pronounced maximum at ℏ ω = 36 eV ( Ekin = 15 eV) that is peaked in the direction of the surface normal and is interpreted as a shape resonance. For the 5 ˜gs and 1 ˜gP levels no shape resonances are observed. Using dipole selection rules, it is demonstrated independently by initial state and final state arguments that in a c(4 × 2) layer the NO molecules are adsorbed with their molecular axis perpendicular to the surface.

  1. First-principles study of the structural and electronic properties of ultrathin silver nanowires

    NASA Astrophysics Data System (ADS)

    Ma, Liang-Cai; Ma, Ling; Lin, Xue-Ling; Yang, You-Zhen; Zhang, Jian-Min

    2015-12-01

    By using first-principles calculations based on density-functional theory, we have systematically investigated the equilibrium structure, stability and electronic properties of silver nanowires (AgNWs) with dimer, triangular, square, pentagonal and hexagonal cross-section. It is found that, using the string tension criterion, for the triangular and square AgNWs with small diameters the preferred structures should be the hollow one with staggered configuration, while for the pentagonal and hexagonal AgNWs with bigger diameters the preferred structures should be the staggered ones which contain a linear chain along the wire axis passes through the center of the polygons, where each chain atom is just located at a point equidistant from the planes of polygons. Electronic band structures and density of states calculations show that the AgNWs with different structures exhibit metallic behavior. Charge density contours show that there is an enhanced interatomic interaction in AgNWs compared with Ag bulk.

  2. Ab initio study of structural, electronic, magnetic alloys: XTiSb (X = Co, Ni and Fe)

    SciTech Connect

    Ibrir, M. Berri, S.; Lakel, S.; Alleg, S.; Bensalem, R.

    2015-03-30

    Structural, electronic and magnetic properties of three semi-Heusler compounds of CoTiSb, NiTiSb and FeTiSb were calculated by the method (FP-LAPW) which is based on the DFT code WIEN2k. We used the generalized gradient approximation (GGA (06)) for the term of the potential exchange and correlation (XC) to calculate structural properties, electronic properties and magnetic properties. Structural properties obtained as the lattice parameter are in good agreement with the experimental results available for the electronic and magnetic properties was that: CoTiSb is a semiconductor NiTiSb is a metal and FeTiSb is a half-metal ferromagnetic.

  3. Electronic structure and correlations of vitamin B12 studied within the Haldane-Anderson impurity model

    NASA Astrophysics Data System (ADS)

    Kandemir, Zafer; Mayda, Selma; Bulut, Nejat

    2016-04-01

    We study the electronic structure and correlations of vitamin B12 (cyanocobalamine) by using the framework of the multi-orbital single-impurity Haldane-Anderson model of a transition-metal impurity in a semiconductor host. The parameters of the effective Haldane-Anderson model are obtained within the Hartree-Fock (HF) approximation. The quantum Monte Carlo (QMC) technique is then used to calculate the one-electron and magnetic correlation functions of this effective model. We observe that new states form inside the semiconductor gap found by HF due to the intra-orbital Coulomb interaction at the impurity 3d orbitals. In particular, the lowest unoccupied states correspond to an impurity bound state, which consists of states from mainly the CN axial ligand and the corrin ring as well as the Co eg-like orbitals. We also observe that the Co (3d) orbitals can develop antiferromagnetic correlations with the surrounding atoms depending on the filling of the impurity bound states. In addition, we make comparisons of the HF+QMC data with the density functional theory calculations. We also discuss the photoabsorption spectrum of cyanocobalamine.

  4. Electronic structure and reactivity of cobalt oxide dimers and their hexacarbonyl complexes: a density functional study.

    PubMed

    Uzunova, Ellie L; Mikosch, Hans

    2012-03-29

    The dimers of cobalt oxide (CoO)(2) with cyclic and open bent structure are studied with the B1LYP density functional; the ordering of states is validated by the CCSD(T) method. The D(2h)-symmetry rhombic dioxide Co(2)O(2) with antiferromagnetically ordered electrons on cobalt centers is the global minimum. The cyclic peroxide Co(2)(O(2)) with side-on-bonded dioxygen in (7)B(2) ground state is separated from the global minimum by an energy gap of 3.15 eV. The dioxide is highly reactive as indicated by the high value of proton affinity and chemical reactivity indices. The four-member ring structures are more stable than those with three-member ring or chain configuration. The thermodynamic stability toward dissociation to CoO increases upon carbonylation, whereas proton affinity and reactivity with release of molecular oxygen also increase. The global minimum of Co(2)O(2)(CO)(6) corresponds to a triplet state (3)A" with oxygen atoms shifted above the molecular plane of the rhombic dioxide Co(2)O(2). The SOMO-LUMO gap in the ground-state carbonylated dioxide is wider, compared to the same gap in the bare dicobalt dioxide. The peroxo-isomer Co(2)(O(2))(CO)(6) retains the planar Co(2)(O(2)) ring and is only stable in a high-spin state (7)A". The carbonylated clusters have increased reactivity in both redox and nucleophilic reactions, as a result of the increased electron density in the Co(2)O(2)-ring area. PMID:22397598

  5. A theoretical study of the electronic structure of Invar Fe*3Pt and related materials

    SciTech Connect

    Zuo, Zhiqi

    1997-01-10

    The Full Potential Linear Augmented Plane Wave (FPLAPW or FLAPW) method is used for a spin-polarized band calculation for ordered Fe{sub 3}Pt. As major purpose, the momentum distributions of the spin-polarized electrons are calculated and compared with results from a magnetic Compton scattering measurement. To get related information, the electronic behavior is also analyzed by examining the partial densities of states and the spatial electron distributions; the role of alloying effects is then explored by studying the electrons in some related alloys: Fe{sub 3}Ni, Fe{sub 3}Pd, Ni{sub 3}Pt and Co{sub 3}Pt.

  6. Structural study of methyl isonicotinate by gas phase electron diffraction combined with ab initio calculations

    NASA Astrophysics Data System (ADS)

    Kiyono, Hajime; Kuze, Nobuhiko; Fujiwara, Hideo; Takeuchi, Hiroshi; Egawa, Toru; Konaka, Shigehiro

    1996-02-01

    The molecular structure of methyl isonicotinate was studied by gas phase electron diffraction combined with ab initio calculations. The molecular skeleton was assumed to be planar. The determined values of principal structure parameters ( rg and ∠ α) are as follows: r( NC) = 1.343(5) Å, r( C…C) ring = 1.401(3) Å, r( Cγ C) = 1.499(9) Å, r( C O) = 1.205(5) Å, r( C( O) O) = 1.331(8) Å, r( OC Me) = 1.430(8) Å, = 1.103(10) Å, ∠CNC = 117.6(9)°, ∠C βC γC β = 118.7(9)°, ∠C β,trans C γC(O) = 118.6(12), ∠C γCO = 121.4(12)°, ∠C γCO = 114.2(10)°, ∠COC = 115.4(15)°, where angled brackets denote average values and C γ,trans denotes the carbon atom which is trans to the carbonyl oxygen atom. Values in parentheses are the estimated limits of error (3σ) referring to the last significant digit. The structure of the ring in methyl isonicotinate agrees with that of pyridine within experimental error. In contrast, the structure parameters of the COOCH 3 group are significantly different from those of methyl acrylate and methyl acetate. These differences have been discussed in terms of hyperconjugation and steric effects.

  7. Visualising the electron density structure of blobs and studying its possible effect on neutral turbulence

    NASA Astrophysics Data System (ADS)

    de la Cal, E.; The TJ-II Team

    2016-10-01

    The electron density n e of turbulent coherent structures (blobs) has been measured at the edge plasma of the TJ-II stellarator using the helium line ratio technique. A spectroscopic high-speed camera set-up allowed 2D imaging of n e with spatial resolutions of a few millimetres and exposure times down to 15 µs. The turbulent plasma density structures have been compared with the raw helium emission structures, which in principle should be similar due to the expected relation between both, and although generally positive (negative) emission structures correspond to n e blobs (holes), we see that the shape is different and that in some cases there is even no correspondence at all. A possible explanation could be that the neutral distribution, which relates the intensity emission with the n e, varies on the same spatio-temporal scale as the plasma turbulence. This would be the case if the local n e variations of blobs and holes regulated the neutral density through ionisation, making it also turbulent within our experimental frequency (<100 kHz) and spatial scale (>1 cm). To study this point we simulate the neutrals with a simple transport model to reconstruct the corresponding measured emission profiles using the experimentally obtained n e and T e radial profiles. We do this for two cases: one where the neutral distribution is stationary and another where the atoms respond to the measured n e blob and get locally depleted through ionisation. Comparing the simulated and experimental emission profiles and looking at the characteristic ionisation times we find clear indications that point to the fact that slow thermal neutrals could react to the plasma fluctuations in the 10-100 kHz frequency range, also becoming turbulent.

  8. Density functional Studies of structural, electronic and vibrational properties of palladium oxide

    NASA Astrophysics Data System (ADS)

    Kansara, Shivam; Singh, Deobrat; Gupta, Sanjeev K.; Sonvane, Yogesh

    2016-11-01

    In the present paper, structural properties, electronic properties, phonon dispersion curve and Raman spectra at different pressure of the tetragonal palladium oxide (PdO) using density functional theory are discussed. The electronic band structure and density of states (DOS) show the poor metallic behavior of the system but through the hybrid potential calculation show 0.71 eV band gap. The phonon dispersion curve and Raman spectra confirm the stability of the structure while Raman peaks are slightly shifted toward higher frequency due to the applied pressure. Phonon calculations indicate that the PdO structure is stable up to 10 GPa and slightly unstable at 15 GPa pressure. There is no change of the crystallinity with applied pressure which is observed from the intensities of Raman active mode. Palladium oxides are mainly used as a catalysts for catalytic hydrogenation in organic synthesis.

  9. Structural, electronic and mechanical properties of rare earth nitride-ErN: A first principles study

    SciTech Connect

    Murugan, A.; Rajeswarapalanichamy, R. Santhosh, M.; Priyanga, G. Sudha; Kanagaprabha, S.; Iyakutti, K.

    2015-06-24

    The structural, electronic and mechanical properties of rare earth nitride ErN is investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At ambient pressure ErN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that ErN is half metallic at normal pressure. A pressure-induced structural phase transition from NaCl (B1) to CsCl (B2) phase is observed in ErN. Ferromagnetic to non magnetic phase transition is predicted in ErN at high pressure.

  10. Electronic structure of aromatic amino acids studied by soft x-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Wenhua; Carravetta, Vincenzo; Plekan, Oksana; Feyer, Vitaliy; Richter, Robert; Coreno, Marcello; Prince, Kevin C.

    2009-07-01

    The electronic structure of phenylalanine, tyrosine, tryptophan, and 3-methylindole in the gas phase was investigated by x-ray photoemission spectroscopy (XPS) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the C, N, and O K-edges. The XPS spectra have been calculated for the four principal conformers of each amino acid, and the spectra weighted by the Boltzmann population ratios calculated from published free energies. Instead of the single peaks expected from the stoichiometry of the compounds, the N 1s core level spectra of phenylalanine and tryptophan show features indicating that more than one conformer is present. The calculations reproduce the experimental features. The C and O 1s spectra do not show evident effects due to conformational isomerism. The calculations predict that such effects are small for carbon, and for oxygen it appears that only broadening occurs. The carbon K-edge NEXAFS spectra of these aromatic amino acids are similar to the published data of the corresponding molecules in the solid state, but show more structure due to the higher resolution in the present study. The N K-edge spectra of tryptophan and 3-methylindole differ from phenylalanine and tyrosine, as the first two both contain a nitrogen atom located in a pyrrole ring. The nitrogen K-edge NEXAFS spectra of aromatic amino acids do not show any measurable effects due to conformational isomerism, in contrast to the photoemission results. Calculations support this result and show that variations of the vertical excitation energies of different conformers are small, and cannot be resolved in the present experiment. The O NEXAFS spectra of these three aromatic compounds are very similar to other, simpler amino acids, which have been studied previously.

  11. Structural and electronic studies of metal carbide clusterfullerene Sc2C2@Cs-C72

    NASA Astrophysics Data System (ADS)

    Feng, Yongqiang; Wang, Taishan; Wu, Jingyi; Feng, Lai; Xiang, Junfeng; Ma, Yihan; Zhang, Zhuxia; Jiang, Li; Shu, Chunying; Wang, Chunru

    2013-07-01

    We present a metal carbide clusterfullerene Sc2C2@Cs(10528)-C72, whose structure has been baffling for many years. A motional endohedral Sc2C2 cluster, special molecule geometry and electronic structure were found in Sc2C2@Cs(10528)-C72. The paramagnetic Sc2C2@Cs-C72 anion radical was successfully prepared by a chemical reduction method and hyperfine couplings in the ESR spectrum were observed.We present a metal carbide clusterfullerene Sc2C2@Cs(10528)-C72, whose structure has been baffling for many years. A motional endohedral Sc2C2 cluster, special molecule geometry and electronic structure were found in Sc2C2@Cs(10528)-C72. The paramagnetic Sc2C2@Cs-C72 anion radical was successfully prepared by a chemical reduction method and hyperfine couplings in the ESR spectrum were observed. Electronic supplementary information (ESI) available: Experimental details, HPLC chromatogram, and DFT calculations. CCDC 917712. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3nr01739g

  12. Soft X-Ray Studies of Pu Electronic Structure: Past Lessons From XAS and Future Direction With BIS

    SciTech Connect

    Tobin, J G; Yu, S W; Chung, B W; Waddill, G D; Kutepov, A L

    2008-12-10

    Synchrotron-radiation-based spectroscopies such as X-ray Absorption Spectroscopy (XAS) have contributed greatly to our improved understanding of Pu electronic structure. However, significant questions remain concerning the nature of Pu electronic structure. Perhaps the missing piece of the puzzle is the direct experimental determination of the unoccupied electronic structure using high energy inverse photoelectron spectroscopy (IPES) or Bremstrahlung Isochromat Spectroscopy (BIS). Past BIS studies of Th and U indicate the feasibility and utility of Pu studies. To this end, a new BIS capability has been developed in our laboratory. Electron stimulated emission of photons has been carried out using the XES-350 monochromator and detector system. Our preliminary results and future plans will be presented.

  13. Theoretical study of the structure and electronic spectra of fully protonated emeraldine oligomers

    NASA Astrophysics Data System (ADS)

    Zhekova, H.; Tadjer, A.; Ivanova, A.; Petrova, J.; Gospodinova, N.

    Polyaniline (PANI) is one of the most studied conducting polymers. Obtained in its conducting form (known as ?emeraldine salt?) by chemical or electrochemical oxidation of aniline in aqueous acidic medium, this polymer manifests an array of attractive properties. Nevertheless, these properties still need to be described at the molecular level. Intense theoretical investigations during the past few years aim at explaining the chain organization, conductivity mechanism, and other structural and spectral characteristics. Most studies adopt simplified models in which hydration effect is underestimated, since all simulations are performed either in vacuum or in the presence of a limited number of water molecules. The present computational study sheds light on the molecular organization of a number of model PANI hydrated clusters with different alignment and multiplicity, which can explain the experimentally recorded UV/VIS spectra. The influence of hydration and interaction with adjacent oligomers is estimated. Short-chain doubly protonated emeraldine oligomers are used as model systems. The calculations are performed at the semi-empirical (AM1) and/or molecular mechanics (AMBER96) level. Proper configurations of the clusters are selected using Monte Carlo simulations. Electron correlation (CIS) is accounted for upon evaluation of the absorption spectra of the clusters. The relative strength of the interchain coupling is estimated by simulation of PANI clusters consisting of two PANI tetramers in water. Comparison to experimental results is made.

  14. Optical and Magnetooptical Studies on the Electronic Structures of Transition Metal Chalcogenides

    NASA Astrophysics Data System (ADS)

    Sato, Katsuaki

    1993-03-01

    The following sections are included: * Introduction * Electronic Structures of Fe Atoms in Chalcopyrite-Type Compounds[41] * Introduction * Origin of Coloration of CuGaS2 and CuAlS2 Single Crystals Grown by Chemical Transport * Assignment and Characterization of Fe-related Infrared Luminescent Centers in CuGaS2 and CuAlS2[16] * Optical Spectrum of Cu-III-S2 with High Iron Concentration * Optical Properties of CuFeS2 * Summary * OPTICAL REFLECTIVITY SPECTRA AND ELECTRONIC STRUCTURES IN Fe7Se8 AND Co7Se8[42] * Introduction * Experimental * Results * Discussion * VUV-REFLECTIVITY, MAGNETO-OPTICAL SPECTRA AND BAND STRUCTURE IN SINGLE CRYSTALS OF Cr3Te4[43] * Introduction * Experimental * Results * Discussion * Conclusion * References

  15. Defects in ion-implanted hcp-titanium: A first-principles study of electronic structures

    NASA Astrophysics Data System (ADS)

    Raji, Abdulrafiu T.; Mazzarello, Riccardo; Scandolo, Sandro; Nsengiyumva, Schadrack; Härting, Margit; Britton, David T.

    2011-12-01

    The electronic structures of hexagonal closed-packed (h.c.p) titanium containing a vacancy and krypton impurity atoms at various insertion sites are calculated by first-principles methods in the framework of the density-functional theory (DFT). The density of states (DOS) for titanium containing a vacancy defect shows resonance-like features. Also, the bulk electron density decreases from ˜0.15/Å 3 to ˜0.05/Å 3 at the vacancy centre. Electronic structure calculations have been performed to investigate what underlies the krypton site preference in titanium. The DOS of the nearest-neighbour (NN) titanium atoms to the octahedral krypton appears to be less distorted (relative to pure titanium) when compared to the NN titanium atoms to the tetrahedral krypton. The electronic density deformation maps show that polarization of the titanium atoms is stronger when the krypton atom is located at the tetrahedral site. Since krypton is a closed-shell atom, thus precluding any bonding with the titanium atoms, we may conclude that the polarization of the electrons in the vicinity of the inserted krypton atoms and the distortion of the DOS of the NN titanium atoms to the krypton serve to indicate which defect site is preferred when a krypton atom is inserted into titanium. Based on these considerations, we conclude that the substitutional site is the most favourable one, and the octahedral is the preferred interstitial site, in agreement with recent DFT calculations of the energetics of krypton impurity sites.

  16. Valence-band electronic structure of iron phthalocyanine: An experimental and theoretical photoelectron spectroscopy study

    NASA Astrophysics Data System (ADS)

    Brena, Barbara; Puglia, Carla; de Simone, Monica; Coreno, Marcello; Tarafder, Kartick; Feyer, Vitaly; Banerjee, Rudra; Göthelid, Emmanuelle; Sanyal, Biplab; Oppeneer, Peter M.; Eriksson, Olle

    2011-02-01

    The electronic structure of iron phthalocyanine (FePc) in the valence region was examined within a joint theoretical-experimental collaboration. Particular emphasis was placed on the determination of the energy position of the Fe 3d levels in proximity of the highest occupied molecular orbital (HOMO). Photoelectron spectroscopy (PES) measurements were performed on FePc in gas phase at several photon energies in the interval between 21 and 150 eV. Significant variations of the relative intensities were observed, indicating a different elemental and atomic orbital composition of the highest lying spectral features. The electronic structure of a single FePc molecule was first computed by quantum chemical calculations by means of density functional theory (DFT). The hybrid Becke 3-parameter, Lee, Yang and Parr (B3LYP) functional and the semilocal 1996 functional of Perdew, Burke and Ernzerhof (PBE) of the generalized gradient approximation (GGA-)type, exchange-correlation functionals were used. The DFT/B3LYP calculations find that the HOMO is a doubly occupied π-type orbital formed by the carbon 2p electrons, and the HOMO-1 is a mixing of carbon 2p and iron 3d electrons. In contrast, the DFT/PBE calculations find an iron 3d contribution in the HOMO. The experimental photoelectron spectra of the valence band taken at different energies were simulated by means of the Gelius model, taking into account the atomic subshell photoionization cross sections. Moreover, calculations of the electronic structure of FePc using the GGA+U method were performed, where the strong correlations of the Fe 3d electronic states were incorporated through the Hubbard model. Through a comparison with our quantum chemical calculations we find that the best agreement with the experimental results is obtained for a Ueff value of 5 eV.

  17. Electronic and structural properties of nitrogen adsorbed Nb(100) surfaces: An ab initio study

    NASA Astrophysics Data System (ADS)

    Carvalho, P. A. S.; Miwa, R. H.

    2013-08-01

    We have performed an ab initio total energy investigation of the electronic and structural properties of nitrogen adsorbed Nb(100) surface, N/Nb(100). We find an energetic preference for the nitrogen adsorption on the hollow sites of the Nb(100) surface. Upon the presence of N adatoms, there is a reduction of the electronic density of states near the Fermi level. However, the metallic character of the Nb(100) surface has been maintained. The (occupied) electronic states of N adatoms are resonant within the valence band of Nb(100), mostly lying at 4 eV below the Fermi level. Further investigations reveal the formation of energetically stable N/Nb(100)-(n × 1) phase, being the (2 × 1), (5 × 1), and (10 × 1) the most likely ones. Those (n × 1) structures are composed by NbN stripes separated by N vacancy lines. Our scanning tunneling microscopy simulations indicate the formation of bright lines lying on the Nb atoms neighboring the (dark) N vacancy lines, giving rise to an anisotropic electronic structure on the N/Nb(100)-(n × 1) surface. That is, the metallic character of the surface has been strengthened along the vacancy-lines.

  18. Two structurally distinct calcium storage sites in rat cardiac sarcoplasmic reticulum: an electron microprobe analysis study

    SciTech Connect

    Jorgensen, A.O.; Broderick, R.; Somlyo, A.P.; Somlyo, A.V.

    1988-12-01

    The elemental composition of subcellular organelles in resting rat papillary muscle was measured by electron probe x-ray microanalysis of cryosections of flash-frozen tissue. Nonmitochondrial electron-dense structures (50-100 nm in diameter) with a phosphorous concentration larger than 375 mmol/kg dry wt were identified in the interfibrillar spaces of the I band region. They were not visible in the proximity of transverse tubules. The sodium, magnesium, phosphorus, sulfur, chlorine, and potassium content of the electron dense structures showed a normal distribution, consistent with a uniform composition of a specific subcellular organelle. However, the distribution of the calcium concentrations in these electron-dense structures was bimodal, suggesting that they are composed of at least two subpopulations. One subpopulation had relatively high calcium (up to 53 mmol/kg dry wt) content with a mean value of 12.5 +/- 1.1 mmol/kg dry wt, while the other one had a relatively low calcium content with a mean value of 2.8 +/- 0.3 mmol/kg dry wt. The mean calcium concentration in the junctional sarcoplasmic reticulum (j-SR) in rat papillary muscle with calcium concentrations larger than 6 mmol/kg dry wt was 14.6 +/- 2.0 mmol/kg dry wt. We propose that the electron-dense structures described above correspond to nonjunctional sarcoplasmic reticulum and that the population containing relatively high calcium concentrations is calsequestrin-containing corbular sarcoplasmic reticulum (c-SR) confined to the I band region, while the population containing relatively low calcium concentrations corresponds to anastomosing regions of the network sarcoplasmic reticulum that lack calsequestrin.

  19. Study on the Relationship Between Valence Electron Structure and Coating Oriented Growth

    NASA Astrophysics Data System (ADS)

    Tan, Shuyong; Zhang, Xuhai; Zhen, Rui; Zhang, Lei; Tian, Zeng; Ba, Zhixin; Wang, Zhangzhong

    2015-04-01

    The coating oriented growth has attracted great attention because of its effect on coating properties. In this paper, the valence electron structures of TiN and Ni were calculated with the empirical electron theory (EET) in solid and molecules for investigating preferred orientation of nitride coatings containing Ni. The calculation results show that Ni(111), CrN(100) and TiN(100) are the maximum crystal-face electron density, respectively. In CrN (or TiN) coatings, if Ni does not form a single nickel phase, CrN(100) (or TiN(100)) preferred orientation appears easily due to its high crystal-face electron density. When Ni exists as a single phase, CrN(100)/Ni(111) (or TiN(100)/Ni(111)) with the minimum crystal-face electron density difference is the most likely to appear in the coatings. Furthermore, high crystal-face electron density difference usually implies fine grain microstructure. The calculation results are consistent with the experimental results.

  20. Electronic Structure of C60/Phthalocyanine/ITO Interfaces Studied using Soft X-ray Spectroscopies

    SciTech Connect

    Cho, S.; Piper, L; DeMasi, A; Preston, A; Smith, K; Chauhan, K; Sullivan, P; Hatton, R; Jones, T

    2010-01-01

    The interface electronic structure of a bilayer heterojunction of C{sub 60} and three different phthalocyanines grown on indium tin oxide (ITO) has been studied using synchrotron radiation-excited photoelectron spectroscopy. The energy difference between the highest occupied molecular orbital level of the phthalocyanine (donor) layer and the lowest unoccupied molecular orbital level of the C{sub 60} (acceptor) layer (E{sub HOMO}{sup D} - E{sub LUMO}{sup A}) was determined. The E{sub HOMO}{sup D} - E{sub LUMO}{sup A} of a heterojunction with boron subphthalocyanine chloride (SubPc) was found to be much larger than those of copper phthalocyanine (CuPc) and chloro-aluminum phthalocyanine (ClAlPc). This observation is discussed in terms of the difference of the ionization energy of each donor material. Additionally, we have studied the molecular orientation of the phthalocyanine films on ITO using angle-dependent X-ray absorption spectroscopy. We found that the SubPc films showed significant disorder compared to the CuPc and ClAlPc films and also found that E{sub HOMO}{sup D} - E{sub LUMO}{sup A} varied with the orientation of the ClAlPc molecules relative to the ITO substrate. This orientation could be controlled by varying the ClAlPc deposition rate.

  1. A study of the valence shell electronic structure and photoionisation dynamics of s-triazine

    NASA Astrophysics Data System (ADS)

    Coriani, S.; Stener, M.; Decleva, P.; Holland, D. M. P.; Potts, A. W.; Karlsson, L.

    2015-04-01

    A joint experimental and theoretical approach has been used to study the valence shell electronic structure and photoionisation dynamics of s-triazine (1,3,5-triazine). Synchrotron radiation has been employed to record angle resolved photoelectron spectra of the complete valence shell for photon energies between 17.5 and 100 eV, thereby allowing photoelectron anisotropy parameters and branching ratios to be determined. Absolute photoionisation partial cross sections have been estimated as the product of these branching ratios and the absolute photoabsorption cross section. The Kohn-Sham and the time-dependent version of density functional theory methods have been used to calculate photoelectron anisotropy parameters and photoionisation partial cross sections, and these have been compared with the corresponding experimental data. The calculations predict that shape resonances affect the photoionisation dynamics of several of the molecular orbitals. The angle resolved photoelectron spectra suggest that the 1 a2″ (π) orbital is more tightly bound than the 5e‧(σ) orbital, and that the 4 a1‧ (σ) orbital is more tightly bound than the 1 a2‧ (σ) orbital, in agreement with the predicted molecular orbital sequence. For the outer valence orbitals the single-particle picture of ionisation holds but electron correlation becomes increasingly important for the inner valence 4e‧, 3e‧ and 3 a1‧ orbitals and leads to a redistribution of intensity. Instead of a readily distinguishable main-line, associated with each of these orbitals, the photoelectron intensity is spread over numerous satellite states and the resulting band is broad and featureless.

  2. Computational Study of the Structure, the Flexibility, and the Electronic Circular Dichroism of Staurosporine - a Powerful Protein Kinase Inhibitor

    NASA Astrophysics Data System (ADS)

    Karabencheva-Christova, Tatyana G.; Singh, Warispreet; Christov, Christo Z.

    2014-07-01

    Staurosporine (STU) is a microbial alkaloid which is an universal kinase inhibitor. In order to understand its mechanism of action it is important to explore its structure-properties relationships. In this paper we provide the results of a computational study of the structure, the chiroptical properties, the conformational flexibility of STU as well as the correlation between the electronic circular dichroism (ECD) spectra and the structure of its complex with anaplastic lymphoma kinase.

  3. Structural and electronic properties of V-doped cubic BN: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Espitia R, Miguel J.; Díaz F, John H.; Rodríguez Martínez, Jairo Arbey

    2016-10-01

    The structural, electronic, and magnetic properties of c-BN compound doped with V atoms were calculated by means of the pseudopotential method, employed exactly as implemented in computational Quantum ESPRESSO code. For the description of the electron-electron interaction, generalized gradient approximation (GGA) was used. A half-metallic behavior is predicted for the concentrations B0.9375V0.0625N and B0.875V0.125N, because of the fact that the majority spins are metallic and the minority spins are semiconducting. We found magnetic moments of 2.0 and 4.0 μβ per supercell, respectively. The main contribution to the magnetic moment comes from the V atom, with local moments of 1.61 μβ/V-atom. These compounds are good candidates for potential applications in spintronics and as spin injectors.

  4. A comparative study of electronic structure and bonding in transition metal monocarbides

    NASA Astrophysics Data System (ADS)

    Soni, Pooja; Pagare, Gitanjali; Sanyal, Sankar P.; Rajagopalan, M.

    2012-07-01

    The structural, electronic, elastic and bonding properties of four transition metal carbides, ScC, YC (group III), VC and NbC (group V), have been investigated systematically using the first principles density functional theory (DFT). The full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA) for the exchange correlation has been used for the calculation of the total energy. The ground state properties, such as equilibrium lattice constant, bulk modulus, are computed and compared with theoretical and experimental data. The electronic and bonding patterns of the two groups of compounds have been analyzed quantitatively and compared with the available data. It is clear from band structures that all the four transition metal monocarbides are metallic in nature. Analysis of elastic constants reveals that the carbides of group III are ductile in nature while those of group V are brittle.

  5. Electronic structure of ion arsenic high temperature superconductors studied by angle resolved photoemission spectroscopy

    SciTech Connect

    Liu, Chang

    2011-01-01

    The main purpose of the present thesis is to present our ARPES results on the iron arsenic superconductors. As revealed by a series of ARPES measurements on both the AEFe2As2 and the RFeAs(O,F) families (parent compound and carrier-doped systems), the electronic structures of the pnictides are complicated, three dimensional, and closely linked to their superconducting behavior (13; 14; 15; 16; 17; 18; 19). Parent compounds of these materials exhibit the basic hole-electron pocket dual plus an apparent Fermi surface reconstruction caused by long range antiferromagnetism (13; 15). When carriers are introduced, the chemical potential shifts in accordance with the Luttinger theorem and the rigid band shifting picture (13). Importantly, both the appearance and disappearance of the superconducting dome at low and high doping levels have intimate relation with topological changes at the Fermi surfaces, resulting in a specific Fermi topology being favored by superconductivity (15; 16). On the low doping side, superconductivity emerges in the phase diagram once the antiferromagnetic reconstruction disappears below the Fermi level, returning the Fermi surface to its paramagnetic-like appearance. On the high doping side, superconductivity disappears around a doping level at which the central hole pocket vanishes due to increasing electron concentration. Such phenomena are evidence for the governing role the electronic structure plays in their superconducting behavior.

  6. Electronic Structures of S-Doped Capped C-SWNT from First Principles Study

    PubMed Central

    2010-01-01

    The semiconducting single-walled carbon nanotube (C-SWNT) has been synthesized by S-doping, and they have extensive potential application in electronic devices. We investigated the electronic structures of S-doped capped (5, 5) C-SWNT with different doping position using first principles calculations. It is found that the electronic structures influence strongly on the workfunction without and with external electric field. It is considered that the extended wave functions at the sidewall of the tube favor for the emission properties. With the S-doping into the C-SWNT, the HOMO and LUMO charges distribution is mainly more localized at the sidewall of the tube and the presence of the unsaturated dangling bond, which are believed to enhance workfunction. When external electric field is applied, the coupled states with mixture of localized and extended states are presented at the cap, which provide the lower workfunction. In addition, the wave functions close to the cap have flowed to the cap as coupled states and to the sidewall of the tube mainly as extended states, which results in the larger workfunction. It is concluded that the S-doped C-SWNT is not incentive to be applied in field emitter fabrication. The results are also helpful to understand and interpret the application in other electronic devices. PMID:20672070

  7. Electron spin resonance study of point defects in thermal GaAs/GaAs-oxide structures

    NASA Astrophysics Data System (ADS)

    Nguyen, S.; Afanas'ev, V. V.; Stesmans, A.

    2012-12-01

    In an attempt to atomically assess interface and oxide-related point defects, a first basic multifrequency low-temperature electron spin resonance study has been carried out on semi-insulating (Fe compensated) GaAs/oxide structures, implying both powders and (100)GaAs/oxide slices, thermally grown in the range Tox=350-615 °C. Various spectra are observed: As for powders, this includes the 4-line EL2 defect spectrum centered at g~2.043 and characterized by the isotropic hyperfine constant Aiso~ 910 G, ascribed to the 75AsGa+ antisite defect. Observed in freshly crushed powder, it substantially increases in density with oxidation, in line with theoretical expectation; A maximum appears reached for at Tox~440 °C. It is not observed in the parent c-GaAs wafer. A second isotropic signal is observed at g~1.937 in powders for Tox in the range 510-615 °C, but only after additional VUV irradiation; it may correspond to As clusters. In bulk (100)GaAs, we observe the 5-branch spectrum of substitutional Fe impurities (spin S=5/2) in GaAs, with inferred crystal field constant a ≈ 360 G, well in line with previous observations. The results are discussed within the framework of advanced theoretical interface and defect models and previous experimental assessment.

  8. Ab-initio study of electronic structure and elastic properties of ZrC

    NASA Astrophysics Data System (ADS)

    Mund, H. S.; Ahuja, B. L.

    2016-05-01

    The electronic and elastic properties of ZrC have been investigated using the linear combination of atomic orbitals method within the framework of density functional theory. Different exchange-correlation functionals are taken into account within generalized gradient approximation. We have computed energy bands, density of states, elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, lattice parameters and pressure derivative of the bulk modulus by calculating ground state energy of the rock salt structure type ZrC.

  9. An experimental study of perovskite-structured mixed ionic- electronic conducting oxides and membranes

    NASA Astrophysics Data System (ADS)

    Zeng, Pingying

    In recent decades, ceramic membranes based on mixed ionic and electronic conducting (MIEC) perovskite-structured oxides have received many attentions for their applications for air separation, or as a membrane reactor for methane oxidation. While numerous perovskite oxide materials have been explored over the past two decades; there are hardly any materials with sufficient practical economic value and performance for large scale applications, which justifies continuing the search for new materials. The main purposes of this thesis study are: (1) develop several novel SrCoO3-delta based MIEC oxides, SrCoCo1-xMxO3-delta, based on which membranes exhibit excellent oxygen permeability; (2) investigate the significant effects of the species and concentration of the dopants M (metal ions with fixed valences) on the various properties of these membranes; (3) investigate the significant effects of sintering temperature on the microstructures and performance of oxygen permeation membranes; and (4) study the performance of oxygen permeation membranes as a membrane reactor for methane combustion. To stabilize the cubic phase structure of the SrCoO3-delta oxide, various amounts of scandium was doped into the B-site of SrCoO 3-delta to form a series of new perovskite oxides, SrScxCoCo 1-xO3-delta (SSCx, x = 0-0.7). The significant effects of scandium-doping concentration on the phase structure, electrical conductivity, sintering performance, thermal and structural stability, cathode performance, and oxygen permeation performance of the SSCx membranes, were systematically studied. Also for a more in-depth understanding, the rate determination steps for the oxygen transport process through the membranes were clarified by theoretical and experimental investigation. It was found that only a minor amount of scandium (5 mol%) doping into the B-site of SrCoO3-delta can effectively stabilize the cubic phase structure, and thus significantly improve the electrical conductivity and

  10. A comparative first-principles study of structural and electronic properties among memantine, amantadine and rimantadine

    NASA Astrophysics Data System (ADS)

    Middleton, Kirsten; Zhang, G. P.; Nichols, Michael R.; George, Thomas F.

    2012-05-01

    Memantine, amantadine and rimantadine are structurally derived from the same diamondoid, adamantane. These derivatives demonstrate therapeutic efficacy in human diseases: memantine for Alzheimer's disease and amantadine and rimantadine for influenza. In order to better understand some of the properties that distinguish these three compounds, we conduct first-principles calculations on their structure and electronic properties. Our results indicate that protonation has a significant effect on the dipole moment, where the dipole moment in protonated memantine is over eight times larger than in the deprotonated form.

  11. Ab initio study of pressure induced structural and electronic properties in TmPo

    SciTech Connect

    Makode, Chandrabhan Pataiya, Jagdish; Sanyal, Sankar P.; Panwar, Y. S.; Aynyas, Mahendra

    2015-06-24

    We report an ab initio calculation of pressure induced structural phase transition and electronic properties of Thulium Polonide (TmPo).The total energy as a function of volume is obtained by means of self-consistent tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA). It is found that TmPo is stable in NaCl-type (B{sub 1}-phase) structure to CsCl-type (B{sub 2}-phase) structure of this compound in the pressure range of 7.0 GPa. We also calculate the lattice parameter (a{sub 0}), bulk modulus (B{sub 0}), band structure and density of states. From energy diagram it is observed that TmPo exhibit metallic behavior. The calculated values of equilibrium lattice parameter and bulk modulus are in general good agreement.

  12. Electronic structure of Calcium hexaborides

    SciTech Connect

    Lee, Byounghak; Wang, Lin-Wang

    2005-06-15

    We present a theoretical study of crystal and electronic structures of CaB6 within a screened-exchange local density approximation (sX-LDA). Our ab initio total energy calculations show that CaB6 is a semiconductor with a gap of >1.2 eV, in agreement with recent experimental observations. We show a very sensitive band gap dependence on the crystal internal parameter, which might partially explain the scatter of previous theoretical results. Our calculation demonstrates that it is essential to study this system simultaneously for both crystal structures and electronic properties, and that the sX-LDA provides an ideal method for this problem.

  13. Chemical and Electronic Structure Studies of Refractory and Dielectric Thin Films.

    NASA Astrophysics Data System (ADS)

    Corneille, Jason Stephen

    This study presents the synthesis and characterization of oxide and refractory thin films under varying conditions. The deposition of the thin films is performed under vacuum conditions. The characterization of the growth, as well as the chemical and electronic properties of the thin films was accomplished using a broad array of surface analytical techniques. These model studies describe the relationship between the preparative processes and the stoichiometry, structure and electronic properties of the film products. From these efforts, the optimal deposition conditions for the production of high quality films have been established. The thin film oxides synthesized and studied here include magnesium oxide, silicon oxide and iron oxide. These oxides were synthesized on a refractory substrate using both post oxidation of thin films as well as reactive vapor deposition of the metals in the presence of an oxygen background. Comparisons and contrasts are presented for the various systems. Metallic magnesium films were grown and characterized as a preliminary study to the synthesis of magnesium oxide. Magnesium oxide (MgO(100)) was synthesized on Mo(100) by evaporating magnesium at a rate of one monolayer per minute in an oxygen background pressure of 1 times 10 ^{-6} Torr at room temperature. The resulting film was found to exhibit spectroscopic characteristics quite similar to those observed for bulk MgO. The acid/base characteristics of the films were studied using carbon monoxide, water and methanol as probe molecules. The film was found to exhibit essentially the same chemical properties as found in analogous powdered catalysts. Silicon dioxide was synthesized by evaporating silicon onto Mo(100) in an oxygen ambient. It is shown that the silicon oxide prepared at room temperature with a silicon deposition rate of {~ }{1.2}A/min and an oxygen pressure of 2 times 10^{ -8} Torr, consisted of predominantly silicon dioxide with a small fraction of suboxides. Annealing to

  14. Structural studies of amorphous titanium diboride thin films by extended x-ray-absorption fine-structure and extended electron-energy-loss fine-structure techniques

    NASA Astrophysics Data System (ADS)

    Kaloyeros, Alain E.; Hoffman, Mark P.; Williams, Wendell S.; Greene, Alex E.; McMillan, Joyce A.

    1988-10-01

    The local atomic structure of amorphous titanium diboride thin films, prepared by electron-beam vaporization (EBV) of the crystalline compound onto liquid-nitrogen-cooled substrates, was studied using extended x-ray-absorption fine-structure (EXAFS) and extended energy-loss fine-structure (EXELFS) techniques. From a comparison of the extended fine-structure spectra of the amorphous films with corresponding spectra of crystalline titanium diboride, accurate information was derived on the nature of the local structure, or short-range order, and on the coordination numbers, interatomic distances, and nanostructural atomic disorder in amorphous TiB2. A relaxation of the interatomic spacing and a reduction of coordination number for the nearest-neighbor atoms was inferred for the amorphous state. Local prismatic coordination with random 90° rotations about prismatic planes is proposed as a likely atomic structure consistent with the data for the amorphous form. Finally, EXAFS and EXELFS were employed to examine in detail the structural changes induced in amorphous TiB2 by variations in the EBV deposition parameters, and to determine a set of optimized parameters for the EBV deposition of a TiB2 stable amorphous phase.

  15. Structural study of new hydrocarbon nano-crystals by energy-filtered electron diffraction.

    PubMed

    Wu, J S; Melcer, N; Sharp, W P; O'Keeffe, M; Spence, J C H; Yaghi, O M

    2004-01-01

    A new brittle hydrocarbon has been successfully synthesized in polycrystalline form, and its crystal structure solved by quantitative electron diffraction. By 3D tilting of the nano-crystals, the lattice type and unit cell parameters were determined. (Triclinic, [Formula: see text] A, [Formula: see text] A, [Formula: see text] A, [Formula: see text] degrees, [Formula: see text] degrees, and [Formula: see text] degrees.) Spot diffraction patterns were obtained at -165 degrees C using the Koehler selected-area mode on a LEO 912 TEM fitted with an omega in-column elastic energy filter. The direct methods algorithm was then applied to merged intensities and a trial structure obtained assuming single scattering. This was further refined to obtain good agreement with a small residual of about 10% using multiple scattering calculations. A diagram of the proposed structure is given.

  16. Electronic structure of boron doped diamond: An x-ray spectroscopic study

    NASA Astrophysics Data System (ADS)

    Glans, P.-A.; Learmonth, T.; Smith, K. E.; Ferro, S.; De Battisti, A.; Mattesini, M.; Ahuja, R.; Guo, J.-H.

    2013-04-01

    The valence and conduction band electronic structure of boron-doped diamond has been measured using soft x-ray emission and absorption spectroscopy. The experimental results reveal p-type doping in the diamond film through the appearance of states in the band-gap. Structure distortion was observed around the doping center, while the long range order of the diamond structure remains. A chemically shifted C 1s level explains why one of the absorption features seems to appear below the valence band maximum. An excitonic feature was observed in the boron-doped diamond, similar to that observed in pure diamond, indicating that the exciton binding energy remains the same upon B-doping.

  17. Electronic structure study of TiB{sub 2} and Ti{sub 2}B

    SciTech Connect

    Vashistha, M. Vyas, V.; Kabra, K.; Sharma, G.

    2015-06-24

    In this paper, the electronic properties of TiB{sub 2} and Ti{sub 2}B are computed within the framework of Density Functional Theory (DFT) based on Linear Combination of Atomic Orbitals (LCAO) method. In the present calculations, the generalized gradient approximation (GGA) proposed by Perdew-Burke-Erenzerhof (PBE) and Becke’s scheme are considered to treat the correlation and exchange effects respectively. TiB{sub 2} crystallizes in the hexagonal AlB{sub 2} type structure which is designated as C32 with the space group P6/mmm. While the crystal structure of Ti{sub 2}B described in this paper is isomorphous to the body centered tetragonal (Al{sub 2}Cu - type) structure with space group I4/mcm.

  18. Theoretical study of the electronic structure with dipole moment calculations of barium monofluoride

    NASA Astrophysics Data System (ADS)

    Tohme, Samir N.; Korek, Mahmoud

    2015-12-01

    The potential energy curves have been investigated for the 41 lowest doublet and quartet electronic states in the 2s+1Λ± representation below 55,000 cm-1 of the molecule BaF via CASSCF and MRCI (single and double excitations with Davidson correction) calculations. Twenty-five electronic states have been studied here theoretically for the first time. The crossing and avoided crossing of 20 doublet electronic states have been studied in the region 30,000-50,000 cm-1. The harmonic frequency ωe, the internuclear distance Re, the rotational constant Be, the electronic energy with respect to the ground state Te, and the permanent and transition dipole moments have been calculated in addition to static dipole polarizability of the ground state. By using the canonical functions approach, the eigenvalue Ev, the rotational constant Bv, and the abscissas of the turning points Rmin and Rmax have been calculated for the electronic states up to the vibrational level v=98. The comparison of these values with the theoretical results available in the literature shows a very good agreement.

  19. Dynamical Mean-Field Theory Study of Correlated Electronic Structures and the Phase Diagram of Hydrocarbon Superconductors

    NASA Astrophysics Data System (ADS)

    Kim, Minjae; Choi, Hong Chul; Shim, Ji Hoon; Min, B. I.

    2014-03-01

    We have studied correlated electronic structures and the phase diagram of electron-doped hydrocarbon molecular solids, based on the dynamical mean-field theory. We have determined the phase diagram of hydrocarbon molecular solids as functions of doping and energy parameters including the Coulomb correlation, the Hund coupling, and the molecular-orbital (MO) energy level splitting. We have found that the hydrocarbon superconductors (electron-doped picene and coronene) belong to the multi-band Fermi liquid state, while non-superconducting electron-doped pentacene belongs to the single-band state in the proximity of the metal-insulator transition. The size of the MO energy level splitting plays an important role in deriving the superconductivity of electron-doped hydrocarbon solids. The multi-band nature of hydrocarbon solids from the small MO energy level splitting boosts the superconductivity through the enhanced density of states at the Fermi level.

  20. Electronic structures of hydrogen functionalized carbon nanotube: Density functional theory (DFT) study

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto; Iyama, Tetsuji; Kawabata, Hiroshi

    2016-05-01

    Electronic structures and formation mechanism of hydrogen functionalized carbon nanotube (CNT) have been investigated by means of density functional theory (DFT) method. The mechanism of hydrogen addition reaction to the CNT surface was also investigated. Pure and boron-nitrogen (BN) substituted CNT (denoted by CNT and BN-CNT, respectively) were examined as the carbon nanotubes. It was found that the additions of hydrogen atom to B (boron atom) and C (carbon atom) sites of BN-CNT proceed without activation barrier, whereas the hydrogenation of N (nitrogen atom) site needs the activation energy. The electronic states of hydrogen functionalized CNT and BN-CNT were discussed on the basis of theoretical results.

  1. Photoelectron spectroscopic study on the electronic structures of the dental gold alloys and their interaction with L-cysteine

    SciTech Connect

    Ogawa, Koji; Takahashi, Kazutoshi; Azuma, Junpei; Kamada, Masao; Tsujibayashi, Toru; Ichimiya, Masayoshi; Fujimoto, Hitoshi; Sumimoto, Michinori

    2011-11-15

    The valence electronic structures of the dental gold alloys, type 1, type 3, and K14, and their interaction with L-cysteine have been studied by ultraviolet photoelectron spectroscopy with synchrotron radiation. It was found that the electronic structures of the type-1 and type-3 dental alloys are similar to that of polycrystalline Au, while that of the K14 dental alloy is much affected by Cu. The peak shift and the change in shape due to alloying are observed in all the dental alloys. It is suggested that the new peak observed around 2 eV for the L-cysteine thin films on all the dental alloys may be due to the bonding of S 3sp orbitals with the dental alloy surfaces, and the Cu-S bond, as well as the Au-S and Au-O bonds, may cause the change in the electronic structure of the L-cysteine on the alloys.

  2. Electronic structure with vibration-rotation study of the NaYb molecule

    NASA Astrophysics Data System (ADS)

    Tohme, Samir N.; Korek, Mahmoud

    2015-10-01

    The potential energy curves have been investigated for the 15 lowest doublet and quartet electronic states in the 2s+1Λ± representation of the molecule NaYb via CASSCF/MRCI (single and double excitations with Davidson correction) calculations. The spectroscopic constants (Te, De, ωe, Be, re, …) have been calculated in addition to the permanent dipole moments μ. By using the canonical functions approach, the eigenvalues Ev, the rotational constants Bv, the centrifugal distortion constant Dv, and the abscissas of the turning points rmin and rmax have been calculated for different electronic states. Fourteen molecular states have been studied theoretically for the first time.

  3. Density Functional Theory Studies of the Electronic Structure of Solid State Actinide Oxides

    SciTech Connect

    Wen, Xiaodong; Martin, Richard L.; Henderson, Thomas M.; Scuseria, Gustavo E.

    2013-02-13

    The actinide oxides have been extensively studied in the context of the nuclear fuel cycle. They are also of fundamental interest as members of a class of strongly correlated materials, the Mott insulators. Their complex physical and chemical properties make them challenging systems to characterize, both experimentally and theoretically. Chiefly, this is because actinide oxides can exhibit both electronic localization and electronic delocalization and have partially occupied f orbitals, which can lead to multiple possibilities for ground states. Of particular concern for theoretical work is that the large number of competing states display strong correlations which are dffcult to capture with computationally tractable methods.

  4. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

    PubMed Central

    Badali, D. S.; Gengler, R. Y. N.; Miller, R. J. D.

    2016-01-01

    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the “medium” energy regime (1–10 kV). An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples. PMID:27226978

  5. Electronic Structures of Silicene Nanoribbons: Two-Edge-Chemistry Modification and First-Principles Study.

    PubMed

    Yao, Yin; Liu, Anping; Bai, Jianhui; Zhang, Xuanmei; Wang, Rui

    2016-12-01

    In this paper, we investigate the structural and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with edge-chemistry modified by H, F, OH, and O, using the ab initio density functional theory method and local spin-density approximation. Three kinds of spin polarized configurations are considered: nonspin polarization (NM), ferromagnetic spin coupling for all electrons (FM), ferromagnetic ordering along each edge, and antiparallel spin orientation between the two edges (AFM). The H, F, and OH groups modified 8-ZSiNRs have the AFM ground state. The directly edge oxidized (O1) ZSiNRs yield the same energy and band structure for NM, FM, and AFM configurations, owning to the same s p (2) hybridization. And replacing the Si atoms on the two edges with O atoms (O2) yields FM ground state. The edge-chemistry-modified ZSiNRs all exhibit metallic band structures. And the modifications introduce special edge state strongly localized at the Si atoms in the edge, except for the O1 form. The modification of the zigzag edges of silicene nanoribbons is a key issue to apply the silicene into the field effect transistors (FETs) and gives more necessity to better understand the experimental findings. PMID:27550051

  6. Electronic Structures of Silicene Nanoribbons: Two-Edge-Chemistry Modification and First-Principles Study

    NASA Astrophysics Data System (ADS)

    Yao, Yin; Liu, Anping; Bai, Jianhui; Zhang, Xuanmei; Wang, Rui

    2016-08-01

    In this paper, we investigate the structural and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with edge-chemistry modified by H, F, OH, and O, using the ab initio density functional theory method and local spin-density approximation. Three kinds of spin polarized configurations are considered: nonspin polarization (NM), ferromagnetic spin coupling for all electrons (FM), ferromagnetic ordering along each edge, and antiparallel spin orientation between the two edges (AFM). The H, F, and OH groups modified 8-ZSiNRs have the AFM ground state. The directly edge oxidized (O1) ZSiNRs yield the same energy and band structure for NM, FM, and AFM configurations, owning to the same s p 2 hybridization. And replacing the Si atoms on the two edges with O atoms (O2) yields FM ground state. The edge-chemistry-modified ZSiNRs all exhibit metallic band structures. And the modifications introduce special edge state strongly localized at the Si atoms in the edge, except for the O1 form. The modification of the zigzag edges of silicene nanoribbons is a key issue to apply the silicene into the field effect transistors (FETs) and gives more necessity to better understand the experimental findings.

  7. Electronic Structures of Silicene Nanoribbons: Two-Edge-Chemistry Modification and First-Principles Study.

    PubMed

    Yao, Yin; Liu, Anping; Bai, Jianhui; Zhang, Xuanmei; Wang, Rui

    2016-12-01

    In this paper, we investigate the structural and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with edge-chemistry modified by H, F, OH, and O, using the ab initio density functional theory method and local spin-density approximation. Three kinds of spin polarized configurations are considered: nonspin polarization (NM), ferromagnetic spin coupling for all electrons (FM), ferromagnetic ordering along each edge, and antiparallel spin orientation between the two edges (AFM). The H, F, and OH groups modified 8-ZSiNRs have the AFM ground state. The directly edge oxidized (O1) ZSiNRs yield the same energy and band structure for NM, FM, and AFM configurations, owning to the same s p (2) hybridization. And replacing the Si atoms on the two edges with O atoms (O2) yields FM ground state. The edge-chemistry-modified ZSiNRs all exhibit metallic band structures. And the modifications introduce special edge state strongly localized at the Si atoms in the edge, except for the O1 form. The modification of the zigzag edges of silicene nanoribbons is a key issue to apply the silicene into the field effect transistors (FETs) and gives more necessity to better understand the experimental findings.

  8. First-Principles Study of Electronic Structure of Type I Hybrid Carbon-Silicon Clathrates

    NASA Astrophysics Data System (ADS)

    Chan, Kwai S.; Peng, Xihong

    2016-08-01

    A new class of type I hybrid carbon-silicon clathrates has been designed using computational methods by substituting some of the Si atoms in the silicon clathrate framework with carbon atoms. In this work, the electronic structure of hybrid carbon-silicon clathrates with and without alkaline or alkaline-earth metal guest atoms has been computed within the density functional theory framework. The theoretical calculations indicate that a small number of carbon substitutions in the Si46 framework slightly reduces the density of states (DOS) near the band edge and narrows the bandgap of carbon-silicon clathrates. Weak hybridization of the conduction band occurs when alkaline metal (Li, Na, K) atoms are inserted into the structure, while strong hybridization of the conduction band occurs when alkaline-earth metal (Mg, Ca, Ba) atoms are inserted into the hybrid structure. Empty C y Si46- y clathrates within the composition range of 2 ≤ y ≤ 15 can be tuned to exhibit indirect bandgaps of 1.5 eV or less, and may be considered as potential electronic materials.

  9. Electronic-structure and quantum dynamical study of the photochromism of the aromatic Schiff base salicylideneaniline

    SciTech Connect

    Ortiz-Sanchez, Juan Manuel; Gelabert, Ricard; Moreno, Miquel; Lluch, Jose M.

    2008-12-07

    The ultrafast proton transfer dynamics of salicylideneaniline has been theoretically analyzed in the ground and first singlet excited electronic states using density functional theory (DFT) and time-dependent DFT calculations, which predict a ({pi},{pi}*) barrierless excited state intramolecular proton transfer (ESIPT). In addition to this, the photochemistry of salicylideneaniline is experimentally known to present fast depopulation processes of the photoexcited species before and after the proton transfer reaction. Such processes are explained by means of conical intersections between the ground and first singlet ({pi},{pi}*) excited electronic states. The electronic energies obtained by the time-dependent density functional theory formalism have been fitted to a monodimensional potential energy surface in order to perform quantum dynamics study of the processes. Our results show that the proton transfer and deactivation of the photoexcited species before the ESIPT processes are completed within 49.6 and 37.7 fs, respectively, which is in remarkable good agreement with experiments.

  10. First-Principles Study of the Geometric and Electronic Structures of Zinc Ferrite with Vacancy Defect

    NASA Astrophysics Data System (ADS)

    Yao, Jinhuan; Li, Yanwei; Li, Xuanhai; Zhu, Xiaodong

    2016-07-01

    The effects of Zn-vacancy (Zn7Fe16O32), Fe-vacancy (Zn8Fe15O32), and O-vacancy (Zn8Fe16O31) on the geometric and electronic structures of normal spinel ZnFe2O4 (Zn8Fe16O32) are studied by using a first-principles method based on density functional theory (DFT) at a generalized gradient approximation (GGA) level. Compared with perfect ZnFe2O4, the lattice parameters of ZnFe2O4 with Zn-vacancy or Fe-vacancy increase slightly, while the lattice parameters of ZnFe2O4 with O-vacancy decrease significantly. All the vacancy defects induce the distortion of the unit cell structure, especially for the O-vacancy. Zn-vacancy, Fe-vacancy, and O-vacancy in ZnFe2O4 cannot be formed spontaneously, but Zn-vacancy is the most prone to form, followed by Fe-vacancy and O-vacancy under the condition of external energy supply. Zn-vacancy, Fe-vacancy, and O-vacancy change the properties of ZnFe2O4 from a semiconducting character to a metallic character. Either ZnFe2O4 or ZnFe2O4 has various vacancy defects, the strength of the O-Zn bond is stronger than that of the O-Fe bond, and both of them have a covalent bond character. Zn-vacancy enhances the strength of O-Fe bonds and slightly weakens the strength of O-Zn bonds around Zn-vacancy. Fe-vacancy induces a significant increase of the strength of O-Fe bonds and O-Zn bonds around Fe-vacancy. O-vacancy leads to a significant decrease in the strength of O-Zn bonds and to a slight increase in the strength of O-Fe bonds around O-vacancy.

  11. Study of variations in structural, optical parameters and bulk etch rate of CR-39 polymer due to electron irradiation

    NASA Astrophysics Data System (ADS)

    Sahoo, G. S.; Tripathy, S. P.; Joshi, D. S.; Bandyopadhyay, T.

    2016-07-01

    In this work, electron induced modifications on the bulk etch rate, structural and optical parameters of CR-39 polymer were studied using gravimetric, FTIR (Fourier Transform Infrared) and UV-vis (Ultraviolet-Visible) techniques, respectively. CR-39 samples were irradiated with 10 MeV electron beam for different durations to have the absorbed doses of 1, 10, 550, 5500, 16 500, and 55 000 kGy. From the FTIR analysis, the peak intensities at different bands were found to be changing with electron dose. A few peaks were observed to shift at high electron doses. From the UV-vis analysis, the optical band gaps for both direct and indirect transitions were found to be decreasing with the increase in electron dose whereas the opacity, number of carbon atoms in conjugation length, and the number of carbon atoms per cluster were found to be increasing. The bulk etch rate was observed to be increasing with the electron dose. The primary objective of this investigation was to study the response of CR-39 to high electron doses and to determine a suitable pre-irradiation condition. The results indicated that, the CR-39 pre-irradiated with electrons can have better sensitivity and thus can be potentially applied for neutron dosimetry.

