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Sample records for electronic structure study

  1. 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.

  2. Electronic Structure Studies of Silicon Carbide Cationic Nanoclusters

    NASA Astrophysics Data System (ADS)

    Pradhan, Prachi

    2005-03-01

    As a continuation of our studies on the high stabilities and associated electronic structure properties of Si8C2 to Si14C2 and Si20Cn (n=3-6) clusters,^1 we report here detailed ab initio electronic and geometric structure studies of small SimCn^+ (1< m, n < 4) cationic clusters. The theoretical formalism used is the local density approximation (LDA) to density functional theory (DFT) and the Gaussian03 suite of programs^2 with an all electron 6-311++G** basis set has been used. Complete geometry optimizations of different possible structures have been carried out. The stability of the clusters varies with the ratio of the number of silicon to carbon atoms in the cluster. In contrast to the neutral clusters,^3 cationic clusters appear to prefer more open structures. Results will be presented for binding energies, relative energies, fragmentation energies, vibrational frequencies, and adiabatic ionization potentials^3 for the optimized clusters. Detailed comparisons with published data in the literature will also be presented. * Work supported, in part, by the Welch Foundation, Houston, Texas (Grant No. Y-1525) ^1M. N. Huda and A. K. Ray, Phys. Rev. A (R) 69, 011201 (2004); Eur. Phys. J. D 31, 63 (2004). ^2 Gaussian03, Revision A.1, M. J. Frisch et al., Gaussian Inc., Pittsburgh, PA , 2003. ^3 P. Pradhan and A. K. Ray, J. Mol. Structure (Theochem), in press.

  3. Electronic Structure Studies of Silicon Carbide Anionic Nanoclusters

    NASA Astrophysics Data System (ADS)

    Pradhan, Prachi

    2005-03-01

    As a continuation of our studies on the high stabilities and electronic structure properties of Si8C2 to Si14C2 clusters and Si60Cn (n=3-6) clusters,^1 we report here ab initio studies of small SimCn^- (1< m, n < 4) anionic clusters. The theoretical formalism used is the local density approximation (LDA) to density functional theory (DFT) and the Gaussian03 suite of programs^2 with an all electron 6-311++G** basis set has been used. Complete geometry optimizations of different possible structures have been carried out. Carbon-rich and silicon rich species show distinctly different patterns with respect to the vertical detachment energies. For carbon-rich aggregates, the VDE's show an even odd alternation, similar to that of the carbon anions. We present results on binding energies, relative energies, fragmentation energies, vertical detachment energies, vibrational frequencies, and adiabatic electron affinities^3 for the optimized clusters. Detailed comparisons with published data in the literature will also be presented. * Work supported, in part, by the Welch Foundation, Houston, Texas (Grant No. Y-1525). ^1M. N. Huda and A. K. Ray, Phys. Rev. A (R) 69, 011201 (2004); Eur. Phys. J. D 31, 63 (2004). ^2 Gaussian03, Revision A.1, M. J. Frisch et al., Gaussian Inc., Pittsburgh, PA , 2003. ^3 P. Pradhan and A. K. Ray, J. Mol. Structure (Theochem), in press.

  4. Electronic Structure Studies of Amorphous Hydrogenated Boron Carbide

    NASA Astrophysics Data System (ADS)

    Sky Driver, M.; Sandstrom, Joseph; Boyko, Teak; Moewes, Alexander; Caruso, Anthony

    2010-03-01

    Boron carbide is a technologically relevant material with importance in voltaic transduction. However, the local physical, chemical and electronic structure of low temperature deposited thin films of amorphous boron carbide is far from understood, hindering its progress in application. X-ray absorption and emission spectroscopies (XAS/XES) were applied to thin films of B4C and B5C:Hx to study the near Fermi edge structure; the films were prepared by RF magnetron sputtering and plasma enhanced chemical vapor deposition (PECVD) and were thermally treated after deposition from 400 to 800 C. XES spectra indicate a physical structure transition from amorphous to nanocrystalline at 700 C, a much lower temperature than expected from traditional physical vapor deposition or flash annealing temperatures reported. These structural differences are of significant interest to transport measurements and will be discussed as a correlation. Further, x-ray and ultraviolet photoemission were also collected as a compliment to XES/XAS and will be discussed in the context of understanding the local intra vs. intermolecular electronic structure of these boron-rich molecular based solids.

  5. Electronic structure of Fe-based amorphous alloys studied using electron-energy-loss spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, H. J.; Gu, X. J.; Poon, S. J.; Shiflet, G. J.

    2008-01-01

    The local atomic electronic structures of Fe-Mo-C-B metallic glasses are investigated using electron energy-loss spectroscopy (EELS). The fracture behavior of this Fe-based amorphous alloy system undergoes the transition from being ductile to exhibiting brittleness when alloyed with Cr or Er atoms. In addition, the glass-forming ability is also enhanced. This plastic-to-brittle transition is suggested to correlate with the change of local atomic short-range order or bonding configurations. Therefore, the bonding configuration of Fe-Mo-C-B-Er(Cr) amorphous alloys is investigated by studying the electronic structure of Fe and C atoms using electron energy-loss spectroscopy. It is shown that the normalized EELS white line intensities of Fe-L2,3 edges decrease slightly with an increasing amount of Er additions, while no noticeable difference is obtained with Cr additions. As for the C K edge, a prominent change of edge shape is observed for both alloy systems, where the first peak corresponding to a 1s→1π* transition increases with increasing Er and Cr additions. Accordingly, it is concluded that changes in the local atomic and electronic structure occur around Fe and C atoms when Er and Cr are introduced into the alloys. Furthermore, it is pointed out that the formation of Er-C and Cr-C carbide like local order inferred from the observed C K edge spectra can provide a plausible explanation for the plastic-to-brittle transition observed in these Fe-based amorphous alloys. In spite of the complexity of electronic and atomic structure in this multicomponent Fe-based metallic glass system, this study could serve as a starting point for providing a qualitative interpretation between electronic structure and plasticity in the Fe-Mo-C-B amorphous alloy system. Complimentary techniques, such as x-ray diffraction and high-resolution transmission electron microscope are also employed, providing a more complete structural characterization.

  6. 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

  7. Electronically induced structure transformations in graphite & silver, studied using ultrafast electron crystallography

    NASA Astrophysics Data System (ADS)

    Raman, Ramani K.

    photoexcited graphite surface. It is shown that such photoemission plays a minor role in the refraction shifts observed in the UEC study and a sub-surface dipole field is sufficient to explain the structural and charge relaxations observed. Investigations utilizing scanning electron microscope imaging of structures generated from laser ablation of graphite reveals the creation of geometrically faceted crystalline features, whose Raman spectrum exhibit sp3 like characteristics, though unambiguous identification of diamond structures generated requires further study. In the case of silver nanocrystals (Ag NC), photoexcitation near the surface plasmon resonance (SPR) is observed to lead to fragmentation at fluences below their melting threshold. By isolating each NC from other neighboring NCs in a surface supported geometry, the normally irreversible process becomes reversible and amenable to multi-shot pump-probe diffraction investigations just below the fragmentation threshold. Transient structural, thermal and Coulombic signatures of the pre-fragmented state are extracted from the UEC investigation and combined with a progressive Reverse Monte-Carlo structure refinement scheme to visualize the atomic dynamics leading up to the fragmentation. Such multi-faceted analysis reveals the fragmentation to proceed through the creation and growth of undercoordinated defect sites along which the lattice is weakened. These defects are likely seeded by the strong coupling between SPR dephasing pathways and inter-band transitions that can lead to bond-softening effects and local valence instabilities. The creation of sufficient number of such defect sites at elevated fluences are believed to lead to the eventual fragmentation of the entire NC. This thesis also details the design and principle of UEC systems employed in a surface probing geometry for the study of nanostructures and interfaces.

  8. Studying nucleon structure using an Electron-Ion Collider

    NASA Astrophysics Data System (ADS)

    Burton, Thomas; EIC Team

    2011-04-01

    The detailed composition of the spin of the nucleon remains unknown. Numerous experiments over the past two decades have shown that the spin of quarks alone cannot account for more than a third of the nucleon's spin. Proton-proton collisions at RHIC suggest a small gluon polarisation, but uncertainties remain large. An Electron-Ion Collider is proposed as future machine for precision studies of nucleon and nuclear structure. It will allow the study of the spin contribution from gluons and quarks, including their flavour decomposition, in heretofore unprecedented precision, and will access a much wider kinematic space than ever before, in particular extending to the currently unmeasured low Bjorken-x sea. The formalism of generalised parton distributions (GPDs), accessible for example via deeply-virtual Compton scattering, promises to allow study of the role of orbital angular momentum in nucleon spin. Furthermore, GPDs will extend understanding of parton distributions beyond the well-known one-dimensional PDFs, accessing three-dimensional structure via the impact parameter distributions of partons.

  9. Theoretical spectroscopic studies on chemical and electronic structures of arginylglycine.

    PubMed

    Li, Hongbao; Li, Leilei; Jiang, Jun; Lin, Zijing; Luo, Yi

    2015-10-14

    The energy differences between canonical and zwitterionic isomers of arginylglycine (ArgGly) at the CCSD/aug-cc-pVDZ level are too small (less than 1 kcal mol(-1)) to determine the dominant form in the gas phase from the energetic point of view. First-principles simulations have been performed for near-edge X-ray absorption fine-structure (NEXAFS) spectra and X-ray photoelectron spectra (XPS) at C, N and O K-edges, as well as for infrared (IR) spectra of neutral ArgGly. Noticeable spectral differences were found which enable the unambiguous identification of different neutral groups. We thus demonstrate X-ray spectroscopy as a powerful technique to study the conformation dependent chemical and electronic properties of neutral ArgGly. PMID:26266331

  10. Structural studies of photoinduced intramolecular electron transfer in cyclopentadienylnickelnitrosyl

    SciTech Connect

    Chen, L.X.; Bowman, M.K.; Wang, Zhiyu; Norris, J.R. |; Montano, P.A. |

    1994-03-01

    A structural study based on EXAFS, FTIR, and optical absorption spectroscopies has been conducted on a photogenerated, metastable state of cyclopentadienylnickelnitrosyl (CpNiNO) produced by a reversible photochemical reaction. The photogenerated, metastable state with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was created by irradiating the sample with the 365 nm line of a mercury lamp at 20K . At the same temperature, the reverse reaction was induced by irradiation with the 313 nm line from the mercury lamp. Based on the analysis of the EXAFS data, the photogenerated, metastable state of CpNiNO has undergone considerable nuclear rearrangements compared to its ground state. The nuclear movement is characterized by a 0.12{angstrom} elongation of Ni-N bond and by a bending of Ni-N-O. A shift of the N-O stretching frequency from 1824 to 1387 cm{sup {minus}1} was observed in the photoinduced reaction with 365 nm light, implying that a NO{sup {minus}} like species results from intramolecular electron transfer from Ni to NO. The changes in the absorption spectra for the same reaction showed reduced absorption of the 385 nm band and a newly generated broad band near IR region. Temperature dependence of the Debye-Waller factor of CpNiNO was in good agreement with the diatomic harmonic oscillator for the Ni-N bond, but deviated for the Ni-O and the Ni-C bonds. Based on the structures obtained from EXAFS, ZINDO calculations for both the ground state and the photogenerated, metastable state of CpNiNO reproduced the general features of the observed absorption spectra and qualitatively explained the wavelength dependence of the reaction. The calculated partial charges on each atom in the ground state and the photogenerated, metastable state of CpNiNO are consistent with intramolecular electron transfer upon photoexcitation by 365 nm light.

  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. Positron annihilation study for cadmium (electronic structure and enhancement effect)

    NASA Astrophysics Data System (ADS)

    Hamid, A.

    2003-12-01

    The three dimensional electron density in momentum space ρ(p) and in wave vector space n(k) was reconstructed for cadmium (Cd). The measurements were performed using the two dimensional angular correlation of annihilation radiation (2D-ACAR) technique. Enhanced contributions in the spectra were observed around 5.5 mrad, discussed in terms of a Kahana-like enhancement effect. From another viewpoint, Fermi radii were analyzed in the (λM K), (ALM) and (AHK) planes, and they showed a maximum deviation of about 4% from the free electron Fermi radius. Moreover, comparisons to a radio-frequency size effect (RFSE) experiment and theoretical band structure calculations (using augmented plane wave (APW), linear combination of atomic orbital (LCAO) and linear muffin tin orbital (LMTO) methods) were examined. The results showed a qualitative agreement with both APW and LCAO calculations. However, a favorable agreement with the APW method was determined via Fermi surface dimensions. The differences of bands' occupation of n(k) between the current work and the APW method were argued in view of positron wave function in Cd.

  13. 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.

  14. Electronic structure of the primary electron donor of Blastochloris viridis heterodimer mutants : high field EPR study.

    SciTech Connect

    Ponomarenko, N. S.; Poluektov, O. G.; Bylina, E. J.; Norris, J. R.; Chemical Sciences and Engineering Division; Univ. of Chicago

    2010-09-01

    High-field electron paramagnetic resonance (HF EPR) has been employed to investigate the primary electron donor electronic structure of Blastochloris viridis heterodimer mutant reaction centers (RCs). In these mutants the amino acid substitution His(M200)Leu or His(L173)Leu eliminates a ligand to the primary electron donor, resulting in the loss of a magnesium in one of the constituent bacteriochlorophylls (BChl). Thus, the native BChl/BChl homodimer primary donor is converted into a BChl/bacteriopheophytin (BPhe) heterodimer. The heterodimer primary donor radical in chemically oxidized RCs exhibits a broadened EPR line indicating a highly asymmetric distribution of the unpaired electron over both dimer constituents. Observed triplet state EPR signals confirm localization of the excitation on the BChl half of the heterodimer primary donor. Theoretical simulation of the triplet EPR lineshapes clearly shows that, in the case of mutants, triplet states are formed by an intersystem crossing mechanism in contrast to the radical pair mechanism in wild type RCs. Photooxidation of the mutant RCs results in formation of a BPhe anion radical within the heterodimer pair. The accumulation of an intradimer BPhe anion is caused by the substantial loss of interaction between constituents of the heterodimer primary donor along with an increase in the reduction potential of the heterodimer primary donor D/D{sup +} couple. This allows oxidation of the cytochrome even at cryogenic temperatures and reduction of each constituent of the heterodimer primary donor individually. Despite a low yield of primary donor radicals, the enhancement of the semiquinone-iron pair EPR signals in these mutants indicates the presence of kinetically viable electron donors.

  15. 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.

  16. Effects of Paramagnetism and Electron Correlations on the Electronic Structure of MnO: Ab Initio Study

    NASA Astrophysics Data System (ADS)

    Yoon, Sangmoon; Jin, Kyoungsuk; Kang, Seoung-Hun; Nam, Ki Tae; Kim, Miyoung; Kwon, Young-Kyun

    Manganese oxide nanoparticles have attracted a lot of attentions as a promising candidate for next-generation catalyst. Therefore, understanding the electronic structure of manganese oxide in room temperature is highly required for the rational design of catalysts. We study the effects of paramagnetism and electron correlations on the electronic structure of MnO using ab initio density functional theory. Spin configurations of paramagnetism are postulated as the ensemble average of various spin disorders. Each initial disordered spin configuration is randomly generated with two constraints on magnetic local moments. We first investigate the influence of magnetic ordering on the elctronic structure of MnO using noncollinear spin calculations and find that the magnetic disorders make valence band maximum more delocalized. Moreover, we examine the role of electron correlations in the electronic structure of paramagnetic MnO using DFT +U calculations. Strong electron correlations modify not only the size of band gap but also the magnitude of local moments as in the antiferromagnetic MnO. Besides, the initialized spin disorder remains almost unchanged as electron correlation get stronger. Furthermore, our results obtained by considering both strong electron correlation and paramagnetism confirm experimentally-observed oxygen K edge X-ray emission spectra [1] reflecting the feature of valence bands. [1] E. Z. Kurmaev et al., Phys. Rev. B. 77, 165127 (2008).

  17. Comparison of the electronic structure of a thermoelectric skutterudite before and after adding rattlers: an electron energy loss study.

    PubMed

    Prytz, O; Saeterli, R; Løvvik, O M; Taftø, J

    2008-08-01

    Skutterudites, with rattler atoms introduced in voids in the crystal unit cell, are promising thermoelectric materials. We modify the binary skutterudite with atomic content Co(8)P(24) in the cubic crystal unit cell by adding La as rattlers in all available voids and replacing Co by Fe to maintain charge balance, resulting in La(2)Fe(8)P(24). The intention is to leave the electronic structure unaltered while decreasing the thermal conductivity due to the presence of the rattlers. We compare the electronic structure of these two compounds by studying the L-edges of P and of the transition elements Co and Fe using electron energy loss spectroscopy (EELS). Our studies of the transition metal white lines show that the 3d electron count is similar for Co and Fe in these compounds. As elemental Fe has one electron less than Co, this supports the notion that each La atom donates three electrons. The L-edges of P in these two skutterudites are quite similar, signalling only minor differences in electronic structure. This is in reasonable agreement with density functional theory (DFT) calculations, and with our multiple scattering FEFF calculations of the near edge structure. However, our experimental plasmon energies and dielectric functions deviate considerably from predictions based on DFT calculations. PMID:18042390

  18. Electronic structure of lanthanum sesquioxide: A Compton scattering study

    NASA Astrophysics Data System (ADS)

    Sharma, Sonu; Sahariya, Jagrati; Arora, Gunjan; Ahuja, B. L.

    2014-10-01

    We present the first-ever experimental and theoretical momentum densities of La2O3. The Compton line shape is measured using a 20 Ci 137Cs Compton spectrometer at an intermediate resolution with full width at half maximum of 0.34 a.u. The experimental Compton profile is compared with the theoretical electron momentum densities computed using linear combination of atomic orbitals (LCAO) method with density functional theory (DFT). It is seen that the generalized gradient approximation (GGA) within DFT reconciles better with the experiment than other DFT based approximations, validating the GGA approximation for rare-earth sesquioxides. The energy bands and density of states computed using LCAO calculations show its wide band gap nature which is in tune with the available reflectivity and photo-absorption data. In addition, Mulliken's population and charge density are also computed and discussed.

  19. 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)

  20. 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.

  1. Study of structural and electronic properties of Mn{sub 3}O{sub 4}

    SciTech Connect

    Kaur, Ramandeep Maitra, Tulika Nautiyal, Tashi

    2014-04-24

    Using density functional theory calculations we have examined the structural and electronic properties of magnetic spinel Mn{sub 3}O{sub 4}. We have optimized the structure (both volume and c/a ratio) within GGA. Then Coulomb correlations are included in the calculations to study the electronic properties. We observe that both the band gap and magnetic moment increase with the increase in Coulomb correlation due to the increased Jahn-Teller splitting and localization of the single e{sub g} electron of Mn{sup 3+}.

  2. Electronic structure, elasticity, bonding features and mechanical behaviour of zinc intermetallics: A DFT study

    NASA Astrophysics Data System (ADS)

    Fatima, Bushra; Acharya, Nikita; Sanyal, Sankar P.

    2016-05-01

    The structural stability, electronic structure, elastic and mechanical properties of TiZn and ZrZn intermetallics have been studied using ab-initio full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation for exchange and correlation potentials. The various structural parameters, such as lattice constant (a0), bulk modulus (B), and its pressure derivative (B') are analysed and compared. The investigation of elastic constants affirm that both TiZn and ZrZn are elastically stable in CsCl (B2 phase) structure. The electronic structures have been analysed quantitatively from the band structure which reveals the metallic nature of these compounds. To better illustrate the nature of bonding and charge transfer, we have also studied the Fermi surfaces. The three well known criterion of ductility namely Pugh's rule, Cauchy's pressure and Frantsevich rule elucidate the ductile nature of these compounds.

  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

    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.

  7. 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.

  8. Support Effects on Electronic Behaviors of Gold Nanoparticles Studied by X-Ray Absorption Fine Structure

    SciTech Connect

    Li Zhongrui; Yan Wensheng; Wei Shiqiang

    2007-02-02

    The electronic properties of gold nanoparticles supported on different supports were studied with X-ray absorption fine structure (XAFS). It was found that the tunability of the d-electron distribution in the nano-sized Au clusters can be realized by selective supporting. The Au atoms in the clusters gain 5d electrons when supported on SiO2, and lose 5d electrons when loaded over MgO, Al2O3, and TiO2. Contractions in bond lengths of between 0.5 and 1.6% from bulk metal values were observed from EXAFS data. This work demonstrates that the important role of the different supports in the 5d-charge distribution of Au nanoparticles and usefulness of XAFS in probing the electronic behavior of noble metal nanoparticles.

  9. Unoccupied-electronic-band structure of graphite studied by angle-resolved secondary-electron emission and inverse photoemission

    NASA Astrophysics Data System (ADS)

    Maeda, F.; Takahashi, T.; Ohsawa, H.; Suzuki, S.; Suematsu, H.

    1988-03-01

    Angle-resolved inverse photoemission spectroscopy (ARIPES) and angle-resolved secondary-electron emission spectroscopy (ARSEES) have been performed for graphite to establish experimentally the unoccupied-electronic-band structure as well as to study the difference between the two techniques. Remarkable differences have been found in the experimental two-dimensional band structures obtained by the two methods. The experimental results have been compared with the two different band calculations by R. C. Tatar and S. Rabii [Phys. Rev. B 25, 4126 (1982)] and by N. A. W. Holzwarth, S. G. Louie, and S. Rabii [Phys. Rev. B 26, 5382 (1982)] with special attention to the energy position of the three-dimensional interlayer band. The possible origin of the difference between ARIPES and ARSEES has also been discussed.

  10. Femtosecond studies of electron dynamics and structure at metal-molecular interfaces

    SciTech Connect

    Miller, Andre D.

    2002-07-15

    Femtosecond angle resolved two photon photoemission spectroscopy is used to study the electronic structure and electron dynamics at interfaces. At interfaces of thiolates chemisorbed on Ag(111), the adsorbate molecular electronic orbitals are observed to be nondispersive at low coverages and become dispersive at higher coverages. This is attributed to a phase transition of the layer. The molecules initially adsorb with their chains parallel to the surface. As the coverage is increased, the molecules order into a layer with the chains standing up from the surface. This closer packing results in a larger overlap between neighboring molecular orbitals and a dispersive electronic state. The lack of a change in the n=1 image potential state electron lifetimes as a function of chain length indicate that the electrons reside in the layer. The n=2 and 3 image potential state electron lifetimes decrease as the chain length is increased. This is attributed to the repulsive potential of the alkyl chains pushing the electron density into the sulfur portion of the layer. At a layer of acetonitrile molecules adsorbed on Ag(111), the image potential state electrons interact strongly with the adsorbate molecular dipoles. The dipoles rotate to solvate the electron, resulting in a decrease of the observed photoemitted electron kinetic energy as a function of time delay between population and photoemission. This is attributed to a change in the local work function resulting from the reorganization of the adsorbate layer molecules. For two layers of acetonitrile adsorbed on the Ag(111) substrate, dynamic electron localization is also observed.

  11. 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

  12. 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.

  13. SPELEEM Studies on the Electronic Structure of MoS2/Graphene Heterostructure

    NASA Astrophysics Data System (ADS)

    Jin, Wencan; Yeh, Po-Chun; Zaki, Nader; Chenet, Daniel; Arefe, Ghidewon; Hao, Yufeng; Sala, Alessandro; Mentes, Tevfik; Locatelli, Andrea; Hone, James; Osgood, Richard; Columbia University Collaboration; Elettra Sincrotrone Trieste Collaboration

    2015-03-01

    Two-dimensional layered materials have been realized through the use of van der Waals heterostructures composed of weakly interacting layers. Among them, MoS2/graphene heterostructures can combine the advantages of high carrier mobility in graphene with the direct band gap of MoS2, which leads to potential applications in nanoelectronic devices with various functionalities. In this work, we study the influence of interlayer twist angle on the electronic structure of a MoS2/graphene heterostructure using Spectroscopic Photoemission and Low Energy Electron Microscopy (SPELEEM) system. MoS2/graphene heterostructures are prepared by transferring chemical-vapor-deposition (CVD)-grown monolayer MoS2 on top of CVD-grown graphene. Twist angles are characterized using the micro-LEED and the electronic structures are directly measured using micro-ARPES.

  14. Computational Study of Electronic and Transport Properties of Novel Boron and Carbon Nano-Structures

    NASA Astrophysics Data System (ADS)

    Sadrzadeh, Arta

    In the first part of this dissertation, we study mainly novel boron structures and their electronic and mechanical properties, using ab initio calculations. The electronic structure and construction of the boron buckyball B80 , and boron nanotubes as the alpha- sheet wrapped around a cylinder are studied. The alpha-sheet is considered so far to be the most stable structure energetically out of the two dimensional boron assemblies. We will argue however that there are other sheets close in energy, using cluster expansion method. The boron buckyball is shown to have different possible isomers. Characterization of these isomers according to their geometry and electronic structure is studied in detail. Since the B80 structure is made of interwoven double-ring clusters, we also investigate double-rings with various diameters. We investigate the properties of nanotubes obtained from alpha-sheet. Computations confirm their high stability and identify mechanical stiffness parameters. Careful relaxation reveals the curvature-induced buckling of certain atoms off the original plane. This distortion opens up the gap in narrow tubes, rendering them semi-conducting. Wider tubes with the diameter d ≥ 1.7 nm retain original metallic character of the alpha-sheet. We conclude this part by investigation into hydrogen storage capacity of boron-rich compounds, namely the metallacarboranes. In the second part of dissertation, we switch our focus to electronic and transport properties of carbon nano-structures. We study the application of carbon nanotubes as electro-chemical gas sensors. The effect of physisorption of NO2 gas molecules on electron transport properties of semi-conducting carbon nanotubes is studied using ab initio calculations and Green's function formalism. It is shown that upon exposure of nanotube to different concentrations of gas, the common feature is the shift in conductance towards lower energies. This suggests that physisorption of NO2 will result in a

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

    DOE PAGESBeta

    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. 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

  17. 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.

  18. 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.

  19. Single-particle electron microscopy in the study of membrane protein structure.

    PubMed

    De Zorzi, Rita; Mi, Wei; Liao, Maofu; Walz, Thomas

    2016-02-01

    Single-particle electron microscopy (EM) provides the great advantage that protein structure can be studied without the need to grow crystals. However, due to technical limitations, this approach played only a minor role in the study of membrane protein structure. This situation has recently changed dramatically with the introduction of direct electron detection device cameras, which allow images of unprecedented quality to be recorded, also making software algorithms, such as three-dimensional classification and structure refinement, much more powerful. The enhanced potential of single-particle EM was impressively demonstrated by delivering the first long-sought atomic model of a member of the biomedically important transient receptor potential channel family. Structures of several more membrane proteins followed in short order. This review recounts the history of single-particle EM in the study of membrane proteins, describes the technical advances that now allow this approach to generate atomic models of membrane proteins and provides a brief overview of some of the membrane protein structures that have been studied by single-particle EM to date. PMID:26470917

  20. Structural and electronic properties of ultrathin copper nanowires: A density-functional theory study

    NASA Astrophysics Data System (ADS)

    Ma, Liang-Cai; Zhang, Jian-Min; Xu, Ke-Wei

    2013-02-01

    By using first-principles calculations based on density-functional theory, we have systematically investigated the equilibrium structure and electronic properties of 22 free-standing copper (Cu) nanowires having different cross-sections with 1-14 Cu atoms per unit cell. The structural properties of the studied Cu nanowires were greatly different from those of face centered cubic bulk Cu. For each wire the equilibrium lattice constant was obtained. The binding energy increases with increasing atom number per unit cell in different structures. As for the polygonal structures of a fixed cross-section, the preferred structures should be the staggered ones which contain a linear chain along the wire axis that passes through the center of the polygons, where each chain atom is just located at a point equidistant from the planes of polygons. All the nanowires are metallic. The numbers of conduction channels were determined from the electronic band structures. In general, the number of conduction channels increases when the nanowire becomes thicker. The density of charge revealed delocalized metallic bonding for all studied Cu nanowires.

  1. 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.

  2. 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.

  3. 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. PMID:26569578

  4. 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.

  5. 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.

  6. Electronic structure and magnetism on FeSiAl alloy: A DFT study

    NASA Astrophysics Data System (ADS)

    Cardoso Schwindt, V.; Sandoval, M.; Ardenghi, J. S.; Bechthold, P.; González, E. A.; Jasen, P. V.

    2015-09-01

    Density functional theory (DFT) calculation has been performed to study the electronic structure and chemical bonding in FeSiAl alloy. These calculations are useful to understand the magnetic properties of this alloy. Our results show that the mean magnetic moment of Fe atoms decreases due to the crystal structure and the effect of Si and Al. Depending on the environment, the magnetic moment of one Fe site (Fe1) increases to about 14.3% while of the other site (Fe2) decreases to about 25.9% (compared with pure bcc Fe). All metal-metal overlap interactions are bonding and slightly weaker than those found in the bcc Fe structure. The electronic structure (DOS) shows an important hybridization among Fe, Si and Al atoms, thus making asymmetric the PDOS with a very slight polarization of Al and Si atoms. Our study explains the importance of crystal structure in determining the magnetic properties of the alloys. FeSiAl is a good candidate for electromagnetic interference shielding combining low price and good mechanical and magnetic properties.

  7. DFT study on the structural and electronic properties of Pt-doped boron nitride nanotubes

    NASA Astrophysics Data System (ADS)

    Vessally, E.; Dehbandi, B.; Edjlali, Ladan

    2016-06-01

    First-principles calculations based on density functional theory were carried out to investigate the structural and electronic properties of Pt substitution-doped boron nitride (BN) nanotubes. The electronic and structural properties were studied for substituted Pt in the boron and the nitrogen sites of the (BN) nanotube. The band gap significantly diminishes to 2.095 eV for Pt doping at the B site while the band gap diminishes to 2.231 eV for Pt doping at the N site. The band density increases in both the valence band and the conduction band after doping. The effects of the hardness and softness group 17 (halogen elements) were calculated by density functional theory (DFT).

  8. 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.

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

    SciTech Connect

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

    2014-02-21

    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 cm{sup 2}/Vs. Such estimate confirms the superior transport properties of triarylamine-based nanowires, and make them an attracting materials platform for organic electronics.

  10. Electronic Structure of Bilayer Graphene Nanoribbon and Its Device Application: A Computational Study

    NASA Astrophysics Data System (ADS)

    Lam, Kai-Tak; Liang, Gengchiau

    Two-dimensional monolayer graphene has the unique electrical and physical properties which can be exploited in new device structures. However, its application in field-effect device structure is limited due to its semi-metal nature. Therefore, a lot of research efforts have been focussed on introducing an energy bandgap in the electronic structure. For example, a commonly studied method involves cutting two-dimensional graphene into one-dimensional narrow ribbons (graphene nanoribbons), where the spatial quantum confinement introduced by the physical edges generates an energy bandgap that is closely related to the width and edge configurations of the ribbon. Similarly for a bilayer graphene, an energy bandgap can also be obtained like the monolayer graphene nanoribbons, and be further controlled by varying its interlayer distance. In this chapter, a review of the electronic structure of monolayer graphene nanoribbon is presented and the study on the bilayer counterpart is subsequently discussed. Furthermore, based on the electrical properties of the bilayer graphene nanoribbon, the device performance of the Schottky barrier diode is investigated. Lastly, a nanoelectromechanical (NEM) switch based on the floating gate design is presented and discussed.

  11. Ab initio study of thermodynamic, electronic, magnetic, structural, and elastic properties of Ni4N allotropes

    NASA Astrophysics Data System (ADS)

    Hemzalová, P.; Friák, M.; Šob, M.; Ma, D.; Udyansky, A.; Raabe, D.; Neugebauer, J.

    2013-11-01

    We have employed parameter-free density functional theory calculations to study the thermodynamic stability and structural parameters as well as elastic and electronic properties of Ni4N in eight selected crystallographic phases. In agreement with the experimental findings, the cubic structure with Pearson symbol cP5, space group Pm3¯m (221) is found to be the most stable and it is also the only thermodynamically stable structure at T=0 K with respect to decomposition to the elemental Ni crystal and N2 gas phase. We determine structural parameters, bulk moduli, and their pressure derivatives for all eight allotropes. The thermodynamic stability and bulk modulus is shown to be anticorrelated. Comparing ferromagnetic and nonmagnetic states, we find common features between the magnetism of elemental Ni and studied ferromagnetic Ni4N structures. For the ground-state Ni4N structure and other two Ni4N cubic allotropes, we predict a complete set of single-crystalline elastic constants (in the equilibrium and under hydrostatic pressure), the Young and area moduli, as well as homogenized polycrystalline elastic moduli obtained by different homogenization methods. We demonstrate that the elastic anisotropy of the ground-state Ni4N is qualitatively opposite to that in the elemental Ni, i.e., these materials have hard and soft crystallographic directions interchanged. Moreover, one of the studied metastable cubic phases is found auxetic, i.e., exhibiting negative Poisson ratio.

  12. 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.

  13. 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

  14. 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.

  15. 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

  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. Resonant Inelastic X-ray Scattering Study of the Electronic Structure of Cu2O

    SciTech Connect

    Hill, J.P.; Kim, Y.-J.; Yamaguchi, H.; Gog, T.; Casa, D.

    2010-05-15

    A resonant inelastic x-ray scattering study of the electronic structure of the semiconductor cuprous oxide, Cu{sub 2}O, is reported. When the incident x-ray energy is tuned to the CuK-absorption edge, large enhancements of the spectral features corresponding to the electronic transitions between the valence band and the conduction band are observed. A feature at 6.5 eV can be well described by an interband transition from occupied states of mostly Cu3d character to unoccupied states with mixed 3d, 4s, and O2p character. In addition, an insulating band gap is observed, and the momentum dependence of the lower bound is measured along the {Gamma}-R direction. This is found to be in good agreement with the valence-band dispersion measured with angle-resolved photoemission spectroscopy.

  18. Experimental and theoretical studies of the electronic structure of Na-doped poly (para-phenylenevinylene)

    NASA Astrophysics Data System (ADS)

    Fahlman, M.; Beljonne, D.; Lögdlund, M.; Friend, R. H.; Holmes, A. B.; Brédas, J. L.; Salaneck, W. R.

    1993-11-01

    The electronic structure of sodium-doped poly ( p-phenylenevinylene), or PPV, has been studied using photoelectron spectroscopy, UPS and XPS. Upon doping, two new states are created in the previously forbidden electronic bandgap. No finite density- of-states is observed at the Fermi energy. The UPS spectra are analysed with the help of VEH-level quantum chemical calculations. It is determined that the Na-doping of PPV results in the formation of bipolaron bands in the otherwise forbidden energy gap at saturation doping. These results are in contrast with the case of poly-hexyl-thiophene doped from NOPF 6, where the existence of a finite density-of-states at EF and a stable polaron lattice was observed at saturation doping at room temperature. This work represents the first direct measure of multiple, resolved gap states in a doped conjugated polymer.

  19. Studies on electronic structure of interfaces between Ag and gelatin for stabilization of Ag nanoparticles

    NASA Astrophysics Data System (ADS)

    Tani, Tadaaki; Uchida, Takayuki

    2015-06-01

    Extremely high stability of Ag nanoparticles in photographic materials has forced us to study the electronic structures of the interfaces between thin layers of Ag, Au, and Pt and their surface membranes in ambient atmosphere by photoelectron yield spectroscopy in air and Kelvin probe method. Owing to the Fermi level equalization between a metal layer and a membrane coming from air, the electron transfer took place from the membrane to Pt and Au layers and from an Ag layer to the membrane, giving the reason for poor stability of Ag nanoparticles in air. The control of the Fermi level of an Ag layer with respect to that of a gelatin membrane in air could be widely made according to Nernst’s equation by changing the pH and pAg values of an aqueous gelatin solution used to form the membrane, and thus available to stabilize Ag nanoparticles in a gelatin matrix.