  12. Ab initio study of the structural, electronic and optical properties of ZnTe compound

    SciTech Connect

    Bahloul, B.; Deghfel, B.; Amirouche, L.; Bounab, S.; Bentabet, A.; Bouhadda, Y.; Fenineche, N.

    2015-03-30

    Structural, electronic and optical properties of ZnTe compound were calculated using Density Functional Theory (DFT) based on the pseudopotentials and planewaves (PP-PW) method as implemented in the ABINIT computer code, where the exchange–correlation functional is approximated using the local density approximation (LDA) and the generalized gradient approximation (GGA). The obtained results from either LDA or GGa calculation for lattice parameter, energy band gap and optical parameters, such as the fundamental absorption edge, the peaks observed in the imaginary part of the dielectric function, the macroscopic dielectric constants and the optical dielectric constant, are compared with the available theoretical results and experimental data.

  13. Soft-x-ray emission spectroscopy study of the electronic structure of nonstoichiometric silicon nitride

    NASA Astrophysics Data System (ADS)

    Nithianandam, V. Jeyasingh; Schnatterly, S. E.

    1987-07-01

    Soft-x-ray emission spectroscopy was used to investigate the electronic structure of nonstoichiometric silicon nitride samples of different compositions. The Si L23 x-ray emission spectra from these samples are presented and interpreted using a two-phase linear superposition model for the valence-band region. We assumed a model for the valence-band edge and for the emission in the gap region due to trap states and the Si 2p core exciton. The results obtained from these fits are compared with relevant models and other experiments.

  14. Electronic structure of herbicides: Atrazine and bromoxynil

    NASA Astrophysics Data System (ADS)

    Novak, Igor; Kovač, Branka

    2011-06-01

    The electronic structures of herbicides atrazine and bromoxynil have been investigated by UV photoelectron spectroscopy (UPS), quantum chemical calculations and comparison with X-ray diffraction, molecular docking and molecular dynamics studies. Their electronic and molecular structures are discussed in the context of their biological activity. This is the first report which correlates the molecular mechanism of biological activity of these herbicides with their experimentally determined electronic and molecular structures.

  15. Electronic structure and anisotropic chemical bonding in TiNF from ab initio study

    SciTech Connect

    Matar, Samir F.

    2012-01-15

    Accounting for disorder in anatase titanium nitride fluoride TiNF is done through atoms re-distributions based on geometry optimizations using ultra soft pseudo potentials within density functional theory DFT. The fully geometry relaxed structures are found to keep the body centering of anatase (I4{sub 1}/amd No. 141). The new structural setups are identified with space groups I-4m2 No. 119 and Imm2 No. 44 which obey the 'group to subgroup' relationships with respect to anatase. In the ground state Imm2 structure identified from energy differences, TiNF is found semi-conducting with similar density of states features to anatase TiO{sub 2} and a chemical bonding differentiated between covalent like Ti-N versus ionic like Ti-F. Inter-anion N-F bonding is also identified. - Graphical Abstract: The geometry optimized ground state anatase derived TiNF structure with arrangement of open faceted TiN3F3 distorted octahedra. The insert shows the arrangement of octahedra in anatase TiO{sub 2}. Highlights: Black-Right-Pointing-Pointer Original approach of TiNF structure for addressing the electronic band structure. Black-Right-Pointing-Pointer Based on anatase, two different ordering scheme models with geometry optimization. Black-Right-Pointing-Pointer New structures obeying the group{yields}subgroup relationships with Imm2 ground state from energy. Black-Right-Pointing-Pointer In the ground state TiNF is found semi-conducting with similar density of states to anatase TiO{sub 2}. Black-Right-Pointing-Pointer Chemical bonding differentiated between covalent like Ti-N and ionic Ti-F.

  16. Structural, electronic and magnetic properties of carbon doped boron nitride nanowire: Ab initio study

    NASA Astrophysics Data System (ADS)

    Jalilian, Jaafar; Kanjouri, Faramarz

    2016-11-01

    Using spin-polarized density functional theory calculations, we demonstrated that carbon doped boron nitride nanowire (C-doped BNNW) has diverse electronic and magnetic properties depending on position of carbon atoms and their percentages. Our results show that only when one carbon atom is situated on the edge of the nanowire, C-doped BNNW is transformed into half-metal. The calculated electronic structure of the C-doped BNNW suggests that doping carbon can induce localized edge states around the Fermi level, and the interaction among localized edge states leads to semiconductor to half-metal transition. Overall, the bond reconstruction causes of appearance of different electronic behavior such as semiconducting, half-metallicity, nonmagnetic metallic, and ferromagnetic metallic characters. The formation energy of the system shows that when a C atom is doped on surface boron site, system is more stable than the other positions of carbon impurity. Our calculations show that C-doped BNNW may offer unique opportunities for developing nanoscale spintronic materials.

  17. First principles study of structural and electronic properties of AlN (n=1 19) clusters

    NASA Astrophysics Data System (ADS)

    Bai, Qiugui; Song, Bin; Hou, Jinyu; He, Pimo

    2008-06-01

    The structural and electronic properties of AlN ( n=1-19) clusters have been investigated using generalized gradient approximation to the density functional theory. The lowest-energy structures of AlN clusters are given based on the extensive search of the local minima of the potential energy surface. The results indicate that the nitrogen atom tends to occupy an inside position for n≦10, but prefers a peripheral position with a bulklike coordination beyond n=10. As cluster size increases, an icosahedral-like motif emerges, and the cluster grows based on the mechanism of capping N and extra Al atoms on the icosahedron of Al 13. It is found that Al 3N and Al 7N exhibit particularly high stability. The Al sbnd N bonds may simultaneously possess the ionic and covalent bonding characteristics. The calculated HOMO-LUMO gaps exhibit odd-even oscillations as n increases. The vertical ionization potential of the clusters tends to decrease as the cluster size increases, while the vertical electron affinity tends to increase as cluster size increases.

  18. Density functional study of structural and electronic properties of Aln@C60

    NASA Astrophysics Data System (ADS)

    Dhiman, Shobhna; Kumar, Ranjan; Dharamvir, Keya

    2014-04-01

    Fullerene derivatives have been shown to make contributions in many types of applications. Ab initio investigation of structural and electronic properties of aluminum doped endohedral fullerene has been performed using numerical atomic orbital density functional theory. We have obtained ground state structures for Aln@C60 (n=1-10). Which shows that C60 molecule can accommodate maximum of nine aluminum atoms, for n > 9 the cage eventually break. Encapsulated large number of aluminum atoms leads to deformation of cage with diameter varies from 7.16Å to 7.95Å. Binding energy/Al atom is found to increase till n = 4 and after that it decreases with the number of Al atoms with a sudden increase for n=10 due to breakage of C60 cage and electronic affinity first increases till n=4 then it decreases up to n=9 with a sharp increase for n=10. Ionization potential also first increases and then decreases. Homo-Lumo gap decreases till n=3 with a sharp increase for n=4, after that it shows an oscillatory nature. The results obtained are consistent with available theoretical and experimental results. The ab-initio calculations were performed using SIESTA code with generalized gradient approximation (GGA).

  19. Ab initio study of structural and electronic properties of Cun@C60

    NASA Astrophysics Data System (ADS)

    Dhiman, Shobhna; Kumar, Ranjan; Dharamvir, Keya

    2013-06-01

    Ab initio investigation of structural and electronic properties of copper doped endohedral fullerene has been performed using numerical atomic orbital density functional theory. We have obtained the ground state structures for Cun@C60 (n=1-10). Which shows that C60 molecule can accommodate maximum of nine copper atoms, for n > 9 the cage eventually break. Encapsulated large number of copper atoms leads to deformation of cage with diameter varies from 7.00Å to 8.38Å. Binding energy/Cu atom is found to increase till n = 4 and after that it decreases with the number of Cu atoms with a sudden increase for n=10 and electronic affinity increases till n=2 then decreases uniformly till up to n=7 with a further sharp decrease for n=10. Ionization potential and Homo-Lumo gap shows a oscillatory nature. The results obtained are consistent with available theoretical and experimental results. The ab-initio calculations were performed using SIESTA code with generalized gradient approximation (GGA).

  20. Performance analysis of electronic structure codes on HPC systems: a case study of SIESTA.

    PubMed

    Corsetti, Fabiano

    2014-01-01

    We report on scaling and timing tests of the SIESTA electronic structure code for ab initio molecular dynamics simulations using density-functional theory. The tests are performed on six large-scale supercomputers belonging to the PRACE Tier-0 network with four different architectures: Cray XE6, IBM BlueGene/Q, BullX, and IBM iDataPlex. We employ a systematic strategy for simultaneously testing weak and strong scaling, and propose a measure which is independent of the range of number of cores on which the tests are performed to quantify strong scaling efficiency as a function of simulation size. We find an increase in efficiency with simulation size for all machines, with a qualitatively different curve depending on the supercomputer topology, and discuss the connection of this functional form with weak scaling behaviour. We also analyze the absolute timings obtained in our tests, showing the range of system sizes and cores favourable for different machines. Our results can be employed as a guide both for running SIESTA on parallel architectures, and for executing similar scaling tests of other electronic structure codes. PMID:24748385

  1. Proposal for a study of laser acceleration of electrons using micrograting structures at ATF (Phase 1)

    SciTech Connect

    Chen, W.; Claus, J.; Fernow, R.C.; Fischer, J.; Gallardo, J.C.; Kirk, H.G.; Kramer, H.; Li, Z.; Palmer, R.B.; Rogers, J.; Shrinvasan-Rao, T.; Tsang, T.; Ulc, S.; Veligdan, J.; Warren, J.; Bigio, I.; Kurnit, N.; Shimada, T.; Wang, X.; McDonald, K.T.; Russell, D.P.; Los Alamos National Lab., NM; Princeton Univ., NJ; California Univ., Los Angeles, CA )

    1989-10-29

    We propose to investigate new methods of particle acceleration using a short-pulse CO{sub 2} laser as the power source and grating-like structures as accelerator cavities''. Phase I of this program is intended to demonstrate the principle of the method. We will focus the laser light to a 3 mm line on the surface of the microstructure. The structure is used to transform the electric field pattern of the incoming transversely polarized laser beam to a mode which has a component along the electron beam direction in the vicinity of the surface. With 6 mJ of laser energy and a 6 ps pulse length, the electric field in the spot will be around 1 GV/m. The electron beam from the Brookhaven Accelerator Test Facility (ATF) will be focused transversely within the few micron transverse dimension of the microstructure. The maximum expected acceleration for a 1 GV/m field and a 3 mm acceleration length is 3 MeV. 17 refs., 11 figs., 2 tabs.

  2. Performance analysis of electronic structure codes on HPC systems: a case study of SIESTA.

    PubMed

    Corsetti, Fabiano

    2014-01-01

    We report on scaling and timing tests of the SIESTA electronic structure code for ab initio molecular dynamics simulations using density-functional theory. The tests are performed on six large-scale supercomputers belonging to the PRACE Tier-0 network with four different architectures: Cray XE6, IBM BlueGene/Q, BullX, and IBM iDataPlex. We employ a systematic strategy for simultaneously testing weak and strong scaling, and propose a measure which is independent of the range of number of cores on which the tests are performed to quantify strong scaling efficiency as a function of simulation size. We find an increase in efficiency with simulation size for all machines, with a qualitatively different curve depending on the supercomputer topology, and discuss the connection of this functional form with weak scaling behaviour. We also analyze the absolute timings obtained in our tests, showing the range of system sizes and cores favourable for different machines. Our results can be employed as a guide both for running SIESTA on parallel architectures, and for executing similar scaling tests of other electronic structure codes.

  3. Performance Analysis of Electronic Structure Codes on HPC Systems: A Case Study of SIESTA

    PubMed Central

    Corsetti, Fabiano

    2014-01-01

    We report on scaling and timing tests of the SIESTA electronic structure code for ab initio molecular dynamics simulations using density-functional theory. The tests are performed on six large-scale supercomputers belonging to the PRACE Tier-0 network with four different architectures: Cray XE6, IBM BlueGene/Q, BullX, and IBM iDataPlex. We employ a systematic strategy for simultaneously testing weak and strong scaling, and propose a measure which is independent of the range of number of cores on which the tests are performed to quantify strong scaling efficiency as a function of simulation size. We find an increase in efficiency with simulation size for all machines, with a qualitatively different curve depending on the supercomputer topology, and discuss the connection of this functional form with weak scaling behaviour. We also analyze the absolute timings obtained in our tests, showing the range of system sizes and cores favourable for different machines. Our results can be employed as a guide both for running SIESTA on parallel architectures, and for executing similar scaling tests of other electronic structure codes. PMID:24748385

  4. A theoretical study of structural and electronic properties of H-silsesquioxanes

    NASA Astrophysics Data System (ADS)

    Xiang, Kai-Hua

    1999-10-01

    The results of first principles calculations on the H- silsesquioxane (HSQ) polymer and the HSQ-derived a-SiO2 are presented in this work. The first principle calculations are based on the local and nonlocal density approximations to density functional theory. The electronic charge density of silicon, oxygen, and hydrogen is described by double numeric basis sets supplemented by diffuse and polarization functions. For the HSQ-derived a-SiO2, various defect centers are simulated in the cluster model consisting of (OH)3Si[-O-]Si(OH) 3. The defects considered are (OH)3Si[-H- ]Si(OH)3, (OH)3Si[-OH- ]Si(OH)3, (OH)3Si[-OH H- ]Si(OH) 3, (OH)3Si[-OH HO]Si(OH)3, (OH)3Si[-NH- ]Si(OH) 3, (OH)3Si[-O-O- ]Si(OH)3 and the missing oxygen atom (i.e. (OH)3Si[- -]Si(OH)3). The silica cluster in the absence of defects is predicted to be an insulator with the HOMO-LUMO gap of 6.0 eV. However, the hydrogen and hydroxyl defect-centers are found to introduce a gap state at about 1.0 eV above HOMO. The remaining defect-centers have not introduced such a gap state in a-SiO2. It is therefore suggested that the presence of hydrogen and hydroxyl defect-centers may be responsible for the NDR characteristics of the MIM device prepared from the HSQ- derived silica thin film. Since the HSQ polymer is formed by the crosslinking of siloxane-containing cages that are formed from the building block unit of the trifunctional monomer, (HSiO3/2), both structural and electronic properties of the individual cages are also studied in this work. First principles calculations of the (HSiO3/2)n cages with n = 4, 6, 8, 10, 12, 14 and 16 have shown that use of the nonlocal density approximation to density functional theory is required for the reliable prediction of the most stable isomer for silsesquioxanes. A progression of the preferred building unit with the increase in size of the HSQ cages is also revealed here. The smaller HSQ cages prefer four- and five-member Si-O rings while the larger cages are found

  5. π Interactions Studied with Electronic Structure Methods: The Ethyne Methyl Isocyanide Complex and Thioanisole.

    PubMed

    Bretherick, Natalie H; van Mourik, Tanja

    2010-09-14

    Two molecular systems for which previous studies had found qualitative differences in the results from calculations with the B3LYP and MP2 methods are investigated with a range of different electronic structure methods, including meta and double hybrid density functionals and DFT-D (DFT augmented with an empirical dispersion term). The performance of the different methods is assessed by comparison to estimated CCSD(T)/CBS (complete basis set) results. The first molecular system studied is the ethyne methyl isocyanide complex (CH3NC-C2H2), which exhibits π hydrogen bonds involving the C≡C and N≡C triple bonds. Earlier work on this system had shown that B3LYP predicts significantly longer hydrogen-bond distances than MP2. Here, we show that this is likely due to missing dispersion in the B3LYP calculations. On the basis of the CCSD(T) results, the ethyne methyl isocyanide interaction energy is estimated to be 12 ± 1 kJ/mol. B3LYP significantly underestimates the stability of the complex, whereas MP2 slightly overestimates. M05-2X, B3LYP-D, and (CP-corrected) mPW2-PLYP-D give results in close proximity to the CCSD(T) reference values. The second molecule investigated is thioanisole (C6H6SCH3), which can adopt two different conformations (thiomethyl group either planar or perpendicular with respect to the benzene ring). Potential energy curves for rotation around the C(sp(2))-S bond are computed and compared to the estimated CCSD(T)/CBS curve. CCSD(T) predicts the planar conformation to be the global minimum, with a plateau region near the perpendicular conformation (∼4 kJ/mol higher in energy than the planar conformation). The shape of the curve, and location of minima and barriers, is very dependent on the method and basis set employed. MP2, B3LYP, M05-2X, mPW2-PLYP, and mPW2-PLYP-D (employing basis sets of double- or triple-ζ quality) give results in reasonable agreement with the CCSD(T) results, whereas B3LYP-D and M06-L give vastly overestimated barriers

  6. Structural and mutational studies of an electron transfer complex of maize sulfite reductase and ferredoxin.

    PubMed

    Kim, Ju Yaen; Nakayama, Masato; Toyota, Hiroshi; Kurisu, Genji; Hase, Toshiharu

    2016-08-01

    The structure of the complex of maize sulfite reductase (SiR) and ferredoxin (Fd) has been determined by X-ray crystallography. Co-crystals of the two proteins prepared under different conditions were subjected to the diffraction analysis and three possible structures of the complex were solved. Although topological relationship of SiR and Fd varied in each of the structures, two characteristics common to all structures were found in the pattern of protein-protein interactions and positional arrangements of redox centres; (i) a few negative residues of Fd contact with a narrow area of SiR with positive electrostatic surface potential and (ii) [2Fe-2S] cluster of Fd and [4Fe-4S] cluster of SiR are in a close proximity with the shortest distance around 12 Å. Mutational analysis of a total of seven basic residues of SiR distributed widely at the interface of the complex showed their importance for supporting an efficient Fd-dependent activity and a strong physical binding to Fd. These combined results suggest that the productive electron transfer complex of SiR and Fd could be formed through multiple processes of the electrostatic intermolecular interaction and this implication is discussed in terms of the multi-functionality of Fd in various redox metabolisms. PMID:26920048

  7. First-principles study of structural stability, electronic, optical and elastic properties of binary intermetallic: PtZr

    NASA Astrophysics Data System (ADS)

    Pagare, Gitanjali; Jain, Ekta; Sanyal, S. P.

    2016-05-01

    Structural, electronic, optical and elastic properties of PtZr have been studied using the full-potential linearized augmented plane wave (FP-LAPW) method within density functional theory (DFT). The energy against volume and enthalpy vs. pressure variation in three different structures i.e. B1, B2 and B3 for PtZr has been presented. The equilibrium lattice parameter, bulk modulus and its pressure derivative have been obtained using optimization method for all the three phases. Furthermore, electronic structure was discussed to reveal the metallic character of the present compound. The linear optical properties are also studied under zero pressure for the first time. Results on elastic properties are obtained using generalized gradient approximation (GGA) for exchange correlation potentials. Ductile nature of PtZr compound is predicted in accordance with Pugh's criteria.

  8. Electronic structure of Mo1-x Re x alloys studied through resonant photoemission spectroscopy.

    PubMed

    Sundar, Shyam; Banik, Soma; Sharath Chandra, L S; Chattopadhyay, M K; Ganguli, Tapas; Lodha, G S; Pandey, Sudhir K; Phase, D M; Roy, S B

    2016-08-10

    We studied the electronic structure of Mo-rich Mo1-x Re x alloys ([Formula: see text]) using valence band photoemission spectroscopy in the photon energy range 23-70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to  -6 eV, whereas s states lie in the binding energy range  -4 to  -10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p-5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p-4d transition (threshold: 42 eV) and the Re 5p-5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE  =  0) to  -5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x  >  0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1-x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s-d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x. PMID:27301550

  9. Electronic structure of Mo1-x Re x alloys studied through resonant photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Sundar, Shyam; Banik, Soma; Sharath Chandra, L. S.; Chattopadhyay, M. K.; Ganguli, Tapas; Lodha, G. S.; Pandey, Sudhir K.; Phase, D. M.; Roy, S. B.

    2016-08-01

    We studied the electronic structure of Mo-rich Mo1-x Re x alloys (0≤slant x≤slant 0.4 ) using valence band photoemission spectroscopy in the photon energy range 23-70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to  -6 eV, whereas s states lie in the binding energy range  -4 to  -10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p-5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p-4d transition (threshold: 42 eV) and the Re 5p-5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE  =  0) to  -5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x  >  0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1-x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s-d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x.

  10. Electronic structure of Mo1‑x Re x alloys studied through resonant photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Sundar, Shyam; Banik, Soma; Sharath Chandra, L. S.; Chattopadhyay, M. K.; Ganguli, Tapas; Lodha, G. S.; Pandey, Sudhir K.; Phase, D. M.; Roy, S. B.

    2016-08-01

    We studied the electronic structure of Mo-rich Mo1‑x Re x alloys (0≤slant x≤slant 0.4 ) using valence band photoemission spectroscopy in the photon energy range 23–70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to  ‑6 eV, whereas s states lie in the binding energy range  ‑4 to  ‑10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p–5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p–4d transition (threshold: 42 eV) and the Re 5p–5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE  =  0) to  ‑5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x  >  0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1‑x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s–d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x.

  11. Valence-band electronic structure of silicon nitride studied with the use of soft-x-ray emission

    NASA Astrophysics Data System (ADS)

    Carson, R. D.; Schnatterly, S. E.

    1986-02-01

    We have studied the valence-band electronic structure of α-phase, β-phase, and amorphous silicon nitride samples, using Si L-x-ray emission. Our results are compared with a recent band-structure calculation and show that Si 3d states are necessary to properly describe the upper-valence-band and lower-conduction-band density of states. A prominent feature is seen above the valence band which is attributed to conduction-band states that are populated by the incident electron beam. By reducing the energy of the electron beam it is possible to enhance the surface emission relative to bulk emission, and such spectra are also presented and discussed.

  12. Electronic and geometric structures of oligothiophenes studied by UPS and MNDO: π-band evolution and effect of disorder

    NASA Astrophysics Data System (ADS)

    Fujimoto, H.; Nagashima, U.; Inokuchi, H.; Seki, K.; Nakahara, N.; Nakayama, J.; Hoshino, M.; Fukuda, K.

    1990-01-01

    Ultraviolet photoelectron spectroscopy (UPS) has been applied to the investigation of the electronic structure of oligothiophenes with 4-8 thiophene ring. In a series of α-linked oligomers (αn, with the number of rings n = 4-8), a systematic evolution of the π band forming levels are observed in the region of 0.7-3eV below the Fermi level (EF) and the bandwidth becomes broader with n. The non-bonding π band is observed at 3.5eV below EF and its energy is almost independent of n. UPS spectra of α7 and α8 are fairly similar to the spectra of polythiophene, showing that these oligomers are good model compounds of the polymer. The effect of irregularity on the π-electron system was also studied by using oligomers which contain a β linkage or a vinylene group in the middle of the molecule. The UPS spectra showed that the β linkages significantly affect the electronic structure of polythiophene, but vinylene does not. In order to analyze the UPS spectra and to investigate the electronic structures of oligomers, the orbital energies and the geometry of these oligomers are calculated by the semi-empirical modified neglect of diatomic overlap self-consistent field molecular orbital (MNDO-SCF-MO) method. The calculated spectra using the obtained orbital energies agree well with the observed ones, particularly in the π region. It is shown from the optimized geometry that (1) αn's have planar structures and π electrons can be delocalized, (2) the oligomer with β-linkages have nonplanar structure leading to limited delocalization of π-electrons, and (3) the oligomers with a vinylene group are almost planar and the disturbance by the vinylene group on the delocalization is small.

  13. Microtubule structure studied by quick freezing: cryo-electron microscopy and freeze fracture.

    PubMed

    Mandelkow, E M; Rapp, R; Mandelkow, E

    1986-03-01

    Microtubules have been quickly frozen and examined by electron microscopy using several techniques: (1) freezing of a thin layer of solution by plunging into cryogen, followed by cryoelectron microscopy of the unstained vitrified samples; (2) freezing by the propane-jet method, followed by freeze fracturing and metal replication. The unstained frozen-hydrated microtubules show a structure in agreement with X-ray diffraction data; they differ from negatively stained particles mainly by the better preservation of cylindrical shape. Secondly, they reveal a supertwist of the profilaments that is not detected reliably by other methods. This allows a determination of the number of protofilaments and the polarity. The structural resolution of unstained microtubules is similar to that of stained ones (about 2-3 nm); it is limited by low contrast and lack of crystalline order. Propane-jet or cryo-block freezing followed by freeze fracturing reveals the structures of the inner and outer surfaces of the microtubule wall at a resolution of 4 nm or better. The outside is dominated by the longitudinal protofilaments whereas on the inside one observes tilted cross-striations. Although the freezing temperatures of the two methods are different (liquid nitrogen or helium) they yield similar results for the case of thin layers of protein solution. PMID:3517351

  14. Excited-state dynamics of oxazole: A combined electronic structure calculations and dynamic simulations study

    NASA Astrophysics Data System (ADS)

    Cao, Jun; Xie, Zhi-Zhong; Yu, Xiaodong

    2016-08-01

    In the present work, the combined electronic structure calculations and surface hopping simulations have been performed to investigate the excited-state decay of the parent oxazole in the gas phase. Our calculations show that the S2 state decay of oxazole is an ultrafast process characterized by the ring-opening and ring-closure of the five-membered oxazole ring, in which the triplet contribution is minor. The ring-opening involves the Osbnd C bond cleavage affording the nitrile ylide and airine intermediates, while the ring-closure gives rise to a bicyclic species through a 2sbnd 5 bond formation. The azirine and bicyclic intermediates in the S0 state are very likely involved in the phototranspositions of oxazoles. This is different from the previous mechanism in which these intermediates in the T1 state have been proposed for these phototranspositions.

  15. Structural stability and electronic properties of InSb nanowires: A first-principles study

    SciTech Connect

    Zhang, Yong; Tang, Li-Ming Ning, Feng; Chen, Ke-Qiu; Wang, Dan

    2015-03-28

    Using first-principles calculations, we investigate the structural stability and electronic properties of InSb nanowires (NWs). The results show that, in contrast to the bulk InSb phase, wurtzite (WZ) NWs are more stable than zinc-blende (ZB) NWs when the NW diameter is smaller than 10 nm. Nonpassivated ZB and WZ NWs are found to be metallic and semiconducting, respectively. After passivation, both ZB and WZ NWs exhibit direct-gap semiconductor character, and the band gap magnitude of the NWs strongly depends on the suppression of surface states by the charge-compensation ability of foreign atoms to surface atoms. Moreover, the carrier mobility of the NW can be strengthened by halogen passivation.

  16. Study of structural, electronic and elastic properties of RPd{sub 3} (R = Lu and Sc) compounds

    SciTech Connect

    Thakur, Veena Pagare, Gitanjali Chouhan, S. S.; Sanyal, S. P.

    2014-04-24

    The structural, electronic and elastic properties of nonmagnetic RPd{sub 3} (R = Lu and Sc) compounds, which crystallize in AuCu{sub 3}-type structure, are studied using first principles density functional theory based on full potential linearized augmented plane wave (FP-LAPW) method. The calculations are carried out within the PBE-GGA and WC-GGA for the exchange correlation potential. Our calculated ground state properties such as lattice constant (a0), bulk modulus (B) and its pressure derivative (B’) are in good agreement with the experimental results. We first time predict the elastic constants for these compounds using different approximations of GGA. These RPd{sup 3} compounds are found to be ductile in nature in accordance with Pugh’s criteria. The computed electronic band structures and density of states show metallic character of these compounds.

  17. Electronic structure studies of chemically synthesized MgFe2O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Singh, Jitendra Pal; Won, Sung Ok; Lim, Weon Cheol; Lee, Ik-Jae; Chae, K. H.

    2016-03-01

    For present work, magnesium ferrite nanoparticles were synthesized using nitrates of metal ions and citric acid. Crystallite size of these nanoparticles varies from 2.1 ± 0.1 to 62 ± 10 nm as annealing temperatures increases from 300 to 1200 °C. Mg K-edge near-edge X-ray absorption fine-structure spectra reflect the presence of Mg2+ ions in both tetrahedral (A-site) and octahedral (B-site) environment for nanoparticles synthesized at all temperatures. The integral area of spectral features of O K-edge spectra is associated with the change of unoccupied O p-projected density of states. Fe L-edge spectra envisage the presence of Fe3+ state in these nanoparticles. Observed changes in the electronic structure of these nanoparticles are discussed on the basis of cation migration from A-site to B-site, degree of crystallization, and unsaturated bonds at crystallite surface. Fe-O distances at A-site and B-site changes with annealing temperature.

  18. Electronics for Piezoelectric Smart Structures

    NASA Technical Reports Server (NTRS)

    Warkentin, D. J.; Tani, J.

    1997-01-01

    This paper briefly presents work addressing some of the basic considerations for the electronic components used in smart structures incorporating piezoelectric elements. After general remarks on the application of piezoelectric elements to the problem of structural vibration control, three main topics are described. Work to date on the development of techniques for embedding electronic components within structural parts is presented, followed by a description of the power flow and dissipation requirements of those components. Finally current work on the development of electronic circuits for use in an 'active wall' for acoustic noise is introduced.

  19. Theoretical Study of Electronic Structure and Thermoelectric Properties of Doped CuAlO2

    NASA Astrophysics Data System (ADS)

    Poopanya, P.; Yangthaisong, A.; Rattanapun, C.; Wichainchai, A.

    2011-05-01

    The doping level dependence of thermoelectric properties of delafossite CuAlO2 has been investigated in the constant scattering time ( τ) approximation, starting from the first principles of electronic structure. In particular, the lattice parameters and the energy band structure were calculated using the total energy plane-wave pseudopotential method. It was found that the lattice parameters of CuAlO2 are a = 2.802 Å and c = 16.704 Å, and the internal parameter is u = 0.1097. CuAlO2 has an indirect band gap of 2.17 eV and a direct gap of 3.31 eV. The calculated energy band structures were then used to calculate the electrical transport coefficients of CuAlO2. By considering the effects of doping level and temperature, it was found that the Seebeck coefficient S( T) increases with increasing acceptor doping ( A d) level. The values of S( T) in our experiments correspond to an A d level at 0.262 eV, which is identified as the Fermi level of CuAlO2. Based on our experimental Seebeck coefficient and the electrical conductivity, the constant relaxation time is estimated to be 1 × 10-16 s. The power factor is large for a low A d level and increases with temperature. It is suggested that delafossite CuAlO2 can be considered as a promising thermoelectric oxide material at high doping and high temperature.

  20. Structural and electronic properties of ZnO/GaN heterostructured nanowires from first-principles study.

    PubMed

    Zhang, Yang; Fang, Dang-Qi; Zhang, Sheng-Li; Huang, Rao; Wen, Yu-Hua

    2016-01-28

    ZnO/GaN alloys have exceptional photocatalytic applications owing to their suitable band gaps corresponding to the range of visible light wavelength and thus have attracted extensive attention over the past few years. In this study, the structural stabilities and electronic properties of core/shell, biaxial, and super-lattice ZnO/GaN heterostructured nanowires have been investigated by means of first-principles calculations based on the density functional theory. The effects of the nanowire size, the GaN ratio, and strain have been explored. It is found that all studied heterostructured nanowires are less stable than pure ZnO nanowires, exhibiting larger sized wires with better structural stabilities and inversely proportional relationship between structural stability and the GaN ratio. Electronic band structures imply that all heterostructured nanowires are semiconductors with the band gaps strongly depending on the GaN ratios as well as mechanical strain. Particularly, for the biaxial and the super-lattice nanowires, their band gaps decrease firstly and then increase with the increasing GaN ratios. Electronic contributions to the valence band maximum (VBM) and the conduction band minimum (CBM) are discussed for exploiting the potential photocatalytic applications.

  1. DFT and TD-DFT study on geometries, electronic structures and electronic absorption of some metal free dye sensitizers for dye sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Mohr, T.; Aroulmoji, V.; Ravindran, R. Samson; Müller, M.; Ranjitha, S.; Rajarajan, G.; Anbarasan, P. M.

    2015-01-01

    The geometries, electronic structures, polarizabilities and hyperpolarizabilities of 2-hydroxynaphthalene-1,4-dione (henna1), 3-(5-((1E)-2-(1,4-dihydro-1,4-dioxonaphthalen-3-yloxy) vinyl) thiophen-2-yl)-2-isocyanoacrylic acid (henna2) and anthocyanin dye sensitizers were studied based on density functional theory (DFT) using the hybrid functional B3LYP. The Ultraviolet-Visible (UV-Vis) spectrum was investigated by using a hybrid method which combines the properties and dynamics of many-body in the presence of time-dependent (TD) potentials, i.e. TDSCF-DFT (B3LYP). Features of the electronic absorption spectrum in the visible and near-UV regions were plotted and assigned based on TD-DFT calculations. Due to the absorption, bands of the metal-organic compound are n → π* present. The calculated results suggest that the three lowest energy excited states of the investigated dye sensitizers are due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer is owing to an electron injection process from excited dye to the semiconductor's conduction band. The role of linking the henna1 dye with a carboxylic acid via a thiophene bridge was analyzed. The results are that using a stronger π-conjugate bridge as well as a strong donator and acceptor group enhances the efficiency.

  2. The role of nanographitic phase on enhancing the electron field emission properties of hybrid granular structured diamond films: the electron energy loss spectroscopic studies

    NASA Astrophysics Data System (ADS)

    Kurian, Joji; Jothiramalingam Sankaran, Kamatchi; Thomas, Joseph P.; Tai, N. H.; Chen, Huang-Chin; Lin, I.-Nan

    2014-10-01

    The electron field emission (EFE) properties of the hybrid granular structured diamond (HiD) films were markedly improved by N-ion implantation and annealing processes. The evolution of microstructure/bonding structure of the films due to these processes was investigated using the transmission electron microscopy (TEM) and the electron energy loss spectroscopy (EELS), respectively. The N-ion implanted/annealed HiD films showed a low turn-on field of (E0)HiD = 7.4 V µm-1 with large current density of (Je)HiD = 600 µA cm-2, at 17.8 V µm-1, compared with pristine HiD films ((E0) = 10.3 V µm-1, (Je) = 95 µA cm-2 at the same applied field). While the TEM studies revealed only the microstructural evolution due to N-ion implantation/annealing processes, the EELS elucidated the change in bonding structure, namely the transformation between the sp3-bonded carbons and the sp2-bonded ones. Therefore, the combined TEM/EELS analyses provided more insight into understand the mechanism by which the N-ion implantation/annealing processes enhanced the EFE properties of HiD films. These studies clearly demonstrated that the N-ion implantation/annealing processes induced the formation of nanographitic clusters. These nanographitic phases form an interconnected path throughout the film surface facilitating the easy transport of electrons and thereby markedly enhancing the EFE properties for the N implanted/annealed HiD films.

  3. Molecular structure of 2-methylthiophene studied by gas electron diffraction combined with microwave spectroscopic data

    NASA Astrophysics Data System (ADS)

    Tanabe, Masayuki; Kuze, Nobuhiko; Fujiwara, Hideo; Takeuchi, Hiroshi; Konaka, Shigehiro

    1995-12-01

    The molecular structure of 2-methylthiophene ? has been determined by gas electron diffraction combined with microwave spectroscopic data. Ab initio calculations at the {HF}/{3-21 G\\lowast } level were carried out and used as an aid to the analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. A C 6H bond was found to be cis with respect to the CC bond in the equilibrium state. The structural parameter values with estimated error limits (3σ) in parentheses are as follows: r g( S C2) = 1.729(1) Å, r g( C2 C3) = 1.374(3) Å, r g( C2 C6) = 1.505(5) Å, r g( C5 H) = 1.096(5) Å, ∠CSC = 92.7(2)°, ∠SC 2C 3 = 110.5(4)°, ÅSC 5C 4 = 111.0(8)°, ÅSC 2C 6 = 121.4(6)°, t = 4(5)° where t is the tilt angle which is defined to be the angle between the C3 axis of the methyl group and the C 2C 6 bond. The values of r(SC 2) - r(SC 5), r(C 2C 3) - r(C 4C 5), r(C 3H) - r(C 5H), r(C 4H) - r(C 5H), r( C6 H) - r( C5\\bgrave H) , ∠CCH, ÅSCH and ÅHCH were taken from the {HF}/{3-21 G}\\lowast calculations.

  4. Structural, electronic, and elastic properties of CuFeS2: first-principles study

    NASA Astrophysics Data System (ADS)

    Zhou, Meng; Gao, Xiang; Cheng, Yan; Chen, Xiangrong; Cai, Lingcang

    2015-03-01

    The structural, electronic, and elastic properties of CuFeS2 have been investigated by using the generalized gradient approximation (GGA), GGA + U (on-site Coulomb repulsion energy), the local density approximation (LDA), and the LDA + U approach in the frame of density functional theory. It is shown that when the GGA + U formalism is selected with a U value of 3 eV for the 3d state of Fe, the calculated lattice constants agree well with the available experimental and other theoretical data. Our GGA + U calculations indicate that CuFeS2 is a semiconductor with a band gap of 0.552 eV and with a magnetic moment of 3.64 µB per Fe atom, which are well consistent with the experimental results. Combined with the density of states, the band structure characteristics of CuFeS2 have been analyzed and their origins have been specified, which reveals a hybridization existing between Fe-3d, Cu-3s, and S-3p, respectively. The charge and Mulliken population analyses indicate that CuFeS2 is a covalent crystal. Moreover, the calculated elastic constants prove that CuFeS2 is mechanically stable but anisotropic. The bulk modulus obtained from elastic constants is 87.1 GPa, which agrees well with the experimental value of 91 ± 15 GPa and better than the theoretical bulk modulus 74 GPa obtained from GGA method by Lazewski et al. The obtained shear modulus and Debye temperature are 21.0 GPa and 287 K, respectively, and the latter accords well with the available experimental value. It is expected that our work can provide useful information to further investigate CuFeS2 from both the experimental and theoretical sides.

  5. Exploring electronic structure of one-atom thick polycrystalline graphene films: A nano angle resolved photoemission study

    PubMed Central

    Avila, José; Razado, Ivy; Lorcy, Stéphane; Fleurier, Romain; Pichonat, Emmanuelle; Vignaud, Dominique; Wallart, Xavier; Asensio, María C.

    2013-01-01

    The ability to produce large, continuous and defect free films of graphene is presently a major challenge for multiple applications. Even though the scalability of graphene films is closely associated to a manifest polycrystalline character, only a few numbers of experiments have explored so far the electronic structure down to single graphene grains. Here we report a high resolution angle and lateral resolved photoelectron spectroscopy (nano-ARPES) study of one-atom thick graphene films on thin copper foils synthesized by chemical vapor deposition. Our results show the robustness of the Dirac relativistic-like electronic spectrum as a function of the size, shape and orientation of the single-crystal pristine grains in the graphene films investigated. Moreover, by mapping grain by grain the electronic dynamics of this unique Dirac system, we show that the single-grain gap-size is 80% smaller than the multi-grain gap recently reported by classical ARPES. PMID:23942471

  6. Electronic structure of Co-Ni-Ga Heusler alloys studied by resonant photoemission

    SciTech Connect

    Baral, Madhusmita Banik, Soma Ganguli, Tapas Chakrabarti, Aparna Deb, S. K.; Thamizhavel, A.; Wadikar, Avinash; Phase, D. M.

    2014-04-24

    The electronic structures of Co{sub 2.01}Ni{sub 1.05}Ga{sub 0.94} and Co{sub 1.76}Ni{sub 1.46}Ga{sub 0.78} Heusler alloys have been investigated by resonant photoemission spectroscopy across the 3p-3d transition of Co and Ni. For the Ni excess composition Co{sub 1.76}Ni{sub 1.46}Ga{sub 0.78}, the valence band peak shows a shift of 0.25 eV as compared to the near stoichiometric composition Co{sub 2.01}N1{sub 1.05}Ga{sub 0.94}. Also an enhancement is observed in the Ni related satellite features in the valence band for the Ni excess composition. Due to hybridization of Co and Ni 3d states in these systems, the Co and Ni 3p-3d resonance energies are found to be higher as compared to Co and Ni metals. Theoretical first principle calculation is performed to understand the features in the valence band and the shape of the resonance profile.

  7. First-Principles Study on Electronic Structure of TiO2-Based Dilute Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Kizaki, Hidetoshi; Toyoda, Masayuki; Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2008-03-01

    We investigate the electronic structure in rutile-TiO2-based dilute magnetic semiconductors (DMS) within self-interaction- corrected local density approximation (SIC-LDA). These results are compared with those calculated within standard LDA. Although the calculated band-gap energy and energetic position of Ti 3d bands are different in the LDA and the SIC-LDA, half-metallic density of states is predicted in transition- metal-doped TiO2 for both methods. While the LDA calculations predict high-spin state only for Fe-doped one, in the SIC-LDA calculations high-spin state is realized in V-, Cr- and Mn-doped one and low-spin state is realized in Fe- and Co- doped one. However, the absorption and soft x-ray magnetic circular dichroism measurements in (Ti0.97, Co0.03)O2-δ indicate the Co^2+ high-spin state in the D2h-symmetry crystal field at the Ti site. These experimental results do not agree with our calculated results. We will discuss the origin of the discrepancy between the theoretical predictions and the experimental observations. In addition, we will discuss the ferromagnetism in TiO2-based DMS.

  8. First-principles study on structural and electronic properties of AlNSix heterosheet

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Zhang, Jian-Min; Xu, Ke-Wei

    2012-06-01

    Under generalized gradient approximation (GGA), the structural and electronic properties of AlN and Si sheets, hydrogen terminated AlN and Si nanoribbons with hexagonal morphology and 2, 4, 6 zigzag chains across the ribbon width and the hexagonally bonded heterosheets AlNSix (x=2, 4, and 6) consisting of hexagonal networks of AlN (h-AlN) strips and silicene sheets with zigzag shaped borders have been investigated using the first-principles projector-augmented wave (PAW) formalism within the density function theory (DFT) framework. The AlN sheet is an indirect semiconductor with a band gap of 2.56 eV, while the Si sheet has a metallic character since the lowest unoccupied conduction band (LUCB) and the highest occupied valence band (HOVB) meet at one k point from Γ to Z. In the semiconductor 6-ZAlNNR, for example, the states of LUCB and HOVB at zone boundary Z are edge states whose charges are localized at edge Al and N atoms, respectively. In metallic 6-ZSiNR, a flat edge state is formed at the Fermi level EF near the zone boundary Z because its charges are localized at edge Si atoms. The hybridizations between the edge states of h-AlN strips and silicene sheets result in the appearance of border states in the zigzag borders of heterosheets AlNSix whose charges are localized at two atoms of the borders with either bonding or antibonding π character.

  9. Structural evolution and strain induced mixing in Cu–Co composites studied by transmission electron microscopy and atom probe tomography

    SciTech Connect

    Bachmaier, A.; Aboulfadl, H.; Pfaff, M.; Mücklich, F.; Motz, C.

    2015-02-15

    A Cu–Co composite material is chosen as a model system to study structural evolution and phase formations during severe plastic deformation. The evolving microstructures as a function of the applied strain were characterized at the micro-, nano-, and atomic scale-levels by combining scanning electron microscopy and transmission electron microscopy including energy-filtered transmission electron microscopy and electron energy-loss spectroscopy. The amount of intermixing between the two phases at different strains was examined at the atomic scale using atom probe tomography as complimentary method. It is shown that Co particles are dissolved in the Cu matrix during severe plastic deformation to a remarkable extent and their size, number, and volume fraction were quantitatively determined during the deformation process. From the results, it can be concluded that supersaturated solid solutions up to 26 at.% Co in a fcc Cu–26 at.% Co alloy are obtained during deformation. However, the distribution of Co was found to be inhomogeneous even at the highest degree of investigated strain. - Highlights: • Structural evolution in a deformed Cu–Co composite is studied on all length scales. • Amount of intermixing is examined by atom-probe tomography. • Supersaturated solid solutions up to 26 at.% Co in Cu are observed.

  10. First principles studies of the electronic and magnetic structures of [Fe(pz)2]x complex

    NASA Astrophysics Data System (ADS)

    Kabalan, L.; Matar, S. F.

    2009-05-01

    Polybis(pyrazolato)iron(II), [Fe(pz)2]x is characterized by doubly bridged iron with pyrazolate ligands. An original DFT study at both the molecular and extended solid levels is carried out for this complex system with the purpose of identifying the magnetic interactions and chemical bonding characteristics. From molecular calculations, the exchange parameter J is obtained, pointing to the expected weakly antiferromagnetic ground state. The IR and Raman spectra have been calculated with relevant assignments, namely for the stretching modes. Computations for the extended solid in different magnetic configurations point to the total moment of 4μB·fu, identifying Fe as divalent in high spin configuration, in accordance with a weak tetrahedral crystal field. From relative energies the ground state is antiferromagnetic. Analyses of the chemical bonding (COOP) and of electron localization function (ELF) illustrate the interactions between Fe and the cycle as well as within the pz cycle.

  11. Electronic structure and mesoscopic simulations of nonylphenol ethoxylate surfactants. a combined DFT and DPD study.

    PubMed

    Valencia, Diego; Aburto, Jorge; García-Cruz, Isidoro

    2013-08-07

    The aim of this work was to gain insight into the effect of ethylene oxide (EO) chains on the properties of a series of nonylphenol ethoxylate (NPE) surfactants. We performed a theoretical study of NPE surfactants by means of density functional theory (DFT) and dissipative particle dynamics (DPD). Both approximations were used separately to obtain different properties. Four NPEs were selected for this purpose (EO = 4, 7, 11 and 15 length chains). DFT methods provided some electronic properties that are related to the EO units. One of them is the solvation Gibbs energy, which exhibited a linear trend with EO chain length. DPD calculations allow us to observe the dynamic behavior in water of the NPE surfactants. We propose a coarse-grained model which properly simulates the mesophases of each surfactant. This model can be used in other NPEs applications.

  12. Electronic structure of rare-earth doped SrFBiS2 superconductors from photoemission spectroscopic studies

    NASA Astrophysics Data System (ADS)

    Mishra, P.; Lohani, H.; Jha, Rajveer; Awana, V. P. S.; Sekhar, B. R.

    2016-06-01

    The electronic structure study of the Rare Earth (La, Ce) doped SrFBiS2 superconductors using valence band photoemission in conjugation with the band structure calculations have been presented. The spectral features shift towards higher binding energy, consistent with the electron doping, for the doped compounds. An enhanced metallicity in addition to the shift in the Fermi level towards the conduction band occurs for the Rare Earth (RE) doped compounds. Further, the degeneracy of bands along X-M direction at valence band maximum (VBM) and conduction band minimum (CBM) is lifted due to RE doping. An enhanced spectral weight near EF accompanied by a decrease in density of states at higher binding energy occurs for the doped compounds. This unusual spectral weight shift is substantiated by the change in Fermi surface topology and reduced distortion of Bi-S plane for the doped compounds.

  13. Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

    SciTech Connect

    Gilbert, Benjamin; Katz, Jordan E.; Denlinger, Jonathan D.; Yin, Yadong; Falcone, Roger; Waychunas, Glenn A.

    2010-10-24

    The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed-valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic acid-coated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe L-edge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic acid-coated sample. However, O K-edge absorption spectroscopy observed a 0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase and can exert an effect on the global electronic and optical properties of the material. This phenomenon resembles the band gap enlargement caused by electron accumulation in the

  14. Electronic structure, vibrational spectral and intervening orbital interactions studies of NLO material: Guanidinium 4-nitrobenzoate

    NASA Astrophysics Data System (ADS)

    Sasikala, V.; Sajan, D.; Job Sabu, K.; Arumanayagam, T.; Murugakoothan, P.

    2015-03-01

    Single crystals of guanidinium 4-nitrobenzoate (GPNB) have been grown by slow evaporation method. Grown crystals were characterized by FT-IR, FT-Raman, UV-Vis absorption and UV-Vis transmission spectroscopies. Crystal defects and surface morphology were studied by etching method. Dielectric properties of the crystal such as dielectric constant, dielectric loss and AC electrical conductivity as function of frequency (50 Hz-5 MHz) at two temperatures (35 °C and 100 °C) were measured. The frequency and temperature dependence of dielectric behaviour were investigated. The equilibrium geometry, vibrational spectral analysis, intramolecular charge transfer interactions using NBO method, first order hyperpolarizability, molecular electrostatic potential and frontier molecular orbital analysis for GPNB have been studied using density functional theory at B3LYP/cc-pVTZ level. Vibrational spectral study reveals the presence of moderate and weak Nsbnd H⋯O bonds in GPNB. NBO analysis also confirms the presence of intramolecular Nsbnd H⋯O hydrogen bonding and investigates the stability as well as the intervening orbital interactions. The electronic absorption spectrum of the gas and water phases of GPNB were simulated using time dependent density functional theory and NBO transitions for the three lowest excited states were assigned and studied.

  15. Electronic structure, vibrational spectral and intervening orbital interactions studies of NLO material: guanidinium 4-nitrobenzoate.

    PubMed

    Sasikala, V; Sajan, D; Sabu, K Job; Arumanayagam, T; Murugakoothan, P

    2015-03-15

    Single crystals of guanidinium 4-nitrobenzoate (GPNB) have been grown by slow evaporation method. Grown crystals were characterized by FT-IR, FT-Raman, UV-Vis absorption and UV-Vis transmission spectroscopies. Crystal defects and surface morphology were studied by etching method. Dielectric properties of the crystal such as dielectric constant, dielectric loss and AC electrical conductivity as function of frequency (50 Hz-5 MHz) at two temperatures (35°C and 100°C) were measured. The frequency and temperature dependence of dielectric behaviour were investigated. The equilibrium geometry, vibrational spectral analysis, intramolecular charge transfer interactions using NBO method, first order hyperpolarizability, molecular electrostatic potential and frontier molecular orbital analysis for GPNB have been studied using density functional theory at B3LYP/cc-pVTZ level. Vibrational spectral study reveals the presence of moderate and weak N-H⋯O bonds in GPNB. NBO analysis also confirms the presence of intramolecular N-H⋯O hydrogen bonding and investigates the stability as well as the intervening orbital interactions. The electronic absorption spectrum of the gas and water phases of GPNB were simulated using time dependent density functional theory and NBO transitions for the three lowest excited states were assigned and studied.

  16. Electronic Properties and 13C NMR Structural Study of Y3N@C88

    PubMed Central

    Fu, Wujun; Zhang, Jianyuan; Champion, Hunter; Fuhrer, Tim; Azuremendi, Hugo; Zuo, Tianming; Zhang, Jianfei; Harich, Kim; Dorn, Harry C.

    2011-01-01

    In this paper we report the synthesis, purification, 13C NMR and other characterization studies of Y3N@C88. The 13C NMR, UV-vis and chromatographic data suggest an Y3N@C88 having IPR allowed cage with D2(35)-C88 symmetry. In earlier density functional theory (DFT) computational and X-ray crystallographic studies, it was reported that lanthanide (A3N)6+ clusters are stabilized in D2(35)-C88 symmetry cages and have reduced HOMO-LUMO gaps relative to other trimetallic nitride endohedral metallofullerene cage systems, for example, A3N@C80. In this paper, we report that the non-lanthanide (Y3N)6+ cluster in the D2(35)-C88 cage exhibits a HOMO-LUMO gap consistent with other lanthanide A3N@C88 molecules based on electrochemical measurements and DFT computational study. These results suggests that the reduced HOMO-LUMO gap of A3N@C88 systems is a property dominated by the D2(35)-C88 carbon cage and not f-orbital lanthanide electronic metal cluster (A3N)6+ orbital participation. PMID:21506556

  17. Transmission electron microscopy studying of structural features of NiTi B2 phase formed under pulsed electron-beam impact

    SciTech Connect

    Meisner, Ludmila L.; Semin, Viktor O.; Gudimova, Ekaterina Y.; Neiman, Alexey A. Lotkov, Alexander I.; Ostapenko, Marina G.; Koval, Nikolai N.; Teresov, Anton D.

    2015-10-27

    By transmission electron microscopy method the evolution of structural-phase states on a depth of close to equiatomic NiTi modified layer has been studied. Modification performed by pulse impact on its surface low-energy high-current electron beam (beam energy density 10 J/sm{sup 2}, 10 pulses, pulse duration 50mks). It is established that during the treatment in the layer thickness of 8–10 μm, the melting of primary B2 phase and contained therein as Ti2Ni phase particles occurs. The result is change in the concentration ratio of titanium and nickel in the direction of increasing titanium content, which was confirmed by X-ray analysis in the form of increased unit cell parameter B2 phase. Analysis of the electron diffraction pattern showed that the modified layer is characterized as a highly distorted structure on the basis of bcc lattice. Lattice distortions are maximal near the surface and extends to a depth of melt. In subjacent layer there is gradual decline lattice distortions is observed.

  18. SPE-LEEM Studies on the Surface and Electronic Structure of 2-D Transition Metal Dichalcogenides (Part II)

    NASA Astrophysics Data System (ADS)

    Jin, Wencan; Yeh, Po-Chun; Zaki, Nader; Zhang, Datong; Sadowski, Jerzy; Al-Mahboob, Abdullah; van de Zande, Arend; Chenet, Daniel; Dadap, Jerry; Herman, Irving; Sutter, Peter; Hone, James; Osgood, Richard

    2014-03-01

    In this work, we studied the surface and electronic structure of monolayer and few-layer exfoliated MoS2 and WSe2, as well as chemical-vapor-deposition (CVD) grown MoS2, using Spectroscopic Photoemission and Low Energy Electron Microscope (SPE-LEEM). LEEM measurements reveal that, unlike exfoliated MoS2, CVD-grown MoS2 exhibits grain-boundary alterations due to surface strain. However, LEEM and micro-probe low energy electron diffraction show that the quality of CVD-grown MoS2 is comparable to that of exfoliated MoS2. Micrometer-scale angle-resolved photoemission spectroscopy (ARPES) measurement on exfoliated MoS2 and WSe2 single-crystals provides direct evidence for the shifting of the valence band maximum from Γ to K, when the layer number is thinned down to one, as predicted by density functional theory. Our measurements of the k-space resolved electronic structure allow for further comparison with other theoretical predictions and with transport measurements. This work is supported by DOE grant DE-FG 02-04-ER-46157, research carried out in part at the CFN and NSLS, Brookhaven National Laboratory.

  19. Electronic band structure calculation of GaNAsBi alloys and effective mass study

    NASA Astrophysics Data System (ADS)

    Habchi, M. M.; Ben Nasr, A.; Rebey, A.; El Jani, B.

    2013-11-01

    Electronic band structures of GaNxAs1-x-yBiy dilute nitrides-bismides have been determined theoretically within the framework of the band anticrossing (BAC) model and k ṡ p method. We have developed computer codes based on our extended BAC model, denoted (16 × 16), in which the dimension of the used states basis was equal to 16. We have investigated the band gap and the spin orbit splitting as a function of Bi composition for alloys lattice matched to GaAs. We have found that the substitution of As element by N and Bi impurities leads to a significant reduction of band gap energy by roughly 198 meV/%Bi. Meanwhile, spin orbit splitting increases by 56 meV/%Bi regardless N content. There is an excellent agreement between the model predictions and experiment reported in the literature. In addition, alloys compositions and oscillator strengths of transition energies have been calculated for GaNAsBi alloys which represent active zone of temperature insensitive (1.55 μm and 1.3 μm) wavelength laser diodes intended for optical fiber communications. A crossover at about 0.6 eV has occurred between Eg and Δso of GaN.039As.893Bi.068. When the quaternary is lattice mismatched to GaAs, resonance energy increases with Bi content if N content decreases. On the other hand, effective mass behavior of carriers at Γ point has been discussed with respect to alloy composition, k-directions and lattice mismatch.

  20. Electronic structures of greigite (Fe3S4): A hybrid functional study and prediction for a Verwey transition

    PubMed Central

    Wu, Min; Tse, John S; Pan, Yuanming

    2016-01-01

    Greigite (Fe3S4) is a ferrimagnetic mineral with vital functions in both the bio-geochemical cycle and novel technological applications. However, the ground state electronic structure of this material has not been fully characterized by either experiment or theory. In the present study, ab initio calculations using the hybrid functional method have been performed to investigate the electronic structure and magnetic properties. It is found that the cubic structure observed under ambient temperature is a half metal and is metastable. A more stable monoclinic structure slightly distorted from the cubic form is found. The structural distortion is induced by charge ordering and associated with a metal-to-insulator transition, resulting in a semiconductive ground state with a bandgap of ~0.8 eV and a magnetic moment of 4 μB per formula unit. The results predict, similar to the magnetite (Fe3O4), a Verwey transition may exist in greigite, although it has not yet been observed experimentally. PMID:26869147

  1. Structural and electron charge density studies of a nonlinear optical compound 4,4 di-methyl amino cyano biphenyl

    NASA Astrophysics Data System (ADS)

    Naima, Boubegra; Abdelkader, Chouaih; Mokhtaria, Drissi; Fodil, Hamzaoui

    2014-01-01

    The 4,4 dimethyl amino cyano biphenyl crystal (DMACB) is characterized by its nonlinear activity. The intra molecular charge transfer of this molecule results mainly from the electronic transmission of the electro-acceptor (cyano) and electro-donor (di-methyl-amino) groups. An accurate electron density distribution around the molecule has been calculated based on a high-resolution X-ray diffraction study. The data were collected at 123 K using graphite-monochromated Mo K α radiation to sin(β)/λ = 1.24 Å-1. The integrated intensities of 13796 reflections were measured and reduced to 6501 independent reflections with I >= 3σ(I). The crystal structure was refined using the experimental model of Hansen and Coppens (1978). The crystal structure has been validated and deposited at the Cambridge Crystallographic Data Centre with the deposition number CCDC 876507. In this article, we present the thermal motion and the structural analysis obtained from the least-square refinement based on F2 and the electron density distribution obtained from the multipolar model.

  2. Cut and paste RNA for nuclear magnetic resonance, paramagnetic resonance enhancement, and electron paramagnetic resonance structural studies.

    PubMed

    Duss, Olivier; Diarra Dit Konté, Nana; Allain, Frédéric H-T

    2015-01-01

    RNA is a crucial regulator involved in most molecular processes of life. Understanding its function at the molecular level requires high-resolution structural information. However, the dynamic nature of RNA complicates structure determination because crystallization is often not possible or can result in crystal-packing artifacts resulting in nonnative structures. To study RNA and its complexes in solution, we described an approach in which large multi-domain RNA or protein-RNA complex structures can be determined at high resolution from isolated domains determined by nuclear magnetic resonance (NMR) spectroscopy, and then constructing the entire macromolecular structure using electron paramagnetic resonance (EPR) long-range distance constraints. Every step in this structure determination approach requires different types of isotope or spin-labeled RNAs. Here, we present a simple modular RNA cut and paste approach including protocols to generate (1) small isotopically labeled RNAs (<10 nucleotides) for NMR structural studies, which cannot be obtained by standard protocols, (2) large segmentally isotope and/or spin-labeled RNAs for diamagnetic NMR and paramagnetic relaxation enhancement NMR, and (3) large spin-labeled RNAs for pulse EPR spectroscopy.

  3. Structural change of graphite during electron irradiation

    SciTech Connect

    Koike, J. . Dept. of Mechanical Engineering); Pedraza, D.F. )

    1992-01-01

    Highly oriented pyrolytic graphite was irradiated at room temperature with 300-keV electrons. High resolution transmission electron microscopy and electron energy loss spectroscopy were employed to study the structure of electron-irradiated graphite. Results consistently indicated absence of long-range order periodicity in the basal plane, and loose retention of the c-axis periodicity. Structure was modeled based on a mixture of sixfold and non-sixfold atom rings. Formation of non-sixfold atom rings was related to the observed buckling and discontinuity of the original graphite basal plane.

  4. Structural change of graphite during electron irradiation

    SciTech Connect

    Koike, J.; Pedraza, D.F.

    1992-12-31

    Highly oriented pyrolytic graphite was irradiated at room temperature with 300-keV electrons. High resolution transmission electron microscopy and electron energy loss spectroscopy were employed to study the structure of electron-irradiated graphite. Results consistently indicated absence of long-range order periodicity in the basal plane, and loose retention of the c-axis periodicity. Structure was modeled based on a mixture of sixfold and non-sixfold atom rings. Formation of non-sixfold atom rings was related to the observed buckling and discontinuity of the original graphite basal plane.

  5. Do enantiomers of benzenesulfonic acid exist? Electron diffraction and quantum chemical study of molecular structure of benzenesulfonic acid

    NASA Astrophysics Data System (ADS)

    Giricheva, Nina I.; Girichev, Georgiy V.; Medvedeva, Yulia S.; Ivanov, Sergey N.; Petrov, Vyacheslav M.; Fedorov, Mikhail S.

    2012-09-01

    Molecular structure of benzenesulfonic acid was studied by gas-phase electron diffraction and quantum chemical (B3LYP/cc-pVTZ, МР2/cc-pVDZ, МР2/cc-pVTZ) methods. On the base of mass spectrometric analysis it was found that saturated vapor at Т = 396(9) K is represented by only molecular species, monomeric benzenesulfonic acid. Theoretical calculations showed that the molecule has two mirror conformers of C1 symmetry which can invert to each other via transition state of Cs symmetry by rotation of OH-group around Ssbnd O(H) bond. Both computational methods, B3LYP and MP2, resulted in the same structure of enantiomers; the MP2/cc-pVDZ calculations denoted a over-barrier transition between enantiomers at the temperature of electron diffraction experiment, while B3LYP and MP2 calculations with cc-pVTZ basis set estimated the barrier height to be comparable with the thermal energy value. Two geometric models of C1 and Cs symmetry were examined in gas electron diffraction structural analysis. It was established that the structure of C1 symmetry (Rf = 3.3%) demonstrated the best fit with GED data in comparison with Cs structure (Rf = 3.8%). In conformer of C1 symmetry an ordinary bond Ssbnd O(Н) is located almost orthogonal to benzene ring plane, and an Osbnd H bond practically eclipses one of Sdbnd O bonds of SO3H fragment. The following internuclear distances (Å) in benzenesulfonic acid were determined: rh1(Csbnd H)av = 1.116(6), rh1(Csbnd C)ср = 1.402(4), rh1(Csbnd S) = 1.770(5), rh1(Sdbnd O)av = 1.438(4), rh1(Ssbnd O) = 1.623(4), rh1(Osbnd H) = 0.870(17). Calculations of internal rotation potential functions and NBO-analysis of electron density distribution in a conformer and transition states between enantiomers were performed to establish the reasons of stability of the found asymmetric structure of the studied molecule. The structure of free molecule of benzenesulfonic acid was compared with that of molecular form in crystal.

  6. Molecular structure of cotinine studied by gas electron diffraction combined with theoretical calculations

    NASA Astrophysics Data System (ADS)

    Takeshima, Tsuguhide; Takeuchi, Hiroshi; Egawa, Toru; Konaka, Shigehiro

    2007-09-01

    The molecular structure of cotinine (( S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone), the major metabolite of nicotine, has been determined at about 182 °C by gas electron diffraction combined with MP2 and DFT calculations. The diffraction data are consistent with the existence of the (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers, where ax and eq indicate the configuration of the pyrrolidinone ring by means of the position (axial and equatorial) of the pyridine ring, and sc, sp and ap distinguish the isomers arising from the internal rotation around the bond connecting the two rings. The (CH 3)NCCC(N) dihedral angles, ϕ, of the (ax, sc) and (eq, sp) conformers were determined independently to be 158(12)° and 129(13)°, respectively, where the numbers in parentheses are three times the standard errors, 3 σ. According to the MP2 calculations, the corresponding dihedral angles for the (ax, ap) and (eq, ap) conformers were assumed to differ by 180° from their syn counterparts. The ratios x(ax, sc)/ x(ax, ap) and x(eq, sp)/ x(eq, ap) were taken from the theoretically estimated free energy differences, Δ G, where x is the abundance of the conformer. The resultant abundances of (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers are 34(6)%, 21% (d.p.), 28% (d.p.), and 17% (d.p.), respectively, where d.p. represents dependent parameters. The determined structural parameters ( rg (Å) and ∠ α (°)) of the most abundant conformer, (ax, sc), are as follows: r(N sbnd C) pyrrol = 1.463(5); r(N sbnd C methyl) = 1.457(←); r(N sbnd C( dbnd O)) = 1.384(12); r(C dbnd O) = 1.219(5); < r(C sbnd C) pyrrol> = 1.541(3); r(C pyrrolsbnd C pyrid) = 1.521(←); < r(C sbnd C) pyrid> = 1.396(2); < r(C sbnd N) pyrid> = 1.343(←); ∠(CNC) pyrrol = 113.9(11); ∠CCC pyrrol(-C pyrid) = 103.6(←); ∠NCO = 124.1(13); ∠NC pyrrolC pyrid = 113.1(12); ∠C pyrrolC pyrrolC pyrid = 113.3(←); ∠(CNC) pyrid = 117.1(2); <∠(NCC) pyrid> = 124.4(←); ∠C methylNC( dbnd O) =

  7. Structures, Electronics, and Reactivity of Strained Phosphazane Cages: A Combined Experimental and Computational Study.

    PubMed

    Roth, Torsten; Vasilenko, Vladislav; Wadepohl, Hubert; Wright, Dominic S; Gade, Lutz H

    2015-08-01

    A series of formamidine-bridged P2N2 cages have been prepared. Upon deprotonation, these compounds serve as valuable precursors to hybrid N-heterocyclic carbene ligands, whereas direct metalation gives rearranged dimetallic complexes as a result of cleavage of the formamidine bridge. The latter metal complexes contain an intact cyclophosphazane moiety that coordinates two distinct metal centers in a monodentate and a chelating fashion. A computational study has been carried out to elucidate the bonding within the P2N2 framework as well as the reactivity patterns. Natural bond orbital analysis indicates that the cage motif is poorly described by localized Lewis structures and that negative hyperconjugation effects govern the stability of the bicyclic framework. The donor capacity of the cyclophosphazane unit was assessed by inspection of the frontier molecular orbitals, highlighting the fact that π-back-donation from the metal fragments is crucial for effective metal-ligand binding. PMID:26181231

  8. Electronic structure and magnetic properties of monoclinic β-Cu2V2O7 : A GGA+U study

    NASA Astrophysics Data System (ADS)

    Yashima, Masatomo; Suzuki, Ryosuke O.

    2009-03-01

    A first-principles study on monoclinic C2/c copper pyrovanadate β-Cu2V2O7 has been performed using the generalized gradient approximation (GGA) and GGA+U method. The optimized unit-cell parameters and atomic coordinates of β-Cu2V2O7 agree well with experimental data. The optimized crystal structure of β-Cu2V2O7 indicates the existence of one-dimensional -Cu-Cu-Cu-Cu- chains. The electronic structure and magnetic properties were evaluated by the GGA+U calculations, which indicate that the β-Cu2V2O7 is a semiconducting antiferromagnetic material with an indirect band gap and local magnetic moment per Cu atom of 0.73μB . The intrachain exchanges for short and long Cu-Cu couples are estimated to be 6.4 and 4.1 meV, respectively, while the calculated interchain exchange (2.1 meV) is smaller, which indicate the one-dimensional character. The top of the valence band is composed of V3d , O2p , and Cu3d electrons while the bottom of the conduction band is primarily composed of Cu3d electrons. Valence electron-density distribution map indicates the V-O and Cu-O covalent bonds. Calculated partial electronic density of states strongly suggests that the V-O and Cu-O covalent bonds are mainly attributed to the overlaps of V3d and O2p atomic orbitals and of Cu3d and O2p , respectively.

  9. Electronic structure of LiCoO{sub 2} thin films: A combined photoemission spectroscopy and density functional theory study

    SciTech Connect

    Ensling, David; Thissen, Andreas; Laubach, Stefan; Schmidt, Peter C.; Jaegermann, Wolfram

    2010-11-15

    The electronic properties of LiCoO{sub 2} 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 LiCoO{sub 2} 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 O K XAS. The structure of the Co L 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=2.9 eV.

  10. Strong interplay between structure and electronic properties in CuIn(S,Se){2}: a first-principles study.

    PubMed

    Vidal, Julien; Botti, Silvana; Olsson, Pär; Guillemoles, Jean-François; Reining, Lucia

    2010-02-01

    We present a first-principles study of the electronic properties of CuIn(S,Se){2} (CIS) using state-of-the-art self-consistent GW and hybrid functionals. The calculated band gap depends strongly on the anion displacement u, an internal structural parameter that measures lattice distortion. This contrasts with the observed stability of the band gap of CIS solar panels under operating conditions, where a relatively large dispersion of values for u occurs. We solve this apparent paradox considering the coupled effect on the band gap of copper vacancies and lattice distortions. The correct treatment of d electrons in these materials requires going beyond density functional theory, and GW self-consistency is critical to evaluate the quasiparticle gap and the valence band maximum. PMID:20366776

  11. A comparison study on the electronic structures, lattice dynamics and thermoelectric properties of bulk silicon and silicon nanotubes

    NASA Astrophysics Data System (ADS)

    Lu, Peng-Xian; Qu, Ling-Bo; Cheng, Qiao-Huan

    2013-11-01

    In order to investigate the mechanism of the electron and phonon transport in a silicon nanotube (SiNT), the electronic structures, the lattice dynamics, and the thermoelectric properties of bulk silicon (bulk Si) and a SiNT have been calculated in this work using density functional theory and Boltzmann transport theory. Our results suggest that the thermal conductivity of a SiNT is reduced by a factor of 1, while its electrical conductivity is improved significantly, although the Seebeck coefficient is increased slightly as compared to those of the bulk Si. As a consequence, the figure of merit (ZT) of a SiNT at 1200 K is enhanced by 12 times from 0.08 for bulk Si to 1.10. The large enhancement in electrical conductivity originates from the largely increased density of states at the Fermi energy level and the obviously narrowed band gap. The significant reduction in thermal conductivity is ascribed to the remarkably suppressed phonon thermal conductivity caused by a weakened covalent bonding, a decreased phonon density of states, a reduced phonon vibration frequency, as well as a shortened mean free path of phonons. The other factors influencing the thermoelectric properties have also been studied from the perspective of electronic structures and lattice dynamics.

  12. Fabrication and interfacial electronic structure studies on polypyrrole/TiO2 nano hybrid systems for photovoltaic aspects.

    PubMed

    Kumar, Ganesan Mohan; Kawakita, Jin; Jayavel, Ramasamy

    2011-05-01

    The progress in studying the interfacial electronic structures of the developing new class of hybrid organic/inorganic material systems have envisaged a new dimension into the field of photovoltaics, which could be of great help in understanding the nature of charge transfer in them. In this regard, electropolymerization of pyrrole monomers have been carried out at room temperature on the surface of TiO2 working electrodes (assisted by UV radiations) and their interfacial electronic structure has been studied as a function of the applied photo anodic potentials. The formation of polypyrrole deposits has been ensured using FT-IR and Raman spectroscopy. Surface analysis of the hybrid matrix revealed the tendency of polymer molecules to cover up the spherical surface of TiO2 nanoparticles that could help in improving the light absorption rate. Signals (bands) corresponding to pyrrole molecules observed in the ultraviolet photoelectron spectroscopy measurements have been correlated with the polaronic states formed and identified to shift as a function of the applied photo anodic potentials, revealing the decrease in work function of the hybrid system to take place (confirmed using cyclic voltammetry measurements). The decreasing trend in the work function elucidates the adjustment in electronic structure of the system (hybrid materials possessing smaller work functions are generally preferred for photovoltaic studies). The aforementioned behavioural aspects have been reasoned with the increase in overpotential values for polarization, from the decrease in up-take rate of the anionic dopant, which increases the current density values, thereby modifying the conductivity of the systems.

  13. Structural evolution and strain induced mixing in Cu–Co composites studied by transmission electron microscopy and atom probe tomography

    PubMed Central

    Bachmaier, A.; Aboulfadl, H.; Pfaff, M.; Mücklich, F.; Motz, C.

    2015-01-01

    A Cu–Co composite material is chosen as a model system to study structural evolution and phase formations during severe plastic deformation. The evolving microstructures as a function of the applied strain were characterized at the micro-, nano-, and atomic scale-levels by combining scanning electron microscopy and transmission electron microscopy including energy-filtered transmission electron microscopy and electron energy-loss spectroscopy. The amount of intermixing between the two phases at different strains was examined at the atomic scale using atom probe tomography as complimentary method. It is shown that Co particles are dissolved in the Cu matrix during severe plastic deformation to a remarkable extent and their size, number, and volume fraction were quantitatively determined during the deformation process. From the results, it can be concluded that supersaturated solid solutions up to 26 at.% Co in a fcc Cu–26 at.% Co alloy are obtained during deformation. However, the distribution of Co was found to be inhomogeneous even at the highest degree of investigated strain. PMID:26523113

  14. Study of structural and electronic properties of ScN and ScAs in rocksalt and zincblende structure: A DFT approach

    SciTech Connect

    Nayak, Vikas Verma, U. P.

    2015-08-28

    In this paper, we have studied the structural and electronic properties of ScN and ScAs in zincblende (ZB) and rocksalt (RS) phases. We have employed the full potential linearized augmented plane wave (FP-APW) method within the density functional theory (DFT). Generalized gradient approximation (GGA), due to Perdew-Burke-Ernzerhof (PBE) has been used to estimate the exchange-correlation functional. Our band structure results for ScN shows the metallic nature, whereas ScAs shows the semiconducting behavior. The obtained results are in excellent agreement with earlier reported data.

  15. First principles study on electronic structure and elastic properties of LaCd and LaHg

    SciTech Connect

    Devi, Hansa E-mail: gita-pagare@yahoo.co.in; Pagare, Gitanjali E-mail: gita-pagare@yahoo.co.in; Chouhan, S. S. E-mail: gita-pagare@yahoo.co.in; Sanyal, Sankar P.

    2014-04-24

    Full -potential linearized augmented plane wave method (FP- LAPW) has been used for the comparative study of electronic structure and elastic properties of CsCl-type LaCd and LaHg intermetallic compounds using generalized gradient approximation (GGA). The density of states at the Fermi Level, N (E{sub F}), is found to be 0.06 and 3.03 states/eV for LaCd and LaHg respectively. We report elastic constants for these compounds for the first time. The ductility/brittleness of these compounds has been analyzed using Pugh rule and Cauchy’s pressure.

  16. Structural physiology based on electron crystallography

    PubMed Central

    Fujiyoshi, Yoshinori

    2011-01-01

    There are many questions in brain science, which are extremely interesting but very difficult to answer. For example, how do education and other experiences during human development influence the ability and personality of the adult? The molecular mechanisms underlying such phenomena are still totally unclear. However, technological and instrumental advancements of electron microscopy have facilitated comprehension of the structures of biological components, cells, and organelles. Electron crystallography is especially good for studying the structure and function of membrane proteins, which are key molecules of signal transduction in neural and other cells. Electron crystallography is now an established technique to analyze the structures of membrane proteins in lipid bilayers, which are close to their natural biological environment. By utilizing cryo-electron microscopes with helium cooled specimen stages, which were developed through a personal motivation to understand functions of neural systems from a structural point of view, structures of membrane proteins were analyzed at a resolution higher than 3 Å. This review has four objectives. First, it is intended to introduce the new research field of structural physiology. Second, it introduces some of the personal struggles, which were involved in developing the cryo-electron microscope. Third, it discusses some of the technology for the structural analysis of membrane proteins based on cryo-electron microscopy. Finally, it reviews structural and functional analyses of membrane proteins. PMID:21416541

  17. Electronic structure of Au-Ta alloys:. An X-ray spectroscopy study

    NASA Astrophysics Data System (ADS)

    Kuhn, M.; Sammynaiken, R.; Sham, T. K.

    1998-07-01

    Au-Ta alloys with the compositions of AuTa, AuTa 2 and AuTa 3, prepared by quenching from the melt, has been studied with X-ray diffraction, photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure (XANES) measurements. It was found that while AuTa 3 is a single-phase solid solution, AuTa 2 and AuTa have mixed phases and that the Au and Ta 4f levels of the alloys shift to higher binding energy, relative to the pure metal; this is accompanied by a narrowing of the Au 5d component of the alloy d-band, which moves away from the Fermi level. This observation is interpreted in terms of a charge compensation model in which Au loses d charge but is overcompensated by s-p charge gain, resulting in a small net charge flow from Ta to Au. The observed Ta 4f binding energy shift is as predicted by electronegativity and indicates charge depletion at the Ta site. The notion of d charge depletion at both Au and Ta sites upon alloying is confirmed independently by XANES measurements which showed that the L 2,3 edge whiteline intensity for both Au and Ta increases as they become more dilute in the host, indicating an increase in d hole count. The experimental results compare favorably with a recent linear-augmented Slater-type-orbital (LASTO) calculations. The implications of these results are discussed.

  18. Computational study and experimental validation of porous structures fabricated by electron beam melting: a challenge to avoid stress shielding.

    PubMed

    Herrera, A; Yánez, A; Martel, O; Afonso, H; Monopoli, D

    2014-12-01

    In this paper, several diamond non-stochastic lattice structures, fabricated by electron beam melting, were mechanically characterized by compression tests. A finite element model of the structures was developed, obtaining an equation that estimates the elastic modulus of the lattice structure. Finally, the differences between the numerical and the experimental results were analyzed and discussed.

  19. Electronic Structure Principles and Aromaticity

    ERIC Educational Resources Information Center

    Chattaraj, P. K.; Sarkar, U.; Roy, D. R.

    2007-01-01

    The relationship between aromaticity and stability in molecules on the basis of quantities such as hardness and electrophilicity is explored. The findings reveal that aromatic molecules are less energetic, harder, less polarizable, and less electrophilic as compared to antiaromatic molecules, as expected from the electronic structure principles.

  20. A combined photoelectron spectroscopy and relativistic ab initio studies of the electronic structures of UFO and UFO-

    NASA Astrophysics Data System (ADS)

    Roy, Soumendra K.; Jian, Tian; Lopez, Gary V.; Li, Wei-Li; Su, Jing; Bross, David H.; Peterson, Kirk A.; Wang, Lai-Sheng; Li, Jun

    2016-02-01

    The observation of the gaseous UFO- anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO- is linear with an O-U-F structure and a 3H4 spectral term derived from a U 7sσ25fφ15fδ1 electron configuration, whereas the ground state of neutral UFO has a 4H7/2 spectral term with a U 7sσ15fφ15fδ1 electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.

  1. Electronic Structure of LiC6 Studied by Soft X-Ray Emission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Mansour, A.; Schnatterly, S.

    1987-04-01

    We present and discuss carbon K soft X-ray emission spectra of Highly Ordered Pyrolytic Graphite (HOPG) and LiC6, stage 1 Li intercalated graphite. These measurements allow us to observe the filling of the carbon π states by the electrons from the donor alkali atoms. By fitting the shape of these donor-filled π states with simple models, we can determine several parameters describing the electronic density of states near the Fermi energy in this material. In addition knowing the charge transfer, and measuring the area under the donor-filled π states allows us to evaluate the intensity enhancement seen in X-ray emission near the Fermi energy relative to the rest of the π band.

  2. First-Principles Electronic Structure Studies of the Current-Voltage Characteristics of Molecular Nanostructures

    NASA Astrophysics Data System (ADS)

    Pati, Ranjit; Karna, Shashi P.

    2001-03-01

    Recent advancements in the experimental measurement of conductance across a single molecule(M. A. Reed et al, Science, 278) , 252 (1997). have generated great deal of interest in the feasibility of molecular electronic devices. A successful realization of molecule based electronic devices rests on a detailed understanding of the physical principles underlying controlled transport of electron/hole across molecular units. In order to develop such a fundamental understanding, we have investigated current-voltage characteristics of metal atom (Ag, Au) substituted 1,4-dithiobenzene within Green's function approach according to Datta and coworkers( W. Tian et al, J. Chem. Phys., 109), 2874 (1998).. Ab initio Hamiltonian matrix elements are used to construct the Green's function. The calculated conductance spectrum for the molecule with S bonded to Au atoms qualitatively agrees with the experiment^1. However, large quantitative difference between the calculated and measured conductance is noted. The Au and Ag bonded 1,4-dithiobenzene molecules exhibit marked difference in their resistance and conductance spectra. The conductance of the Ag-bonded molecule is calculated to be about 1.5 times larger than that bonded with Au.

  3. A QUANTUM MECHANICAL STUDY OF STRUCTURAL AND ELECTRONIC DILUTION EFFECTS IN PARAMAGNETIC CHEMICAL EXCHANGE SATURATION TRANSFER AGENTS

    PubMed Central

    Miller, Whelton A.; Moore, Preston B.

    2014-01-01

    We present a computational study of the effect of chemical modifications of the meta and para substituents in the coordinating pendant arm of a modified 1,4,7,10-tetraazacyclododecane-N, N’, N″, N‴-tetraamide (DOTAM) ligand on the Chemical Exchange Saturation Transfer (CEST) signal. Magnetic Resonance Imaging (MRI) is currently one of the most widely used techniques available. MRI has led to a new class of pharmaceuticals termed “imagining” or “contrast” agents. These agents usually work by incorporating lanthanide metals such as Gadolinium (Gd) and Europium (Eu). This allows the contrast agents to take advantage of the paramagnetic properties of the metals, which in turn enhances the signal detectable by MRI. The effect of simple electron-withdrawing (e.g., nitro) and electron-donating (e.g., methyl) substituents chemically attached to a modified chelate arm (pendant arm) is quantified by charge transfer interactions in the coordinated water-chelate system computed from quantum mechanics. This study attempts to reveal the origin of the substituent effect on the CEST signal and the electronic structure of the complex. We find that the extent of Charge Transfer (CT) depends on orbital orientations and overlaps. However, CT interactions occur simultaneously from all arms, which causes a dilution effect with respect to the pendant arm. PMID:25485283

  4. A QUANTUM MECHANICAL STUDY OF STRUCTURAL AND ELECTRONIC DILUTION EFFECTS IN PARAMAGNETIC CHEMICAL EXCHANGE SATURATION TRANSFER AGENTS.

    PubMed

    Miller, Whelton A; Moore, Preston B

    2014-01-01

    We present a computational study of the effect of chemical modifications of the meta and para substituents in the coordinating pendant arm of a modified 1,4,7,10-tetraazacyclododecane-N, N', N″, N‴-tetraamide (DOTAM) ligand on the Chemical Exchange Saturation Transfer (CEST) signal. Magnetic Resonance Imaging (MRI) is currently one of the most widely used techniques available. MRI has led to a new class of pharmaceuticals termed "imagining" or "contrast" agents. These agents usually work by incorporating lanthanide metals such as Gadolinium (Gd) and Europium (Eu). This allows the contrast agents to take advantage of the paramagnetic properties of the metals, which in turn enhances the signal detectable by MRI. The effect of simple electron-withdrawing (e.g., nitro) and electron-donating (e.g., methyl) substituents chemically attached to a modified chelate arm (pendant arm) is quantified by charge transfer interactions in the coordinated water-chelate system computed from quantum mechanics. This study attempts to reveal the origin of the substituent effect on the CEST signal and the electronic structure of the complex. We find that the extent of Charge Transfer (CT) depends on orbital orientations and overlaps. However, CT interactions occur simultaneously from all arms, which causes a dilution effect with respect to the pendant arm. PMID:25485283

  5. Electronic Structure and Energy Transfer in Europium(III)-Ciprofloxacin Complexes: A Theoretical Study.

    PubMed

    Emelina, Tatiana B; Freidzon, Alexandra Ya; Bagaturyants, Alexander A; Karasev, Vladimir E

    2016-09-29

    The structure and ligand-localized excited states of [Eu(cfqH) (cfq)(H2O)4]Cl2 (cfqH is ciprofloxacin) are studied by XMCQDPT2/CASSCF with full geometry optimization. The complex includes one anionic and one zwitterionic ligand. Two low-lying triplet states, both localized on the anionic ligand, are found. One of them has sufficient energy to transfer to the (5)D1 sublevel of Eu(3+), because its T-S0 vertical transition energy is equal (or very close) to the (7)F0-(5)D1 Eu(3+) excitation energy. The other triplet state has a very small S0-T1 gap, which favors fast nonradiative relaxation. Two other triplet states are localized on the zwitterionic ligand. One low-lying excited singlet state (S1) is localized on the anionic ligand; the other excited singlet is localized on the zwitterionic one. Spin-orbit coupling constants were calculated for the relaxed geometry of each state (ground state, two low-lying triplets, and one low-lying excited singlet) by spin-orbit configuration interaction (CI) with Pauli-Breit Hamiltonian. Large spin-orbit coupling constants between S1 and both triplets together with small energy gaps are indicative of fast intersystem crossing (ISC) from the excited singlet state to the triplet manifold. This ISC process is followed by energy transfer from the ligand-localized triplet states to the (5)D1 sublevel of Eu(3+). However, relatively large spin-orbit coupling constants between S0 and one of the triplet states together with the small T-S0 energy gap shows that this state can decay without transferring its energy to Eu(3+). This mechanism is expected to be common for other Ln(3+)-fluoroquinolone complexes.

  6. A structural study of solid electrolyte interface on negative electrode of lithium-Ion battery by electron microscopy.

    PubMed

    Matsushita, Tadashi; Watanabe, Jiro; Nakao, Tatsuya; Yamashita, Seiichi

    2014-11-01

    For the last decades, the performance of the lithium-ion battery (LIB) has been significantly improved and its applications have been expanding rapidly. However, its performance has yet to be enhanced.In the lithium-ion battery development, it is important to elucidate the electrode structure change in detail during the charge and discharge cycling. In particular, solid electrolyte interface (SEI) formed by decomposition of the electrolytes on the graphite negative electrode surface should play an important role for battery properties. Therefore, it is essential to control the structure and composition of SEI to improve the battery performance. Here, we conducted a scanning electron microscope (SEM) and transmission electron microscope (TEM) study to elucidate the structures of the SEI during the charge and discharge process using LiNi1/3Co1/3Mn1/3O2 [1] cathode and graphite anode. [2] Since SEI is a lithium-containing compound with high activity, it was observed without being exposed to the atmosphere. The electrodes including SEI were sampled after dismantling batteries with cutoff voltages of 3V and 4.2V for the charge process and 3V for the discharge process. Fig.1 shows SEM images of the graphite electrode surface during the charge and discharge process. The change of the SEI structure during the process was clearly observed. Further, TEM images showed that the SEI grew thicker during the charge process and becomes thinner when discharged. These results with regard to the reversible SEI structure could give a new insight for the battery development.jmicro;63/suppl_1/i21/DFU056F1F1DFU056F1Fig. 1.SEM images of the graphite electrode surface:(a) before charge process;(b) with charge-cutoff voltage of 3.0V; (c) with charge-cutoff voltage of 4.2V; (d) with discharge-cutoff voltage of 3.0V.

  7. Theoretical study of the influence of vacancies on the electronic structure of a hexagonal boron nitride monolayer

    SciTech Connect

    Serzhantova, M. V. Kuzubov, A. A.; Fedorov, A. S.; Krasnov, P. O.; Tomilin, F. N.

    2011-04-15

    The influence of boron and nitrogen vacancies and divacancies on the electronic structure of a hexagonal boron nitride h-BN monolayer is studied. In the presence of vacancies in the structure, the introduced states appear in the forbidden band. The position of an introduced state with respect to the upper occupied level and the lower vacant level depends on deformation. Calculations show that, depending on the defect type and the magnitude of the applied deformation, the introduced state can be both localized and not localized on atoms surrounding the defect. When the state is localized in the system, the inhomogeneous distribution of the spin density is observed, resulting in the appearance of the magnetic moment in the system.

  8. First-principles study of structural, electronic, vibrational, dielectric and elastic properties of tetragonal Ba₂YTaO₆

    SciTech Connect

    Ganeshraj, C.; Santhosh, P. N.

    2014-10-14

    We report first-principles study of structural, electronic, vibrational, dielectric, and elastic properties of Ba₂YTaO₆, a pinning material in high temperature superconductors (HTS), by using density functional theory. By using different exchange-correlation potentials, the accuracy of the calculated lattice constants of Ba₂YTaO₆ has been achieved with GGA-RPBE, since many important physical quantities crucially depend on change in volume. We have calculated the electronic band structure dispersion, total and partial density of states to study the band gap origin and found that Ba₂YTaO₆ is an insulator with a direct band gap of 3.50 eV. From Mulliken population and charge density studies, we conclude that Ba₂YTaO₆ have a mixed ionic-covalent character. Moreover, the vibrational properties, born effective charges, and the dielectric permittivity tensor have been calculated using linear response method. Vibrational spectrum determined through our calculations agrees well with the observed Raman spectrum, and allows assignment of symmetry labels to modes. We perform a detailed analysis of the contribution of the various infrared-active modes to the static dielectric constant to explain its anisotropy, while electronic dielectric tensor of Ba₂YTaO₆ is nearly isotropic, and found that static dielectric constant is in good agreement with experimental value. The six independent elastic constants were calculated and found that tetragonal Ba₂YTaO₆ is mechanically stable. Other elastic properties, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and elastic anisotropy ratios are also investigated and found that Poisson's ratio and Young's modulus of Ba₂YTaO₆ are similar to that of other pinning materials in HTS.

  9. Ab initio study of structural, electronic and optical properties of ternary CdO1-xSex alloys using special quasi-random structures

    NASA Astrophysics Data System (ADS)

    Muhammad, Rashid; Fayyaz, Hussain; Muhammad, Imran; A. Ahmad, S.; A. Noor, N.

    2014-01-01

    The structural, electronic, and optical properties of binary CdO, CdSe, and their ternary CdO1-xSex alloys (0 <= x <= 1) in the rock salt and zinc blend phases have been studied by the special quasi-random structure (SQS) method. All the calculations are performed using full-potential linearized augmented plane wave plus local orbital's (FP-LAPW+lo) method within the framework of density function theory (DFT). We use Wu—Cohen (WC) generalized gradient approximation (GGA) to calculate structural parameters, whereas both Wu—Cohen and Engel—Vosko (EV) GGA have been applied to calculate electronic structure of the materials. Our predicted results of lattice constant and bulk modulus show only a slight deviation from Vegard's law for the whole concentrations. The obtained band structure indicates that for the rock-salt phase, the ternary alloys present semi-metallic behavior, while for the zinc blend phase, semiconductor behavior with direct bandgap is observed with decreasing order of x except for CdSe. Finally, by incorporating the basic optical properties, we discuss the dielectric function, refractive index, optical reflectivity, the absorption coefficient, and optical conductivity in terms of incident photon energy up to 14 eV. The calculated results of both binaries are in agreement with existing experimental and theoretical values.

  10. First principles study of structural, electronic, elastic and thermal properties of YX (X = Cd, In, Au, Hg and Tl) intermetallics

    NASA Astrophysics Data System (ADS)

    Chouhan, Sunil Singh; Pagare, Gitanjali; Rajagopalan, M.; Sanyal, S. P.

    2012-08-01

    The structural, electronic, elastic and thermal properties of YX (X = Cd, In, Au, Hg and Tl) intermetallic compounds crystallizing in B2-type structure have been studied using first principles density functional theory within generalized gradient approximation (GGA) for the exchange correlation potential. Amongst all the YX compounds, YIn is stable in distorted tetragonal (P4/mmm) CuAu-type structure at ambient pressure with very small energy difference of 0.00681 Ry. but it undergoes to CsCl-type (B2 phase) structure at 23.3 GPa. Rest of the compounds are stable in B2 structure at ambient condition. The values of elastic moduli as a function of pressure are also reported. The ductility of these compounds has been analyzed using the Pugh rule. Our calculated results indicate that YTl is the most ductile amongst all the B2-YX compounds. YAu is the hardest and less compressible compound due to the largest bulk modulus. The elastic properties such as Young's modulus (E), Poisson's ratio (σ) and anisotropic ratio (A) are also predicted. The anisotropic factor is found to be unity for YHg which shows that this compound is isotropic.

  11. Antiphase Modulated Structure of Fe 2O 3(ZnO) 15Studied by High-Resolution Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Li, Chunfei; Bando, Yoshio; Nakamura, Masaki; Kimizuka, Noboru

    1999-01-01

    As one of our systematic studies of the modulated structures of a series of new homologous compoundsRMO3(ZnO)m(R=Sc, In, Y, and La;M=In, Fe Ga, and Al;m=integer), this paper reports the modulated structure of Fe2O3(ZnO)15(R=Fe;M=Fe) studied by high-resolution electron microscopy. It is found that the main and satellite spots in the diffraction patterns can be indexed asha*+kb*+lc*+mq by considering a monoclinic unit cell ofa=0.57 nm,b=0.33 nm,c=4.5 nm, andβ=92° and a modulation wave vector of q=b*/34.8+c*/2. The possible space groups for the basic structure areC2,Cm, andC2/m, and the possible four-dimensional superspace groups for the modulated structure areCC21,CCmoverline1, andCC2/m1overline1. The crystal structure of Fe2O3(ZnO)15consists of Fe-O layers interleaved with 16 Fe/Zn-O layers. In the high-resolution image, the modulated structure appeared as zigzag-shaped contrasts among the Fe/Zn-O layers, where Fe is in high concentration. Compared with those of InMO3(ZnO)m(R=In;M=In, Fe and Ga) reported in our earlier paper, the special features of the present modulated structure are the half-periodicity relative shift of the neighboring zigzag-shaped contrasts and the appearance of modulation within the Fe-O layers.

  12. The electronic structure, mechanical flexibility and carrier mobility of black arsenic-phosphorus monolayers: a first principles study.

    PubMed

    Sun, Jie; Lin, Na; Ren, Hao; Tang, Cheng; Yang, Letao; Zhao, Xian

    2016-04-14

    New artificial layered semiconductors - black arsenic-phosphorus (b-AsP) - which have tunable band gaps owing to good tunability of the chemical compositions have been synthesized in a recent experiment. In the present work, first principles calculations are performed to systematically study the structure, and mechanical, electrical, and transport properties of b-AsP monolayers. The mechanical analysis demonstrates that the exfoliation of single-layer b-AsP systems from the bulk form is more difficult compared with that of pure black phosphorus (BP). In addition, the breaking strain of the b-AsP monolayer is comparable with other widely studied two dimensional materials, indicating their excellent mechanical flexibility and good potential for flexible device applications. Besides, the electronic structures of b-AsP system monolayers are not sensitive to their specific compositions, which however, can be flexibly modulated by the strain effect. The predicted carrier mobilities of b-AsP systems are directionally anisotropic, similar to pure BP. However, the degradation of their carrier mobilities may become a practical limitation in real electronic device applications. PMID:27003857

  13. Electronic structure and magnetism of Mn-doped GaSb for spintronic applications: A DFT study

    NASA Astrophysics Data System (ADS)

    Seña, N.; Dussan, A.; Mesa, F.; Castaño, E.; González-Hernández, R.

    2016-08-01

    We have carried out first-principles spin polarized calculations to obtain comprehensive information regarding the structural, magnetic, and electronic properties of the Mn-doped GaSb compound with dopant concentrations: x = 0.062, 0.083, 0.125, 0.25, and 0.50. The plane-wave pseudopotential method was used in order to calculate total energies and electronic structures. It was found that the MnGa substitution is the most stable configuration with a formation energy of ˜1.60 eV/Mn-atom. The calculated density of states shows that the half-metallic ferromagnetism is energetically stable for all dopant concentrations with a total magnetization of about 4.0 μB/Mn-atom. The results indicate that the magnetic ground state originates from the strong hybridization between Mn-d and Sb-p states, which agree with previous studies on Mn-doped wide gap semiconductors. This study gives new clues to the fabrication of diluted magnetic semiconductors.

  14. The Role of Electron Microscopy in Studying the Continuum of Changes in Membranous Structures during Poliovirus Infection

    PubMed Central

    Rossignol, Evan D.; Yang, Jie E.; Bullitt, Esther

    2015-01-01

    Replication of the poliovirus genome is localized to cytoplasmic replication factories that are fashioned out of a mixture of viral proteins, scavenged cellular components, and new components that are synthesized within the cell due to viral manipulation/up-regulation of protein and phospholipid synthesis. These membranous replication factories are quite complex, and include markers from multiple cytoplasmic cellular organelles. This review focuses on the role of electron microscopy in advancing our understanding of poliovirus RNA replication factories. Structural data from the literature provide the basis for interpreting a wide range of biochemical studies that have been published on virus-induced lipid biosynthesis. In combination, structural and biochemical experiments elucidate the dramatic membrane remodeling that is a hallmark of poliovirus infection. Temporal and spatial membrane modifications throughout the infection cycle are discussed. Early electron microscopy studies of morphological changes following viral infection are re-considered in light of more recent data on viral manipulation of lipid and protein biosynthesis. These data suggest the existence of distinct subcellular vesicle populations, each of which serves specialized roles in poliovirus replication processes. PMID:26473912

  15. A study of 3D structure of nighttime electron density enhancement in the mid-latitude ionosphere by GPS tomography

    NASA Astrophysics Data System (ADS)

    Chen, C.; Saito, A.

    2011-12-01

    The mid-latitude summer nighttime anomaly (MSNA) is a feature that the nighttime electron density larger than that in the daytime mid-latitude ionosphere. This anomaly was first detected in the southern hemisphere five decades ago and observed in the northern hemisphere recently by ionosondes and satellites. Previous studies presented the electron density structure of MSNA by using COSMIC occultation data and found that MSNA is clearly seen around 300 km altitude during local summer. However, due to lack of observation, the day-to-day variation of MSNA was not investigated. A GPS tomography method by SPEL of Kyoto University using the total electron content (TEC) data measured by the ground-based GPS receiver network is employed in this study. The wide coverage and continuous observation of GPS receivers are suitable for investigating the spatial and day-to-day variations of ionospheric electron densities. The algorithm of the GPS tomography developed by SPEL of Kyoto University use a constraint condition that the gradient of election density tends to be smooth in the horizontal direction and steep in the vicinity of the F2 peak, instead of inputting the initial conditions. Therefore, the algorithm is independent of any ionospheric and plasmaspheric electron density distribution models. The dense ground-based GPS receiver network around European region is used to study the three dimensional (3D) structure of MSNA with GPS tomography. Results show that the MSNA usually appear around the geomagnetic mid-latitude region during local summer nighttime. The feature of MSNA is most obvious at the ionospheric F2-peak altitudes. The result also shows a day-to-day variation in the formation of MSNA, in terms of the occurrence time, intensity, and spatial extent. The tomographic results are compared with the ionosondes, satellites, and radar measurements. A theoretical model simulation, SAMI2, is also used to further discuss the mechanism of MSNA. The comparison with other

  16. Electronic structure of disordered CuPd alloys: A two-dimensional positron-annihilation study

    NASA Astrophysics Data System (ADS)

    Smedskjaer, L. C.; Benedek, R.; Siegel, R. W.; Legnini, D. G.; Stahulak, M. D.; Bansil, A.

    1987-11-01

    Two-dimensional-angular-correlation experiments using posi- tron-annihilation spectroscopy were performed on a series of disordered Cu-rich CuPd-alloy single crystals. The results are compared with theoretical calculations based on the Korringa-Kohn-Rostoker coherent-potential approximation. Our experiments confirm the theoretically predicted flattening of the alloy Fermi surface near [110] with increasing Pd concentration. The momentum densities and the two-dimensional-angular-correlation spectra around zero momentum exhibit a characteristic signature of the electronic states near the valence-band edge in the alloy.

  17. Electronic structure of disordered CuPd alloys: A two-dimensional positron-annihilation study

    SciTech Connect

    Smedskjaer, L.C.; Benedek, R.; Siegel, R.W.; Legnini, D.G.; Stahulak, M.D.; Bansil, A.

    1987-11-23

    Two-dimensional--angular-correlation experiments using posi- tron-annihilation spectroscopy were performed on a series of disordered Cu-rich CuPd-alloy single crystals. The results are compared with theoretical calculations based on the Korringa-Kohn-Rostoker coherent-potential approximation. Our experiments confirm the theoretically predicted flattening of the alloy Fermi surface near (110) with increasing Pd concentration. The momentum densities and the two-dimensional--angular-correlation spectra around zero momentum exhibit a characteristic signature of the electronic states near the valence-band edge in the alloy.

  18. Electronic structure and ground-state properties of Na{sub 2}Po: A first-principles study

    SciTech Connect

    Eithiraj, R. D.

    2015-06-24

    Self-consistent scalar-relativistic band structure calculations have been performed to investigate the electronic structure and ground-state properties of Na{sub 2}Po in cubic antifluorite (anti-CaF{sub 2}-type) structure using the linear muffin-tin orbital in its tight-binding representation (TB-LMTO) method. Ground state properties such as equilibrium lattice constant and bulk modulus were calculated. The results of the electronic structure calculations show that Na{sub 2}Po is direct bandgap semiconductor.

  19. High-resolution transmission electron microscopy studies of quantum wire structures grown on submicrometre gratings of V-grooves

    NASA Astrophysics Data System (ADS)

    Gustafsson, A.; Malm, J.-O.; Carlsson, A.; Vermeire, G.

    1996-11-01

    We present an extensive characterization of a quantum wire (QWR) structure using transmission electron microscopy (TEM). The structure consisted of a single GaAs layer in between AlGaAs barriers, grown on a GaAs substrate patterned with a submicrometre grating of V-grooves. For reference we also studied other QWR, as well as, quantum well (QW) samples, fabricated under similar conditions. We used bright field and dark field imaging to study the overall structure, high-resolution TEM to study the layer thickness and the interface quality, and chemical lattice imaging to study the compositional variations across the interfaces. In the QWR sample, there were mainly two distinctly different areas of the QW: on the (100) planes between the V-grooves, the QW was flat, whereas the QW on the near 0268-1242/11/11/018/img5 side walls of the V-grooves had a flat lower interface and a saw-tooth shaped upper interface. The QWRs at the bottom of the V-grooves were crescent shaped. We also observed a fundamental difference in growth of the GaAs and the AlGaAs on the side wall, where the AlGaAs formed straight interfaces, determined by high-index planes, whereas the GaAs tended to form alternating low-index planes giving a saw-tooth appearance of the GaAs QW.

  20. Structural and electronic properties of stable Lin (n=2-10) clusters: A density functional study

    NASA Astrophysics Data System (ADS)

    Chetri, Pawan; Deka, Ramesh Ch.; Choudhury, Amarjyoti

    2013-12-01

    Structure and relative stability of Lin clusters for n=1-10 were investigated using density functional methods based DMol3 program. The structures of Li clusters were determined in terms of Li-Li bond length and the results are in very good agreement with experimental values. Stability of the clusters was determined from their relative energy values binding energies and second difference energy. We also determined fragmentation energy of each size of cluster. We arrived at some interesting result like the transition of Lin from 2-dimension to 3-dimension for a particular value of n and also the variation of HOMO-LUMO gap with cluster size. Many structures are characterized for the first time in this work.

  1. First Principles Study on the Electronic Structure and Interface Stability of Hybrid Silicene/Fluorosilicene Nanoribbons

    NASA Astrophysics Data System (ADS)

    Jiang, Q. G.; Zhang, J. F.; Ao, Z. M.; Wu, Y. P.

    2015-10-01

    The interface stability of hybrid silicene/fluorosilicene nanoribbons (SFNRs) has been investigated by using density functional theory calculations, where fluorosilicene is the fully fluorinated silicene. It is found that the diffusion of F atoms at the zigzag and armchair interfaces of SFNRs is endothermic, and the corresponding minimum energy barriers are respectively 1.66 and 1.56 eV, which are remarkably higher than the minimum diffusion energy barrier of one F atom and two F atoms on pristine silicene 1.00 and 1.29 eV, respectively. Therefore, the thermal stability of SFNRs can be significantly enhanced by increasing the F diffusion barriers through silicene/fluorosilicene interface engineering. In addition, the electronic and magnetic properties of SFNRs are also investigated. It is found that the armchair SFNRs are nonmagnetic semiconductors, and the band gap of armchair SFNRs presents oscillatory behavior when the width of silicene part changing. For the zigzag SFNRs, the antiferromagnetic semiconducting state is the most stable one. This work provides fundamental insights for the applications of SFNRs in electronic devices.

  2. First Principles Study on the Electronic Structure and Interface Stability of Hybrid Silicene/Fluorosilicene Nanoribbons

    PubMed Central

    Jiang, Q. G.; Zhang, J. F.; Ao, Z. M.; Wu, Y. P.

    2015-01-01

    The interface stability of hybrid silicene/fluorosilicene nanoribbons (SFNRs) has been investigated by using density functional theory calculations, where fluorosilicene is the fully fluorinated silicene. It is found that the diffusion of F atoms at the zigzag and armchair interfaces of SFNRs is endothermic, and the corresponding minimum energy barriers are respectively 1.66 and 1.56 eV, which are remarkably higher than the minimum diffusion energy barrier of one F atom and two F atoms on pristine silicene 1.00 and 1.29 eV, respectively. Therefore, the thermal stability of SFNRs can be significantly enhanced by increasing the F diffusion barriers through silicene/fluorosilicene interface engineering. In addition, the electronic and magnetic properties of SFNRs are also investigated. It is found that the armchair SFNRs are nonmagnetic semiconductors, and the band gap of armchair SFNRs presents oscillatory behavior when the width of silicene part changing. For the zigzag SFNRs, the antiferromagnetic semiconducting state is the most stable one. This work provides fundamental insights for the applications of SFNRs in electronic devices. PMID:26496976

  3. First Principles Study on the Electronic Structure and Interface Stability of Hybrid Silicene/Fluorosilicene Nanoribbons.

    PubMed

    Jiang, Q G; Zhang, J F; Ao, Z M; Wu, Y P

    2015-10-26

    The interface stability of hybrid silicene/fluorosilicene nanoribbons (SFNRs) has been investigated by using density functional theory calculations, where fluorosilicene is the fully fluorinated silicene. It is found that the diffusion of F atoms at the zigzag and armchair interfaces of SFNRs is endothermic, and the corresponding minimum energy barriers are respectively 1.66 and 1.56 eV, which are remarkably higher than the minimum diffusion energy barrier of one F atom and two F atoms on pristine silicene 1.00 and 1.29 eV, respectively. Therefore, the thermal stability of SFNRs can be significantly enhanced by increasing the F diffusion barriers through silicene/fluorosilicene interface engineering. In addition, the electronic and magnetic properties of SFNRs are also investigated. It is found that the armchair SFNRs are nonmagnetic semiconductors, and the band gap of armchair SFNRs presents oscillatory behavior when the width of silicene part changing. For the zigzag SFNRs, the antiferromagnetic semiconducting state is the most stable one. This work provides fundamental insights for the applications of SFNRs in electronic devices.

  4. The electronic structure of VO in its ground and electronically excited states: A combined matrix isolation and quantum chemical (MRCI) study

    SciTech Connect

    Hübner, Olaf; Hornung, Julius; Himmel, Hans-Jörg

    2015-07-14

    The electronic ground and excited states of the vanadium monoxide (VO) molecule were studied in detail. Electronic absorption spectra for the molecule isolated in Ne matrices complement the previous gas-phase spectra. A thorough quantum chemical (multi-reference configuration interaction) study essentially confirms the assignment and characterization of the electronic excitations observed for VO in the gas-phase and in Ne matrices and allows the clarification of open issues. It provides a complete overview over the electronically excited states up to about 3 eV of this archetypical compound.

  5. Electronic Band Structures of the Highly Desirable III-V Semiconductors: TB-mBJ DFT Studies

    NASA Astrophysics Data System (ADS)

    Rehman, Gul; Shafiq, M.; Saifullah; Ahmad, Rashid; Jalali-Asadabadi, S.; Maqbool, M.; Khan, Imad; Rahnamaye-Aliabad, H.; Ahmad, Iftikhar

    2016-07-01

    The correct band gaps of semiconductors are highly desirable for their effective use in optoelectronic and other photonic devices. However, the experimental and theoretical results of the exact band gaps are quite challenging and sometimes tricky. In this article, we explore the electronic band structures of the highly desirable optical materials, III-V semiconductors. The main reason of the ineffectiveness of the theoretical band gaps of these compounds is their mixed bonding character, where large proportions of electrons reside outside atomic spheres in the intestinal regions, which are challenging for proper theoretical treatment. In this article, the band gaps of the compounds are revisited and successfully reproduced by properly treating the density of electrons using the recently developed non-regular Tran and Blaha's modified Becke-Johnson (nTB-mBJ) approach. This study additionally suggests that this theoretical scheme could also be useful for the band gap engineering of the III-V semiconductors. Furthermore, the optical properties of these compounds are also calculated and compared with the experimental results.

  6. Study of materials and machines for 3D printed large-scale, flexible electronic structures using fused deposition modeling

    NASA Astrophysics Data System (ADS)

    Hwang, Seyeon

    The 3 dimensional printing (3DP), called to additive manufacturing (AM) or rapid prototyping (RP), is emerged to revolutionize manufacturing and completely transform how products are designed and fabricated. A great deal of research activities have been carried out to apply this new technology to a variety of fields. In spite of many endeavors, much more research is still required to perfect the processes of the 3D printing techniques especially in the area of the large-scale additive manufacturing and flexible printed electronics. The principles of various 3D printing processes are briefly outlined in the Introduction Section. New types of thermoplastic polymer composites aiming to specified functional applications are also introduced in this section. Chapter 2 shows studies about the metal/polymer composite filaments for fused deposition modeling (FDM) process. Various metal particles, copper and iron particles, are added into thermoplastics polymer matrices as the reinforcement filler. The thermo-mechanical properties, such as thermal conductivity, hardness, tensile strength, and fracture mechanism, of composites are tested to figure out the effects of metal fillers on 3D printed composite structures for the large-scale printing process. In Chapter 3, carbon/polymer composite filaments are developed by a simple mechanical blending process with an aim of fabricating the flexible 3D printed electronics as a single structure. Various types of carbon particles consisting of multi-wall carbon nanotube (MWCNT), conductive carbon black (CCB), and graphite are used as the conductive fillers to provide the thermoplastic polyurethane (TPU) with improved electrical conductivity. The mechanical behavior and conduction mechanisms of the developed composite materials are observed in terms of the loading amount of carbon fillers in this section. Finally, the prototype flexible electronics are modeled and manufactured by the FDM process using Carbon/TPU composite filaments and

  7. Ab-initio study of structural, electronic, and transport properties of zigzag GaP nanotubes.

    PubMed

    Srivastava, Anurag; Jain, Sumit Kumar; Khare, Purnima Swarup

    2014-03-01

    Stability and electronic properties of zigzag (3 ≤ n ≤ 16) gallium phosphide nanotubes (GaP NTs) have been analyzed by employing a systematic ab-intio approach based on density functional theory using generalized gradient approximation with revised Perdew Burke Ernzerhoff type parameterization. Diameter dependence of bond length, buckling, binding energy, and band gap has been investigated and the analysis shows that the bond length and buckling decreases with increasing diameter of the tube, highest binding energy of (16, 0) confirms this as the most stable amongst all the NTs taken into consideration. The present GaP NTs shows direct band gap and it increases with diameter of the tubes. Using a two probe model for (4, 0) NT the I-V relationship shows an exponential increase in current on applying bias voltage beyond 1.73 volt.

  8. Scanning tunneling microscopy studies of metal clusters supported on TiO 2 (110): Morphology and electronic structure

    NASA Astrophysics Data System (ADS)

    Lai, X.; Clair, T. P. St.; Valden, M.; Goodman, D. W.

    1998-12-01

    A brief review of our laboratory's recent scanning tunneling microscopy (STM) studies on nanoclusters supported on TiO 2(110) is presented. Particular emphasis is placed on the system {Au}/{TiO2(110) }. The nucleation and growth of the clusters, which were vapor-deposited on TiO 2(110) under ultra high vacuum (UHV) conditions, were investigated using STM. It was found that Au, Pd, and Ag clusters all grow in a three-dimensional (3D) (Volmer-Weber) fashion on TiO 2(110), but that at low coverages, quasi-two dimensional (quasi-2D) Au and Pd clusters were observed. These quasi-2D clusters are characterized by heights of 1-2 atomic layers. Annealing studies show that Au and Pd clusters form large microcrystals with well-defined hexagonal shapes. Al clusters, which have a strong interaction with the substrate, are oxidized upon deposition, “wetting” the surface and forming small clusters. In addition to the topographic studies, the local electronic properties of these clusters have been studied using scanning tunneling spectroscopy (STS) to measure the cluster band gaps. The electronic structure was found to be cluster size-dependent, as seen by the appearance of a band gap as the cluster size decreased. More specifically, the onset of cluster metallic properties correlates with the transition from quasi-2D to 3D cluster growth.

  9. First-principles study of the electronic structure of nonmetal-doped anatase TiO2

    NASA Astrophysics Data System (ADS)

    Wang, Yuan; Ma, Jing; Zhou, Jian-Ping; Chen, Xiao-Ming; Wang, Jing-Zhou

    2016-02-01

    In this paper, we present a detailed study of the structure, defect formation energy, and electronic and magnetic properties of nonmetal-doped TiO2 by using the first-principles projector augmented wave (PAW) potential within the generalized gradient approximation (GGA). The formation energy reduces with increasing electronegativity of the dopant. After doping with nonmetal elements, some band gaps of the doped-TiO2 become narrow, and others become wide, in which impurity states appear in the band gap. The relative positions of the impurity states are much different, mainly caused by the different electronegativities of the nonmetal elements F, O, B, C and N. When H is added to achieve a charge balance, the impurity states approach the valence band maximum, because the electronegativity difference among the nonmetal elements is decreased. Therefore, nonmetal and H codoping is an effective way to improve the visible-light catalytic activity of anatase TiO2. In addition, N-doping and C-doping can cause spin polarization of the TiO2 electronic structure and form 1.0 μ B and 2.0 μ B magnetic moment, respectively.

  10. First-principle study of the electronic structure and magnetism of lithium-adsorbed 3d transition-metal phthalocyanines

    NASA Astrophysics Data System (ADS)

    Wang, M.; Hu, Y.; Zhang, Z.; Li, Y.; Zhou, T.; Ren, J.

    2016-02-01

    Based on density functional theory (DFT) calculations, the electronic structures and magnetic properties of 3d transition-metal phthalocyanine (TMPc, TM = Ti, V, Cr, Mn, Fe, Co, Ni and Cu), as well as Li-adsorbed phthalocyanines have been studied. The results show that the pristine TMPcs all have a good D4h symmetry. When there is one Li atom adsorbed on TMPcs directly over (LiTMPc-α) or slantly above (LiTMPc-β) the TM atoms, the geometries and electronic structures will be changed. For LiTMPc-α systems, the central TM atoms will deviate from the molecular plane and the molecules exhibit good C4v symmetry. LiTMPc-β systems are more stable than LiTMPc-α systems but it do not possess D4h and C4v symmetries. The total and local magnetic moments and the charge transfer are also presented. Finally, by using the orbit mixing and splitting theory under D4h and C4v symmetry, we get the ordering of the energy levels of the central TM atoms.

  11. Quantum entanglement in manganese(II) hexakisimidazole nitrate: on electronic structure imaging - A polarized neutron diffraction and DFT study

    NASA Astrophysics Data System (ADS)

    Wallace, Warren A.