  20. 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.

  1. 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.

  2. ARPES studies of the electronic structure of LaOFe(P,As)

    SciTech Connect

    Analytis, J.G.

    2010-06-02

    We report a comparison study of LaOFeP and LaOFeAs, two parent compounds of recently discovered iron-pnictide superconductors, using angle-resolved photoemission spectroscopy. Both systems exhibit some common features that are very different from well-studied cuprates. In addition, important differences have also been observed between these two ferrooxypnictides. For LaOFeP, quantitative agreement can be found between our photoemission data and the LDA band structure calculations, suggesting that a weak coupling approach based on an itinerant ground state may be more appropriate for understanding this new superconducting compound. In contrast, the agreement between LDA calculations and experiments in LaOFeAs is relatively poor, as highlighted by the unexpected Fermi surface topology around ({pi},{pi}). Further investigations are required for a comprehensive understanding of the electronic structure of LaOFeAs and related compounds.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. First-principle studies of electronic structure and magnetic excitations in FeSe monolayer

    NASA Astrophysics Data System (ADS)

    Bazhirov, Timur; Cohen, Marvin L.

    2013-03-01

    Recent experimental advances made it possible to study single-layered superconducting systems of iron-based compounds. The results show evidence of significant enhancement of superconducting properties compared to the bulk case. We use first-principle pseudopotential density functional theory techniques and the local spin-density approximation to study the electronic properties of an FeSe monolayer in different spin configurations. The results show that the experimental shape of the Fermi surface is best described by a checkerboard antiferromagnetic (AFM) spin arrangement. To explore the underlying pairing mechanism, we study the evolution of the non-magnetic to the AFM-ordered structures under constrained magnetization, and we estimate the electronic coupling to magnetic excitations involving transfer and increase of iron magnetic moments and compare it to the electron-phonon coupling. Finally, we simulate the substrate-induced interaction by using uniform charge doping and show that the latter can lead to an increase in the density of states at the Fermi level and possibly produce higher superconducting transition temperatures. 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 Lawrence Berkeley National Laboratory's NERSC facility

  8. 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.

  9. Soft x-ray spectroscopic studies of the electronic structure of organic semiconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Yufeng

    Organic semiconductors have several unique properties, different from traditional inorganic semiconductors, such as flexibility and low cost production on a large scale. Potentially, they can be used in several new optoelectronic devices, such as organic solar cells, and organic light-emitting devices (OLEDs) Phthalocyanines (Pc's) are one important type of molecular organic semiconductor. The ease with which a diverse set of cations can bond to the phthalocyanine ligand leads to Pc-based thin films that display a wide variety of optical and electrical properties. In these materials, the ligand has a complex electronic structure in itself, and the introduction of metal cations adds further complexity to the states near the Fermi level (EF) due to the overlap of metal d states with carbon and nitrogen 2p states. In this thesis, the electronic structure of several Pc's has been studied by soft x-ray spectroscopies, such as x-ray photoemission spectroscopy (XPS), x-ray absorption spectroscopy (XAS), and x-ray emission spectroscopy (XES). To avoid potential contamination and beam damage, the large area thin film samples have been prepared in situ by using organic molecular beam deposition (OMBD). The structure of samples were characterized ex situ by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The soft x-ray spectra recorded from stationary samples are found to represent the electronic structure from damaged molecules, which is caused by intense x-ray beams. Continuously translating samples during measurement overcomes this problem. Element, chemical, and symmetry specific occupied and unoccupied partial density of states (PDOS) from Pc's were observed. They show good agreement with density functional theory (DFT) calculations. Studies of potassium doping non-transition metal Pc, fluorinated metal Pc, and metal oxide Pc's show several interesting phenomena, such as variation of molecular symmetry, and charge transfer and d-d* resonant inelastic x

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

    PubMed

    Roth, Friedrich; Knupfer, Martin

    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. PMID:26493923

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

    NASA Astrophysics Data System (ADS)

    Roth, Friedrich; Knupfer, Martin

    2015-10-01

    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. 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.

  13. Ab initio quantum mechanical studies in electronic and structural properties of carbon nanotubes and silicon nanowires

    NASA Astrophysics Data System (ADS)

    Matsuda, Yuki

    This dissertation focuses on ab-initio quantum mechanical calculations of nanoelectronics in three research topics: contact resistance properties of carbon nanotubes and graphenes (Chapters 1 through 3), electrical properties of carbon nanotubes (Chapter 4) and silicon nanowires (Chapter 5). Through all the chapters, the aim of the research is to provide useful guidelines for experimentalists. Chapter 1 presents the contact resistance of metal electrode-carbon nanotube and metal electrode-graphene interfaces for various deposited metals, based on first-principles quantum mechanical density functional and matrix Green's function methods. Chapters 2 and 3 describe inventive ways to enhance contact resistance properties as well as mechanical stabilities using "molecular anchors" (Chapter 2) or using "end-contacted" (or end-on) electrodes (Chapter 3). Chapters 1 through 3 also provide useful guidelines for nanotube assembly process which is one of the main obstacles in nanoelectronics. Chapter 4 shows accurate and detailed band structure properties of single-walled carbon nanotubes using B3LYP hybrid functional, which are critical parameters in determining the electronic properties such as small band gaps (˜0.1 eV) and effective masses. Chapter 5 details both structural and electronic properties of silicon nanowires. These results lead to the findings controlling the diameter and surface coverage by adsorbates (e.g., hydrogen) of silicon nanowires can be effectively used to optimize their properties for various applications. All the theoretical results are compared with other theoretical studies and experimental data. Notably, electronic studies using B3LYP show excellent agreement with experimental studies quantitatively, which previous quantum mechanical calculations had failed. These studies show how quantum mechanical predictions of complex phenomena can be effectively investigated computationally in nanomaterials and nanodevices. Given the difficulty, expense

  14. 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.

  15. Density functional study of fullerene-based solids: Crystal structure, doping, and electron-phonon interaction

    NASA Astrophysics Data System (ADS)

    Romero, Nichols Anthony

    Two decades after the discovery of C60, fullerenes continue to be intensely studied for their diverse properties, not the least of which is their unusually high superconducting transition temperature T c (up to 40 K in Cs3C60). Ab initio electronic structure methods are able to contribute to our understanding of these materials by providing electron densities, band structures, density-of-states, binding energies, and even the electron-phonon coupling. Because of the increasing computational feasibility of these large-scale calculations, these methods now play a prominent role in verifying and guiding experimental investigation of new materials. This dissertation presents results of a theoretical investigation of several scenarios where Tc enhancement exceeding those found in the alkali-doped fullerides could be exhibited: (1) field-effect doping of C60 layers, (2) C28-derived molecular solids and (3) covalently bonded C28 solids. The method employed is the Kohn-Sham formulation of density functional theory. Simpler tight-binding calculations are also used when appropriate. The study of field-effect doping was stimulated by the reports of large Tc enhancements by Schon et al., which were later retracted and found to be falsified. Even before the legitimacy of these reports came into question, we concluded that our calculations did not substantiate their claims. We present our electronic structure calculations and conclusions which are independent and potentially useful for future work on field-effect devices. The main part of this dissertation is a separate study on C28-based solids motivated by theoretical arguments suggesting that solids based on smaller fullerenes could exhibit a Tc enhancement. Among many molecular solids formed from closed-shell C28-derived molecules, we have found that solid C28H4 binds weakly and exhibit many of the salient features of solid C60, with an estimated Tc of 58 K. In this same spirit, we also study covalent solids based on

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

    NASA Astrophysics Data System (ADS)

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

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

  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. X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations

    NASA Astrophysics Data System (ADS)

    Clancy, J. P.; Gretarsson, H.; Lee, E. K. H.; Tian, Di; Kim, J.; Upton, M. H.; Casa, D.; Gog, T.; Islam, Z.; Jeon, Byung-Gu; Kim, Kee Hoon; Desgreniers, S.; Kim, Yong Baek; Julian, S. J.; Kim, Young-June

    2016-07-01

    We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu2Ir2O7 and Pr2Ir2O7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu2Ir2O7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (˜6 to 300 K) and pressures (˜0.1 to 17 GPa) studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of Eu2Ir2O7 and Pr2Ir2O7 using high-resolution Ir L3-edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ˜3 -5 eV, spin-orbit excitations at ˜0.5 -1 eV, and broad low-lying excitations below ˜0.15 eV. In single-crystal samples of "Eu-rich" Eu2Ir2O7 (found to possess an actual stoichiometry of Eu2.18Ir1.82O7.06 ) we observe highly damped magnetic excitations at ˜45 meV, which display significant momentum dependence. We compare these results with recent dynamical structure factor calculations.

  19. Theoretical study of geometrical and electronic structures of various thiophene-based tricyclic polymers

    NASA Astrophysics Data System (ADS)

    Hong, Sung Y.; Song, Jung M.

    1997-12-01

    A theoretical study of a variety of tricyclic polymers [-(C8H2X2Y)n-] with two different types of bridging groups was performed, X=S and Y=CH2, SiH2, C=O, C=S, or C=CH2 for the fused bithiophene system and vice versa for the thieno-bicyclic system. These two types of the bridging groups are different from each other in that S favors the aromatic form of a cyclic polymer and the other groups prefer the quinonoid form. Geometrical structures of the polymers were obtained from semiempirical self-consistent-field (SCF) band calculations and the electronic properties from the modified extended Hückel band calculations. It is found that the ground-state geometrical structures of the tricyclic polymers are determined by the bridging groups in the outer rings. That is, the fused bithiophene system is aromatic in the ground state and the thieno-bicyclic system is quinonoid. The ground-state band gaps (which correspond to the absorption peaks of π-π* band transition) of the polymers were estimated to be in the range of 0.7-2.0 eV. The band gaps were analyzed in terms of the bond-length alternation along the conjugated carbon backbone, the C1-C4 interactions, and the electronic effect of the bridging groups. We also investigated the geometrical and electronic structures of polydicyanomethylene-cyclopenta-dicyclopentadiene (PDICNCY). Unlike the theoretical predictions of Toussaint and Bredas [Synth. Met. 69, 637 (1995)], PDICNCY in the ground state was estimated to be of the quinonoid form and to possess a large band gap (2.55 eV) comparable with the gap of polythiophene.

  20. XAFS and XEOL of tetramesityldigermene - An electronic structure study of a heavy group 14 ethylene analogue

    SciTech Connect

    Ward, Matthew J.; Rupar, Paul A.; Murphy, Michael W.; Yiu, Yun-Mui; Baines, Kim M.; Sham, Tsun-Kong

    2013-05-29

    Digermene, the germanium analogue of ethylene, has a multiple bonding motif that differs greatly from that of alkenes and exhibits no pure σ or π type bonds. The electronic structure of digermenes is difficult to study experimentally due to their reactivity, and is computationally challenging because of their shallow potential energy surfaces. Using X-ray absorption near edge structures at both the germanium K and L edges we have been able to directly probe the unoccupied electronic states, or the lowest unoccupied molecular orbital (LUMO), and LUMO+ etc. in the Ge=Ge bond of tetramesityldigermene. We have demonstrated that the LUMO, LUMO+, etc. are composed of hybrid Ge 4s and 4p orbitals. Additionally, our data suggest that the LUMO exhibits relatively more Ge 4s character, whereas the LUMO+ and LUMO+2 exhibit relatively more Ge 4p character. An X-ray excited optical luminescence study of Ge2Mes4 revealed one broad optical emission band at 620 nm, which is significantly red shifted compared to the known energy gap of this molecular germanium compound.

  1. 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.

  2. 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.

  3. 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

  4. First-principles study of the electronic and molecular structure of protein nanotubes

    NASA Astrophysics Data System (ADS)

    Okamoto, Hajime; Takeda, Kyozaburo; Shiraishi, Kenji

    2001-09-01

    The electronic and molecular structures of protein nanotubes (PNT's) have been investigated theoretically by first-principles electronic structure calculations. The results have been discussed in comparison to those of the polypeptide open chains (POC's) and polypeptide closed rings (PCR's) in order to give a systematic understanding. Focusing on the intra-ring and inter-ring hydrogen bonds (HB's), we also investigate the PCR stacking mechanism. The present calculation reveals that PNT's are semiconductors and that an extra proton in the tube interior has the potential to be an electron acceptor.

  5. 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

  6. Ab Initio Study of the Structural, Electronic, and Thermal Properties of Alloy

    NASA Astrophysics Data System (ADS)

    Benkaddour, I.; Khachai, H.; Chiker, F.; Benosman, N.; Benkaddour, Y.; Murtaza, G.; Omran, S. Bin; Khenata, R.

    2015-07-01

    The results of a first-principle study of the structural, electronic, and thermal properties of a alloy, using the full-potential linear muffin-tin-orbital (FP-LMTO) method in the framework of density functional theory, within both the local density approximation and the generalized gradient approximation are presented. The composition effect on lattice constants, bulk moduli, band gaps, and effective masses is analyzed. The quasi-harmonic Debye model, using a set of total energy versus volume calculations obtained with the FP-LMTO method, is applied to study the thermal and vibrational effects. The temperature effect on the lattice parameters, thermal expansions, heat capacities, and Debye temperatures is determined from the non-equilibrium Gibbs functions. The microscopic origins of the bowing parameter were explained using the approach of Zunger and coworkers.

  7. 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.

  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. 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.

  10. 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.

  11. Ab initio electronic structure study for TTF-TCNQ under uniaxial compression

    NASA Astrophysics Data System (ADS)

    Ishibashi, Shoji; Hashimoto, Tamotsu; Kohyama, Masanori; Terakura, Kiyoyuki

    2004-04-01

    We have investigated the electronic structure of TTF-TCNQ under uniaxial compression with ab initio plane-wave pseudopotential calculations within the local-density approximation and generalized gradient approximation. Depending on the compression direction, the constituent molecules are deformed in different ways. Along with these structural deformations, quasi-one-dimensional Fermi surfaces show dramatic changes in their shapes and sizes.

  12. A density functional study of the electronic structure and spin Hamiltonian parameters of mononuclear thiomolybdenyl complexes.

    PubMed

    Drew, Simon C; Young, Charles G; Hanson, Graeme R

    2007-04-01

    The electron paramagnetic resonance spin Hamiltonian parameters of mononuclear thiomolybdenyl complexes based upon the tris(pyrazolyl)borate ligand, together with their molybdenyl analogues, are calculated using density functional theory. The electronic g matrix and 95Mo hyperfine matrix are calculated as second-order response properties from the coupled-perturbed Kohn-Sham equations. The scalar relativistic zero-order regular approximation (ZORA) is used with an all-electron basis and an accurate mean-field spin-orbit operator which includes all one- and two-electron terms. The principal values and relative orientations of the g and A interaction matrices obtained from the experimental spectra in a previous EPR study are compared with those obtained from unrestricted Kohn-Sham calculations at the BP86 and B3LYP level, and the latter are found to be in good quantitative agreement. A quasi-restricted approach is used to analyze the influence of the various molecular orbitals on g and A. In all complexes the ground state magnetic orbital is dX2-Y2-based and the orientation of the A matrix is directly related to the orientation of this orbital. The largest single contribution to the orientation of the g matrix arises from the spin-orbit coupling of the dYZ-based lowest-unoccupied molecular orbital into the ground state. A number of smaller, cumulative charge-transfer contributions augment the d-d contributions. A comparison of the theoretical EPR parameters obtained using both crystallographic and gas-phase geometry-optimized structures of Tp*MoO(bdt) (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate, bdt = 1,2-benzenedithiolate) suggests a correspondence between the metal-dithiolate fold angle and the angle of noncoincidence between g and A. PMID:17305330

  13. Structural, Dynamical, and Electronic Properties of Liquid Water: A Hybrid Functional Study.

    PubMed

    Ambrosio, Francesco; Miceli, Giacomo; Pasquarello, Alfredo

    2016-08-01

    We study structural, dynamical, and electronic properties of liquid water through ab initio molecular dynamics (MD) simulations based on a hybrid functional which includes nonlocal van der Waals (vdW) interactions. The water dimer, the water hexamer, and two phases of ice are studied as benchmark cases. The hydrogen-bond energy depends on the balance between Fock exchange and vdW interactions. Moreover, the energetic competition between extended and compact structural motifs is found to be well described by theory provided vdW interactions are accounted for. Applied to the hydrogen-bond network of liquid water, the dispersion interactions favor more compact structural motifs, bring the density closer to the experimental value, and improve the agreement with experimental observables such as radial distribution functions. The description of the self-diffusion coefficient is also found to improve upon the combined consideration of Fock exchange and vdW interactions. The band gap and the band edges are found to agree with experiment within 0.1 eV. PMID:27404717

  14. First-principles study of electronic structure, phonons and electron-phonon interaction in hexagonal PdTe

    NASA Astrophysics Data System (ADS)

    Cao, Jin-Jin; Gou, Xiao-Fan

    2016-01-01

    The electronic structure, phonons and electron-phonon interaction of hexagonal PdTe have been investigated in detail by employing a plane wave pseudopotential method and a linear-response scheme within Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA). Consistent with available theoretical and experimental results, it has been found that the intermediate strength electron-phonon coupling constant (λ) with the calculated value of 0.542 on the LDA and 0.648 on the GGA is due to the coupling of phonons from Pd and Te atoms and electrons from Pd-d and Te-p states. Through comparison, the calculations on the GGA produce better quality than that on the LDA. On the basis of appropriate Coulomb pseudopotential (μ∗) and λ of 0.648 together with experimental Debye temperature (Θ), via the McMillan formula, the superconducting transition temperature with the value of 4.5 K is obtained, same to the experimental value. The results indicate that conventional electron-phonon coupling mechanism can explain the superconductivity in this compound.

  15. First-Principles Study of Electronic Structure and Thermoelectric Properties of Ge-Doped Tin Clathrates

    NASA Astrophysics Data System (ADS)

    Akai, K.; Kishimoto, K.; Koyanagi, T.; Kono, Y.; Yamamoto, S.

    2014-06-01

    We calculated the electronic structure and thermoelectric properties of the Ge-doped quaternary clathrate Ba-Ga-Sn-Ge. The electronic structure was calculated by using the WIEN2k code, which is based on the full-potential augmented plane-wave method. Using this method, we calculated the total energies for several Ge configurations to determine the positions of Ge atoms in the unit cell. The calculated Ge positions were in good agreement with the experimental results. Based on the resulting Ge positions, the band structure and thermoelectric properties of the Ba-Ga-Sn-Ge clathrates were calculated.

  16. Electronic structure and optical properties of Cs2HgI4: Experimental study and band-structure DFT calculations

    NASA Astrophysics Data System (ADS)

    Lavrentyev, A. A.; Gabrelian, B. V.; Vu, V. T.; Shkumat, P. N.; Myronchuk, G. L.; Khvyshchun, M.; Fedorchuk, A. O.; Parasyuk, O. V.; Khyzhun, O. Y.

    2015-04-01

    High-quality single crystal of cesium mercury tetraiodide, Cs2HgI4, has been synthesized by the vertical Bridgman-Stockbarger method and its crystal structure has been refined. In addition, electronic structure and optical properties of Cs2HgI4 have been studied. For the crystal under study, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+-ion irradiated surfaces have been measured. The present X-ray photoelectron spectroscopy (XPS) results indicate that the Cs2HgI4 single crystal surface is very sensitive with respect to Ar+ ion-irradiation. In particular, Ar+ bombardment of the single crystal surface alters the elemental stoichiometry of the Cs2HgI4 surface. To elucidate peculiarities of the energy distribution of the electronic states within the valence-band and conduction-band regions of the Cs2HgI4 compound, we have performed first-principles band-structure calculations based on density functional theory (DFT) as incorporated in the WIEN2k package. Total and partial densities of states for Cs2HgI4 have been calculated. The DFT calculations reveal that the I p states make the major contributions in the upper portion of the valence band, while the Hg d, Cs p and I s states are the dominant contributors in its lower portion. Temperature dependence of the light absorption coefficient and specific electrical conductivity has been explored for Cs2HgI4 in the temperature range of 77-300 K. Main optical characteristics of the Cs2HgI4 compound have been elucidated by the first-principles calculations.

  17. First principles study of electronic structures of defects in zirconium germanium phosphate and defect chalcopyrites

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaoshu

    2005-11-01

    This thesis mainly focuses on a study of the point defects in ZnGeP 2. Density functional theory (DFT) is used in the local density approximation (LDA) in conjunction with the full-potential linearized muffin-tin orbital (FP-LMTO) method, modeling defects with the supercell approach. Under prevalent Zn-poor conditions, the GeZn double donor and VZn shallow acceptor are found to have the lowest formation energies, which explains the compensated p-type nature of the material. Good agreement is obtained with the energy levels deduced from optical quenching and activation of the EPR signals, if a direct transfer of electrons from V2-Zn to Ge2+Zn is assumed to occur rather than a process via the conduction band. The VGe is found to have high energy of formation under any chemical potential conditions and is found to be unstable towards formation of VZn and GeZn. Structural relaxation of all defects is performed but no symmetry breaking distortions are found. The defect wavefunctions of the unpaired electron in the V-Zn is found to be spread equally over the four neighboring P atoms, in disagreement with electron nuclear double resonance (ENDOR) data which indicate primary localization on a pair of P atoms. Several possible origins for this discrepancy are examined. Alternative assignments of the AL1 EPR signal to ZnGe, or complexes such as Zni-VZn, V-Zn -G2+Zn-V- Zn are discarded although the latter complex is found to be favorable in energy. The possibility of a failure of the LDA due to its incompletely cancelled self-interaction is examined using Hartree-Fock cluster calculations. A distortion is found to occur in Hartree-Fock but not in LDA. However, it is different from the experimental one. Finally, a dangling bond and group theory model is proposed for a Jahn-Teller distortion which can explain the localization observed by ENDOR. In the final chapter, the electronic band structures of the ordered vacancy defect chalcopyrites with formula II-III2-VI4 for II=Zn, Cd

  18. 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. PMID:26593689

  19. 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.

  20. 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.

  1. Electronic structure, magnetic, and transport studies of single-crystalline UCoGa{sub 5}

    SciTech Connect

    Troc, R.; Bukowski, Z.; Sulkowski, C.; Misiorek, H.; Morkowski, J.A.; Szajek, A.; Chelkowska, G.

    2004-11-01

    The magnetic susceptibility, electrical resistivity in zero and in magnetic fields up to 8 T, thermopower and thermal conductivity measurements in a wide temperature range have been performed on UCoGa{sub 5} single crystals. On the basis of the susceptibility maximum at 650 K and the phonon part of the thermal conductivity, a mixed-valence state of uranium in this compound has been postulated. On the other hand, a normal positive behavior of magnetoresistivity rules out the possibility of spin fluctuation as a mechanism driving the susceptibility through the maximum. In turn, the thermopower results may support both kinds of many-body behaviors. The electronic structure has also been studied by combining x-ray photoemission spectroscopy results with those obtained in the band structure calculations. In the latter the tight-binding linear muffin-tin orbital method in the atomic sphere approximation has been applied. A very good agreement between the experimental and calculated data has been achieved. A complex satellite structure of the core level spectra supports an idea of the presence of the valence instability in this compound. This idea is also concluded from the comparison of obtained experimental data with some similar rare earth and uranium ternary compounds.

  2. 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.

  3. First-principles study of the electronic structure and magnetism of CaIrO3

    NASA Astrophysics Data System (ADS)

    Subedi, Alaska

    2012-01-01

    I study the electronic structure and magnetism of postperovskite CaIrO3 using first-principles calculations. The density functional calculations within the local density approximation without the combined effect of spin-orbit coupling and on-site Coulomb repulsion show the system to be metallic, which is in disagreement with the recent experimental evidences that show CaIrO3 to be an antiferromagnetic Mott insulator in the Jeff=1/2 state. However, when spin-orbit coupling is taken into account, the Ir t2g bands split into fully filled Jeff=3/2 bands and half-filled Jeff=1/2 bands. I find that spin-orbit coupling along with a modest on-site Coulomb repulsion opens a gap leading to a Mott insulating state. The ordering is antiferromagnetic along the c axis with total moments aligned antiparallel along the c axis and canted along the b axis.

  4. 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.

  5. 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.

  6. 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.

  7. Electron microscopy structure study of laser-clad TiC-Ni particle-reinforced coating

    SciTech Connect

    Ouyang, J.H.; Li, X.; Lei, T.C.

    2000-04-01

    The microstructure of a laser-clad TiC-Ni particle-reinforced coating on 1045 steel was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ion microprobe mass spectroscopy (IMMS). The microstructural constituents of the clad layers (CLs) were analyzed to be TiC particles, {gamma}-Ni primary dendrites, and interdendritic eutectics of {gamma}{sub E}-Ni plus M{sub 23}(CB){sub 6} and M{sub 6}(CB) carboborides. Three growth mechanisms of the original TiC particles were found: (1) stepped lateral growth at the edges, (2) radiated and cylindrically coupled growth at the edges, and (3) bridging growth of the clustered particles. Ordered and modulated structures were found in the original TiC particles. In addition to the original TiC particles, fine TiC particles precipitated from the liquid phase and {gamma}-Ni solid solution during laser cladding. The microstructures of the bonding zones (BZs) were intimately associated with laser processing parameters. The BZs of the clad coatings can be categorized into three types according to the combination of the CL with heat-affected zone (HAZ): (1) straight interface combination, (2) zigzag connection, and (3) combination by partial melting of prior austenitic grain boundaries of the substrate. The microstructural evolution of the CLs was discussed. The formation and phase transformation models of the BZs were proposed.

  8. Experimental and theoretical study on the structure and electronic spectra of imiquimod and its synthetic intermediates.

    PubMed

    Zhao, Bo; Rong, Yu-Zhi; Huang, Xiao-Hua; Shen, Jing-Shan

    2007-09-01

    Crystal structure of the imiquimod has been determined by single crystal X-ray analysis, imiquimod crystallizes in orthorhombic space group P2(1)2(1)2(1) and the molecules are linked along the c axis by the strong N-H ... N hydrogen bonds. A density functional theory (DFT) study on the electronic properties of imiquimod and its synthetic intermediates has been performed at B3LYP/6-31G* level, while taking solvent effects into account. Both the single configuration interaction (CIS) method and the time-dependent DFT (TDDFT) approaches have been used to calculate the electronic absorption spectra, and there is a good agreement between the calculated and experimental UV-visible absorption spectra. The fluorescence emission spectra of these three compounds in solution have also been measured, the relatively low fluorescence intensity is attributed to a chlorine-modulated heavy atom effect that enhances intersystem crossing between excited singlet and triplet states, and the relatively high fluorescence intensity of imiquimod results from an extended pi-conjugated system which enhances S(1)-->S(0) radiant transition. PMID:17601733

  9. 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

    2016-05-01

    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 3 d 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 e g -like orbitals. We also observe that the Co (3 d) 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.

  10. 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.

  11. Electronic, structural, and elastic properties of metal nitrides XN (X = Sc, Y): A first principle study

    NASA Astrophysics Data System (ADS)

    Ekuma, Chinedu E.; Bagayoko, Diola; Jarrell, Mark; Moreno, Juana

    2012-09-01

    We utilized a simple, robust, first principle method, based on basis set optimization with the BZW-EF method, to study the electronic and related properties of transition metal mono-nitrides: ScN and YN. We solved the KS system of equations self-consistently within the linear combination of atomic orbitals (LCAO) formalism. It is shown that the band gap and low energy conduction bands, as well as elastic and structural properties, can be calculated with a reasonable accuracy when the LCAO formalism is used to obtain an optimal basis. Our calculated, indirect electronic band gap (E^Γ -X_g) is 0.79 (LDA) and 0.88 eV (GGA) for ScN. In the case of YN, we predict an indirect band gap (E^Γ -X_g) of 1.09 (LDA) and 1.15 eV (GGA). We also calculated the equilibrium lattice constants, the bulk moduli (Bo), effective masses, and elastic constants for both systems. Our calculated values are in excellent agreement with experimental ones where the latter are available.

  12. Low-lying electronic excited states of pentacene oligomers: a comparative electronic structure study in the context of singlet fission.

    PubMed

    Coto, Pedro B; Sharifzadeh, Sahar; Neaton, Jeffrey B; Thoss, Michael

    2015-01-13

    The lowest-lying electronic excited states of pentacene and its oligomers are investigated using accurate multireference wave function methods (CASPT2/CASSCF) and the many-body Greens's function approach (GW/BSE). The results obtained for dimers and trimers of different geometry reveal a complex electronic structure, which includes locally excited, charge transfer, and multiexciton states. For singlets of single-excitation character, both approaches yield excitation energies that are in good overall quantitative agreement. While the multiexciton states are located relatively high in energy in all systems investigated, charge transfer states exist in close proximity to the lowest-lying absorbing states. The implications of the results for the mechanisms of singlet fission in pentacene are discussed. PMID:26574213

  13. First principles study of the structural, electronic and optical properties of crystalline o-phenanthroline

    NASA Astrophysics Data System (ADS)

    Nejatipour, Hajar; Dadsetani, Mehrdad

    2016-05-01

    In a comprehensive study, structural properties, electronic structure and optical response of crystalline o-phenanthroline were investigated. Our results show that in generalized gradient approximation (GGA) approximation, o-phenanthroline is a direct bandgap semiconductor of 2.60 eV. In the framework of many-body approach, by solving the Bethe-Salpeter equation (BSE), dielectric properties of crystalline o-phenanthroline were studied and compared with phenanthrene. Highly anisotropic components of the imaginary part of the macroscopic dielectric function in o-phenanthroline show four main excitonic features in the bandgap region. In comparison to phenanthrene, these excitons occur at lower energies. Due to smaller bond lengths originated from the polarity nature of bonds in presence of nitrogen atoms, denser packing, and therefore, a weaker screening effect, exciton binding energies in o-phenanthroline were found to be larger than those in phenanthrene. Our results showed that in comparison to the independent-particle picture, excitonic effects highly redistribute the oscillator strength.

  14. First-principles study of electronic structures of graphene on Y2O3

    NASA Astrophysics Data System (ADS)

    Kaneko, Tomoaki; Ohno, Takahisa

    2016-06-01

    We investigate the structures, stability and electronic properties of graphene adsorbed on Y2O3(111) using first-principles calculations based on density functional theories. When the interface of Y2O3(111) is terminated by an Y-layer, graphene is chemisorbed on Y2O3, resulting in the strong modification of electronic band structures. When the Y2O3(111) surface is terminated with O atoms and extra O atoms, on the other hand, graphene is physisorbed on Y2O3(111). Therefore, an O-rich environment is preferable for the graphene and Y2O3 interface.

  15. Positron annihilation studies of the electronic structure and fermiology of the high-{Tc} superconductors

    SciTech Connect

    Smedskjaer, L.C.; Bansil, A.

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T{sub c} superconductors, with focus on the YBa{sub 2}Cu{sub 3}O{sub 7} system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  16. Positron annihilation studies of the electronic structure and fermiology of the high-[Tc] superconductors

    SciTech Connect

    Smedskjaer, L.C. ); Bansil, A. . Dept. of Physics)

    1992-09-01

    We discuss the application of the positron annihilation angular correlation (ACAR) spectroscopy for investigating the electronic structure and Fermiology of the high-T[sub c] superconductors, with focus on the YBa[sub 2]Cu[sub 3]O[sub 7] system where most of the experimental and theoretical work has to date been concentrated. Comparisons between measured 2D-ACAR positron spectra and band theory predictions show a remarkable agreement (for the normal state), indicating that the electronic structure and Fermi surface of this material is described reasonably by the conventional picture.

  17. 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

  18. 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.

  19. 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.

  20. AM1 study of the electronic structure of some androgens 5{beta}-reduced

    SciTech Connect

    Kubli-Garfias, C.; Vazquez, R.; Vega-Velazquez, C. |

    1996-12-31

    Among the possible derivatives of testosterone are known the metabolites reduced at position 5. From this, two conformations are feasible; trans and cis resulting in 5{alpha} and 5{beta}-configured compounds. In this work four of the most important 5{beta}-reduced androgens were studied, namely: 5{beta}-androstanedione (5{beta}- androstane-3,17-dione (1)), 5{beta}-dihydrotestosterone (17{beta}-hydroxy-5{beta} androstan-3- one; (2)), etiocholanol-one (3{alpha}-hyroxy-5{beta}-androstan-17-one (3)) and epietiocholanolone (3{beta}-hydroxy-5{beta}-androstan-17-one; (4)). Initially geometries were optimized with molecular mechanics (MM2), and refined by the Austin Model 1 method (AM1). Thus, the following electronic structure properties were calculated: heat of formation ({Delta}Hf), dipole moment, and frontier orbitals (HOMO and LUMO). Although HOMO and LUMO were somewhat similar in energies, they were located differently into the molecular frame. Thus, HOMO was located at 17C-carbonyl group in structures 1,3 and 4 and at the carbonyl at C3 in 2; The LUMO was placed in the carbonyl at C3 in 1 and 2, whereas in 3 and 4 was placed at C17. It is concluded that these location of valence orbitals might facilitate the action of enzymes yielding androstanediols, explaining the last step in the metabolism of androgens.

  1. ARPES studies of the electronic structure of Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Lu, Donghui

    2009-03-01

    The recent discovery of superconductivity in Fe-based layered compounds has created renewed interest in high temperature superconductivity. With a superconducting transition temperature as high as 55 K, this discovery provides a new direction to understand the essential ingredients for achieving a high superconducting transition temperature. In this talk, I will present our recent angle-resolved photoemission spectroscopy (ARPES) studies on LaOFeP and (Ba,K)Fe2As2 systems, with special emphasis on the basic electronic structure of the parent compounds. For LaOFeP, quantitative agreement can be found between our ARPES data and the LDA band structure calculations, suggesting that a weak coupling approach based on an itinerant ground state may be more appropriate for understanding this new superconducting compound [1]. On the other hand, the picture for (Ba,K)Fe2As2 system is more complicated. I will discuss two important issues in these FeAs compounds: 1) the unexpected Fermi surface topology in both undoped and doped compounds; 2) the peculiar signature of the SDW transition in ARPES spectra for the parent compound. [4pt] [1] D. H. Lu, M. Yi, S.-K. Mo, A. S. Erickson, J. Analytis, J.-H. Chu, D. J. Singh, Z. Hussain, T. H. Geballe, I. R. Fisher & Z.-X. Shen, Nature 455, 81 (2008).

  2. Electronic structures, vibrational spectra, and revised assignment of aniline and its radical cation: Theoretical study

    NASA Astrophysics Data System (ADS)

    Wojciechowski, Piotr M.; Zierkiewicz, Wiktor; Michalska, Danuta; Hobza, Pavel

    2003-06-01

    Comprehensive studies of the molecular and electronic structures, vibrational frequencies, and infrared and Raman intensities of the aniline radical cation, C6H5NH2+ have been performed by using the unrestricted density functional (UB3LYP) and second-order Møller-Plesset (UMP2) methods with the extended 6-311++G(df,pd) basis set. For comparison, analogous calculations were carried out for the closed-shell neutral aniline. The studies provided detailed insight into the bonding changes that take place in aniline upon ionization. The natural bond orbital (NBO) analysis has revealed that the pπ-radical conjugative interactions are of prime importance in stabilizing the planar, quinoid-type structure of the aniline radical cation. It is shown that the natural charges calculated for aniline are consistent with the chemical properties of this molecule (an ortho- and para-directing power of the NH2 group in electrophilic substitutions), whereas Mulliken charges are not reliable. The theoretical vibrational frequencies of aniline, calculated by the B3LYP method, show excellent agreement with the available experimental data. In contrast, the MP2 method is deficient in predicting the frequencies of several modes in aniline, despite the use of the extended basis set in calculations. The frequencies of aniline radical cation, calculated at the UB3LYP/6-311++G(df,pd) level, are in very good agreement with the recently reported experimental data from zero kinetic energy photoelectron and infrared depletion spectroscopic studies. The clear- cut assignment of the IR and Raman spectra of the investigated molecules has been made on the basis of the calculated potential energy distributions. Several bands in the spectra have been reassigned. It is shown that ionization of aniline can be easily identified by the appearance of the very strong band at about 1490 cm-1, in the Raman spectrum. The redshift of the N-H stretching frequencies and the blueshift of the C-H stretching

  3. First principles study of structural, electronic and magnetic properties of magnesium

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    We investigated the structural, electronic, and magnetic properties of Mg, in the CS (simple cubic), NiAs (Nickel arsenide), FCC (rock-salt), R (Rhombohedral), Diamond and WZ (wurtzite) phases. Calculations were performed using the first-principles pseudo-potential method within the framework of spin-density functional theory (DFT).