    2016-04-01

    Quantum entanglement has been visualized for the first time, in view of the spin density distribution and electronic structure for manganese in manganese(II)hexakisimidazole nitrate. Using polarized neutron diffraction and density functional theory modelling we have found for the complex, which crystallizes in the R3¯ spacegroup, a = b = 12.4898(3) Å, c = 14.5526(4) Å, α = γ = 90°, β = 120°, Z = 3, that spatially antisymmetric and spatially symmetric shaped regions of negative spin density, in the spin density map for manganese, are a result of quantum entanglement of the high spin d5 configuration due to dative imidazole- manganese π- donation and σ-bonding interactions respectively. We have found leakage of the entangled states for manganese observed as regions of positive spin density with spherical (3.758(2) μB) and non-spherical (1.242(3) μB) contributions. Our results, which are supportive of Einstein's theory of general relativity, provide evidence for the existence of a black hole spin density distribution at the origin of an electronic structure and also address the paradoxical views of entanglement and quantum mechanics. We have also found the complex, which is an insulator, to be suitable for spintronic studies.

  12. Electronic structure of octane on Cu(1 1 1) and Ni(1 1 1) studied by near edge X-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Kiguchi, Manabu; Entani, Shiro; Ikeda, Susumu; Yoshikawa, Genki; Nakai, Ikuyo; Kondoh, Hiroshi; Ohta, Toshiaki; Saiki, Koichiro

    2007-09-01

    The electronic structure of an octane film grown on Cu(1 1 1) and Ni(1 1 1) was studied using C K-edge near edge X-ray absorption fine structure (NEXAFS). A pre-peak was observed on the bulk edge onset for the 1 ML thick octane films on the metal substrates. The pre-peak originated from metal induced gap states (MIGS) in the band gap of octane. The intensity of the pre-peak for octane/Ni(1 1 1) was the same as that of octane/Cu(1 1 1), suggesting that there was little difference in the density of unoccupied MIGS between the octane film on Ni(1 1 1) and Cu(1 1 1). We discuss the metal dependence of the density of unoccupied MIGS on the band structure of the metals.

  13. Theoretical Studies on Docking Dynamics and Electronic Structure in Metalloprotein Complexes

    NASA Astrophysics Data System (ADS)

    Sugiyama, Ayumu; Nishikawa, Keigo; Yamamoto, Tetsunori; Purqon, Acep; Nishikawa, Kiyoshi; Nagao, Hidemi

    2007-12-01

    An investigating of docking structure and dynamics between metalloprotein is interested from the viewpoint of searching the function of protein. We investigate the cytochrome c551 and azurin complexes by three computational methods, quantum mechanical calculation, docking searching algorism and molecular dynamics simulation. At first we present the docking structure of the cytochrome c551-azurin complexes expected by ZDOCK searching algorism. Quantum chemical calculation is tools to estimate the charge distrubution around the active site for each protein and force field parameters. From these parameters, we reproduce the protein docking dynamics by molecular dynamics simulation. We analyze some physical properties of complex system such as binding free energy, dynamical cross correlation map, and so on. We discuss the docking stability and dynamical effect of the cytochrome c551-azurin complexes.

  14. Crystal structure of CD155 and electron microscopic studies of its complexes with polioviruses

    SciTech Connect

    Zhang, Ping; Mueller, Steffen; Morais, Marc C.; Bator, Carol M.; Bowman, Valorie D.; Hafenstein, Susan; Wimmer, Eckard; Rossmann, Michael G.

    2010-11-02

    When poliovirus (PV) recognizes its receptor, CD155, the virus changes from a 160S to a 135S particle before releasing its genome into the cytoplasm. CD155 is a transmembrane protein with 3 Ig-like extracellular domains, D1-D3, where D1 is recognized by the virus. The crystal structure of D1D2 has been determined to 3.5-{angstrom} resolution and fitted into {approx}8.5-{angstrom} resolution cryoelectron microscopy reconstructions of the virus-receptor complexes for the 3 PV serotypes. These structures show that, compared with human rhinoviruses, the virus-receptor interactions for PVs have a greater dependence on hydrophobic interactions, as might be required for a virus that can inhabit environments of different pH. The pocket factor was shown to remain in the virus during the first recognition stage. The present structures, when combined with earlier mutational investigations, show that in the subsequent entry stage the receptor moves further into the canyon when at a physiological temperature, thereby expelling the pocket factor and separating the viral subunits to form 135S particles. These results provide a detailed analysis of how a nonenveloped virus can enter its host cell.

  15. Electronic structure calculations in arbitrary electrostatic environments

    NASA Astrophysics Data System (ADS)

    Watson, Mark A.; Rappoport, Dmitrij; Lee, Elizabeth M. Y.; Olivares-Amaya, Roberto; Aspuru-Guzik, Alán

    2012-01-01

    Modeling of electronic structure of molecules in electrostatic environments is of considerable relevance for surface-enhanced spectroscopy and molecular electronics. We have developed and implemented a novel approach to the molecular electronic structure in arbitrary electrostatic environments that is compatible with standard quantum chemical methods and can be applied to medium-sized and large molecules. The scheme denoted CheESE (chemistry in electrostatic environments) is based on the description of molecular electronic structure subject to a boundary condition on the system/environment interface. Thus, it is particularly suited to study molecules on metallic surfaces. The proposed model is capable of describing both electrostatic effects near nanostructured metallic surfaces and image-charge effects. We present an implementation of the CheESE model as a library module and show example applications to neutral and negatively charged molecules.

  16. The Electronic Structure of Heavy Element Complexes

    SciTech Connect

    Bursten, Bruce E.

    2000-07-25

    The area of study is the bonding in heavy element complexes, and the application of more sophisticated electronic structure theories. Progress is recounted in several areas: (a) technological advances and current methodologies - Relativistic effects are extremely important in gaining an understanding of the electronic structure of compounds of the actinides, transactinides, and other heavy elements. Therefore, a major part of the continual benchmarking was the proper inclusion of the appropriate relativistic effects for the properties under study. (b) specific applications - These include organoactinide sandwich complexes, CO activation by actinide atoms, and theoretical studies of molecules of the transactinide elements. Finally, specific directions in proposed research are described.

  17. Tunable electronic structures of germanium monochalcogenide nanosheets via light non-metallic atom functionalization: a first-principles study.

    PubMed

    Ding, Yi; Wang, Yanli

    2016-08-17

    Germanium monochalcogenides, i.e. GeS and GeSe sheets, are isoelectronic analogues of phosphorene, which have been synthesized in recent experiments (P. Ramasamy et al., J. Mater. Chem. C, 2016, 4, 479). Utilizing first-principles calculations, we have investigated their tunable electronic and magnetic properties via light non-metallic atom (B, C, N, O, Si, P, S) functionalization. We find that on these GeS and GeSe sheets O and S adatoms prefer to locate at the top site above the Ge atom, while the other ones like to occupy the anion site, which push the original S/Se atom to the hollow site instead. O and S adatoms slightly affect the semiconducting behaviour of the doped systems, while B, C, N, Si, P ones will drastically modify their band structures and induce versatile spintronic properties. Through the supercell calculations, B and C adatoms are found to induce a bipolar semiconducting behaviour in the decorated systems, while the N/P adatom will cause a spin-gapless-semiconducting/nearly-half-metallic feature in them. The B/C/N/Si/P-substituted GeS/GeSe sheet can be formed by removing the hollow-site S/Se atom from the adatom-decorated structures, which exhibit an opposite semiconducting/metallic behaviour to their phosphorene counterparts. A general odd-even rule is proposed for this phenomenon, which shows that an odd (even) number of valence electron difference between the substitution and host atoms would cause a metallic (semiconducting) feature in the substituted systems. Our study demonstrates that atom functionalization is an efficient way to tailor the properties of GeS and GeSe nanosheets, which have adaptable electronic properties for potential applications in nanoelectronics and spintronics. PMID:27491896

  18. Tunable electronic structures of germanium monochalcogenide nanosheets via light non-metallic atom functionalization: a first-principles study.

    PubMed

    Ding, Yi; Wang, Yanli

    2016-08-17

    Germanium monochalcogenides, i.e. GeS and GeSe sheets, are isoelectronic analogues of phosphorene, which have been synthesized in recent experiments (P. Ramasamy et al., J. Mater. Chem. C, 2016, 4, 479). Utilizing first-principles calculations, we have investigated their tunable electronic and magnetic properties via light non-metallic atom (B, C, N, O, Si, P, S) functionalization. We find that on these GeS and GeSe sheets O and S adatoms prefer to locate at the top site above the Ge atom, while the other ones like to occupy the anion site, which push the original S/Se atom to the hollow site instead. O and S adatoms slightly affect the semiconducting behaviour of the doped systems, while B, C, N, Si, P ones will drastically modify their band structures and induce versatile spintronic properties. Through the supercell calculations, B and C adatoms are found to induce a bipolar semiconducting behaviour in the decorated systems, while the N/P adatom will cause a spin-gapless-semiconducting/nearly-half-metallic feature in them. The B/C/N/Si/P-substituted GeS/GeSe sheet can be formed by removing the hollow-site S/Se atom from the adatom-decorated structures, which exhibit an opposite semiconducting/metallic behaviour to their phosphorene counterparts. A general odd-even rule is proposed for this phenomenon, which shows that an odd (even) number of valence electron difference between the substitution and host atoms would cause a metallic (semiconducting) feature in the substituted systems. Our study demonstrates that atom functionalization is an efficient way to tailor the properties of GeS and GeSe nanosheets, which have adaptable electronic properties for potential applications in nanoelectronics and spintronics.

  19. Electron Coherence in Mesoscopic Structures

    SciTech Connect

    Kamenev, Alex; Glazman, Leonid

    2011-03-20

    The recent rapid progress in nanofabrication and experimental techniques made it possible to investigate a variety of meso-- and nano--scale systems, which were unavailable only a few years ago. Examples include fabrication of high-quality quantum wires in semiconductor heterostructures, of nanoscale hybrid superconductor--normal metal structures, and of a variety of novel (and much smaller) quantum dot and q-bit designs. These technological advances have led to formulation of a number of condensed matter theory problems which are equally important for applications and for the fundamental science. The present proposal aims at filling the exposed gaps in knowledge and at facilitating further development of experimental and theoretical physics of nanoscale structures. Specifically, the two PIs address the following issues: (i) The theory of interacting electrons in a quantum wire which accounts adequately for the non-linear dispersion relation of the electrons. The existing approaches rely on models with {\\em linearized} electron spectrum, which fall short of addressing a growing list of experimentally relevant phenomena. (ii) Dynamics of hybrid normal--superconducting systems. A reliable treatment of dissipative phenomena in such structures is not developed as of yet, while rapid progress in fabrication makes finding the proper theoretical treatment methods highly desirable. (iii)~The fundamental limits on relaxation times of a superconducting charge q-bit. The latter is one of the most advanced scalable realizations of a quantum computing device. (iv)~The dynamics and relaxation times of a spin of an electron in a small semiconductor quantum dot. Besides the fundamental importance, these structures are also valuable candidates for quantum computing applications.

  20. A first principles study of structural, electronic mechanical and magnetic properties of rare earth nitride:TmN

    NASA Astrophysics Data System (ADS)

    Murugan, A.; Rajeswarapalanichamy, R.; Santhosh, M.; Manikandan, M.

    2016-05-01

    The structural, electronic and mechanical properties of rare earth nitride TmN is investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At ambient pressure TmN is stable in the ferromagnetic state with NaCl structure. The calculated lattice parameters are in good agreement with the available results. The electronic structure reveals that TmN is metallic at normal pressure. Ferromagnetic to non magnetic phase transition is predicted in TmN at high pressure.

  1. Ab initio study of electron-ion structure factors in binary liquids with different types of chemical bonding

    SciTech Connect

    Klevets, Ivan; Bryk, Taras

    2014-12-07

    Electron-ion structure factors, calculated in ab initio molecular dynamics simulations, are reported for several binary liquids with different kinds of chemical bonding: metallic liquid alloy Bi–Pb, molten salt RbF, and liquid water. We derive analytical expressions for the long-wavelength asymptotes of the partial electron-ion structure factors of binary systems and show that the analytical results are in good agreement with the ab initio simulation data. The long-wavelength behaviour of the total charge structure factors for the three binary liquids is discussed.

  2. Electron microscope studies

    SciTech Connect

    Crewe, A.V.; Kapp, O.H.

    1991-06-01

    This year our laboratory has continued to make progress in the design of electron-optical systems, in the study of structure-function relationships of large multi-subunit proteins, in the development of new image processing software and in achieving a workable sub-angstrom STEM. We present an algebraic approach to the symmetrical Einzel (unipotential) lens wherein we simplify the analysis by specifying a field shape that meets some preferred set of boundary or other conditions and then calculate the fields. In a second study we generalize this approach to study of three element electrostatic lenses of which the symmetrical Einzel lens is a particular form. The purpose is to develop a method for assisting in the design of a lens for a particular purpose. In our biological work we study a stable and functional dodecameric complex of globin chains from the hemoglobin of Lumbricus terrestris. This is a complex lacking the linker'' subunit first imaged in this lab and required for maintenance of the native structure. In addition, we do a complete work-up on the hemoglobin of the marine polychaete Eudistylia vancouverii demonstrating the presence of a hierarchy of globin complexes. We demonstrate stable field-emission in the sub-angstrom STEM and the preliminary alignment of the beam. We continue our exploration of a algorithms for alignment of sequences of protein and DNA. Our computer facilities now include four second generation RISC workstations and we continue to take increasing advantage of the floating-point and graphical performance of these devices.

  3. Electron microscope studies

    NASA Astrophysics Data System (ADS)

    Crewe, A. V.; Kapp, O. H.

    1991-06-01

    This year our laboratory has continued to make progress in the design of electron-optical systems, in the study of structure-function relationships of large multi-subunit proteins, in the development of new image processing software and in achieving a workable sub-angstrom STEM. We present an algebraic approach to the symmetrical Einzel (unipotential) lens wherein we simplify the analysis by specifying a field shape that meets some preferred set of boundary or other conditions and then calculate the fields. In a second study we generalize this approach to study of three element electrostatic lenses of which the symmetrical Einzel lens is a particular form. The purpose is to develop a method for assisting in the design of a lens for a particular purpose. In our biological work we study a stable and functional dodecameric complex of globin chains from the hemoglobin of Lumbricus terrestris. This is a complex lacking the 'linker' subunit first imaged in this lab and required for maintenance of the native structure. In addition, we do a complete work-up on the hemoglobin of the marine polychaete Eudistylia vancouverii, demonstrating the presence of a hierarchy of globin complexes. We demonstrate stable field-emission in the sub-angstrom STEM and the preliminary alignment of the beam. We continue our exploration of a algorithms for alignment of sequences of protein and DNA. Our computer facilities now include four second generation RISC workstations and we continue to take increasing advantage of the floating-point and graphical performance of these devices.

  4. Study of the structural and electronic properties of YC using DFT: The true ground state is a NiAs-like structure

    NASA Astrophysics Data System (ADS)

    Abdel-Rahim, G. P.; Rodríguez M, J. A.; Moreno-Armenta, M. G.

    2013-11-01

    We study the structural and electronic properties of YC in volume using density functional theory (DFT) within the generalized gradient approximation (GGA), using the scheme of Wu-Cohen 2006 and Tran et al. 2007. Several crystal structures were considered: Nickel Arsenide (NiAs), Sodium Chloride (NaCl), Cesium Chloride (CsCl), and zincblende (ZB). A new fact that we present in this paper is the inclusion of the NiAs-like structure, which is the true ground state (GS) for YC. We calculated the density of states (DOS) and the band structure and found that YC is non-magnetic and its behavior is metallic-like. The lattice parameter alatt is 3.69 Å and the c/a = 1.47. Cohesion energy (Ecoh) is -12.90 eV, which is very close to Ecoh of the NaCl structure. Therefore, YC exists in these two structures. Our results with respect to alatt, bulk modulus (B), Ecoh, and the main features of the electronic properties are in good agreement with those found by other researchers. Other researchers found a transition from NaCl to CsCl, but we found a new transition from NiAs to CsCl, where the volume diminishes ~10% and its transition pressure (PT ~79 GPa) is very close to the 80 GPa of the former. The contraction can fracture the material if it is worked on near the transition. For pressures before and after the transition, YC maintains non-magnetic and metallic behaviors.

  5. Theoretical studies on the SiC radical: electronic structure, spectroscopy and spin-orbit couplings

    NASA Astrophysics Data System (ADS)

    Shi, D. H.; Xing, W.; Sun, J. F.; Zhu, Z. L.

    2012-10-01

    The potential energy curves (PECs) of twenty-five Λ-S states and twenty Ω states generated from eight Λ-S states of the SiC radical are calculated by using an ab initio quantum chemical method. The PEC calculations are performed for internuclear separations from 0.10 to 1.00 nm using the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction (MRCI) approach in combination with a correlation-consistent aug-cc-pV6Z basis set. To improve the quality of the PECs, core-valence correlation and relativistic corrections are included. Core-valence correlations are included using a cc-pCVTZ basis set. Relativistic corrections are calculated using the third-order Douglas-Kroll Hamiltonian approximation at the level of cc-pV5Z basis set. The spin-orbit coupling effect is accounted for by the Breit-Pauli Hamiltonian in combination with the aug-cc-pVTZ basis set. To obtain more reliable results, the PECs determined by the MRCI calculations are corrected for size-extensivity errors by means of the Davidson modification. The PECs are extrapolated to the complete basis set (CBS) limit by the total-energy extrapolation scheme. The spectroscopic parameters are obtained by fitting the vibrational levels, which are calculated by solving the ro-vibrational Schrödinger equation using the Numerov's method. The spectroscopic results are compared with those reported in the literature. Excellent agreement has been found between the present results and the measurements. The vibrational manifolds of the first 30 vibrational states are calculated for each electronic state of the non-rotating radical. Comparison with the measurements demonstrates that the present results are accurate. The spectroscopic parameters and the molecular constants reported here are expected to be reliable predicted results. Tables S1-S5 are only available in eletronic form at http://www.epj.org

  6. A first principles study of structural stability, electronic structure and mechanical properties of ABeH{sub 3} (A = Li, Na)

    SciTech Connect

    Santhosh, M.; Rajeswarapalanichamy, R.; Priyanga, G. Sudha; Murugan, A.; Kanagaprabha, S.; Iyakutti, K.

    2015-06-24

    Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of ABeH{sub 3} (A = Li, Na) for three different crystal structures, namely orthorhombic (Pnma), monoclinic (P2{sub 1}/c) and triclinic (P-1) phase. Among the considered structures monoclinic (P2{sub 1}/c) phase is found to be the most stable one for all the three hydrides at ambient condition. The electronic structure reveals that these materials are wide band gap semiconductors. The calculated elastic constants indicate that these materials are mechanically stable at ambient condition.

  7. A combined photoelectron spectroscopy and relativistic ab initio studies of the electronic structures of UFO and UFO(-).

    PubMed

    Roy, Soumendra K; Jian, Tian; Lopez, Gary V; Li, Wei-Li; Su, Jing; Bross, David H; Peterson, Kirk A; Wang, Lai-Sheng; Li, Jun

    2016-02-28

    The observation of the gaseous UFO(-) anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO(-) is linear with an O-U-F structure and a (3)H4 spectral term derived from a U 7sσ(2)5fφ(1)5fδ(1) electron configuration, whereas the ground state of neutral UFO has a (4)H(7/2) spectral term with a U 7sσ(1)5fφ(1)5fδ(1) electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations. PMID:26931704

  8. A combined photoelectron spectroscopy and relativistic ab initio studies of the electronic structures of UFO and UFO(-).

    PubMed

    Roy, Soumendra K; Jian, Tian; Lopez, Gary V; Li, Wei-Li; Su, Jing; Bross, David H; Peterson, Kirk A; Wang, Lai-Sheng; Li, Jun

    2016-02-28

    The observation of the gaseous UFO(-) anion is reported, which is investigated using photoelectron spectroscopy and relativisitic ab initio calculations. Two strong photoelectron bands are observed at low binding energies due to electron detachment from the U-7sσ orbital. Numerous weak detachment bands are also observed due to the strongly correlated U-5f electrons. The electron affinity of UFO is measured to be 1.27(3) eV. High-level relativistic quantum chemical calculations have been carried out on the ground state and many low-lying excited states of UFO to help interpret the photoelectron spectra and understand the electronic structure of UFO. The ground state of UFO(-) is linear with an O-U-F structure and a (3)H4 spectral term derived from a U 7sσ(2)5fφ(1)5fδ(1) electron configuration, whereas the ground state of neutral UFO has a (4)H(7/2) spectral term with a U 7sσ(1)5fφ(1)5fδ(1) electron configuration. Strong electron correlation effects are found in both the anionic and neutral electronic configurations. In the UFO neutral, a high density of electronic states with strong configuration mixing is observed in most of the scalar relativistic and spin-orbit coupled states. The strong electron correlation, state mixing, and spin-orbit coupling of the electronic states make the excited states of UFO very challenging for accurate quantum chemical calculations.

  9. Electronic structure of individual hybrid colloid particles studied by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the X-ray microscope.

    PubMed

    Henzler, Katja; Guttmann, Peter; Lu, Yan; Polzer, Frank; Schneider, Gerd; Ballauff, Matthias

    2013-02-13

    The electronic structure of individual hybrid particles was studied by nanoscale near-edge X-ray absorption spectromicroscopy. The colloidal particles consist of a solid polystyrene core and a cross-linked poly-N-(isopropylacrylamide) shell with embedded crystalline titanium dioxide (TiO(2)) nanoparticles (d = 6 ± 3 nm). The TiO(2) particles are generated in the carrier network by a sol-gel process at room temperature. The hybrid particles were imaged with photon energy steps of 0.1 eV in their hydrated environment with a cryo transmission X-ray microscope (TXM) at the Ti L(2,3)-edge. By analyzing the image stacks, the obtained near-edge X-ray absorption fine structure (NEXAFS) spectra of our individual hybrid particles show clearly that our synthesis generates TiO(2) in the anastase phase. Additionally, our spectromicroscopy method permits the determination of the density distribution of TiO(2) in single carrier particles. Therefore, NEXAFS spectroscopy combined with TXM presents a unique method to get in-depth insight into the electronic structure of hybrid materials. PMID:23360082

  10. CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES: First-Principles Study of Structural, Elastic and Electronic Properties of OsSi

    NASA Astrophysics Data System (ADS)

    Li, Jin; Linghu, Rong-Feng; Yang, Ze-Jin; Cao, Yang; Yang, Xiang-Dong

    2009-10-01

    First-principles study of structural, elastic, and electronic properties of the B20 structure OsSi has been reported using the plane-wave pseudopotential density functional theory method. The calculated equilibrium lattice and elastic constants are in good agreement with the experimental data and other theoretical results. The dependence of the elastic constants, the aggregate elastic modulus, the deviation from the Cauchy relation, the elastic wave velocities in different directions and the elastic anisotropy on pressure have been obtained and discussed. This could be the first quantitative theoretical prediction of the elastic properties under high pressure of OsSi compound. Moreover, the electronic structure calculations show that OsSi is a degenerate semiconductor with the gap value of 0.68 eV, which is higher than the experimental value of 0.26 eV. The analysis of the PDOS reveals that hybridization between Os d and Si p states indicates a certain covalency of the Os-Si bonds.

  11. Density functional theory study of the electronic structure and the thermoelectric properties of strained Mn4Si7

    NASA Astrophysics Data System (ADS)

    Cuong, Do Duc; Park, Jin Sik; Rhim, S. H.; Hong, Soon Cheol; Lee, Joo-Hyong

    2016-08-01

    The effect of strain on the electronic structure and the thermoelectric properties of higher manganese silicide (HMS) Mn4Si7 was studied by using density functional theory (DFT) and by solving Boltzmann transport equation (BTE). We found that tensile strain reduced the band gap while compressive strain did not affect the band gap much. The electrical conductivity shows highly anisotropic with the in-plane direction being more dominant while the Seebeck coefficient does not change much, which leads to the the power factor along the in-plane direction being higher compared with that along the out-of-plane direction. The anisotropy of the electrical conductivity was due to a change of the band dispersion in the valence-band maximum (VBM). It was suggested that compressive strain can improve the power factor of Mn4Si7.

  12. Structural, electronic and magnetic properties of (N, C)-codoped ZnO nanotube: First principles study

    NASA Astrophysics Data System (ADS)

    Esmailian, Amirhosein; Shahrokhi, Masoud; Kanjouri, Faramarz

    2015-04-01

    We have studied the electronic structure and magnetic properties of Nitrogen and Carbon codoped ZnO (5,0) single-walled zigzag nanotube using first-principle calculations based on the density functional theory. We performed our calculations for N- and C- codoping ZnO nanotube in two different configurations. For the first configuration in which the two impurity atoms (N or C) are on first nearest-neighbor sites in the plane of codoping, our calculation predicts that the N- and C-codoped ZnO nanotubes are antiferromagnetic material with no net magnetization. On the other hand, it is found that for the configuration in which the two impurity atoms are next nearest-neighbors, a spin polarization results in a magnetic moment in the N- and C-codoped ZnO nanotubes.

  13. X-ray spectroscopy study of electronic structure of laser-irradiated Au nanoparticles in a silica film

    SciTech Connect

    Jonnard, P.; Bercegol, H.; Lamaignere, L.; Morreeuw, J.-P.; Rullier, J.-L.; Cottancin, E.; Pellarin, M.

    2005-03-15

    The electronic structure of gold nanoparticles embedded in a silica film is studied, both before and after irradiation at 355 nm 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 0.5 J/cm{sup 2}, 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, 1 J/cm{sup 2}, we find a higher percentage of metallic gold that could be attributed to annealing in the silica matrix.

  14. Comparative Study of Electronic Structure and Thermoelectric Properties of SnSe for Pnma and Cmcm Phase

    NASA Astrophysics Data System (ADS)

    Xu, Bin; Zhang, Jing; Yu, Gongqi; Ma, Shanshan; Wang, Yusheng; Yi, Lin

    2016-10-01

    The electronic structure and thermoelectric properties of SnSe have been studied according to first principles and semiclassical Boltzmann theory. The decrease of the density of states (DOS) for SnSe from Pnma to Cmcm phase is mainly due to the decrease of Sn p-states and Se p-states. The main Seebeck coefficient peaks are higher for Pnma than Cmcm phase. The peak values of S 2 σ/ τ increase faster with carrier concentration and temperature for n- compared with p-doping, indicating that n-doping can greatly enhance the electrical transport properties for Pnma phase, whereas the peak values for n-doping are almost the same as with p-doping for the Cmcm phase. It is also found that n-doping in the SnSe compound may be more favorable for thermoelectric performance for Pnma phase.

  15. High-energy x-ray and transmission electron microscopy study of structural transformations in Ti-V

    NASA Astrophysics Data System (ADS)

    Ramsteiner, I. B.; Schöps, A.; Phillipp, F.; Kelsch, M.; Reichert, H.; Dosch, H.; Honkimäki, V.

    2006-01-01

    The binary system Ti-V is a paradigm for the technically important class of Ti β alloys. In the past, it received attention as a candidate for transient ordering. We elucidate the nature of structural transformations by combining transmission electron microscopy (TEM) and a high-energy x-ray diffraction technique. The latter allows to study precipitation processes time resolved and in situ, while TEM is a powerful tool to identify individual phases. In addition to α -Ti precipitation we observe the formation of TiC from minor carbon impurities. Additional diffraction peaks accompanying the α -Ti precipitation and hinting at the existence of a B2-type superstructure are shown to originate from the precipitates. No transient ordering was found.

  16. Fluorophore(s) appended fullerene dyads and triads for probing photoinduced energy transfer: syntheses, electronic structure, and fluorescence studies.

    PubMed

    Deviprasad, Gollapalli R; Smith, Phillip M; Zandler, Melvin E; Rogers, Lisa M; D'Souza, Francis

    2006-01-01

    Fullerene, C(60) was functionalized to possess one or two fluorophore entities. The fluorophore-fullerene dyads thus synthesized contain either a naphthalene, pyrene, or fluorene entity while the triads contain either a pyrene or fluorene entity in addition to a naphthalene entity. The redox behavior of these dyads and triads were probed by cyclic voltammetric technique, while the geometry and electronic structures were deduced from ab initio B3LYP/3-21G(*) method. Steady-state emission studies revealed the occurrence of energy transfer from the singlet excited fluorophore to the fullerene entity in the case of the dyads while the occurrence of step-by-step sequential energy transfer is envisioned in the case of the triads. A better 'antenna-effect' owing to the extended range of excitation wavelength to induce energy transfer to the appended fullerene has been achieved in the case of the triads. PMID:16404521

  17. Opportunities and challenges for time-resolved studies of protein structural dynamics at X-ray free-electron lasers

    PubMed Central

    Neutze, Richard

    2014-01-01

    X-ray free-electron lasers (XFELs) are revolutionary X-ray sources. Their time structure, providing X-ray pulses of a few tens of femtoseconds in duration; and their extreme peak brilliance, delivering approximately 1012 X-ray photons per pulse and facilitating sub-micrometre focusing, distinguish XFEL sources from synchrotron radiation. In this opinion piece, I argue that these properties of XFEL radiation will facilitate new discoveries in life science. I reason that time-resolved serial femtosecond crystallography and time-resolved wide angle X-ray scattering are promising areas of scientific investigation that will be advanced by XFEL capabilities, allowing new scientific questions to be addressed that are not accessible using established methods at storage ring facilities. These questions include visualizing ultrafast protein structural dynamics on the femtosecond to picosecond time-scale, as well as time-resolved diffraction studies of non-cyclic reactions. I argue that these emerging opportunities will stimulate a renaissance of interest in time-resolved structural biochemistry. PMID:24914150

  18. Orientation and electronic structure of ion exchanged dye molecules on mica: An X-ray absorption study

    SciTech Connect

    Fischer, D.; Caseri, W.R.; Haehner, G.

    1998-02-15

    Dye molecules are frequently used to determine the specific surface area and the ion exchange capacity of high-surface-area materials such as mica. The organic molecules are often considered to be planar and to adsorb in a flat orientation. In the present study the authors have investigated the orientation and electronic structure of crystal violet (CV) and malachite green (MG) on muscovite mica, prepared by immersing the substrates for extended periods into aqueous solutions of the dyes of various concentrations. The K{sup +} ions of the mica surface are replaced by the organic cations via ion exchange. X-ray photoelectron spectroscopy reveals that only one amino group is involved in the interaction of CV and MG with the muscovite surface, i.e., certain resonance structures are abolished upon adsorption. With near edge X-ray absorption fine structure spectroscopy a significant tilt angle with respect to the surface was found for all investigated species. A flat orientation, as has often been proposed before, can effectively be ruled out. Hence, results are in marked contrast to the often quoted orientation and suggest that the specific surface areas determined with dyes may, in general, be overestimated.

  19. Opportunities and challenges for time-resolved studies of protein structural dynamics at X-ray free-electron lasers.

    PubMed

    Neutze, Richard

    2014-07-17

    X-ray free-electron lasers (XFELs) are revolutionary X-ray sources. Their time structure, providing X-ray pulses of a few tens of femtoseconds in duration; and their extreme peak brilliance, delivering approximately 10(12) X-ray photons per pulse and facilitating sub-micrometre focusing, distinguish XFEL sources from synchrotron radiation. In this opinion piece, I argue that these properties of XFEL radiation will facilitate new discoveries in life science. I reason that time-resolved serial femtosecond crystallography and time-resolved wide angle X-ray scattering are promising areas of scientific investigation that will be advanced by XFEL capabilities, allowing new scientific questions to be addressed that are not accessible using established methods at storage ring facilities. These questions include visualizing ultrafast protein structural dynamics on the femtosecond to picosecond time-scale, as well as time-resolved diffraction studies of non-cyclic reactions. I argue that these emerging opportunities will stimulate a renaissance of interest in time-resolved structural biochemistry.

  20. Structural Dynamics of Electronic Systems

    NASA Astrophysics Data System (ADS)

    Suhir, E.

    2013-03-01

    The published work on analytical ("mathematical") and computer-aided, primarily finite-element-analysis (FEA) based, predictive modeling of the dynamic response of electronic systems to shocks and vibrations is reviewed. While understanding the physics of and the ability to predict the response of an electronic structure to dynamic loading has been always of significant importance in military, avionic, aeronautic, automotive and maritime electronics, during the last decade this problem has become especially important also in commercial, and, particularly, in portable electronics in connection with accelerated testing of various surface mount technology (SMT) systems on the board level. The emphasis of the review is on the nonlinear shock-excited vibrations of flexible printed circuit boards (PCBs) experiencing shock loading applied to their support contours during drop tests. At the end of the review we provide, as a suitable and useful illustration, the exact solution to a highly nonlinear problem of the dynamic response of a "flexible-and-heavy" PCB to an impact load applied to its support contour during drop testing.

  1. Ab initio study of the structural, elastic, thermodynamic, electronic and vibration properties of TbMg intermetallic compound

    NASA Astrophysics Data System (ADS)

    Mogulkoc, Y.; Ciftci, Y. O.; Kabak, M.; Colakoglu, K.

    2014-07-01

    The structural, elastic, thermodynamic, electronic and vibrational properties of CsCl-type TbMg have been studied by performing ab initio calculations based on density functional theory using the Vienna Ab initio Simulation Package (VASP). The exchange correlation potential within the generalized-gradient approximation (GGA) of projector augmented wave (PAW) method is used. The calculated structural parameters, such as the lattice constant, bulk modulus, its pressure derivative, formation energy and second-order elastic constants are presented in this paper. The obtained results are compared with related experimental and theoretical studies. The electronic band calculations, total density of states (DOS), partial DOS and charge density are also presented. Formation enthalpy and Cauchy pressure are determined. In order to obtain more information the elastic properties such as Zener anisotropy factor, Poisson’s ratio, Young modulus, isotropic shear modulus, Debye temperature and melting point have been carried out. The elastic constants are calculated in zero and different pressure ranges (0-50 GPa) with bulk modulus. We have performed the thermodynamic properties of TbMg by using quasi-harmonic Debye model. The temperature and pressure variation of the volume, bulk modulus, and thermal expansion coefficient have been predicted over a pressure range of 0-25 GPa for of TbMg. Pressure dependence of the anisotropy factors, Young’s modulus, Poisson’s ratios, bulk modulus and axis compressibility of TbMg are presented along different directions and planes. Finally, the phonon dispersion curves are presented for TbMg.

  2. Theoretical study of the adsorption of CHO radicals on hexagonal boron nitride sheet: Structural and electronic changes

    NASA Astrophysics Data System (ADS)

    Tian, Yu; Pan, Xiao-fan; Liu, Yue-jie; Zhao, Jing-xiang

    2014-03-01

    It is well known that pristine hexagonal boron nitride sheet (h-BN sheet) exhibits large insulating band gap, thus hindering its application to some extent. In this regard, surface chemisorption of certain groups on h-BN sheet is shown to be the most popular method to tune its band gap and thus modify its electronic properties. In the present work, we performed density functional theory (DFT) calculations to study the adsorption of CHO radicals with different coverages on h-BN sheet. Particular attention is paid to explore the effects of CHO adsorption on the geometrical structures and electronic properties of h-BN sheet. The results indicate that the adsorption of a single CHO radical on pristine h-BN sheet is very weak with a negligible adsorption energy (-0.09 eV). In contrast, upon adsorption of more CHO radicals on h-BN sheet, these adsorbates prefer to adsorb in pairs on the B and the nearest N atoms from both sides of h-BN sheet. An energy diagram of the average adsorption energy of CHO radicals on h-BN sheet as a function of its coverage indicates that up to 20 CHO radicals (40%) can be attached to h-BN sheet with the adsorption energy of -0.29 eV. More importantly, the adsorption of CHO radicals can induce certain impurity states within the band gap of h-BN sheet, thus reducing the band gap and enhancing its electrical conductivity.

  3. Phosphine oxide derivatives as hosts for blue phosphors: A joint theoretical and experimental study of their electronic structure

    SciTech Connect

    Kim, Dongwook; Salman, Seyhan; Coropceanu, Veaceslav; Salomon, Eric; Padmaperuma, Asanga B.; Sapochak, Linda S.; Kahn, Antoine; Bredas, Jean-Luc

    2010-01-12

    We report on a joint theoretical and experimental investigation of the electronic structure of a series of bis(diphenylphosphine oxide) derivatives containing a central aromatic core with high triplet energy. Such molecules can serve as host material in the emissive layer of blue electro-phosphorescent organic devices. The aromatic cores considered in the theoretical study consist of biphenyl, fluorene, dibenzofuran, dibenzothiophene, dibenzothiophenesulfone or carbazole, linked to the two phosphoryl groups in either para or meta positions. With respect to the isolated core molecules, it is found that addition of the diphenylphosphine oxide moieties has hardly any impact on the core geometry and only slightly reduces the energy of the lowest triplet state (by at most ~0.2 eV). However, the diphenylphosphine oxide functionalities significantly impact the ionization potential and electron affinity values, in a way that is different for para and meta substitutions. Excellent comparison is obtained between the experimental UPS and IPES spectra of the para biphenyl and meta dibenzothiophene and dibenzothiophenesulfone compounds and the simulated spectra. In general, the phosphine oxide derivatives present triplet energies that are calculated to be at least 0.2 eV higher than those of currently widely used blue phosphorescent emitters.

  4. Structural changes in iron oxide and gold catalysts during nucleation of carbon nanotubes studied by in situ transmission electron microscopy.

    PubMed

    Tang, Dai-Ming; Liu, Chang; Yu, Wan-Jing; Zhang, Li-Li; Hou, Peng-Xiang; Li, Jin-Cheng; Li, Feng; Bando, Yoshio; Golberg, Dmitri; Cheng, Hui-Ming

    2014-01-28

    We report a simple, versatile in situ transmission electron microscopy (TEM) approach for investigating the nucleation and growth mechanism of carbon nanotubes (CNTs), by which the composition, phase transition, and physical state of various catalysts can be clearly resolved. In our approach, catalyst nanoparticles (NPs) are placed in a multiwall CNT "tubular furnace" with two open ends, and a high temperature is obtained by Joule heating in the specimen chamber of a TEM. The carbon is supplied by electron irradiation-induced injection of carbon atoms. Comparative studies on the catalytic behavior of traditional iron oxide and recently discovered gold catalysts were performed. It was found that the growth of CNTs from iron oxide involves the reduction of Fe2O3 to Fe3C, nucleation and growth of CNTs from partially liquefied Fe3C, and finally the formation of elemental Fe when the growth stops. In contrast, while changes in shape, size, and orientation were also observed for the fluctuating Au NPs, no chemical reactions or phase transitions occurred during the nucleation of CNTs. These two distinct nucleation and growth processes and mechanisms would be valuable for the structure-controlled growth of CNTs by catalyst design and engineering. PMID:24354297

  5. Ferrocene-isocoumarin conjugated molecules: synthesis, structural characterization, electronic properties, and DFT-TDDFT computational study.

    PubMed

    Peng, Ye-Dong; Zhou, Lin-Sen; Chen, Li-Li; Ma, Lu; Zhao, Yue; Zhang, Wen-Wei; Zuo, Jing-Lin

    2015-08-28

    Two ferrocene-isocoumarin conjugated molecules, methyl 3-ferrocenyl-1-oxo-1H-isochromene-6-carboxylate () and 3,8-bisferrocenylpyrano[3,4-g]isochromene-1,6-dione (), have been synthesized through the acid-prompted regioselective oxidative cyclization from dimethyl 2-(ferrocenylethynyl)terephthalate () and dimethyl 2,5-bis(ferrocenylethynyl)terephthalate (), respectively. Single-crystal X-ray diffraction, together with the density functional theory (DFT) calculations, shows that the ferrocene-isocoumarin conjugated compounds display better coplanarity than the corresponding ferrocenylethynyl terephthalates. All the compounds exhibit characteristic MLCT, ICT and π-π* transitions in the UV-visible range in solution, and and show higher oscillator strength of the absorption than and , which are verified by time-dependent DFT (TDDFT) theoretical calculations. The electrochemical properties are studied by cyclic voltammetry (CV), which are also in accord with the theoretical calculations.

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

    SciTech Connect

    Sagdeo, Archna Ghosh, Haranath Chakrabarti, Aparna Kamal, C. Ganguli, Tapas Deb, S. K.; Phase, D. M.

    2014-04-24

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

  7. Electronic structure and reactivity in water splitting of the iron oxide dimers and their hexacarbonyls: A density functional study

    SciTech Connect

    Uzunova, Ellie L.; Mikosch, Hans

    2014-01-14

    The iron oxide dimers (FeO){sub 2} and their peroxide isomers are studied with the B3LYP density functional as bare clusters and as hexacarbonyls. Among the bare clusters the planar four-member ring structures are more stable than the non-planar ones and the rhombic dioxide Fe{sub 2}O{sub 2} with antiferromagnetically ordered electrons on iron centers is the global minimum. Water adsorption on the bare diiron dioxide is exothermic, but dissociation does not occur. Carbonylation favors a non-planar Fe{sub 2}O{sub 2} ring for both the dioxides and the peroxides and high electron density at the Fe centers is induced, evidenced by the natural charge distribution, the high proton affinity, and the values of global electronegativity and hardness. The iron dioxide hexacarbonyl Fe{sub 2}O{sub 2}(CO){sub 6} is diamagnetic in the state of the global minimum. It is separated from the next low-lying triplet state by a small energy gap of 0.22 eV. Time-dependent density functional theory methods were applied to examine electron excitations from the ground state to the low-lying triplet states in the hexacarbonyls and their adsorption complexes with water. Singlet-to-triplet state excitations occur via ligand-to-metal charge transfer in the hexacarbonyls; in the adsorption complexes excitations from the oxygen lone pairs to the adsorption center also occur and they appear in the IR-visible region. The lowest energy singlet and triplet state reaction paths for water splitting were followed. On the singlet potential energy surface (PES), water splitting is spontaneous, while for the triplet PES an activation barrier of 14.1 kJ mol{sup −1} was determined.

  8. Electronic structure of interstitial hydrogen in lutetium oxide from DFT+U calculations and comparison study with μ SR spectroscopy

    NASA Astrophysics Data System (ADS)

    da Silva, E. Lora; Marinopoulos, A. G.; Vieira, R. B. L.; Vilão, R. C.; Alberto, H. V.; Gil, J. M.; Lichti, R. L.; Mengyan, P. W.; Baker, B. B.

    2016-07-01

    The electronic structure of hydrogen impurity in Lu2O3 was studied by first-principles calculations and muonium spectroscopy. The computational scheme was based on two methods which are well suited to treat defect calculations in f -electron systems: first, a semilocal functional of conventional density-functional theory (DFT) and secondly a DFT+U approach which accounts for the on-site correlation of the 4 f electrons via an effective Hubbard-type interaction. Three different types of stable configurations were found for hydrogen depending upon its charge state. In its negatively charged and neutral states, hydrogen favors interstitial configurations residing either at the unoccupied sites of the oxygen sublattice or at the empty cube centers surrounded by the lanthanide ions. In contrast, the positively charged state stabilized only as a bond configuration, where hydrogen binds to oxygen ions. Overall, the results between the two methods agree in the ordering of the formation energies of the different impurity configurations, though within DFT+U the charge-transition (electrical) levels are found at Fermi-level positions with higher energies. Both methods predict that hydrogen is an amphoteric defect in Lu2O3 if the lowest-energy configurations are used to obtain the charge-transition, thermodynamic levels. The calculations of hyperfine constants for the neutral interstitial configurations show a predominantly isotropic hyperfine interaction with two distinct values of 926 MHz and 1061 MHz for the Fermi-contact term originating from the two corresponding interstitial positions of hydrogen in the lattice. These high values are consistent with the muonium spectroscopy measurements which also reveal a strongly isotropic hyperfine signature for the neutral muonium fraction with a magnitude slightly larger (1130 MHz) from the ab initio results (after scaling with the magnetic moments of the respective nuclei).

  9. Electronic instrumentation for smart structures

    NASA Astrophysics Data System (ADS)

    Blanar, George J.

    1995-04-01

    The requirements of electronic instrumentation for smart structures are similar to those of data acquisition systems at our national particle physics laboratories. Modern high energy and heavy ion physics experiments may have tens of thousands of channels of data sources producing data that must be converted to digital form, compacted, stored and interpreted. In parallel, multiple sensors distributed in and around smart structures generate either binary or analog signals that are voltage, charge, or time like in their information content. In all cases, they must be transmitted, converted and preserved into a unified digital format for real-time processing. This paper will review the current status of practical large scale electronic measurement systems with special attention to architectures and physical organization. Brief surveys of the current state of the art will include preamplifiers and amplifiers, comparators and discriminators, voltage or charge analog-to-digital converters, time internal meters or time-to-digital converters, and finally, counting or scalar systems. The paper will conclude by integrating all of these ideas in a concept for an all-digital readout of a smart structure using the latest techniques used in physics research today.

  10. Study of MgxCd1-xO applying density functional theory: Stability, structural phase transition and electronic properties

    NASA Astrophysics Data System (ADS)

    Joshi, K. B.; Paliwal, U.; Galav, K. L.; Trivedi, D. K.; Bredow, T.

    2013-08-01

    Stability of B1 and B2 phases of MgxCd1-xO is studied by calculating the formation energy within the framework of density functional theory applying the crystalline-orbital program package. Structural and electronic properties of the two polymorphs are reported for x=0.25, 0.50 and 0.75. The equilibrium lattice constants and bulk moduli are computed. Enthalpy calculations show pressure induced B1→B2 phase transitions at 92 GPa, 138 GPa and 212 GPa, respectively, for Mg0.25Cd0.75O, Mg0.50Cd0.50O and Mg0.75Cd0.25O compositions. Formation energy of ternary oxides in the B1 phase is negative with respect to mixing of B2-MgO with B1-CdO. Mixing B1-MgO with B2-CdO also leads to negative formation energy in Cd rich B1 phase ternary oxides (0≤x≤0.5). Band structure calculations predict direct band gaps in the B1 phase and indirect band gaps in the B2 phase ternary oxides. Mulliken population analysis is performed for the two polymorphs to study the charge transfer.

  11. Structural Transformation and Physical Properties of a Hydrogel-Forming Peptide Studied by NMR, Transmission Electron Microscopy, and Dynamic Rheometer

    PubMed Central

    Huang, Hongzhou; Herrera, Alvaro I.; Luo, Zhiping; Prakash, Om; Sun, Xiuzhi S.

    2012-01-01

    Peptide-based hydrogels are attractive biological materials. Study of their self-assembly pathways from their monomer structures is important not only for undertaking the rational design of peptide-based materials, but also for understanding their biological functions and the mechanism of many human diseases relative to protein aggregation. In this work, we have monitored the conformation, morphological, and mechanical properties of a hydrogel-forming peptide during hydrogelation in different dimethylsulfoxide (DMSO)/H2O solutions. The peptide shows nanofiber morphologies in DMSO/H2O solution with a ratio lower than 4:1. Increased water percentage in the solution enhanced the hydrogelation rate and gel strength. One-dimensional and two-dimensional proton NMR and electron microscopy studies performed on the peptide in DMSO/H2O solution with different ratios indicate that the peptide monomer tends to adopt a more helical structure during the hydrogelation as the DMSO/H2O ratio is reduced. Interestingly, at the same DMSO/H2O ratio, adding Ca2+ not only promotes peptide hydrogelation and gel strength, but also leads to special shear-thinning and recovery properties of the hydrogel. Without changing the peptide conformation, Ca2+ binds to the charged Asp residues and induces the change of interfiber interactions that play an important role in hydrogel properties. PMID:23009847

  12. Hartree-Fock Cluster Study of Electronic Structures and Nuclear Quadrupole Interactions in Solid Nucleobases.

    NASA Astrophysics Data System (ADS)

    Scheicher, R. H.; Dubey, Archana; Badu, S. R.; Saha, H. P.; Pink, R. H.; Nagamine, K.; Torikai, E.; Chow, Lee; Das, T. P.

    2008-03-01

    In recent work [1] we have studied nucleobases attached to a CH3 group to simulate the influence of their binding to the sugar rings and the phosphate groups in DNA and RNA and the effect of this binding on the nuclear quadrupole interactions of ^14N, ^17O and ^2H nuclei. Our results from this work have indicated that for ^17O, the binding to the CH3 group moves our results from the free nucleobases closer to the experimentally observed data [2] in the solid nucleobases. We are now investigating the solid nucleobases by the first --principles Hartree-Fock cluster procedure that we have employed earlier for the halogen molecular solids [3]. Our results for the binding energy of an imidazole molecule in the molecular solid system and the ^14N, ^17O and ^2H nuclear quadrupole interaction parameters will be presented. [1] T.P. Das et al (at this APS meeting), [2] Gang Wu et al, J. Am.Chem. Soc. 124, 1768(2002). [3] M.M. Aryal et al Hyperfine Interactions (to be published).

  13. Examination of electronic structure differences between CIGSSe and CZTSSe by photoluminescence study

    SciTech Connect

    Tai, Kong Fai; Huan, Cheng Hon Alfred; Gershon, Talia; Gunawan, Oki

    2015-06-21

    In this paper, we elaborate on the interpretation and use of photoluminescence (PL) measurements as they relate to the “donor/acceptor” and “electrostatic potential fluctuations” models for compensated semiconductors. Low-temperature (7 K) PL measurements were performed on high-efficiency Cu(In,Ga)(S,Se){sub 2} and two Cu{sub 2}ZnSn(S,Se){sub 4} solar cells with high- and low-S/(S + Se) ratio, all fabricated by a hydrazine solution-processing method. From excitation-dependent PL, the total defect density (which include radiative and non-radiative defects) within the band gap (E{sub g}) was estimated for each material and the consequent depth of the electrostatic potential fluctuation (γ) was calculated. The quasi-donor-acceptor pair (QDAP) density was estimated from the blue-shift magnitude of the QDAP PL peak position in power-dependent PL spectra. As a further verification, we show that the slope of the lifetime as a function of photon energies (dτ/dE) is consistent with our estimate for the magnitude of γ. Lastly, the energetic depth of the QDAP defects is examined by studying the spectral evolution of the PL as a function of temperature. The shallow defect levels in CIGSSe resulted in a significant blue-shift of the PL peak with temperature, whereas no obvious shift was observed for either CZTSSe sample, indicating an increase in the depth of the defects. Further improvement on Cu{sub 2}ZnSn(S,Se){sub 4} solar cell should focus on reducing the sub-E{sub g} defect density and avoiding the formation of deep defects.

  14. Ionization of cytosine monomer and dimer studied by VUV photoionization and electronic structure calculations

    SciTech Connect

    Kostko, Oleg; Bravaya, Ksenia; Krylov, Anna; Ahmed, Musahid

    2009-12-14

    We report a combined theoretical and experimental study of ionization of cytosine monomers and dimers. Gas-phase molecules are generated by thermal vaporization of cytosine followed by expansion of the vapor in a continuous supersonic jet seeded in Ar. The resulting species are investigated by single photon ionization with tunable vacuum-ultraviolet (VUV) synchrotron radiation and mass analyzed using reflectron mass spectrometry. Energy onsets for the measured photoionization efficiency (PIE) spectra are 8.60+-0.05 eV and 7.6+-0.1 eV for the monomer and the dimer, respectively, and provide an estimate for the adiabatic ionization energies (AIE). The first AIE and the ten lowest vertical ionization energies (VIEs) for selected isomers of cytosine dimer computed using equation-of-motion coupled-cluster (EOM-IP-CCSD) method are reported. The comparison of the computed VIEs with the derivative of the PIE spectra, suggests that multiple isomers of the cytosine dimer are present in the molecular beam. The calculations reveal that the large red shift (0.7 eV) of the first IE of the lowest-energy cytosine dimer is due to strong inter-fragment electrostatic interactions, i.e., the hole localized on one of the fragments is stabilized by the dipole moment of the other. A sharp rise in the CH+ signal at 9.20+-0.05 eV is ascribed to the formation of protonated cytosine by dissociation of the ionized dimers. The dominant role of this channel is supported by the computed energy thresholds for the CH+ appearance and the barrierless or nearly barrierless ionization-induced proton transfer observed for five isomers of the dimer.

  15. Ionization of cytosine monomer and dimer studied by VUV photoionization and electronic structure calculations.

    PubMed

    Kostko, Oleg; Bravaya, Ksenia; Krylov, Anna; Ahmed, Musahid

    2010-03-28

    We report a combined theoretical and experimental study of ionization of cytosine monomers and dimers. Gas-phase molecules are generated by thermal vaporization of cytosine followed by expansion of the vapor in a continuous supersonic jet seeded in Ar. The resulting species are investigated by single photon ionization with tunable vacuum-ultraviolet (VUV) synchrotron radiation and mass analyzed using reflectron mass spectrometry. Energy onsets for the measured photoionization efficiency (PIE) spectra are 8.60 +/- 0.05 eV and 7.6 +/- 0.1 eV for the monomer and the dimer, respectively, and provide an estimate for the adiabatic ionization energies (AIE). The first AIE and the ten lowest vertical ionization energies (VIEs) for selected isomers of cytosine dimer computed using equation-of-motion coupled-cluster (EOM-IP-CCSD) method are reported. The comparison of the computed VIEs with the derivative of the PIE spectra suggests that multiple isomers of the cytosine dimer are present in the molecular beam. The calculations reveal that the large red shift (0.7 eV) of the first IE of the lowest-energy cytosine dimer is due to strong inter-fragment electrostatic interactions, i.e., the hole localized on one of the fragments is stabilized by the dipole moment of the other. A sharp rise in the protonated cytosine ion (CH(+)) signal at 9.20 +/- 0.05 eV is ascribed to the formation of protonated cytosine by dissociation of the ionized dimers. The dominant role of this channel is supported by the computed energy thresholds for the CH(+) appearance and the barrierless or nearly barrierless ionization-induced proton transfer observed for five isomers of the dimer.

  16. Structure-function studies of blood and air capillaries in chicken lung using 3D electron microscopy.

    PubMed

    West, John B; Fu, Zhenxing; Deerinck, Thomas J; Mackey, Mason R; Obayashi, James T; Ellisman, Mark H

    2010-02-28

    Avian pulmonary capillaries differ from those of mammals in three important ways. The blood-gas barrier is much thinner, it is more uniform in thickness, and the capillaries are far more rigid when their transmural pressure is altered. The thinness of the barrier is surprising because it predisposes the capillaries to stress failure. A possible mechanism for these differences is that avian pulmonary capillaries, unlike mammalian, are supported from the outside by air capillaries, but the details of the support are poorly understood. To clarify this we studied the blood and air capillaries in chicken lung using transmission electron microscopy (EM) and two relatively new techniques that allow 3D visualization: electron tomography and serial block-face scanning EM. These studies show that the pulmonary capillaries are flanked by epithelial bridges composed of two extremely thin epithelial cells with large surface areas. The junctions of the bridges with the capillary walls show thickening of the epithelial cells and an accumulation of extracellular matrix. Collapse of the pulmonary capillaries when the pressure outside them is increased is apparently prevented by the guy wire-like action of the epithelial bridges. The enlarged junctions between the bridges and the walls could provide a mechanism that limits the hoop stress in the capillary walls when the pressure inside them is increased. The support of the pulmonary capillaries may also be explained by an interdependence mechanism whereby the capillaries are linked to a rigid assemblage of air capillaries. These EM studies show the supporting structures in greater detail than has previously been possible, particularly in 3D, and they allow a more complete analysis of the mechanical forces affecting avian pulmonary capillaries. PMID:20038456

  17. Electronic-structure study of an edge dislocation in Aluminum and the role of macroscopic deformations on its energetics

    NASA Astrophysics Data System (ADS)

    Iyer, Mrinal; Radhakrishnan, Balachandran; Gavini, Vikram

    2015-03-01

    We employed a real-space formulation of orbital-free density functional theory using finite-element basis to study the defect-core and energetics of an edge dislocation in Aluminum. Our study shows that the core-size of a perfect edge dislocation is around ten times the magnitude of the Burgers vector. This finding is contrary to the widely accepted notion that continuum descriptions of dislocation energetics are accurate beyond ∼1-3 Burgers vector from the dislocation line. Consistent with prior electronic-structure studies, we find that the perfect edge dislocation dissociates into two Shockley partials with a partial separation distance of 12.8 Å. Interestingly, our study revealed a significant influence of macroscopic deformations on the core-energy of Shockley partials. We show that this dependence of the core-energy on macroscopic deformations results in an additional force on dislocations, beyond the Peach-Koehler force, that is proportional to strain gradients. Further, we demonstrate that this force from core-effects can be significant and can play an important role in governing the dislocation behavior in regions of inhomogeneous deformations.

  18. Electronic Structure and Magnetic Properties of Dioxo-Bridged Diuranium Complexes with Diamond-Core Structural Motifs: A Relativistic DFT Study.

    PubMed

    Teyar, Billel; Belkhiri, Lotfi; Costuas, Karine; Boucekkine, Abdou; Meyer, Karsten

    2016-03-21

    Electronic structures and magnetic properties of the binuclear bis(μ-oxo) U(IV)/U(IV) K2[{(((nP,Me)ArO)3tacn)U(IV)}2(μ-O)2] and U(V)/U(V) [{(((nP,Me)ArO)3tacn)U(V)}2(μ-O)2] (tacn = triazacyclononane, nP = neopentyl) complexes, exhibiting [U(μ-O)2U] diamond-core structural motifs, have been investigated computationally using scalar relativistic Density Functional Theory (DFT) combined with the Broken Symmetry (BS) approach for their magnetic properties. Using the B3LYP hybrid functional, the BS ground state of the pentavalent [U(V)(μ-O)2U(V)] 5f(1)-5f(1) complex has been found of lower energy than the high spin (HS) triplet state, thus confirming the antiferromagnetic character in agreement with experimental magnetic susceptibility measurements. The nonmagnetic character observed for the tetravalent K2[U(IV)(μ-O)2U(IV)] 5f(2)-5f(2) species is also predicted by our DFT calculations, which led practically to the same energy for the HS and BS states. As reported for related dioxo diuranium(V) systems, superexchange is likely to be responsible for the antiferromagnetic coupling through the π-network orbital pathway within the (μ-O)2 bridge, the dissymmetrical structure of the U2O2 core playing a determining role. In the case of the U(IV) species, our computations indicate that the K(+) counterions are likely to play a role for the observed magnetic property. Finally, the MO analysis, in conjunction with NPA and QTAIM analyses, clarify the electronic structures of the studied complexes. In particular, the fact that the experimentally attempted chemical oxidation of the U(V) species does not lead straightforwardly to binuclear complexes U(VI) is clarified by the MO analysis.

  19. 42214 layered Fe-based superconductors: An ab initio study of their structural, magnetic, and electronic properties

    NASA Astrophysics Data System (ADS)

    Bucci, F.; Sanna, A.; Continenza, A.; Katrych, S.; Karpinski, J.; Gross, E. K. U.; Profeta, G.

    2016-01-01

    As a follow-up to the discovery of a new family of Fe-based superconductors, namely, the RE4Fe2As2Te1 -xO4 (42214) (RE = Pr, Sm, and Gd), we present a detailed ab initio study of these compounds highlighting the role of rare-earth (RE) atoms, external pressure, and Te content on their physical properties. Modifications of the structural, magnetic, and electronic properties of the pure (e.g., x =0.0 ) 42214 compounds and their possible correlations with the observed superconducting properties are calculated and discussed. The careful analysis of the results obtained shows that (i) changing the RE atoms allows one to tune the internal pressure acting on the As height with respect to the Fe planes; (ii) similarly to other Fe pnictides, the 42214 pure compounds show an antiferromagnetic-stripe magnetic ground state phase joined by an orthorhombic distortion (not experimentally found yet); (iii) smaller RE atoms increase the magnetic instability of the compounds possibly favoring the onset of the superconducting state; (iv) external pressure induces the vanishing of the magnetic order with a transition to the tetragonal phase and can be a possible experimental route towards higher superconducting critical temperature (Tc) ; and (v) Te vacancies act on the structural parameters, changing the As height and affecting the stability of the magnetic phase.

  20. Electronic structure of trioxide, oxoperoxide, oxosuperoxide, and ozonide clusters of the 3d elements: density functional theory study.

    PubMed

    Uzunova, Ellie L

    2011-03-01

    The trioxide clusters with stoichiometry MO3, and the structural isomers with side-on and end-on bonded oxygen atoms, are studied by DFT with the B1LYP functional. For the first half of the 3d elements row (Sc to Cr), pyramidal or distorted pyramidal structures dominate among the trioxide and oxoperoxide ground states, while the remaining elements form planar trioxides, oxoperoxides, oxosuperoxides, and ozonides. Low-lying trioxide clusters are formed by Ti, V, Cr, and Mn, among which the distorted pyramidal VO3 in the (2)A'' state, the pyramidal CrO3 in the (1)A1 state, and the planar MnO3 in the (2)A1' state are global minima. With the exception of the middle-row elements Mn, Fe, and Co, the magnetic moment of the ground-state clusters is formed with a major contribution from unpaired electrons located at the oxygen atoms. The stability of trioxides and oxoperoxides toward release of molecular oxygen is significantly higher for Sc, Ti, and V than for the remaining elements of the row. A trend of increasing the capability to dissociate one oxygen molecule is observed from Cr to Cu, with the exception of OFe(O2) being more reactive than OCo(O2). A gradual increase of reactivity from Ti to Cu is observed for the complete fragmentation reaction M + O + O2.

  1. Contribution of interlayer hybridization to the electronic structure in iron pnictides: a study of EELS and first-principles calculations.

    PubMed

    Ma, Chao; Yang, Huaixin; Tian, Huanfang; Shi, Honglong; Wang, Zhiwei; Li, Jianqi

    2013-03-20

    Using electron energy loss spectroscopy (EELS) measurements and first-principles electronic structure calculations, the significant interlayer hybridization between the insulating layers (ReO or Ba) and the conducting FeAs layers was investigated in the layered iron pnictides, which is quite different from the case in the cuprate superconductors. This interlayer hybridization would result in an increase in the bandwidth near the Fermi level and interorbital charge transfer in the Fe 3d orbitals, which subsequently leads to a decrease in the Fe local moment and the modification of the Fermi surface topology. Therefore, a three-dimensional character of the electronic structure due to the interlayer hybridization is expected, as observed in previous experiments. These findings indicate that reduced dimensionality is no longer a necessary condition in the search for high-T(c) superconductors in iron pnictides.

  2. Electronic structure and rovibrational properties of ZnOH in the X{sup ~2}A{sup ′} electronic state: A computational molecular spectroscopy study

    SciTech Connect

    Hirano, Tsuneo; Andaloussi, Mounir Ben Dahman; Jensen, Per; Nagashima, Umpei

    2014-09-07

    The three-dimensional ground-state potential energy surface of ZnOH has been calculated ab initio at the MR-SDCI+Q-DK3/[QZP ANO-RCC (Zn, O, H)] level of theory and used as basis for a study of the rovibrational properties carried out by means of the program MORBID (Morse Oscillator Rigid Bender Internal Dynamics). The electronic ground state is  {sup 2}A′ (correlating with {sup 2}Σ{sup +} at the linear configuration). The equilibrium structure has r{sub e}(Zn–O) = 1.8028 Å, r{sub e}(O–H) = 0.9606 Å, and ∠{sub e}(Zn–O–H) = 114.9°. The Zn–O bond is essentially ionic, with appreciable covalency. The bonding character is compared with those of FeOH (quasi-linear) and CsOH (linear). The rovibrationally averaged structural parameters, determined as expectation values over MORBID wavefunctions, are 〈r(Zn–O)〉{sub 0} = 1.8078 Å, 〈r(O–H)〉{sub 0} = 0.9778 Å, and 〈∠(Zn–O–H)〉{sub 0} = 117°. The Yamada-Winnewisser quasi-linearity parameter is found to be γ{sub 0} = 0.84, which is close to 1.0 as expected for a bent molecule. Since no experimental rovibrational spectrum has been reported thus far, this spectrum has been simulated from the ab initio potential energy and dipole moment surfaces. The amphoteric character of ZnOH is also discussed.

  3. Quantum-chemical calculations and electron diffraction study of the equilibrium molecular structure of vitamin K3

    NASA Astrophysics Data System (ADS)

    Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.

    2014-05-01

    The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.

  4. Temperature dependent evolution of the local electronic structure of atmospheric plasma treated carbon nanotubes: Near edge x-ray absorption fine structure study

    SciTech Connect

    Roy, S. S.; Papakonstantinou, P.; Okpalugo, T. I. T.; Murphy, H.

    2006-09-01

    Near edge x-ray absorption fine structure (NEXAFS) spectroscopy has been employed to obtain the temperature dependent evolution of the electronic structure of acid treated carbon nanotubes, which were further modified by dielectric barrier discharge plasma processing in an ammonia atmosphere. The NEXAFS studies were performed from room temperature up to 900 deg. C. The presence of oxygen and nitrogen containing functional groups was observed in C K edge, N K edge, and O K edge NEXAFS spectra of the multiwalled carbon nanotubes. The N K edge spectra revealed three types of {pi}* features, the source of which was decisively identified by their temperature dependent evolution. It was established that these features are attributed to pyridinelike, NO, and graphitelike structures, respectively. The O K edge indicated that both carbonyl (C=O), {pi}*(CO), and ether C-O-C, {sigma}*(CO), functionalities were present. Upon heating in a vacuum to 900 deg. C the {pi}*(CO) resonances disappeared while the {sigma}*(CO) resonances were still present confirming their higher thermal stability. Heating did not produce a significant change in the {pi}* feature of the C K edge spectrum indicating that the tabular structure of the nanotubes is essentially preserved following the thermal decomposition of the functional groups on the nanotube surface.

  5. Electronic structure of Si/disilicide interfaces

    NASA Astrophysics Data System (ADS)

    Fujitani, Hideaki; Asano, Setsuro

    1990-01-01

    Using supercells, the electronic structures of Si(111)/CoSi2 and Si(111)/NiSi2 interfaces are studied by the linear muffin-tin orbital atomic sphere approximation method (LMTO-ASA). Schottky barrier heights (SBH's) are strongly correlated with the interface atomic structures and are determined mainly by interface bonding states and the screening effect of the semiconductor. Metal-induced gap states (MIGS) are metal wave function tails caused by the Schottky barriers.

  6. Electronic structure of Si/disilicide interfaces

    NASA Astrophysics Data System (ADS)

    Fujitani, Hideaki; Asano, Setsuro

    1989-11-01

    Using supercells, the electronic structures of Si(111)/CoSi 2 and Si(111)/NiSi 2 interfaces are studied by the linear muffin-tin orbital atomic sphere approximation method (LMTO-ASA). Schottky barrier heights (SBH's) are strongly correlated with the interface atomic structures and are determined mainly by interface bonding states and the screening effect of the semiconductor. Metal-induced gap states (MIGS) are metal wave function tails caused by the Schottky barriers.

  7. Studies of local structural distortions in strained ultrathin BaTiO3 films using scanning transmission electron microscopy.

    PubMed

    Park, Daesung; Herpers, Anja; Menke, Tobias; Heidelmann, Markus; Houben, Lothar; Dittmann, Regina; Mayer, Joachim

    2014-06-01

    Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.

  8. Structural and electronic properties for atomic clusters

    NASA Astrophysics Data System (ADS)

    Sun, Yan

    We have studied the structural and electronic properties for different groups of atomic clusters by doing a global search on the potential energy surface using the Taboo Search in Descriptors Space (TSDS) method and calculating the energies with Kohn-Sham Density Functional Theory (KS-DFT). Our goal was to find the structural and electronic principles for predicting the structure and stability of clusters. For Ben (n = 3--20), we have found that the evolution of geometric and electronic properties with size reflects a change in the nature of the bonding from van der Waals to metallic and then bulk-like. The cluster sizes with extra stability agree well with the predictions of the jellium model. In the 4d series of transition metal (TM) clusters, as the d-type bonding becomes more important, the preferred geometric structure changes from icosahedral (Y, Zr), to distorted compact structures (Nb, Mo), and FCC or simple cubic crystal fragments (Tc, Ru, Rh) due to the localized nature of the d-type orbital. Analysis of relative isomer energies and their electronic density of states suggest that these clusters tend to follow a maximum hardness principle (MHP). For A4B12 clusters (A is divalent, B is monovalent), we found unusually large (on average 1.95 eV) HOMO-LUMO gap values. This shows the extra stability at an electronic closed shell (20 electrons) predicted by the jellium model. The importance of symmetry, closed electronic and ionic shells in stability is shown by the relative stability of homotops of Mg4Ag12 which also provides support for the hypothesis that clusters that satisfy more than one stability criterion ("double magic") should be particularly stable.

  9. Electronic structure of disordered conjugated polymers: Polythiophenes

    SciTech Connect

    Vukmirovic, Nenad; Wang, Lin-Wang

    2008-11-26

    Electronic structure of disordered semiconducting conjugated polymers was studied. Atomic structure was found from a classical molecular dynamics simulation and the charge patching method was used to calculate the electronic structure with the accuracy similar to the one of density functional theory in local density approximation. The total density of states, the local density of states at different points in the system and the wavefunctions of several states around the gap were calculated in the case of poly(3-hexylthiophene) (P3HT) and polythiophene (PT) systems to gain insight into the origin of disorder in the system, the degree of carrier localization and the role of chain interactions. The results indicated that disorder in the electronic structure of alkyl substituted polythiophenes comes from disorder in the conformation of individualchains, while in the case of polythiophene there is an additional contribution due to disorder in the electronic coupling between the chains. Each of the first several wavefunctions in the conduction and valence band of P3HT is localized over several rings of a single chain. It was shown that the localization can be caused in principle both by ring torsions and chain bending, however the effect of ring torsions is much stronger. PT wavefunctions are more complicated due to larger interchain electronic coupling and are not necessarily localized on a single chain.

  10. Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter

    NASA Astrophysics Data System (ADS)

    Mo, M. Z.; Shen, X.; Chen, Z.; Li, R. K.; Dunning, M.; Sokolowski-Tinten, K.; Zheng, Q.; Weathersby, S. P.; Reid, A. H.; Coffee, R.; Makasyuk, I.; Edstrom, S.; McCormick, D.; Jobe, K.; Hast, C.; Glenzer, S. H.; Wang, X.

    2016-11-01

    We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 μm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime.

  11. Studies in electron phenomena in MOS structures: The pulsed C-V method. M.S. Thesis. Abstract Only

    NASA Technical Reports Server (NTRS)

    Kaplan, G.

    1983-01-01

    The pulse hysteresis capacitance voltage (C-V) provides a straight forward technique for measuring the change of various charges in MOS structures and a tool for investigating the kinetics of various electron phenomena is developed and described. The method can be used for measuring the energy distribution and kinetics of surface states with the resolution of about 1/5 x 10 to the -9 power cm eV. Some transients in an MOS structure, particularly, the thermal generation of minority charge carriers via surface states and the relaxation of minority charge carriers supplied from the inversion layer outside the MOS structure are theoretically investigated. Analytical expressions which clearly present the physics of those electron phenomena are derived.

  12. Structural, elastic, electronic and optical properties of Cu3MTe4 (M = Nb, Ta) sulvanites — An ab initio study

    NASA Astrophysics Data System (ADS)

    Ali, M. A.; Roknuzzaman, M.; Nasir, M. T.; Islam, A. K. M. A.; Naqib, S. H.

    2016-04-01

    The elastic, electronic, and optical properties of Cu3MTe4 (M = Nb, Ta) are investigated for the first time using the density-functional formalism. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. Different elastic moduli are calculated. The Born criteria for mechanical stability are found to be fulfilled from the estimated values of the elastic moduli, Cij. The band structure and the electronic energy density of states (EDOS) are also determined. The band structure calculations show semiconducting behavior for both the compounds. The theoretically calculated values of the band gaps are found to be strongly dependent on the nature of the functional representing the exchange correlations. Technologically significant optical parameters (e.g., dielectric function, refractive index, absorption coefficient, optical conductivity, reflectivity, and loss function) have been determined. Important conclusions are drawn based on the theoretical findings.

  13. Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter

    DOE PAGES

    Mo, M. Z.; Shen, X.; Chen, Z.; Li, R. K.; Dunning, M.; Sokolowski-Tinten, K.; Zheng, Q.; Weathersby, S. P.; Reid, A. H.; Coffee, R.; et al

    2016-08-04

    We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 µm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined.more » This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime« less

  14. A first principles study of structural stability, electronic structure and mechanical properties of beryllium alanate BeAlH{sub 5}

    SciTech Connect

    Santhosh, M.; Rajeswarapalanichamy, R. Priyanga, G. Sudha; Cinthia, A. Jemmy; Kanagaprabha, S.; Iyakutti, K.

    2015-06-24

    Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of BeAlH{sub 5} for monoclinic crystal structures with two different types of space group namely P2{sub 1} and C{sub 2}/c. Among the considered structures monoclinic (P2{sub 1}) phase is found to be the most stable at ambient condition. The structural phase transition from monoclinic (P2{sub 1}) to monoclinic (C{sub 2}/c) phase is observed in BeAlH{sub 5}. The electronic structure reveals that this compound is insulator. The calculated elastic constants indicate that this material is mechanically stable at ambient condition.

  15. DFT study on the electronic structure and chemical state of Americium in an (Am,U) mixed oxide

    NASA Astrophysics Data System (ADS)

    Suzuki, Chikashi; Nishi, Tsuyoshi; Nakada, Masami; Tsuru, Tomohito; Akabori, Mitsuo; Hirata, Masaru; Kaji, Yoshiyuki

    2013-12-01

    We investigated the electronic state of an (Am,U) mixed oxide with the fluorite structure using the all-electron full potential linear augmented plane wave method and compared it with those of Am2O3, AmO2, UO2, and La0.5U0.5O2. The valence of Am in the mixed oxide was close to that of Am2O3 and the valence of U in the mixed oxide was pentavalent. The electronic structure of AmO2 was different from that of Am2O3, particularly just above the Fermi level. In addition, the electronic states of Am and U in the mixed oxide were similar to those of trivalent Am and pentavalent U oxides. These electronic states reflected the high oxygen potential of AmO2 and the heightened oxygen potential resulting from the addition of Am to UO2 and also suggested the occurrence of charge transfer from Am to U in the solid solution process.

  16. Electronic and crystallographic structure of apatites

    NASA Astrophysics Data System (ADS)

    Calderín, L.; Stott, M. J.; Rubio, A.

    2003-04-01

    An ab initio study of four different stoichiometric apatites (oxyapatite, hydroxyapatite, fluorapatite, and chlorapatite) is presented. The calculations were performed using density-functional theory with the local-density approximation for exchange and correlation, and a full relaxation of the electronic structure, the atomic arrangement, and the unit cell. Hexagonal unit cells were obtained for all four apatites, and the calculated atomic arrangements are in close agreement with observation in those cases for which the structure is firmly established. A zero-temperature structure is predicted for oxyapatite, and two possible configurations were found for the Cl- ions in chlorapatite. The possibility of the monoclinic structure in hydroxyapatite and chlorapatite was also studied but no indication of greater stability with respect to the hexagonal structure was found. A relationship between the structure of the apatites and that of pure calcium is discussed.

  17. Study of the molecular structure, ionization spectrum, and electronic wave function of 1,3-butadiene using electron momentum spectroscopy and benchmark Dyson orbital theories

    NASA Astrophysics Data System (ADS)

    Deleuze, M. S.; Knippenberg, S.

    2006-09-01

    The scope of the present work is to reconcile electron momentum spectroscopy with elementary thermodynamics, and refute conclusions drawn by Saha et al. in J. Chem. Phys. 123, 124315 (2005) regarding fingerprints of the gauche conformational isomer of 1,3-butadiene in electron momentum distributions that were experimentally inferred from gas phase (e,2e) measurements on this compound [M. J. Brunger et al., J. Chem. Phys. 108, 1859 (1998)]. Our analysis is based on thorough calculations of one-electron and shake-up ionization spectra employing one-particle Green's function theory along with the benchmark third-order algebraic diagrammatic construction [ADC(3)] scheme. Accurate spherically averaged electron momentum distributions are correspondingly computed from the related Dyson orbitals. The ionization spectra and Dyson orbital momentum distributions that were computed for the trans-conformer of 1,3-butadiene alone are amply sufficient to quantitatively unravel the shape of all available experimental (e,2e) electron momentum distributions. A comparison of theoretical ADC(3) spectra for the s-trans and gauche energy minima with inner- and outer-valence high-resolution photoelectron measurements employing a synchrotron radiation beam [D. M. P. Holland et al., J. Phys. B 29, 3091 (1996)] demonstrates that the gauche structure is incompatible with ionization experiments in high-vacuum conditions and at standard temperatures. On the other hand, outer-valence Green's function calculations on the s-trans energy minimum form and approaching basis set completeness provide highly quantitative insights, within ˜0.2eV accuracy, into the available experimental one-electron ionization energies. At last, analysis of the angular dependence of relative (e,2e) ionization intensities nicely confirms the presence of one rather intense π-2 π*+1 satellite at ˜13.1eV in the ionization spectrum of the s-trans conformer.

  18. DFT Study of Structural and Electronic Properties of Endohedral Complexes of Group V Atoms with C60

    NASA Astrophysics Data System (ADS)

    Pahuja, Akshu; Srivastava, Sunita

    2013-09-01

    The structural and electronic properties of endohedral fullerenes formed by encapsulation of each of the group V elements inside the buckminsterfullerene cage have been investigated. The calculations reveal that all these species are thermodynamically stable, though the formation of Sb@C60 and Bi@C60 is slightly endothermic. The central atom preserves its electronic configuration and the quartet state. The energy gap and energy levels are perturbed by the inclusion of a foreign atom. The band gap of Sb@C60 and Bi@C60 is found to be significantly smaller than pristine C60, suggesting the reactivity of these complexes.

  19. Assessing two-dimensional crystallization trials of small membrane proteins for structural biology studies by electron crystallography.

    PubMed

    Johnson, Matthew C; Rudolph, Frederik; Dreaden, Tina M; Zhao, Gengxiang; Barry, Bridgette A; Schmidt-Krey, Ingeborg

    2010-10-29

    Electron crystallography has evolved as a method that can be used either alternatively or in combination with three-dimensional crystallization and X-ray crystallography to study structure-function questions of membrane proteins, as well as soluble proteins. Screening for two-dimensional (2D) crystals by transmission electron microscopy (EM) is the critical step in finding, optimizing, and selecting samples for high-resolution data collection by cryo-EM. Here we describe the fundamental steps in identifying both large and ordered, as well as small 2D arrays, that can potentially supply critical information for optimization of crystallization conditions. By working with different magnifications at the EM, data on a range of critical parameters is obtained. Lower magnification supplies valuable data on the morphology and membrane size. At higher magnifications, possible order and 2D crystal dimensions are determined. In this context, it is described how CCD cameras and online-Fourier Transforms are used at higher magnifications to assess proteoliposomes for order and size. While 2D crystals of membrane proteins are most commonly grown by reconstitution by dialysis, the screening technique is equally applicable for crystals produced with the help of monolayers, native 2D crystals, and ordered arrays of soluble proteins. In addition, the methods described here are applicable to the screening for 2D crystals of even smaller as well as larger membrane proteins, where smaller proteins require the same amount of care in identification as our examples and the lattice of larger proteins might be more easily identifiable at earlier stages of the screening.

  20. Combined Quantum Chemistry and Photoelectron Spectroscopy Study of the Electronic Structure and Reduction Potentials of Rubredoxin Redox Site Analogues

    SciTech Connect

    Niu, Shuqiang; Wang, Xue B.; Nichols, J. A.; Wang, Lai S.; Ichiye, Toshiko

    2003-04-24

    Iron-sulfur proteins are an important class of electron carriers in a wide variety of biological reactions. Determining the intrinsic contribution of the metal site to the redox potential is crucial in understanding how the protein environment influences the overall redox properties of the Fe-S proteins. Here we combine density functional theory and coupled cluster methods with photodetachment spectroscopy to study the electronic structures and gas-phase redox potentials of the [Fe(SCH3)(4)](2-/-/0) and [Fe(SCH3)(3)](-/0) analogues of the rubredoxin redox site. The calculations show that oxidations of [Fe(SCH3)(4)](2-) and [Fe(SCH3)(4)](-) involve mainly the Fe 3d and S 3p orbitals, respectively. The calculated adiabatic and vertical detachment energies are in good agreement with the experiment for [Fe(SCH3)(3)](-) and [Fe(SCH3)(4)](-). The current results further confirm the "inverted level scheme" for the high-spin [1Fe] systems. The redox couple, [Fe(SCH3)(4)](- /2), which is the one found in rubredoxin, but cannot be accessed experimentally in the gas phase, was investigated using a thermodynamic cycle that relates it to the [Fe(SCH3)(3)](-/0) couple and the ligand association reaction, [Fe(SCH3)(3)](0/-) + SCH3- --> [Fe(SCH3)(4)](-/2-). The calculated reduction energy of [Fe(SCH3)(4)](-) (1.7 eV) compares well with the value (1.6 eV) estimated from the calculated bond energies and the experimental detachment energy of [Fe(SCH3)(3)](-). Thus, this thermodynamic cycle method can be used to estimate metal-ligand bonding energies and determine intrinsic reduction potentials from photodetachment experiments when the reduced forms are not stable in the gas phase.

  1. Spatially-resolved in-situ structural study of organic electronic devices with nanoscale resolution: the plasmonic photovoltaic case study.

    PubMed

    Paci, B; Bailo, D; Albertini, V Rossi; Wright, J; Ferrero, C; Spyropoulos, G D; Stratakis, E; Kymakis, E

    2013-09-14

    A novel high spatial resolution synchrotron X-ray diffraction stratigraphy technique has been applied in-situ to an integrated plasmonic nanoparticle-based organic photovoltaic device. This original approach allows for the disclosure of structure-property relations linking large scale organic devices to length scales of local nano/hetero structures and interfaces between the different components.

  2. Theoretical study of the structure and electronic properties of carbon and B{sub X}C{sub Y}N{sub Z} nanotubes

    SciTech Connect

    Louie, S.G. |

    1995-06-01

    Theoretical studies of the electronic and structural properties of carbon nanotubes and nanotubes composed of boron, carbon and nitrogen are presented. Structural stability, hybridization effects, static dielectric response, incorporation of metal atoms, and collapsed tube structures are calculated. Nanotubes of BN, BC{sub 3}, and BC{sub 2}N are predicted to form and have very different properties from those of the carbon systems. BN nanotubes are found to be constant band gap insulators with novel free-electron tubule states at the conduction band minimum. The possibility of chiral currents in doped BC{sub 2}N nanotubes is shown.

  3. Crystal structure refinement from electron diffraction data

    SciTech Connect

    Dudka, A. P. Avilov, A. S.; Lepeshov, G. G.

    2008-05-15

    A procedure of crystal structure refinement from electron diffraction data is described. The electron diffraction data on polycrystalline films are processed taking into account possible overlap of reflections and two-beam interaction. The diffraction from individual single crystals in an electron microscope equipped with a precession attachment is described using the Bloch-wave method, which takes into account multibeam scattering, and a special approach taking into consideration the specific features of the diffraction geometry in the precession technique. Investigations were performed on LiF, NaF, CaF{sub 2}, and Si crystals. A method for reducing experimental data, which allows joint electron and X-ray diffraction study, is proposed.

  4. Relationship between molecular structure and electron targets in the electroreduction of benzocarbazolediones and anilinenaphthoquinones. Experimental and theoretical study.

    PubMed

    Macías-Ruvalcaba, N; Cuevas, G; González, I; Aguilar-Martínez, M

    2002-05-31

    We report the synthesis and voltamperometric reduction of 5H-benzo[b]carbazole-6,11-dione (BCD) and its 2-R-substituted derivatives (R = -OMe, -Me, -COMe, -CF(3)). The electrochemical behavior of BCDs was compared to that of the 2-[(R-phenyl)amine]-1,4-naphthalenediones (PANs) previously studied. Like PANs, BCDs exhibit two reduction waves in acetonitrile. The first reduction step for the BCDs represents formation of the radical anion, and the half-wave potential (E(1/2)) values for this step are less negative than for that of the PANs. The second reduction wave, corresponding to the formation of dianion hydroquinone, has E(1/2) values that shift to more negative potentials. A good linear Hammett-Zuman (E(1/2) vs sigma(p)) relationship, similar to that for the PAN series, was also obtained for the BCDs. However, unlike the PANs, in the BCDs, the first reduction wave was more susceptible to the effect of the substituent groups than was the second wave, suggesting that the ordering of the two successive one-electron reductions in BCDs is opposite that in PANs. This is explained by the fact that the electron delocalizations in the two systems are different; in the case of BCDs there is an extra aromatic indole ring, which resists loss of its aromatic character. The electronic structures of BCD compounds were, therefore, investigated within the framework of the density functional theory, using the B3LYP hybrid functional with a double zeta split valence basis set. Our theoretical calculations show that the O(1).H-N hydrogen bond, analogous to that previously described for the PAN series, is not observed in the BCDs. Laplacians of the critical points (nabla(2)rho) and the natural charges for the C-O bonds indicate that the first reduction wave for the BCDs corresponds to the C(4)-O(2) carbonyl, while in the PAN series the first one-electron transfer occurred at the C(1)-O(1) carbonyl. Natural bond orbital analysis showed that, in all the BCDs, the lowest unoccupied

  5. Electron density analysis of the effects of sugars on the structure of lipid bilayers at low hydration - a preliminary study

    SciTech Connect

    Lenné, T.; Kent, B.; Koster, K.L.; Garvey, C.J.; Bryant, G.

    2012-02-06

    Small angle X-ray scattering is used to study the effects of sugars on membranes during dehydration. Previous work has shown that the bilayer and chain-chain repeat spacings of DPPC bilayers are relatively unaffected by the presence of sugars. In this work we present a preliminary analysis of the electron density profiles of DPPC in the presence of sugars at low hydration. The difficulties of determining the correct phasing are discussed. Sugars and other small solutes have been shown to have an important role in improving the tolerance of a range of species to desiccation and freezing. In particular it has been shown that sugars can stabilize membranes in the fluid membrane phase during dehydration, and in the fully dehydrated state. Equivalently, at a particular hydration, the presence of sugars lowers the transition temperature between the fluid and gel phases. There are two competing models for explaining the effects of sugars on membrane phase transition temperatures. One, designated the water replacement hypothesis (WRH) states that sugars hydrogen bond to phospholipid headgroups, thus hindering the fluid-gel phase transition. One version of this model suggests that certain sugars (such as trehalose) achieve the measured effects by inserting between the phospholipid head groups. An alternative model explains the observed effects of sugars in terms of the sugars effect on the hydration repulsion that develops between opposing membranes during dehydration. The hydration repulsion leads to a lateral compressive stress in the bilayer which squeezes adjacent lipids more closely together, resulting in a transition to the gel phase. When sugars are present, their osmotic and volumetric effects reduce the hydration repulsion, reduce the compressive stress in the membranes, and therefore tend to maintain the average lateral separation between lipids. This model is called the hydration forces explanation (HFE). We recently showed that neither mono- nor di

  6. Density functional theory based comparative study of electronic structures and magnetic properties of spinel ACr2O4 (A  =  Mn, Fe, Co, Ni) compounds

    NASA Astrophysics Data System (ADS)

    Das, Debashish; Ghosh, Subhradip

    2015-10-01

    Using the DFT+U method and generalized gradient approximation (GGA) we perform the first systematic study of the chromite series ACr2O4 (A  =  Mn, Fe, Co, Ni) by computing their structural and magnetic properties. The results are analyzed by their electronic structures. We find that in spite of varying structural distortions, the electronic structures are very similar across the series. Such similarities are responsible for qualitative uniformities in their magnetic phases at low temperatures, as observed in the experiments. We find that the strong electron-electron correlation, along with competing magnetic exchange splitting and the crystal field splitting, are responsible for their electronic properties such as the electronic band gaps. Our results regarding the magnetic exchange parameters are in good agreement with the available results and show the relative importance of the pairwise exchange interactions in each of the compounds. The ground state magnetic spin structures and the ferrimagnetic transition temperatures obtained from these exchange parameters, in combination with a phenomenological theory, qualitatively agree with the experiments and other theoretical results.

  7. Electronic structure of Al- and Ga-doped ZnO films studied by hard X-ray photoelectron spectroscopy

    SciTech Connect

    Gabás, M.; Ramos Barrado, José R.; Torelli, P.; Barrett, N. T.

    2014-01-01

    Al- and Ga-doped sputtered ZnO films (AZO, GZO) are semiconducting and metallic, respectively, despite the same electronic valence structure of the dopants. Using hard X-ray photoelectron spectroscopy we observe that both dopants induce a band in the electronic structure near the Fermi level, accompanied by a narrowing of the Zn 3d/O 2p gap in the valence band and, in the case of GZO, a substantial shift in the Zn 3d. Ga occupies substitutional sites, whereas Al dopants are in both substitutional and interstitial sites. The latter could induce O and Zn defects, which act as acceptors explaining the semiconducting character of AZO and the lack of variation in the optical gap. By contrast, mainly substitutional doping is consistent with the metallic-like behavior of GZO.

  8. Screened Hybrid and DFT + U Studies of the Structural, Electronic, and Optical Properties of U3O8

    SciTech Connect

    Wen, Xiaodong; Martin, Richard L.; Scuseria, Gustavo E.; Rudin, Sven P.; Batista, Enrique R.; Burrell, Anthony K.

    2012-11-26

    A systematic comparison of the structures and electronic and optical properties of U3O8 in the c2mm, P¯62m, and P21/m structures (the α, β, and γ phases, respectively) is performed using density functional theory + U (PBE + U) and the Heyd–Scuseria–Ernzerhof screened hybrid functional (HSE). The relationship between the semiconducting C2mm phase of U3O8 and the high temperature, metallic P¯62m phase is explored in more detail. Our calculated results show that the HSE functional gives a better description of the electronic and optical properties when compared with available experimental data for the α and β phases, but neither approach does particularly well for the high pressure γ phase.

  9. A First-Principles Study on the Structural and Electronic Properties of Sn-Based Organic-Inorganic Halide Perovskites

    NASA Astrophysics Data System (ADS)

    Ma, Zi-Qian; Pan, Hui; Wong, Pak Kin

    2016-11-01

    Organic-inorganic halide perovskites have attracted increasing interest on solar-energy harvesting because of their outstanding electronic properties. In this work, we systematically investigate the structural and electronic properties of Sn-based hybrid perovskites MASnX3 and FASnX3 (X = I, Br) based on density-functional-theory calculations. We find that their electronic properties strongly depend on the organic molecules, halide atoms, and structures. We show that there is a general rule to predict the band gap of the Sn-based hybrid perovskite: its band gap increases as the size of halide atom decreases as well as that of organic molecule increase. The band gap of high temperature phase (cubic structure) is smaller than that of low temperature phase (orthorhombic structure). The band gap of tetragonal structure (medium-temperature phase) may be larger or smaller than that of cubic phase, depending on the orientation of the molecule. Tunable band gap within a range of 0.73-1.53 eV can be achieved by choosing halide atom and organic molecule, and controlling structure. We further show that carrier effective mass also reduces as the size of halide atom increases and that of molecule decreases. By comparing with Pb-based hybrid perovskites, the Sn-based systems show enhanced visible-light absorption and carrier mobility due to narrowed band gap and reduced carrier effective mass. These Sn-based organic-inorganic halide perovskites may find applications in solar energy harvesting with improved performance.

  10. A First-Principles Study on the Structural and Electronic Properties of Sn-Based Organic-Inorganic Halide Perovskites

    NASA Astrophysics Data System (ADS)

    Ma, Zi-Qian; Pan, Hui; Wong, Pak Kin

    2016-08-01

    Organic-inorganic halide perovskites have attracted increasing interest on solar-energy harvesting because of their outstanding electronic properties. In this work, we systematically investigate the structural and electronic properties of Sn-based hybrid perovskites MASnX3 and FASnX3 (X = I, Br) based on density-functional-theory calculations. We find that their electronic properties strongly depend on the organic molecules, halide atoms, and structures. We show that there is a general rule to predict the band gap of the Sn-based hybrid perovskite: its band gap increases as the size of halide atom decreases as well as that of organic molecule increase. The band gap of high temperature phase (cubic structure) is smaller than that of low temperature phase (orthorhombic structure). The band gap of tetragonal structure (medium-temperature phase) may be larger or smaller than that of cubic phase, depending on the orientation of the molecule. Tunable band gap within a range of 0.73-1.53 eV can be achieved by choosing halide atom and organic molecule, and controlling structure. We further show that carrier effective mass also reduces as the size of halide atom increases and that of molecule decreases. By comparing with Pb-based hybrid perovskites, the Sn-based systems show enhanced visible-light absorption and carrier mobility due to narrowed band gap and reduced carrier effective mass. These Sn-based organic-inorganic halide perovskites may find applications in solar energy harvesting with improved performance.

  11. Occupied and unoccupied electronic structures of an L-cysteine film studied by core-absorption and resonant photoelectron spectroscopies

    NASA Astrophysics Data System (ADS)

    Kamada, M.; Hideshima, T.; Azuma, J.; Yamamoto, I.; Imamura, M.; Takahashi, K.

    2016-04-01

    Unoccupied and occupied electronic structures of an L-cysteine film have been studied by absorption and resonant photoelectron spectroscopies. Core absorptions at S-L, C-K, N-K, and O-K levels indicate that the lower unoccupied states are predominantly composed of oxygen-2p, carbon-2p, and sulfur-4s+3d orbitals, while higher unoccupied states may be attributed dominantly to nitrogen-np (n ≥ 3), oxygen-np (n ≥ 3), and sulfur-ns+md (n ≥ 4, m ≥ 3) orbitals. Resonant photoelectron spectra at S-L23 and O-K levels indicate that the highest occupied state is originated from sulfur-3sp orbitals, while oxygen-2sp orbitals contribute to the deeper valence states. The delocalization lifetimes of the oxygen-1s and sulfur-2p excited states are estimated from a core-hole clock method to be about 9 ± 1 and 125 ± 25 fs, respectively.

  12. Study of molecular structure, vibrational, electronic and NMR spectra of oncocalyxone A using DFT and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Joshi, Bhawani Datt; Srivastava, Anubha; Honorato, Sara Braga; Tandon, Poonam; Pessoa, Otília Deusdênia Loiola; Fechine, Pierre Basílio Almeida; Ayala, Alejandro Pedro

    2013-09-01

    Oncocalyxone A (C17H18O5) is the major secondary metabolite isolated from ethanol extract from the heartwood of Auxemma oncocalyx Taub popularly known as “pau branco”. Oncocalyxone A (Onco A) has many pharmaceutical uses such as: antitumor, analgesic, antioxidant and causative of inhibition of platelet activation. We have performed the optimized geometry, total energy, conformational study, molecular electrostatic potential mapping, frontier orbital energy gap and vibrational frequencies of Onco A employing ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) method with 6-311++G(d, p) basis set. Stability of the molecule arising from hyperconjugative interactions and/or charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV-vis spectrum of the compound was recorded in DMSO and MeOH solvent. The TD-DFT calculations have been performed to explore the influence of electronic absorption spectra in the gas phase, as well as in solution environment using IEF-PCM and 6-31G basis set. The 13C NMR chemical shifts have been calculated with the B3LYP/6-311++G(d, p) basis set and compared with the experimental values. These methods have been used as tools for structural characterization of Onco A.

  13. Stability and electronic structure of the low- Σ grain boundaries in CdTe: a density functional study

    DOE PAGES

    Park, Ji-Sang; Kang, Joongoo; Yang, Ji-Hui; Metzger, Wyatt; Wei, Su-Huai

    2015-01-15

    Using first-principles density functional calculations, we investigate the relative stability and electronic structure of the grain boundaries (GBs) in zinc-blende CdTe. Among the low-Σ-value symmetric tilt Σ3 (111), Σ3 (112), Σ5 (120), and Σ5 (130) GBs, we show that the Σ3 (111)GB is always the most stable due to the absence of dangling bonds and wrong bonds. The Σ5 (120) GBs, however, are shown to be more stable than the Σ3 (112) GBs, even though the former has a higher Σ value, and the latter is often used as a model system to study GB effects in zinc-blende semiconductors. Furthermore,more » we find that although containing wrong bonds, the Σ5 (120) GBs are electrically benign due to the short wrong bond lengths, and thus are not as harmful as the Σ3 (112) GBs also having wrong bonds but with longer bond lengths.« less

  14. Structural and electronic properties of CdS/ZnS core/shell nanowires: A first-principles study

    NASA Astrophysics Data System (ADS)

    Kim, Hyo Seok; Kim, Yong-Hoon

    2015-03-01

    Carrying out density functional theory (DFT) calculation, we studied the relative effects of quantum confinement and strain on the electronic structures of II-IV semiconductor compounds with a large lattice-mismatch, CdS and ZnS, in the core/shell nanowire geometry. We considered different core radii and shell thickness of the CdS/ZnS core/shell nanowire, different surface facets, and various defects in the core/shell interface and surface regions. To properly describe the band level alignment at the core/shell boundary, we adopted the self-interaction correction (SIC)-DFT scheme. Implications of our findings in the context of device applications will be also discussed. This work was supported by the Basic Science Research Grant (No. 2012R1A1A2044793), Global Frontier Program (No. 2013-073298), and Nano-Material Technology Development Program (2012M3A7B4049888) of the National Research Foundation funded by the Ministry of Education, Science and Technology of Korea. Corresponding author

  15. Two ferromagnetic azido-bridged copper(ll) complexes studied by first-principle electronic-structure calculation.

    PubMed

    Zhang, Y S; Yao, K L; Liu, Z L

    2005-09-22

    The electronic structures of two ferromagnetic polynuclear copper(II) complexes, derived from end-to-end azido ligand and tridentate (NNN donor) Schiff base ligand, have been studied using the full-potential linearized augmented plane-wave method based on the density-functional theory. They are [Cu(L1)(micro-1,3-N3)]n(ClO4)n (1) and [Cu(L2)(micro-1,3-N3)]n(ClO4)n (2). The result shows that the spin populations in these two complexes are mainly distributed on the equatorial planes of a square pyramidal that surround the copper(II) ions. There are large and positive spin populations on copper(II) ions, small and positive spin populations on the three nitrogen atoms of tridentate Schiff base ligand, and the two terminal nitrogen atoms of asymmetrical end-to-end azido ligand, while weak and negative spin populations on the central nitrogen atoms of asymmetrical end-to-end azido ligand. Ferromagnetic coupling through the asymmetrical azido ligand in these two complexes has been mainly attributed to the spin delocalization, also with weak spin-polarization effect. PMID:16392483

  16. Two ferromagnetic azido-bridged copper(II) complexes studied by first-principle electronic-structure calculation

    NASA Astrophysics Data System (ADS)

    Zhang, Y. S.; Yao, K. L.; Liu, Z. L.

    2005-09-01

    The electronic structures of two ferromagnetic polynuclear copper(II) complexes, derived from end-to-end azido ligand and tridentate (NNN donor) Schiff base ligand, have been studied using the full-potential linearized augmented plane-wave method based on the density-functional theory. They are [Cu(L1)(μ-1,3-N3)]n(ClO4)n (1) and [Cu(L2)(μ-1,3-N3)]n(ClO4)n (2). The result shows that the spin populations in these two complexes are mainly distributed on the equatorial planes of a square pyramidal that surround the copper(II) ions. There are large and positive spin populations on copper(II) ions, small and positive spin populations on the three nitrogen atoms of tridentate Schiff base ligand, and the two terminal nitrogen atoms of asymmetrical end-to-end azido ligand, while weak and negative spin populations on the central nitrogen atoms of asymmetrical end-to-end azido ligand. Ferromagnetic coupling through the asymmetrical azido ligand in these two complexes has been mainly attributed to the spin delocalization, also with weak spin-polarization effect.

  17. Structural and electronic properties of free standing one-sided and two-sided hydrogenated silicene: A first principle study

    SciTech Connect

    Mohan, Brij Kumar, Ashok Ahluwalia, P. K.

    2014-04-24

    We performed first-principle study of the structural and electronic properties of two-dimensional hydrogenated silicene for two configurations; one is hydrogenation along one side of silicene sheet and second is hydrogenation in both sides of silicene sheet. The one-side hydrogenated silicene is found stable at planar geometry while increased buckling of 0.725 Å is found for both-side hydrogenated silicene. The result shows that the hydrogenation occupy the extended π-bonding network of silicene, and thus it exhibits semi-conducting behaviour with a band gap of 1.77 eV and 2.19 eV for one-side hydrogenated silicene and both-side hydrogenated silicene respectively. However, both-side hydrogenated silicene of binding energy 4.56 eV is more stable than one-side hydrogenated silicene of binding energy 4.30 eV, but experimentally silicene is synthesized on substrates which interacts one side of silicene layer and only other side is available for H-atoms. Therefore, practically one-side hydrogenation is also important.

  18. First-principles study on the structural, electronic, and optical properties of Ca1- x Sr x Se alloys

    NASA Astrophysics Data System (ADS)

    Ahmadian, F.; Salary, A.

    2016-01-01

    The structural, electronic, and optical properties of binary CaSe and SrSe compounds and Ca1- x Sr x Se alloys were studied by using the full potential linearized augmented plane wave (FPLAPW) method within density functional theory (DFT). The band structure calculations showed that the CaSe and the SrSe binary compounds in the rocksalt (RS), zinc-blende (ZB) and wurtzite (WZ) phases were semiconductors while they had a metallic characteristic in the CsCl phase. The lattice constant and bulk modulus values for the Ca1- x Sr x Se alloys in the RS and the ZB phases at different concentrations were calculated and compared with those obtained by using Vegard's law. The energy band gap values in the RS and the ZB phases were estimated for different x values by using both define acronyms the Perdew, Burke, and Ernzerhof (PBE-GGA) and the Engel and Vosko (EV-GGA) schemes, and the results were compared with those obtained by using the empirical electronegativity expression. The band gap bowing parameters were calculated by using quadratic functions and the procedure of Bernard and Zunger to fit the non-linear variation of the band gaps. The static dielectric constant ɛ 1(0) was calculated at different concentrations. The energy loss function L( ω) for the Ca1- x Sr x Se alloys in the RS and the ZB phases has a main peak corresponding to the plasmon frequency. The values of the static refractive index ( n(0)) for the Ca1- x Sr x Se alloys were calculated and compared with the values predicted by using the Moss, Ravindra, and Vandamme models. Finally, the extinction indic incident photon energies. es ( k( ω)) and the reflectivities ( R( ω)) for the Ca1- x Sr x Se alloys were calculated within a wide range of incident photon energies.

  19. Theoretical and Electrochemical Study of the Quinone-Benzoic Acid Adduct Linked by Hydrogen Bonds DFT Study of Electronic Structure and Geometry of Neutral and Anionic Silver Clusters

    SciTech Connect

    Matulis, Vitaly E.; Ivashkevich, Oleg A.; Gurin, Valerij

    2003-12-15

    A comparative analysis of bond lengths vertical detachment energies (VDE), excitation energies of neutral clusters with geometry of anions and vertical ionization potentials of neutral clusters calculated within density functional theory (DFT) using different functionals with both effective core potential (ECP) and all-electron basis sets for silver clusters Ag n, have been carried out. DFT methods provide a good agreement between calculated and experimental data of some characteristics. The accurate prediction of all characteristics simultaneously can be achieved with all-electron DZVP basis set only. A new functional has been developed. It provides results close to experimental data using the moderate basis set. For anionic clusters Ag2?10-, the difference between calculations with this functional and experimental values of VDE and for the most stable isomers does not exceed 0.1 eV. Based on both total energy calculations and comparison of experimental and calculated photoelectron spectra, the structural assignment of clusters Ag7-, Ag9- and Ag10- has been made. The electronic structure and geometrical characteristics of the low-lying isomers has been studied.

  20. First principles study on the electronic structures and stability of Cr 7C 3 type multi-component carbides

    NASA Astrophysics Data System (ADS)

    Xiao, B.; Feng, J.; Zhou, C. T.; Xing, J. D.; Xie, X. J.; Chen, Y. H.

    2008-06-01

    First principles calculations were conducted to investigate the stabilities of six multi-component carbides of Cr 7C 3 by calculating the cohesive energy and formation enthalpy of them. The theoretical predictions were compared with the experimental results and they were in agreement with each other. The electronic structures of the six carbides were also calculated in order to provide more information about the relationship between the stability and crystal compositions at atomic scale.

  1. First-principles study of graphene under c-HfO2(111) layers: Electronic structures and transport properties

    NASA Astrophysics Data System (ADS)

    Kaneko, Tomoaki; Ohno, Takahisa

    2016-08-01

    We investigated the electronic properties, stability, and transport of graphene under c-HfO2(111) layers by performing first-principles calculations with special attention to the chemical bonding between graphene and HfO2 surfaces. When the interface of HfO2/graphene is terminated by an O layer, the linear dispersion of graphene is preserved and the degradation of transport is suppressed. For other interface structures, HfO2 is tightly adsorbed on graphene and the transport is strictly limited. In terms of the stability of the interface structures, an O-terminated interface is preferable, which is achieved under an O-deficient condition.

  2. Density Functional Study of Structures and Electron Affinities of BrO4F/BrO4F−

    PubMed Central

    Gong, Liangfa; Xiong, Jieming; Wu, Xinmin; Qi, Chuansong; Li, Wei; Guo, Wenli

    2009-01-01

    The structures, electron affinities and bond dissociation energies of BrO4F/BrO4F− species have been investigated with five density functional theory (DFT) methods with DZP++ basis sets. The planar F-Br…O2…O2 complexes possess 3A′ electronic state for neutral molecule and 4A′ state for the corresponding anion. Three types of the neutral-anion energy separations are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The EAad value predicted by B3LYP method is 4.52 eV. The bond dissociation energies De (BrO4F → BrO4-mF + Om) (m = 1–4) and De− (BrO4F− → BrO4-mF− + Om and BrO4F− → BrO4-mF + Om−) are predicted. The adiabatic electron affinities (EAad) were predicted to be 4.52 eV for F-Br…O2…O2 (3A′←4A′) (B3LYP method). PMID:19742128

  3. Equivalence of electronic and mechanical stresses in structural phase stabilization: A case study of indium wires on Si(111)

    NASA Astrophysics Data System (ADS)

    Kim, Sun-Woo; Kim, Hyun-Jung; Ming, Fangfei; Jia, Yu; Zeng, Changgan; Cho, Jun-Hyung; Zhang, Zhenyu

    2015-05-01

    It was recently proposed that the stress state of a material can also be altered via electron or hole doping, a concept termed electronic stress (ES), which is different from the traditional mechanical stress (MS) due to lattice contraction or expansion. Here we demonstrate the equivalence of ES and MS in structural stabilization, using In wires on Si(111) as a prototypical example. Our systematic density-functional theory calculations reveal that, first, for the same degrees of carrier doping into the In wires, the ES of the high-temperature metallic 4 ×1 structure is only slightly compressive, while that of the low-temperature insulating 8 ×2 structure is much larger and highly anisotropic. As a consequence, the intrinsic energy difference between the two phases is significantly reduced towards electronically phase-separated ground states. Our calculations further demonstrate quantitatively that such intriguing phase tunabilities can be achieved equivalently via lattice-contraction induced MS in the absence of charge doping. We also validate the equivalence through our detailed scanning tunneling microscopy experiments. The present findings have important implications for understanding the underlying driving forces involved in various phase transitions of simple and complex systems alike.

  4. Comparison of Electronic and Optical Properties of GaN Monolayer and Bulk Structure: a First Principle Study

    NASA Astrophysics Data System (ADS)

    Imran, Muhammad; Hussain, Fayyaz; Rashid, Muhammad; Ullah, Hafeez; Sattar, Atif; Iqbal, Faisal; Ahmad, Ejaz

    2016-03-01

    The semiconducting two-dimensional (2D) architectures materials have potential applications in electronics and optics. The design and search of new 2D materials have attracted extensive attention recently. In this study, first principle calculation has been done on 2D gallium nitride (GaN) monolayer with respect to its formation and binding energies. The electronic and optical properties are also investigated. It is found that the single isolated GaN sheet is forming mainly ionic GaN bonds despite a slightly weaker GaN interaction as compared with its bulk counterpart. The dielectric constant value of 2D GaN is smaller as compared to 3D GaN due to less effective electronic screening effect in the layer, which is accompanied by lesser optical adsorption range and suggested to be a promising candidate in electronic and optoelectronic devices.

  5. X-ray absorption and infrared spectra of water and ice: A first-principles electronic structure study

    NASA Astrophysics Data System (ADS)

    Chen, Wei

    Water is of essential importance for chemistry and biology, yet the physics concerning many of its distinctive properties is not well known. In this thesis we present a theoretical study of the x-ray absorption (XA) and infrared (IR) spectra of water in liquid and solid phase. Our theoretical tools are the density functional theory (DFT), Car-Parrinello (CP) molecular dynamics (MD), and the so-called GW method. Since a systematic review of these ab initio methods is not the task of this thesis, we only briefly recall the main concepts of these methods as needed in the course of our exposition. The focus is, instead, an investigation of what is the important physics necessary for a better description of these excitation processes, in particular, core electron excitations (in XA) that reveal the local electronic structure, and vibrational excitations (in IR) associated to the molecular dynamics. The most interesting question we are trying to answer is: as we include better approximations and more complete physical descriptions of these processes, how do the aforementioned spectra reflect the underlying hydrogen-bonding network of water? The first part of this thesis consists of the first four chapters, which focus on the study of core level excitation of water and ice. The x-ray absorption spectra of water and ice are calculated with a many-body approach for electron-hole excitations. The experimental features, even the small effects of a temperature change in the liquid, are reproduced with quantitative detail using molecular configurations generated by ab initio molecular dynamics. We find that the spectral shape is controlled by two major modifications of the short range order that mark the transition from ice to water. One is associated to dynamic breaking of the hydrogen bonds which leads to a strong enhancement of the pre-edge intensity in the liquid. The other is due to densification, which follows the partial collapse of the hydrogen bond network and is

  6. Ab-initio study of the magnetism, structure and spin dependent electronic states of Ti substituted MO (M = Mg, Ca, Sr)

    SciTech Connect

    Jaiganesh, G. Jaya, S. Mathi

    2015-06-24

    The magnetism, structure and spin polarized electronic structure of Ti substituted MO (M = Mg, Ca, Sr) are studied using the ab-initio techniques within the framework of the density functional theory. Appropriately constructed supercell along with the full structural optimization of these cells is used for studying the influence of Ti substitution on the magnetism and electronic structure of these compounds. We find from our calculations that the Ti substituted MO compounds energetically favor magnetically ordered state. The Ti concentration is found to be important in deciding the magnetic order and we have observed antiferromagnetic order for the Ti concentration of 0.25. The Ti substituted MO compounds are thus an interesting class of materials that deserve further studies.

  7. Dependency of magnetic microwave absorption on surface architecture of Co20Ni80 hierarchical structures studied by electron holography

    NASA Astrophysics Data System (ADS)

    Liu, Qinhe; Xu, Xianhui; Xia, Weixing; Che, Renchao; Chen, Chen; Cao, Qi; He, Jingang

    2015-01-01

    To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a series of Co20Ni80 hierarchical structures with different surface morphologies, including flower-, urchin-, ball-, and chain-like morphologies, were obtained using structure-directing templates via a facile one-step solvothermal treatment. The microwave reflection loss (RL) of urchin-like Co20Ni80 hierarchical structures reaches as high as -33.5 dB at 3 GHz, with almost twice the RL intensity of the ball- and chain-like structures, and the absorption bandwidth (<-10 dB) is about 5.5 GHz for the flower-like morphology, indicating that the surface nanospikes and nanoflakes on the Co20Ni80 microsphere surfaces have great influences on their magnetic microwave absorption properties. Electron holography analysis reveals that the surface nanospikes and nanoflakes could generate a high density of stray magnetic flux lines and contribute a large saturation magnetization (105.62 emu g-1 for urchin-like and 96.41 emu g-1 for flower-like morphology), leading the urchin-like and flower-like Co20Ni80 to possess stronger microwave RL compared with the ball-like and chain-like Co20Ni80 alloys. The eddy-current absorption mechanism μ''(μ')-2(f)-1 is dominant in the frequency region above 8 GHz, implying that eddy-current loss is a vital factor for microwave RL in the high frequency range. It can be supposed from our findings that different surface morphologies of magnetic hierarchical structures might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a

  8. First-principles study on the structural and electronic properties of metallic HfH2 under pressure

    PubMed Central

    Liu, Yunxian; Huang, Xiaoli; Duan, Defang; Tian, Fubo; Liu, Hanyu; Li, Da; Zhao, Zhonglong; Sha, Xiaojing; Yu, Hongyu; Zhang, Huadi; Liu, Bingbing; Cui, Tian

    2015-01-01

    The crystal structures and properties of hafnium hydride under pressure are explored using the first-principles calculations based on density function theory. The material undergoes pressure-induced structural phase transition I4/mmm→Cmma→P21/m at 180 and 250 GPa, respectively, and all of these structures are metallic. The superconducting critical temperature Tc values of I4/mmm, Cmma, and P21/m are 47–193 mK, 5.99–8.16 K and 10.62–12.8 K at 1 atm, 180 and 260 GPa, respectively. Furthermore, the bonding nature of HfH2 is investigated with the help of the electron localization function, the difference charge density and Bader charge analyses, which show that HfH2 is classified as a ionic crystal with the charges transferring from Hf atom to H. PMID:26096298

  9. Ab initio study of structural, mechanical, thermal and electronic properties of perovskites Sr(Li,Pd)H3

    NASA Astrophysics Data System (ADS)

    Benlamari, S.; Amara Korba, S.; Lakel, S.; Meradji, H.; Ghemid, S.; El Haj Hassan, F.

    2016-01-01

    The structural, elastic, thermal and electronic properties of perovskite hydrides SrLiH3 and SrPdH3 have been investigated using the all-electron full-potential linear augmented plane wave (FP-LAPW) method based on the density functional theory (DFT). For the exchange-correlation potential, local-density approximation (LDA) and generalized gradient approximation (GGA) have been used to calculate theoretical lattice parameters, bulk modulus, and its pressure derivative. The present results are in good agreement with available theoretical and experimental data. The three independent elastic constants (C11, C12 and C44) are also reported. From electronic band structure and density of states (DOSs), it is found that SrLiH3 is an insulator characterized by an indirect gap of 3.48 eV, while SrPdH3 is metallic with a calculated DOSs at Fermi energy of 0.745 states/eV-unit cell. Poisson’s ratio (σ), Young’s modulus (E), shear modulus (G), anisotropy factor (A), average sound velocities (vm) and density (ρ) of these compounds are also estimated for the first time. The Debye temperature is deduced from the average sound velocity. Variation of elastic constants and bulk modulus of these compounds as a function of pressure is also reported. Pressure and thermal effects on some macroscopic properties are predicted using the quasi-harmonic Debye model.

  10. Exploring the electronic structure of nitrogen-modified TiO 2 photocatalysts through photocurrent and surface photovoltage studies

    NASA Astrophysics Data System (ADS)

    Beranek, Radim; Neumann, Bernhard; Sakthivel, Shanmugasundaram; Janczarek, Marcin; Dittrich, Thomas; Tributsch, Helmut; Kisch, Horst

    2007-10-01

    Wavelength resolved surface photovoltage (SPV) and photocurrent measurements in the presence of various reducing agents were conducted to obtain experimental evidence for the electronic structure of the valence band region in novel nitrogen modified anatase powders containing 0.5, 1.0, and 11.7 wt% of nitrogen. In the presence of air and absence of a hole scavenger a weak SPV signal was observable already in the visible region but completely vanished in the UV above 3.40 eV suggesting complete charge recombination. Whereas in the presence of formic acid only upon UV excitation the signal was increased, this occurred already upon Vis light irradiation when iodide was the hole scavenger. Similarly, in the photocurrent measurements visible light irradiation induced an enhancement only in the presence of iodide or hydroquinone, whereas water, thiocyanate, and formate were not oxidized efficiently since their redox potential is more positive than that of holes trapped in the region of the upper valence band edge. These findings were rationalized by assuming a strong electronic coupling of N 2p states with titania O 2p levels that generates a novel valence band with a red-shifted band edge. It is therefore expected that holes produced in this band will efficiently relax to the band edge followed by recombination with conduction band electrons. Depending on the reduction potential of the hole scavenger, interfacial electron transfer may successfully compete with this process.