  4. 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

  5. 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.

  6. Electron Scattering and Nuclear Structure

    ERIC Educational Resources Information Center

    Trower, W. P.; Ficenec, J. R.

    1971-01-01

    Presents information about the nucleus gained by studies of electron scattering. Discusses what can be implied about the shape of the charge distribution, the nucleus positions, the vibrational modes of the nucleus, the momentum of the nucleus, and the granularity and core structures of the nucleus. (DS)

  7. 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.

  8. Ab initio study of pressure induced structural and electronic properties in uranium monobismuthide

    NASA Astrophysics Data System (ADS)

    Pataiya, Jagdish; Aynyas, Mahendra; Makode, C.; Singh, A.; Sanyal, Sankar P.

    2014-04-01

    We have investigated the pressure induced structural and electronic properties of uranium monobismuthide. 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). We predict structural phase transition from NaCl to CsCl-type structure at a pressure of 4.6 GPa. From energy band diagram it is observed that UBi exhibits metallic behavior. The calculated equilibrium lattice parameter is in good agreement with the experimental and other theoretical work.

  9. Ab initio study of pressure induced structural and electronic properties in uranium monobismuthide

    SciTech Connect

    Pataiya, Jagdish Makode, C.; Aynyas, Mahendra; Singh, A.; Sanyal, Sankar P.

    2014-04-24

    We have investigated the pressure induced structural and electronic properties of uranium monobismuthide. 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). We predict structural phase transition from NaCl to CsCl-type structure at a pressure of 4.6 GPa. From energy band diagram it is observed that UBi exhibits metallic behavior. The calculated equilibrium lattice parameter is in good agreement with the experimental and other theoretical work.

  10. 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.

  11. Computational full electron structure study of biological activity in Cyclophilin A.

    PubMed

    Zhou, Wenjin; Rossetto, Allison M; Pang, Xiaodong; Zhou, Linxiang

    2016-01-01

    Cyclosporine (CsA) is widely used in organ transplant patients to help prevent the patient's body from rejecting the organ. CsA has been shown to be a safe and highly effective immunosuppressive drug that binds with the protein Cyclophilin A (CypA) at active sites. However, the exact mechanism of this binding at the molecular level remains unknown. In this project, we elucidate the binding of CsA to CypA at the molecular level by computing their electron structures and revealing their interactions. We employ a novel technique called electron Computer-Aided Drug Design (eCADD) on the protein's full electron structure along with its hydrophobic pocket and the perturbation theory of the interaction between two wave functions. We have identified the wave function of CypA, the biological active residues and active atoms of CypA and CsA, the interaction site between CypA and CsA, and the hydrogen bonds in the ligand CsA binding site. All these calculated active residues, active atoms, and hydrogen bonds are in good agreement with recorded laboratory experiments and provide guidelines for designing new ligands of CypA. We believe that our eCADD framework can provide researchers with a cost-efficient new method of drug design based on the full electron structure of proteins. PMID:26264861

  12. 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.

  13. Electronic correlations, magnetism, and structure of Fe-Al subsystems: An LDA+U study

    NASA Astrophysics Data System (ADS)

    Lechermann, F.; Fähnle, M.; Meyer, B.; Elsässer, C.

    2004-04-01

    The influence of electronic correlations on the intimate relations between magnetism and structure of Fe-Al subsystems is investigated by the LDA+U method in the two currently used versions, around mean field (AMF) and fully localized limit (FLL). The calculations were performed with the new Stuttgart spin-polarized ab initio mixed-basis pseudopotential LDA+U code which is able to calculate both total energies and forces and thus to deal with structural relaxations. Both LDA+U versions yield coherent results concerning the energetical hierarchy for Fe3Al, i.e., a stabilization of the experimentally stable D03 structure against the L12 structure at moderate values of U, although the details concerning absolute energy shifts, lattice constant, and magnetism differ. For Fe impurities in Al the AMF result resembles the local-spin-density approximation result of a vanishing magnetic moment through structural relaxations, whereas with the FLL functional the magnetic moment remains finite.

  14. 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.

  15. The molecular structure of barium dibromide: an electron diffraction and quantum chemical study

    NASA Astrophysics Data System (ADS)

    Hargittai, Magdolna; Kolonits, Mária; Schultz, György

    2001-06-01

    The molecular structure of barium dibromide was determined by gas-phase electron diffraction, ab initio quantum chemical calculations, and joint electron diffraction/vibratonal spectroscopic analyses. All techniques yield consistently an unambiguously bent geometry. The following geometrical parameters were obtained: rg(Ba-Br) 2.911±0.006 Å, re(Ba-Br) 2.899±0.007 Å, ∠ aBr-Ba-Br 137.0±2.5° and ∠ eBr-Ba-Br 137.1±4.9°.

  16. 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.

  17. 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.

  18. Hybrid density functional study of the structural, bonding, and electronic properties of bismuth vanadate

    NASA Astrophysics Data System (ADS)

    Kweon, Kyoung E.; Hwang, Gyeong S.

    2012-10-01

    The structure and property prediction of metal oxides can significantly be improved by incorporating exact Hartree-Fock (HF) exchange into density functional theory (DFT), which is the so-called hybrid DFT. We explored the impact of HF exchange inclusion on the predicted structural, bonding, and electronic properties of bismuth vanadate (BiVO4), with particular attention to the difference between its monoclinic and tetragonal scheelite phases. The applied exchange-correlation (xc) functionals include the gradient corrected Perdew-Burke-Ernzerhof (PBE) and the PBE-HF hybrid functionals with HF exchange amounts of 10%, 25%, and 50%. We find that the PBE-HF25% yields a monoclinic structure in very close agreement with the experimentally determined structure, while the PBE-HF50% tends to overestimate the monoclinic distortion and the PBE/PBE-HF10% can hardly identify a distinct monoclinic configuration at ambient conditions. Electronic structure analysis reveals that the increasing monoclinic distortion with the amount of HF exchange is related to the enhancement of hybridization between Bi 6s-O 2p antibonding states and unoccupied Bi 6p states. The bonding mechanisms and band structures of the monoclinic and tetragonal phases of BiVO4 were also investigated, and we discuss how the predictions are sensitive to the xc functional choice.

  19. Study of structural, electronic and optical properties of tungsten doped bismuth oxychloride by DFT calculations.

    PubMed

    Yang, Wenjuan; Wen, Yanwei; Chen, Rong; Zeng, Dawen; Shan, Bin

    2014-10-21

    First-principle calculations have been carried out to investigate structural stabilities, electronic structures and optical properties of tungsten doped bismuth oxychloride (BiOCl). The structures of substitutional and interstitial tungsten, and in the form of WO6-ligand-doped BiOCl are examined. The substitutional and interstitial tungsten doping leads to discrete midgap states within the forbidden band gap, which has an adverse effect on the photocatalytic properties. On the other hand, the WO6-ligand-doped BiOCl structure induces a continuum of hybridized states in the forbidden gap, which favors transport of electrons and holes and could result in enhancement of visible light activity. In addition, the band gap of WO6-BiOCl decreases by 0.25 eV with valence band maximum (VBM) shifting upwards compared to that of pure BiOCl. By calculating optical absorption spectra of pure BiOCl and WO6-ligand-doped BiOCl structure, it is found that the absorption peak of the WO6-ligand-doped BiOCl structure has a red shift towards visible light compared with that of pure BiOCl, which agrees well with experimental observations. These results reveal the tungsten doped BiOCl system as a promising material in photocatalytic decomposition of organics and water splitting under sunlight irradiation. PMID:25179434

  20. Density functional theory studies of the structure and electronic structure of pure and defective low index surfaces of ceria

    NASA Astrophysics Data System (ADS)

    Nolan, Michael; Grigoleit, Sonja; Sayle, Dean C.; Parker, Stephen C.; Watson, Graeme W.

    2005-02-01

    We present periodic density functional theory (DFT) calculations of bulk ceria and its low index surfaces (1 1 1), (1 1 0) and (1 0 0). We find that the surface energies increase in the order (1 1 1) > (1 1 0) > (1 0 0), while the magnitude of the surface relaxations follows the inverse order. The electronic properties of the bulk and surfaces are analysed by means of the electronic density of states and the electron density. We demonstrate that the bonding in pure ceria is partially covalent and analysis of the resulting electronic states confirms the presence of localised Ce 4f states above the Fermi level. The surface atoms show only a small change in the charge distribution in comparison to the bulk and from the DOS the main differences are due to the changes in the oxygen 2p and cerium 5 d states. Investigation of the atomic and electronic structure of an oxygen vacancy on the (1 0 0) surface shows the problems DFT can have with the description of strongly localised systems, wrongly predicting electron delocalisation over all of the cerium atoms in the simulation cell. We demonstrate an improvement in the description of the strongly correlated cerium 4f states in partially reduced ceria by applying the DFT+U methodology, which leads to the appearance of a new gap state between the valence band and the empty Ce 4f band. Analysis of the partial charge density shows that these states are localised on the Ce III ions neighbouring the oxygen vacancy. In terms of classical defect chemistry, the vacancy is bound by two neighbouring Ce III ions, which have been reduced from Ce IV, i.e. VO··+2CeCe'. The remaining Ce ions are in the Ce IV oxidation state. The localisation of Ce 4f electrons modifies the predicted structure of the defective surface.

  1. Experimental (FT-IR and FT-Raman), electronic structure and DFT studies on 1-methoxynaphthalene

    NASA Astrophysics Data System (ADS)

    Govindarajan, M.; Ganasan, K.; Periandy, S.; Karabacak, M.

    2011-08-01

    In this work, FT-IR and FT-Raman spectra of 1-methoxynapthalene (C 11H 10O) have been reported in the regions 4000-400 cm -1 and 3500-100 cm -1, respectively. Density functional method (DFT) has been used to calculate the optimized geometrical parameters, atomic charges, vibrational wavenumbers and intensity of the vibrational bands. The vibrational frequencies have been calculated and scaled values are compared with experimental FT-IR and FT-Raman spectra. The structure optimizations and normal coordinate force field calculations are based on density functional theory (DFT) method with B3LYP/3-21G, B3LYP/6-31G, B3LYP/6-31G(d,p) and B3LYP/6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers are made on the basis of potential energy distribution (PED). The optimized geometric parameters are compared with experimental values of naphthoic acid. The results of the calculation shows excellent agreement between experimental and calculated frequencies in B3LYP/6-311++G(d,p) basis set. The effects due to the substitutions of methyl group and carbon-oxygen bond are also investigated. A study on the electronic properties, such as excitation energies and wavelengths, were performed by time-dependent DFT (TD-DFT) approach. HOMO and LUMO energies are calculated that these energies show charge transfer occurs within the molecule.

  2. 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.

  3. 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

  4. First-principles study of the electronic structure of organic semiconductors

    NASA Astrophysics Data System (ADS)

    Sharifzadeh, Sahar; Biller, Ariel J.; Kronik, Leeor; Neaton, Jeffrey B.

    2010-03-01

    Organic semiconductors are promising materials for next generation organic photovoltaics, with the characterization of their spectroscopic properties vital to improving the potential of such technologies. Here, we use density functional theory and many-body perturbation theory within the GW approximation to explore quantitatively the electronic structure of prototypical organic semiconductor crystals and compare directly with valence-band photoemission data. For pentacene and PTCDA, computed gas-phase ionization energies and electron affinities are compared with calculated crystal-phase quasiparticle band structures, and relationships between shifts in orbital energy with change of phase and static polarization of the bulk are discussed and compared with experiment. We acknowledge DOE, NSF, BASF, and ISF for financial support, and NERSC for computational resources.

  5. High-Pressure and Electronic Band Structure Studies on MoBC

    NASA Astrophysics Data System (ADS)

    Falconi, R.; de la Mora, P.; Morales, F.; Escamilla, R.; Camacho, C. O.; Acosta, M.; Escudero, R.

    2015-05-01

    In this work, high-pressure electrical resistivity measurements and electronic structure analysis on the intermetallic MoBC system are presented. Electrical resistivity measurements up to about 5 GPa using a diamond anvil cell on MoBC revealed that decreases in a non-monotonic way. Using Linearized Augmented Plane Wave method based on Density Functional Theory, we investigate the changes in the electronic structure of this compound as a function of pressure. The states at the Fermi level mainly come from the d orbitals of molybdenum atoms. As the pressure increases, the band width is enhanced and the total density of states at the Fermi level decreases. The Fermi surface for this compound possesses a two-dimensional character which prevails under an applied pressure of about 10 GPa. The results are compared with the chemical pressure effects on induced by the gradual and non-simultaneous elimination of B and C in the compound.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Structural and electronic studies of metal hexacyanoferrates based cathodes for Li rechargeable batteries

    NASA Astrophysics Data System (ADS)

    Giorgetti, Marco; Mignani, Adriana; Aquilanti, Giuliana; Conti, Paolo; Fehse, Marcus; Stievano, Lorenzo

    2016-05-01

    Operando XANES and EXAFS spectra on the newly prepared Fe hexacyanocobaltate active material for positive electrodes in lithium batteries have been recorded at the XAFS beamline of Elettra using a suitable in situ cell. In this way, it was possible to follow in detail the main structural and electronic changes during the charge and discharge processes of the battery. The use of a chemometric approach for data analysis is also underlined.

  11. Theoretical study of structure and electronic properties of cyano-substituted pyrroles

    NASA Astrophysics Data System (ADS)

    Rimarčík, Ján; Lukeš, Vladimír; Klein, Erik; Griesser, Markus; Kelterer, Anne-Marie

    2008-11-01

    DFT and ab initio MP2 calculations of optimal geometries, dipole moments, polarizabilities, excitation energies and enthalpies of hydrogen or proton transfer from N-H group for cyano derivatives of pyrrole are presented. CN groups in α and β positions have distinct effects on electron spectra absorption bands. CN in α position causes larger bathochromic shift in comparison to β position. N-H bond dissociation enthalpies (BDE) of substituted pyrroles are higher by 7 kJ mol -1 than pyrrole BDE. Number and position of CN groups do not affect BDEs. Proton affinities of pyrrolyl anions and enthalpies of electron transfer from these anions are proportional to the number of CN groups in molecule. Each CN group causes decrease in proton affinity by 72 kJ mol -1 and 73 kJ mol -1 rise in electron transfer enthalpy. For several studied pyrroles, BDEs, proton affinities and electron transfer enthalpies in water and benzene were computed.

  12. Systematic study of the electronic structure and optical properties of icosahedral boron and boron compounds

    NASA Astrophysics Data System (ADS)

    Li, Dong

    1997-11-01

    A systematic study of the electronic structures, total energies and optical properties of B12-based boron and boron-rich compounds and boron oxide compounds has been conducted by the first-principles orthogonalized linear combination of atomic orbitals method. The materials involved are: α-r-B12, B12As2,/ B12P2,/ B11C(CBC)/ (or/ B4C),/ B13C2,/ B12O2,/ (B10Si2)Si2,/ (B10Si2)Si2-I, B2O3-I and B2O3-II. The band structures show that α-r-B12,/ B12As2,/ B12P2,/ B11C(CBC),/ B12O2,/ (B10Si2)Si2, and (B10Si2)Si2-I are semiconductors with band gaps ranging from 1.29 eV to 3.04 eV while B13C2 is a metal with an intrinsic hole at the top of the valence band below a semiconductor-like gap. The study also shows that B2O3-I and B2O3-II are wide gap insulators with calculated LDA gaps of 6.20 eV and 8.85 eV separately. The calculated density of states are resolved into atomic and orbital partial components and the valence-charge distributions are also studied. The natural bonding characteristics in these crystals are illuminated by evaluating the Mulliken effective charges on each atom and overlap populations between pairs of atoms. It is shown that inter-icosahedral bonding is much stronger than the intra-icosahedral bonding in the B12- based crystals. The chain elements in B12As2,/ B12P2,/ (B10Si2)Si2 and (B10Si2)Si2-I donate electrons to the icosahedra, while B11C(CBC),/ B13C2 and B12O2 gain a slight amount of charge in forming strong covalent bonds. For boron oxide compounds, B2O3-II is found to be more ionic than B2O3-I. It is also concluded that the sp2 planar bonding in B2O3-I is stronger than the sp3 tetrahedral bonding in B2O3-II. The bulk moduli of α-r-B12,/ B12As2,/ B12P2,/ B11C(CBC),/ B13C2 and B12O2 are estimated by means of total energy calculation as a function of crystal volume, and are to be considered as upper limits. We have also calculated the interband optical conductivities and the complex dielectric functions. Static dielectric constants for icosahedral

  13. 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.

  14. Electronic structure study of TiB2 and Ti2B

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    In this paper, the electronic properties of TiB2 and Ti2B 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. TiB2 crystallizes in the hexagonal AlB2 type structure which is designated as C32 with the space group P6/mmm. While the crystal structure of Ti2B described in this paper is isomorphous to the body centered tetragonal (Al2Cu - type) structure with space group I4/mcm.

  15. The Hydrogen Catalyst Cobaloxime – a Multifrequency EPR & DFT Study of Cobaloxime’s Electronic Structure

    PubMed Central

    Niklas, Jens; Mardis, Kristy L.; Rakhimov, Rakhim R.; Mulfort, Karen L.; Tiede, David M.; Poluektov, Oleg G.

    2012-01-01

    Solar fuels research aims to mimic photosynthesis and devise integrated systems that can capture, convert, and store solar energy in the form of high-energy molecular bonds. Molecular hydrogen is generally considered an ideal solar fuel as its combustion is essentially pollution-free. Cobaloximes rank among the most promising earth-abundant catalysts for the reduction of protons to molecular hydrogen. We have used multifrequency EPR spectroscopy at X-band, Q-band, and D-band combined with DFT calculations to reveal electronic structure and establish correlations between structure, surroundings and catalytic activity of these complexes. To assess the strength and nature of ligand cobalt interactions, the BF2-capped cobaloxime, Co(dmgBF2)2, was studied in a variety of different solvents with a range of polarities and stoichiometric amounts of potential ligands to the cobalt ion. This allows the differentiation of labile and strongly coordinating axial ligands for the Co(II) complex. Labile, or weakly coordinating, ligands like methanol result in larger g-tensor anisotropy than strongly coordinating ligands like pyridine. Additionally, a coordination number effect is seen for the strongly coordinating ligands with both singly-ligated LCo(dmgBF2)2 and doubly-ligated L2Co(dmgBF2)2. The presence of two strongly coordinating axial ligands leads to the smallest g-tensor anisotropy. The relevance of the strength of the axial ligand(s) to the catalytic efficiency of Co(dmgBF2)2 is discussed. Finally, the influence of molecular oxygen and formation of Co(III) superoxide radicals LCo(dmgBF2)2O2• is studied. The experimental results are compared with a comprehensive set of DFT calculations on Co(dmgBF2)2 model systems with various axial ligands. Comparison with experimental values for the “key” magnetic parameters like g-tensor and 59Co hyperfine coupling tensor allows the determination of the conformation of the axially ligated Co(dmgBF2)2 complexes. The data presented

  16. First-principles study of the crystal and electronic structures of {alpha}-tetragonal boron

    SciTech Connect

    Hayami, Wataru; Otani, Shigeki

    2010-07-15

    The crystal and electronic structures of {alpha}-tetragonal ({alpha}-t) boron were investigated by first-principles calculation. Application of a simple model assuming 50 atoms in the unit cell indicated that {alpha}-t boron had a metallic density of state, thus contradicting the experimental fact that it is a p-type semiconductor. The presence of an additional two interstitial boron atoms at the 4c site made {alpha}-t boron semiconductive and the most stable. The cohesive energy per atom was as high as those of {alpha}- and {beta}-rhombohedral boron, suggesting that {alpha}-t boron is produced more easily than was previously thought. The experimentally obtained {alpha}-t boron in nanobelt form had about two interstitial atoms at the 8i sites. We consider that the shallow potential at 8i sites generates low-energy phonon modes, which increase the entropy and consequently decrease the free energy at high temperatures. Calculation of the electronic band structure showed that the highest valence band had a larger dispersion from {Gamma} to Z than from {Gamma} to X; this indicated a strong anisotropy in hole conduction. - Graphical abstract: Calculated electron densities of B{sub 50} and B{sub 50}+2B at site 4c (configuration B).

  17. First-principles study of structural, electronic and optical properties of ZnF2

    NASA Astrophysics Data System (ADS)

    Wu, Jian-Bang; Cheng, Xin-Lu; Zhang, Hong; Xiong, Zheng-Wei

    2014-07-01

    The structural, electronic, and optical properties of rutile—, CaCl2-, and PdF2—ZnF2 are calculated by the plane-wave pseudopotential method within the density functional theory. The calculated equilibrium lattice constants are in reasonable agreement with the available experimental and other calculated results. The band structures show that the rutile—, CaCl2-, and PdF2—ZnF2 are all direct band insulator. The band gaps are 3.63, 3.62, and 3.36 eV, respectively. The contribution of the different bands was analyzed by the density of states. The Mulliken population analysis is performed. A mixture of covalent and weak ionic chemical bonding exists in ZnF2. Furthermore, in order to understand the optical properties of ZnF2, the dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, and optical reflectivity are also performed in the energy range from 0 to 30 eV. It is found that the main absorption parts locate in the UV region for ZnF2. This is the first quantitative theoretical prediction of the electronic and optical properties of ZnF2 compound, and it still awaits experimental confirmation.

  18. First-principles study of electronic structures and phase transitions of lithiated molybdenum disulphide

    NASA Astrophysics Data System (ADS)

    Li, Jun; Chen, Xiaobo

    2012-02-01

    By first-principles calculations, electronic structures of MoS2, intercalation-induced 2H to 1T phase transition and reversibility are investigated. It is revealed that change of interlayer stacking from 2H to 3R imposes negligible influence on the band structure and stability of MoS2. In contrast, the change of intralayer stacking from 2H to 1T changes the character of p-d repulsion, resulting in a semiconductor-to-metal transition. We demonstrate that the Kohn-Sham band energy, rather than the coulomb repulsion energy, plays dominant roles in both the phase stabilization and transition during Li intercalation. It is found that the evolution of 1T phase is crucially determined by chemical hardness, which underlies the cycle irreversibility. Due to the charge-density-wave (CDW) phase, Li extraction is impeded by the enhancement of Li-host binding. It is indicated that the cycle reversibility can be improved by electron-donor doping in MoS2, because the resultant pre-reduction of Mo and S eliminates the electron transfer from Li to host.

  19. 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.

  20. Van der Waals density functional study of the structural and electronic properties of La-doped phenanthrene

    SciTech Connect

    Yan, Xun-Wang; Faculty of Physics and Electronic Technology, Hubei University, Wuhan 430062; State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Science, Beijing 100190, China and School of Physics and Electrical Engineering, Anyang Normal University, Henan 455000 ; Huang, Zhongbing; Faculty of Physics and Electronic Technology, Hubei University, Wuhan 430062 ; Lin, Hai-Qing

    2013-11-28

    By the first principle calculations based on the van der Waals density functional theory, we study the crystal structures and electronic properties of La-doped phenanthrene. Two stable atomic geometries of La{sub 1}phenanthrene are obtained by relaxation of atomic positions from various initial structures. The structure-I is a metal with two energy bands crossing the Fermi level, while the structure-II displays a semiconducting state with an energy gap of 0.15 eV, which has an energy gain of 0.42 eV per unit cell compared to the structure-I. The most striking feature of La{sub 1}phenanthrene is that La 5d electrons make a significant contribution to the total density of state around the Fermi level, which is distinct from potassium doped phenanthrene and picene. Our findings provide an important foundation for the understanding of superconductivity in La-doped phenanthrene.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

    Chan, Kwai S.; Peng, Xihong

    2016-05-01

    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.

  7. 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.

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

    PubMed

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

    2016-05-01

    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

  9. 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

  10. 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.

  11. 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.

  12. 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

    2016-04-01

    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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Electronic structure of some thymol derivatives correlated with the radical scavenging activity: theoretical study.

    PubMed

    Javan, Ashkan Jebelli; Javan, Marjan Jebeli

    2014-12-15

    Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of upmost importance in the living cell. Thymol derivatives exhibit various antioxidant activities and potential health benefits. Exploration of structure-radical scavenging activity (SAR) was approached with a wide range of thymol derivatives. To accomplish this task, the DPPH experimental assay along with quantum-chemical calculations were also employed for these compounds. By comparing the structural properties of the derivatives of interest, their antioxidant activity was explained by the formation of an intramolecular hydrogen bond and the presence of unsaturated double bond (-CHCH substituent) in their radical spices. Moreover, the delocalization of odd electrons in these radicals has been investigated by natural bond orbital analysis and interpretation of spin density maps. Reactivity order of the compound towards the ROS: HO, HOO, and O2(-) was found to be as HO>HOO > O2(-). PMID:25038698

  18. 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.

  19. Electronic structure studies of high-T/sub c/ perovskites and related materials

    SciTech Connect

    Wachs, A.L.; Turchi, P.E.A.; Kaiser, J.H.; West, R.N.; Howell, R.H.; Jean, Y.C.; Merkle, K.L.; Revcolevschi, A.; Fluss, M.J.

    1988-10-01

    We have performed 2D-ACPAR measurements on La/sub 2/CuO/sub 4/ and NiO. The ACPAR distributions were very isotropic, with small anisotropic deviations on the order of 10% of the total counts. It was not possible to clearly discern a Fermi surface in either set of data, nor was it possible to identify any features with the symmetry and periodicity of the crystalline reciprocal lattices. Attempts to model both systems by starting with a localized ionic picture and allowing covalency overlap to take place among the atoms comprising an isolated metal atom-oxygen octahedral cluster have proven successful. This result suggests that it might be appropriate for analyses of the electronic structure for high-T/sub c/ perovskites to begin with the ansatz of localized electronic states. This approach has worked very well for the transition-metal monoxides. Finally, application of the LCW formalism to data from both systems yields a result very close to filled-band behavior. We believe the deviations from the latter are significant, but that they originate from positronic wavefunction mixing of the electronic states and not from a Fermi surface. 9 refs., 3 figs.

  20. Resonance Raman studies of substituent effects on the electronic structure of phenoxyl radicals

    SciTech Connect

    Tripathi, G.N.R.; Schuler, R.H.

    1988-09-08

    The resonance Raman spectra of para-substituted phenoxyl radicals (XC/sub 6/H/sub 4/O/center dot/; X = CH/sub 3/, F, Cl, Br, OCH/sub 3/, OH) observed by time-resolved techniques in aqueous medium, exhibit a wide variation in spectral features intermediate between phenoxyl and /rho/-benzosemiquinone anion radicals. The ..nu../sub 7a/ (CO stretch) vibration, which is strongly enhanced on Raman excitation in resonance with the electronic transition in the approx. 400-nm region, appears in a narrow frequency range 1511-1518 cm/sup /minus/1/, indicating that the CO bond in the ground electronic state of these radicals is very similar to that of phenoxyl (..nu../sub 7a/ at 1505 cm/sup /minus/1/). The relative intensities of the ..nu../sub 8a/ bands (CC stretch), observed in the 1552-1613-cm/sup /minus/1/ region, change dramatically with the electronic properties of the substituent group. This vibration, which is not apparent in the Raman spectrum of phenoxyl excited at 400 nm, is observed with an intensity comparable to the of the ..nu../sub 7a/ vibration in the /rho/-bromo, /rho/-methoxy, and /rho/-hydroxy derivatives. The Raman intensities show that the electronic structures in the excited states of the /rho/-methoxy and /rho/-fluoro-, and p-chloro-substituted radicals are essentially phenoxyl like, while the structures in p-methoxy and p-hydroxy derivatives approach that of /rho/-benzosemiquinone anion radical as a result of strong interaction of the substituent's p..pi.. electrons with the phenoxyl ..pi.. system. The excited state of /rho/-bromophenoxyl radical represents an important intermediate case. The resonance enhancement of the ..nu../sub 9a/ CH bending vibration, observed at approx. 1160 cm/sup /minus/1/, parallels that of the ..nu../sub 8a/ phenyl mode and provides an important diagnostic for assignment of the latter vibration.

  1. Electronic structure of black sodalite

    NASA Astrophysics Data System (ADS)

    Sankey, Otto F.; Demkov, Alexander A.; Lenosky, Thomas

    1998-06-01

    The electronic structure of black sodalite, Na8(AlSiO4)6, is determined in the local-spin-density approximation (LSDA). This structure has six Na atoms to compensate the six Al atoms, leaving two excess Na atoms. A band-gap electronic state is induced in the wide oxide gap by the excess sodium, and has ``particle in a box'' behavior. Magnetic orderings of these gap states are studied. Analytic models show that an antiferromagnetic ordering is lowest in energy in the LSDA. A self-consistent LSDA calculation shows the system to change from a metal to an antiferromagnetic insulator when spin orderings are allowed. Hopping and Hubbard-U parameters are estimated, and the many-body correlated Hubbard model is solved using a constrained path Monte Carlo technique, which again predicts the system to be antiferromagnetic with a Tc of order 50 K.

  2. 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.

  3. 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

  4. Ab initio study on the electronic structure and vibration modes of alkali and alkaline-earth amides and alanates

    NASA Astrophysics Data System (ADS)

    Tsumuraya, Takao; Shishidou, Tatsuya; Oguchi, Tamio

    2009-05-01

    We study the electronic structure and vibrational modes of several amides M(NH2)n and alanates M(AlH4)n (M = K, Na, Li, Ca and Mg), focusing on the role of cation states. Calculated breathing stretching vibration modes for these compounds are compared with measured infrared and Raman spectra. In the amides, we find a significant tendency such that the breathing mode frequencies and the structural parameters of NH2 vary in accordance with the ionization energy of cation. The tendency may be explained by the strength in hybridization between cation orbitals and molecular orbitals of (NH2)-. The microscopic mechanism of correlations between the vibration frequencies and structural parameters is elucidated in relation to the electronic structure. A possible similar tendency in the alanates is also discussed.

  5. Ab initio study of the electronic structures of lithium containing diatomic molecules and ions

    NASA Astrophysics Data System (ADS)

    Boldyrev, Alexander I.; Simons, Jack; Schleyer, Paul von R.

    1993-12-01

    Ab initio calculations are used to provide bond lengths, harmonic frequencies, and dissociation energies of low-lying electronic states for LiX, LiX+, and LiX- (with X=Li through F and Na through Cl). Most of these species represent hitherto experimentally unknown molecules or ions, which provides the focus of the work presented here. All of these species are stable to dissociation and the anions are stable to loss of an electron. Differences among the electronic structures of the valence isoelectronic LiX; and HX, LiX+, and HX+; and LiX- and HX- species are analyzed. Optimized geometries, dissociation energies, ionization potentials, and electron affinities were calculated for the following ground states of the respective species: 1Σ+ for Li2(1Σ+g) LiNa, LiBe+, LiBe-, LiMg+, LiMg-, LiF, LiAl, LiS-, and LiCl; 2Σ+ for Li+2(2Σ+g), Li-2(2Σ+u) LiBe, LiB+, LiF-, LiNa+, LiNa-, LiMg, LiAl+, and LiCl-; 2Πr for LiB-, LiAl-; 2Πi for LiO, LiF+, LiS, and LiCl+; 3Πr for LiB, LiC+, and LiSi+; 3Σ- for LiN, LiO+, LiSi-, LiP, and LiS+; 4Σ- for LiC, LiN+, LiN-, LiSi, LiP+, and LiP-; and 5Σ- for LiC-.

  6. Electronic structure of CeO studied by a four-component relativistic configuration interaction method.

    PubMed

    Moriyama, Hiroko; Tatewaki, Hiroshi; Yamamoto, Shigeyoshi

    2013-06-14

    We studied the ground and excited states of CeO using the restricted active space CI method in the energy range below 25,000 cm(-1). Energy levels are computed to within errors of 2700 cm(-1). Electron correlation effects arising from the ionic core composed of Ce5s, 5p, 4f(*), 5d(*), and O2s, 2p spinors play crucial role to CeO spectra, as well as correlation effects of electrons distributed in the valence Ce 4f, 5d, 6s, and 6p spinors. Here, 4f(*) and 5d(*) denote spinors expanded to describe electron polarization between Ce and O. A bonding mechanism is proposed for CeO. As the two separate atoms in their ground states, Ce(4f(1)5d(1)6s(2))(1)G4 and O(2s(2)2p(4))(3)P2, approach each other, a CeO(2+) core is formed by two-electron transfer from Ce5d, 6s to O2p. Inside this ellipsoidal ion, a valence bond between Ce5p and O2s and an ionic bond between O2p and Ce5p are formed with back-donation through Ce 4f(*) and 5d(*). PMID:23781798

  7. 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.

  8. 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.

  9. 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

  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. Study of the electronic structure of CaFeO3

    NASA Astrophysics Data System (ADS)

    Yang, J. B.; Kim, M. S.; Cai, Q.; Zhou, X. D.; Anderson, H. U.; James, W. J.; Yelon, W. B.

    2005-05-01

    We have studied the charge disproportionation phenomenon in CaFeO3 using the local-spin density approximation with the on-site Coulomb interaction parameter U and exchange parameter J. The calculation reveals that the total number of the 3d electrons is about 5.1 for both Fe(1)(Fe5+) and Fe(2)(Fe3+) atoms, and that there are about 0.25 electron holes in the O-2p band. Therefore, the charge disproportionation can be more accurately described as 2d5L(Fe4+)=d5L2(Fe5+)+d5(Fe3+), where L denotes a hole in the oxygen 2p band, instead of 2d4(Fe4+)=d3(Fe5+)+d5(Fe3+). The hybridization between the Fe-3d and O-2p orbitals is stronger for Fe(1) than for Fe(2) due to the shorter Fe(1)-O bond. The hyperfine magnetic field contributed from conduction electron polarization is larger for Fe(2), resulting from a stronger s-d hybridization between the s orbital of Fe(2) and the d orbitals of its neighboring Fe(1) atoms. The on-site Coulomb repulsion and the exchange interaction increase the splitting between the occupied spin up and unoccupied spin down bands of Fe atoms. Fe-3d electrons become localized and the occupied d-band shifts to a lower energy range, even below the O-2p level. The calculated magnetic moments, hyperfine fields, and electron charge density agree well with the experimental data.

  12. On the Electronic and Geometric Structures of Armchair GeC Nanotubes: A Hybrid Density Functional Study

    NASA Astrophysics Data System (ADS)

    Rathi, Somilkumar; Ray, Asok

    2008-03-01

    Ab initio calculations within the framework of hybrid density functional theory and finite cluster approximation have been performed for the electronic and geometric structures of three different types of armchair germanium carbide nanotubes from (3, 3) to (11, 11). Full geometry and spin optimizations with unrestricted symmetry have been performed. A detailed comparison of the structures and stabilities of the three types of nanotubes will be presented. The dependence of the electronic band gaps on the respective tube diameters, energy density of states, dipole moments as well as Mulliken charge distributions have been investigated. Radial buckling of tube along with bond length variations is also studied. All armchair GeC nanotubes investigated so far are semiconducting in nature. Applications in the field of nano-optoelectronic devices, molecular electronics and band gap engineering are envisioned for GeC nanotubes.

  13. Electron diffraction study of the molecular structure of 2,5-dimethylthiophene

    NASA Astrophysics Data System (ADS)

    Tanabe, Masayuki; Takeuchi, Hiroshi; Konaka, Shigehiro

    1993-12-01

    The molecular structure of 2,5-dimethylthiophene has been determined by gas electron diffraction. Ab initio SCF calculations at the 3-21G* level were carried out and used as an aid to the analysis. The torsional vibrations of two methyl groups were treated as large-amplitude motions. A CH Me bond was found to be cis with respect to the SC bond in the equilibrium structure and the three-fold potential barrier was determined to be 1.0(7) kcal mol -1. The structural parameter values with estimated error limits (3σ) in parentheses are as follows: rg(SC) = 1.736(2) Å, rg(CC) = 1.372(4) Å, rg(CC Me) = 1.510(5) Å, rg(CH ring) = 1.098(6) Å, rg(CH Me) = 1.112 Å, ∠ αCSC = 92.6(5)°, ∠ αSCC ring = 110.7(5)°, ∠ αSCC Me = 121.6(4)°, ∠ αCCH = 123.4° and <∠ αHCH> = 108.1°, where <> denotes the average value. The values of r(CH Me) - r(CH ring), ∠CCH and <∠HCH> were taken from the 3-21G* calculations.

  14. Theoretical study of the electronic structure of binary and ternary first-stage alkali intercalation compounds of graphite

    SciTech Connect

    Tatar, R.C.

    1985-01-01

    Despite the tremendous number of theoretical and experimental studies of the electronic properties of the first-stage heavy alkali intercalation compounds of graphite - KC8, RbC8, and CsC8 - there is still a great deal of uncertainty in the electronic structures of these materials. The electronic structures of these materials - required for the interpretation of experimental results - were calculated previously by several techniques. Because of the inability of these calculations to satisfactorily resolve the interpretation of experiments, and questions concerning the approximations used in the previous calculations, an attempt is made to estimate the electronic structure in these materials using a state-of-the-art, self consistent pseudopotential technique with a mixed basis of plane waves and localized atomic orbitals. The goal is to provide a detailed first principles model of the electronic interactions in these materials that can form the basis for a variety of additional, model calculations that address the experimental issues. In addition, and attempt is made to elucidate more fully the microscopic basis for differences between the heavy-alkali compounds as well as the difference between the heavy-alkali compounds as a class and the compounds formed from the light alkali, lithium.

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  17. Re-examining the electronic structure of germanium: A first-principle study

    NASA Astrophysics Data System (ADS)

    Ekuma, C. E.; Jarrell, M.; Moreno, J.; Bagayoko, D.

    2013-11-01

    We report results from an efficient, ab initio method for self-consistent calculations of electronic and structural properties of Ge. Our non-relativistic calculations employed a GGA potential and LCAO formalism. The distinctive feature of our computations stem from the use of Bagayoko-Zhao-Williams-Ekuma-Franklin method. Our results are in agreement with experimental ones where the latter are available. In particular, our theoretical, indirect band gap (EgΓ-L) of 0.65 eV, at the experimental lattice constant of 5.66 Å, is in excellent agreement with experiment. Our predicted, equilibrium lattice constant is 5.63 Å, with corresponding EgΓ-L of 0.65 eV and a bulk modulus of 80 GPa.

  18. 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.

  19. Density-functional study of atomic and electronic structures of multivacancies in silicon carbide

    NASA Astrophysics Data System (ADS)

    Iwata, Jun-Ichi; Shinei, Chikara; Oshiyama, Atsushi

    2016-03-01

    We report the density-functional calculations that provide a firm theoretical framework to identify the multivacancies and unravel the underlying physics in the most stable silicon carbide polytype 4H-SiC. The calculations with the generalized gradient approximation (GGA) for the Si and C monovacancy, VSi and VC, have clarified the significantly lower formation energy of the C vacancy accompanied by the efficient pairing relaxation of the surrounding Si dangling bonds. Our GGA calculation also predicts a stable next-neighbor VCVC divacancy which is lower in the formation energy than the usual nearest-neighbor divacancy VCVSi discussed in the past. We also perform the calculations with the hybrid functional and confirm the stability of the next-neighbor VCVC divacancy. Our calculations indeed clarify that it is possible to detect the VCVC with its peculiar hyperfine coupling constants by the electron paramagnetic resonance (EPR) measurements. Based on the structural characteristics and the energetics for the monovacancy, we further propose an extended dangling-bond-counting (EDBC) model to choose the energetically favorable topological network of the vacant sites for the multivacancy. The GGA calculations combined with the EDBC model reveal that V3 and V6 are energetically favorable. The stable V3 is a nearest-neighbor complex of VC-VSi-VC , whereas the V6 is the high-symmetry V5 (the central VSi surrounded by four VC) plus a symmetry-breaking next-neighbor VC. We perform the GGA calculations for the electronic structure of such V3 and V6 and discuss the possibility of detecting these multivacancies. In particular, the EPR-detected ANN1 center is provisionally identified as the doubly positive trivacancy VC-VSi-VC .

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

    NASA Astrophysics Data System (ADS)

    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.

    2015-04-01

    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.

  1. A joint photoelectron spectroscopy and theoretical study on the electronic structure of UCl5- and UCl5.

    PubMed

    Su, Jing; Dau, Phuong Diem; Xu, Chao-Fei; Huang, Dao-Ling; Liu, Hong-Tao; Wei, Fan; Wang, Lai-Sheng; Li, Jun

    2013-10-01

    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(z³) and 5f(xyz) based molecular orbitals. The structures of both UCl5(-) and UCl5 are theoretically optimized and confirmed to have C(4v) 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 U-X interactions in UX5(-) are dominated by ionic bonding, with increasing covalent contributions for the heavier halogen complexes. PMID:23853153

  2. 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.

  3. Study on mutual interactions and electronic structures of hyaluronan with Lysine, 6-Aminocaproic acid and Arginine.

    PubMed

    Chytil, Martin; Trojan, Martin; Kovalenko, Alexander

    2016-05-20

    Interactions between polyelectrolytes and oppositely charged surfactants have been in a great interest for several decades, yet the conventional surfactants may cause a problem in medical applications. Interactivity between polysaccharide hyaluronan (HA) and amino acids Lysine, 6-Aminocaproic acid (6-AcA), and Arginine as an alternative system is reported. The interactions were investigated by means of rheology and electric conductance and the electronic structures were explored by the density functional theory (DFT). Lysine exhibits the strongest interaction of all, which was manifested, e.g. by nearly 6-time drop of the initial viscosity comparing with only 1.3-time lower value in the case of 6-AcA. Arginine interaction with HA was surprisingly weaker in terms of viscosity than that of Lysine due to a lower and delocalized charge density on its guanidine group. According to the DFT calculations, the binding of Lysine to HA was found to be more flexible, while Arginine creates more rigid structure with HA. PMID:26917367

  4. 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.

  5. Molecular structure and nicotinic activity of arecoline. A gas electron diffraction study combined with theoretical calculations

    NASA Astrophysics Data System (ADS)

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

    2005-01-01

    The molecular structure of arecoline (methyl 1,2,5,6-tetrahydro-1-methylnicotinate, ? has been determined by gas electron diffraction. Diffraction patterns were taken at about 370 K. Structural constraints for the data analysis were obtained from MP2/6-31G** calculations. Vibrational mean amplitudes and shrinkage corrections were calculated from the force constants obtained from the gas-phase vibrational frequencies and the B3LYP/6-31G** calculations. The electron diffraction data were well reproduced by assuming the mixture of four conformers. The determined structural parameters ( rg (Å) and ∠ (°)) for the main conformer with 3 σ in parentheses are as follows: < rg(N-C ring)>=1.456(4); rg(N-C methyl)=1.451 (d.p.); rg(C dbnd6 C)=1.339(9); < rg(C-C)>=1.512(3); rg(O-C methyl)=1.434(5); rg(C(O)-O)=1.355 (d.p.); rg(C dbnd6 O)=1.209(4); the out-of-plane angle of the methyl group=50.3(23); ∠C ringN ringC ring=112.8(30); ∠N ringC ringC ring(H 2)=110.5(16); <∠C ringC ringC ring>=118.4(5); ∠C dbnd6 CC(O)=116.8(7); ∠CC dbnd6 O=127.6(9); ∠CC-O=109.8(8), where the angle brackets denote averaged values and d.p. denotes dependent parameters. Fixing the abundances of the minor conformers, Ax-s- cis and Ax-s- trans, at the theoretical values (13% in total), those of the Eq-s- cis and Eq-s- trans conformers were determined to be 46(16) and 41(16)%, respectively. Here Ax and Eq denote the axial and equatorial directions of the N-CH 3 bond and s- cis and s- trans show the orientation of the methoxycarbonyl group expressed by the configuration of the C dbnd6 O and C dbnd6 C bonds. The N⋯O carbonyl distances of the Eq-s- cis and Ax-s- cis conformers are 4.832(13) and 4.874(16) Å, respectively. They are close to the N⋯N distance of the most abundant conformer of nicotine, 4.885(6) Å, suggesting that the Eq-s- cis and Ax-s- cis conformers have nicotinic activity.

  6. The electronic structure of alkali aurides. A four-component Dirac-Kohn-Sham study.

    PubMed

    Belpassi, Leonardo; Tarantelli, Francesco; Sgamellotti, Antonio; Quiney, Harry M

    2006-04-01

    Spectroscopic constants, including dissociation energies, harmonic and anharmonic vibrational frequencies, and dipole moments, are calculated for the complete alkali auride series (LiAu, NaAu, KAu, RbAu, CsAu). The four-component formulation of relativistic density functional theory has been employed in this study, using the G-spinor basis sets implemented recently in the program BERTHA. The performance of four standard nonrelativistic density functionals employed is investigated by comparing the results with the best available theoretical and experimental data. The present work provides the first theoretical predictions on the molecular properties of RbAu. The intermetallic bond that occurs in the alkali auride series is highly polar and is characterized by a large charge transfer from the alkali metals to gold. The extent of this electron transfer has been investigated using several different charge analysis methods, enabling us to reach some general conclusions on their relative performance. We further report a detailed analysis of the topological properties of relativistic electron density in the bonding region, discussing the features of this approach which characterize the nature of the chemical bond. We have also computed the fully relativistic density for the alkali halides MBr and MI (M = Li, Na, K, Rb, and Cs). The comparative study shows that, on the basis of several topological properties and the variation in bond lengths, the gold atom behaves similarly to a halogen intermediate between Br and I. PMID:16571062

  7. Inelastic Scattering in STEM for Studying Structural and Electronic Properties of Chalcogenide-Based Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Gunawan, Aloysius Andhika

    Transmission electron microscopy (TEM) relies upon elastic and inelastic scattering signals to perform imaging and analysis of materials. TEM images typically contain contributions from both types of scattering. The ability to separate the contributions from elastic and inelastic processes individually through energy filter or electron energy loss spectroscopy (EELS) allows unique analysis that is otherwise unachievable. Two prominent types of inelastic scattering probed by EELS, namely plasmon and core-loss excitations, are useful for elucidating structural and electronic properties of chalcogenide-based semiconductor nanocrystals. The elastic scattering, however, is still a critical part of the analysis and used in conjunction with the separated inelastic scattering signals. The capability of TEM operated in scanning mode (STEM) to perform localized atomic length scale analysis also permits the understanding of the nanocrystals unattainable by other techniques. Despite the pivotal role of inelastic scatterings, their contributions for STEM imaging, particularly high-angle annular dark field STEM (HAADF-STEM), are not completely understood. This is not surprising since it is currently impossible to experimentally separate the inelastic signals contributing to HAADF-STEM images although images obtained under bright-field TEM mode can be analyzed separately from their scattering contributions using energy-filtering devices. In order to circumvent such problem, analysis based on simulation was done. The existing TEM image simulation algorithm called Multislice method, however, only accounts for elastic scattering. The existing Multislice algorithm was modified to incorporate (bulk or volume) plasmon inelastic scattering. The results were verified based on data from convergent-beam electron diffraction (CBED), electron energy loss spectroscopy (EELS), and HAADF-STEM imaging as well as comparison to experimental data. Dopant atoms are crucial factors which control

  8. Electron Affinities and Electronic Structures of o-, m-, and p- Hydroxyphenoxyl Radicals: A Combined Low-Temperature Photoelectron Spectroscopic and Ab initio Calculation Study

    SciTech Connect

    Wang, Xue B.; Fu, Qiang; Yang, Jinlong

    2010-09-02

    Hydroxyl substituted phenoxide, o-, m-, p- HO(C6H4)O– and the corresponding neutral radicals are important species, in particularly, the p- isomer pair is directly involved in the proton-coupled electron transfer in biological photosynthetic centers. Here we report the first spectroscopic study of these species in the gas phase by means of low-temperature photoelectron spectroscopy (PES) and ab initio calculations. Vibrationally resolved PES spectra were obtained at 70 K and several photon energies for each anion, directly yielding electron affinity (EA) and electronic structure information of the corresponding hydroxyphenoxyl radical. The EAs are found to vary with OH positions, from 1.990 ± 0.010 eV (p-) to 2.315 ± 0.010 (o-) and 2.330 ± 0.010 (m-). Theoretical calculations were carried out to identify the optimized molecular structures for both anions and neutral radicals. The electron binding energies and excited state energies were also calculated to compare with experimental data. Excellent agreement is found between calculations and experiments. Molecular orbital analyses indicate strong OH anti-bonding interaction with the phenoxide moiety for o- as well as p- isomers, whereas such interaction is largely missing for the m- anion. The variance of EAs among three isomers is interpreted primarily due to the interplay between two competing factors: the OH anti-bonding interaction and H-bonding stabilization (existed only in the o- anion).

  9. 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.

  10. 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.

  11. Electronic Structure and Carrier Mobilities of Arsenene and Antimonene Nanoribbons: A First-Principle Study

    NASA Astrophysics Data System (ADS)

    Wang, Yanli; Ding, Yi

    2015-06-01

    Arsenene and antimonene, i.e. two-dimensional (2D) As and Sb monolayers, are the recently proposed cousins of phosphorene (Angew. Chem. Int. Ed., 54, 3112 (2015)). Through first-principle calculations, we systematically investigate electronic and transport properties of the corresponding As and Sb nanoribbons, which are cut from the arsenene and antimonene nanosheets. We find that different from the 2D systems, band features of As and Sb nanoribbons are dependent on edge shapes. All armchair As/Sb nanoribbons keep the indirect band gap feature, while the zigzag ones transfer to direct semiconductors. Quantum confinement in nanoribbons enhances the gap sizes, for which both the armchair and zigzag ones have a gap scaling rule inversely proportional to the ribbon width. Comparing to phosphorene, the large deformation potential constants in the As and Sb nanoribbons cause small carrier mobilities in the orders of magnitude of 101-102 cm2/Vs. Our study demonstrates that the nanostructures of group-Vb elements would possess different electronic properties for the P, As, and Sb ones, which have diverse potential applications for nanoelectronics and nanodevices.

  12. Use of inside-out chloroplast thylakoid membrane vesicles for studying electron transport and membrane structure

    SciTech Connect

    Atta-Asafo-Adjei, E.

    1987-01-01

    Inside-out and right-side-out thylakoid vesicles were isolated from spinach chloroplasts by aqueous-polymer two-phase partitioning following mechanical fragmentation of thylakoid membranes by Yeda press treatment. Externally added plastocyanin stimulated the whole-chain and PSI electron transport rates in the inside-out thylakoid vesicles by about 500 and 350%, respectively, compared to about 50% stimulation for both assays in the fraction enriched in right-side-out vesicles. The electron transport between PSII and PSI in inside-out thylakoid vesicles appears to be interrupted due to plastocyanin release from the thylakoids by the Yeda press treatment, but it was restored by externally added plastocyanin. Acetic anhydride chemical modification and uncoupler-induced proton release from dark-adapted membranes are probes for detecting the sequested proton domains in thylakoid membranes. Both assays were used to find out if inside-out membranes retain metastable, localized proton binding domains. Treatment of dark-maintained inside-out thylakoid membrane vesicles with ({sup 3}H)acetic anhydride showed no uncoupler-induced increase in acetylation of the 33, 24, and 18 kDa polypeptides of the oxygen-evolving-complex, indicating complete loss of the implicated proton domains in these polypeptides. The various steps in the inside-out preparation were studied to discern which steps(s) leads to the loss of the metastable domain proton pool.

  13. 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.

  14. First-principles Study on the Vibration Modes and Electronic Structure of Alkali and Alkaline-earth Amides and Alanates

    NASA Astrophysics Data System (ADS)

    Tsumuraya, Takao; Shishidou, Tatsuya; Oguchi, Tamio

    2009-03-01

    Light alkaline and alkaline-earth metal hydrides such as amides M(NH2)n and alanates M(AlH4)n (M=K, Na, Li, Ca, and Mg) have attracted a growing interest as reversible hydrogen storage materials recently because of their innately high hydrogen contents. [1, 2] We study the electronic structure of the amides and alanates with different cations, focusing on the role of cation states from first-principles calculations based on the all-electron FLAPW method. Calculated breathing stretch vibration modes for these compounds are compared with measured infrared and Raman spectra. In the amides, we find a significant tendency such that the breathing stretch vibration frequencies and the structural parameters of NH2 vary in accordance with the ionization energy of cation, which may be explained by the strength in hybridization between cation orbitals and molecular orbitals of (NH2)^-. We elucidate the microscopic mechanism of correlations between the breathing stretch vibration frequencies of N-H and structural parameters by analyzing the calculated electronic structure from a view point of the molecular-orbitals. A similar tendency in the alanates is also discussed. [1] P. Chen, Z. Xiong, J. Luo, J. Lin and K.L. Tan, Nature 420, 302 (2002). [2] B. Bogdanovi and M. Schwickardi, J. Alloys Compd. 253-254, 1 (1997).

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    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.

  16. ARPES study of the effect of Cu substitution on the electronic structure of NaFeAs

    NASA Astrophysics Data System (ADS)

    Cui, S. T.; Kong, S.; Ju, S. L.; Wu, P.; Wang, A. F.; Luo, X. G.; Chen, X. H.; Zhang, G. B.; Sun, Z.

    2013-12-01

    Using high-resolution angle-resolved photoemission spectroscopy, we studied the electronic structure of NaFe1-xCuxAs (x=0.019,0.045,0.14). With increasing the doping concentration, we found that the Cu dopant introduces extra charge carriers. The overall band dispersions barely change with doping, suggesting that the Cu substitution does not affect local correlations. Similar to the case of NaFe1-xCoxAs, one electron pocket emerges at the Brillouin zone center at high doping levels. Moreover, the near-EF spectral weight decreases with increasing the Cu dopant, which explains why the NaFe1-xCuxAs shows a poor electronical conductivity at high doping levels.

  17. 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

  18. 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.

  19. Electronic structure, magnetism and stability of Co2CrX (X =Al, Ga, In) ab initio study

    NASA Astrophysics Data System (ADS)

    Dahmane, F.; Mesri, D.; Tadjer, A.; Khenata, R.; Benalia, S.; Djoudi, L.; Doumi, B.; Boumia, L.; Aourag, H.

    2016-01-01

    The structural, electronic as well as the magnetic properties of the Co2CrX (X =Al, Ga and In) full-Heusler alloy have been studied using first-principles calculations performed in the framework of density functional theory (DFT) within the generalized gradient approximation (GGA). It was taken into account both possible L21 structures (i.e. Hg2CuTi- and Cu2MnAl-type). Basically, for all compounds, the Cu2MnAl-type structure is energetically more stable than Hg2CuTi-type structure at the equilibrium volume. The electronic structure calculations for Co2CrAl reveal that half-metallic (HM) character in Cu2MnAl-type structure, Co2CrGa show nearly HM behavior and Co2CrIn has a metallic character. The predicted total magnetic moment is 3μB for Co2CrX (X =Al, Ga) which is in good convergence with the Slater-Pauling (SP) rule.

  20. Synchrotron-based soft X-ray spectroscopic studies of the electronic structure of organic semiconducting molecules

    NASA Astrophysics Data System (ADS)

    Demasi, Alexander

    Organic molecules have been the subject of many scientific studies due to their potential for use in a new generation of optoelectronic and semiconducting devices, such as organic photovoltaics and organic light emitting diodes. These studies are motivated by the fact that organic semiconductor devices have several advantages over traditional inorganic semiconductor devices. Unlike inorganic semiconductors, where the electronic properties are a result of the deliberate introduction of dopants to the material, the properties of organic semiconductors are often intrinsic to the molecules themselves. As a result, organic semiconductor devices are frequently less susceptible to contamination by impurities than their inorganic counterparts, which results in the relatively lower cost of producing such devices. Accurate experimental determination of the bulk and surface electronic structure of organic semiconductors is a prerequisite in developing a comprehensive understanding of such materials. The organic materials studied in this thesis were N,N-Ethylene-bis(1,1,1trifluoropentane-2,4-dioneiminato)-copper(ii) (abbreviated Cu-TFAC), aluminum tris-8hydroxyquinoline (A1g3), lithium quinolate (Liq), tetracyanoquinodimethane (TCNQ), and tetrafluorotetracyanoquinodimethane (F4TCNQ). The electronic structures of these materials were measured with several synchrotron-based x-ray spectroscopies. X-ray photoemission spectroscopy was used to measure the occupied total density of states and the core-level states of the aforementioned materials. X-ray absorption spectroscopy (XAS) was used to probe the element-specific unoccupied partial density of states (PDOS); its angle-resolved variant was used to measure the orientation of the molecules in a film and, in some circumstances, to gauge the extent of an organic film's crystallinity. Most notably, x-ray emission spectroscopy (XES) measures the element- specific occupied PDOS and, when aided by XAS, resonant XES can additionally be

  1. An experimental study on arsoles: structural variation, optical and electronic properties, and emission behavior.

    PubMed

    Ishidoshiro, Makoto; Imoto, Hiroaki; Tanaka, Susumu; Naka, Kensuke

    2016-06-01

    We experimentally demonstrated the intrinsic nature of arsoles as promising functional heteroles. A series of 2,5-diarylarsoles are easily and safely prepared through the procedure in which non-volatile arsenic intermediates are employed to overcome the synthetic barrier due to the concern of volatility of the arsenic precursors used in conventional methods. A Pd-catalyzed Suzuki-Miyaura coupling reaction can be applied to the obtained arsoles for fine molecular design, unlikely to phospholes. It was demonstrated that the optical and electronic properties, i.e. emission colors, quantum yields, and energy levels of the frontier orbitals, are similar to those of phospholes, as conventional theoretical studies have predicted. Furthermore, it was found that arsoles showed mechanochromic properties. PMID:27080400

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

    PubMed

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

    2013-01-01

    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. PMID:23966071

  3. 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.

  4. 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. PMID:25600681

  5. 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.

  6. 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

  7. Study of the surface structure of butterfly wings using the scanning electron microscopic moiré method

    NASA Astrophysics Data System (ADS)

    Kishimoto, Satoshi; Wang, Qinghua; Xie, Huimin; Zhao, Yapu

    2007-10-01

    Scanning electron microscopic (SEM) moiré method was used to study the surface structure of three kinds of butterfly wings: Papilio maackii Menetries, Euploea midamus (Linnaeus), and Stichophthalma howqua (Westwood). Gratings composed of curves with different orientations were found on scales. The planar characteristics of gratings and some other planar features of the surface structure of these wings were revealed, respectively, in terms of virtual strain. Experimental results demonstrate that SEM moiré method is a simple, nonlocal, economical, effective technique for determining which grating exists on one whole scale, measuring the dimension and the whole planar structural character of the grating on each scale, as well as characterizing the relationship between gratings on different scales of each butterfly wing. Thus, the SEM moiré method is a useful tool to assist with characterizing the structure of butterfly wings and explaining their excellent properties.

  8. Detailed electronic structure studies on superconducting MgB2 and related compounds

    NASA Astrophysics Data System (ADS)

    Ravindran, P.; Vajeeston, P.; Vidya, R.; Kjekshus, A.; Fjellvåg, H.

    2001-12-01

    In order to understand the unexpected superconducting behavior of MgB2 we have made electronic structure calculations for MgB2 and closely related systems. Our calculated Debye temperature from the elastic properties indicate that the average phonon frequency is very large in MgB2 compared with other superconducting intermetallics and its exceptionally higher Tc can be explained through a BCS mechanism only if phonon softening occurs or the phonon modes are highly anisotropic. We identified a doubly degenerate quasi-two-dimensional key-energy band in the vicinity of EF along the Γ-A direction of BZ (having equal amount of B px and py character) which plays an important role in deciding the superconducting behavior. Based on this result, we have searched for a similar electronic feature in isoelectronic compounds such as BeB2, CaB2, SrB2, LiBC, and MgB2C2 and found that hole doped LiBC and MgB2C2 are potential superconducting materials. We have found that EF in the closely related compound MgB4 is lying in a pseudogap with a negligibly small density of states at EF, which is not favorable for superconductivity. There are contradictory experimental results regarding the anisotropy in the elastic properties of MgB2 ranging from isotropic to moderately anisotropic to highly anisotropic. In order to settle this issue we have calculated the single-crystal elastic constants for MgB2 by the accurate full-potential method and derived the directional-dependent linear compressibility, Young's modulus, shear modulus, and relevant elastic properties from these results. We have observed large anisotropy in the elastic properties consistent with recent high-pressure findings. Our calculated polarized optical dielectric tensor shows highly anisotropic behavior even though it possesses isotropic transport property. MgB2 possesses a mixed bonding character and this has been verified from density of states, charge density, and crystal orbital Hamiltonian population analyses.

  9. Theoretical study of electronic structure, phase transition, elastic, and thermodynamic properties of ReN

    NASA Astrophysics Data System (ADS)

    Lei, Hui-Ru; Zhu, Jun; Hao, Yan-Jun; Zhang, Lin; Yu, Bai-Ru; Chen, Long-Qing; Zou, Yang-Chun

    2015-02-01

    Phase transition of rhenium mononitride (ReN) in NaCl, CsCl, zincblende (ZB), NbO, wurtzite (WZ), NiAs, WC, PtS, Pmn21 and Cmc21 structures have been studied by using the projector augmented wave method. It is found that NbO-type structure is the most stable. This conclusion is consistent with the report of Wang et al., while contrary to the results of Zhao et al., Chen et al., Asvini et al., and Hlynsson et al. The phase transition from NbO-type to NiAs-type occurs at ca. 52.8 GPa, which is also in good agreement with that of Wang et al. The elastic constants of NbO- and NiAs-type ReN under high pressure are calculated and found to be increased with the increasing pressures. At the same time, the ductile-brittle behavior is evaluated by Pugh's criteria. Also, we have predicted the density of states and Vickers hardness for NbO and NiAs types of ReN. Finally, the Debye temperature ΘD, thermal expansion α and heat capacity CV for NbO-type structure at high pressures are also derived through the quasi-harmonic Debye model.

  10. 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.

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    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.

  13. 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

  14. 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.

  15. The use of SMALPs as a novel membrane protein scaffold for structure study by negative stain electron microscopy.

    PubMed

    Postis, Vincent; Rawson, Shaun; Mitchell, Jennifer K; Lee, Sarah C; Parslow, Rosemary A; Dafforn, Tim R; Baldwin, Stephen A; Muench, Stephen P

    2015-02-01

    Despite the great progress recently made in resolving their structures, investigation of the structural biology of membrane proteins still presents major challenges. Even with new technical advances such as lipidic cubic phase crystallisation, obtaining well-ordered crystals remains a significant hurdle in membrane protein X-ray crystallographic studies. As an alternative, electron microscopy has been shown to be capable of resolving >3.5Å resolution detail in membrane proteins of modest (~300 kDa) size, without the need for crystals. However, the conventional use of detergents for either approach presents several issues, including the possible effects on structure of removing the proteins from their natural membrane environment. As an alternative, it has recently been demonstrated that membrane proteins can be effectively isolated, in the absence of detergents, using a styrene maleic acid co-polymer (SMA). This approach yields SMA lipid particles (SMALPs) in which the membrane proteins are surrounded by a small disk of lipid bilayer encircled by polymer. Here we use the Escherichia coli secondary transporter AcrB as a model membrane protein to demonstrate how a SMALP scaffold can be used to visualise membrane proteins, embedded in a near-native lipid environment, by negative stain electron microscopy, yielding structures at a modest resolution in a short (days) timeframe. Moreover, we show that AcrB within a SMALP scaffold is significantly more active than the equivalent DDM stabilised form. The advantages of SMALP scaffolds within electron microscopy are discussed and we conclude that they may prove to be an important tool in studying membrane protein structure and function. PMID:25450810

  16. NMR studies of electronic structure in crystalline and amorphous Zr2PdH/x/

    NASA Technical Reports Server (NTRS)

    Bowman, R. C., Jr.; Johnson, W. L.; Maeland, A. J.; Rhim, W.-K.

    1983-01-01

    The proton Knight shifts and spin-lattice relaxation times have been measured in crystalline and amorphous Ze2PdH(x). Core polarization from the Zr d-band dominates the proton hyperfine interactions. The density of Fermi level d-electron states is reduced in the amorphous phase relative to the electron density in crystalline Zr2PdH(x).

  17. 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.

  18. Structural, Morphological, and Electron Transport Studies of Annealing Dependent In2O3 Dye-Sensitized Solar Cell

    PubMed Central

    Mahalingam, S.; Abdullah, H.; Shaari, S.; Muchtar, A.; Asshari, I.

    2015-01-01

    Indium oxide (In2O3) thin films annealed at various annealing temperatures were prepared by using spin-coating method for dye-sensitized solar cells (DSSCs). The objective of this research is to enhance the photovoltaic conversion efficiency in In2O3 thin films by finding the optimum annealing temperature and also to study the reason for high and low performance in the annealed In2O3 thin films. The structural and morphological characteristics of In2O3 thin films were studied via XRD patterns, atomic force microscopy (AFM), field-emission scanning electron microscopy (FESEM), EDX sampling, and transmission electron microscopy (TEM). The annealing treatment modified the nanostructures of the In2O3 thin films viewed through FESEM images. The In2O3-450°C-based DSSC exhibited better photovoltaic performance than the other annealed thin films of 1.54%. The electron properties were studied by electrochemical impedance spectroscopy (EIS) unit. The In2O3-450°C thin films provide larger diffusion rate, low recombination effect, and longer electron lifetime, thus enhancing the performance of DSSC. PMID:26146652

  19. Structural, Morphological, and Electron Transport Studies of Annealing Dependent In2O3 Dye-Sensitized Solar Cell.

    PubMed

    Mahalingam, S; Abdullah, H; Shaari, S; Muchtar, A; Asshari, I

    2015-01-01

    Indium oxide (In2O3) thin films annealed at various annealing temperatures were prepared by using spin-coating method for dye-sensitized solar cells (DSSCs). The objective of this research is to enhance the photovoltaic conversion efficiency in In2O3 thin films by finding the optimum annealing temperature and also to study the reason for high and low performance in the annealed In2O3 thin films. The structural and morphological characteristics of In2O3 thin films were studied via XRD patterns, atomic force microscopy (AFM), field-emission scanning electron microscopy (FESEM), EDX sampling, and transmission electron microscopy (TEM). The annealing treatment modified the nanostructures of the In2O3 thin films viewed through FESEM images. The In2O3-450 °C-based DSSC exhibited better photovoltaic performance than the other annealed thin films of 1.54%. The electron properties were studied by electrochemical impedance spectroscopy (EIS) unit. The In2O3-450 °C thin films provide larger diffusion rate, low recombination effect, and longer electron lifetime, thus enhancing the performance of DSSC. PMID:26146652

  20. Four-coordinate cobalt pincer complexes: electronic structure studies and ligand modification by homolytic and heterolytic pathways.

    PubMed

    Semproni, Scott P; Milsmann, Carsten; Chirik, Paul J

    2014-06-25

    A family of cobalt chloride, methyl, acetylide and hydride complexes bearing both intact and modified tert-butyl substituted bis(phosphino)pyridine pincer ligands has been synthesized and structurally characterized and their electronic structures evaluated. Treatment of the unmodified compounds with the stable nitroxyl radical, TEMPO (2,2,6,6-tetramethylpiperidin-1-yloxidanyl) resulted in immediate H- atom abstraction from the benzylic position of the chelate yielding the corresponding modified pincer complexes, ((tBu)mPNP)CoX (X = H, CH3, Cl, CCPh). Thermolysis of the methyl and hydride derivatives, ((tBu)PNP)CoCH3 and ((tBu)PNP)CoH, at 110 °C also resulted in pincer modification by H atom loss while the chloride and acetylide derivatives proved inert. The relative ordering of benzylic C-H bond strengths was corroborated by H atom exchange experiments between appropriate intact and modified pincer complexes. The electronic structures of the modified compounds, ((tBu)mPNP)CoX were established by EPR spectroscopy and DFT computations and are best described as low spin Co(II) complexes with no evidence for ligand centered radicals. The electronic structures of the intact complexes, ((tBu)PNP)CoX were studied computationally and bond dissociation free energies of the benzylic C-H bonds were correlated to the identity of the X-type ligand on cobalt where pure σ donors such as hydride and methyl produce the weakest C-H bonds. Comparison to a rhodium congener highlights the impact of the energetically accessible one-electron redox couple of the first row metal ion in generating weak C-H bonds in remote positions of the supporting pincer ligand. PMID:24897302

  1. 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.

  2. Total energy study of the microscopic structure and electronic properties of tetragonal perovskite SrTiO{sub 3}

    SciTech Connect

    Rubio-Ponce, A.; Olguín, D.

    2014-05-15

    To study the structural and electronic properties of cubic perovskite SrTiO{sub 3} and its stress-induced tetragonal phase, we have performed total energy calculations and studied the effect of oxygen vacancies on the electronic properties of tetragonal perovskite SrTiO{sub 3}. The method used was the relativistic full-potential linearized augmented plane wave (FLAPW) method. To obtain the geometry that minimizes the total energy, we relaxed the internal atomic sites of the tetragonal cell. As a result of this procedure, we have found that the titanium atoms move toward the plane of the vacancy by 0.03 Å, and the apical oxygen atoms move to the same plane by approximately 0.14 Å. These results are discussed in comparison with experimental data.

  3. Structural and Electronic Properties of Amino Acid Based Ionic Liquids: A Theoretical Study

    NASA Astrophysics Data System (ADS)

    Wu, Yang; Zhang, Tiantian

    2009-10-01

    The gas-phase ion pairs of the ionic liquids containing 1-ethyl-3-methylimidazolium ([emim]+) and 20 natural amino acids ([AA]-) are studied at the B3LYP/6-311+G (d,p) level. The optimized structures, energies, and natural population analysis are presented and analyzed in terms of their possible correlation with the interaction energies and the H-bond separations. It is found that all the ion pairs of [emim][AA] can form strong H-bond interactions, which are dominated by the side-chain structure and the functional group of amino acid anions. The calculations indicate that an increase of the alkyl side-chain length coincides with a gradual decrease of H-bond energy, while the functional groups lead to the different localized charges on the anions, consequently affecting the electrostatic force. In addition, the intramolecular H bond in [AA]- can weaken the interaction, due to the decrease of the proton-accepting ability of the carbonyl O atoms. The H-bond chemical nature of [emim][AA] is investigated by atoms in molecules and natural bond orbital analyses. The preliminary analysis of 20 kinds of [emim][AA] ion pairs provides some initial hints as to the relationship between the interaction energy and the experimental glass transition temperature.

  4. The electronic structure of Fe2+ in reaction centers from Rhodopseudomonas sphaeroides. II. Extended x-ray fine structure studies.