  11. Electronic structure of oxide, peroxide, and superoxide clusters of the 3d elements: A comparative density functional study

    NASA Astrophysics Data System (ADS)

    Uzunova, Ellie L.; Mikosch, Hans; Nikolov, Georgi St.

    2008-03-01

    The 3d-element transition metal dioxide MO2, peroxide M(O2), and superoxide MOO clusters (M=Sc-Zn), are studied by density functional theory with the B1LYP functional. The reliability of the methods and basis sets employed was tested by a reinvestigation of the monoxides, for which a database of experimental data is available. The global minima on the M+O2 potential energy surfaces correspond to dioxide structure, the only exception being CuOO, with a superoxide structure. All Zn dioxygen clusters are thermodynamically unstable-their ground states lie higher than the dissociation limit to Zn+O2. Our calculations are in favor of the high-spin configurations for the FeO2, CoO2, and NiO2 ground states, which are still a subject of extensive theoretical and experimental studies. These assignments are confirmed by the coupled-cluster method, CCSD(T), except for NiO2. Based on the existence of a stable NiO2 monoanion in a 4B1 state, however, it can be concluded that NiO2 in its 5A1 state should also be stable. The vibrational frequencies are calculated for clusters entrapped in the cubic cell of solid Ar matrix and compared with those obtained for gas-phase clusters. The matrix has no influence on the vibrations of the monoxides and most of the dioxides; however, Co and Ni-dioxoclusters interact strongly with the atoms from the noble gas matrix. The most intense frequencies in the IR spectra are shifted to lower energies and the ordering of the low-lying electronic states by stability is also reversed. According to the electrostatic potential maps, the oxygen atoms in the peroxides are more nucleophilic than those in the dioxides and superoxides. The terminal oxygen atom in superoxides is more nucleophilic than its M-bonded oxygen atom, though charge distribution analysis predicts a smaller negative charge on the terminal oxygen. TiO2 is the only dioxide in which nucleophilic character in the vicinity of the metal cation is induced.

  12. Ab initio study on structural, electronic properties, and hardness of re-doped W2B5

    NASA Astrophysics Data System (ADS)

    Feng, ShiQuan; Li, XiaoDong; Su, Lei; Li, HaiNing; Yang, Hongyan; Cheng, Xinlu

    2016-11-01

    Using first principle calculations method, we calculated the structural stability, electronic properties and hardness for three Re-doped hexagonal W2B5 compounds. The electronic properties were carried out to discuss the effect of doped Re on the conductivity, chemical bonding components and orbital hybridization of W2B5. What is more, the hardness of these three doped crystals was calculated by a semiempirical method considering the role of metallic components. A Re-doped W2B5 compound with a greater hardness value than that of pure W2B5 was obtained. And the effect of doping on the hardness of hexagonal W2B5was discussed.

  13. First-principles study of the structural, elastic, electronic, optical, and vibrational properties of intermetallic Pd2Ga

    NASA Astrophysics Data System (ADS)

    Yildirim, A.; Koc, H.; Deligoz, E.

    2012-03-01

    The structural, elastic, electronic, optical, and vibrational properties of the orthorhombic Pd2Ga compound are investigated using the norm-conserving pseudopotentials within the local density approximation in the frame of density functional theory. The calculated lattice parameters have been compared with the experimental values and found to be in good agreement with these results. The second-order elastic constants and the other relevant quantities, such as the Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocity, and Debye temperature, have been calculated. It is shown that this compound is mechanically stable after analysing the calculated elastic constants. Furthermore, the real and imaginary parts of the dielectric function and the optical constants, such as the optical dielectric constant and the effective number of electrons per unit cell, are calculated and presented. The phonon dispersion curves are derived using the direct method. The present results demonstrate that this compound is dynamically stable.

  14. A comparative density functional theory study of electronic structure and optical properties of γ-aminobutyric acid and its cocrystals with oxalic and benzoic acid

    NASA Astrophysics Data System (ADS)

    da Silva Filho, J. G.; Freire, V. N.; Caetano, E. W. S.; Ladeira, L. O.; Fulco, U. L.; Albuquerque, E. L.

    2013-11-01

    In this letter, we study the electronic structure and optical properties of the active medicinal component γ-aminobutyric acid (GABA) and its cocrystals with oxalic (OXA) and benzoic (BZA) acid by means of the density functional theory formalism. It is shown that the cocrystallization strongly weakens the zwitterionic character of the GABA molecule leading to striking differences among the electronic band structures and optical absorption spectra of the GABA crystal and GABA:OXA, GABA:BZA cocrystals, originating from distinct sets of hydrogen bonds. Calculated band widths and Δ-sol band gap estimates indicate that both GABA and GABA:OXA, GABA:BZA cocrystals are indirect gap insulators.

  15. Ab initio Study of the Structural, Tautomeric, Pairing and Electronic Properties of Seleno-Derivatives of Thymine

    SciTech Connect

    Vazquez-Mayagoitia, Alvaro; Fuentes-Cabrera, Miguel A; Sumpter, Bobby G; Luque, Javier; Huertas, Oscar; Orozco, Modesto; Felice, Rosa; Brancolini, Giorgia; Migliore, Agostino

    2009-01-01

    The structural, tautomeric, hydrogen-bonding, stacking and electronic properties of a seleno-derivative of thymine (T), denoted here as 4SeT and created by replacing O4 in T with Se, are investigated by means of ab initio computational techniques. The structural properties of T and 4SeT are very similar and the geometrical differences are mainly limited to the adjacent environment of the C-Se bond. The canonical keto form is the most stable tautomer, in gas phase and in aqueous solution, for both T and 4SeT. It is argued that the competition between two opposite trends, i.e. a decrease in the base-pairing ability and an increase of the stacking interaction upon incorporation of 4SeT into a duplex, likely explains the similar experimental melting points of a seleno-derivative duplex (Se-DNA) and its native counterpart. Interestingly, the underlying electronic structure shows that replacement of O4 with Se promotes a reduction in the HOMO-LUMO gap and an increase in inter-plane coupling, which suggests that Se-DNA could be potentially useful for nanodevice applications. This finding is further supported by the fact that transfer integrals between 4SeT---A stacked base pairs are larger than those determined for similarly stacked natural T---A pairs.

  16. EPR, ENDOR, and Electronic Structure Studies of the Jahn–Teller Distortion in an FeV Nitride

    PubMed Central

    2015-01-01

    The recently synthesized and isolated low-coordinate FeV nitride complex has numerous implications as a model for high-oxidation states in biological and industrial systems. The trigonal [PhB(tBuIm)3FeV≡N]+ (where (PhB(tBuIm)3– = phenyltris(3-tert-butylimidazol-2-ylidene)), (1) low-spin d3 (S = 1/2) coordination compound is subject to a Jahn–Teller (JT) distortion of its doubly degenerate 2E ground state. The electronic structure of this complex is analyzed by a combination of extended versions of the formal two-orbital pseudo Jahn–Teller (PJT) treatment and of quantum chemical computations of the PJT effect. The formal treatment is extended to incorporate mixing of the two e orbital doublets (30%) that results from a lowering of the idealized molecular symmetry from D3h to C3v through strong “doming” of the Fe–C3 core. Correspondingly we introduce novel DFT/CASSCF computational methods in the computation of electronic structure, which reveal a quadratic JT distortion and significant e–e mixing, thus reaching a new level of synergism between computational and formal treatments. Hyperfine and quadrupole tensors are obtained by pulsed 35 GHz ENDOR measurements for the 14/15N-nitride and the 11B axial ligands, and spectra are obtained from the imidazole-2-ylidene 13C atoms that are not bound to Fe. Analysis of the nitride ENDOR tensors surprisingly reveals an essentially spherical nitride trianion bound to Fe, with negative spin density and minimal charge density anisotropy. The four-coordinate 11B, as expected, exhibits negligible bonding to Fe. A detailed analysis of the frontier orbitals provided by the electronic structure calculations provides insight into the reactivity of 1: JT-induced symmetry lowering provides an orbital selection mechanism for proton or H atom transfer reactivity. PMID:25137531

  17. An ab initio study of electronic structure and spectra of 8-bromoguanine: a comparative study with guanine.

    PubMed

    Mishra, S K; Mishra, P C

    2001-10-01

    Ground state geometries of the four tautomeric forms keto-N9H, keto-N7H, enol-N9H and enol-N7H of 8-bromoguanine (8BG) were optimized using the ab initio RHF procedure employing a mixed basis set consisting of the 6-311 + G* basis set for the nitrogen atom of the amino group and the bromine atom, and the 4-31G basis set for all other atoms. These calculations were followed by correlation correction of the total energy at the MP2 level using the same basis set. The different tautomeric forms of 8BG in the ground state were solvated using the isodensity surface polarized continuum model (IPCM) of the SCRF theory both at the RHF and MP2 levels. Excited states were generated employing configuration interaction among singly excited configurations (CIS) obtained using a limited window of filled and empty molecular orbitals. Formation of hydrogen-bonded complexes between 8BG and three water molecules in the ground and excited states was considered in order to account for solvent effects approximately. Excited state geometry was optimized in each case for the lowest singlet excited state which was found to be of pi-pi* type. Vibrational frequency analysis was performed in order to ensure that the stationary points located on the potential energy surfaces by geometry optimization were minima. It is found that 8BG would occur in the ground state dominantly in the keto-N7H form both at the aqueous solution-air interface and inside the bulk liquid. The observed absorption and fluorescence spectra of 8BG can be explained satisfactorily considering only the keto-N7H form of the molecule. The enol tautomers of 8BG do not appear to be important from the point of view of ground state properties or electronic spectra. The observed differences between the behaviors of guanine and 8BG can be easily explained on the basis of the results obtained.

  18. Electronic structure calculations on helical conducting polymers.

    PubMed

    Ripoll, Juan D; Serna, Andrei; Guerra, Doris; Restrepo, Albeiro

    2010-10-21

    We present a study of the electronic structure and derived properties of polyfurane (PFu), polypyrrol (PPy), and polythiophene (PTh). Two spatial arrangements are considered: trans chain (tc-PFu, tc-PPy, tc-PTh) and cis α-helical (α-PFu, α-PPy, α-PTh). Even at the small sizes considered here, helical conformations appear to be stable. Band gaps of pure, undoped oligomers fall into the semiconductor range. Density of states (DOS) analysis suggest dense valence and conduction bands. Bond length alternation analysis predicts almost complete delocalization of the π clouds in all spatial arrangements. Doping with electron donors or electron-withdrawing impurities reduces all band gaps close to the metallic regime in addition to increasing the DOS for the valence and conduction bands.

  19. Density functional study of the electronic structure and magnetism of LaFeAsO alloyed with Zn

    SciTech Connect

    Zhang, Lijun; Singh, David J

    2009-01-01

    We report first-principles supercell investigations of LaFe{sub 1-x}Zn{sub x}AsO. These are discussed in relation to existing experimental data on Zn-doped LaFeAsO. As expected, Zn occurs in a d{sup 10} configuration in the alloy, similar to the pure Zn compound LaZnAsO. This is highly disruptive to the electronic structure of LaFeAsO near the Fermi energy, which is heavily derived from Fe-d states. This favors localization and the formation of local moments on the Fe atoms near the Zn.

  20. First-principles study of electronic structure, optical and phonon properties of α-ZrW2O8

    NASA Astrophysics Data System (ADS)

    Li, Jinping; Meng, Songhe; Qin, Liyuan; Lu, Hantao

    2016-12-01

    ZrW2O8 exhibits isotropic negative thermal expansions over its entire temperature range of stability, yet so far its physical properties and mechanism have not been fully addressed. In this article, the electronic structure, elastic, thermal, optical and phonon properties of α-ZrW2O8 are systematically investigated from first principles. The agreements between the generalized gradient approximation (GGA) calculation and experiments are found to be quite satisfactory. The calculation results can be useful in relevant material designs, e.g., when ZrW2O8 is employed to adjust the thermal expansion coefficient of ceramic matrix composites.

  1. The structure of the hydrated electron. Part 2. A mixed quantum/classical molecular dynamics embedded cluster density functional theory: single-excitation configuration interaction study.

    PubMed

    Shkrob, Ilya A; Glover, William J; Larsen, Ross E; Schwartz, Benjamin J

    2007-06-21

    Adiabatic mixed quantum/classical (MQC) molecular dynamics (MD) simulations were used to generate snapshots of the hydrated electron in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the hydrated electron were extracted from the MQC MD simulations and embedded in a roughly 18 Ax18 Ax18 A matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory (DFT) with the Becke-Lee-Yang-Parr functional and single-excitation configuration interaction (CIS) methods were then applied to these embedded clusters. The salient feature of these hybrid DFT(CIS)/MQC MD calculations is significant transfer (approximately 18%) of the excess electron's charge density into the 2p orbitals of oxygen atoms in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the singly occupied and the lower unoccupied molecular orbitals, the density of states, the absorption spectra in the visible and ultraviolet, the hyperfine coupling (hfcc) tensors, and the infrared (IR) and Raman spectra of these embedded water cluster anions. The calculated hfcc tensors were used to compute electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectra for the hydrated electron that compared favorably to the experimental spectra of trapped electrons in alkaline ice. The calculated vibrational spectra of the hydrated electron are consistent with the red-shifted bending and stretching frequencies observed in resonance Raman experiments. In addition to reproducing the visible/near IR absorption spectrum, the hybrid DFT model also accounts for the hydrated electron's 190-nm absorption band in the ultraviolet. Thus, our study suggests that to explain several important experimentally observed properties of the hydrated electron, many-electron effects must be accounted for: one-electron models that do not allow for mixing of the excess

  2. Plane wave density functional theory studies of the structural and the electronic properties of amino acids attached to graphene oxide via peptide bonding

    NASA Astrophysics Data System (ADS)

    Min, Byeong June; Jeong, Hae Kyung; Lee, ChangWoo

    2015-08-01

    We studied via plane wave pseudopotential total-energy calculations within the local spin density approximation (LSDA) the electronic and the structural properties of amino acids (alanine, glycine, and histidine) attached to graphene oxide (GO) by peptide bonding. The HOMO-LUMO gap, the Hirshfeld charges, and the equilibrium geometrical structures exhibit distinctive variations that depend on the species of the attached amino acid. The GO-amino acid system appears to be a good candidate for a biosensor.

  3. Electronic structure of CuTPP and CuTPP(F) complexes: a combined experimental and theoretical study II.

    PubMed

    Mangione, Giulia; Sambi, Mauro; Carlotto, Silvia; Vittadini, Andrea; Ligorio, Giovanni; Timpel, Melanie; Pasquali, Luca; Giglia, Angelo; Nardi, Marco Vittorio; Casarin, Maurizio

    2016-09-28

    The unoccupied electronic structure of thick films of tetraphenylporphyrin and tetrakis(pentafluorophenyl)porphyrin Cu(ii) complexes (hereafter, CuTPP and CuTPP(F)) deposited on Au(111) has been studied by combining the outcomes of near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with those of spin-unrestricted time-dependent density functional (TD-DFT) calculations carried out either within the scalar relativistic zeroth order regular approximation (ZORA) framework (C, N and F K-edges) or by using the Tamm-Dancoff approximation coupled to ZORA and including spin-orbit effects (Cu L2,3-edges). Similarly to the modelling of NEXAFS outcomes pertaining to other Cu(ii) complexes, the agreement between theory and experiment is more than satisfactory, thus confirming the open-shell TD-DFT to be a useful tool to look into NEXAFS results pertinent to Cu(ii) compounds. The combined effect of metalation and phenyl (Ph) fluorine decoration is found to favour an extensive mixing between (Ph)σ* and pristine porphyrin macrocyle (pmc) (pmc)π* virtual levels. The lowest lying excitation in the C and N K-edge spectra of both CuTPP and CuTPP(F) is associated with a ligand-to-metal-charge-transfer transition, unambiguously revealed in the (CuTPP)N K-edge spectral pattern. Moreover, the comparison with literature data pertaining to the modelling of the (Cu(II))L2,3 features in the phthalocyanine-Cu(ii) (CuPc) complex provided further insights into how metal-to-ligand-charge-transfer transitions associated with excitations from 2p(Cu(II)) AOs to low-lying, ligand-based π* MOs may contribute to the Cu(ii) L2,3-edge intensity and thus weaken its believed relationship with the Cu(ii)-ligand symmetry-restricted covalency. Despite the coordinative pocket of CuTPP/CuTPP(F) mirroring CuPc, the ligand-field strength exerted by the phthalocyanine ligand on the Cu(ii) centre is experimentally found and theoretically confirmed to be slightly stronger than that experienced by Cu

  4. Electronic structure modification and Fermi level shifting in niobium-doped anatase titanium dioxide thin films: a comparative study of NEXAFS, work function and stiffening of phonons.

    PubMed

    Gautam, Subodh K; Das, Arkaprava; Ojha, S; Shukla, D K; Phase, D M; Singh, Fouran

    2016-02-01

    The electronic structure and tuning of work function (WF) by electronic excitations (EEs) induced by swift heavy ions (SHIs) in anatase niobium-doped titanium dioxide (NTO) thin films is reported. The densities of EEs were varied using 80 MeV O, 130 MeV Ni and 120 MeV Ag ions for irradiation. The EE-induced modifications in electronic structure were studied by O K-edge and Ti L3,2 edge absorption spectra using near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The reduction of hybridized O 2p and Ti 3d unoccupied states in the conduction band with a decrease in energy of the crystal field strength of ∼ 480 meV and the correlated effect on the decrease in the WF value of ∼ 520 meV upon increasing the total energy deposition in the lattice are evident from the study of NEXAFS and scanning Kelvin probe microscopy (SKPM), respectively. The observed stiffening in the low frequency Raman mode (LFRM) of ∼ 9 cm(-1) further validates the electronic structure modification under the influence of EE-induced strain in TiO6 octahedra. The reduction of hybridized valence states, stiffening behavior of LFRM and decrease in WF by nano-crystallization followed by amorphization and defects in NTO lattice are explained in terms of continuous, discontinuous amorphous ion tracks containing intestinally created defects and non-stoichiometry in the lattice. These studies are very appropriate for better insights of electronic structure modification during phase transformation and controlled Fermi level shifting, which plays a crucial role in controlling the charge carrier injection efficiency in opto-electronic applications and also provides a deeper understanding of the involved physical processes. PMID:26752253

  5. In situ electron microscope study of the phase transformation, structure and growth of thin Te1-xSex films

    NASA Astrophysics Data System (ADS)

    Vermaak, J. S.; Raubenheimer, D.

    1988-01-01

    An in-situ electron microscope technique was utilized to observe directly the amorphous-to-crystalline phase transformation, the isothermal growth rates, as well as the orientation and structure of the recrystallized films for the Te1-xSex alloy system for x=0.2, 0.3 and 0.4. Activation energies of E=0.91, 0.93 and 0.96 eV and crystallization temperatures of Tc=-14, 81.5 and 85°C for the three alloys, respectively, were found. In all three cases the crystallization process originated from single crystalline nuclei with a hexagonal structure and with the c-axis in general parallel to the substrate surface.

  6. Theoretical and experimental studies on the electronic structure of crystalline and amorphous ZnSnO3 thin films

    NASA Astrophysics Data System (ADS)

    Lee, Joohwi; Cho, Deok-Yong; Jung, Jisim; Ki Kim, Un; Ho Rha, Sang; Seong Hwang, Cheol; Choi, Jung-Hae

    2013-06-01

    The influence of structural disorder on the electronic structure of amorphous ZnSnO3 was examined by ab-initio calculations. The calculation results are compared with the experimental results using as-deposited and annealed ZnSnO3 films grown by atomic layer deposition. The O K-edge X-ray absorption spectroscopy, X-ray diffraction, and thin-film transistors were employed in the experiment. The conduction band minima of amorphous and crystalline ZnSnO3 mainly consisted of Sn 5s state, while a higher non-uniform localization of these states was observed in the amorphous phase compared with the crystalline counterpart. The experimental results coincide well with the theoretical results.

  7. Density functional theory study : Electronic structures of RE:GaN in wurtzite Gα15RE1N16

    NASA Astrophysics Data System (ADS)

    Andiwijayakusuma, Dinan; Saito, Mineo; Purqon, Acep

    2016-08-01

    Gallium nitride (GaN) is a wide-band gap (Eg=3.4eV) semiconductor. Rare-earth (RE) in GaN have attracted interest due to their potential applications. Electronic structure calculations were performed for substitutional rare-earth (Pr, Er, Eu, Nd, and Dy) in wurtzite supercell GaN using density functional theory calculations within the GGA approach. Our calculations show that RE doped in GaN exhibit an indirect band gap and introduces an impurity level. We found the equilibrium bond lengths of RE-N are vary between 2.13 to 2.253Å in good agreement with structural data available for Eu and Er. We confirm that the present supercell model well describes the state of RE in GaN. Its predicts the band gap narrowing that expected to improve the optical performance of GaN.

  8. FP-LAPW study of structural, electronic, elastic, mechanical and thermal properties of AlFe intermetallic

    NASA Astrophysics Data System (ADS)

    Jain, Ekta; Pagare, Gitanjali; Sanyal, S. P.

    2016-05-01

    The structural, electronic, elastic, mechanical and thermal properties of AlFe intermetallic compound in B2-type (CsCl) structure have been investigated using first-principles calculations. The exchange-correlation term was treated within generalized gradient approximation. Ground state properties i.e. lattice constants (a0), bulk modulus (B) and first-order pressure derivative of bulk modulus (B') are presented. The density of states are derived which show the metallic character of present compound. Our results for C11, C12 and C44 agree well with previous theoretical data. Using Pugh's criteria (B/GH < 1.75), brittle character of AlFe is satisfied. In addition shear modulus (GH), Young's modulus (E), sound wave velocities and Debye temperature (θD) have also been estimated.

  9. Periodic density functional theory study of structural and electronic properties of single-walled zinc oxide and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Marana, Naiara L.; Albuquerque, Anderson R.; La Porta, Felipe A.; Longo, Elson; Sambrano, Julio R.

    2016-05-01

    Periodic density functional theory calculations with the B3LYP hybrid functional and all-electron Gaussian basis set were performed to simulate the structural and electronic properties as well as the strain and formation energies of single-walled ZnO nanotubes (SWZnONTs) and Carbon nanotubes (SWCNTs) with different chiralities as functions of their diameters. For all SWZnONTs, the band gap, strain energy, and formation energy converge to ~4.5 eV, 0.0 eV/atom, and 0.40 eV/atom, respectively. This result suggests that the nanotubes are formed more easily from the surface than from the bulk. For SWCNTs, the strain energy is always positive, while the formation energy is negative for armchair and zigzag nanotubes, therefore suggesting that these types of nanotubes can be preferentially formed from the bulk. The electronic properties of SWCNTs depend on the chirality; all armchair nanotubes are metallic, while zigzag and chiral nanotubes can be metallic or semiconducting, depending on the n and m vectors.

  10. Stability and Electronic Structures of Al-, Si- and Au-incorporated Divacancy Graphenes: A First-principles Study

    NASA Astrophysics Data System (ADS)

    Kim, Na-Young; Lee, Eui-Sup; Kim, Yong-Hyun

    2013-03-01

    C, N, and O decorated divacancy pores in graphene have been reported as well. Especially, the N4 divacancy pore can strongly bind with the divalent 3d transition metals (TMs) because of the large enough pore size and the strong p-d hybridization. Recently, the Si- and Au-incorporated divacancy pore have been also proposed, but understanding of the stability or electronic properties is largerly lacking. In this work, we invesgated the stability and electronic structure of Al-, Si- and Au-incoporated divacancy graphenes decorated with reactangular CmNn, NnOl, and OlCm, based on first-principles density-functional theory (DFT) calculations. We found that the Al-CN3, Si-C2N2, and Au-CN3 are most stable configurations for each cations because the unpaired electrons of edge atoms of divacancy pore could be completely passivated. The binding energies are also higher than cohessive energies due to the strong p-p or p-d hybridization. Because of the strong hybridizaition, the restoration of π-network of graphene or small band-gap opening near the fermi-level are also observed.

  11. Density functional study of structural and electronic properties of Al{sub n}@C{sub 60}

    SciTech Connect

    Dhiman, Shobhna; Kumar, Ranjan; Dharamvir, Keya

    2014-04-24

    Fullerene derivatives have been shown to make contributions in many types of applications. Ab initio investigation of structural and electronic properties of aluminum doped endohedral fullerene has been performed using numerical atomic orbital density functional theory. We have obtained ground state structures for Al{sub n}@C{sub 60} (n=1–10). Which shows that C{sub 60} molecule can accommodate maximum of nine aluminum atoms, for n > 9 the cage eventually break. Encapsulated large number of aluminum atoms leads to deformation of cage with diameter varies from 7.16Å to 7.95Å. Binding energy/Al atom is found to increase till n = 4 and after that it decreases with the number of Al atoms with a sudden increase for n=10 due to breakage of C{sub 60} cage and electronic affinity first increases till n=4 then it decreases up to n=9 with a sharp increase for n=10. Ionization potential also first increases and then decreases. Homo-Lumo gap decreases till n=3 with a sharp increase for n=4, after that it shows an oscillatory nature. The results obtained are consistent with available theoretical and experimental results. The ab-initio calculations were performed using SIESTA code with generalized gradient approximation (GGA)

  12. Interfacial properties and electron structure of Al/B4C interface: A first-principles study

    NASA Astrophysics Data System (ADS)

    Xian, Yajiang; Qiu, Ruizhi; Wang, Xin; Zhang, Pengcheng

    2016-09-01

    This research aims at investigating the structural, mechanical and electronic properties of the Al (111)/B4C (0001) interface by first-principles calculations. This model geometry Al (111)/B4C (0001) is chosen because the close-packed planes of Al and B4C have the (111) and (0001) orientation, respectively, and the lattice mismatch is only ∼2.1%. Among four B4C (0001) surfaces with different terminations, our calculation of surface free energies predicted that C-terminated B4C (0001) surface is the most stable one. Relaxed atomic geometries, the work of adhesion and interfacial free energies were calculated for three C-terminated B4C (0001)/Al (111) interfaces with different stacking sequences (top-site, hollow-site, and bridge-site). Results reveal that the relaxed top-site (hollow-site-like) Al/B4C interface has the best adhesion force and also be the most stable. The interfacial electron structure including charge density difference, Bader charge and density of states (DOS) is analyzed to determine the nature of metal/carbide bonding and we find the formation of Alsbnd C bond and possibly the formation of Al4C3 in the interface.

  13. Mechanical Properties and Electronic Structure of N and Ta Doped TiC: A First-Principles Study

    NASA Astrophysics Data System (ADS)

    Ma, Shi-Qing; Liu, Ying; Ye, Jin-Wen; Wang, Bin

    2014-12-01

    The first principles calculations based on density functional theory (DFT) are employed to investigate the mechanical properties and electronic structure of N and Ta doped TiC. The result shows that the co-doping of nitrogen and tantalum dilates the lattice constant and improves the stability of TiC. Nitrogen and tantalum can signiβcantly enhance the elastic constants and elastic moduli of TiC. The results of B/G and C12-C44 indicate tantalum can markedly increase the ductility of TiC. The electronic structure is calculated to describe the bonding characteristic, which revealed the strong hybridization between C-p and Ta-d and between N-p and Ti-d. The hardnessis is estimated by a semi-empirical model that is based on the Mulliken overlap population and bond length. While the weakest bond takes determinative role of the hardness of materials, the addition of Ta sharply reduces the hardness of TiC.

  14. Interfacial bonding and electronic structure of GaN/GaAs interface: A first-principles study

    SciTech Connect

    Cao, Ruyue; Zhang, Zhaofu; Wang, Changhong; Li, Haobo; Dong, Hong; Liu, Hui; Wang, Weichao; Xie, Xinjian

    2015-04-07

    Understanding of GaN interfacing with GaAs is crucial for GaN to be an effective interfacial layer between high-k oxides and III-V materials with the application in high-mobility metal-oxide-semiconductor field effect transistor (MOSFET) devices. Utilizing first principles calculations, here, we investigate the structural and electronic properties of the GaN/GaAs interface with respect to the interfacial nitrogen contents. The decrease of interfacial N contents leads to more Ga dangling bonds and As-As dimers. At the N-rich limit, the interface with N concentration of 87.5% shows the most stability. Furthermore, a strong band offsets dependence on the interfacial N concentration is also observed. The valance band offset of N7 with hybrid functional calculation is 0.51 eV. The electronic structure analysis shows that significant interface states exist in all the GaN/GaAs models with various N contents, which originate from the interfacial dangling bonds and some unsaturated Ga and N atoms. These large amounts of gap states result in Fermi level pinning and essentially degrade the device performance.

  15. Interfacial properties and electronic structure of β-SiC(111)/α-Ti(0001): A first principle study

    NASA Astrophysics Data System (ADS)

    Li, Jian; Yang, Yanqing; Li, Lili; Lou, Juhong; Luo, Xian; Huang, Bin

    2013-01-01

    First-principles calculations of β-SiC(111)/α-Ti(0001) interface have been performed and the adhesion strength, interface energy, interfacial fracture toughness, and electronic structure are obtained. Six C-terminated β-SiC(111)/α-Ti(0001) interface models are investigated to clarify the influence of stacking sites and Ti atoms tilt direction on the interface bonding and fracture toughness. The hollow-site-stacked interfaces, in which Ti atoms locate on the hollow site of interfacial C atoms (cases III and IV), are more thermodynamically stable with larger work of adhesion, and interfacial fracture toughness. The center-site-stacked (cases I and II) and top-site-stacked (cases V and VI) interfaces have a decreasing interface adhesion as the order. The electronic structure of hollow-site-stacked interface (case IV) gives the evidence that atomic bonding exists between interfacial C, Si, and Ti atoms, and the C-Ti bonds exhibit more covalent features than Si-Ti. The tilt direction of Ti atoms, namely the stacking style of Ti, has a subtle and secondary effect on the interface stability.

  16. Interfacial bonding and electronic structure of GaN/GaAs interface: A first-principles study

    NASA Astrophysics Data System (ADS)

    Cao, Ruyue; Zhang, Zhaofu; Wang, Changhong; Li, Haobo; Xie, Xinjian; Dong, Hong; Liu, Hui; Wang, Weichao

    2015-04-01

    Understanding of GaN interfacing with GaAs is crucial for GaN to be an effective interfacial layer between high-k oxides and III-V materials with the application in high-mobility metal-oxide-semiconductor field effect transistor (MOSFET) devices. Utilizing first principles calculations, here, we investigate the structural and electronic properties of the GaN/GaAs interface with respect to the interfacial nitrogen contents. The decrease of interfacial N contents leads to more Ga dangling bonds and As-As dimers. At the N-rich limit, the interface with N concentration of 87.5% shows the most stability. Furthermore, a strong band offsets dependence on the interfacial N concentration is also observed. The valance band offset of N7 with hybrid functional calculation is 0.51 eV. The electronic structure analysis shows that significant interface states exist in all the GaN/GaAs models with various N contents, which originate from the interfacial dangling bonds and some unsaturated Ga and N atoms. These large amounts of gap states result in Fermi level pinning and essentially degrade the device performance.

  17. [Scanning electron microscopy studies of the structure of tissue in the cochlear opening of the cochlear aqueduct].

    PubMed

    Galić, M; Giebel, W

    1987-01-01

    The structure of the internal and external tissue of the cochlear opening of the cochlear aquaeduct was examined by light microscopy on semithin sections and by scanning electron microscopy. The whole area is filled with a net of mesenchymal cells. The cell axes are randomly orientated inside the aquaeduct. On the outside of the cochlear aquaeduct fibrocytic tissue fills a space which is triangular in cross-section between the basal part of the cochlea wall of the tympanic scala and the middle portion of the round window membrane. In this area the direction of the net is uniform and it gives the impression of anchorage of the round window membrane on the perilymphatic side. The rim bordering the perilymphatic space is a dense net but not fully closed. The scanning electron microscopic pictures taken perpendicular to this border structure show clearly a texture of mesenchymal cells with open spaces. No closed "membrana limitans" was found. The possible function of the fixation of the round window membrane to the perilymphatic space giving rise to an asymmetric perilymph movement is discussed with regard to the physiology of sound transmission. PMID:3561119

  18. Experimental and Theoretical Electron Paramagnetic Resonance (EPR) Study on the Temperature-Dependent Structural Changes of Methylsulfanylmethane

    PubMed Central

    Tapramaz, Recep; Türkkan, Ercan; Dereli, Ömer

    2011-01-01

    Methylsulfonylmethane (or dimethyl sulfone), a naturally produced and vitally important organosulfur compound in living organisms, was irradiated with gamma rays, and the produced radicals were investigated using electron paramagnetic resonance spectroscopy at different temperatures. The structure and behavior of the radical changed when the temperatures varied. The hyperfine splitting of the CH3 group was small, and the 33S splitting was relatively high between 80 and −50 °C. When the temperature was between −50 and −160 °C, the 33S splitting became small and the CH3 splitting was higher. However, the group kept rotating; therefore, only the isotropic splitting values were measured, and the g-values were anisotropic. When the temperature decreased below −180 °C, the CH3 group stopped rotating, and the hydrogen splitting values became nonequivalent due to an inhomogeneous electron distribution. The observed structures can be explained by referring to both the experimental and theoretically calculated values reported. PMID:21954334

  19. Density functional study of the electronic structure of dye-functionalized fullerenes and their model donor-acceptor complexes containing P3HT.

    PubMed

    Baruah, Tunna; Garnica, Amanda; Paggen, Marina; Basurto, Luis; Zope, Rajendra R

    2016-04-14

    We study the electronic structure of C60 fullerenes functionalized with a thiophene-diketo-pyrrolopyrrole-thiophene based chromophore using density functional theory combined with large polarized basis sets. As the attached chromophore has electron donor character, the functionalization of the fullerene leads to a donor-acceptor (DA) system. We examine in detail the effect of the linker and the addition site on the electronic structure of the functionalized fullerenes. We further study the electronic structure of these DA complexes with a focus on the charge transfer excitations. Finally, we examine the interface of the functionalized fullerenes with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor. Our results show that all functionalized fullerenes with an exception of the C60-pyrrolidine [6,6], where the pyrrolidine is attached at a [6,6] site, have larger electron affinities relative to the pristine C60 fullerene. We also estimate the quasi-particle gap, lowest charge transfer excitation energy, and the exciton binding energies of the functionalized fullerene-P3MT model systems. Results show that the exciton binding energies in these model complexes are slightly smaller compared to a similarly prepared phenyl-C61-butyric acid methyl ester (PCBM)-P3MT complex.

  20. Density functional study of the electronic structure of dye-functionalized fullerenes and their model donor-acceptor complexes containing P3HT

    NASA Astrophysics Data System (ADS)

    Baruah, Tunna; Garnica, Amanda; Paggen, Marina; Basurto, Luis; Zope, Rajendra R.

    2016-04-01

    We study the electronic structure of C60 fullerenes functionalized with a thiophene-diketo-pyrrolopyrrole-thiophene based chromophore using density functional theory combined with large polarized basis sets. As the attached chromophore has electron donor character, the functionalization of the fullerene leads to a donor-acceptor (DA) system. We examine in detail the effect of the linker and the addition site on the electronic structure of the functionalized fullerenes. We further study the electronic structure of these DA complexes with a focus on the charge transfer excitations. Finally, we examine the interface of the functionalized fullerenes with the widely used poly(3-hexylthiophene-2,5-diyl) (P3HT) donor. Our results show that all functionalized fullerenes with an exception of the C60-pyrrolidine [6,6], where the pyrrolidine is attached at a [6,6] site, have larger electron affinities relative to the pristine C60 fullerene. We also estimate the quasi-particle gap, lowest charge transfer excitation energy, and the exciton binding energies of the functionalized fullerene-P3MT model systems. Results show that the exciton binding energies in these model complexes are slightly smaller compared to a similarly prepared phenyl-C61-butyric acid methyl ester (PCBM)-P3MT complex.

  1. Effects of Side-Chain and Electron Exchange Correlation on the Band Structure of Perylene Diimide Liquid Crystals: A Density Functional Study

    SciTech Connect

    Arantes, J. T.; Lima, M. P.; Fazzio, A.; Xiang, H.; Wei, S. H.; Dalpian, G. M.

    2009-04-01

    The structural and electronic properties of perylene diimide liquid crystal PPEEB are studied using ab initio methods based on the density functional theory (DFT). Using available experimental crystallographic data as a guide, we propose a detailed structural model for the packing of solid PPEEB. We find that due to the localized nature of the band edge wave function, theoretical approaches beyond the standard method, such as hybrid functional (PBE0), are required to correctly characterize the band structure of this material. Moreover, unlike previous assumptions, we observe the formation of hydrogen bonds between the side chains of different molecules, which leads to a dispersion of the energy levels. This result indicates that the side chains of the molecular crystal not only are responsible for its structural conformation but also can be used for tuning the electronic and optical properties of these materials.

  2. The electronic and structural properties of BN and BP nano-cages interacting with OCN-: A DFT study

    NASA Astrophysics Data System (ADS)

    Soltani, Alireza; Baei, Mohammad T.; Mirarab, Mehdi; Sheikhi, Masoome; Tazikeh Lemeski, E.

    2014-10-01

    The adsorption of OCN- (cyanato anion) on boron nitride (B12N12 and B16N16) and boron phosphide nano-cages (B12P12 and B16P16) in terms of energetic, geometric, and electronic properties are studied using density functional theory calculations. Our study results indicated that the first OCN- strongly prefers to be adsorbed from its N atom upon B atoms of the nano-cages than the O atoms of OCN-. These findings have been rationalized using frontier molecular orbitals and total electron density plots. The energy gap of the B12P12 is significantly reduced upon the adsorption of OCN- compared to B12N12, thus leading to the increase in electrical conductance of nano-cage.

  3. Electronic correlation contributions to structural energies

    NASA Astrophysics Data System (ADS)

    Haydock, Roger

    2015-03-01

    The recursion method is used to calculate electronic excitation spectra including electron-electron interactions within the Hubbard model. The effects of correlation on structural energies are then obtained from these spectra and applied to stacking faults. http://arxiv.org/abs/1405.2288 Supported by the Richmond F. Snyder Fund and Gifts.

  4. Theoretical studies on the electronic structure and properties of complex ceramic crystals and glasses. Annual progress report, July 1, 1991--June 30, 1992

    SciTech Connect

    Ching, Wai-Yim

    1991-01-24

    This progress report summarizes the accomplishment of the DOE-support research program at the University of Missouri-Kansas City for the period July 1, 1991--June 30, 1992. This is the second year of a three-year renewal. The major accomplishments for the year are: (a) Initiation of fundamental studies on the electronic properties of C{sub 60} and related crystals; (b) study of electronic structures and optical properties of several important ceramic crystals, especially on AlN, SiO{sub 2} and Al{sub 2}O{sub 3}; (c) first-principles calculation of total energies and structural phase transitions in oxides, nitrides, and borides; (d) theory of magnetism in Nd{sub 2}Fe{sub 14}B permanent magnetic alloy. The major focus for the next year`s effort will be on the following areas: (1) Continuation of the fundamental studies on the buckminsterfullerene system with particular emphasis on the alkali-doped superconducting fullerides. (2) Fundamental studies on the structure and properties of Boron and B-related compounds. (3) Basic studies on the structural and electronic properties of metallic glasses with particular emphasis on the magnetic glasses. (4) Further development of the first-principles OLCAO method for applications to super-complex systems.

  5. Theoretical study on the electronic structures and phosphorescent properties of four Ir(III) complexes with different substituents on the ancillary ligand

    NASA Astrophysics Data System (ADS)

    Han, Deming; Shang, Xiaohong; Zhang, Gang; Zhao, Lihui

    2013-12-01

    The geometry structures, electronic structures, absorption and phosphorescent properties of four Ir(III) complexes {[(F2-ppy)2Ir(pta-X)], where F2-ppy = (2,4-difluoro)phenylpyridine; pta = pyridine-1,2,4-triazole; X = -CF3; -H; -CH3; -N(CH3)2}, are investigated using the density functional method. The results reveal that the electron-accepting group -CF3 has no obvious effect on absorption and emission properties, while the substitutive group -N(CH3)2 with strong electron-donating ability has obvious effect on the emission properties. The mobility of hole and electron were studied computationally based on the Marcus-Hush theory. Calculations of ionisation potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. We hope that this theoretical work can provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes.

  6. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    PubMed Central

    Bublitz, Maike; Nass, Karol; Drachmann, Nikolaj D.; Markvardsen, Anders J.; Gutmann, Matthias J.; Barends, Thomas R. M.; Mattle, Daniel; Shoeman, Robert L.; Doak, R. Bruce; Boutet, Sébastien; Messerschmidt, Marc; Seibert, Marvin M.; Williams, Garth J.; Foucar, Lutz; Reinhard, Linda; Sitsel, Oleg; Gregersen, Jonas L.; Clausen, Johannes D.; Boesen, Thomas; Gotfryd, Kamil; Wang, Kai-Tuo; Olesen, Claus; Møller, Jesper V.; Nissen, Poul; Schlichting, Ilme

    2015-01-01

    Membrane proteins are key players in biological systems, mediating signalling events and the specific transport of e.g. ions and metabolites. Consequently, membrane proteins are targeted by a large number of currently approved drugs. Understanding their functions and molecular mechanisms is greatly dependent on structural information, not least on complexes with functionally or medically important ligands. Structure determination, however, is hampered by the difficulty of obtaining well diffracting, macroscopic crystals. Here, the feasibility of X-ray free-electron-laser-based serial femtosecond crystallography (SFX) for the structure determination of membrane protein–ligand complexes using microcrystals of various native-source and recombinant P-type ATPase complexes is demonstrated. The data reveal the binding sites of a variety of ligands, including lipids and inhibitors such as the hallmark P-type ATPase inhibitor orthovanadate. By analyzing the resolution dependence of ligand densities and overall model qualities, SFX data quality metrics as well as suitable refinement procedures are discussed. Even at relatively low resolution and multiplicity, the identification of ligands can be demonstrated. This makes SFX a useful tool for ligand screening and thus for unravelling the molecular mechanisms of biologically active proteins. PMID:26175901

  7. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    SciTech Connect

    Bublitz, Maike; Nass, Karol; Drachmann, Nikolaj D.; Markvardsen, Anders J.; Gutmann, Matthias J.; Barends, Thomas R. M.; Mattle, Daniel; Shoeman, Robert L.; Doak, R. Bruce; Boutet, Sébastien; Messerschmidt, Marc; Seibert, Marvin M.; Williams, Garth J.; Foucar, Lutz; Reinhard, Linda; Sitsel, Oleg; Gregersen, Jonas L.; Clausen, Johannes D.; Boesen, Thomas; Gotfryd, Kamil; Wang, Kai-Tuo; Olesen, Claus; Møller, Jesper V.; Nissen, Poul; Schlichting, Ilme

    2015-06-11

    Membrane proteins are key players in biological systems, mediating signalling events and the specific transport ofe.g.ions and metabolites. Consequently, membrane proteins are targeted by a large number of currently approved drugs. Understanding their functions and molecular mechanisms is greatly dependent on structural information, not least on complexes with functionally or medically important ligands. Structure determination, however, is hampered by the difficulty of obtaining well diffracting, macroscopic crystals. Here, the feasibility of X-ray free-electron-laser-based serial femtosecond crystallography (SFX) for the structure determination of membrane protein–ligand complexes using microcrystals of various native-source and recombinant P-type ATPase complexes is demonstrated. The data reveal the binding sites of a variety of ligands, including lipids and inhibitors such as the hallmark P-type ATPase inhibitor orthovanadate. By analyzing the resolution dependence of ligand densities and overall model qualities, SFX data quality metrics as well as suitable refinement procedures are discussed. Even at relatively low resolution and multiplicity, the identification of ligands can be demonstrated. This makes SFX a useful tool for ligand screening and thus for unravelling the molecular mechanisms of biologically active proteins.

  8. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    DOE PAGES

    Bublitz, Maike; Nass, Karol; Drachmann, Nikolaj D.; Markvardsen, Anders J.; Gutmann, Matthias J.; Barends, Thomas R. M.; Mattle, Daniel; Shoeman, Robert L.; Doak, R. Bruce; Boutet, Sébastien; et al

    2015-06-11

    Membrane proteins are key players in biological systems, mediating signalling events and the specific transport ofe.g.ions and metabolites. Consequently, membrane proteins are targeted by a large number of currently approved drugs. Understanding their functions and molecular mechanisms is greatly dependent on structural information, not least on complexes with functionally or medically important ligands. Structure determination, however, is hampered by the difficulty of obtaining well diffracting, macroscopic crystals. Here, the feasibility of X-ray free-electron-laser-based serial femtosecond crystallography (SFX) for the structure determination of membrane protein–ligand complexes using microcrystals of various native-source and recombinant P-type ATPase complexes is demonstrated. The data revealmore » the binding sites of a variety of ligands, including lipids and inhibitors such as the hallmark P-type ATPase inhibitor orthovanadate. By analyzing the resolution dependence of ligand densities and overall model qualities, SFX data quality metrics as well as suitable refinement procedures are discussed. Even at relatively low resolution and multiplicity, the identification of ligands can be demonstrated. This makes SFX a useful tool for ligand screening and thus for unravelling the molecular mechanisms of biologically active proteins.« less

  9. Structural, elastic, electronic and optical properties of KAlQ2 (Q = Se, Te): A DFT study

    NASA Astrophysics Data System (ADS)

    Benmakhlouf, A.; Bentabet, A.; Bouhemadou, A.; Maabed, S.; Khenata, R.; Bin-Omran, S.

    2015-10-01

    First-principles calculations in the framework of density functional theory have been conducted to explore the structural, elastic, electronic and optical properties of two layered ternary compounds chalcogenides of aluminum KAlSe2 and KAlTe2. We have calculated all of the equilibrium structural parameters; the lattice parameters (a, b and c), angle β and twenty three internal atomic coordinates. The obtained results are in excellent agreement with the available experimental data. We have predicted the single-crystal elastic constants Cij of the title materials using stress-strain approach and then derived the elastic moduli of the polycrystalline aggregates and related properties via the Voigt-Reuss-Hill approximations. The band structure and density of states diagrams have been calculated and analyzed. Both compounds demonstrate semiconducting behavior with direct band gap. The linear optical properties, namely the frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and energy-loss function, have been calculated and analyzed in a wide energy range up to 20 eV.

  10. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    SciTech Connect

    Bublitz, Maike; Nass, Karol; Drachmann, Nikolaj D.; Markvardsen, Anders J.; Gutmann, Matthias J.; Barends, Thomas R. M.; Mattle, Daniel; Shoeman, Robert L.; Doak, R. Bruce; Boutet, Sébastien; Messerschmidt, Marc; Seibert, Marvin M.; Williams, Garth J.; Foucar, Lutz; Reinhard, Linda; Sitsel, Oleg; Gregersen, Jonas L.; Clausen, Johannes D.; Boesen, Thomas; Gotfryd, Kamil; Wang, Kai -Tuo; Olesen, Claus; Møller, Jesper V.; Nissen, Poul; Schlichting, Ilme

    2015-06-11

    Membrane proteins are key players in biological systems, mediating signalling events and the specific transport ofe.g.ions and metabolites. Consequently, membrane proteins are targeted by a large number of currently approved drugs. Understanding their functions and molecular mechanisms is greatly dependent on structural information, not least on complexes with functionally or medically important ligands. Structure determination, however, is hampered by the difficulty of obtaining well diffracting, macroscopic crystals. Here, the feasibility of X-ray free-electron-laser-based serial femtosecond crystallography (SFX) for the structure determination of membrane protein–ligand complexes using microcrystals of various native-source and recombinant P-type ATPase complexes is demonstrated. The data reveal the binding sites of a variety of ligands, including lipids and inhibitors such as the hallmark P-type ATPase inhibitor orthovanadate. By analyzing the resolution dependence of ligand densities and overall model qualities, SFX data quality metrics as well as suitable refinement procedures are discussed. Even at relatively low resolution and multiplicity, the identification of ligands can be demonstrated. This makes SFX a useful tool for ligand screening and thus for unravelling the molecular mechanisms of biologically active proteins.

  11. Valence Electronic Structure of Oxygen-Modified α-Mo2C(0001) Surface:. Angle-Resolved Photoemission Study

    NASA Astrophysics Data System (ADS)

    Kato, M.; Ozawa, K.; Sato, T.; Edamoto, K.

    Adsorption of oxygen on α-Mo2C(0001) is investigated with Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) utilizing synchrotron radiation. It is found that C KLL Auger peak intensity does not change during O2 exposure, indicating that the depletion of C atoms does not proceed. It is deduced from ARPES and LEED results that adsorbed oxygen atoms from a well-ordered (1 × 1) lattice on the α-Mo2C(0001) surface. The ARPES study shows that oxygen adsorption induces a peculiar state around Fermi level (EF). Off-normal-emission measurements prove that the state is a half-filled metallic state.

  12. Structural, electronic and elastic properties of the cubic CaTiO{sub 3} under pressure: A DFT study

    SciTech Connect

    Tariq, Saad Ahmed, Afaq; Tariq, Samar; Saad, Saher

    2015-07-15

    Using highly accurate FP-LAPW method with GGA approximation structural, electronic and elastic properties of cubic CaTiO{sub 3} have been calculated from 0-120 GPa range of pressure. It is observed that lattice constant, bond length and anisotropy factor decrease with increase in pressure. Also the brittle nature and indirect band-gap of the compound become ductile and direct band-gap respectively at 120 GPa. Moduli of elasticity, density of the material, Debye temperature and wave elastic wave velocities increase with increase in pressure. Spin dependent DOS’s plots show invariant anti-ferromagnetic nature of the compound under pressure. Our calculated results are in good agreement with available theoretical and experimental results.

  13. Density functional theory study of the structures, electronic states and stabilities of Al n Pt ( n = 1-15) clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao; Guo, Ling; Guo, Jian; Ren, Ning-Ning

    2014-03-01

    The binding energy, dissociation energy, ionization potentials, electron affinities, gap and stability of small Al n Pt ( n = 1-15) clusters, in comparison with pure aluminum clusters have been systematically investigated by means of density functional calculations at the B3LYP level. The growth patten for Al n Pt clusters is that the Pt atom substituted the surface atom of the Al n + 1 clusters for n < 13. Starting from n = 13, the Pt atom completely falls into the center of the Al-frame. The Pt atom substituted the center atom of the Al n + 1 clusters to form the Pt-encapsulated Aln geometries for n > 13. We also find that the impurity Pt atom causes local structural distortion due to different atomic radii and different bonding characteristics. The clusters with total atom numbers of 2, 7, and 11 exhibit high stability.

  14. Electronic structure and biological activity of chosen DDT-type insecticides studied by 35Cl-NQR.

    PubMed

    Jadzyn, Maciej; Nogaj, Bolesław

    2009-02-01

    A correlation between the electronic structure and biological activity of chosen dichlorodiphenyltrichloroethane (DDT)-type insecticides: 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane, 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene, 2,2-bis(4-chlorophenyl)ethanoic acid and 4,4'-dichlorobenzophenone (used in agriculture) has been analysed on the basis of the (35)Cl-nuclear quadrupole resonance (NQR) spectroscopy. The (35)Cl-NQR resonance frequencies measured at 77 K have been correlated with the lethal dose (LD(50)) parameter that characterises the biological activity of these insecticides.

  15. Focused ion beam as a tool for graphene technology: Structural study of processing sequence by electron microscopy

    NASA Astrophysics Data System (ADS)

    Rius, Gemma; Tavabi, Amir H.; Mestres, Narcis; Eryu, Osamu; Tanji, Takayoshi; Yoshimura, Masamichi

    2014-02-01

    Electron microscopy (EM) techniques are used to investigate the microstructure of ultrathin carbon layers obtained by focused ion beam induced deposition (FIBID). The investigation determines the crystalline structure, chemical bonding and elemental contents of FIBID-C materials. The effect of a thermal treatment to the ultrathin C films is analyzed. As-deposited FIBID-C is a metastable material transforming at mid-high temperatures. Evidence of its graphitization by metal catalysis is presented. Understanding of the heat transformation and crystallization is established based on the observations. Specifically, carbonization, H desorption decomposition, and graphitization, driven by high temperature metal-induced crystallization, are the identified processes. Demonstration of the graphitization of ultrathin FIBID-C enables a strategy towards graphene integrative planar technologies.

  16. Density functional studies of small Au clusters adsorbed on α-FeOOH: Structural and electronic properties

    NASA Astrophysics Data System (ADS)

    Fortunato, Leandro F.; Zubieta, Carolina E.; Fuente, Silvia A.; Belelli, Patricia G.; Ferullo, Ricardo M.

    2016-11-01

    We report a density functional theory (DFT) investigation on the interaction of tiny Aun (n = 1-5) clusters with the bare and hydroxylated (110) surfaces of goethite (α-FeOOH). Both adsorption and atom-by-atom nucleation processes were modeled. The adsorption is shown to be strong on the bare surface and takes place preferentially through the interaction of Au atoms with unsaturated surface oxygen anions, accompanied with an electronic charge transfer from the metal to the support. Au3, Au4 and Au5 planar structures resulted to be particularly stable due to polarization effects; indeed, Coulombic repulsion between basal Au atoms and surface oxygen anions promotes the displacement of the electronic density toward terminal Au atoms producing a Au+δ(basal)/Au-δ(terminal) polarization. On the hydroxylated surface, Au clusters adsorb more weakly with respect to the bare surface, mainly through monocoordinated surface hydroxyl groups and tricoordinated oxygen ions. Concerning the nucleation mechanism, while on the hydroxylated surface the nucleation energy is governed by the spin of the interacting systems, on the bare surface polarization effects seems to play a predominant role.

  17. Collision-energy-resolved Penning ionization electron spectroscopy of p-benzoquinone: Study of electronic structure and anisotropic interaction with He*(2 3S) metastable atoms

    NASA Astrophysics Data System (ADS)

    Kishimoto, Naoki; Okamura, Kohji; Ohno, Koichi

    2004-06-01

    Collision energy dependence of partial ionization cross sections (CEDPICS) of p-benzoquinone with He*(2 3S) metastable atoms indicates that interaction potentials between p-benzoquinone and He*(2 3S) are highly anisotropic in the studied collision energy range (100-250 meV). Attractive interactions were found around the C=O groups for in-plane and out-of-plane directions, while repulsive interactions were found around CH bonds and the benzenoid ring. Assignment of the first four ionic states of p-benzoquinone and an analogous methyl-substituted compound was examined with CEDPICS and anisotropic distributions of the corresponding two nonbonding oxygen orbitals (nO+,nO-) and two πCC orbitals (πCC+,πCC-). An extra band that shows negative CEDPICS was observed at ca. 7.2 eV in Penning ionization electron spectrum.

  18. Electron tomography of dislocation structures

    SciTech Connect

    Liu, G.S.; House, S.D.; Kacher, J.; Tanaka, M.; Higashida, K.; Robertson, I.M.

    2014-01-15

    Recent developments in the application of electron tomography for characterizing microstructures in crystalline solids are described. The underlying principles for electron tomography are presented in the context of typical challenges in adapting the technique to crystalline systems and in using diffraction contrast imaging conditions. Methods for overcoming the limitations associated with the angular range, the number of acquired images, and uniformity of image contrast are introduced. In addition, a method for incorporating the real space coordinate system into the tomogram is presented. As the approach emphasizes development of experimental solutions to the challenges, the solutions developed and implemented are presented in the form of examples.

  19. A Joint Photoelectron Spectroscopy and Theoretical Study on the Electronic Structure of UCl 5 - and UCl 5

    SciTech Connect

    Su, Jing; Dau, Phuong Diem; Xu, Chao-Fei; Huang, Dao-Ling; Liu, Hong-Tao; Wei, Fan; Wang, Lai-Sheng; Li, Jun

    2013-07-12

    We report a combined photoelectron spectroscopic and relativistic quantum chemistry study on gaseous UCl5- and UCl5. The UCl5- anion is produced using electrospray ionization and found to be highly electronically stable with an adiabatic electron binding energy of 4.76±0.03 eV, which also represents the electron affinity of the neutral UCl5 molecule. Theoretical investigations reveal that the ground state of UCl5- has an open shell with two unpaired electrons occupying two primarily U 5f and 5fxyz based molecular orbitals. The structures of both UCl5- and UCl5 are theoretically optimized and confirmed to have C4v symmetry. The computational results are in good agreement with the photoelectron spectra, providing insights into the electronic structures and valence molecular orbitals of UCl5- and UCl5. We also performed systematic theoretical studies on all the uranium pentahalide complexes UX5- (X=F, Cl, Br, I). Chemical bonding analyses indicate that the UX interactions in UX5- are dominated by ionic bonding, with increasing covalent contributions for the heavier halogen complexes.

  20. Probing Structural and Electronic Dynamics with Ultrafast Electron Microscopy

    SciTech Connect

    Plemmons, DA; Suri, PK; Flannigan, DJ

    2015-05-12

    In this Perspective, we provide an overview,of the field of ultrafast electron microscopy (UEM). We begin by briefly discussing the emergence of methods for probing ultrafast structural dynamics and the information that can be obtained. Distinctions are drawn between the two main types a probes for femtosecond (fs) dynamics fast electrons and X-ray photons and emphasis is placed on hour the nature of charged particles is exploited in ultrafast electron-based' experiments:. Following this, we describe the versatility enabled by the ease with which electron trajectories and velocities can be manipulated with transmission electron microscopy (TEM): hardware configurations, and we emphasize how this is translated to the ability to measure scattering intensities in real, reciprocal, and energy space from presurveyed and selected rianoscale volumes. Owing to decades of ongoing research and development into TEM instrumentation combined with advances in specimen holder technology, comprehensive experiments can be conducted on a wide range of materials in various phases via in situ methods. Next, we describe the basic operating concepts, of UEM, and we emphasize that its development has led to extension of several of the formidable capabilities of TEM into the fs domain, dins increasing the accessible temporal parameter spade by several orders of magnitude. We then divide UEM studies into those conducted in real (imaging), reciprocal (diffraction), and energy (spectroscopy) spate. We begin each of these sections by providing a brief description of the basic operating principles and the types of information that can be gathered followed by descriptions of how these approaches are applied in UM, the type of specimen parameter space that can be probed, and an example of the types of dynamics that can be resolved. We conclude with an Outlook section, wherein we share our perspective on some future directions of the field pertaining to continued instrument development and

  1. Electronic structure theory of the superheavy elements

    NASA Astrophysics Data System (ADS)

    Eliav, Ephraim; Fritzsche, Stephan; Kaldor, Uzi

    2015-12-01

    High-accuracy calculations of atomic properties of the superheavy elements (SHE) up to element 122 are reviewed. The properties discussed include ionization potentials, electron affinities and excitation energies, which are associated with the spectroscopic and chemical behavior of these elements, and are therefore of considerable interest. Accurate predictions of these quantities require high-order inclusion of relativity and electron correlation, as well as large, converged basis sets. The Dirac-Coulomb-Breit Hamiltonian, which includes all terms up to second order in the fine-structure constant α, serves as the framework for the treatment; higher-order Lamb shift terms are considered in some selected cases. Electron correlation is treated by either the multiconfiguration self-consistent-field approach or by Fock-space coupled cluster theory. The latter is enhanced by the intermediate Hamiltonian scheme, allowing the use of larger model (P) spaces. The quality of the calculations is assessed by applying the same methods to lighter homologs of the SHEs and comparing with available experimental information. Very good agreement is obtained, within a few hundredths of an eV, and similar accuracy is expected for the SHEs. Many of the properties predicted for the SHEs differ significantly from what may be expected by straightforward extrapolation of lighter homologs, demonstrating that the structure and chemistry of SHEs are strongly affected by relativity. The major scientific challenge of the calculations is to find the electronic structure and basic atomic properties of the SHE and assign its proper place in the periodic table. Significant recent developments include joint experimental-computational studies of the excitation spectrum of Fm and the ionization energy of Lr, with excellent agreement of experiment and theory, auguring well for the future of research in the field.

  2. Electronic structures of endohedral fullerenes

    SciTech Connect

    Jin, Changming; Hettich, R.L.; Puretzky, A.A.; Ying, Z.C.; Haufler, R.E.; Compton, R.N.

    1994-12-31

    Fullerenes with different elements trapped inside the cage have been the subject of active research both experimentally and theoretically ever since the initial discovery of C{sub 60}. La@C{sub n}, were the first endohedral fullerenes produced both in gas phase and in macroscopic quantities. Early electron spin resonance investigation of La@C{sub 82} by R.D. Johnson, et.al indicated that La transfer nearly all of the three valence electrons to the fullerene cage, forming a La{sup 3+}@C{sub 82}{sup 3-} complex. Theoretical calculations also have shown that La transfers its valence electrons to the fullerene cage in molecules of La@C{sub n}. Investigations with ultraviolet photoelectron spectroscopy by L. Wang, et.al. indicated that attaching a potassium atom outside the C{sub 60} cage lowers the electron affinity (EA) while trapping Ca atom inside the C{sub 60} sphere increases the EA compared with parent C{sub 60} molecule. These results indicate that metallofullerenes appear to have substantially lower ionization potentials (IP) and higher EA than empty fullerenes.

  3. Electron gun controlled smart structure

    DOEpatents

    Martin, Jeffrey W.; Main, John Alan; Redmond, James M.; Henson, Tammy D.; Watson, Robert D.

    2001-01-01

    Disclosed is a method and system for actively controlling the shape of a sheet of electroactive material; the system comprising: one or more electrodes attached to the frontside of the electroactive sheet; a charged particle generator, disposed so as to direct a beam of charged particles (e.g. electrons) onto the electrode; a conductive substrate attached to the backside of the sheet; and a power supply electrically connected to the conductive substrate; whereby the sheet changes its shape in response to an electric field created across the sheet by an accumulation of electric charge within the electrode(s), relative to a potential applied to the conductive substrate. Use of multiple electrodes distributed across on the frontside ensures a uniform distribution of the charge with a single point of e-beam incidence, thereby greatly simplifying the beam scanning algorithm and raster control electronics, and reducing the problems associated with "blooming". By placing a distribution of electrodes over the front surface of a piezoelectric film (or other electroactive material), this arrangement enables improved control over the distribution of surface electric charges (e.g. electrons) by creating uniform (and possibly different) charge distributions within each individual electrode. Removal or deposition of net electric charge can be affected by controlling the secondary electron yield through manipulation of the backside electric potential with the power supply. The system can be used for actively controlling the shape of space-based deployable optics, such as adaptive mirrors and inflatable antennae.

  4. A first-principles study of the electronic and structural properties of Sb and F doped SnO{sub 2} nanocrystals

    SciTech Connect

    Kim, Minjung; Scott Bobbitt, N.; Marom, Noa; Chelikowsky, James R.

    2015-01-28

    We examine the electronic properties of Sb and F doped SnO{sub 2} nanocrystals up to 2.4 nm in diameter. A real-space pseudopotential implementation of density functional theory is employed within the local density approximation. We calculate electron binding energies and dopant formation energies as function of nanocrystal size, dopant concentration, and dopant species. Structural changes for different dopant species are also investigated. Our study should provide useful information for the design of transparent conducting oxides at the nanoscale.

  5. Theoretical calculations of structural, electronic, and elastic properties of CdSe1‑x Te x : A first principles study

    NASA Astrophysics Data System (ADS)

    M, Shakil; Muhammad, Zafar; Shabbir, Ahmed; Muhammad Raza-ur-rehman, Hashmi; M, A. Choudhary; T, Iqbal

    2016-07-01

    The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of CdSe1‑x Te x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA+U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure CdSe and CdTe binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature.

  6. An electronic structure perspective of graphene interfaces

    NASA Astrophysics Data System (ADS)

    Schultz, Brian J.; Dennis, Robert V.; Lee, Vincent; Banerjee, Sarbajit

    2014-03-01

    The unusual electronic structure of graphene characterized by linear energy dispersion of bands adjacent to the Fermi level underpins its remarkable transport properties. However, for practical device integration, graphene will need to be interfaced with other materials: 2D layered structures, metals (as ad-atoms, nanoparticles, extended surfaces, and patterned metamaterial geometries), dielectrics, organics, or hybrid structures that in turn are constituted from various inorganic or organic components. The structural complexity at these nanoscale interfaces holds much promise for manifestation of novel emergent phenomena and provides a means to modulate the electronic structure of graphene. In this feature article, we review the modifications to the electronic structure of graphene induced upon interfacing with disparate types of materials with an emphasis on iterative learnings from theoretical calculations and electronic spectroscopy (X-ray absorption fine structure (XAFS) spectroscopy, scanning transmission X-ray microscopy (STXM), angle-resolved photoemission spectroscopy (ARPES), and X-ray magnetic circular dichroism (XMCD)). We discuss approaches for engineering and modulating a bandgap in graphene through interfacial hybridization, outline experimental methods for examining electronic structure at interfaces, and overview device implications of engineered interfaces. A unified view of how geometric and electronic structure are correlated at interfaces will provide a rational means for designing heterostructures exhibiting emergent physical phenomena with implications for plasmonics, photonics, spintronics, and engineered polymer and metal matrix composites.

  7. An electronic structure perspective of graphene interfaces.

    PubMed

    Schultz, Brian J; Dennis, Robert V; Lee, Vincent; Banerjee, Sarbajit

    2014-04-01

    The unusual electronic structure of graphene characterized by linear energy dispersion of bands adjacent to the Fermi level underpins its remarkable transport properties. However, for practical device integration, graphene will need to be interfaced with other materials: 2D layered structures, metals (as ad-atoms, nanoparticles, extended surfaces, and patterned metamaterial geometries), dielectrics, organics, or hybrid structures that in turn are constituted from various inorganic or organic components. The structural complexity at these nanoscale interfaces holds much promise for manifestation of novel emergent phenomena and provides a means to modulate the electronic structure of graphene. In this feature article, we review the modifications to the electronic structure of graphene induced upon interfacing with disparate types of materials with an emphasis on iterative learnings from theoretical calculations and electronic spectroscopy (X-ray absorption fine structure (XAFS) spectroscopy, scanning transmission X-ray microscopy (STXM), angle-resolved photoemission spectroscopy (ARPES), and X-ray magnetic circular dichroism (XMCD)). We discuss approaches for engineering and modulating a bandgap in graphene through interfacial hybridization, outline experimental methods for examining electronic structure at interfaces, and overview device implications of engineered interfaces. A unified view of how geometric and electronic structure are correlated at interfaces will provide a rational means for designing heterostructures exhibiting emergent physical phenomena with implications for plasmonics, photonics, spintronics, and engineered polymer and metal matrix composites.

  8. Electronic structure and optical properties of resin

    NASA Astrophysics Data System (ADS)

    Rao, Zhi-Fan; Zhou, Rong-Feng

    2013-03-01

    We used the density of functional theory (DFT) to study the electronic structure and density of states of resin by ab initio calculation. The results show the band gap of resin is 1.7 eV. The covalent bond is combined C/O atoms with H atoms. The O 2p orbital is the biggest effect near the Fermi level. The results of optical properties show the reflectivity is low, and the refractive index is 1.7 in visible light range. The highest absorption coefficient peak is in 490 nm and the value is 75,000.

  9. Ab-initio study of structural and electronic properties of thin film and bulk forms of Bi2Q3 (Q = Se, Te) as topological insulators

    NASA Astrophysics Data System (ADS)

    Ranjbardizaj, Ahmad; Mizuseki, Hiroshi; Kawazoe, Yoshiyuki

    2013-03-01

    Bi2Q3 (Q =Se, Te) are the best-known bulk thermoelectric materials, which have been demonstrated to be topological insulators (TI). TI's are insulators with conductive surface states consisting of a single Dirac cones. These materials have layered structures consisting of stacked quintuple layers (QL), with relatively weak coupling between the QL's. Therefore, it might be easy to prepare the Bi2Q3 in the form of thin films with particular thicknesses using the available experimental techniques. In this study, the electronic and structural properties of bulk Bi2Se3 are investigated using density functional theory. Our results show that the Bi2Se3 is an indirect semiconductor with energy gap of ~ 0.27 eV. Additionally, the electronic structure dependence of Bi2Se3to the thicknesses of thin films (n-QL's with n =1,2...9) is considered. It is observed that the electronic structure of this kind of thin films depends on the number of QL's. For n-QL's with n larger than three, the thin film has a bulk band gap and has protected conducting states on its surface. Moreover, the effect of number of layers (n) on band-gap energy is studied. Similar calculations and discussions are carried out for Bi2Te3 and the results are compared to the Bi2Se3 case and also the available theoretical and experimental results.

  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. Density functional theory study of structural, electronic, and thermal properties of Pt, Pd, Rh, Ir, Os and PtPd X (X = Ir, Os, and Rh) alloys

    NASA Astrophysics Data System (ADS)

    Shabbir, Ahmed; Muhammad, Zafar; M, Shakil; M, A. Choudhary

    2016-03-01

    The structural, electronic, mechanical, and thermal properties of Pt, Pd, Rh, Ir, Os metals and their alloys PtPdX (X = Ir, Os and Rh) are studied systematically using ab initio density functional theory. The groundstate properties such as lattice constant and bulk modulus are calculated to find the equilibrium atomic position for stable alloys. The electronic band structure and density of states are calculated to study the electronic behavior of metals on making their alloys. The electronic properties substantiate the metallic behavior for all studied materials. The firstprinciples density functional perturbation theory as implemented in quasi-harmonic approximation is used for the calculations of thermal properties. We have calculated the thermal properties such as the Debye temperature, vibrational energy, entropy and constant-volume specific heat. The calculated properties are compared with the previously reported experimental and theoretical data for metals and are found to be in good agreement. Calculated results for alloys could not be compared because there is no data available in the literature with such alloy composition.

  12. Electronic structure of metallic glasses

    SciTech Connect

    Oelhafen, P.; Lapka, R.; Gubler, U.; Krieg, J.; DasGupta, A.; Guentherodt, H.J.; Mizoguchi, T.; Hague, C.; Kuebler, J.; Nagel, S.R.

    1981-01-01

    This paper is organized in six sections and deals with (1) the glassy transition metal alloys, their d-band structure, the d-band shifts on alloying and their relation to the alloy heat of formation (..delta..H) and the glass forming ability, (2) the glass to crystal phase transition viewed by valence band spectroscopy, (3) band structure calculations, (4) metallic glasses prepared by laser glazing, (5) glassy normal metal alloys, and (6) glassy hydrides.

  13. The Conversion Electron Study for 110Cd

    NASA Astrophysics Data System (ADS)

    Jigmeddorj, B.; Garrett, P. E.; Diaz-Varela, A.; Bangay, J. C.; Demand, G. A.; Green, K. L.; Leach, K. G.; Sumithrarachchi, C.; Svensson, C. E.; Triambak, S.; Wong, J.; Garnsworthy, A. B.; Ball, G.; Hackman, G.; Cross, D.; Kulp, W. D.; Wood, J. L.; Yates, S. W.

    2013-03-01

    The nuclear structure of 110Cd is investigated using conversion electron transitions and γ-ray spectroscopy techniques following the β decay of 110Inm. Electron-γcoincidence spectra are analyzed and conversion sub-shell ratios for selected transitions are determined. The conversion electron study is important to extend the knowledge of intruder structures in Cd, since in principle they should have enhanced E0 transitions to the spherical phonon states, and to extend the level scheme of 110Cd. The conversion electron transition level scheme and sub-shell ratios are presented.

  14. Structural and electronic properties of protein/thiolate-protected gold nanocluster with ``staple'' motif: A XAS, L-DOS, and XPS study

    NASA Astrophysics Data System (ADS)

    Simms, Gordon A.; Padmos, J. Daniel; Zhang, Peng

    2009-12-01

    Following the recent breakthrough of total structural determination of a Au-thiolate nanocluster [P. Jadzinsky et al., Science 318, 430 (2007)], extensive interests have been stimulated to unveil (or revisit) the structure-property relationship of various thiolate-Au nanostructures in light of the new finding of -SR-(Au-SR)x- "staple" motif. Here, we present experimental x-ray absorption spectroscopy (XAS) and x-ray photoelectron spectroscopy (XPS) results on the local structure and electronic properties of thiolate-protected Au nanocluster encapsulated in bovine serum albumin (Au-BSA) together with theoretical calculation of projected local density of states (l-DOS) of Au25(SR)18 model cluster. Analysis of the Au L3-edge extended x-ray absorption fine structure (EXAFS) of Au-BSA suggested that the nanocluster is Au25 with Au-thiolate "staple" motif. X-ray absorption near-edge structure (XANES) and Au 4f XPS were used to probe the electronic behavior of Au-BSA. The Au d-electron density of Au-BSA was found to decrease by 0.047 e- relative to that of the bulk. A self-consistent real space Green's function approach implemented in ab initio FEFF8 program was used to calculate the l-DOS of Au25(SR)18 and other model clusters from a site-specific perspective. The theoretical results are in good agreement with the experimental d-DOS data of Au-BSA and, importantly, systematically illustrate the effect of Au-thiolate "staple" motif on the electronic behavior of Au25(SR)18. The present work sheds light on the structure-property relationship of thiolate-protected Au25 from both experimental and theoretical perspectives and illustrates the usefulness of XAS/l-DOS method in such studies.

  15. First principles study of electronic structure for cubane-like and ring-shaped structures of M{sub 4}O{sub 4}, M{sub 4}S{sub 4} clusters (M = Mn, Fe, Co, Ni, Cu)

    SciTech Connect

    Datta, Soumendu; Rahaman, Badiur

    2015-11-15

    Spin-polarized DFT has been used to perform a comparative study of the geometric structures and electronic properties for isolated M{sub 4}X{sub 4} nano clusters between their two stable isomers - a planar rhombus-like 2D structure and a cubane-like 3D structure with M = Mn, Fe, Co, Ni, Cu ; X = O, S. These two structural patterns of the M{sub 4}X{sub 4} clusters are commonly found as building blocks in several poly-nuclear transition metal complexes in inorganic chemistry. The effects of the van der Waals corrections to the physical properties have been considered in the electronic structure calculations employing the empirical Grimme’s correction (DFT+D2). We report here an interesting trend in their relative structural stability - the isolated M{sub 4}O{sub 4} clusters prefer to stabilize more in the planar structure, while the cubane-like 3D structure is more favorable for most of the isolated M{sub 4}S{sub 4} clusters than their planar 2D counterparts. Our study reveals that this contrasting trend in the relative structural stability is expected to be driven by an interesting interplay between the s-d and p-d hybridization effects of the constituents’ valence electrons.

  16. Electronic Structure of Buried Interfaces - Oral Presentation

    SciTech Connect

    Porter, Zachary

    2015-08-25

    In the electronics behind computer memory storage, the speed and size are dictated by the performance of permanent magnets inside devices called read heads. Complicated magnets made of stacked layers of thin films can be engineered to have properties that yield more energy storage and faster switching times compared to conventional iron or cobalt magnets. The reason is that magnetism is a result of subtle interactions amongst electrons; just how neurons come together on large scales to make cat brains and dog brains, ensembles of electrons interact and become ferromagnets and paramagnets. These interactions make magnets too difficult to study in their entirety, so I focus on the interfaces between layers, which are responsible for the coupling materials physicists hope to exploit to produce next-generation magnets. This project, I study a transition metal oxide material called LSCO, Lanthanum Cobaltite, which can be a paramagnet or a ferromagnet depending on how you tweak the electronic structure. It exhibits an exciting behavior: its sum is greater than the sum of its parts. When another similar material called a LSMO, Lanthanum Manganite, is grown on top of it, their interface has a different type of magnetism from the LSCO or the LSMO! I hope to explain this by demonstrating differently charged ions in the interface. The typical method for quantifying this is x-ray absorption, but all conventional techniques look at every layer simultaneously, averaging the interfaces and the LSCO layers that we want to characterize separately. Instead, I must use a new reflectivity technique, which tracks the intensity of reflected x-rays at different angles, at energies near the absorption peaks of certain elements, to track changes in the electronic structure of the material. The samples were grown by collaborators at the Takamura group at U.C. Davis and probed with this “resonant reflectivity” technique on Beamline 2-1 at the Stanford Synchrotron Radiation Lightsource

  17. Comparative study between LMTO and FPLAPW into the calculation of the electronic structure of carbide Cr 23C 6

    NASA Astrophysics Data System (ADS)

    dos Santos, A. V.

    2007-01-01

    Considering the actual state of the art in Materials Science, it is necessary to do a theoretical analysis of the compounds obtained through experimenting, with the objective of understanding them better, by foreseeing their behaviour and possible new compounds. For this, in this work, we calculate electronic structures of Cr 23C 6 chromium carbide, which are present in fast steels, using two methods of calculating the band structure of first principles, the method of linear muffin-tin orbital (LMTO) with the Andersen's atomic sphere approximation (ASA) and the method of linear plain and expanded waves (LAPW) with generalized gradient approximation (GGA). Through calculations of formation energy in relation to its volume we obtain the equilibrium volume of 379.16 u.a. using the LMTO, and 375.13 u.a, using the LAPW. In the equilibrium volume we calculated some fundamental state properties. We observed an extremely low magnetization in both methods; nevertheless, in LAPW we verified a little magnetic moment in the Crl site that is 0.2512μB. The method LAPW affirms the existence of an interstitial region motivating the charge transference to this region. As the LMTO does not have the interstitial region, we do not see the charge transference to this region; in this case the charges come out of the C and Crl sites to take place in the Crll site. The density of states (DOS) shows that there is an interaction between the “s” states of C with the other sites and in a more intense way with the Crll site. When we compared the DOS, in relation to the methods used, we saw that in case of the LMTO, these are slightly placed in regions where energy is lower as well as its Fermi energy.

  18. Density functional study for crystalline structures and electronic properties of Si1- x Sn x binary alloys

    NASA Astrophysics Data System (ADS)

    Nagae, Yuki; Kurosawa, Masashi; Shibayama, Shigehisa; Araidai, Masaaki; Sakashita, Mitsuo; Nakatsuka, Osamu; Shiraishi, Kenji; Zaima, Shigeaki

    2016-08-01

    We have carried out density functional theory (DFT) calculation for Si1- x Sn x alloy and investigated the effect of the displacement of Si and Sn atoms with strain relaxation on the lattice constant and E- k dispersion. We calculated the formation probabilities for all atomic configurations of Si1- x Sn x according to the Boltzmann distribution. The average lattice constant and E- k dispersion were weighted by the formation probability of each configuration of Si1- x Sn x . We estimated the displacement of Si and Sn atoms from the initial tetrahedral site in the Si1- x Sn x unit cell considering structural relaxation under hydrostatic pressure, and we found that the breaking of the degenerated electronic levels of the valence band edge could be caused by the breaking of the tetrahedral symmetry. We also calculated the E- k dispersion of the Si1- x Sn x alloy by the DFT+U method and found that a Sn content above 50% would be required for the indirect-direct transition.

  19. First-Principles Study of Electronic Structure and Hydrogen Adsorption of 3d Transition Metal Exposed Paddle Wheel Frameworks

    SciTech Connect

    Bak, J. H.; Le, V. D.; Kang, J.; Wei, S. H.; Kim, Y. H.

    2012-04-05

    Open-site paddle wheels, comprised of two transition metals bridged with four carboxylate ions, have been widely used for constructing metal-organic frameworks with large surface area and high binding energy sites. Using first-principles density functional theory calculations, we have investigated atomic and electronic structures of various 3d transition metal paddle wheels before and after metal exposure and their hydrogen adsorption properties at open metal sites. Notably, the hydrogen adsorption is impeded by covalent metal-metal bonds in early transition metal paddle wheels from Sc to Cr and by the strong ferromagnetic coupling of diatomic Mn and Fe in the paddle wheel configurations. A significantly enhanced H{sub 2} adsorption is predicted in the nonmagnetic Co{sub 2} and Zn{sub 2} paddle wheel with the binding energy of {approx}0.2 eV per H{sub 2}. We also propose the use of two-dimensional Co{sub 2} and Zn{sub 2} paddle wheel frameworks that could have strongly adsorbed dihydrogen up to 1.35 wt % for noncryogenic hydrogen storage applications.

  20. First-principles study of structural, elastic, electronic and thermodynamic properties of topological insulator Bi2Se3 under pressure

    NASA Astrophysics Data System (ADS)

    Gao, Xiang; Zhou, Meng; Cheng, Yan; Ji, Guangfu

    2016-01-01

    The structural, elastic, electronic and thermodynamic properties of the rhombohedral topological insulator Bi2Se3 are investigated by the generalized gradient approximation (GGA) with the Wu-Cohen (WC) exchange-correlation functional. The calculated lattice constants agree well with the available experimental and other theoretical data. Our GGA calculations indicate that Bi2Se3 is a 3D topological insulator with a band gap of 0.287 eV, which are well consistent with the experimental value of 0.3 eV. The pressure dependence of the elastic constants Cij, bulk modulus B, shear modulus G, Young's modulus E, and Poisson's ratio σ of Bi2Se3 are also obtained successfully. The bulk modulus obtained from elastic constants is 53.5 GPa, which agrees well with the experimental value of 53 GPa. We also investigate the shear sound velocity VS, longitudinal sound velocity VL, and Debye temperature ΘE from our elastic constants, as well as the thermodynamic properties from quasi-harmonic Debye model. We obtain that the heat capacity Cv and the thermal expansion coefficient α at 0 GPa and 300 K are 120.78 J mol-1 K-1 and 4.70 × 10-5 K-1, respectively.

  1. Density functional study for crystalline structures and electronic properties of Si1‑ x Sn x binary alloys

    NASA Astrophysics Data System (ADS)

    Nagae, Yuki; Kurosawa, Masashi; Shibayama, Shigehisa; Araidai, Masaaki; Sakashita, Mitsuo; Nakatsuka, Osamu; Shiraishi, Kenji; Zaima, Shigeaki

    2016-08-01

    We have carried out density functional theory (DFT) calculation for Si1‑ x Sn x alloy and investigated the effect of the displacement of Si and Sn atoms with strain relaxation on the lattice constant and E– k dispersion. We calculated the formation probabilities for all atomic configurations of Si1‑ x Sn x according to the Boltzmann distribution. The average lattice constant and E– k dispersion were weighted by the formation probability of each configuration of Si1‑ x Sn x . We estimated the displacement of Si and Sn atoms from the initial tetrahedral site in the Si1‑ x Sn x unit cell considering structural relaxation under hydrostatic pressure, and we found that the breaking of the degenerated electronic levels of the valence band edge could be caused by the breaking of the tetrahedral symmetry. We also calculated the E– k dispersion of the Si1‑ x Sn x alloy by the DFT+U method and found that a Sn content above 50% would be required for the indirect–direct transition.

  2. DFT-based ab initio study of structural and electronic properties of lithium fluorooxoborate LiB6O9F and experimentally observed second harmonic generation

    NASA Astrophysics Data System (ADS)

    Andriyevsky, B.; Doll, K.; Cakmak, G.; Jansen, M.; Niemer, A.; Betzler, K.

    2011-09-01

    An ab initio density functional theory-based study of the electronic band structure, the elastic, electric, elastoelectric, and linear and nonlinear optical properties of the new ion conductor LiB6O9F, has been performed. The computed band structure reveals a wide direct band gap. The coefficients of the second order nonlinear susceptibility χ(2) were found to be comparable to those of KH2PO4. Corresponding experimental investigations of second harmonic generation comply with the respective ab initio calculations.

  3. Computational Chemistry Using Modern Electronic Structure Methods

    ERIC Educational Resources Information Center

    Bell, Stephen; Dines, Trevor J.; Chowdhry, Babur Z.; Withnall, Robert

    2007-01-01

    Various modern electronic structure methods are now days used to teach computational chemistry to undergraduate students. Such quantum calculations can now be easily used even for large size molecules.

  4. Structure of Wet Specimens in Electron Microscopy

    ERIC Educational Resources Information Center

    Parsons, D. F.

    1974-01-01

    Discussed are past work and recent advances in the use of electron microscopes for viewing structures immersed in gas and liquid. Improved environmental chambers make it possible to examine wet specimens easily. (Author/RH)

  5. Instructional Approach to Molecular Electronic Structure Theory

    ERIC Educational Resources Information Center

    Dykstra, Clifford E.; Schaefer, Henry F.

    1977-01-01

    Describes a graduate quantum mechanics projects in which students write a computer program that performs ab initio calculations on the electronic structure of a simple molecule. Theoretical potential energy curves are produced. (MLH)

  6. Structural and electronic properties of a large-scale Moiré pattern of hexagonal boron nitride on Cu(111) studied with density functional theory.

    PubMed

    Koitz, Ralph; Seitsonen, Ari P; Iannuzzi, Marcella; Hutter, Jürg

    2013-06-21

    Hexagonal boron nitride (h-BN) adsorbed on metal surfaces shows great promise for applications in nanoscience. Depending on the nature of the substrate, effects such as an extended corrugation of the monolayer can be observed and utilized, e.g. for the patterning of adsorbed molecules. Here we present an in-depth computational study of the structural and electronic properties of a 6 nm Moiré pattern formed by a rotated layer of h-BN on a Cu(111) surface. In contrast to related systems, the h-BN layer undergoes only minute structural changes upon adsorption. Nevertheless, the projected density of states at various atoms in the cell and the electrostatic potential above the surface are periodically modulated, leading to the experimentally observed electronic corrugation. We rationalize this observation with the variation in adsorption registry resulting in periodic changes of the lateral, rather than vertical, h-BN-Cu distances. PMID:23681111

  7. The change of the electronic structure of alkali halide films on W(110) under electron bombardment

    NASA Astrophysics Data System (ADS)

    Dieckhoff, S.; Maus-Friedrichs, W.; Kempter, V.

    1992-03-01

    NaCl and Csl films of up to four layers were deposited onto W(110) surfaces and investigated by metastable impact electron spectroscopy (MIES), UPS and AES. The electronic structure of the films under electron bombardment was then studied by MIES/UPS. The results are compared with the corresponding ones obtained by thermal desorption spectroscopy (TDS). An interpretation of the results is attempted on the basis of existing theories for desorption induced by electronic transitions (DIET) of alkali halides.

  8. Hybrid density functional study of structural, bonding, and electronic properties of the manganite series La1-xCaxMnO3 (x =0,1/4,1)

    NASA Astrophysics Data System (ADS)

    Korotana, R.; Mallia, G.; Gercsi, Z.; Liborio, L.; Harrison, N. M.

    2014-05-01

    Hybrid-exchange density functional theory calculations are carried out to determine the effects of A-site doping on the electronic and magnetic properties of the manganite series La1-xCaxMnO3. This study focuses on the ground state of an ordered Ca occupancy in a periodic structure. It is shown that the hybrid-exchange functional, Becke three-parameter Lee-Yang-Parr (B3LYP), provides an accurate and consistent description of the electronic structure for LaMnO3, CaMnO3, and La0.75Ca0.25MnO3. We have quantified the relevant structural, magnetic, and electronic energy contributions to the stability of the doped compound. An insight into the exchange coupling mechanism for the low hole density region of the phase diagram, where a polaron (anti-Jahn-Teller) forms, is also provided. This study completes a microscopic description of the lightly doped insulator with an antiferromagnetic-to-ferromagnetic and metal-to-insulator transition.

  9. First principles study of the structural and electronic properties of double perovskite Ba2YTaO6 in cubic and tetragonal phases

    NASA Astrophysics Data System (ADS)

    Deluque Toro, C. E.; Rodríguez M., Jairo Arbey; Landínez Téllez, D. A.; Moreno Salazar, N. O.; Roa-Rojas, J.

    2014-12-01

    The Ba2YTaO6 double perovskite presents a transition from cubic (Fm-3m) to tetragonal structure (I4/m) at high temperature. In this work, we present a detailed study of the structural and electronic properties of the double perovskite Ba2YTaO6 in space group Fm-3m and I4/m. Calculations were made with the Full-Potential Linear Augmented Plane Wave method (FP-LAPW) within the framework of the Density Functional Theory (DFT) with exchange and correlation effects in the Generalized Gradient (GGA) and Local Density (LDA) approximations. From the minimization of energy as a function of volume and the fitting of the Murnaghan equation some structural characteristics were determined as, for example, total energy, lattice parameter (a=8.50 Å in cubic phase and a=5.985 Å and c=8.576 Å in tetragonal), bulk modulus (135.6 GPa in cubic phase and 134.1 GPa in tetragonal phase) and its derivative. The study of the electronic characteristics was performed from the analysis of the electronic density of states (DOS). We find a non-metallic behavior for this with a direct band gap of approximately 3.5 eV and we found that the Ba2YTaO6 (I4/m) phase is the most stable one. © 2013 Elsevier Science.

  10. Electronic structure and thermoelectric properties of (PbSe)m/(SnSe)n superlattice: A first principles study

    NASA Astrophysics Data System (ADS)

    Do, Duc Cuong; Rhim, S. H.; Hong, Soon Cheol

    2015-03-01

    Figure of merit (ZT) of thermoelectric materials can be enhanced by lowering thermal conductivity or/and increasing electrical conductivity. The extremely high ZT of layered structure SnSe opened up a new direction in study of thermoelectricity due to its low thermal conductivity, which, however, is limited to high temperature. Here, we performed first principles density functional calculations to explore room-temperature thermoelectricity. We consider (PbSe)m/(SnSe)n superlattices with different period, whose quantum well structure is expected to increase electrical conductivity by modulation of charge doping at interface. Calculations of Seebeck coefficients for the superlattices are presented. Supported by the Ministry of Trade, Industry & Energy, Korea (20132020000110) and Priority Research Centers Program (2009-0093818) through National Research Foundation of Korea.

  11. A Initio Mr-Rci Calculations of ((n - 1)D + Ns)(n) Atomic Bound States: Application to Hyperfine Structure and Electron Affinity Studies.

    NASA Astrophysics Data System (ADS)

    Datta, Debasis

    Systematic inclusion of many-body effects in open d and f subshell atoms has long been known as a formidable challenge in atomic structure theory. Due to the presence of competing relativistic effects in such systems, an appropriate theoretical approach needs to incorporate electron correlation within the framework of the Special Theory of Relativity. To this aim, the Relativistic Configuration Interaction methodology as developed by Beck and others has been extended and applied to multi-reference situations in ((n - 1)d + ns) ^{rm N} type valence configurations. Specific focus has been on the hyperfine structure and electron affinity studies of the transition metal ions and the rare earths respectively. Energies and magnetic dipole and electric quadrupole hyperfine structure constants of all the fifteen Zr II (4d + 5s)^3 J = 0.5, 1.5 levels and the twenty one Nb II (4d + 5s)^4 J = 2 levels have been determined with unprecedented accuracies. The average errors in energy are 0.087 eV and 0.050 eV for Zr II J = 3/2 & 1/2 respectively while that for the ten bottom levels of Nb II J = 2 is 0.055 eV. For the levels known experimentally, the corresponding errors in magnetic dipole hyperfine structure constants are 9.2%, 31.8% and 3.8%. Quite a few of the many-body hyperfine constant values exhibit striking improvements over the Multi-Configurational Dirac Fock values. A new value of nuclear quadrupole moment has also been predicted for Zr II. In all cases certain previous level assignments have been corrected and five previously unknown levels have been identified in Nb II. The rigorous systematics of the many-body effects important for the energy level and hyperfine structure of these systems has been presented including core-valence and core-core effects. Contrary to the conventional wisdom and theoretical predictions of the last decade, the attachment of an f electron has been discarded as the most likely mechanism for the formation of Lanthanide and Actinide negative

  12. a Study of F-Electrons Behavior in Cerium-Based Intermetallics with the COPPER(3) Gold Structure

    NASA Astrophysics Data System (ADS)

    Rahman, Shamsur

    We have measured the thermodynamic and transport properties of new system CeTl_3 and then alloying Tl with Pb, Sn and In to see how the f-electrons behavior evolves as one goes in between two radically different groundstates. The measurements include the room temperature lattice constant, magnetic susceptibility, specific heat and electrical resistivity of the pseudobinary alloys Ce(Tl_{1-x}Pb _{x})_3, Ce(Tl_{1-x}Sn _{x})_3 and Ce(Tl_{1-x}In _{x})_3, where 0 <=q x < 1. The results are summarized as follows. The data strongly suggests that CeTl_3 orders antiferromagnetically at ~ 3.8K. The Ce-ions are in the trivalent state with well localized magnetic moments corresponding to the Hund's rule J = 5/2 spin-orbit groundmultiplet with mu = 2.55mu_beta. The J = 5/2 multiplet is split by the cubic crystalline field into a Gamma_7-grounddoublet and an excited Gamma_8-quartet, the splitting energy being of the order of 100K to 150K. The properties of CeTl_3 are found to be similar to those of CeIn_3 except that the Kondo scattering in CeTl_3 is much weaker than CeIn_3. In Ce(Tl_{1-x} Pb_{x})_3 alloy, the electronic specific heat coefficient above Neel temperature increases as x increases. The " gamma_{HT}" reaches 431 mJ/mole-K^2 for x = 0.6. This indicates that the localized f- electron antiferromagnetic behavior is driven to an itinerant heavy fermion antiferromagnetic one. Also the Neel temperature has nonmonotonic variation with Pb concentration. Here we found a striking similarity with the previously studied Ce(In_{ 1-x}Pb_{x})_3 system regarding T_ {N} and gamma_ {HT} behavior except that we do not see a concentration range for which T_ {N} = 0 as is observed in Ce(In _{rm 1-x}Pb _{x})_3 system. In Ce(Tl_{1-x} Sn_{x})_3 alloy, the data indicates a gradual transition from local moment to mixed valence behavior similar to the prior study Ce(In_{1-x }Sn_{x}) _3. We found enhancement in gamma _{HT}, chi (0) and rho(0) as predicted by Newns and Hewson theory in a mixed

  13. Analysis of boron carbides' electronic structure

    NASA Technical Reports Server (NTRS)

    Howard, Iris A.; Beckel, Charles L.

    1986-01-01

    The electronic properties of boron-rich icosahedral clusters were studied as a means of understanding the electronic structure of the icosahedral borides such as boron carbide. A lower bound was estimated on bipolaron formation energies in B12 and B11C icosahedra, and the associated distortions. While the magnitude of the distortion associated with bipolaron formation is similar in both cases, the calculated formation energies differ greatly, formation being much more favorable on B11C icosahedra. The stable positions of a divalent atom relative to an icosahedral borane was also investigated, with the result that a stable energy minimum was found when the atom is at the center of the borane, internal to the B12 cage. If incorporation of dopant atoms into B12 cages in icosahedral boride solids is feasible, novel materials might result. In addition, the normal modes of a B12H12 cluster, of the C2B10 cage in para-carborane, and of a B12 icosahedron of reduced (D sub 3d) symmetry, such as is found in the icosahedral borides, were calculated. The nature of these vibrational modes will be important in determining, for instance, the character of the electron-lattice coupling in the borides, and in analyzing the lattice contribution to the thermal conductivity.

  14. Reversible Hydrogen Storage Materials – Structure, Chemistry, and Electronic Structure

    SciTech Connect

    Robertson, Ian M.; Johnson, Duane D.

    2014-06-21

    To understand the processes involved in the uptake and release of hydrogen from candidate light-weight metal hydride storage systems, a combination of materials characterization techniques and first principle calculation methods have been employed. In addition to conventional microstructural characterization in the transmission electron microscope, which provides projected information about the through thickness microstructure, electron tomography methods were employed to determine the three-dimensional spatial distribution of catalyst species for select systems both before and after dehydrogenation. Catalyst species identification as well as compositional analysis of the storage material before and after hydrogen charging and discharging was performed using a combination of energy dispersive spectroscopy, EDS, and electron energy loss spectroscopy, EELS. The characterization effort was coupled with first-principles, electronic-structure and thermodynamic techniques to predict and assess meta-stable and stable phases, reaction pathways, and thermodynamic and kinetic barriers. Systems studied included:NaAlH4, CaH2/CaB6 and Ca(BH4)2, MgH2/MgB2, Ni-Catalyzed Magnesium Hydride, TiH2-Catalyzed Magnesium Hydride, LiBH4, Aluminum-based systems and Aluminum

  15. High-resolution spectroscopy using synchrotron radiation for surface structure determination and the study of correlated electron systems

    SciTech Connect

    Moler, E.J. Jr.

    1996-05-01

    The surface structure of three molecular adsorbate systems on transition metal surfaces, ({radical}3 x {radical}3)R30{degrees} and (1.5 x 1.5)R18{degrees} CO adsorbed on Cu(111), and c(2x2) N2/Ni(100), have been determined using Angle-Resolved Photoemission Extended Fine Structure (ARPEFS). The adsorption site and bond lengths are reported for the adsorbate-metal bond and the first two substrate layers. The ARPEFS diffraction pattern of the shake-up peak for c(2x2) N2/Ni(100) is also discussed. A unique method of experimentally determining the angular momentum and intrinsic/extrinsic origin of core-level satellites is presented. We show for the first time that satellite peaks not associated with chemically differentiated atomic species display an ARPEFS intensity oscillation. Specifically, we present data for the C 1s from ({radical}3x{radical}3)R30 CO/Cu(111) and p2mg(2x1)CO/Ni(110), N is from c(2x2) N2/Ni(100), and Ni 3p from clean nickel(111). The satellite peaks in all cases exhibit ARPEFS curves which indicate an angular momentum identical to the main peak and are of an intrinsic nature. A Fourier Transform Soft X-ray spectrometer (FF-SX) has been designed and is under construction for the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. The spectrometer is designed for ultra-high resolution theoretical resolving power E/{Delta}E{approx}-10{sup 6} in the photon energy region of 60-120 eV. This instrument is expected to provide experimental results which sensitively test models of correlated electron processes in atomic and molecular physics. The design criteria and consequent technical challenges posed by the short wavelengths of x-rays and desired resolving power are discussed. The fundamental and practical aspects of soft x-ray interferometry are also explored.

  16. Strain effect on electronic structure and thermoelectric properties of orthorhombic SnSe: A first principles study

    SciTech Connect

    Cuong, Do Duc; Rhim, S. H. Hong, Soon Cheol; Lee, Joo-Hyong

    2015-11-15

    Strain effect on thermoelectricity of orthorhombic SnSe is studied using density function theory. The Seebeck coefficients are obtained by solving Boltzmann Transport equation (BTE) with interpolated band energies. As expected from the crystal structure, calculated Seebeck coefficients are highly anisotropic, and agree well with experiment. Changes in the Seebeck coefficients are presented, when strain is applied along b and c direction with strength from -3% to +3%, where influence by band gaps and band dispersions are significant. Moreover, for compressive strains, the sign change of Seebeck coefficients at particular direction suggests that the bipolar transport is possible for SnSe.

  17. Electronic structure of Ce2RhIn8: A two-dimensional heavy-fermion system studied by angle-resolved photoemission spectroscopy

    DOE PAGES

    Jiang, Rui; Mou, Daixing; Liu, Chang; Zhao, Xin; Yao, Yongxin; Ryu, Hyejin; Petrovic, C.; Ho, Kai -Ming; Kaminski, Adam

    2015-04-01

    We use angle-resolved photoemission spectroscopy (ARPES) to study the 2D heavy fermion superconductor, Ce₂RhIn₈. The Fermi surface is rather complicated and consists of several hole and electron pockets with one of the sheets displaying strong nesting properties with a q-vector of (0.32, 0.32) π/a. We do not observe kz dispersion of the Fermi sheets, which is consistent with the expected 2D character of the electronic structure. Comparison of the ARPES data to band structure calculations suggests that a localized picture of the f-electrons works best. While there is some agreement in the overall band dispersion and location of the Fermimore » sheets, the model does not reproduce all observed bands and is not completely accurate for those it does. As a result, our data paves the way for improving the band structure calculations and the general understanding of the transport and thermodynamical properties of this material.« less

  18. Studying electron-PAG interactions using electron-induced fluorescence

    NASA Astrophysics Data System (ADS)

    Narasimhan, Amrit; Grzeskowiak, Steven; Ostrander, Jonathan; Schad, Jonathon; Rebeyev, Eliran; Neisser, Mark; Ocola, Leonidas E.; Denbeaux, Gregory; Brainard, Robert L.

    2016-03-01

    In extreme ultraviolet (EUV) lithography, 92 eV photons are used to expose photoresists. Typical EUV resists are organic-based and chemically amplified using photoacid generators (PAGs). Upon exposure, PAGs produce acids which catalyze reactions that result in changes in solubility. In EUV lithography, photo- and secondary electrons (energies of 10- 80 eV) play a large role in PAG acid-production. Several mechanisms for electron-PAG interactions (e.g. electron trapping, and hole-initiated chemistry) have been proposed. The aim of this study is to explore another mechanism - internal excitation - in which a bound PAG electron can be excited by receiving energy from another energetic electron, causing a reaction that produces acid. This paper explores the mechanism of internal excitation through the analogous process of electron-induced fluorescence, in which an electron loses energy by transferring that energy to a molecule and that molecule emits a photon rather than decomposing. We will show and quantify electron-induced fluorescence of several fluorophores in polymer films to mimic resist materials, and use this information to refine our proposed mechanism. Relationships between the molecular structure of fluorophores and fluorescent quantum yield may aid in the development of novel PAGs for EUV lithography.

  19. Electronic and structural properties of metallic microclusters

    SciTech Connect

    Maiti, A.

    1992-04-01

    The first part of this thesis presents a first-order pseudopotential calculation at T=O of the total energy of small sodium clusters of size N<800. The calculation is based on a local-pseudopotential scheme and local-density correlation and exchange. A temperature-size (T-N) phase-diagram is then derived using the T=O results and Lindemann`s criterion for melting. The phase-diagram contains three regions of stability: (1) a liquid (jellium) phase at temperatures above the melting line T{sub M}(N) where cluster-stability occurs at electronic magic numbers: (2) a phase related to complete geometrical shells of body-centered-cubic structure at temperatures below the melting line; and (3) a close-packed structure at very low temperatures and sufficiently large N. The melting line drops to T{sub M}(N)=O for N<65, where electronic magic numbers are stable even at T=O. The phase diagram reduces asymptotically to the known phases of sodium as N{yields}{infinity}, including the known martensitic transformation at T{approximately}5 K. The second and the last part of this thesis consists of a study of small-cluster many-body systems by means of an on-site ``local`` chemical potential which allows the continuous variation of local electron-density. This method yields a criterion to distinguish particular features of a small cluster that are likely to survive in the large-N thermodynamic limit from those discontinuities that arise only from finite-size effects.

  20. Electronic and structural properties of metallic microclusters

    SciTech Connect

    Maiti, A.

    1992-04-01

    The first part of this thesis presents a first-order pseudopotential calculation at T=O of the total energy of small sodium clusters of size N<800. The calculation is based on a local-pseudopotential scheme and local-density correlation and exchange. A temperature-size (T-N) phase-diagram is then derived using the T=O results and Lindemann's criterion for melting. The phase-diagram contains three regions of stability: (1) a liquid (jellium) phase at temperatures above the melting line T{sub M}(N) where cluster-stability occurs at electronic magic numbers: (2) a phase related to complete geometrical shells of body-centered-cubic structure at temperatures below the melting line; and (3) a close-packed structure at very low temperatures and sufficiently large N. The melting line drops to T{sub M}(N)=O for N<65, where electronic magic numbers are stable even at T=O. The phase diagram reduces asymptotically to the known phases of sodium as N{yields}{infinity}, including the known martensitic transformation at T{approximately}5 K. The second and the last part of this thesis consists of a study of small-cluster many-body systems by means of an on-site local'' chemical potential which allows the continuous variation of local electron-density. This method yields a criterion to distinguish particular features of a small cluster that are likely to survive in the large-N thermodynamic limit from those discontinuities that arise only from finite-size effects.

  1. Multigrid Methods in Electronic Structure Calculations

    NASA Astrophysics Data System (ADS)

    Briggs, Emil

    1996-03-01

    Multigrid techniques have become the method of choice for a broad range of computational problems. Their use in electronic structure calculations introduces a new set of issues when compared to traditional plane wave approaches. We have developed a set of techniques that address these issues and permit multigrid algorithms to be applied to the electronic structure problem in an efficient manner. In our approach the Kohn-Sham equations are discretized on a real-space mesh using a compact representation of the Hamiltonian. The resulting equations are solved directly on the mesh using multigrid iterations. This produces rapid convergence rates even for ill-conditioned systems with large length and/or energy scales. The method has been applied to both periodic and non-periodic systems containing over 400 atoms and the results are in very good agreement with both theory and experiment. Example applications include a vacancy in diamond, an isolated C60 molecule, and a 64-atom cell of GaN with the Ga d-electrons in valence which required a 250 Ry cutoff. A particular strength of a real-space multigrid approach is its ready adaptability to massively parallel computer architectures. The compact representation of the Hamiltonian is especially well suited to such machines. Tests on the Cray-T3D have shown nearly linear scaling of the execution time up to the maximum number of processors (512). The MPP implementation has been used for studies of a large Amyloid Beta Peptide (C_146O_45N_42H_210) found in the brains of Alzheimers disease patients. Further applications of the multigrid method will also be described. (in collaboration D. J. Sullivan and J. Bernholc)

  2. Electronic structure and mechanical properties of ternary ZrTaN alloys studied by ab initio calculations and thin-film growth experiments

    NASA Astrophysics Data System (ADS)

    Abadias, G.; Kanoun, M. B.; Goumri-Said, S.; Koutsokeras, L.; Dub, S. N.; Djemia, Ph.

    2014-10-01

    The structure, phase stability, and mechanical properties of ternary alloys of the Zr-Ta-N system are investigated by combining thin-film growth and ab initio calculations. Zr1-xTaxN films with 0≤x≤1 were deposited by reactive magnetron cosputtering in Ar +N2 plasma discharge and their structural properties characterized by x-ray diffraction. We considered both ordered and disordered alloys, using supercells and special quasirandom structure approaches, to account for different possible metal atom distributions on the cation sublattice. Density functional theory within the generalized gradient approximation was employed to calculate the electronic structure as well as predict the evolution of the lattice parameter and key mechanical properties, including single-crystal elastic constants and polycrystalline elastic moduli, of ternary Zr1-xTaxN compounds with cubic rocksalt structure. These calculated values are compared with experimental data from thin-film measurements using Brillouin light scattering and nanoindentation tests. We also study the validity of Vegard's empirical rule and the effect of growth-dependent stresses on the lattice parameter. The thermal stability of these Zr1-xTaxN films is also studied, based on their structural and mechanical response upon vacuum annealing at 850 °C for 3 h. Our findings demonstrate that Zr1-xTaxN alloys with Ta fraction 0.51⩽x⩽0.78 exhibit enhanced toughness, while retaining high hardness ˜30 GPa, as a result of increased valence electron concentration and phase stability tuning. Calculations performed for disordered or ordered structures both lead to the same conclusion regarding the mechanical behavior of these nitride alloys, in agreement with recent literature findings [H. Kindlund, D. G. Sangiovanni, L. Martinez-de-Olcoz, J. Lu, J. Jensen, J. Birch, I. Petrov, J. E. Greene, V. Chirita, and L. Hultman, APL Materials 1, 042104 (2013), 10.1063/1.4822440].

  3. Theoretical studies of the structures and electronic properties of U(NH{sub 2}){sub 3} and Np(NH{sub 2}){sub 3}

    SciTech Connect

    Hay, P.J.; Martin, R.L.

    1993-10-01

    The electronic structure of the model compounds U(NH{sub 2}){sub 3} and Np(NH{sub 2}){sub 3} is investigated with the aid of ab initio electronic structure techniques. The electronic ground states and equilibrium geometries of these complexes are determined using multi-configuration SCF techniques. Comparisons are made to their counterparts U(CH{sub 3}){sub 3} and Np(CH{sub 3}){sub 3}.

  4. The fine structure of the human fetal urinary bladder. Development and maturation. A light, transmission and scanning electron microscopic study.

    PubMed Central

    Newman, J; Antonakopoulos, G N

    1989-01-01

    The urinary bladders of 27 human fetuses, aged 7 weeks to full term, were studied by light, transmission and scanning electron microscopy to establish the sequence of events in the development and maturation of the organ during fetal life. In the early specimens, 7-12 weeks old, the urinary bladder was lined by a bilayered, cuboidal and glycogen-rich epithelium. During the 13-17th weeks the epithelium thickened, a third layer developed and by light microscopy it now resembled urothelium. By 21 weeks this had evolved into a 3-4 layer thick epithelium with typical ultrastructural urothelial characteristics. Smooth muscle cells emerged from the condensed mesenchyme of the bladder wall by the 12th week of gestation, initially in the cephalic part of the organ but spreading within a week into the caudal end. Our findings indicate that the human fetal bladder undergoes a series of vital developmental changes during 13-21 weeks of gestation finally acquiring the typical urothelial lining and a well-developed muscular coat. Images Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 Fig. 9 Fig. 10 Fig. 11 Fig. 12 Fig. 13 Fig. 14 Fig. 15 Fig. 16 Fig. 17 PMID:2621133

  5. Electronic structures of CuTPP and CuTPP(F) complexes. A combined experimental and theoretical study I.

    PubMed

    Mangione, Giulia; Carlotto, Silvia; Sambi, Mauro; Ligorio, Giovanni; Timpel, Melanie; Vittadini, Andrea; Nardi, Marco Vittorio; Casarin, Maurizio

    2016-07-28

    Copper complexes of tetraphenylporphyrin (H2TPP) and tetrakis(pentafluorophenyl)porphyrin (H2TPP(F)) deposited as thin films on Au(111) have been studied experimentally and theoretically. Core level emissions from C 1s, N 1s, F 1s and Cu 2p as well as valence states of CuTPP and CuTPP(F) have been investigated using surface photoelectron spectroscopy. The interpretation of experimental results has been guided by theoretical calculations carried out on isolated species in the habit of the density functional theory. Reference to experimental and theoretical outcomes pertaining to H2TPP and H2TPP(F) allowed a confident and detailed assignment of the title molecules' X-ray and ultraviolet photoemission data. With specific reference to the latter, similar to copper phthalocyanine (CuPc), whose coordinative pocket mirrors the CuTPP/CuTPP(F) ones, the lowest ionization energy of the title compounds implies electron ejection from a ring orbital rather than from the Cu 3d-based singly occupied molecular orbital. Moreover, analogous to CuPc, the ionic contribution appears to play an important role in the Cu-N bonding. Nevertheless, differences in the number, symmetry, nature and relative position of CuTPP/CuTPP(F) occupied frontier orbitals compared to CuPc may be stated only by considering in great detail the Cu-ligand covalent interactions. PMID:27166746

  6. Electron microscope studies

    SciTech Connect

    Crewe, A.V.; Kapp, O.H.

    1992-07-01

    This is a report covering the research performed in the Crewe laboratory between 1964 and 1992. Because of limitations of space we have provided relatively brief summaries of the major research directions of the facility during these years. A complete bibliography has been included and we have referenced groups of pertinent publications at the beginning of each section. This report summarizes our efforts to develop better electron microscopes and chronicles many of the experimental programs, in materials science and biology, that acted both as a stimulus to better microscope design and also as a testing ground for many instrumental innovations.

  7. First-principles studies of BN sheets with absorbed transition metal single atoms or dimers: stabilities, electronic structures, and magnetic properties.

    PubMed

    Ma, Dongwei; Lu, Zhansheng; Ju, Weiwei; Tang, Yanan

    2012-04-11

    BN sheets with absorbed transition metal (TM) single atoms, including Fe, Co, and Ni, and their dimers have been investigated by using a first-principles method within the generalized gradient approximation. All of the TM atoms studied are found to be chemically adsorbed on BN sheets. Upon adsorption, the binding energies of the Fe and Co single atoms are modest and almost independent of the adsorption sites, indicating the high mobility of the adatoms and isolated particles to be easily formed on the surface. However, Ni atoms are found to bind tightly to BN sheets and may adopt a layer-by-layer growth mode. The Fe, Co, and Ni dimers tend to lie (nearly) perpendicular to the BN plane. Due to the wide band gap of the pure BN sheet, the electronic structures of the BN sheets with TM adatoms are determined primarily by the distribution of TM electronic states around the Fermi level. Very interesting spin gapless semiconductors or half-metals can be obtained in the studied systems. The magnetism of the TM atoms is preserved well on the BN sheet, very close to that of the corresponding free atoms and often weakly dependent on the adsorption sites. The present results indicate that BN sheets with adsorbed TM atoms have potential applications in fields such as spintronics and magnetic data storage due to the special spin-polarized electronic structures and magnetic properties they possess.

  8. An in-situ study of magnetic domain structures in undercooled Fe-29.5 at. %Pd magnetostrictive alloys by Lorentz microscopy and electron holography

    SciTech Connect

    Sun, Wen; Xu, Xianhui; Liu, Jian E-mail: xiawxing@nimte.ac.cn; Xia, Weixing E-mail: xiawxing@nimte.ac.cn; Yan, Aru

    2015-04-28

    Understanding of correlation between magnetic domain structure and functional properties is of importance for the magnetic field driven phase transition (e.g., martensitic transformation) or microstructure variation (e.g., twin boundary motion) materials. In this work, we report a Fe-29.5 at. %Pd shape memory alloy treated by undercooling processing upon a degree of 320 K below the liquid temperature. The effect of high undercooling on the solidified microstructure and martensitic transformation temperatures was investigated. By in-situ Lorentz transmission electron microscopy and electron holography, magnetic domain structure and the field-induced domain wall motion behavior in as-cast and undercooled samples have been schematically studied. The irregular domain structure can be observed in these alloys. On the application of a field up to 300 Oe, the domain walls for both samples are able to move along the direction of the external magnetic field, but structural transition and rearrangement of variants are not observed in the undercooled alloy. The large magnetostriction of Fe-29.5 at. %Pd undercooled alloy originates from the irregular domain walls motion instead of the rearrangement of martensitic twin variants.

  9. Density functional theoretical study of pentacene/noble metal interfaces with van der Waals corrections: Vacuum level shifts and electronic structures

    NASA Astrophysics Data System (ADS)

    Toyoda, Kenji; Hamada, Ikutaro; Lee, Kyuho; Yanagisawa, Susumu; Morikawa, Yoshitada

    2010-04-01

    In order to clarify factors determining the interface dipole, we have studied the electronic structures of pentacene adsorbed on Cu(111), Ag(111), and Au(111) by using first-principles density functional theoretical calculations. In the structural optimization, a semiempirical van der Waals (vdW) approach [S. Grimme, J. Comput. Chem. 27, 1787 (2006)] is employed to include long-range vdW interactions and is shown to reproduce pentacene-metal distances quite accurately. The pentacene-metal distances for Cu, Ag, and Au are evaluated to be 0.24, 0.29, and 0.32 nm, respectively, and work function changes calculated by using the theoretically optimized adsorption geometries are in good agreement with the experimental values, indicating the validity of the present approach in the prediction of the interface dipole at metal/organic interfaces. We examined systematically how the geometric factors, especially the pentacene-substrate distance ( Z C ) , and the electronic properties of the metal substrates contribute to the interface dipole. We found that at Z C ≥ 0.35 nm , the work function changes ( Δ ϕ 's) do not depend on the substrate work function ( ϕ m ) , indicating that the interface level alignment is nearly in the Schottky limit, whereas at Z C ≤ 0.25 nm , Δ ϕ 's vary nearly linearly with ϕ m , and the interface level alignment is in the Bardeen limit. Our results indicate the importance of both the geometric and the electronic factors in predicting the interface dipoles. The calculated electronic structure shows that on Au, the long-range vdW interaction dominates the pentacene-substrate interaction, whereas on Cu and Ag, the chemical hybridization contributes to the interaction.