    PubMed Central

    Eisenberger, P; Okamura, M Y; Feher, G

    1982-01-01

    Extended x-ray absorption fine structure (EXAFS) studies were performed on reaction centers (RC) of the photosynthetic bacterium Rhodopseudomonas sphaeroides R-26. RC containing two, one, and no quinones (2Q, 1Q, 0Q) samples were studied. The average ligand distance of the first coordination shell was determined to be 2.10 +/- 0.02 A with a more distant shell at 4.14 +/- 0.05 A. The Fe2+ site in RC was found to have a very large structural disorder parameter, from which a spread in ligand distance per iron site of approximately +/- 0.1 A was deduced. The most likely coordination number of the first shell is six, with a mixture of oxygens and nitrogens as ligands. The edge absorption results are consistent with the Fe2+ being in distorted octahedral environment. The EXAFS spectra of the 2Q and 1Q samples with and without O-phenanthroline were found to be the same. This indicates that either the secondary quinone and o-phenanthroline do not bind to Fe2+ or that they replace an equivalent ligand. The 0Q sample showed a 12% decrease in the EXAFS amplitude, which was restored upon addition of o-phenanthroline. These results can be explained by either a loss of a ligand or a severe conformational change when the primary quinone was removed. PMID:6977381

  5. The structure, stability, and electronic properties of ultra-thin BC2N nanotubes: a first-principles study.

    PubMed

    Wang, Yue; Zhang, Juan; Huang, Gang; Yao, Xinhua; Shao, Qingyi

    2014-12-01

    Rapid developments of the silicon electronics industry have close to the physical limits and nanotube materials are the ideal materials to replace silicon for the preparation of next generation electronic devices. Boron-carbon-nitrogen nanotubes (BCNNT) can be formed by joining carbon nanotube (CNT) and boron nitride nanotube (BNNT) segments, and BC2N nanotubes have been widely and deeply studied. Here, we employed first-principles calculations based on density function theory (DFT) to study the structure, stability, and electronic properties of ultra thin (4 Å diameter) BC2N nanotubes. Our results showed that the cross sections of BC2N nanotubes can transform from round to oval when CNT and BNNT segments are parallel to the tube axis. It results when the curvature of BNNT segments become larger than CNT segments. Further, we found the stability of BC2N nanotubes is sensitive to the number of B-N bonds, and the phase segregation of BNNT and CNT segments is energetically favored. We also obtained that all (3,3) BC2N nanotubes are semiconductor, whereas (5,0) BC2N nanotubes are conductor when CNT and BNNT segments are perpendicular to the tube axis; and semiconductor when CNT and BNNT segments are parallel to the tube axis. These electronic properties are abnormal when compared to the relative big ones. PMID:25451142

  6. First-principles study of the atomic and electronic structures of crystalline and amorphous B4C

    NASA Astrophysics Data System (ADS)

    Ivashchenko, V. I.; Shevchenko, V. I.; Turchi, P. E. A.

    2009-12-01

    The atomic and electronic structures of crystalline and amorphous B4C were determined within density function theory using the local density approximation and a plane-wave pseudopotential method. For the crystalline phases, chain, and polar structures were considered. The structural parameters were obtained by minimizing the total energy with respect to the size, shape, and internal degrees of freedom of 15 and 45-atom unit cells. The amorphous 120 and 135-atom samples of a-B4C were generated using molecular dynamic simulations in the NVT ensemble using different initial structures. The 120-atom sample was generated from a rhombohedral c-B4C cell, whereas the a-135 sample was obtained from a fcc B4C initial structure that differs essentially from the real crystalline B4C structure. Analysis of the computed results shows that: (i) a random icosahedral network connected with the amorphous B-C matrix is identified in the case of a-B4C ; (ii) carbon clusters are observed in the case of the 120-atom sample of an amorphous matrix; (iii) no chain atoms are found in both amorphous samples that can be explained by their bulk moduli that are lower compared to those of their crystalline counterparts; (iv) the chain and polar B4C phases transform into a-B4C under high pressure; and (v) all crystalline structures studied so far are semiconducting, whereas a-B4C is a semimetal.

  7. 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) =

  8. Density functional study of electronic structure, elastic and optical properties of MNH2 (M=Li, Na, K, Rb).

    PubMed

    Ramesh Babu, K; Vaitheeswaran, G

    2014-06-11

    We report a systematic first principles density functional study on the electronic structure, elastic and optical properties of nitrogen based solid hydrogen storage materials LiNH2, NaNH2, KNH2, and RbNH2. The ground state structural properties are calculated by using standard density functional theory, and also dispersion corrected density functional theory. We find that van der Waals interactions are dominant in LiNH2 whereas they are relatively weak in other alkali metal amides. The calculated elastic constants show that all the compounds are mechanically stable and LiNH2 is found to be a stiffer material among the alkali metal amides. The melting temperatures are calculated and follow the order RbNH2 < KNH2 < NaNH2 < LiNH2. The electronic band structure is calculated by using the Tran–Blaha modified Becke–Johnson potential and found that all the compounds are insulators, with a considerable band gap. The [NH2]− derived states completely dominate in the entire valence band region while the metal atom states occupy the conduction band. The calculated band structure is used to analyze the different interband optical transitions occurring between valence and conduction bands. Our calculations show that these materials have considerable optical anisotropy. PMID:25932472

  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. 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.

  11. 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.

  12. 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

  13. Theoretical study on structure, conformation, stability and electronic transition of C4 and C5 anions of ascorbic acid stereoisomers

    NASA Astrophysics Data System (ADS)

    Dabbagh, Hossein A.; Azami, Fatemeh; Farrokhpour, Hossein; Chermahini, Alireza Najafi

    2014-03-01

    The structures, stabilities, conformational analysis and electronic transitions of L-ascorbic acid anions (four stereoisomers) were studied theoretically. These anions are produced from the de-protonation of C4-H and C5-H sites of L-ascorbic acid stereoisomers. The geometries of these anions were fully optimized in gas phase and aqueous phase in order to determine their relative stabilities. It was observed that the de-protonation at C5 site of two stereoisomers leads to the ring opening in both phases. Isomerization of the L-form to one of the D-form was observed during the optimization of the anions at C5. Conformational analysis (potential energy surface scan) of the opened ring anions was performed in search of energy minima and/or maxima. The absorption electronic transitions of the anions in the UV region were calculated using Time-Dependent Density Functional Theory (TD-DFT).

  14. First principle studies on the electronic structures and absorption spectra in KMgF 3 crystal with fluorine vacancy

    NASA Astrophysics Data System (ADS)

    Cheng, Fang; Liu, Tingyu; Zhang, Qiren; Qiao, Hailin; Zhou, Xiuwen

    2010-08-01

    The experiments indicate that the perfect KMgF 3 crystal has no absorption in the visible range, however the electron irradiation induces a complex absorption spectrum. The absorption spectra can be decomposed by five Gaussian bands peaking at 2.5 eV (488 nm), 3.4 eV (359 nm), 4.2 eV (295 nm), 4.6 eV (270 nm) and 5.2 eV (239 nm), respectively. The purpose of this paper is to seek the origins of the absorption bands. The electronic structures and absorption spectra either for the perfect KMgF 3 or for KMgF 3: VF+ with electrical neutrality have been studied by using density functional theory code CASTEP with the lattice structure optimized. The calculation results predicate that KMgF 3: VF+ also exhibits five absorption bands caused by the existence of the fluorine ion vacancy VF+ and the five absorption bands well coincide with the experimental results. It is believable that the five absorption bands are related to VF+ in KMgF 3 crystal produced by the electron irradiation.

  15. Structural, electronic, and magnetic properties of Y(n)O (n=2-14) clusters: Density functional study.

    PubMed

    Yang, Zhi; Xiong, Shi-Jie

    2008-09-28

    The geometries stability, electronic properties, and magnetism of Y(n)O clusters up to n=14 are systematically studied with density functional theory. In the lowest-energy structures of Y(n)O clusters, the equilibrium site of the oxygen atom gradually moves from an outer site of the cluster, via a surface site, and finally, to an interior site as the number of the Y atoms increases from 2 to 14. Starting from n=12, the O atom falls into the center of the cluster with the Y atoms forming the outer frame. The results show that clusters with n=2, 4, 8, and 12 are more stable than their respective neighbors, and that the total magnetic moments of Y(n)O clusters are all quite small except Y(12)O cluster. The lowest-energy structure of Y(12)O cluster is a perfect icosahedron with a large magnetic moment 6mu(B). In addition, we find that the total magnetic moments are quenched for n=2, 6, and 8 due to the closed-shell electronic configuration. The calculated ionization potentials and electron affinities are in good agreement with the experimental results, which imply that the present theoretical treatments are satisfactory. PMID:19045024

  16. 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.

  17. 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

  18. 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.

  19. Studies of laser wakefield structures and electron acceleration in underdense plasmas

    SciTech Connect

    Maksimchuk, A.; Reed, S.; Bulanov, S. S.; Chvykov, V.; Kalintchenko, G.; Matsuoka, T.; McGuffey, C.; Mourou, G.; Naumova, N.; Nees, J.; Rousseau, P.; Yanovsky, V.; Krushelnick, K.; Matlis, N. H.; Kalmykov, S.; Shvets, G.; Downer, M. C.; Vane, C. R.; Beene, J. R.; Stracener, D.

    2008-05-15

    Experiments on electron acceleration and optical diagnostics of laser wakes were performed on the HERCULES facility in a wide range of laser and plasma parameters. Using frequency domain holography we demonstrated single shot visualization of individual plasma waves, produced by 40 TW, 30 fs laser pulses focused to the intensity of 10{sup 19} W/cm{sup 2} onto a supersonic He gas jet with plasma densities n{sub e}<10{sup 19} cm{sup -3}. These holographic 'snapshots' capture the variation in shape of the plasma wave with distance behind the driver, and resolve wave front curvature seen previously only in simulations. High-energy quasimonoenergetic electron beams were generated using plasma density in the range 1.5x10{sup 19}{<=}n{sub e}{<=}3.5x10{sup 19} cm{sup -3}. These experiments demonstrated that the energy, charge, divergence, and pointing stability of the beam can be controlled by changing n{sub e}, and that higher electron energies and more stable beams are produced for lower densities. An optimized quasimonoenergetic beam of over 300 MeV and 10 mrad angular divergence is demonstrated at a plasma density of n{sub e}{approx_equal}1.5x10{sup 19} cm{sup -3}. The resultant relativistic electron beams have been used to perform photo-fission of {sup 238}U with a record high reaction yields of {approx}3x10{sup 5}/J. The results of initial experiments on electron acceleration at 70 TW are discussed.

  20. Periodic DFT study of the structural and electronic properties of bulk CoAl2O4 spinel.

    PubMed

    Tielens, F; Calatayud, M; Franco, R; Recio, J M; Pérez-Ramírez, J; Minot, C

    2006-01-19

    In this study, structural and electronic properties of CoAl2O4 spinel are investigated for the first time by means of quantum chemical computational tools. Coupling supercell periodic calculations under the density functional theory formalism with a nonempirical quasi-harmonic Debye model, we examine the influence of temperature on the relative stability of several cation distributions of Co2+ and Al3+ over tetrahedral and octahedral interstices of the oxygen sublattice. Our simulations are able to reproduce the experimentally observed trend: (i) the normal spinel is calculated to be the stable structure at static and low-temperature conditions, and (ii) as the temperature increases, the preference of structures with Al3+ at tetrahedral sites (and Co2+ at octahedral sites) is found to progress following an asymptotic conduct. The effects of the cation distributions on geometrical variations of electronic and magnetic properties of CoAl2O4 can be interpreted as dominated by the local behavior of Co2+ at octahedral sites. PMID:16471633

  1. First-principles study of structural, elastic, electronic and vibrational properties of BiCoO3

    NASA Astrophysics Data System (ADS)

    Koroglu, Ulas; Cabuk, Suleyman; Deligoz, Engin

    2014-08-01

    We used density functional theory (DFT) to study the structural, elastic, electronic, and lattice dynamical properties of tetragonal BiCoO3 applying the “norm-conserving” pseudopotentials within the local spin density approximation (LSDA). The calculated equilibrium lattice parameters and atomic displacements are in agreement with the available experimental and theoretical results. Moreover, the structural stability of tetragonal BiCoO3 were confirmed by the calculated elastic constants. In addition, the elastic properties of polycrystalline aggregates including bulk, shear and Young's moduli, and Poisson's ratio are also determined. The electronic band structure, total and partial density of states (DOS and PDOS) with ferromagnetic spin configuration are obtained. The results show that tetragonal BiCoO3 has an indirect band gap with both up- and down-spin configurations and its bonding behavior is of covalent nature. We compute Born effective charge (BEC) which is found to be quite anisotropic of Bi, Co and O atoms. The infrared and Raman active phonon mode frequencies at the Г point are found. The phonon dispersion curves exhibit imaginary frequencies which lead from the high-symmetry tetragonal phase to low-symmetry rhombohedral phase in BiCoO3. The six independent elastic constants, including bulk, shear and Young's moduli, and Poisson's ratio, complete BEC tensor and phonon dispersion relations in tetragonal BiCoO3 are predicted for the first time. Results of the calculations are compared with the existing experimental and theoretical data.

  2. Theoretical electronic structure of structurally modified graphene

    NASA Astrophysics Data System (ADS)

    Dvorak, Marc David

    Graphene has emerged as a promising replacement for silicon in next-generation electronics and optoelectronic devices. If graphene is to be used in semiconductor devices, however, it must acquire an electronic band gap. Numerous approaches have been proposed to control the band gap of graphene, including the periodic patterning of defects. However, the mechanism for band gap opening and the associated physics in graphene patterned with defects remain unclear. Using both analytic theory and first-principles calculations, we show that periodic patterning of defects on graphene can open a large and tunable band gap, induce strong absorption peaks at optical wavelengths, and host a giant band gap quantum spin Hall phase. First, a geometric rule is analytically derived for the arrangements of defects that open a band gap in graphene, with one ninth of all possible patterns opening a band gap. Next, we perform ab-initio density functional calculations to compare the effects of structural vacancies, hexagonal BN dopants, and passivants on the electronic structure of graphene. Qualitatively, these three types of structural defects behave the same, with only slight differences in their resulting band structures. By adjusting the shape of structural defects, we show how to move the Dirac cones in reciprocal space in accordance with the tight-binding model for the anisotropic honeycomb lattice, while the fundamental mechanism for band gap opening remains the same. To quantitatively predict the band gap and optical properties of these materials, we employ many-body perturbation theory with Green's functions (GW/Bethe-Salpeter equation) to directly include electron-electron and electron-hole interactions. Structurally modified graphene shows a strong renormalization of the fundamental band gap over single particle descriptions, and a strong electron-hole interaction as indicated by strong exciton binding energies (> 0.5 eV). Finally, we show that structurally modified graphene

  3. Theoretical study for pyridinium-based ionic liquid 1-ethylpyridinium trifluoroacetate: synthesis mechanism, electronic structure, and catalytic reactivity.

    PubMed

    Zhu, Xueying; Cui, Peng; Zhang, Dongju; Liu, Chengbu

    2011-07-28

    By performing density functional theory calculations, we have studied the synthesis mechanism, electronic structure, and catalytic reactivity of a pyridinium-based ionic liquid, 1-ethylpyridinium trifluoroacetate ([epy](+)[CF(3)COO](-)). It is found that the synthesis of the pyridinium salt follows a S(N)2 mechanism. The electronic structural analyses show that multiple H bonds are generally involved in the pyridinium-based ionic liquid, which may play a decisive role for stabilizing the ionic liquid. The cation-anion interaction mainly involves electron transfer between the lone pair of the oxygen atom in the anion and the antibonding orbital of the C*-H bond (C* denotes the carbon atom at the ortho-position of nitrogen atom in the cation). This present work has also given clearly the catalytic mechanism of [epy](+)[CF(3)COO](-) toward to the Diels-Alder (D-A) reaction of acrylonitrile with 2-methyl-1,3-butadiene. Both the cation and anion are shown to play important roles in promoting the D-A reaction. The cation [epy](+), as a Lewis acid, associates the C≡N group by C≡N···H H bond to increase the polarity of the C═C double bond in acrylonitrile, while the anion CF(3)COO(-) links with the methyl group in 2-methyl-1,3-butadiene by C-H···O H bond, which weakens the electron-donating capability of methyl and thereby lowers the energy barrier of the D-A reaction. The present results are expected to provide valuable information for the design and application of pyridinium-based ionic liquids. PMID:21671599

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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

  12. Electronic structure and correlation effects in actinides

    SciTech Connect

    Albers, R.C.

    1998-12-01

    This report consists of the vugraphs given at a conference on electronic structure. Topics discussed are electronic structure, f-bonding, crystal structure, and crystal structure stability of the actinides and how they are inter-related.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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

    2015-01-01

    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

  18. 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.

  19. 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

    2016-05-01

    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.

  20. 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

  1. Electronic band structures of Ge1-xSnx semiconductors: A first-principles density functional theory study

    NASA Astrophysics Data System (ADS)

    Lee, Ming-Hsien; Liu, Po-Liang; Hong, Yung-An; Chou, Yen-Ting; Hong, Jia-Yang; Siao, Yu-Jin

    2013-02-01

    We conduct first-principles total-energy density functional calculations to study the band structures in Ge1-xSnx infrared semiconductor alloys. The norm-conserving optimized pseudopotentials of Ge and Sn have been constructed for electronic structure calculations. The composition-bandgap relationships in Ge1-xSnx lattices are evaluated by a detailed comparison of structural models and their electronic band structures. The critical Sn composition related to the transition from indirect- to direct-gap in Ge1-xSnx alloys is estimated to be as low as x ˜ 0.016 determined from the parametric fit. Our results show that the crossover Sn concentration occurs at a lower critical Sn concentration than the values predicted from the absorption measurements. However, early results indicate that the reliability of the critical Sn concentration from such measurements is hard to establish, since the indirect gap absorption is much weaker than the direct gap absorption. We find that the direct band gap decreases exponentially with the Sn composition over the range 0 0.375, in very good agreement with the theoretical observed behavior [D. W. Jenkins and J. D. Dow, Phys. Rev. B 36, 7994, 1987]. For homonuclear and heteronuclear complexes of Ge1-xSnx alloys, the indirect band gap at L-pointis is found to decrease homonuclear Ge-Ge bonds or increase homonuclear Sn-Sn bonds as a result of the reduced L valley. All findings agree with previously reported experimental and theoretical results. The analysis suggests that the top of valence band exhibits the localization of bond charge and the bottom of the conduction band is composed of the Ge 4s4p and/or Sn 5s5p atomic orbits.

  2. Multicatalytic proteinase is associated with characteristic oval structures in cortical Lewy bodies: an immunocytochemical study with light and electron microscopy.

    PubMed

    Masaki, T; Ishiura, S; Sugita, H; Kwak, S

    1994-04-01

    The ATP-ubiquitin-dependent proteolytic pathway (ubiquitin pathway) is believed to be involved in the formation of various neuronal inclusion bodies including Lewy bodies (LBs), a pathological hallmark of Parkinson disease and diffuse Lewy body disease (DLBD). Since multicatalytic proteinase (MCP) is involved in the ubiquitin pathway, an investigation of whether MCP is involved in neuronal inclusion bodies would provide a clue to the mechanism underlying the formation of neuronal inclusion bodies as well as to the pathogenesis of degenerative neurological disorders. In this study, we investigated detailed immunolocalization of MCP in LBs in DLBD brains using light and electron microscopy. We raised three different monoclonal antibodies against purified human MCP. Each of them recognized different sets of MCP subunits on Western blotting. Immunohistochemically, anti-MCP antibodies recognized all ubiquitin-positive cortical LBs in situ as well as those isolated from frozen DLBD cortices, suggesting that MCP is present in LBs as a whole molecule exhibiting protease activity. In electron microscopy, MCP immunoreactivity (MCP-IR) was exclusively localized on a characteristic oval structure with an approximate diameter of 100 nm. This structure was distributed throughout the LBs and was devoid of ubiquitin immunoreactivity. Treatment of isolated LBs with 2% SDS, but not with 0.5% Triton X-100, removed this structure from LBs in which fibrous materials predominated. Ubiquitin immunoreactivity was also decreased in isolated LBs treated with 2% SDS, suggesting that the fibrous structures in LBs were not ubiquitinated in situ. Thus, it is suggested that LBs are subjected to a proteolytic process in which MCP plays a role via processing of specific components of LBs. PMID:8021694

  3. Controlling Electronic Structures by Irradiation in Single-walled SiC Nanotubes: A First-Principles Molecular Dynamics Study

    SciTech Connect

    Wang, Zhiguo; Gao, Fei; Li , Jingbo; Zu, Xiaotao T.; Weber, William J.

    2009-02-18

    Using first principles molecular dynamics simulations, the displacement threshold energy and defect configurations are determined in SiC nanotubes. The simulation results reveal that a rich variety of defect structures (vacancies, Stone-Wales defects, and antisite defects) are formed with threshold energies of from 11 to 64 eV. The threshold energy shows an anisotropic behavior and exhibits a dramatic decrease with decreasing tube diameter. The electronic structure can be altered by the defects formed by irradiation, which suggests that the electron irradiation may be a way to use defect engineering to tailor electronic properties of SiC nanotubes.

  4. Electron-phonon renormalization of the electronic structure of diamond

    NASA Astrophysics Data System (ADS)

    Giustino, Feliciano; Louie, Steven G.; Cohen, Marvin L.

    2011-03-01

    The calculation of band structures from first-principles has reached a high level of accuracy. Calculations combining density-functional theory with many-body perturbation theory often are in good agreement with measurements by photoemission, tunneling, and other spectroscopic probes. While significant efforts have been devoted to improving the description of electron-electron interactions in these calculations, the effect of lattice vibrations has largely been overlooked so far. In this work we study from first principles the electron-phonon renormalization of the band gap of diamond. The calculated temperature dependence of the gap and the broadening of the absorption edge are in excellent agreement with spectroscopic ellipsometry data. Interestingly we find a gap renormalization due to zero-point vibrations as large as 0.6 eV. We discuss the implications of our findings for the electronic structure of other carbon-based bulk materials and nanostructures.

  5. 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.

  6. 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.

  7. Novel Silicon-Carbon Nanostructures: Electronic structure study on the stability of Si60C2n Clusters.

    NASA Astrophysics Data System (ADS)

    Srinivasan, A.

    2005-03-01

    The formalism of generalized gradient approximation to density functional theory has been used to study the electronic and geometric structures of Si60C2n fullerene-like nanostructures. In our previous work, we have shown that the additions of carbon atoms increase the stability of smaller silicon cages [1]. In this talk, we will present our results on the addition of two and four carbon atoms on the surface of the Si60 cages by substitution as also inside the cage at various symmetry orientations. Full geometry optimizations have been performed using the Hay-Wadt basis set without any symmetry constraints using the Gaussian 03 suite of programs [2]. Binding energies, ionization potentials, electron affinities and the ``band'' gaps of the stable silicon-carbon fullerene like nanostructures will be presented and discussed in detail. In general, we find that the optimized silicon-carbon fullerene-like cages have increased stability compared to the bare Si60 cage. Possibilities of adding larger carbon clusters to the Si60 structure will also be discussed. *Work supported, in part, by the Welch Foundation, Houston, Texas (Grant No. Y-1525). [1] M. N. Huda and A. K. Ray, Phys. Rev. A 69, 011201(R) (2004); Eur. Phys. J. D 31, 63 (2004). [2] Gaussian 03, M. J. Frisch et al. Gaussian Inc., Pittsburgh, PA.

  8. Electron spin echo studies of the solvation structure of O/sub 2//sup -/ in methanol and ethanol

    SciTech Connect

    Narayana, P.A.; Suryanarayana, D.; Kevan, L.

    1982-07-08

    Electron spin echo modulation studies of O/sub 2//sup -/ in specifically deuterated methanol and ethanol glasses have been carried out at 4.2/sup 0/K to determine the solvation structure around O/sub 2//sup -/. The results of the analysis indicate that in both the cases each O/sub 2//sup -/ is solvated by four alcohol molecules. In the case of methanol, the solvent molecules have their H-O bonds oriented toward the II* orbitals of O/sub 2//sup -/ to maximize hydrogen-bonding interactions. This is similar to the O/sub 2//sup -/ solvation structure in water. However, in ethanol the H-O bonds are tilted away from the II* orbitals so that partial molecular dipole orientation of ethanol occurs. As the polar solvent molecule becomes bulkier it appears that molecular dipole orientation becoms more important. This tend is compared with results for solvated electrons in the same solvents. 9 figures, 1 table.

  9. 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.

  10. Electronic structures and optical properties of Ca5(BO3)3F: a systematical first-principles study.

    PubMed

    Hu, Chun-Li; Xu, Xiang; Sun, Chuan-Fu; Mao, Jiang-Gao

    2011-10-01

    A first-principles study of the electronic structure, the linear optical properties and second-order NLO properties of calcium fluoroborate (Ca(5)(BO(3))(3)F, or CBF) crystal has been performed within density functional theory and the independent-particle approximation. The results indicate that the calculated birefringence Δn and the second-order susceptibilities are very coincident with the experimental measured values, and the χ((2)) curves show stronger anisotropy than the linear optical properties. Further analysis based on the spectral and spatial decomposition of χ((2)) reveals that the main sources of the SHG response of CBF are from the planar BO(3) groups (74%-77%) and Ca(2+) cations (23%-26%) and can be attributed to the interband electronic transition from the nonbonding O 2p states to the B 2p and Ca 4s4p states. The packing arrangement of BO(3) is the principal contributor to the significant differences among SHG tensors in CBF. Meanwhile, for a certain crystal CBF, the SHG tensors' trend can be the trend of the optical transition matrix elements, which are high when the corresponding subscript directions have more parallel BO(3) triangular planes in the structure. PMID:21918290

  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. An x-ray absorption spectroscopic study of the electronic structure and bonding of rare-earth orthoferrites.

    PubMed

    Hayes, J R; Grosvenor, A P

    2011-11-23

    Rare-earth orthoferrites, REFeO₃ (RE D rare earth; Y), are tremendously adaptable compounds that are being investigated for use in a wide variety of applications including gas sensors, vehicle catalytic converters, and solid-oxide fuel cells. They also exhibit interesting magnetic properties such as high-temperature antiferromagnetism, making them useful for data storage applications. The compounds adopt a distorted perovskite-type structure where the tilt angle of the octahedra increases (Fe-O-Fe bond angle decreases) as the size of the rare-earth atom decreases. Despite intensive study of the physical properties of these compounds, very few studies have investigated how the bonding and electronic structure of these systems change with substitution of the RE. X-ray absorption near-edge spectroscopy (XANES) is a technique well-suited for such a study, and, in view of this, Fe L-, Fe K- and O K-edge spectra from a series of REFeO₃ compounds (RE D La, Pr, Nd, Sm, Eu, Gd, Ho, Yb, Y) have been collected, and are presented here. Fe L-edge spectra show that Fe is octahedrally coordinated and that the Fe-centered octahedra do not appear to distort with changes in the identity of the RE. The Fe K-edge spectra contain an intersite hybrid peak, which is an ill-studied feature that is attributed to non-local transitions of 1s electrons to 3d states on the next-nearest-neighbor atom that are hybridized with 4p states on the absorbing atom through O 2p states. In this study, it is shown that the intensity of this feature is strongly dependent on the Fe-O-Fe bond angle; the lower the Fe-O-Fe bond angle, the less intense the intersite hybrid peak is. PMID:22056809

  13. An x-ray absorption spectroscopic study of the electronic structure and bonding of rare-earth orthoferrites

    SciTech Connect

    Hayes, J.R.; Grosvenor, A.P.

    2011-11-07

    Rare-earth orthoferrites, REFeO{sub 3} (RE=rare earth; Y), are tremendously adaptable compounds that are being investigated for use in a wide variety of applications including gas sensors, vehicle catalytic converters, and solid-oxide fuel cells. They also exhibit interesting magnetic properties such as high-temperature antiferromagnetism, making them useful for data storage applications. The compounds adopt a distorted perovskite-type structure where the tilt angle of the octahedra increases (Fe-O-Fe bond angle decreases) as the size of the rare-earth atom decreases. Despite intensive study of the physical properties of these compounds, very few studies have investigated how the bonding and electronic structure of these systems change with substitution of the RE. X-ray absorption near-edge spectroscopy (XANES) is a technique well-suited for such a study, and, in view of this, Fe L-, Fe K- and O K-edge spectra from a series of REFeO{sub 3} compounds (RE=La, Pr, Nd, Sm, Eu, Gd, Ho, Yb, Y) have been collected, and are presented here. Fe L-edge spectra show that Fe is octahedrally coordinated and that the Fe-centered octahedra do not appear to distort with changes in the identity of the RE. The Fe K-edge spectra contain an intersite hybrid peak, which is an ill-studied feature that is attributed to non-local transitions of 1s electrons to 3d states on the next-nearest-neighbor atom that are hybridized with 4p states on the absorbing atom through O 2p states. In this study, it is shown that the intensity of this feature is strongly dependent on the Fe-O-Fe bond angle; the lower the Fe-O-Fe bond angle, the less intense the intersite hybrid peak is.

  14. An x-ray absorption spectroscopic study of the electronic structure and bonding of rare-earth orthoferrites

    NASA Astrophysics Data System (ADS)

    Hayes, J. R.; Grosvenor, A. P.

    2011-11-01

    Rare-earth orthoferrites, REFeO3 (RE=rare earth; Y), are tremendously adaptable compounds that are being investigated for use in a wide variety of applications including gas sensors, vehicle catalytic converters, and solid-oxide fuel cells. They also exhibit interesting magnetic properties such as high-temperature antiferromagnetism, making them useful for data storage applications. The compounds adopt a distorted perovskite-type structure where the tilt angle of the octahedra increases (Fe-O-Fe bond angle decreases) as the size of the rare-earth atom decreases. Despite intensive study of the physical properties of these compounds, very few studies have investigated how the bonding and electronic structure of these systems change with substitution of the RE. X-ray absorption near-edge spectroscopy (XANES) is a technique well-suited for such a study, and, in view of this, Fe L-, Fe K- and O K-edge spectra from a series of REFeO3 compounds (RE=La, Pr, Nd, Sm, Eu, Gd, Ho, Yb, Y) have been collected, and are presented here. Fe L-edge spectra show that Fe is octahedrally coordinated and that the Fe-centered octahedra do not appear to distort with changes in the identity of the RE. The Fe K-edge spectra contain an intersite hybrid peak, which is an ill-studied feature that is attributed to non-local transitions of 1s electrons to 3d states on the next-nearest-neighbor atom that are hybridized with 4p states on the absorbing atom through O 2p states. In this study, it is shown that the intensity of this feature is strongly dependent on the Fe-O-Fe bond angle; the lower the Fe-O-Fe bond angle, the less intense the intersite hybrid peak is.

  15. 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.

  16. 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.

  17. Time-resolved structural studies at synchrotrons and X-ray free electron lasers: opportunities and challenges

    PubMed Central

    Neutze, Richard; Moffat, Keith

    2012-01-01

    X-ray free electron lasers (XFELs) are potentially revolutionary X-ray sources because of their very short pulse duration, extreme peak brilliance and high spatial coherence, features that distinguish them from today’s synchrotron sources. We review recent time-resolved Laue diffraction and time-resolved wide angle X-ray scattering (WAXS) studies at synchrotron sources, and initial static studies at XFELs. XFELs have the potential to transform the field of time-resolved structural biology, yet many challenges arise in devising and adapting hardware, experimental design and data analysis strategies to exploit their unusual properties. Despite these challenges, we are confident that XFEL sources are poised to shed new light on ultrafast protein reaction dynamics. PMID:23021004

  18. Full-potential LAPW electronic structure study of δ - plutonium and the (001) surface

    NASA Astrophysics Data System (ADS)

    Wu, Xueyuan; Ray, Asok K.

    2005-07-01

    The electronic and geometric properties of bulk fcc δ -plutonium and the quantum size effects in the surface energies and the work functions of the (001) ultrathin films (UTF) up to seven layers have been investigated with periodic density-functional theory calculations within the full-potential-linearized-augmented-plane-wave (FP-LAPW) approach as implemented in the WIEN2k package. The effects of several approximations have been examined: (i) nonspin polarization (NSP) versus spin polarization (SP); (ii) scalar-relativity [no spin-orbit coupling (NSO)] versus full-relativity [i.e., with spin-orbit (SO) coupling included]. Our calculations show that both spin-polarization and spin-orbit coupling play important roles in determining the equilibrium atomic volume and bulk modulus for δ -plutonium. Our calculated equilibrium atomic volume of 178.3a.u.3 and bulk modulus of 24.9 GPa at the fully relativistic level of theory, i.e., spin-polarization and spin-orbit coupling included, are in good agreement with the experimental values of 168.2a.u.3 and 25 GPa (593 K), respectively. In particular, the energy difference brought by spin-orbit coupling, ˜7-8eV , is dominant, but the energy difference brought by spin-polarization, from a few tenths to 2 eV, has a stronger dependence on the atomic volume. Features of the density of states show that 5f electrons are more itinerant when the volume of δ -plutonium is compressed and they are more localized when the volume is expanded, which provides evidence to explain the origin of the volume expansion between the α and δ phases. The calculated equilibrium lattice constants at different levels of approximation are used in the surface property calculations for the thin films. The surface energy is found to be rapidly converged at all four level approximations, NSP-NSO, NSP-SO, SP-NSO, and SP-SO. The semi-infinite surface energy is predicted to be 0.692 eV at the full relativistic level with spin-polarization and spin

  19. 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

  20. A comparative DFT study of the structural and electronic properties of nonpolar GaN surfaces

    NASA Astrophysics Data System (ADS)

    González-Hernández, Rafael; González-García, Alvaro; Barragán-Yani, Daniel; López-Pérez, William

    2014-09-01

    A comparative analysis of the geometry and the electronic characteristics of nonpolar GaN surfaces was carried out using density-functional theory (DFT) with different approximations for the exchange-correlation energy (LDA, PBE, PBEsol, RPBE, TPSS, revTPSS, and HSE). The obtained data show that the GaN(1 0 1bar 0) (m-plane) is more energetically stable than the GaN(1 1 2bar 0) (a-plane) surface. However, these surfaces have similar surface relaxation geometry, with a Ga-N surface bond-length contraction of around 6-7% and a Ga-N surface rotational angle in the range of 6-9°. Our results show that the use of different exchange-correlation functionals does not significantly change the surface energy and surface geometry. In addition, we found the presence of surface intra-gap states that reduce the band gap of the nonpolar GaN surface with respect to the bulk value, in agreement with recent photoelectron and surface optical spectroscopy experiments.

  1. Synthesis, Electronic Structure, and Reactivity Studies of a 4-Coordinate Square Planar Germanium(IV) Cation.

    PubMed

    Fang, Huayi; Jing, Huize; Zhang, Aixi; Ge, Haonan; Yao, Zhengmin; Brothers, Penelope J; Fu, Xuefeng

    2016-06-22

    A tetra-coordinate, square planar germanium(IV) cation [(TPFC)Ge](+) (TPFC = tris(pentafluorophenyl)corrole) was synthesized quantitatively by the reaction of (TPFC)Ge-H with [Ph3C](+)[B(C6F5)4](¯). The highly reactive [(TPFC)Ge](+) cation reacted with benzene to form phenyl complex (TPFC)Ge-C6H5 through an electrophilic pathway. The key intermediate, a σ-type germylium-benzene adduct, [(TPFC)Ge(η(1)-C6H6)](+), was isolated and characterized by single-crystal X-ray diffraction. Deprotonation of [(TPFC)Ge(η(1)-C6H6)](+) cation led to the formation of (TPFC)Ge-C6H5. [(TPFC)Ge](+) also reacted with ethylene and cyclopropane in benzene at room temperature to form (TPFC)Ge-CH2CH2C6H5 and (TPFC)Ge-CH2CH2CH2C6H5, respectively. The observed electrophilic reactivity is ascribed to the highly exposed cationic germanium center with novel frontier orbitals comprising two vacant sp-hybridized orbitals that are not conjugated to π-system. The three electron-withdrawing pentafluorophenyl groups on the corrole ligand also enhance the electrophilicity of the cationic germanium corrole. PMID:27243114

  2. Scanning tunneling spectroscopy study of the electronic structure of Fe3O4 surfaces

    NASA Astrophysics Data System (ADS)

    Jordan, K.; Cazacu, A.; Manai, G.; Ceballos, S. F.; Murphy, S.; Shvets, I. V.

    2006-08-01

    Scanning tunneling spectroscopy (STS) experiments were performed on the (001) and (111) surfaces of single crystalline magnetite. Room temperature spectra exhibit a ˜0.2eV gap around Ef . The importance of perfect surface order to the existence of this gap is illustrated. STS is also carried out on the (111) surface, at 140 and 95K , just above and below the Verwey transition temperature (TV˜120K) , respectively. It is confirmed that above TV a ˜0.2eV gap exists in the surface density of states (DOS) around Ef . Furthermore, broad bands are resolved on both sides of Ef , with peaks centered on ˜+0.5eV and ˜-0.45eV . Below TV it is shown that the value of the gap in the surface DOS remains similar, however, the peaks resolved in the conduction and valence bands shift markedly away from Ef . The similarity of the gap value before and after the transition points away from an ionic charge ordering occurring at the magnetite surface below TV . However, the shifting of the bands points to a certain degree of electronic ordering or charge disproportionation playing an integral part in the Verwey transition, at the magnetite surface.

  3. 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.

  4. 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.

  5. Temperature dependent electron spin echo studies of polarons in donor- and acceptor-doped poly(p-phenylene): Structural studies

    SciTech Connect

    Kispert, L.D.; Joseph, J.; Tang, J.; Bowman, M.K.; Van Brakel, G.H.; Norris, J.R.

    1986-06-06

    Electron spin echo (ESE) measurements of donor-doped (Li, Na, K and Cs) and acceptor-doped (AsF/sub 5/) poly(p-phenylene), PPP, and fully deuterated PPP samples predict a temperature independent EPR linewidth equal to less than 0.65 gauss that decreases with increasing conductivity. In contrast, EPR linewidths either decrease or increase with decreasing temperature, are dependent on dopant and always exhibit a linewidth either equal to or larger than that predicted from ESE measurements. Deuteration studies indicate that rapid spin exchange is present. Analysis of these results suggest that an exchange exists between isolated radicals in equilibrium with polarons and bipolarons with the equilibrium in favor of bipolarons at 4 K.

  6. Electronic and spectroscopic properties of Ge nanocrystals using diamondoid structures: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Abdulsattar, Mudar Ahmed

    2016-04-01

    Energetically stable Ge diamondoids are used as building blocks to investigate Ge nanocrystal properties using density functional theory (DFT). Energy gap, HOMO and LUMO of Ge diamondoids vary according to confinement theory with shape fluctuations. Ge diamondoid vibrational force constants reach 2.18 mDyne/Å which is between that of bulk silicon and tin. Ge-Ge vibrational frequencies and reduced masses reach 357.47 cm‑1 and 41.93 amu, respectively, which are higher than the values of bulk Ge. Size variation of UV-Vis shows that the maximum optical peak moves from 163 nm to nearly 290 nm as the size of Ge diamondoids and molecules increases. The higher peak value approaches that of experimental Ge quantum dots at 300 nm. NMR spectra of Ge diamondoids are analyzed as a function of diamondoid sizes. Our results show that all investigated spectroscopic tools are sensitive to molecular or nanocrystals size. NMR is particularly good size indicator. Natural bond orbital (NBO) population analysis shows present diamondoid bondings differ from ideal sp3 bonding. The bonding for Ge valence orbitals is in the range (4s1.244p2.60) ‑ (4s1.274p2.73) depending on distance between Ge atom and diamondoid surface. Highest Ge diamondoids vibrational longitudinal optical (LO) mode is blue shifted with respect to experimental bulk value which is the opposite case for C and Si. H surface atom effects on electronic and vibrational properties are discussed.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. Reversible dioxygen binding and arene hydroxylation reactions: Kinetic and thermodynamic studies involving ligand electronic and structural variations

    PubMed Central

    Karlin, Kenneth D.; Zhang, Christiana Xin; Rheingold, Arnold L.; Galliker, Benedikt; Kaderli, Susan; Zuberbühler, Andreas D.

    2012-01-01

    Copper-dioxygen interactions are of intrinsic importance in a wide range of biological and industrial processes. Here, we present detailed kinetic/thermodynamic studies on the O2-binding and arene hydroxylation reactions of a series of xylyl-bridged binuclear copper(I) complexes, where the effects of ligand electronic and structural elements on these reactions are investigated. Ligand 4-pyridyl substituents influence the reversible formation of side-on bound μ-η2:η2-peroxodicopper(II) complexes, with stronger donors leading to more rapid formation and greater thermodynamic stability of product complexes [CuII2(RXYL)(O22−)]2+. An interaction of the latter with the xylyl π-system is indicated. Subsequent peroxo electrophilic attack on the arene leads to C–H activation and oxygenation with hydroxylated products [CuII2(RXYLO2−)(−OH)]2+ being formed. A related unsymmetrical binucleating ligand was also employed. Its corresponding O2-adduct [CuII2(UN)(O22−)]2+ is more stable, but primarily because the subsequent decay by hydroxylation is in a relative sense slower. The study emphasizes how ligand electronic effects can and do influence and tune copper(I)–dioxygen complex formation and subsequent reactivity. PMID:23420124

  14. 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.

  15. Compton scattering study and electronic structure of different phases of NH4NO3

    NASA Astrophysics Data System (ADS)

    Jain, Pradeep; Sahariya, Jagrati; Ahuja, B. L.

    2013-06-01

    In this paper, we present energy bands, density of states and the nature of hydrogen bonding in different temperature-dependent phases of NH4NO3, namely phases II (357-398 K), III (305-357 K) and IV (257-305 K), using the full potential linearized augmented plane wave and linear combination of atomic orbitals (LCAO) methods. Both band structure calculations show the insulating character of the II-IV phases of NH4NO3. In addition, we have reported the isotropic Compton profile of NH4NO3(IV) measured using 661.65 keV γ-radiation from a 137Cs isotope. The experimental momentum density has been compared with that based on density functional theory (DFT) and Hartree-Fock schemes within the LCAO method. It is seen that the LCAO with hybridization of DFT and Hartree-Fock (so-called B3LYP) gives better agreement with the present Compton profile measurement.

  16. HFEPR and Computational Studies on the Electronic Structure of a High-Spin Oxidoiron(IV) Complex in Solution.

    PubMed

    Bucinsky, Lukas; Rohde, Gregory T; Que, Lawrence; Ozarowski, Andrew; Krzystek, J; Breza, Martin; Telser, Joshua

    2016-04-18

    Nonheme iron enzymes perform diverse and important functions in biochemistry. The active form of these enzymes comprises the ferryl, oxidoiron(IV), [FeO](2+) unit. In enzymes, this unit is in the high-spin, quintet, S = 2, ground state, while many synthetic model compounds exist in the spin triplet, S = 1, ground state. Recently, however, Que and co-workers reported an oxidoiron(IV) complex with a quintet ground state, [FeO(TMG3tren)](OTf)2, where TMG3tren = 1,1,1-tris{2-[N2-(1,1,3,3-tetramethylguanidino)]ethyl}amine and OTf = CF3SO3(-). The trigonal geometry imposed by this ligand, as opposed to the tetragonal geometry of earlier model complexes, favors the high-spin ground state. Although [FeO(TMG3tren)](2+) has been earlier probed by magnetic circular dichroism (MCD) and Mössbauer spectroscopies, the technique of high-frequency and -field electron paramagnetic resonance (HFEPR) is superior for describing the electronic structure of the iron(IV) center because of its ability to establish directly the spin-Hamiltonian parameters of high-spin metal centers with high precision. Herein we describe HFEPR studies on [FeO(TMG3tren)](OTf)2 generated in situ and confirm the S = 2 ground state with the following parameters: D = +4.940(5) cm(-1), E = 0.000(5), B4(0) = -14(1) × 10(-4) cm(-1), g⊥ = 2.006(2), and g∥ = 2.03(2). Extraction of a fourth-order spin-Hamiltonian parameter is unusual for HFEPR and impossible by other techniques. These experimental results are combined with state-of-the-art computational studies along with previous structural and spectroscopic results to provide a complete picture of the electronic structure of this biomimetic complex. Specifically, the calculations reproduce well the spin-Hamiltonian parameters of the complex, provide a satisfying geometrical picture of the S = 2 oxidoiron(IV) moiety, and demonstrate that the TMG3tren is an "innocent" ligand. PMID:27031000

  17. Electronic structure and rovibrational properties of ZnOH in the tilde{X} 2A^' electronic state: A computational molecular spectroscopy study

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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 2A' (correlating with 2Σ+ at the linear configuration). The equilibrium structure has re(Zn-O) = 1.8028 Å, re(O-H) = 0.9606 Å, and ∠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)⟩0 = 1.8078 Å, ⟨r(O-H)⟩0 = 0.9778 Å, and ⟨∠(Zn-O-H)⟩0 = 117°. The Yamada-Winnewisser quasi-linearity parameter is found to be γ0 = 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.

  18. Electronic structure and rovibrational properties of ZnOH in the X̃²A' electronic state: a computational molecular spectroscopy study.

    PubMed

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

    2014-09-01

    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  (2)A' (correlating with (2)Σ(+) at the linear configuration). The equilibrium structure has r(e)(Zn-O) = 1.8028 Å, r(e)(O-H) = 0.9606 Å, and ∠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)⟩0 = 1.8078 Å, ⟨r(O-H)⟩0 = 0.9778 Å, and ⟨∠(Zn-O-H)⟩0 = 117°. The Yamada-Winnewisser quasi-linearity parameter is found to be γ0 = 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. PMID:25194373

  19. 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

  20. 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

  1. Computational study of structural, elastic and electronic properties of lithium disilicate (Li(2)Si(2)O(5)) glass-ceramic.

    PubMed

    Biskri, Zine Elabidine; Rached, Habib; Bouchear, Merzoug; Rached, Djamel

    2014-04-01

    The objective of this study is to investigate theoretically the structural, elastic and electronic properties of Lithium Disilicate (LD) crystal (Li2Si2O5), using the pseudo potential method based on Density Functional Theory (DFT) with the Local Density Approximation (LDA) and the Generalized Gradient Approximation (GGA). The calculated structural properties namely the equilibrium lattice parameters and cell volume are in good agreement with the available experimental results. However, for the LD crystal elastic moduli: Shear modulus G, Young's modulus E and Poisson's ratio ν we have found a discrepancy between our theoretical values and experimental ones reported in polycrystalline sample containing LD crystals. The calculated elastic properties show that LD is more rigid compared with other components. We also investigated the mechanical stability of Li2Si2O5 compound and we have noticed that this compound is stable against elastic deformations. On the basis of shear to bulk modulus ratio analysis, we inferred that Li2Si2O5 compound is brittle in nature. In order to complete the fundamental characteristics of this compound we have measured the elastic anisotropy. Our results for the energy band structure and Density of States (DOS) show that Li2Si2O5 compound has an insulator characteristic. PMID:24411692

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. Transmission electron microscopy and time resolved optical spectroscopy study of the electronic and structural interactions of ZnO nanorods with bovine serum albumin.

    PubMed

    Klaumünzer, M; Weichsel, U; Mačković, M; Spiecker, E; Peukert, W; Kryschi, C

    2013-08-22

    The adsorption behavior and electronic interactions of bovine serum albumin (BSA) with ZnO nanorod surfaces were investigated using high-resolution transmission electron microscopy as well as stationary and time-resolved optical spectroscopy techniques. Transmission electron microscopy shows that ZnO nanorod surfaces are surrounded by a homogeneous amorphous BSA film with thicknesses between ~2.5 and 5.0 nm. The electronic structure and adsorption geometry of BSA were examined using high-angle annular dark field scanning transmission electron microscopy combined with electron energy loss spectroscopy. The adsorption process was observed to result into an unfolded conformation of BSA becoming predominantly bound in the side-on orientation at the ZnO surface. This adsorption mode of the BSA molecules allows for a strong interaction with surface states of the ZnO nanorods. This is obvious from its efficient quenching of the defect-center photoluminescence of ZnO. Complementary information of electronic interactions across the ZnO nanorod interface was obtained from femtosecond transient absorption spectroscopy experiments. The rise dynamics of the measured transients revealed altered hole trapping dynamics and, thus, indicated to heterogeneous charge transfer as emerging from adsorbed BSA molecules to defect centers of the ZnO interface. PMID:23889004

  8. 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}.

  9. Experimental and first principle studies on electronic structure of BaTiO3

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    We have carried out photoemission experiments to obtain valence band spectra of various crystallographic symmetries of BaTiO3 system which arise as a function of temperature. We also present results of a detailed first principle study of these symmetries of BaTiO3 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 BaTiO3.

  10. Structural, electrochemical and spectroelectrochemical study on the geometric and electronic structures of [(corrolato)Au(III)](n) (n = 0, +1, -1) complexes.

    PubMed

    Sinha, Woormileela; Sommer, Michael G; van der Meer, Margarethe; Plebst, Sebastian; Sarkar, Biprajit; Kar, Sanjib

    2016-02-21

    Synthesis of two new Au(III) corrole complexes with unsymmetrically substituted corrole ligands is presented here. The newly synthesized Au-compounds have been characterized by various spectroscopic techniques. The structural characterization of a representative Au(III) corrole has also been possible. Electrochemical, UV-vis-NIR/EPR spectroelectrochemical and DFT studies have been used to decipher the electronic structures of various electro-generated species. These are the first UV-vis-NIR/EPR spectroelectrochemical investigations on Au(III) corroles. Assignment of redox states of electro-generated Au(III) corroles is supported by DFT analysis. In contrast to the metal centered reduction reported in Au(III) porphyrins, one electron reduction in Au(III) corroles has been assigned to corrole centered on the basis of experimental and theoretical studies. Thus, the Au(III) corroles (not the analogous Au(III) porphyrin derivatives!) bear a truly redox inactive Au(III) center. Additionally, these Au-corrole complexes display NIR electrochromism, the origin of which is all on corrole-centered processes. PMID:26750146

  11. 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.

  12. 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

  13. Effects of atomic geometry and electronic structure of platinum surfaces on molecular adsorbates studied by gap-mode SERS.

    PubMed

    Hu, Jian; Tanabe, Masahiro; Sato, Jun; Uosaki, Kohei; Ikeda, Katsuyoshi

    2014-07-23

    Surface enhanced Raman scattering (SERS) spectra of organic monolayers were measured on various types of polycrystalline and single crystalline Pt substrates with nanometric or atomic surface features, including heteroepitaxial Pt monolayers, using sphere-plane type nanogap structures. Although atomic geometry and electronic structures of a metal surface significantly influence metal-molecule interactions, such effects are often hindered in conventional SERS measured on a roughened surface because of the spectral information averaging at various adsorption sites. In this study, the use of atomically defined Pt surfaces revealed detailed surface effects; the observed preferential adsorption geometry on each surface was well explained by atomic surface arrangements. The peak shift of the intramolecular vibration in the anchor group was in good agreement with the variation of the d-band center of Pt substrates. Moreover, in electrochemical SERS study the Stark shift of an extramolecular vibrational mode at around 400 cm(-1), which is not accessible in infrared absorption spectroscopy, was monitored on an atomically defined heteroepitaxial Pt monolayer electrode. PMID:24802029

  14. 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.

  15. 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).

  16. 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.

  17. 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.

  18. Structural and electronic studies of a-SiGe:H alloys

    SciTech Connect

    Paul, W. )

    1993-04-01

    This report describes work to produce alloys of a-Si[sub 1-x]Ge[sub x]:H of improved photoelectronic quality by plasma-enhanced chemical vapor deposition (PECVD). The goal was to discover optimum preparation conditions for the end-component, a-Ge:H, to establish whether modification of the usual practice of starting from a-Si:H preparation conditions was advisable. Such modification, found to be necessary, gave films of a-Ge:H with efficiency-mobility-lifetime products ([eta][mu][tau]) 10[sup 2] to 10[sup 3] higher than were earlier available, in homogeneous environmentally stable material. Both a-Ge:H and a-Si[sub 1-x]Ge[sub x]:H of large x were studied in detail. Alloy material was shown to have [eta][mu][tau] 10[sup 2] larger than found earlier. However, just as the [eta][mu][tau] of a-Si:H decreases when Ge is added, so also the [eta][mu][tau] of these alloys with Si addition. By contrast, the ambipolar diffusion lengths, L[sub o] which are governed by the hole mobility, vary by only a factor of two over the whole alloy series. Using the experimental finding of a small valence band offset between a-Si:H and a-Ge:H compositional fluctuations on a 10-mm scale are suggested to explain the behavior of [eta][mu][tau] and L[sub o] The implications for eventual improvement of the alloys are profound, but require direct experimental tests of the postulated compositional fluctuations.

  19. Ab initio study of electronic structure, elastic and optical properties of anti-perovskite type alkali metal oxyhalides

    NASA Astrophysics Data System (ADS)

    Ramanna, J.; Yedukondalu, N.; Ramesh Babu, K.; Vaitheeswaran, G.

    2013-06-01

    We report the structural, elastic, electronic, and optical properties of antiperovskite alkali metal oxyhalides Na3OCl, Na3OBr, and K3OBr using two different density functional methods within generalized gradient approximation (GGA). Plane wave pseudo potential (PW-PP) method has been used to calculate the ground state structural and elastic properties while the electronic structure and optical properties are calculated explicitly using full potential-linearized augmented plane wave (FP-LAPW) method. The calculated ground state properties of the investigated compounds agree quite well with the available experimental data. The predicted elastic constants using both PW-PP and FP-LAPW methods are in good accord with each other and show that the materials are mechanically stable. The low values of the elastic moduli indicate that these materials are soft in nature. The bulk properties such as shear moduli, Young's moduli, and Poisson's ratio are derived from the calculated elastic constants. Tran-Blaha modified Becke-Johnson (TB-mBJ) potential improves the band gaps over GGA and Engel-Vosko GGA. The computed TB-mBJ electronic band structure reveals that these materials are direct band gap insulators. The complex dielectric function of the metal oxyhalide compounds have been calculated and the observed prominent peaks are analyzed through the TB-mBJ electronic structures. By using the knowledge of complex dielectric function other important optical properties including absorption, reflectivity, refractive index and loss function have been obtained as a function of energy.

  20. The 5f localization/delocalization in square and hexagonal americium monolayers: a FP-LAPW electronic structure study

    NASA Astrophysics Data System (ADS)

    Gao, D.; Ray, A. K.

    2006-04-01

    The electronic and geometrical properties of bulk americium and square and hexagonal americium monolayers have been studied with the full-potential linearized augmented plane wave (FP-LAPW) method. The effects of several common approximations are examined: (1) non-spin polarization (NSP) vs. spin polarization (SP); (2) scalar-relativity (no spin-orbit coupling (NSO)) vs. full-relativity (i.e., with spin-orbit (SO) coupling included); (3) local-density approximation (LDA) vs. generalized-gradient approximation (GGA). Our results indicate that both spin polarization and spin orbit coupling play important roles in determining the geometrical and electronic properties of americium bulk and monolayers. A compression of both americium square and hexagonal monolayers compared to the americium bulk is also observed. In general, the LDA is found to underestimate the equilibrium lattice constant and give a larger total energy compared to the GGA calculations. While spin orbit coupling shows a similar effect on both square and hexagonal monolayer calculations regardless of the model, GGA versus LDA, an unusual spin polarization effect on both square and hexagonal monolayers is found in the LDA results as compared with the GGA results. The 5f delocalization transition of americium is employed to explain our observed unusual spin polarization effect. In addition, our results at the LDA level of theory indicate a possible 5f delocalization could happen in the americium surface within the same Am II (fcc crystal structure) phase, unlike the usually reported americium 5f delocalization which is associated with crystal structure change. The similarities and dissimilarities between the properties of an Am monolayer and a Pu monolayer are discussed in detail.

  1. Growth and structure of rapid thermal silicon oxides and nitroxides studied by spectroellipsometry and Auger electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Gonon, N.; Gagnaire, A.; Barbier, D.; Glachant, A.

    1994-11-01

    Rapid thermal oxidation of Czochralski-grown silicon in either O2 or N2O atmospheres have been studied using spectroellipsometry and Auger electron spectroscopy. Multiwavelength ellipsometric data were processed in order to separately derive the thickness and refractive indexes of rapid thermal dielectrics. Results revealed a significant increase of the mean refractive index as the film thickness falls below 20 nm for both O2 or N2O oxidant species. A multilayer structure including an about 0.3-nm-thick interfacial region of either SiO(x) or nitroxide in the case of O2 and N2O growth, respectively, followed by a densified SiO2 layer, was found to accurately fit the experimental data. The interfacial region together with the densified state of SiO2 close to the interface suggest a dielectric structure in agreement with the continuous random network model proposed for classical thermal oxides. Auger electron spectroscopy analysis confirmed the presence of noncrystalline Si-Si bonds in the interfacial region, mostly in the case of thin oxides grown in O2. It was speculated that the initial fast growth regime was due to a transient oxygen supersaturation in the interfacial region. Besides, the self-limiting growth in N2O was confirmed and explained in agreement with several recently published data, by the early formation of a very thin nitride or oxynitride membrane in the highly densified oxide beneath the interface. The beneficial effect of direct nitrogen incorporation by rapid thermal oxidation in N2O instead of O2 for the electrical behavior of metal-oxide-semiconductor capacitors is likely a better SiO2/Si lattice accommodation through the reduction of stresses and Si-Si bonds in the interfacial region of the dielectric.

  2. 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.

  3. 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.

  4. 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. PMID:26930424

  5. A Comparative Study of Enzymatically and Photochemically Polymerized Artificial Lignin Supramolecular Structures Using Environmental Scanning Electron Microscopy.

    PubMed

    Micic; Jeremic; Radotic; Leblanc

    2000-11-01

    Environmental scanning electron microscopy images of the self-assembled structures of enzymatically (DHP) and photochemically polymerized (PCP) artificial lignin are herein presented. Differences in the structural organization between DHP and PCP polymer at the supramolecular level were reported. Based on topological information, we proposed a hypothesis about possible new physiological roles of lignin in live plant cells and the ecological significance of possible in-vivo photochemical lignin polymerization. Copyright 2000 Academic Press. PMID:11082264

  6. Electronic structure of graphite oxide

    NASA Astrophysics Data System (ADS)

    Jeong, Hae Kyung; Yang, Cheolsoo; Kim, Bong Soo; Kim, Ki-Jeong

    2011-03-01

    We have investigated the electronic structure of graphite oxide by photoelectron spectroscopy at the Pohang Accelerator Laboratory, Korea. The typical sp 2 hybridization states found in graphite were also seen in graphite oxide. However, the π state disappeared near the Fermi level because of bonding between the π and oxygen-related states originating from graphite oxide, indicating electron transfer from graphite to oxygen and resulting in a downward shift of the highest occupied molecular orbital (HOMO) state to higher binding energies. The band gap opening increased to about 1.8 eV, and additional oxygen-related peaks were observed at 8.5 and 27 eV. This research was supported by the Basic Science Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (2010-0004592), and partly by the MEST (2009-0087138). Experiments at the PLS were supported in part by POSTECH and MEST.

  7. 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.

  8. 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. PMID:21299242

  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. 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.

  11. The Electronic Structure of Amorphous Carbon Nanodots.

    PubMed

    Margraf, Johannes T; Strauss, Volker; Guldi, Dirk M; Clark, Timothy

    2015-06-18

    We have studied hydrogen-passivated amorphous carbon nanostructures with semiempirical molecular orbital theory in order to provide an understanding of the factors that affect their electronic properties. Amorphous structures were first constructed using periodic calculations in a melt/quench protocol. Pure periodic amorphous carbon structures and their counterparts doped with nitrogen and/or oxygen feature large electronic band gaps. Surprisingly, descriptors such as the elemental composition and the number of sp(3)-atoms only influence the electronic structure weakly. Instead, the exact topology of the sp(2)-network in terms of effective conjugation defines the band gap. Amorphous carbon nanodots of different structures and sizes were cut out of the periodic structures. Our calculations predict the occurrence of localized electronic surface states, which give rise to interesting effects such as amphoteric reactivity and predicted optical band gaps in the near-UV/visible range. Optical and electronic gaps display a dependence on particle size similar to that of inorganic colloidal quantum dots. PMID:25731776

  12. 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.

  13. On the Electronic Structures and Electron Affinities of the m- Benzoquinone (BQ) Diradical and the o-, p- BQ Molecules. A Synergetic Photoelectron Spectroscopic and Theoretical Study

    SciTech Connect

    Fu, Qiang; Yang, Jinlong; Wang, Xue B.

    2011-03-30

    Electron affinities (EAs) and electronic structures of benzoquinone molecules (BQs) play a vital role in a wide range of applications involving these molecules from biological photosynthesis to energy conversion processes. In this article, we report a systematic spectroscopic probe on the electronic structures and EAs of all three isomers (o-, m-, and p- BQs) employing photodetachment photoelectron spectroscopy (PES) and ab initio electronic structure calculations. PES spectra of three radical anions (BQ•-) were taken with different photon energies and at low temperature in order to accurately determine the EAs and probe ground as well as the excited states of the corresponding neutral molecules. Similar spectral pattern was observed in the o- and p- BQ•- spectra, each revealing a broad ground state feature and a large band gap, followed by well-resolved excited states peaks. The EAs of o- and p- BQ are determined to be 1.90, 1.85 eV, and singlet-triplet band gaps to be 1.68, and 2.32 eV, respectively. In contrast, the spectrum of m- BQ•- is distinctly different from its two congeners, with no clear band gap and a much higher EA (2.89 eV). Accompanying theoretical calculations confirm experimental EAs and band gaps, and further unravel a triplet ground state for m-BQ in contrast to singlet ground states for o- and p- isomers. The diradical nature of m-BQ, consistent with its non-Kekulé structure, is primarily responsible for the observed high EA and also explains its nonexistence in bulk materials.

  14. Structural, electronic, magnetic and thermodynamic properties of full-Heusler compound Co2VSi: Ab initio study

    NASA Astrophysics Data System (ADS)

    Bentouaf, Ali; Hassan, Fouad El Haj

    2015-05-01

    Density functional theory based on full-potential linearized augmented plane wave (FP LAPW) method is used to investigate the structural, electronic and magnetic properties of Co2VSi Heusler alloys, with L21 structure. It is shown that calculated lattice constants and spin magnetic moments using the general gradient approximation method are in good agreement with experimental values. We also presented the thermal effects using the quasi-harmonic Debye model, in which the lattice vibrations are taken into account. Temperature and pressure effects on the structural parameters, heat capacities, thermal expansion coefficient, and Debye temperatures are determined from the non-equilibrium Gibbs functions.

  15. 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.

  16. 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.

  17. Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter

    DOE PAGESBeta

    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

  18. [Electron-microscopic studies on fine structure and enzyme activity in the axenic and conventional strains of Entamoeba histolytica

    PubMed

    Yong, Tai Soon; Chung, Pyung Rim; Lee, Keun Tae

    1985-12-01

    The metabolism of Entamoeba histolytica would be affected by various environmental factors, and alteration of the environment was known to affect the fine structure of E. histolytica. The present study was designed electronmicroscopically to investigate the ultrastructure and enzyme activities in the axenic and conventional strains of E. histolytica. The trophozoites of axenically cultivated HK-9 strain and conventional YS-27 and YS-49 strains of E. histolytica were collected and fixed with 4 percent paraformaldehyde/0.1 M cacodylate buffer (pH 7.4). After washing them by centrifugation, 1 percent warm agar was added in the sediment. Solidified agar with the trophozoites was cut into 1 mm(3) cubes, and incubated in the various substrates to observe enzyme activities. Then, the specimen was post-fixed with 3 percent glutaraldehyde/0.1 M cacodylate buffer (pH 7.4) and 1 percent osmium tetroxide/0.1 M cacodylate buffer (pH 7.4), dehydrated in ascending ethanol series and embedded in epoxy resin. These were sectioned on an ultramicrotome and observed with a transmission electron microscope. The procedures for the observation of the fine structure were same as the above, except for the incubation in the substrate. The sections were stained with uranyl scetate and lead citrate. For the observation of the surface of the amoebae, scanning electron microscopy was carried out. The results obtained in the present study are summarized as follows: 1. The fuzzy coat around double-layered plasma membrane of E. histolytica was more irregularly and densely distributed in the conventional strains (YS-27, YS-49 strains) than in the axenic strain (HK-9 strain). 2. The endosomes, button bodies and chromatin material were surrounded by a double-layered nuclear membrane having scattered nuclear pores. The paranuclear body, mono- or double-layered vacuoles, vacuolar membrane whorls, rosette-like cylindrical bodies, aggregation of cylindrical bodies and helical bodies were found in the

  19. 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.

  20. ARPES Studies of Low-energy electronic structure of the strong spin-orbit semimetal SrIrO3

    NASA Astrophysics Data System (ADS)

    Nie, Yuefeng; King, Philip D. C.; Wei, Haofei; Uchida, Masaki; Harter, John; Monkman, Eric; Shai, Daniel; Schlom, Darrell; Shen, Kyle

    2013-03-01

    The similar energy scales of spin-orbit coupling and electron-electron correlation strength lead to exotic Jeff = 1/2 Mott insulating ground states for layered Ruddlesden-Popper 5d iridates, Srn+1IrnO3n+1. A metal-insulator transition occurs upon increasing dimensionality from the two-dimensional layered Sr2IrO4 to the three-dimensional perovskite SrIrO3. However, little is known about the electronic structure and nature of the metallic states in SrIrO3. We synthesized epitaxial SrIrO3 films on (001) LSAT substrates by molecular beam epitaxy and investigated their electronic structure using angle-resolved photoemission spectroscopy. We find an exotic semi-metallic state comprised of massive hole-like bands, whose extrema are pinned very close to the chemical potential, and rapidly dispersive electron bands which dominate the transport. Intriguingly, the bandwidths of SrIrO3 are smaller than in its Mott insulating counterpart Sr2IrO4, indicating that metal-insulator transitions in Ruddlesden-Popper iridates are not simply driven by band narrowing resulting from reduced dimensionality.

  1. A theoretical study of CO and NO interaction with Cu sites in ZSM-5: Electronic structure and vibrational spectra

    SciTech Connect

    Ramprasad, R.; Hass, K.C.; Schneider, W.F.

    1996-10-01

    The interaction of CO and NO with various Cu sites in zeolites were studied theoretically within the framework of density functional theory. Our models of the active sites are simple charged clusters, with Cu ions coordinated to a certain number of water ligands and in some cases to a hydroxyl ligand in addition to water ligands. We have studied the electronic and geometric structure of monocarbonyl, mono- and dinitrosyl complexes. We find that in all mono- and dinitrosyl complexes that we considered, the Cu preferred to be in its 1+ oxidation state, irrespective of the overall cluster charge or the degree of coordination resulting in three different binding modes. We have also performed vibrational frequency calculations for the optimal monocarbonyl, mono- and dinitrosyl geometries. Of all the complexes that we considered, our results for low coordinated Cu(I) (coordinated to about 2 water ligands) and hydroxyl ligand coordinated Cu(II) are consistent with experimentally observed CO and NO stretch frequencies in Cu-ZSM-5.

  2. First-principle study of the electronic structure and optical property of Nb-doped anatase TiO2

    NASA Astrophysics Data System (ADS)

    Hou, Q. Y.; Liu, Q. L.; Zhao, C. W.; Zhang, Y.

    2014-04-01

    The absorption edge shifted to long wavelength direction and short wavelength direction of two opposite experimental conclusions have been reported, when the band-gap and absorption spectra of Nb-doped anatase TiO2 were studied. In order to solve this contradiction, the electronic structure and the optical property of Nb heavy doped anatase TiO2 have been studied by the first-principles plane-wave ultrasoft pseudopotential method based on the density functional theory with +U method modification. The calculated results indicate that the higher the Nb-doping is, the higher the total energy is, the worse the stability is, the higher the formation energy is, the more difficult the doping is, the wider the optical band-gap is, the more obvious the absorption edge shifting to short wavelength direction is, the lower the absorptivity and the reflectivity is, which is in agreement with the experimental results. The reasonable interpretation of the contradiction has been reported in this paper, too.

  3. Study on the electronic structures and the optical properties of the Mg-doped LiBaF 3 crystal

    NASA Astrophysics Data System (ADS)

    Qiao, Hailing; Liu, Tingyu; Zhang, Qiren; Cheng, Fang; Zhou, Xiuwen

    2010-04-01

    The most possible substituting positions of impurity magnesium ions in LiBaF 3 crystal are studied using the general utility lattice program (GULP). The electronic structures of Mg-doped LiBaF 3 crystal are studied within the framework of the fully relativistic self-consistent Dirac-Slater theory using DV-X α software. It is predicted that the most possible defect model is the [MgLi·+] in the Mg: LiBaF 3 crystal, which exhibits donor level in the forbidden band. The optical transition energy from the Mg 3s state to the Ba 5d state is 2.975 eV, which is very close to the experimental result. It is indicated that the 420 nm absorption band originates from [MgLi·+] and the presence of the 510 nm luminescence band is related to the defect cluster [MgLi·+] in the Mg:LiBaF 3 crystal too.

  4. Electronic structure of lithium amide

    NASA Astrophysics Data System (ADS)

    Kamakura, N.; Takeda, Y.; Saitoh, Y.; Yamagami, H.; Tsubota, M.; Paik, B.; Ichikawa, T.; Kojima, Y.; Muro, T.; Kato, Y.; Kinoshita, T.

    2011-01-01

    The electronic structure of the insulator lithium amide (LiNH2), which is a lightweight complex hydride being considered as a high-capacity hydrogen storage material, is investigated by N 1s soft x-ray emission spectroscopy (XES) and absorption spectroscopy (XAS). The XES and XAS spectra show a band gap between the valence and conduction bands. The valence band in the XES spectrum consists of three peaks, which extend up to ~-8 eV from the valence band top. The band calculation within the local-density approximation (LDA) for LiNH2shows energetically separated three peaks in the occupied N 2p partial density of states (pDOS) and the band gap. The energy distribution of three peaks in the XES spectrum agrees with that in the calculated pDOS except for the peak at the highest binding energy, which is attributed to the strongly hybridized state between N 2p and H 1s. The XES experiment has clarified that the strongly hybridized state with H 1s in LiNH2is located at binding energy higher than that of the LDA calculation, while the overall feature of the electronic structure of LiNH2experimentally obtained by XES and XAS is consistent with the calculated result.

  5. 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.

  6. 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.

  7. Structural and electronic properties of TiX (X=N, As) in rock salt and zinc blende phase: A DFT study

    NASA Astrophysics Data System (ADS)

    Verma, U. P.; Nayak, V.

    2016-05-01

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

  8. 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

  9. A hybrid-exchange density functional study of the bonding and electronic structure in bulk CuFeS2.

    PubMed

    Martínez-Casado, Ruth; Chen, Vincent H-Y; Mallia, Giuseppe; Harrison, Nicholas M

    2016-05-14

    The geometric, electronic, and magnetic properties of bulk chalcopyrite CuFeS2 have been investigated using hybrid-exchange density functional theory calculations. The results are compared with available theoretical and experimental data. The theoretical description of the bonding and electronic structure in CuFeS2 is analyzed in detail and compared to those computed for chalcocite (CuS2) and greigite (Fe3S4). In particular, the behavior of the 3d electrons of Fe(3+) is discussed in terms of the Hubbard-Anderson model in the strongly correlated regime and found to be similarly described in both materials by an on-site Coulomb repulsion (U) of ∼8.9 eV and a transfer integral (t) of ∼0.3 eV. PMID:27179495

  10. A hybrid-exchange density functional study of the bonding and electronic structure in bulk CuFeS2

    NASA Astrophysics Data System (ADS)

    Martínez-Casado, Ruth; Chen, Vincent H.-Y.; Mallia, Giuseppe; Harrison, Nicholas M.