  10. Electronic Structure Calculations of Highly Charged Ions

    NASA Astrophysics Data System (ADS)

    Bromley, Steve; Ziolkowski, Marcin; Marler, Joan

    2016-05-01

    Exotic systems like Highly Charged Ions (HCIs) are attracting more attention based on their properties and possible interactions. Abundance of HCIs in the solar wind and their interaction with the upper atmosphere puts them in the attention of astro- and atmospheric physicists. Also, their unique properties originating in the high charge make them an excellent candidate for precision measurements and the next generation of atomic clocks. For a better understanding of the dynamics of processes involving HCIs a combined theoretical and experimental effort is needed to study their basic properties and interactions. Both theory and experiment need to be combined due to the extreme nature of these systems. We present preliminary insight into electronic structure of light HCIs, their interactions with neutral atoms and dynamics of charge transfer processes.

  11. Electronic structure and stability of some silicon compounds

    NASA Astrophysics Data System (ADS)

    Novak, Igor; Abu-Izneid, Tareq; Kovač, Branka

    2010-05-01

    The electronic structures of N,1,3-tris(1,1-dimethylethyl)-cyclodisilazan-2-amine ( I) and 2,3,5,5-tetrakis(trimethylsilyl)cyclopentadiene ( II) have been investigated by HeI and HeII UV photoelectron spectroscopy (UPS) and quantum chemical calculations. We discuss the influence of substituent effects on their electronic structure and thermodynamic stability. Our study shows that trimethylsilyl substituents have strong influence on the electronic structure of cyclopentadiene via inductive effect. Their influence on thermodynamic stability is also pronounced. In substituted cyclodisilazanes hyperconjugative influence of alkylsilyl groups was shown to cause relative thermodynamic stabilization of the cyclodisilazane system.

  12. First-principles study of crystal structure, electronic structure, and second-harmonic generation in a polar double perovskite Bi2ZnTiO6.

    PubMed

    Ju, Sheng; Guo, Guang-Yu

    2008-11-21

    Within the density functional theory with the generalized gradient approximation, we present a systematic ab initio investigation of crystal structure, electronic structure, and linear and nonlinear optical responses in a polar double perovskite Bi(2)ZnTiO(6). The effect of B-site ordering is explored by comparing three possible configurations: A-type with alternative Zn and Ti layers stacking along the c axis; C-type with Zn and Ti c axis chains; and G-type with every Zn(Ti) atoms is surrounded by its nearby six Ti(Zn) atoms. It is found that the system with G-type B-site ordering is energetically favorable, which is lower in the total energies of 0.055 and 0.133 eV/formula unit than C-type and A-type, respectively. Optical calculations indicate that all the three configurations show large second-harmonic generation (SHG) coefficients, and the largest static SHG observed in the C-type system reaches 123 (10(-9) esu), the value of which is much larger than ever known polar oxides, e.g., 72 (10(-9) esu) in LiNbO(3). The predicted significant nonlinear optical properties are consistent with the calculated high tetragonality as well as the large off-center displacement of Zn, Ti, and Bi atoms. In particular, a large off-center displacement greater than 0.5 A in Zn atoms is revealed for the first time. A further microscopic picture is presented via the successful connection of the prominent feature of SHG in Bi(2)ZnTiO(6) with that of the linear optical dielectric function in terms of single-photon and double-photon resonances. Our calculations demonstrate the promising application of Bi(2)ZnTiO(6) in optoelectronics.

  13. Electron spin echo envelope modulation studies of the Cu(II)-substituted derivative of isopenicillin N synthase: A structural and spectroscopic model

    SciTech Connect

    Feng Jiang; Peisach, J. ); Lijune Ming; Que, L. Jr. ); Chen, V.J. )

    1991-12-03

    Electron spin echo envelope modulation spectroscopy (ESEEM) was used to study the active site structure of isopenicillin N synthase (IPNS) from Cephalosporium acremonium with Cu(II) as a spectroscopic probe. Fourier transform of the simulated electron spin-echo envelope for the Cu(II)-substituted enzyme, Cu(II)IPNS, revealed two nearly magnetically equivalent, equatorially coordinated His imidazoles. The superhyperfine coupling constant, A{sub iso}, for the remote {sup 14}N of each imidazole was 1.65 MHz. The binding of substrate to the enzyme altered the magnetic coupling so that A{sub iso} is 1.30 MHz for one nitrogen and 2.16 MHz for the other. From a comparison of the ESSEM of Cu(II)IPNS in D{sub 2}O and H{sub 2}O, it is suggested that water is a ligand of Cu(II) and this is displaced upon the addition of substrate.

  14. High-resolution electron-energy-loss spectroscopy and photoelectron-diffraction studies of the geometric structure of adsorbates on single-crystal metal surfaces

    SciTech Connect

    Rosenblatt, D.H.

    1982-11-01

    Two techniques which have made important contributions to the understanding of surface phenomena are high resolution electron energy loss spectroscopy (EELS) and photoelectron diffraction (PD). EELS is capable of directly measuring the vibrational modes of clean and adsorbate covered metal surfaces. In this work, the design, construction, and performance of a new EELS spectrometer are described. These results are discussed in terms of possible structures of the O-Cu(001) system. Recommendations for improvements in this EELS spectrometer and guidelines for future spectrometers are given. PD experiments provide accurate quantitative information about the geometry of atoms and molecules adsorbed on metal surfaces. The technique has advantages when used to study disordered overlayers, molecular overlayers, multiple site systems, and adsorbates which are weak electron scatterers. Four experiments were carried out which exploit these advantages.

  15. Electronic structure of the heavy-fermion caged compound Ce3Pd20X6(X=Si,Ge) studied by density functional theory and photoelectron spectroscopy

    DOE PAGES

    Yamaoka, Hitoshi; Schwier, Eike F.; Arita, Masashi; Shimada, Kenya; Tsujii, Naohito; Jarrige, Ignace; Jiang, Jian; Hayashi, Hirokazu; Iwasawa, Hideaki; Namatame, Hirofumi; et al

    2015-03-30

    The electronic structure of Ce₃Pd₂₀X₆ (X = Si, Ge) has been studied using detailed density functional theory (DFT) calculations and high-resolution photoelectron spectroscopy (PES) measurements. The orbital decomposition of the electronic structure by DFT calculations indicates that Ce atoms at the (8c) site surrounded by 16 Pd atoms have a more localized nature and a tendency to be magnetic. Ce atoms in the (4a) site surrounded by 12 Pd and 6 X atoms, on the other, show only a negligible magnetic moment. In the photoemission valence-band spectra we observe a strong f⁰ (Ce⁴⁺) component with a small fraction of f¹more » (Ce³⁺) component. The spectral weight of f¹ component near the Fermi level Ce₃Pd₂₀Si₆ is stronger than that for Ce₃Pd₂₀Ge₆ at the 4d-4f resonance, suggesting stronger c-f hybridization in the former. This may hint to the origin of the large electronic specific coefficient of Ce₃Pd₂₀Si₆ compared to Ce₃Pd₂₀Ge₆.« less

  16. First-Principle Study of the Structural, Electronic, and Optical Properties of Cubic InNxP1-x Ternary Alloys under Hydrostatic Pressure

    NASA Astrophysics Data System (ADS)

    Hattabi, I.; Abdiche, A.; Moussa, R.; Riane, R.; Hadji, K.; Soyalp, F.; Varshney, Dinesh; Syrotyuk, S. V.; Khenata, R.

    2016-09-01

    In this article, we present results of the first-principle study of the structural, electronic, and optical properties of the InN, InP binary compounds and their related ternary alloy InNxP1-x in the zinc-blend (ZB) phase within a nonrelativistic full potential linearised augmented plan wave (FP-LAPW) method using Wien2k code based on the density functional theory (DFT). Different approximations of exchange-correlation energy were used for the calculation of the lattice constant, bulk modulus, and first-order pressure derivative of the bulk modulus. Whereas the lattice constant decreases with increasing nitride composition x. Our results present a good agreement with theoretical and experimental data. The electronic band structures calculated using Tran-Blaha-modified Becke-Johnson (TB-mBJ) approach present a direct band gap semiconductor character for InNxP1-x compounds at different x values. The electronic properties were also calculated under hydrostatic pressure for (P=0.00, 5.00, 10.0, 15.0, 20.0, 25.0 GPa) where it is found that the InP compound change from direct to indirect band gap at the pressure P≥7.80 GPa. Furthermore, the pressure effect on the dielectric function and the refractive index was carried out. Results obtained in our calculations present a good agreement with available theoretical reports and experimental data.

  17. Quantum fluid dynamics approach for electronic structure calculation: application to the study of ground-state properties of rare gas atoms

    NASA Astrophysics Data System (ADS)

    Roy, Amlan K.; Chu, Shih-I.

    2002-05-01

    We explore the usefulness of a quantum fluid dynamics (QFD) approach for quantitative electronic structure calculations of many-electron systems. By combining QFD and density functional theory, a single time-dependent nonlinear QFD equation can be derived. The equation is further transformed into a diffusion-type form by an imaginary-time evolution method, whose asymptotic solution reaches a global minimum and the many-body ground-state wavefunction. The time-dependent generalized pseudospectral method is extended to solve the diffusion equation in spherical coordinates, allowing optimal and nonuniform spatial discretization and accurate and efficient solution of the diffusion function in space and time. The procedure is applied to the study of electronic energies, densities and other ground-state properties of noble gas atoms (He, Ne, Ar, Kr, Xe). The results are in good agreement with other best available values. The method offers a conceptually appealing and computationally practical procedure for the treatment of many-electron systems beyond the Hartree-Fock level.

  18. Beam Studies with Electron Columns

    SciTech Connect

    Shiltsev, V.; Valishev, A.; Kuznetsov, G.; Kamerdzhiev, V.; Romanov, A.; /Novosibirsk, IYF

    2009-04-01

    We report preliminary results of experimental studies of 'electron columns' in the Tevatron and in a specialized test setup. In the Tevatron, a beam of 150 GeV protons ionizes residual gas and ionization electrons are stored in an electrostatic trap immersed into strong longitudinal magnetic field. Shifts of proton betatron frequencies are observed. In the test setup, we observe effects pointing to accumulation and escape of ionization electrons.

  19. Energetic stability, oxidation states, and electronic structure of Bi-doped NaTaO3: a first-principles hybrid functional study.

    PubMed

    Joo, Paul H; Behtash, Maziar; Yang, Kesong

    2016-01-14

    We studied the defect formation energies, oxidation states of the dopants, and electronic structures of Bi-doped NaTaO3 using first-principles hybrid density functional theory calculations. Three possible structural models, including Bi-doped NaTaO3 with Bi at the Na site (Bi@Na), with Bi at the Ta site (Bi@Ta), and with Bi at both Na and Ta sites [Bi@(Na,Ta)], are constructed. Our results show that the preferred doping sites of Bi are strongly related to the preparation conditions of NaTaO3. It is energetically more favorable to form a Bi@Na structure under Na-poor conditions, to form a Bi@Ta structure under Na-rich conditions, and to form a Bi@(Na,Ta) structure under mildly Na-rich conditions. The Bi@Na doped model shows an n-type conducting character along with an expected blueshift of the optical absorption edge, in which the Bi atoms exist as Bi(3+) (6s(2)6p(0)). The Bi@Ta doped model has empty gap states consisting of Bi 6s states in its band gap, which can lead to visible-light absorption via the electron transition among the valence band, the conduction band, and the gap states. The Bi dopant is present as a Bi(5+) ion in this model, consistent with the experimental results. In contrast, the Bi@(Na,Ta) doped model has occupied gap states consisting of Bi 6s states in its band gap, and thus visible-light absorption is also expected in this system due to electron excitation from these occupied states to the conduction band, in which the Bi dopants exist as Bi(3+) ions. Our first-principles electronic structure calculations revealed the relationship between the Bi doping sites and the material preparation conditions, and clarified the oxidation states of Bi dopants in NaTaO3 as well as the origin of different visible-light photocatalytic hydrogen evolution behaviors in Bi@Ta and Bi@(Na,Ta) doped NaTaO3. This work can provide a useful reference for preparing a Bi-doped NaTaO3 photocatalyst with desired doping sites.

  20. Structural and electronic study of neutral, positive, and negative small rhodium clusters [Rh(n), Rh(n)(+), Rh(n)(-) ; n = 10-13].

    PubMed

    Mora, M A; Mora-Ramirez, M A

    2014-07-01

    We have carried out a systematic study for the determination of the structure and the fundamental state of neutral and ionic small rhodium clusters [Rhn, Rhn(+), Rhn(-); n = 10-13] using ab initio Hartree-Fock methods with a LANL2DZ basis set. A range of spin multiplicities is investigated for each cluster. We present the bond lengths, angles, and geometric configuration adopted by the clusters in its minimum energy conformation showing the differences when the clusters have different number of unpaired electrons. Also we report the vertical ionization potential and the adiabatic one calculated by the Koopmans' theorem.

  1. Structural and electronic study of neutral, positive, and negative small rhodium clusters [Rh(n), Rh(n)(+), Rh(n)(-) ; n = 10-13].

    PubMed

    Mora, M A; Mora-Ramirez, M A

    2014-07-01

    We have carried out a systematic study for the determination of the structure and the fundamental state of neutral and ionic small rhodium clusters [Rhn, Rhn(+), Rhn(-); n = 10-13] using ab initio Hartree-Fock methods with a LANL2DZ basis set. A range of spin multiplicities is investigated for each cluster. We present the bond lengths, angles, and geometric configuration adopted by the clusters in its minimum energy conformation showing the differences when the clusters have different number of unpaired electrons. Also we report the vertical ionization potential and the adiabatic one calculated by the Koopmans' theorem. PMID:24944092

  2. Defect Induced Electronic Structure of Uranofullerene

    PubMed Central

    Dai, Xing; Cheng, Cheng; Zhang, Wei; Xin, Minsi; Huai, Ping; Zhang, Ruiqin; Wang, Zhigang

    2013-01-01

    The interaction between the inner atoms/cluster and the outer fullerene cage is the source of various novel properties of endohedral metallofullerenes. Herein, we introduce an adatom-type spin polarization defect on the surface of a typical endohedral stable U2@C60 to predict the associated structure and electronic properties of U2@C61 based on the density functional theory method. We found that defect induces obvious changes in the electronic structure of this metallofullerene. More interestingly, the ground state of U2@C61 is nonet spin in contrast to the septet of U2@C60. Electronic structure analysis shows that the inner U atoms and the C ad-atom on the surface of the cage contribute together to this spin state, which is brought about by a ferromagnetic coupling between the spin of the unpaired electrons of the U atoms and the C ad-atom. This discovery may provide a possible approach to adapt the electronic structure properties of endohedral metallofullerenes. PMID:23439318

  3. Theoretical study on the structure, stability, and electronic properties of the guanine-Zn-cytosine base pair in M-DNA.

    PubMed

    Fuentes-Cabrera, Miguel; Sumpter, Bobby G; Sponer, Judit E; Sponer, Jirí; Petit, Leon; Wells, Jack C

    2007-02-01

    M-DNA is a type of metalated DNA that forms at high pH and in the presence of Zn, Ni, and Co, with the metals placed in between each base pair, as in G-Zn-C. Experiments have found that M-DNA could be a promising candidate for a variety of nanotechnological applications, as it is speculated that the metal d-states enhance the conductivity, but controversy still clouds these findings. In this paper, we carry out a comprehensive ab initio study of eight G-Zn-C models in the gas phase to help discern the structure and electronic properties of Zn-DNA. Specifically, we study whether a model prefers to be planar and has electronic properties that correlate with Zn-DNA having a metallic-like conductivity. Out of all the studied models, there is only one which preserves its planarity upon full geometry optimization. Nevertheless, starting from this model, one can deduce a parallel Zn-DNA architecture only. This duplex would contain the imino proton, in contrast to what has been proposed experimentally. Among the nonplanar models, there is one that requires less than 8 kcal/mol to flatten (both in gas and solvent conditions), and we propose that it is a plausible model for building an antiparallel duplex. In this duplex, the imino proton would be replaced by Zn, in accordance with experimental models. Neither planar nor nonplanar models have electronic properties that correlate with Zn-DNA having a metallic-like conductivity due to Zn d-states. To understand whether density functional theory (DFT) can describe appropriately the electronic properties of M-DNAs, we have investigated the electronic properties of G-Co-C base pairs. We have found that when self-interaction corrections (SIC) are not included the HOMO state contains Co d-levels, whereas these levels are moved below the HOMO state when SIC are considered. This result indicates that caution should be exercised when studying the electronic properties of M-DNAs with functionals that do not account for strong

  4. Electronic Structure of Ethynyl Substituted Cyclobutadienes

    NASA Astrophysics Data System (ADS)

    Emmert, Frank Lee Emmert, III; Thompson, Stephanie J.; Slipchenko, Lyudmila V.

    2011-06-01

    We investigated the effects of ethynyl substitution on the electronic structure of cyclobutadiene. These species are involved in Bergman Cyclization reactionsand are possible intermediates in the formation of fullerenes and graphite sheets. Prediction of the electronic energy of cyclobutadiene is challenging for single-reference ab initio methods such as HF, MP2 or DFT because of Jahn-Teller distortions and the diradical character of the singlet state. We determined the vertical and adiabatic singlet-triplet energy splittings, the natural charges and spin densities in substituted cyclobutadienes, using the equations of motion spin flip coupled cluster with single and double excitations (EOM-SF-CCSD) method that accurately describes diradical states. The adiabatic singlet-triplet gaps decrease upon substituent addition, but the singlet state is always lower in energy. However, we found that the results are affected by spin-contamination of the reference state and deteriorate when an unrestricted HF reference is employed. O. L. Chapman, C. L. McIntosh, J. Pacansky, "Cyclobutadiene" J. Am. Chem. Soc. 1973, 95, (2), 614-617. N. S. Goroff, "Mechanism of Fullerene Formation." Acc. Chem. Res. 1996, 29, (2), 77-83. L.V. Slipchenko and A.I. Krylov, "Singlet-triplet gaps in diradicals by the Spin-Flip approach: A benchmark study", J. Chem. Phys. 2002, 117, 4694-4708.

  5. Angle-resolved photoemission spectroscopy study of adsorption process and electronic structure of silver on ZnO(1010).

    PubMed

    Ozawa, K; Sato, T; Kato, M; Edamoto, K; Aiura, Y

    2005-08-01

    The adsorption process and valence band structure of Ag on ZnO(1010) have been investigated by angle-resolved photoelectron spectroscopy utilizing synchrotron radiation. The coverage-dependent measurements of the Ag 4d band structure reveal that the Ag bands with a dispersing feature are formed even at low coverages and that the basic structure of the bands is essentially the same throughout the submonolayer region. These results indicate that the Ag atoms aggregate to form islands with an atomically ordered structure from the low coverages. Upon annealing the Ag-covered surface at 900 K, the Ag 4d band undergoes only a minor change, suggesting that the ordered structure within the Ag islands is persistent against mild annealing. From the dispersive feature of the Ag 4d states, we propose that the atomic structure has locally rectangular symmetry with a good lattice matching with the ZnO(1010) surface.

  6. First-principles study on the structure, elastic properties, hardness and electronic structure of TMB{sub 4} (TM=Cr, Re, Ru and Os) compounds

    SciTech Connect

    Pan, Y.; Zheng, W.T.; Guan, W.M.; Zhang, K.H.; Fan, X.F.

    2013-11-15

    The structural formation, elastic properties, hardness and electronic structure of TMB{sub 4} (TM=Cr, Re, Ru and Os) compounds are investigated using first-principles approach. The value of C{sub 22} for these compounds is almost two times bigger than the C{sub 11} and C{sub 33}. The intrinsic hardness, shear modulus and Young's modulus are calculated to be in a sequence of CrB{sub 4}>ReB{sub 4}>RuB{sub 4}>OsB{sub 4}, and the Poisson's ratio and B/G ratio of TMB{sub 4} follow the order of CrB{sub 4}structure. Display Omitted - Highlights: • The intrinsic hardness of CrB{sub 4} and ReB{sub 4} is bigger than 40 GPa. • The hardness of TMB{sub 4} is calculated to be in a sequence of CrB{sub 4}>ReB{sub 4}>RuB{sub 4}>OsB{sub 4}. • The trend of hardness for TMB{sub 4} is consistent with the variation of elastic modulus. • The C{sub 22} value of TMB{sub 4} is bigger than that of C{sub 11} and C{sub 33}. • The high hardness of TMB{sub 4} is originated from the B–B bonds cage.

  7. Synthesis, structure, vibrational spectral, nonlinear optical and electron-behavioral studies of N-(5-chloro-2-hydroxyphenyl)-(3-hydroxyphenyl)-methalimine

    NASA Astrophysics Data System (ADS)

    Sun, Yuxi; Liu, Zengwei; Song, Ruojing; Yu, Cheng; Hao, Qingli; Xu, Laixiang

    2013-10-01

    In recent years, the imine-bridged organics has been one of the hot spots in the field of photo-responsive materials. Herein, N-(5-chloro-2-hydroxyphenyl)-(3-hydroxyphenyl)-methalimine (CHPHPMI) was synthesized by a condensation reaction of 3-hydroxybenzaldehyde and 2-amino-4-chlorophen with formic acid as catalyst in ethanol solvent, and characterized by the single crystal X-ray diffraction and FT-IR measurement techniques as well as theoretical calculations. The studied molecule adopts trans configuration about the central Cdbnd N bond, in which a five-numbered ring is formed by an intramolecular hydrogen bonding Osbnd H⋯N. The adjacent molecules are linked by three kinds of intermolecular hydrogen bonds to form a one-dimensional columnar supermolecular structure along b axis in the monoclinic crystal system with space group P21. The spectral bands were assigned to the molecular structure in details with the aid of the theoretical calculation. Furthermore, the physical parameters of thermodynamics, NLO, atomic charges, natural bond orbitals and frontier molecular orbitals were presented by the theoretical analysis for the studied molecule. The first-order hyperpolarizability of CHPHPMI is 30 times that of urea. The studied molecule presents the molecular battery characteristics connected by six directional batteries in a parallel-series mode to transport electrons in a long range. The HOMO and LUMO orbitals with an energy gap 3.632 eV are responsible for the nonlinear optical and electron-transfer properties. The electron-behavioral characteristics of the studied molecule indicate the studied compound will be an excellent molecular semiconductor candidate of photovoltaic materials.

  8. Study of hard disk and slider surfaces using X-ray photoemission electron microscopy and near-edge X-ray absorption fine structure spectroscopy

    SciTech Connect

    Anders, S.; Stammler, T.; Bhatia, C.S.; Fong, W.; Chen, C.Y.; Bogy, D.B.

    1998-04-01

    X-ray Photo Emission Electron Microscopy (X-PEEM) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy were applied to study the properties of amorphous hard carbon overcoats on disks and sliders, and the properties of the lubricant. The modification of lubricants after performing thermal desorption studies was measured by NEXAFS, and the results are compared to the thermal desorption data. The study of lubricant degradation in wear tracks is described. Sliders were investigated before and after wear test, and the modification of the slider coating as well as the transfer of lubricant to the slider was studied. The studies show that the lubricant is altered chemically during the wear. Fluorine is removed and carboxyl groups are formed.

  9. Structure, energetics, and electronic properties of the surface of a promoted MoS{sub 2} catalyst: An ab initio local density functional study

    SciTech Connect

    Raybaud, P.; Hafner, J.; Kresse, G.; Kasztelan, S.; Toulhoat, H.

    2000-02-15

    The determination of the local structure of cobalt- or nickel-promoted MoS{sub 2}-based hydrodesulfurization catalysts is of interest for understanding the mechanism leading to an increased activity brought by cobalt or nickel, the so-called synergetic effect. For that reason, the authors carried out ab initio calculations using density functional theory under the generalized gradient approximation for periodic systems. The edge substitution model emerges as the most stable structure and provides an excellent agreement with local structures experimentally determined on real catalysts by in situ extended X-ray absorption fine structure. The authors studied the absorption of sulfur on the active edge surface of the promoted MoS{sub 2} catalyst and determined the equilibrium coverage under sulfiding conditions. It is demonstrated that the incorporation of promoter atoms has a strong influence on the sulfur-metal bond energy at the surface and in particular leads to a reduction of the equilibrium S coverage of the active metal sites. A comparative study on the effects of Co, Ni, and Cu atoms as promoters was performed. Detailed results on the surface electronic structure of promoted MoS{sub 2} are presented.

  10. Stacking dependent electronic structures of transition metal dichalcogenides heterobilayer

    NASA Astrophysics Data System (ADS)

    Lee, Yea-Lee; Park, Cheol-Hwan; Ihm, Jisoon

    The systematic study of the electronic structures and optical properties of the transition metal dichalcogenides (TMD) heterobilayers can significantly improve the designing of new electronic and optoelectronic devices. Here, we theoretically study the electronic structures and optical properties of TMD heterobilayers using the first-principles methods. The band structures of TMD heterobilayer are shown to be determined by the band alignments of the each layer, the weak interlayer interactions, and angle dependent stacking patterns. The photoluminescence spectra are investigated using the calculated band structures, and the optical absorption spectra are examined by the GW approximations including the electron-hole interaction through the solution of the Bethe-Salpeter equation. It is expected that the weak interlayer interaction gives rise to the substantial interlayer optical transition which will be corresponding to the interlayer exciton.

  11. Electronic structure and optical properties of Sr{sub 2}SnO{sub 4} studied with FP-LAPW method in density functional theory

    SciTech Connect

    Prijamboedi, B. Umar, S.; Failamani, F.

    2015-04-16

    Oxide material of Sr{sub 2}SnO{sub 4}, when it is doped with Ti becomes a phosphor material that can emit intense blue light at room temperature. It is important to study the electronic structure of this material in order to determine the optical processes that occur in Ti-doped Sr{sub 2}SnO{sub 4}. Electronic structure and optical properties of Sr{sub 2}SnO{sub 4} is studied using density functional theory framework with full potential linearized augmented plane waves plus local orbitals (FP-LAPW+lo) method. We use modified Becke-Johnson (mBJ) exchange-correlation potential to calculate the energy gap. Our calculation showed that Sr{sub 2}SnO{sub 4} has indirect band gap with band gap energy of around 4.2 eV. The experimental absorption spectra of Sr{sub 2}SnO{sub 4} indicated that this oxide has band gap of around 4.6 eV and it is closer to the results given by mBJ exchange-correlation potential. We also studied other optical properties of Sr{sub 2}SnO{sub 4} and it is found in agreement with the experimental results.

  12. First-principles study of atomic and electronic structures of 60° perfect and 30°/90° partial glide dislocations in CdTe

    DOE PAGES

    Kweon, Kyoung E.; Aberg, Daniel; Lordi, Vincenzo

    2016-05-16

    The atomic and electronic structures of 60° glide perfect and 30°/90° glide partial dislocations in CdTe are studied using combined semi-empirical and density functional theory calculations. The calculations predict that the dislocation cores tend to undergo significant reconstructions along the dislocation lines from the singly-periodic (SP) structures, yielding either doubly-periodic (DP) ordering by forming a dimer or quadruply-periodic (QP) ordering by alternating a dimer and a missing dimer. Charge modulation along the dislocation line, accompanied by the QP reconstruction for the Cd-/Te-core 60° perfect and 30° partials or the DP reconstruction for the Cd-core 90° partial, results in semiconducting character,more » as opposed to the metallic character of the SP dislocation cores. Dislocation-induced defect states for the 60° Cd-/Te-core are located relatively close to the band edges, whereas the defect states lie in the middle of the band gap for the 30° Cd-/Te-core partial dislocations. In addition to the intracore charge modulation within each QP core, the possibility of intercore charge transfer between two different dislocation cores when they are paired together in the same system is discussed. As a result, the analysis of the electronic structures reveals the potential role of the dislocations on charge transport in CdTe, particularly in terms of charge trapping and recombination.« less

  13. First-principles study of atomic and electronic structures of 60∘ perfect and 30∘/90∘ partial glide dislocations in CdTe

    NASA Astrophysics Data System (ADS)

    Kweon, Kyoung E.; Åberg, Daniel; Lordi, Vincenzo

    2016-05-01

    The atomic and electronic structures of 60∘ glide perfect and 30∘/90∘ glide partial dislocations in CdTe are studied using combined semi-empirical and density functional theory calculations. The calculations predict that the dislocation cores tend to undergo significant reconstructions along the dislocation lines from the singly-periodic (SP) structures, yielding either doubly-periodic (DP) ordering by forming a dimer or quadruply-periodic (QP) ordering by alternating a dimer and a missing dimer. Charge modulation along the dislocation line, accompanied by the QP reconstruction for the Cd-/Te-core 60∘ perfect and 30∘ partials or the DP reconstruction for the Cd-core 90∘ partial, results in semiconducting character, as opposed to the metallic character of the SP dislocation cores. Dislocation-induced defect states for the 60∘ Cd-/Te-core are located relatively close to the band edges, whereas the defect states lie in the middle of the band gap for the 30∘ Cd-/Te-core partial dislocations. In addition to the intracore charge modulation within each QP core, the possibility of intercore charge transfer between two different dislocation cores when they are paired together in the same system is discussed. The analysis of the electronic structures reveals the potential role of the dislocations on charge transport in CdTe, particularly in terms of charge trapping and recombination.

  14. Ab initio study of the structures and electronic states of small neutral and ionic DABCO--Ar(n) clusters.

    PubMed

    Mathivon, Kevin; Linguerri, Roberto; Hochlaf, Majdi

    2014-03-01

    In the present theoretical work, we investigated the stationary points (minima and transition states) on the ground state potential energy surfaces of neutral and ionic 1,4-diazabicyclo[2.2.2]octane (DABCO)--Ar(n)⁰,⁺¹ (n = 1-4) clusters. As established in our systematic work on DABCO--Ar cluster (Mathivon et al., J Chem Phys 139:164306, 2013), the (R)MP2/aug-cc-pVDZ level is accurate enough for validating the prediction of stable forms. For n = 1 and 2, further computations at the MP2/aug-cc-pVTZ level confirm these assumptions. We show that some of the already known isomers of these heteroclusters derived using lower levels of theory are not realistic. More interestingly, our work reveals that DABCO is subject to slight deformations when binding to a small number of Ar atoms. Moreover, we computed the potential energy surfaces of the lowest singlet electronic states of DABCO--Ar(n)(n = 1-3) and of DABCO⁺--Ar(n)(n = 1-3), and the transition moments for the Sp(p = 1-3) ← S0 neutral transitions. These electronic states are found to be Rydberg in nature. The shape of their potentials is mainly repulsive with slight stabilization in the S2 potentials. Finally, the effects of microsolvation of DABCO in Ar clusters in ground and electronic excited states are discussed. The photophysical and photochemical dynamics of these electronic states may be complex. PMID:24549795

  15. Ab initio study of the structures and electronic states of small neutral and ionic DABCO--Ar(n) clusters.

    PubMed

    Mathivon, Kevin; Linguerri, Roberto; Hochlaf, Majdi

    2014-03-01

    In the present theoretical work, we investigated the stationary points (minima and transition states) on the ground state potential energy surfaces of neutral and ionic 1,4-diazabicyclo[2.2.2]octane (DABCO)--Ar(n)⁰,⁺¹ (n = 1-4) clusters. As established in our systematic work on DABCO--Ar cluster (Mathivon et al., J Chem Phys 139:164306, 2013), the (R)MP2/aug-cc-pVDZ level is accurate enough for validating the prediction of stable forms. For n = 1 and 2, further computations at the MP2/aug-cc-pVTZ level confirm these assumptions. We show that some of the already known isomers of these heteroclusters derived using lower levels of theory are not realistic. More interestingly, our work reveals that DABCO is subject to slight deformations when binding to a small number of Ar atoms. Moreover, we computed the potential energy surfaces of the lowest singlet electronic states of DABCO--Ar(n)(n = 1-3) and of DABCO⁺--Ar(n)(n = 1-3), and the transition moments for the Sp(p = 1-3) ← S0 neutral transitions. These electronic states are found to be Rydberg in nature. The shape of their potentials is mainly repulsive with slight stabilization in the S2 potentials. Finally, the effects of microsolvation of DABCO in Ar clusters in ground and electronic excited states are discussed. The photophysical and photochemical dynamics of these electronic states may be complex.

  16. The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures

    SciTech Connect

    Radaelli, P. G.; Dhesi, S. S.

    2015-01-26

    We review some of the significant contributions to the field of strongly correlated materials and complex magnets, arising from experiments performed at the Diamond Light Source (Harwell Science and Innovation Campus, Didcot, UK) during the first few years of operation (2007–2014). We provide a comprehensive overview of Diamond research on topological insulators, multiferroics, complex oxides and magnetic nanostructures. Several experiments on ultrafast dynamics, magnetic imaging, photoemission electron microscopy, soft X-ray holography and resonant magnetic hard and soft X-ray scattering are described.

  17. Crystallization of Photosystem II for Time-Resolved Structural Studies Using an X-ray Free Electron Laser

    PubMed Central

    Coe, Jesse; Kupitz, Christopher; Basu, Shibom; Conrad, Chelsie E.; Roy-Chowdhury, Shatabdi; Fromme, Raimund; Fromme, Petra

    2015-01-01

    Photosystem II (PSII) is a membrane protein supercomplex that executes the initial reaction of photosynthesis in higher plants, algae, and cyanobacteria. It captures the light from the sun to catalyze a transmembrane charge separation. In a series of four charge separation events, utilizing the energy from four photons, PSII oxidizes two water molecules to obtain dioxygen, four protons, and four electrons. The light reactions of photosystems I and II (PSI and PSII) result in the formation of an electrochemical transmembrane proton gradient that is used for the production of ATP. Electrons that are subsequently transferred from PSI via the soluble protein ferredoxin to ferredoxin-NADP+ reductase that reduces NADP+ to NADPH. The products of photosynthesis and the elemental oxygen evolved sustain all higher life on Earth. All oxygen in the atmosphere is produced by the oxygen-evolving complex in PSII, a process that changed our planet from an anoxygenic to an oxygenic atmosphere 2.5 billion years ago. In this chapter, we provide recent insight into the mechanisms of this process and methods used in probing this question. PMID:25950978

  18. Crystallization of Photosystem II for Time-Resolved Structural Studies Using an X-ray Free Electron Laser.

    PubMed

    Coe, Jesse; Kupitz, Christopher; Basu, Shibom; Conrad, Chelsie E; Roy-Chowdhury, Shatabdi; Fromme, Raimund; Fromme, Petra

    2015-01-01

    Photosystem II (PSII) is a membrane protein supercomplex that executes the initial reaction of photosynthesis in higher plants, algae, and cyanobacteria. It captures the light from the sun to catalyze a transmembrane charge separation. In a series of four charge separation events, utilizing the energy from four photons, PSII oxidizes two water molecules to obtain dioxygen, four protons, and four electrons. The light reactions of photosystems I and II (PSI and PSII) result in the formation of an electrochemical transmembrane proton gradient that is used for the production of ATP. Electrons that are subsequently transferred from PSI via the soluble protein ferredoxin to ferredoxin-NADP(+) reductase that reduces NADP(+) to NADPH. The products of photosynthesis and the elemental oxygen evolved sustain all higher life on Earth. All oxygen in the atmosphere is produced by the oxygen-evolving complex in PSII, a process that changed our planet from an anoxygenic to an oxygenic atmosphere 2.5 billion years ago. In this chapter, we provide recent insight into the mechanisms of this process and methods used in probing this question.

  19. Electronic structure engineering of various structural phases of phosphorene.

    PubMed

    Kaur, Sumandeep; Kumar, Ashok; Srivastava, Sunita; Tankeshwar, K

    2016-07-21

    We report the tailoring of the electronic structures of various structural phases of phosphorene (α-P, β-P, γ-P and δ-P) based homo- and hetero-bilayers through in-plane mechanical strains, vertical pressure and transverse electric field by employing density functional theory. In-plane biaxial strains have considerably modified the electronic bandgap of both homo- and hetero-bilayers while vertical pressure induces metallization in the considered structures. The γ-P homo-bilayer structure showed the highest ultimate tensile strength (UTS ∼ 6.21 GPa) upon in-plane stretching. Upon application of a transverse electric field, the variation in the bandgap of hetero-bilayers was found to be strongly dependent on the polarity of the applied field which is attributed to the counterbalance between the external electric field and the internal field induced by different structural phases and heterogeneity in the arrangements of atoms of each surface of the hetero-bilayer system. Our results demonstrate that the electronic structures of the considered hetero- and homo-bilayers of phosphorene could be modified by biaxial strain, pressure and electric field to achieve the desired properties for future nano-electronic devices.

  20. Electronic structure of a graphene superlattice with massive Dirac fermions

    SciTech Connect

    Lima, Jonas R. F.

    2015-02-28

    We study the electronic and transport properties of a graphene-based superlattice theoretically by using an effective Dirac equation. The superlattice consists of a periodic potential applied on a single-layer graphene deposited on a substrate that opens an energy gap of 2Δ in its electronic structure. We find that extra Dirac points appear in the electronic band structure under certain conditions, so it is possible to close the gap between the conduction and valence minibands. We show that the energy gap E{sub g} can be tuned in the range 0 ≤ E{sub g} ≤ 2Δ by changing the periodic potential. We analyze the low energy electronic structure around the contact points and find that the effective Fermi velocity in very anisotropic and depends on the energy gap. We show that the extra Dirac points obtained here behave differently compared to previously studied systems.

  1. Electronic structure of EuFe2As2.

    PubMed

    Adhikary, Ganesh; Sahadev, Nishaina; Biswas, Deepnarayan; Bindu, R; Kumar, Neeraj; Thamizhavel, A; Dhar, S K; Maiti, Kalobaran

    2013-06-01

    Employing high resolution photoemission spectroscopy, we studied the temperature evolution of the electronic structure of EuFe2As2, a unique pnictide, where antiferromagnetism of the Eu layer survives within the superconducting phase due to 'FeAs' layers, achieved via substitution and/or pressure. High energy and angle resolution helped to reveal the signature of peak-dip features, having significant p orbital character and spin density wave transition induced band folding in the electronic structure. A significant spectral weight redistribution is observed below 20 K manifesting the influence of antiferromagnetic order on the conduction electrons.

  2. Electronic structure and topological features of tin-based binary nanosheets and their hydrogenated/fluorinated derivatives: A first-principles study

    NASA Astrophysics Data System (ADS)

    Wang, Yanli; Ding, Yi

    2016-09-01

    Utilizing first-principles calculations, we have investigated the structural, electronic and topological properties of binary SnSi and SnGe nanosheets as well as their H-/F-derivatives. It is found that all these systems have chair-like buckled configurations with robust structural stabilities. Unlike the elemental group-IV sheets, SnSi and SnGe sheets are narrow-band-gap semiconductors, which have a gapped Dirac cone with massive Fermions. Under the strains, a direct-to-indirect band gap transition and a semiconductor-to-metal transition would occur in these systems. Although these binary systems are trivial band insulators with ℤ2 = 0, their topological features can be altered by the surface decorations. Particularly, the fluorinated SiGe sheet becomes a topological insulator with ℤ2 = 1, and such non-trivial state can also be found in the strained fluorinated SnSi and hydrogenated SnGe sheets. Large non-trivial SOC band gaps of 0.09-0.17 eV are obtained in these 2D topological insulating systems, which will be beneficial for realizing the room-temperature quantum spin Hall effect. Our study demonstrates that binary Sn-based nanomaterials possess tunable electronic and topological properties, which have potential applications in low-power nano-electrics and devices.

  3. First principles study of hydrogen storage material NaBH4 and LiAlH4 compounds: electronic structure and optical properties

    NASA Astrophysics Data System (ADS)

    Ghellab, T.; Charifi, Z.; Baaziz, H.; Uğur, Ş.; Uğur, G.; Soyalp, F.

    2016-04-01

    A comprehensive study of structure, phase stability, optical and electronic properties of LiAlH4 and NaBH4 light-metal hydrides is presented. The calculations are carried out within density functional theory using the full potential linear augmented plane wave method. The exchange-correlation potential is treated within the local density approximation and the generalized gradient approximation (GGA) to calculate the total energy. Furthermore, the Engel-Vosko GGA approach is employed to compute electronic and optical properties such as reflectivity spectra. The phases α, β and γ of LiAlH4 and NaBH4 hydrides are investigated, the phase transition from the β to the high-pressure γ phase is determined for NaBH4 and is accompanied by a 1% volume decrease. For LiAlH4, no phase transition is detected. The materials under consideration are classified as wide band gap compounds. From the analysis of the structures at different phases, it is deduced that the hydrides show strong covalent interaction between B (Al) and H in the [BH4]- ([AlH4]-) anions and ionic bonding character between [BH4]- and Na+ for NaBH4, and [AlH4]- and Li+ for LiAlH4. The complex dielectric function, absorption coefficient and the reflectivity spectra are also computed and analyzed in different phases.

  4. First-principle study on electronic structure and optical properties of GaN nanowires with different cross-sections

    NASA Astrophysics Data System (ADS)

    Kong, Yike; Liu, Lei; Xia, Sihao; Wang, Honggang; Wang, Meishan

    2016-08-01

    This paper explores the properties of intrinsic gallium nitride (GaN) nanowires (NWs) in terms of formation energy, band structure, density of state (DOS) and optical properties with plane-wave ultrasoft pseudopotential method based on first-principles. Results show that after relaxation, N atoms of the outer layers move outwards, while Ga atoms move inwards, and the relaxation of surface atomic structure appears less obvious with the increasing cross-sectional area. Comparing different cross-sections of GaN NWs, it is found that the formation energy decreases and the stability goes stronger with the increasing size. With the increasing cross-section, the bandgap is decreased. Moreover, through comparative investigation in optical properties between GaN NWs and bulk GaN, a valuable phenomenom is found that the static dielectric constants of GaN NWs are notably lower, which contributes remarkably to the excellent absorbing performance of GaN NWs.

  5. Electronic structure of bacterial surface protein layers

    SciTech Connect

    Maslyuk, Volodymyr V.; Mertig, Ingrid; Bredow, Thomas; Mertig, Michael; Vyalikh, Denis V.; Molodtsov, Serguei L.

    2008-01-15

    We report an approach for the calculation of the electronic density of states of the dried two-dimensional crystalline surface protein layer (S layer) of the bacterium Bacillus sphaericus NCTC 9602. The proposed model is based on the consideration of individual amino acids in the corresponding conformation of the peptide chain which additively contribute to the electronic structure of the entire protein complex. The derived results agree well with the experimental data obtained by means of photoemission (PE), resonant PE, and near-edge x-ray absorption spectroscopy.

  6. Study of the extra-ionic electron distributions in semi-metallic structures by nuclear quadrupole resonance techniques

    NASA Technical Reports Server (NTRS)

    Murty, A. N.

    1976-01-01

    A straightforward self-consistent method was developed to estimate solid state electrostatic potentials, fields and field gradients in ionic solids. The method is a direct practical application of basic electrostatics to solid state and also helps in the understanding of the principles of crystal structure. The necessary mathematical equations, derived from first principles, were presented and the systematic computational procedure developed to arrive at the solid state electrostatic field gradients values was given.

  7. The evolution of the structural, vibrational and electronic properties of the cyclic ethers - on ring size. An ab initio study

    NASA Astrophysics Data System (ADS)

    Ford, Thomas A.

    2014-09-01

    The molecular structures, vibrational spectra and atomic charges of the alicyclic ethers containing from two to five carbon atoms have been determined by means of ab initio calculations, at the level of second order Møller-Plesset perturbation theory and using Dunning's augmented correlation-consistent polarized valence triple-zeta basis set. Two isomers of the oxetane, tetrahydrofuran and tetrahydropyran molecules have been identified and their relative energies determined. Structural properties, such as the COC bond angles and the CH bond lengths, are found to increase steadily with increasing ring size and with decreasing ionization energy. The mean CH2 stretching and bending wavenumbers exhibit the reverse behaviour, while the mean wavenumbers of the CH2 wagging and twisting modes follow the same trend as the structural features. The ring mode wavenumbers vary in a less regular way. The charges of the oxygen, α-carbon and axial and equatorial α- and β-hydrogen atoms also do not show systematic dependences on ring size or ionization energy. The trends in the values of these properties have been rationalized.

  8. Study of structural order in porphyrin-fullerene dyad ZnDHD6ee monolayers by electron diffraction and atomic force microscopy

    SciTech Connect

    D'yakova, Yu. A.; Suvorova, E. I.; Orekhov, Andrei S.; Orekhov, Anton S.; Alekseev, A. S.; Gainutdinov, R. V.; Klechkovskaya, V. V. Tereschenko, E. Yu.; Tkachenko, N. V.; Lemmetyinen, H.; Feigin, L. A.; Kovalchuk, M. V.

    2013-11-15

    The structure of porphyrin-fullerene dyad ZnDHD6ee monolayers formed on the surface of aqueous subphase in a Langmuir trough and transferred onto solid substrates has been studied. The data obtained are interpreted using simulation of the structure of isolated molecules and their packing in monolayer and modeling of diffraction patterns from molecular aggregates having different sizes and degrees of order. Experiments on the formation of condensed ZnDHD6ee monolayers are described. The structure of these monolayers on a water surface is analyzed using {pi}-A isotherms. The structure of the monolayers transferred onto solid substrates is investigated by electron diffraction and atomic force microscopy. The unit-cell parameters of two-dimensional domains, which are characteristic of molecular packing in monolayers and deposited films, are determined. Domains are found to be organized into a texture (the molecular axes are oriented by the [001] direction perpendicular to the substrate). The monolayers contain a limited number of small 3D domains.

  9. Studies of the electronic structure and biological activity of chosen 1,4-benzodiazepines by 35Cl NQR spectroscopy and DFT calculations

    NASA Astrophysics Data System (ADS)

    Bronisz, K.; Ostafin, M.; Poleshchuk, O. Kh.; Mielcarek, J.; Nogaj, B.

    2006-11-01

    Selected derivatives of 1,4-benzodiazepine: lorazepam, lormetazepam, oxazepam and temazepam, used as active substances in anxiolytic drugs, have been studied by 35Cl NQR method in order to find the correlation between electronic structure and biological activity. The 35Cl NQR resonance frequencies ( νQ) measured at 77 K have been correlated with the following parameters characterising their biological activity: biological half-life period ( t0.5), affinity to benzodiazepine receptor (IC 50) and mean dose equivalent. The results of experimental study of some benzodiazepine derivatives by nuclear quadrupole resonance of 35Cl nuclei are compared with theoretical results based on DFT calculations which were carried out by means of Gaussian'98 W software.

  10. Ab initio studies of structural, electronic, optical, elastic and thermal properties of silver gallium dichalcogenides (AgGaX{sub 2}: X = S, Se, Te)

    SciTech Connect

    Sharma, Sheetal; Verma, A.S.; Jindal, V.K.

    2014-05-01

    Graphical abstract: - Highlights: • FP-LAPW method has been used to compute the solid state properties of AgGaX{sub 2} (X = S, Se, Te). • Electronic and optical properties reported with recently developed mBJ potential. • Thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter were evaluated. • Hardness was calculated for the first time at different temperature and pressure. - Abstract: We have performed ab initio calculations for the structural, electronic, optical, elastic and thermal properties of the silver gallium dichalcogenides (AgGaX{sub 2}: X = S, Se, Te). In this study, we have used the accurate full potential linearized augmented plane wave (FP-LAPW) method to find the equilibrium structural parameters and to compute the six elastic constants (C{sub 11}, C{sub 12}, C{sub 13}, C{sub 33}, C{sub 44} and C{sub 66}). We have reported electronic and optical properties with the recently developed density functional theory of Tran and Blaha, and this theory is used along with the Wu-Cohen generalized gradient approximation (WC-GGA) for the exchange-correlation potential. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients and optical conductivities were calculated for photon energies up to 40 eV. The thermodynamical properties such as thermal expansion, heat capacity, debye temperature, entropy, Grüneisen parameter and bulk modulus were calculated employing the quasi-harmonic Debye model at different temperatures (0–900 K) and pressures (0–8 GPa) and the silent results were interpreted. Hardness of the materials was calculated for the first time at different temperatures and pressures.

  11. An electron microscopy study of dislocation structures in Mg single crystals compressed along [0 0 0 1] at room temperature

    DOE PAGES

    Kumar, K. S.; Chisholm, Matthew F.; Geng, J.; Mishra, R. K.

    2016-01-09

    We compressed Mg single crystals along [0 0 0 1] at room temperature to various stress levels (40, 80, 120, 160 and 320 MPa) and the evolution of dislocation structure with stress increment was investigated by TEM slip is confirmed to be the dominant deformation mode; the predominance of edge dislocation debris lying along the <1 0more » $$\\bar{1}$$ 0> implies that screw dislocations are more mobile than their edge counterpart. The edge dislocation may dissociate into and dislocations, and the latter can extend further on the basal plane and bound a basal-stacking fault.« less

  12. Structure of expanded porphyrins: electron-nuclear multiple resonance and molecular orbital studies of texaphyrin anion radicals in solution

    NASA Astrophysics Data System (ADS)

    Endeward, B.; Regev, A.; Plato, M.; Levanon, H.; Sessler, J. L.; Möbius, K.

    1994-08-01

    Liquid solution ENDOR and TRIPLE resonance experiments have been performed on texaphyrin radical anions generated by sodium reduction in tetrahydrofuran. Six proton and two nitrogen hyperfine couplings could be determined, including their signs. The results were compared with theoretical isotropic hyperfine couplings. They were calculated for energy-minimized texaphyrin structures, including the sodium metallo-derivative, by state-of-the-art SCF-MO methods (RHF-INDO/SP). This comparison suggests that in the course of the alkali metal reduction of texaphyrin the acidic hydrogen in the macrocycle is replaced by sodium.

  13. Structural, electronic, elastic and magnetic properties of RuFe{sub 3}N and OsFe{sub 3}N: A first principle study

    SciTech Connect

    Puvaneswari, S.; Priyanga, G. Sudha; Rajeswarapalanichamy, R. Santhosh, M.

    2015-06-24

    The structural, electronic, elastic and magnetic properties of the perovskite structure of RuFe{sub 3}N, and OsFe{sub 3}N have been reported using the VASP within the gradient generalized approximation. Total energy calculations are performed using both spin and non-spin polarized calculations and it is found that, at ambient pressure both RuFe{sub 3}N and OsFe{sub 3}N are stable in ferromagnetic phase. The electronic structure reveals that both RuFe{sub 3}N and OsFe{sub 3}N are metallic in nature at ambient pressure.

  14. Electronic structure and vibrational spectra of cis-diammine(orotato)platinum(II), a potential cisplatin analogue: DFT and experimental study

    NASA Astrophysics Data System (ADS)

    Wysokiński, Rafał; Hernik, Katarzyna; Szostak, Roman; Michalska, Danuta

    2007-03-01

    Orotic acid (vitamin B 13) is a key intermediate in biosynthesis of the pyrimidine nucleotides in living organisms, moreover, it may serve as the biological carrier for some metal ions. cis-Diammine(orotato)platinum(II), cis-[Pt(C 5H 2N 2O 4)(NH 3) 2] can be considered as a new potential cisplatin analogue. The FT-Raman and FT-IR spectra of the title complex are reported, for the first time. The molecular structure, vibrational frequencies, and the theoretical infrared and Raman intensities have been calculated by the density functional mPW1PW91 method. The detailed vibrational assignment has been made on the basis of the calculated potential energy distribution. The theoretically predicted IR and Raman spectra show very good agreement with experiment. Natural bond orbital (NBO) analyses were performed for cisplatin, carboplatin and the title complex. The results provided new data on the nature of platinum-ligand bonding in these compounds. Strong intramolecular hydrogen bond between the orotate ligand and the coordinated ammonia group stabilizes the structure of the platinum(II) complex. Thus, it is suggested that the orotate ligand in the title complex is more inert to the substitution reactions than the chloride ligands in cisplatin.

  15. Electronic band structure of surface-doped black phosphorus

    NASA Astrophysics Data System (ADS)

    Kim, Jimin; Ryu, Sae Hee; Sohn, Yeongsup; Kim, Keun Su

    2015-03-01

    There are rapidly growing interests in the study of few-layer black phosphorus owing to its promising device characteristics that may impact our future electronics technology. The low-energy band structure of black phosphorus has been widely predicted to be controllable by external perturbations, such as strain and doping. In this work, we attempt to control the electronic band structure of black phosphorous by in-situ surface deposition of alkali-metal atoms. We found that surface doping induces steep band bending towards the bulk, leading to the emergence of new 2D electronic states that are confined within only few phosphorene layers of black phosphorus. Using angle-resolved photoemission spectroscopy, we directly measured the electronic band structure and its evolution as a function of dopant density. Supported by IBS.

  16. Electronic structure of Sr{sub 2}RuO{sub 4}: X-ray fluorescence emission study

    SciTech Connect

    Kurmaev, E.Z.; Stadler, S.; Ederer, D.L.; Harada, Y.; Shin, S.; Grush, M.M.; Callcott, T.A.; Perera, R.C.; Zatsepin, D.A.; Ovechkina, N.; Kasai, M.; Tokura, Y. |; Takahashi, T.; Chandrasekaran, K.; Vijayaraghavan, R.; Varadaraju, U.V.

    1998-01-01

    The results of measurements of O 1s total x-ray-fluorescence yield and Ru N{sub 2,3} and O K{sub {alpha}} x-ray fluorescence emission spectra of Sr{sub 2}RuO{sub 4} and Sr{sub 2}RuO{sub 4.25} are presented. An excitation energy dependence of the O K{sub {alpha}} x-ray emission spectra (XES) was observed in both compounds. The energy dependence of the spectra is attributed to the excitation of inequivalent O (1) in-plane and O(2) apical oxygens. The O(1) 2p and O(2) 2p density of states distribution in the valence band of Sr{sub 2}RuO{sub 4} was found to be different in accordance with the results of band-structure calculations. O(1) 2p states are found to be mixed with Ru 4d(t{sub 2g}) states providing the formation of {pi} bonds. While the O K{sub a} XES spectra are in fair agreement with band structure calculations, the theoretical two-peak distribution of Ru N{sub 2,3} XES is found to be different with respect to the intensity ratios and widths of the peaks of Ru N{sub 2,3} XES. These differences are attributed to a decrease of intensity of radiative 4d{r_arrow}4p transitions in the vicinity of the Fermi level (where the localization of Ru 4d states is higher than at the bottom of the valence band) due to a strong Koster-Kronig transition. {copyright} {ital 1998} {ital The American Physical Society}

  17. Electronic Structure of Iridium Clusters on Graphene

    NASA Astrophysics Data System (ADS)

    Barker, Bradford A.; Bradley, Aaron J.; Ugeda, Miguel M.; Coh, Sinisa; Zettl, Alex; Crommie, Michael F.; Cohen, Marvin L.; Louie, Steven G.

    2015-03-01

    Graphene was predicted to exhibit non-trivial Z2 topology, but its exceedingly weak spin-orbit coupling prevented this from being observed. Previous theoretical work has proposed enhancing the spin-orbit coupling strength by depositing individual adatoms adsorbed onto the surface of graphene. We show experimental evidence that the iridium adatoms cluster, with a cluster size of at least two atoms. We investigate through theoretical calculations the orientation of the iridium dimers on graphene, contrast the electronic structure of iridium dimers with iridium monomers, and compare the theoretical iridium dimer electronic structure calculations with the experimental results determined via scanning tunneling spectroscopy. This work was supported by NSF Grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility.

  18. AB INITIO STUDY OF STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF MgxCd1-xX (X = S, Se, Te) ALLOYS

    NASA Astrophysics Data System (ADS)

    Noor, N. A.; Shaukat, A.

    2012-12-01

    This study describes structural, electronic and optical properties of MgxCd1-xX (X = S, Se, Te) alloys in the complete range 0≤x ≤1 of composition x in the zinc-blende (ZB) phase with the help of full-potential linearized augmented plane wave plus local orbitals (FP-LAPW+lo) method within density functional theory (DFT). In order to calculate total energy, generalized gradient approximation (Wu-Cohen GGA) has been applied, which is based on optimization energy. For electronic structure calculations, the corresponding potential is being optimized by Engel-Vosko GGA formalism. Our calculations reveal the nonlinear variation of lattice constant and bulk modulus with different concentration for the end binary and their ternary alloys, which slightly deviates from Vegard's law. The calculated band structures show a direct band gap for all three alloys with increasing order in the complete range of the compositional parameter x. In addition, we have discussed the disorder parameter (gap bowing) and concluded that the total band gap bowing is substantially influenced by the chemical (electronegativity) contribution. The calculated density of states (DOS) of these alloys is discussed in terms of contribution from various s-, p- and d-states of the constituent atoms and charge density distributions plots are analyzed. Optical properties have been presented in the form of the complex dielectric function ɛ(ω), refractive index n(ω) and extinction coefficient k(ω) as function of the incident photon energy, and the results have been compared with existing experimental data and other theoretical calculations.

  19. Structure and Electronic Properties of Polycrystalline Dielectrics

    SciTech Connect

    Mckenna, Keith P.; Shluger, AL

    2013-07-07

    We present an overview of the theoretical approaches that can be employed to model polycrystalline oxides along with a discussion of their limitations and associated challenges. We then present results for two metal oxide materials, MgO and HfO2, where theory and experiment have come together to provide insight into the structure and electronic properties of grain boundaries. Finally, we conclude with a discussion and outlook.

  20. Structural and electronic properties of thallium compounds

    NASA Astrophysics Data System (ADS)

    Paliwal, Neetu; Srivastava, Vipul

    2016-05-01

    The tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA has been used to calculate structural and electronic properties of thallium pnictides TlX (X=Sb, Bi) at high pressure. As a function of volume, the total energy is evaluated. Apart from this, the lattice parameter (a0), bulk modulus (B0), band structure (BS) and density of states (DOS) are calculated. From energy band diagram we observed metallic behaviour in TlSb and TlBi compounds. The values of equilibrium lattice constants and bulk modulus are agreed well with the available data.