    2016-05-01

    The geometric, electronic, and magnetic properties of bulk chalcopyrite CuFeS2 have been investigated using hybrid-exchange density functional theory calculations. The results are compared with available theoretical and experimental data. The theoretical description of the bonding and electronic structure in CuFeS2 is analyzed in detail and compared to those computed for chalcocite (CuS2) and greigite (Fe3S4). In particular, the behavior of the 3d electrons of Fe3+ is discussed in terms of the Hubbard-Anderson model in the strongly correlated regime and found to be similarly described in both materials by an on-site Coulomb repulsion (U) of ˜8.9 eV and a transfer integral (t) of ˜0.3 eV.

  11. An experimental study of the electronic structures of the first row transition metal monoxides and dioxides by anion photoelectron spectroscopy

    SciTech Connect

    Wu, Hongbin; Wang, Lai-Sheng

    1997-12-31

    The electronic structures of the monoxides and dioxides of the first row transition metals from Ti to Zn are investigated systematically by anion photoelectron spectroscopy. The electron affinities of these novel molecules are measured. The electronic states of the monoxides are assigned according to existing theoretical calculations. We also observed an excited state for the CuO- anion at 0.5ev above the anion ground state. The vibrational frequencies of the v1 mode for the ground states of VO2, MnO2, CoO2, and NiO2 are observed, which are 906cm-1, 828cm-1, 809cm-1, and 751cm-1 respectively.

  12. 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.

  13. 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.

  14. Electronic Structure of ClAlPc/pentacene/ITO Interfaces Studied by Using Soft X-ray Spectroscopy

    SciTech Connect

    Cho, Sang Wan; Lee, Sangho; Kim, Minsoo; Heo, Nari; Lee, Geunjeong; Smith, Kevin E.

    2014-12-06

    The interfacial electronic structure of a bilayer of chloroaluminum phthalocyanine (ClAlPc) and pentacene grown on indium tin oxide (ITO) has been studied using synchrotron-radiation-excited photoelectron spectroscopy. The energy difference between the highest occupied molecular orbital (HOMO) level of the pentacene layer and the lowest unoccupied molecular orbital (LUMO) level of the ClAlPc layer (E HOMO D - E LUMO A ) was determined and compared with that of C60/pentacene bilayers. The E HOMO D - E LUMO A of a heterojunction with ClAlPc was found to be 1.3 eV while that with C60 was 0.9 eV. This difference is discussed in terms of the difference in the ionization energy of each acceptor materials. We also obtained the complete energy level diagrams of both ClAlPc/pentacene/ITO and C60/pentacene/ITO.

  15. Theoretical study of the structural, elastic, electronic and optical properties of XCaF3 (X = K and Rb)

    NASA Astrophysics Data System (ADS)

    Ghebouli, B.; Fatmi, M.; Ghebouli, M. A.; Choutri, H.; Louail, L.; Chihi, T.; Bouhemadou, A.; Bin-Omran, S.

    2015-05-01

    The PLANE WAVE pseudo-potential method within density functional theory (DFT) has been used to investigate the structural, elastic, electronic and optical properties of XCaF3 (X = K and Rb) insulating. The studied compounds show a weak resistance to shear deformation compared to the resistance to the unidirectional compression. KCaF3 and RbCaF3 are considered ductile. The elastic constants and related parameters were predicted. The stiffness is more important in KCaF3, whereas, the lateral expansion is more important in RbCaF3. KCaF3 and RbCaF3 have R- Г indirect band gap. The main peaks in the imaginary part of the dielectric function correspond to the transition from the occupied state F-p to the unoccupied states Ca: s or K, Rb: p. At lower energies, KCaF3 and RbCaF3 show the same optical properties. Under pressure effect, the peaks of imaginary part of dielectric function were shifted toward high energy.

  16. 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

  17. Stability and electronic structure of the low- Σ grain boundaries in CdTe: a density functional study

    DOE PAGESBeta

    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

  18. 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.

  19. 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.

  20. First-principles electronic structure study of the monoclinic crystal bismuth triborate BiB3O6.

    PubMed

    Yang, Jun; Dolg, Michael

    2006-10-01

    Monoclinic BiB(3)O(6) is an excellent nonlinear optical material with many advantages compared to other borate crystals. The origins of the optical effects and the chemical stability of BiB(3)O(6) are studied with gradient-corrected hybrid B3PW density functional theory within the Gaussian-orbital-based CO-LCAO scheme. Including spin-orbit coupling, the B3PW hybrid functional provides an estimate of the indirect band gap of 4.29-4.99 eV closer to the experimental value of 4.3 eV than HF, LDA, or GGA. The crystal orbital overlap population to give a detailed first-principles analysis of chemical bonding and the density of optical absorptions by convoluting the occupied density of states and the virtual density of states have been calculated. Obvious Bi-O covalent bonds have been found with different energy ranges for 6s-2p and 6p-2p interactions. The reason that [BiO(4)](5-) units are mainly responsible for the optics of BiB(3)O(6) in the long-wavelength region is due to the electronic transfer from occupied O 2p to empty Bi 6p orbitals favored by the Bi-O covalent bonds. The relativistic and correlation effects lead to fundamental differences of the band structure, chemical bonds, and optical effects for BiB(3)O(6) compared with nonrelativistic and uncorrelated calculations. PMID:17004777

  1. 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.

  2. How Klingler's dissection permits exploration of brain structural connectivity? An electron microscopy study of human white matter.

    PubMed

    Zemmoura, Ilyess; Blanchard, Emmanuelle; Raynal, Pierre-Ivan; Rousselot-Denis, Cécilia; Destrieux, Christophe; Velut, Stéphane

    2016-06-01

    The objective of this study is to explore histological and ultrastructural changes induced by Klingler's method. Five human brains were prepared. First, the effects of freezing-defrosting on white matter were explored with optical microscopy on corpus callosum samples of two brains; one prepared in accordance with the description of Klingler (1956) and the other without freezing-defrosting. Then, the combined effect of formalin fixation and freezing-defrosting was explored with transmission electron microscopy (EM) on samples of cingulum from one brain: samples from one hemisphere were fixed in paraformaldehyde-glutaraldehyde (para/gluta), other samples from the other hemisphere were fixed in formalin; once fixed, half of the samples were frozen-defrosted. Finally, the effect of dissection was explored from three formalin-fixed brains: one hemisphere of each brain was frozen-defrosted; samples of the corpus callosum were dissected before preparation for scanning EM. Optical microscopy showed enlarged extracellular space on frozen samples. Transmission EM showed no significant alteration of white matter ultrastructure after formalin or para/gluta fixation. Freezing-defrosting created extra-axonal lacunas, larger on formalin-fixed than on para/gluta-fixed samples. In all cases, myelin sheaths were preserved, allowing maintenance of axonal integrity. Scanning EM showed the destruction of most of the extra-axonal structures after freezing-defrosting and the preservation of most of the axons after dissection. Our results are the first to highlight the effects of Klingler's preparation and dissection on white matter ultrastructure. Preservation of myelinated axons is a strong argument to support the reliability of Klingler's dissection to explore the structure of human white matter. PMID:25905864

  3. 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.

  4. 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.

  5. Screened hybrid and DFT + U studies of the structural, electronic, and optical properties of U3O8.

    PubMed

    Wen, Xiao-Dong; Martin, Richard L; Scuseria, Gustavo E; Rudin, Sven P; Batista, Enrique R; Burrell, Anthony K

    2013-01-16

    A systematic comparison of the structures and electronic and optical properties of U(3)O(8) in the c2mm, P62m, 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 U(3)O(8) and the high temperature, metallic P62m 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. PMID:23178751

  6. 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.

  7. Screened hybrid and DFT + U studies of the structural, electronic, and optical properties of U3O8

    NASA Astrophysics Data System (ADS)

    Wen, Xiao-Dong; Martin, Richard L.; Scuseria, Gustavo E.; Rudin, Sven P.; Batista, Enrique R.; Burrell, Anthony K.

    2013-01-01

    A systematic comparison of the structures and electronic and optical properties of U3O8 in the c2mm, P\\bar {6}2 m, 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\\bar {6}2 m 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.

  8. Experimental and theoretical Electron Paramagnetic Resonance (EPR) study on the temperature-dependent structural changes of methylsulfanylmethane.

    PubMed

    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 CH(3) group was small, and the (33)S splitting was relatively high between 80 and -50 °C. When the temperature was between -50 and -160 °C, the (33)S splitting became small and the CH(3) 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 CH(3) 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

  9. 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.

  10. Studies on the electronic structure of Ag 2NiO 2, an intercalated delafossite containing subvalent silver

    NASA Astrophysics Data System (ADS)

    Wedig, Ulrich; Adler, Peter; Nuss, Jürgen; Modrow, Hartwig; Jansen, Martin

    2006-07-01

    Structural and electronic properties of Ag 2NiO 2 and AgNiO 2 were investigated and compared. Single crystal X-ray diffraction experiments on Ag 2NiO 2 at 100 K provide evidence for a ferrodistortive phase below 260 K. Ni K-edge and Ag L III-edge XANES spectra, both measured and simulated, as well as core level and valence band photoelectron spectra are analysed. They agree well with the results of bandstructure calculations, where pure DFT and mixed Hartree-Fock/DFT (hybrid) functionals were applied and spin-polarisation was considered. The electronic structure of the [NiO 2] - layers with Ni 3+ in a low spin state, forming a spin-1/2 triangular lattice, is very similar in both compounds. A ferrimagnetic alignment of the spins within the [NiO 2] - layers and their antiferromagnetic coupling via the intermediate silver layers is suggested.

  11. Self-consistent linearized augmented-plane-wave study of the electronic structure and superconductivity of fcc lanthanum under pressure

    NASA Astrophysics Data System (ADS)

    Pickett, Warren E.; Freeman, A. J.; Koelling, D. D.

    1980-09-01

    We report the results of a linearized augmented-plane-wave calculation of the electronic structure of fcc La at three lattice constants corresponding to ambient pressure, 50, and 120 kbars. The Kohn-Sham-Gáspar approximation for exchange and correlation is used and the potential is allowed a fully non-muffin-tin form. The f bands lie ~2-2.5 eV above the Fermi level and are ~1 eV wide, resulting in a very small (0.05 electrons) localized f occupation. Under pressure the f bands rise and broaden appreciably, resulting in only a slight increase in f occupation. The rigid-muffin-tin approximation for the electron-phonon interaction λ overestimates the superconducting transition temperature Tc by 40%, but we find that the drastic increase in Tc under pressure can be attributed primarily to changes in the electronic stiffness η. Structural transitions which occur at 25 and 53 kbars may be related to changes in Fermi-surface topology which we find to occur approximately at these pressures.

  12. Molecular structures of vinylarsine, vinyldichloroarsine and arsine studied by gas-phase electron diffraction and quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Noble-Eddy, Robert; Masters, Sarah L.; Rankin, David W. H.; Robertson, Heather E.; Guillemin, Jean-Claude

    2010-08-01

    The molecular structures of vinylarsine (CH 2dbnd CHAsH 2), vinyldichloroarsine (CH 2dbnd CHAsCl 2) and arsine (AsH 3) have been determined from gas-phase electron diffraction data and, in the case of vinylarsine, rotation constants, employing the SARACEN method. The structure of vinylarsine represents the first complete gas-phase structure of a primary arsine. The experimental geometric parameters generally show good agreement with those obtained using ab initio calculations. Key structural parameters ( rh1) for vinylarsine are rAs-H = 150.5(4) pm, rAs-C = 195.1(1) pm and ∠C-C-As = 119.4(2)°. The bonding and conformational trends in both vinylarsine and vinyldichloroarsine are compared to those found in the analogous amines and phosphines.

  13. 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.

  14. 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

  15. Structure-function relationships of the yeast fatty acid synthase: negative-stain, cryo-electron microscopy, and image analysis studies of the end views of the structure.

    PubMed

    Stoops, J K; Kolodziej, S J; Schroeter, J P; Bretaudiere, J P; Wakil, S J

    1992-07-15

    The yeast fatty acid synthase (M(r) = 2.5 x 10(6)) is organized in an alpha 6 beta 6 complex. In these studies, the synthase structure has been examined by negative-stain and cryo-electron microscopy. Side and end views of the structure indicate that the molecule, shaped similar to a prolate ellipsoid, has a high-density band of protein bisecting its major axis. Stained and frozen-hydrated average images of the end views show an excellent concordance and a hexagonal ring having three each alternating egg- and kidney-shaped features with low-protein-density protrusions extending outward from the egg-shaped features. Images also show that the barrel-like structure is not hollow but has a Y-shaped central core, which appears to make contact with the three egg-shaped features. Numerous side views of the structure give good evidence that the beta subunits have an archlike shape. We propose a model for the synthase that has point-group symmetry 32 and six equivalent sites of fatty acid synthesis. The protomeric unit is alpha 2 beta 2. The ends of each of the two archlike beta subunits interact with opposite sides of the two dichotomously arranged disclike alpha subunits. Three such protomeric units form the ring. We propose that the six fatty acid synthesizing centers are composed of two complementary half-alpha subunits and a beta subunit, an arrangement having all the partial activities of the multifunctional enzyme required for fatty acid synthesis. PMID:1631160

  16. Theoretical studies on the bonding and electron structures of a [Au3Sb6](3-) complex and its oligomers.

    PubMed

    Li, Wan-Lu; Xu, Cong-Qiao; Hu, Shu-Xian; Li, Jun

    2016-08-01

    Recently an all-metal aromatic sandwich compound of a [Sb3Au3Sb3](3-) ion has been synthesized and characterized experimentally, which indicates that there might exist a variety of stable all-metal sandwich complexes. The intralayer and interlayer chemical bonding interaction in this system plays significant roles in their stability, chemical properties and functionalities. Here we report a systematic theoretical study on the geometries, electronic structures, and chemical bonding of the [Sb3Au3Sb3](3-) ion and its congeners of [X3Au3X3](3-) (X = N, P, As, Sb, Bi, Uup) as well as [X3M3X3](3-) (M, X = Cu, As; Ag, Bi; Au, Sb; Rg, Uup) to understand the special stabilities of these species. Additional studies are also performed on the oligomers [Sb3(Au3Sb3)n](3-) (n = 1-4) to explore whether the sandwich compound can form stable extended systems. Through extensive theoretical analyses, we have shown that among the [Au3X6](3-) (X = N, P, As, Sb, Bi, Uup) species, [Sb3Au3Sb3](3-) is most stable due to superb matching of Sb3 and Au3 in both geometric size and fragment orbital energies. The significant stability of the [Au3Sb6](3-) ion is determined by the interlayer (p-d-p)σ interactions between the vertical Au 5d6s hybrid orbitals of Au3 and Sb 5pπ orbitals of the Sb3 rings. Each Sb3 ring demonstrates unique σ aromaticity, which remains when the complex is extended to oligomers. The results suggest that it is likely that there might exist other stable [ApMpAp](x-) (M = transition metals, A = main group elements, p = 3, 4, 5, …) sandwich ions and oligomers. PMID:27010416

  17. Theoretical Study of the Structural and Electronic Properties of KxSi136, (x = 1, 8, 18)

    NASA Astrophysics Data System (ADS)

    Higgins, Craig; Myles, Charles

    2012-10-01

    Type II clathrate semiconductors have cage-like lattices in which Group IV atoms are tetrahedrally-coordinated and sp^3 covalently bonded. The cages can contain ``guest'' atoms; usually alkali or alkaline earth atoms. These materials are of interest because of their thermoelectric properties. Measurements of the lattice constant [1] as a function of Na concentration x in NaxSi136 (0 <= x <= 24) have shown the interesting property that, as x is increased in the range (0 <= x <= 8), the lattice constant decreases and that as x is increased further in the range (8 <= x <= 24), the lattice constant increases. We note that some measurements of the properties of K17.8Si136 have also recently been reported [2]. These observations have motivated us to study the behavior of the lattice constant and other properties as a function of guest concentration in other Type II clathrates. In the present paper, we report the results of a theoretical study of the properties of KxSi136 as a function of x. We have used density functional theory to investigate the properties of this material with guest concentrations of x = 1, 8, and 18. Our results show that, similar to previous results for NaxSi136, the lattice constant as a function of x has a minimum at x = 8. We also report results for other structural and electronic properties of KxSi136.[4pt] [1] M. Beekman, E. Nenghabi, K. Biswas, C. Myles, M. Baitinger, Y. Grin, G.S. Nolas, Inorg. Chem. 49 2010, DOI: 10.1021/ic1005049[0pt] [2] S. Stefanoski and G. Nolas, Cryst. Growth Des. 2011, dx.doi.org/10.1021/cg200756r

  18. Ab-initio study of the magnetism, structure and spin dependent electronic states of Ti substituted MO (M = Mg, Ca, Sr)

    NASA Astrophysics Data System (ADS)

    Jaiganesh, G.; Jaya, S. Mathi

    2015-06-01

    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.

  19. 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.

  20. 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

  1. 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

  2. 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

  3. Geometries and electronic structures of the hydrogenated diamond (100) surface upon exposure to active ions: A first principles study

    NASA Astrophysics Data System (ADS)

    Liu, Feng-Bin; Li, Jing-Lin; Chen, Wen-Bin; Cui, Yan; Jiao, Zhi-Wei; Yan, Hong-Juan; Qu, Min; Di, Jie-Jian

    2016-02-01

    To elucidate the effects of physisorbed active ions on the geometries and electronic structures of hydrogenated diamond films, models of HCO 3 - , H3O+, and OH- ions physisorbed on hydrogenated diamond (100) surfaces were constructed. Density functional theory was used to calculate the geometries, adsorption energies, and partial density of states. The results showed that the geometries of the hydrogenated diamond (100) surfaces all changed to different degrees after ion adsorption. Among them, the H3O+ ion affected the geometry of the hydrogenated diamond (100) surfaces the most. This is well consistent with the results of the calculated adsorption energies, which indicated that a strong electrostatic attraction occurs between the hydrogenated diamond (100) surface and H3O+ ions. In addition, electrons transfer significantly from the hydrogenated diamond (100) surface to the adsorbed H3O+ ion, which induces a downward shift in the HOMO and LUMO energy levels of the H3O+ ion. However, for active ions like OH- and HCO 3 - , no dramatic change appears for the electronic structures of the adsorbed ions.

  4. 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.

  5. Electronic structure at the perylene-tetracarboxylic acid dianhydride/Ag(111) interface studied with two-photon photoelectron spectroscopy.

    PubMed

    Sachs, Sönke; Schwalb, Christian H; Marks, Manuel; Schöll, Achim; Reinert, Friedrich; Umbach, Eberhard; Höfer, Ulrich

    2009-10-14

    The electronic structure of the prototype metal/organic contact 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on a Ag(111)-surface has been investigated using time- and angle-resolved two-photon photoelectron spectroscopy (2PPE). Our analysis addresses particularly the nature of the interface state (IS) emerging at the interface due to the substrate-adsorbate interaction [C. H. Schwalb, S. Sachs, M. Marks et al., Phys. Rev. Lett. 101, 146801 (2008)]. Its free-electron-like dispersion and a possible backfolding at the surface Brillouin zone boundaries are discussed. Time-resolved pump-probe experiments reveal the inelastic electron lifetime along the dispersion parabola and show its decrease for increasing parallel momentum. The temperature dependence of the peak linewidth indicates a coupling of the IS to molecular vibrations. Moreover, additional aspects are addressed, such as the determination of the electron attenuation length of photoelectrons for low kinetic energy originating from the IS and the work function change of the sample upon PTCDA adsorption with very high energy resolution. PMID:19831458

  6. 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.

  7. A benchmark study of molecular structure by experimental and theoretical methods: Equilibrium structure of uracil from gas-phase electron diffraction data and coupled-cluster calculations

    NASA Astrophysics Data System (ADS)

    Vogt, Natalja; Khaikin, Leonid S.; Grikina, Olga E.; Rykov, Anatolii N.

    2013-10-01

    The equilibrium structure of uracil, one of the nucleobases, which build nucleic acids, has been determined for the first time by the gas-phase electron diffraction (GED) method. The necessary rovibrational corrections to the experimental internuclear distances have been calculated with quadratic and cubic force constants in the MP2(all)/cc-pVTZ approximation. For the first time, the equilibrium structure has been optimized by the very time-consuming coupled-cluster method with single and double excitations and perturbative treatment of connected triples using the correlation-consistent polarized weighted core-valence triple-zeta basis set with all electrons being correlated (CCSD(T)(all)/cc-pwCVTZ). The optimized structural parameters have been corrected for the diffuse-function effects and extrapolated to the higher basis set (cc-pwCVQZ) using results of MP2 computations (named as best ab initio structure). The GED equilibrium structure remarkably agrees with the best ab initio one as well as with that one derived from microwave (MW) rotational constants by Puzzarini and Barone. Thus, it has been revealed that the precise experiment and coupled-cluster calculations yield the same results when accurate vibrational corrections (including anharmonic ones) are considered in the experimental structural analysis. Moreover, it has been shown that the equilibrium structure derived from the GED data, being in general of one order less accurate than that determined from the MW rotational constants, is still reliable and accurate.

  8. Ab initio study of the structural, tautomeric, pairing, and electronic properties of seleno-derivatives of thymine.

    PubMed

    Vázquez-Mayagoitia, Alvaro; Huertas, Oscar; Brancolini, Giorgia; Migliore, Agostino; Sumpter, Bobby G; Orozco, Modesto; Luque, F Javier; Di Felice, Rosa; Fuentes-Cabrera, Miguel

    2009-10-29

    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 the 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 interplane 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. PMID:19813710

  9. Lattice dynamics and electronic structure of energetic solids LiN3 and NaN3: A first principles study

    NASA Astrophysics Data System (ADS)

    Ramesh Babu, K.; Vaitheeswaran, G.

    2013-10-01

    We report density functional theory calculations on the crystal structure, elastic, lattice dynamics and electronic properties of iso-structural layered monoclinic alkali azides, LiN3 and NaN3. The effect of van der Waals interactions on the ground- state structural properties is studied by using various dispersion corrected density functionals. Based on the equilibrium crystal structure, the elastic constants, phonon dispersion and phonon density of states of the compounds are calculated. The accurate energy band gaps are obtained by using the recently developed Tran Blaha-modified Becke Johnson (TB-mBJ) functional and found that both the azides are direct band gap insulators.

  10. 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

  11. EPR, ENDOR, and electronic structure studies of the Jahn-Teller distortion in an Fe(V) nitride.

    PubMed

    Cutsail, George E; Stein, Benjamin W; Subedi, Deepak; Smith, Jeremy M; Kirk, Martin L; Hoffman, Brian M

    2014-09-01

    The recently synthesized and isolated low-coordinate Fe(V) nitride complex has numerous implications as a model for high-oxidation states in biological and industrial systems. The trigonal [PhB((t)BuIm)3Fe(V)≡N](+) (where (PhB((t)BuIm)3(-) = phenyltris(3-tert-butylimidazol-2-ylidene)), (1) low-spin d(3) (S = 1/2) coordination compound is subject to a Jahn-Teller (JT) distortion of its doubly degenerate (2)E 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 (14/15)N-nitride and the (11)B axial ligands, and spectra are obtained from the imidazole-2-ylidene (13)C 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 (11)B, 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

  12. 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.

  13. First-principles study on the structural, elastic and electronic properties of Ti2SiN under high pressure

    NASA Astrophysics Data System (ADS)

    Li, Hui; Wang, Zhenjun; Sun, Guodong; Yu, Pengfei; Zhang, Wenxue

    2016-07-01

    The structural, elastic and electronic properties of Ti2SiN under pressure range of 0-50 GPa have been systemically investigated by first-principles calculations. It is found that both Poisson's ratio and shear anisotropy factor of Ti2SiN increase with pressure, and Ti2SiN is elastic anisotropic. The DOS and Mulliken population analysis have been explored, which indicts that Ti2SiN is metallic-covalent-ionic in nature. The present calculations may contribute preliminary results and a better understanding of Ti2SiN for its applications under high pressure environments.

  14. 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

  15. 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.

  16. Crystal structure and electronic properties of two nimesulide derivatives: A combined X-ray powder diffraction and quantum mechanical study

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Abir; Ghosh, Soumen; Kankanala, Kavitha; Reddy, Vangala Ranga; Mukkanti, Khagga; Pal, Sarbani; Mukherjee, Alok K.

    2010-06-01

    Crystal structures of two nimesulide derivatives, C 13H 14O 3N 2S ( 2) and C 21H 16O 5N 2S ( 3), have been determined from X-ray powder diffraction data and their electronic structures were calculated at the DFT level. The optimized molecular geometries of 2 and 3 correspond closely to that obtained from the crystallographic analysis. Intermolecular hydrogen bonds and π… π stacking interactions form supramolecular assembly in both compounds. The HOMO-LUMO energy gap (>2.2 eV) indicates a high kinetic stability of both compounds. Although the compound 2 does not exhibit any anti-inflammatory activity, 3 can induce 34% edema inhibition in rat paws.

  17. 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.

  18. Electronic structure of the carbon nanotube tips studied by x-ray-absorption spectroscopy and scanning photoelectron microscopy

    NASA Astrophysics Data System (ADS)

    Chiou, J. W.; Yueh, C. L.; Jan, J. C.; Tsai, H. M.; Pong, W. F.; Hong, I.-H.; Klauser, R.; Tsai, M.-H.; Chang, Y. K.; Chen, Y. Y.; Wu, C. T.; Chen, K. H.; Wei, S. L.; Wen, C. Y.; Chen, L. C.; Chuang, T. J.

    2002-11-01

    Angle-dependent x-ray absorption near edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been performed to differentiate local electronic structures of the tips and sidewalls of highly aligned carbon nanotubes. The intensities of both π*- and σ*-band C K-edge XANES features are found to be significantly enhanced at the tip. SPEM results also show that the tips have a larger density of states and a higher C 1s binding energy than those of sidewalls. The increase of the tip XANES and SPEM intensities are quite uniform over an energy range wider than 10 eV in contrast to earlier finding that the enhancement is only near the Fermi level.

  19. 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.

  20. 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.

  1. Ab initio studies of the structural, elastic, electronic and thermal properties of NiTi2 intermetallic

    NASA Astrophysics Data System (ADS)

    Toprek, Dragan; Belosevic-Cavor, Jelena; Koteski, Vasil

    2015-10-01

    First principles calculations were performed in the framework of the density functional theory (DFT) using the Full Potential-Linear Augment Plane Wave method (FP-LAPW) within the generalized gradient approximation (GGA) to predict the structural, electronic, elastic and thermal properties of NiTi2 intermetallic compound. By using the Wien2k all-electron code, calculations of the ground state and electronic properties such as lattice constants, bulk modulus, presure derivative of bulk modulus, total energies and density of states were also included. The elastic constants and mechanical properties such as Poisson's ratio, Young's modulus and shear modulus are estimated from the calculated elastic constants of the single crystal. Through the quasi-harmonic Debye model, the preasure and temperature dependences of the linear expansion coefficient, bulk modulus and heat capacity have been investigated. Finally, the Debye temperature has been estimated from the average sound velocity according to the predicted polycrystal bulk properties and from the single crystal elastic constants.

  2. Site-dependent electronic structures of a single molecule on a metal surface studied by scanning tunneling microscopy and spectroscopy

    NASA Astrophysics Data System (ADS)

    Katano, Satoshi; Hori, Masafumi; Kim, Yousoo; Kawai, Maki

    2014-10-01

    Single-molecule observation of the electronic structures of para-cyanobenzoate (pCB) adsorbed on Cu(1 1 0) has been performed using scanning tunneling microscopy (STM) and spectroscopy (STS). We found that pCB has two types of the adsorption site on Cu(1 1 0); i.e., two oxygen atoms of pCB are bridged between adjacent Cu atoms at the short- or long-bridge sites. STS and STS mapping revealed that the pCB adsorbed at the short-bridge site has a resonant peak at 2.0 V above the Fermi level, which is assigned to the lowest unoccupied molecular orbital (LUMO) of pCB. However, the LUMO state is shifted toward lower voltage (1.2 V) when the pCB molecule is adsorbed at the long-bridge site. The energy levels of the LUMO state, depending on the adsorption site of pCB, can thus be ascribed to the degree of the electronic interaction between pCB and the Cu substrate. The site transformation of pCB induced by the injection of tunneling electrons from the STM tip has also been presented.

  3. First-principles study of boron oxygen hole centers in crystals: Electronic structures and nuclear hyperfine and quadrupole parameters

    SciTech Connect

    Li Zucheng; Pan Yuanming

    2011-09-15

    The electronic structures, nuclear hyperfine coupling constants, and nuclear quadrupole parameters of fundamental boron oxygen hole centers (BOHCs) in zircon (ZrSiO{sub 4}, I4{sub 1}/amd) and calcite (CaCO{sub 3}, R3c) have been investigated using ab initio Hartree-Fock (HF) and various density functional theory (DFT) methods based on the supercell models with all-electron localized basis sets. Both exact HF exchange and appropriate correlation functionals are important in describing the BOHCs, and the parameter-free hybrid method based on Perdew, Burke, and Ernzerhof density functionals (PBE0) turns out to be the best DFT method in reproducing the electron paramagnetic resonance (EPR) data. Our results reveal three distinct types of simple-spin (S = 1/2) [BO{sub 3}]{sup 2-} centers in calcite: (i) the classic [BO{sub 3}]{sup 2-} radical with the D{sub 3h} symmetry and the unpaired spin equally distributed on the three oxygen atoms (i.e. the O{sub 3}{sup 5-} type); (ii) the previously reported [BO{sub 2}]{sup 0} center with the unpaired spin equally distributed on two of the three oxygen atoms (O{sub 2}{sup 3-}); and (iii) a new variety with {approx}90% of its unpaired spin localized on one (O{sup -}) of the three oxygen atoms with a long B-O bond (1.44 A). Calculations confirm the unusual [BO{sub 4}]{sup 0} center in zircon and show it to arise from a highly distorted configuration with 90% of the unpaired spin on one oxygen atom that has a considerably longer B-O bond (1.68 A) than its three counterparts (1.45 A). The calculated magnitudes and directions of {sup 11}B and {sup 17}O hyperfine coupling constants and nuclear quadrupole constants for the [BO{sub 4}]{sup 0} center in zircon are in excellent agreement with the 15 K EPR experimental data. These BOHCs are all characterized by a small negative spin density on the central B atom arising from spin polarization. Our calculations also demonstrate that the spin densities on BOHCs are affected substantially by

  4. First-principles study on equation of states and electronic structures of shock compressed Ar up to warm dense regime

    NASA Astrophysics Data System (ADS)

    Sun, Huayang; Kang, Dongdong; Dai, Jiayu; Ma, Wen; Zhou, Liangyuan; Zeng, Jiaolong

    2016-03-01

    The equation of states (EOS) and electronic structures of argon with temperatures from 0.02 eV to 3 eV and densities from 0.5 g/cm3 to 5.5 g/cm3 are calculated using the pair potential and many-body potential molecular dynamics and the density functional theory (DFT) molecular dynamics with van der Waals (vdW) corrections. First-principles molecular dynamics is implemented above 2.0 g/cm3. For the cases of low densities below 3 g/cm3, we performed pair potential molecular dynamics in order to obtain the ionic configurations, which are used in density functional theory to calculate the EOS and electronic structures. We checked the validity of different methods at different densities and temperatures, showing their behaviors by comparing EOS. DFT without vdW correction works well above 1 eV and 3.5 g/cm3. Below 1 eV and 2.0 g/cm3, it overestimates the pressure apparently and results in incorrect behaviors of the internal energy. With vdW corrections, the semi-empirical force-field correction (DFT-D2) method gives consistent results in the whole density and temperature region, and the vdW density functional (vdW-DF2) method gives good results below 2.5 g/cm3, but it overestimates the pressure at higher densities. The interactions among the atoms are overestimated by the pair potential above 1 eV, and a temperature dependent scaled pair potential can be used to correct the ionic configurations of the pair potential up to 3 eV. The comparisons between our calculations and the experimental multi-shock compression results show that the Hugoniot line of DFT-D2 and DFT tends to give larger pressure than the results of the self-consistent fluid variational theory, and the difference increases with the density. The electronic energy gap exists for all our cases up to 5.5 g/cm3 and 1 eV. The effect of vdW interactions on the electronic structures are also discussed.

  5. 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)

  6. First-Principles Study on Electronic Structure and Thermodynamic Stability of Sr(Ti,Ru)O3

    NASA Astrophysics Data System (ADS)

    Shimizu, Tatsuo; Kawakubo, Takashi

    2001-02-01

    Not only the electronic structure but also the thermodynamic stability of Sr(Ti,Ru)O3 is investigated using the first-principles method. For the electronic structure with small Ru concentration, the Ru t2g states appear below the middle of the band gap of SrTiO3. In this case, the wave functions of the Ru t2g states are localized at the Ru site. As a Ru concentration increases to more than 50 mol%, the inside-gap states gradually become delocalized. Therefore, a conductive Sr(Ti,Ru)O3 thin film is expected. On the other hand, thermodynamic stability of a Sr(Ti,Ru)O3 thin film is enhanced drastically relative to that of SrRuO3, as Ru concentration decreases. Sr(Ti,Ru)O3 with Ru concentration of more than 60 mol% may oxidize the neighboring (Ti,Al)N layer, which is often used as a barrier metal in memory-cell capacitors. In short, Sr(Ti,Ru)O3 with Ru concentration of about 50 mol% is proposed as a promising candidate material for new electrodes.

  7. [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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Electronic structure of oxygen functionalized graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Simbeck, Adam; Gu, Deyang; Kharche, Neerav; Nayak, Saroj

    2013-03-01

    We investigate the electronic and magnetic properties of armchair graphene nanoribbons whose edges are passivated by oxygen. Using a first-principles density functional approach and the many-body GW method we find that oxygen-passivation results in a rich geometrical environment which in turn determines the electronic and magnetic properties of the ribbon. For planar systems we report magnetic ground states whose electronic structure depends upon the magnetic coupling between edges. For non-planar ribbons we report a nonmagnetic ground state with a band gap that decreases as a function of increasing ribbon width. Our results will be discussed in light of previous experimental and computational studies. Interconnect Focus Center (MARCO program), State of New York, NSF IGERT program, Grant no. 0333314, and computing resources of the Computationial Center for Nanotechnology Innovation (CCNI), RPI

  13. 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. PMID:27083718

  14. 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.

  15. Adatom-induced variations of the atomic and electronic structures of Si(111)3×3-Ag : A first-principles study

    NASA Astrophysics Data System (ADS)

    Jeong, Hojin; Yeom, Han Woong; Jeong, Sukmin

    2008-06-01

    Using a first-principles calculation method, we study the changes in the atomic and electronic structures of the Si(111)3×3-Ag surface (hereafter 3-Ag ) via doping of extra Ag adatoms. We present a structural model for the adatom-induced 21×21 superstructure (21-Ag) , which has three Ag adatoms immersed into the substrate Ag layer within a unit cell. The present structural model reproduces well the measured scanning-tunneling-microscopy images as well as the electronic band structure measured by angle-resolved photoelectron spectroscopy. We find out that the complex band structure seen on the 21-Ag phase basically arises from the band folding of the original surface bands of 3-Ag . The extra Ag adatoms doped on 3-Ag modify only the band alignment without any additional adatom-induced surface state. The almost unoccupied two-dimensional free-electron-like band, generally called S1 , at pristine 3-Ag is gradually filled and shifted downward with an increase in the dopant coverage. As this shifted S1 band crosses other surface bands, it loses its free-electron nature.

  16. 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.

  17. Electronic structure theory: Applications and geometrical aspects

    NASA Astrophysics Data System (ADS)

    Coh, Sinisa

    This thesis contains several applications of the first-principles electronic-structure theory with special emphasis in parts of the thesis on the geometrical aspects of the theory. We start by reviewing the basics of the first-principles electronic-structure methods which are then used throughout the thesis. The first application of these methods is on the analysis of the stability and lattice dynamics of alpha- and beta-cristobalite phases of SiO2. We also map the complete low-energy landscape connecting these two structures and give implications on the phase transition in this compound. Next we study a family of Pbnm perovskites that are promising candidates for silicon-compatible high-K dielectrics. We calculate their structure and dielectric response, and compare with experimental results where available. The third application of these methods is to the large isosymmetric reorientation of oxygen octahedra rotation axes in epitaxially strained perovskites. We explain the origin of the peculiar energy landscape topology as a function of epitaxial strain. In the part of the thesis devoted to the geometrical aspects of electronic structure theory, we begin by extending the concept of electronic polarization to a Chern insulators. These insulators are characterized by a non-zero off-diagonal sigma_xy conductivity tensor component, quantized in units of e 2/h. Finally we discuss another geometrical quantity, the Chern-Simons orbital magnetoelectric coupling. We present a first-principles based calculation of this quantity in several compounds, and motivated by recent developments in the theory of topological insulators, we speculate about the existence of "large-theta materials," in which this kind of coupling could be unusually large.

  18. Electron Density Structures Measured By The Whisper/cluster Instrument: Case Studies At Magnetopause Traversals and In The Magnetosphere

    NASA Astrophysics Data System (ADS)

    Décréau, P. M. E.; Le Guirriec, E.; Rauch, J. L.; Trotignon, J. G.; Darrouzet, F.; Soucek, J.; Canu, P.; Dunlop, M.; Balogh, A.; Sedgemore, F.

    The WHISPER instruments on CLUSTER derive unambiguously the total electron density values from spectral characteristics of sounder stimulated emissions or from spectral characteristics of natural emissions validated by sounderSs diagnostics, this in most magnetospheric regions. Electron density variations are obtained, in combin- ing both types of measurements, with a time resolution of about 2s. As frequency values measured on board are highly stable, the density values yielded from the four CLUSTER spacecraft are measured without need of any evolving calibration factor; differences can thus be calculated with a good reliability and precision. Gradient vec- tors of the scalar density are subsequently calculated at the spatial scale corresponding to the separation parameter of the CLUSTER constellation, along its trajectory. On the other hand, normal velocity vectors of travelling planar density boundaries are derived from time delays of density structure positions identified either by eye, or by use of specific correlation techniques. In this paper, we compare the evolution of those two vectors as obtained in two different regions explored by CLUSTER. One region, swept by the constellation on February 26th 2001, at high latitude in the noon MLT sector, experiences several traversals of the magnetopause boundary, at different orientations and velocity values. In this case, the structures observed in magnetic field variations are analysed, also in terms of orientation and velocities of boundaries. The second re- gion chosen is a dusk side cut of the inner magnetosphere on November 16th 2001, at low or medium latitudes and high L values. Large densities are observed in this case up to the magnetopause boundary crossed at low latitude. The topology and dynam- ics of structures are different in both cases. We discuss what views can be derived on those, from the data and analysis tools considered.

  19. 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.

  20. 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.

  1. Structural studies of P-type ATPase–ligand complexes using an X-ray free-electron laser

    DOE PAGESBeta

    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

  2. Structural studies of P-type ATPase-ligand complexes using an X-ray free-electron laser.

    PubMed

    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

    2015-07-01

    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

  3. 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

  4. 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.

  5. An electronic structure study of acetone by electron momentum spectroscopy: a comparison with SCF, MRSD-CI and density functional theory

    NASA Astrophysics Data System (ADS)

    Zheng, Y.; Neville, J. J.; Brion, C. E.; Wang, Y.; Davidson, E. R.

    1994-11-01

    The binding energy spectra and momentum distributions of all valence orbitals of acetone have been studied by electron momentum spectroscopy (EMS) and SCF, MRSD-CI, and density functional theory (DFT) calculations. The experiment was performed using a multichannel EMS spectrometer at a total energy of 1200 eV. Binding energy spectra measured in the energy range of 6-60 eV are compared with the results of OVGF and 2ph-TDA many-body Green's function calculations. In the inner valence region strong splitting of the 5a 1 and 4a 1 orbitals due to final state electron correlation is observed. The distribution of energies and pole strengths predicted by the Green's function calculations deviates considerably from the measured ionization energies and strengths in the innervalence region. The measured momentum distributions are compared with calculations at the level of the target Hartree-Fock approximation (THFA) using the SCF method and the target Kohn-Sham approximation (TKSA) using DFT and the local-density approximation. Basis sets used for the SCF calculations ranged from the simplest (STO-3G) to large (204-GTO) and for the DFT calculations very large atomic natural orbital (ANO) basis sets were used. The effects of electron correlation and relaxation are also investigated in MRSD-CI calculations of the full ion-neutral overlap amplitude using large and saturated basis sets. In general, the THFA model with an intermediate basis set and very diffuse functions (6-311 + +G ∗∗) and with a near Hartree-Fock limit SCF wavefunction (204-GTO), and the TKSA-DFT model with an ANO basis set all provide reasonable predictions of momentum distributions for most orbitals. However, none of these calculations gives a completely satisfactory description of the momentum distribution of the HOMO (5b 2) orbital.

  6. Transmission electron microscopy and Rutherford backscattering studies of different damage structures in P/sup +/ implanted Si

    SciTech Connect

    Sadana, D.K.; Stratham, M.; Washburn, J.; Booker, G.R.

    1980-11-01

    Cross-sectional transmission electron microscopy (TEM) and MeV He/sup +/ channelling methods have been used to examine different damage structures present under the color bands visible at the surface of a high-dose-rate P/sup +/ implanted (111) Si implanted to a dose of 7.5 x 10/sup 15/ ions/cm/sup 2/. TEM and channelling results obtained from individual colored regions showed a good qualitative correlation in that discrete damage layers observed in the cross-sectional TEM micrographs appeared as discrete peaks in the channelled spectra. The mean depths of the damage layers obtained from these two methods were in agreement. However, the widths of the deeper lying damage layers calculated from the channelling measurements were always greater than the widths observed by TEM. An empirical method based on subtraction of dechannelling background in the channelling spectra gave damage layer widths that were in close agreement with the TEM results.

  7. 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.

  8. 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.

  9. Quasiparticle self-consistent GW study of cuprates: electronic structure, model parameters, and the two-band theory for Tc

    PubMed Central

    Jang, Seung Woo; Kotani, Takao; Kino, Hiori; Kuroki, Kazuhiko; Han, Myung Joon

    2015-01-01

    Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between and is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc. PMID:26206417

  10. Structural, electronic and magnetic properties of the (Co, Ni) codoped ZnS: A first-principles study

    NASA Astrophysics Data System (ADS)

    Yin, Zhu-Hua; Zhang, Jian-Min

    2016-08-01

    Using spin-polarized first-principles calculation, we investigate the structural, electronic and magnetic properties of the Zn31Co1S32, Zn31Ni1S32 and Zn30Co1Ni1S32 systems. The results show that the Zn31Co1S32 system is a magnetic semiconductor, while the Zn31Ni1S32 system exhibits a magnetic half-metallic (HM) character. The Zn30Co1Ni1S32 system exhibits a HM ferrimagnetic character explained by the superexchange mechanism. The Co and Ni atoms favorably occupy nearest neighbor positions of the metal sublattice with antiparallel arrangement of their magnetic moments. Furthermore, it is observed that the magnetic moment of Co/Ni atom reduces from an isolated atom magnetic moment due to p-d hybridization which yields small parallel magnetic moments on the nearest S atoms.

  11. Structural vs electronic origin of renormalized band widths in TTF-TCNQ: An angular dependent NEXAFS study

    NASA Astrophysics Data System (ADS)

    Sing, M.; Meyer, J.; Hoinkis, M.; Glawion, S.; Blaha, P.; Gavrila, G.; Jacobsen, C. S.; Claessen, R.

    2007-12-01

    We have performed angle-dependent near-edge x-ray absorption fine structure measurements in the Auger electron yield mode on the correlated quasi-one-dimensional organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) in order to determine the orientation of the molecules in the topmost surface layer. We find that the tilt angles of the molecules with respect to the one-dimensional axis are essentially the same as in the bulk. Thus, we can rule out surface relaxation as the origin of the renormalized band widths which were inferred from the analysis of photoemission data within the one-dimensional Hubbard model. Thereby, recent theoretical results are corroborated which invoke long-range Coulomb repulsion as alternative explanation to understand the spectral dispersions of TTF-TCNQ quantitatively within an extended Hubbard model.

  12. Structural vs electronic origin of renormalized band widths in TTF-TCNQ: An angular dependent NEXAFS study

    SciTech Connect

    Sing, M.; Meyer, J.; Glawion, S.; Claessen, R.; Hoinkis, M.; Blaha, P.; Gavrila, G.; Jacobsen, C. S.

    2007-12-15

    We have performed angle-dependent near-edge x-ray absorption fine structure measurements in the Auger electron yield mode on the correlated quasi-one-dimensional organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) in order to determine the orientation of the molecules in the topmost surface layer. We find that the tilt angles of the molecules with respect to the one-dimensional axis are essentially the same as in the bulk. Thus, we can rule out surface relaxation as the origin of the renormalized band widths which were inferred from the analysis of photoemission data within the one-dimensional Hubbard model. Thereby, recent theoretical results are corroborated which invoke long-range Coulomb repulsion as alternative explanation to understand the spectral dispersions of TTF-TCNQ quantitatively within an extended Hubbard model.

  13. 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.

  14. Structural, electronic and elastic properties of the cubic CaTiO3 under pressure: A DFT study

    NASA Astrophysics Data System (ADS)

    Tariq, Saad; Ahmed, Afaq; Saad, Saher; Tariq, Samar

    2015-07-01

    Using highly accurate FP-LAPW method with GGA approximation structural, electronic and elastic properties of cubic CaTiO3 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.

  15. 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.

  16. Time-resolved photoemission study of the electronic structure and dynamics of chemisorbed alkali atoms on Ru(0001)

    NASA Astrophysics Data System (ADS)

    Zhang, Shengmin; Wang, Cong; Cui, Xuefeng; Wang, Yanan; Argondizzo, Adam; Zhao, Jin; Petek, Hrvoje

    2016-01-01

    We investigate the electronic structure and photoexcitation dynamics of alkali atoms (Rb and Cs) chemisorbed on transition-metal Ru(0001) single-crystal surface by angle- and time-resolved multiphoton photoemission. Three- and four-photon photoemission (3PP and 4PP) spectroscopic features due to the σ and π resonances arising from the n s and n p states of free alkali atoms are observed from ˜2 eV below the vacuum level in the zero-coverage limit. As the alkali coverage is increased to a maximum of 0.02 monolayers, the resonances are stabilized by formation of a surface dipole layer, but in contrast to alkali chemisorption on noble metals, both resonances form dispersive bands with nearly free-electron mass. Density functional theory calculations attribute the band formation to substrate-mediated interaction involving hybridization with the unoccupied d bands of the substrate. Time-resolved measurements quantify the phase and population relaxation times in the three-photon photoemission (3PP) process via the σ and π resonances. Differences between alkali-atom chemisorption on noble and transition metals are discussed.

  17. 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.

  18. Structural, stability and electronic properties of C15-AB2 (A = Ti, Zr; B = Cr) intermetallic compounds and their hydrides: An ab initio study

    NASA Astrophysics Data System (ADS)

    Sarhaddi, Reza; Arabi, Hadi; Pourarian, Faiz

    2014-05-01

    The structural, stability and electronic properties of C15-AB2 (A = Ti, Zr; B = Cr) isomeric intermetallic compounds were systematically investigated by using density functional theory (DFT) and plane-wave pseudo-potential (PW-PP) method. The macroscopic properties including the lattice constant, bulk modulus and stability for these compounds were studied before and after hydrogenation. For parent compounds, the enthalpy of formation was evaluated with regard to their bulk modules and electronic structures. After hydrogenation of compounds at different interstitial tetrahedral sites (A2B2, A1B3, B4), a volume expansion was found for hydrides. The stability properties of hydrides characterized the A2B2 sites as the site preference of hydrogen atoms for both compounds. The Miedema's "reverse stability" rule is also satisfied in these compounds as lower the enthalpy of formation for the host compound, the more stable the hydride. Analysis of microscopic properties (electronic structures) after hydrogenation at more stable interstitial site (A2B2) shows that the H atoms interact stronger with the weaker (or non) hydride forming element B (Cr) than the hydride forming element A (Ti/Zr). A correlation was also found between the stability of the hydrides and their electronic structure: the deeper the hydrogen band, the less stable the hydride.

  19. Electronic structure of lithium tetraborate

    NASA Astrophysics Data System (ADS)

    Wooten, David J.

    Due to many of its attributes, Li2B4O7 provides a possible material for incorporation as either a primary or companion material in future solid state neutron detectors. There is however a lack of fundamental characterization information regarding this useful material, particularly its electronic configuration. To address this, an investigation of Li2B4O7(110) and Li2B 4O7(100) was undertaken, utilizing photoemission and inverse photoemission spectroscopic techniques. The measured band gap depended on crystallographic direction with the band gaps ranging from 8.9+/-0.5 eV to 10.1+/-0.5 eV. The measurement yielded a density of states that qualitatively agreed with the theoretical results from model bulk band structure calculations for Li2B4O7; albeit with a larger band gap than predicted, but consistent with the known deficiencies of Local Density Approximation and Density Functional Theory calculations. The occupied states of both surfaces were extremely flat; to the degree that resolving periodic dispersion of the occupied states was inconclusive, within the resolution of the system. However, both surfaces demonstrated clear periodic dispersion within the empty states very close to theoretical Brillouin zone values. These attributes also translated to a lighter charge carrier effective mass in the unoccupied states. Of the two surfaces, Li2B4O 7(110) yielded the more consistent values in orthogonal directions for energy states. The presence of a bulk band gap surface state and image potential state in Li2B4O7(110) was indicative of a defect-free surface. The absence of both in the more polar, more dielectric Li2B4O7(100) was attributed to the presence of defects determined to be O vacancies. The results from Li2B 4O7(110) were indicative of a more stable surface than Li 2B4O7(100). In addition, Li 1s bulk and surface core level components were determined at the binding energies of -56.5+0.4 and -53.7+0.5 eV. Resonance features were observed along the [001

  20. 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.

  1. First-principle electronic structure calculations for magnetic moment in iron-based superconductors: An LSDA + negative U study

    NASA Astrophysics Data System (ADS)

    Nakamura, H.; Hayashi, N.; Nakai, N.; Okumura, M.; Machida, M.

    2009-10-01

    In order to resolve a discrepancy of the magnetic moment on Fe between the experimental and calculation results, we perform first-principle electronic structure calculations for iron-based superconductors LaFeAsO1-x and LiFeAs also show similar SDW. So far, the first-principle calculations on LaFeAsO actually predicted the SDW state as a ground state. However, the predicted magnetic moment (∼2 μB) per an Fe atom is much larger than the observed one (∼0.35 μB) in experiments [2,4]. The authors suggested that the discrepancy can be resolved by expanding U into a negative U range within LSDA + U framework. In this paper, we revisit the discrepancy and clarify why the negative correction is essential in these compounds. See Ref. [5] for the details of calculation data by LSDA + negative U. In the first-principle calculation on compounds including transition metals, the total energy is frequently corrected by “LSDA + U” approach. The parameter U is theoretically re-expressed as U(≡U-J), where U is the on-site Coulomb repulsion (Hubbard U) and J is the atomic-orbital intra-exchange energy (Hund’s coupling parameter) [6]. The parameter U employed in the electronic structure calculations is usually positive. The positivity promotes the localized character of d-electrons and enhances the magnetic moment in the cases of magnetically ordered compounds. Normally, this positive correction successfully works. In choosing the parameter, one can principally extend the parameter U range to a negative region. The negative case [7] is not popular, but it can occur in the following two cases [8]: (i) the Hubbard U becomes negative and (ii) the intra-exchange J is effectively larger than the Hubbard U. The case (i) has been suggested by many authors based on various theoretical considerations. Here, we note that U should be estimated once screening effects on the long-range Coulomb interaction are taken into account. In fact, small U has been reported [9]. Thus, when the

  2. 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.

  3. 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.

  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. Study on the electronic structure and Fermi surface of 3d-transition-metal disilisides CoSi2

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.

    2012-09-01

    We have investigated the electronic structure, the momentum density distribution ρ( p), and the Fermi surface FS of single crystals of the Pyrite-type 3d-transition-metal disilisides CoSi2. The band structure calculations, the density of states DOS, and the FS, in vicinity of Fermi level, have been carried out using the full-potential linearized augmented plane wave FP-LAPW method within generalized gradient approximation GGA for exchange and correlation potential. The measurements have been performed via the 2D angular correlation of annihilation radiation ACAR experiments. ρ( p) has been reconstructed by using the Fourier transformation technique. The FS has been reconstructed within the first Brillion zone BZ through the Locks, Crisp, and West LCW folding procedures. The analysis confirmed that Si 3 sp states hybrid with both Co 3 d- t 2 g and Co 3 d- e g states around Γ and X points, respectively. The dimensions of the FS of CoSi2 have been compared to the present calculations as well as to the earlier results.

  6. 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.

  7. 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.

  8. On the electronic and geometric structures of armchair GeC nanotubes: a hybrid density functional study

    NASA Astrophysics Data System (ADS)

    Rathi, Somilkumar J.; Ray, Asok K.

    2008-08-01

    Ab initio calculations within the framework of hybrid density functional theory and the finite cluster approximation have been performed for the electronic and geometric structures of three different types of armchair germanium carbide nanotube, from (3, 3) to (11, 11). Full geometry and spin optimizations with unrestricted symmetry have been performed. Physically pertinent quantities of interest such as the cohesive energies, band gaps, radial buckling, density of states, dipole moments, and Mulliken charge distributions have been investigated in detail for all nanotubes. For type I nanotubes, the largest cohesive energy obtained is 4.092 eV/atom, whereas for type II and type III nanotubes, the values are 3.987 eV/atom and 3.968 eV/atom, respectively. For optimized type I nanotubes, Ge atoms moved toward the tube axis and C atoms moved in the opposite direction after relaxation, opposite to the trends observed in types II and III. The band gaps for type I nanotubes are larger than the bulk 3C-GeC gap, varying between 2.666 and 3.016 eV, while type II and type III nanotubes have significantly lower band gaps, with all nanotubes being semiconducting in nature. Mulliken charge analysis indicates primarily ionic behavior for type I GeC nanotubes and a mixed ionic with covalent behavior for the other two types. None of the tubes appear to be magnetic. Applications in the field of nano-optoelectronic devices, molecular electronics, and band gap engineering are envisioned for GeC nanotubes.

  9. On the electronic and geometric structures of armchair GeC nanotubes: a hybrid density functional study.

    PubMed

    Rathi, Somilkumar J; Ray, Asok K

    2008-08-20

    Ab initio calculations within the framework of hybrid density functional theory and the finite cluster approximation have been performed for the electronic and geometric structures of three different types of armchair germanium carbide nanotube, from (3, 3) to (11, 11). Full geometry and spin optimizations with unrestricted symmetry have been performed. Physically pertinent quantities of interest such as the cohesive energies, band gaps, radial buckling, density of states, dipole moments, and Mulliken charge distributions have been investigated in detail for all nanotubes. For type I nanotubes, the largest cohesive energy obtained is 4.092 eV/atom, whereas for type II and type III nanotubes, the values are 3.987 eV/atom and 3.968 eV/atom, respectively. For optimized type I nanotubes, Ge atoms moved toward the tube axis and C atoms moved in the opposite direction after relaxation, opposite to the trends observed in types II and III. The band gaps for type I nanotubes are larger than the bulk 3C-GeC gap, varying between 2.666 and 3.016 eV, while type II and type III nanotubes have significantly lower band gaps, with all nanotubes being semiconducting in nature. Mulliken charge analysis indicates primarily ionic behavior for type I GeC nanotubes and a mixed ionic with covalent behavior for the other two types. None of the tubes appear to be magnetic. Applications in the field of nano-optoelectronic devices, molecular electronics, and band gap engineering are envisioned for GeC nanotubes. PMID:21730632

  10. 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.

  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. 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.

  13. Theoretical Study of L-Edge Resonant Inelastic X-ray Scattering in La2CuO4 on the Basis of Detailed Electronic Band Structure

    NASA Astrophysics Data System (ADS)

    Nomura, Takuji

    2015-09-01

    We study theoretically resonant inelastic x-ray scattering (RIXS) at the Cu L3-edge in a typical parent compound of high-Tc cuprate superconductors La2CuO4 on the basis of a detailed electronic band structure. We construct a realistic and precise tight-binding model by employing the maximally-localized Wannier functions derived from a first-principles electronic structure calculation, and then take account of the Coulomb repulsion between d electrons at each Cu site. The antiferromagnetic ground state is described within the Hartree-Fock approximation, and take account of electron correlations in the intermediate states of RIXS within the random-phase approximation (RPA). Calculated RIXS spectra agree well with the experimentally observed features including low-energy magnon excitation, d-d excitations, and charge-transfer excitations, over a wide excitation-energy range. In particular, we stress the importance of photon polarization dependence: the intensity of magnon excitation and the spectral structure of d-d excitations depend significantly not only on the polarization direction of incident incoming photons but also that of outgoing photons. It is demonstrated that the single-magnon excitation intensity is maximized when the polarization directions of incoming and outgoing photons are perpendicular to each other.

  14. 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.

  15. 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

  16. Atom-probe and field emission electron spectroscopy studies of ordered structures and electronic properties of Ge overlayers on Ir-tips

    NASA Astrophysics Data System (ADS)

    Ashino, Makoto; Tomitori, Masahiko; Nishikawa, Osamu

    1994-03-01

    The combined instrument of an atom probe (AP) and a field emission electron spectroscope (FEES) was employed to investigate the crystallinity and the surface electronic state of Ge overlayers deposited on Ir tips. The crystallinity of Ge overlayers deposited at 300 and 420 K, and those annealed after the deposition, is better than that of the overlayers deposited at 50 K. The surface electronic state of the well-crystallized Ge overlayer is semiconductive at the thickness of ≈4 ML. When the degree of crystallinity is rather low or Ir atoms exist in the Ge overlayer, even a thick overlayer exhibits metallic surface electronic states. When an Ir atom exists on the overlayer surface, a small peak appears at ≈ 0.3 eV below the Fermi level in the field emission electron distribution (FEED), indicating a local state of the Ir atom.

  17. 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.

  18. Electronic structure of cobalt nanocrystals suspended inliquid

    SciTech Connect

    Liu, Hongjian; Guo, Jinghua; Yin, Yadong; Augustsson, Andreas; Dong, Chungli; Nordgren, Joseph; Chang, Chinglin; Alivisatos, Paul; Thornton, Geoff; Ogletree, D. Frank; Requejo, Felix G.; de Groot, Frank; Salmeron, Miquel

    2007-07-16

    The electronic structure of cobalt nanocrystals suspended in liquid as a function of size has been investigated using in-situ x-ray absorption and emission spectroscopy. A sharp absorption peak associated with the ligand molecules is found that increases in intensity upon reducing the nanocrystal size. X-ray Raman features due to d-d and to charge-transfer excitations of ligand molecules are identified. The study reveals the local symmetry of the surface of {var_epsilon}-Co phase nanocrystals, which originates from a dynamic interaction between Co nanocrystals and surfactant + solvent molecules.

  19. 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.

  20. Electronic and magnetic structures of chain structured iron selenide compounds

    NASA Astrophysics Data System (ADS)

    Li, Wei; Setty, Chandan; Chen, X. H.; Hu, Jiangping

    2014-08-01

    Electronic and magnetic structures of iron selenide compounds Ce2O2FeSe2 (2212*) and BaFe2Se3 (123*) are studied by the first-principles calculations. We find that while all these compounds are composed of one-dimensional (1D) Fe chain (or ladder) structures, their electronic structures are not close to be quasi-1D. The magnetic exchange couplings between two nearest-neighbor (NN) chains in 2212* and between two NN two-leg-ladders in 123* are both antiferromagnetic (AFM), which is consistent with the presence of significant third NN AFM coupling, a common feature shared in other iron-chalcogenides, FeTe (11*) and K y Fe2- x Se2 (122*). In magnetic ground states, each Fe chain of 2212* is ferromagnetic and each two-leg ladder of 123* form a block-AFM structure. We suggest that all magnetic structures in iron-selenide compounds can be unified into an extended J 1- J 2- J 3 model. Spin-wave excitations of the model are calculated and can be tested by future experiments on these two systems.

  1. Equilibrium structure and relative stability of glyceraldehyde conformers: Gas-phase electron diffraction (GED) and quantum-chemical studies

    NASA Astrophysics Data System (ADS)

    Vogt, Natalja; Atavin, Evgenii G.; Rykov, Anatolii N.; Popov, Evgenii V.; Vilkov, Lev V.

    2009-11-01

    For the first time, the five dimensional (5-D) analysis of potential energy surface (PES) from quantum-chemical calculations was carried out to predict reliably the various glyceraldehyde (GLA) conformers. 36 conformers with relative stabilities up to 38 kJ/mol were found in the B3LYP approximation. According to results of MP2/cc-pVQZ calculations, the molecule exists at the experimental temperature of 388 K as a mixture of five conformers in the ratio I:II:III:IV:V = 63:18:4:10:5. Contrary to the theoretical conclusion of Lovas et al., the conformer IV is predicted to be more stable than the conformer III. Our result can explain why the conformer IV could be detected in the microwave (MW) spectroscopic experiment by Lovas et al., whereas the conformer III could not. For the first time, thermal-average and equilibrium structural parameters of GLA (main conformer) have been determined from gas-phase electron diffraction (GED) data. Vibrational corrections to the experimental bond lengths were determined using quadratic and cubic force constants from high-level ab initio calculations (MP2/cc-pVTZ). It was shown that the experimental intensities are sensitive to the contribution of the second conformer (27(15)%). Rotational constants calculated from MP2/cc-pVQZ geometries were found to be in excellent agreement with the experimental rotational constants corrected for anharmonic effects.

  2. Electronic Structure Theory Study of the Microsolvated F(-)(H2O) + CH3I SN2 Reaction.

    PubMed

    Zhang, Jiaxu; Yang, Li; Sheng, Li

    2016-05-26

    The potential energy profile of microhydrated fluorine ion reaction with methyl iodine has been characterized by extensive electronic structure calculations. Both hydrogen-bonded F(-)(H2O)---HCH2I and ion-dipole F(-)(H2O)---CH3I complexes are formed for the reaction entrance and the PES in vicinity of these complexes is very flat, which may have important implications for the reaction dynamics. The water molecule remains on the fluorine side until the reactive system goes to the SN2 saddle point. It can easily move to the iodine side with little barrier, but in a nonsynchronous reaction path after the dynamical bottleneck to the reaction, which supports the previous prediction for microsolvated SN2 systems. The influence of solvating water molecule on the reaction mechanism is probed by comparing with the influence of the nonsolvated analogue and other microsolvated SN2 systems. Taking the CCSD(T) single-point calculations based on MP2-optimized geometries as benchmark, the DFT functionals B97-1 and B3LYP are found to better characterize the potential energy profile for the title reaction and are recommended as the preferred methods for the direct dynamics simulations to uncover the dynamic behaviors. PMID:27126610

  3. Hydration, structure, and molecular interactions in the headgroup region of dioleoylphosphatidylcholine bilayers: an electron spin resonance study.

    PubMed

    Ge, Mingtao; Freed, Jack H

    2003-12-01

    The relationship between bilayer hydration and the dynamic structure of headgroups and interbilayer water in multilamellar vesicles is investigated by electron spin resonance methods. Temperature variations of the order parameter of a headgroup spin label DPP-Tempo in DOPC in excess water and partially dehydrated (10 wt % water) show a cusp-like pattern around the main phase transition, Tc. This pattern is similar to those of temperature variations of the quadrupolar splitting of interbilayer D2O in PC and PE bilayers previously measured by 2H NMR, indicating that the ordering of the headgroup and the interbilayer water are correlated. The cusp-like pattern of these and other physical properties around Tc are suggestive of quasicritical fluctuations. Also, an increase (a decrease) in ordering of DPP-Tempo is correlated with water moving out of (into) interbilayer region into (from) the bulk water phase near the freezing point, Tf. Addition of cholesterol lowers Tf, which remains the point of increasing headgroup ordering. Using the small water-soluble spin probe 4-PT, it is shown that the ordering of interbilayer water increases with bilayer dehydration. It is suggested that increased ordering in the interbilayer region, implying a lowering of entropy, will itself lead to further dehydration of the interbilayer region until its lowered pressure resists further flow, i.e., an osmotic phenomenon. PMID:14645091

  4. 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.

  5. 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.

  6. 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.

  7. About zitterbewegung and electron structure

    NASA Astrophysics Data System (ADS)

    Rodrigues, Waldyr A.; Vaz, Jayme; Recami, Erasmo; Salesi, Giovanni

    1993-12-01

    We start from the spinning electron model by Barut and Zanghi, which has been recently translated into the Clifford algebra language. We ``complete'' such a translation, first of all, by expressing in the Clifford formalism a particular Barut-Zanghi (BZ) solution, which refers (at the classical limit) to an ``internal'' helical motion with a time-like speed (and is here shown to originate from the superposition of positive and negative frequency solutions of the Dirac equation). Then, we show how to construct solutions of the Dirac equation describing helical motions with light-like speed, which meet very well the standard interpretation of the velocity operator in the Dirac equation theory (and agree with the solution proposed by Hestenes, on the basis - however - of ad-hoc assumptions that are unnecessary in the present approach). The above results appear to support the conjecture that the zitterbewegung motion (a helical motion, at the classical limit) is responsible for the electron spin.

  8. Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Moosburger-Will, Judith; Kündel, Jörg; Klemm, Matthias; Horn, Siegfried; Hofmann, Philip; Schwingenschlögl, Udo; Eyert, Volker

    2009-03-01

    A comprehensive study of the electronic properties of monoclinic MoO2 from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations. For the latter, the full-potential augmented spherical wave method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional holelike surfaces centered around the Z and B points could be resolved; these surfaces were artifacts of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of MoO2 and the neighboring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of VO2 and NbO2 , which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.

  9. Electronic structure and orientation relationship of Li nanoclusters embedded in MgO studied by depth-selective positron annihilation two-dimensional angular correlation

    NASA Astrophysics Data System (ADS)

    Falub, C. V.; Mijnarends, P. E.; Eijt, S. W.; van Huis, M. A.; van Veen, A.; Schut, H.

    2002-08-01

    Quantum-confined positrons are sensitive probes for determining the electronic structure of nanoclusters embedded in materials. In this work, a depth-selective positron annihilation 2D-ACAR (two-dimensional angular correlation of annihilation radiation) method is used to determine the electronic structure of Li nanoclusters formed by implantation of 1016-cm-2 30-keV 6Li ions in MgO (100) and (110) crystals and by subsequent annealing at 950 K. Owing to the difference between the positron affinities of lithium and MgO, the Li nanoclusters act as quantum dots for positrons. 2D-ACAR distributions for different projections reveal a semicoherent fitting of the embedded metallic Li nanoclusters to the host MgO lattice. Ab initio Korringa-Kohn-Rostoker calculations of the momentum density show that the anisotropies of the experimental distributions are consistent with an fcc crystal structure of the Li nanoclusters. The observed reduction of the width of the experimental 2D-ACAR distribution is attributed to positron trapping in vacancies associated with Li clusters. This work proposes a method for studying the electronic structure of metallic quantum dots embedded in an insulating material.

  10. 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.

  11. First-principles study on electronic structure and optical properties of Cu-doped β-Ga2O3

    NASA Astrophysics Data System (ADS)

    Yan, Huiyu; Guo, Yanrui; Song, Qinggong; Chen, Yifei

    2014-02-01

    The electronic and optical properties of the Cu-doped and intrinsic β-Ga2O3 are studied by using the first-principles calculation method. Results show that Cu-doped β-Ga2O3 can be fabricated in experiments. Two acceptor impurity levels are introduced near the top of the valence band by Cu dopant, indicating that Cu-doped gallium oxide is a promising p-type semiconductor. Cu-doped β-Ga2O3 can be used as intermediate band semiconductor in solar cell. Cu dopant induced 100% spin polarization near the Fermi level. The analysis results of optical properties reveal that Cu-doped β-Ga2O3 is a promising potential candidate for p-type ultraviolet (UV) transparent semiconductor.

  12. 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

  13. Structural and electronic changes in the growth of mercury overlayers on Cu(001) - A helium beam scattering, LEED and ARPES study

    NASA Technical Reports Server (NTRS)

    Vidali, G.; Li, W.; Dowben, P. A.; Karimi, M.; Hutchings, C. W.; Lin, J.; Moses, C.; Ila, D.; Dalins, I.

    1990-01-01

    We used ABS, LEED and angle-resolved photo-electron spectroscopy (ARPES) to study bilayer films of Hg on Cu(001). In the surface temperature range of 180 to 330 K, the first Hg layer forms two ordered phases, a c(2x2) (with coverage-0.5 of Cu(001)) and a high density (partially commensurate) c(4x4) (coverage-0.62). ARPES data show that there is little or no dispersion of the 5d band of Hg. ABS data show that this layer is not flat, with in-registry Hg atoms lying about 0.15 below the not-in-registry Hg atoms. From ABS we find that the second layer forms a completely registered c(4x4) phase. From ARPES we obtain that the second layer has an electronic structure, particularly the 5d levels, characteristic of bulk mercury. Preliminary results of calculations of the structure of the bilayer are given.

  14. 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.

  15. 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.

  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. 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

  18. Tuning the Electronic Structure of Fe(II) Polypyridines via Donor Atom and Ligand Scaffold Modifications: A Computational Study.

    PubMed

    Bowman, David N; Bondarev, Alexey; Mukherjee, Sriparna; Jakubikova, Elena

    2015-09-01

    Fe(II) polypyridines are an important class of pseudo-octahedral metal complexes known for their potential applications in molecular electronic switches, data storage and display devices, sensors, and dye-sensitized solar cells. Fe(II) polypyridines have a d(6) electronic configuration and pseudo-octahedral geometry and can therefore possess either a high-spin (quintet) or a low-spin (singlet) ground state. In this study, we investigate a series of complexes based on [Fe(tpy)2](2+) (tpy = 2,2';6',2″-terpyridine) and [Fe(dcpp)2](2+) (dcpp = 2,6-bis(2-carboxypyridyl)pyridine). The ligand field strength in these complexes is systematically tuned by replacing the central pyridine with five-membered (N-heterocyclic carbene, pyrrole, furan) or six-membered (aryl, thiazine-1,1-dioxide, 4-pyrone) moieties. To determine the impact of ligand substitutions on the relative energies of metal-centered states, the singlet, triplet, and quintet states of the Fe(II) complexes were optimized in water (PCM) using density functional theory at the B3LYP+D2 level with 6-311G* (nonmetals) and SDD (Fe) basis sets. It was found that the dcpp ligand scaffold allows for a more ideal octahedral coordination environment in comparison to the tpy ligand scaffold. The presence of six-membered central rings also allows for a more ideally octahedral coordination environment relative to five-membered central rings, regardless of the ligand scaffold. We find that the ligand field strength in the Fe(II) polypyridines can be tuned by altering the donor atom identity, with C donor atoms providing the strongest ligand field. PMID:26295275

  19. Structure and Energetics of Encapsidated DNA in Bacteriophage HK97 Studied by Scanning Calorimetry and Cryo-electron Microscopy

    PubMed Central

    Duda, Robert L.; Ross, Philip D.; Cheng, Naiqian; Firek, Brian A.; Hendrix, Roger W.; Conway, James F.; Steven, Alasdair C.

    2009-01-01

    Encapsidation of duplex DNA by bacteriophages represents an extreme case of genome condensation, reaching near-crystalline concentrations of DNA. The HK97 system is well suited to study this phenomenon in view of detailed knowledge of its capsid structure. To characterize the interactions involved, we combined calorimetry with cryo-EM and native gel electrophoresis. We found that, as in other phages, HK97 DNA is organized in coaxially wound nested shells. When scanned in buffer containing 1mM [Mg++], filled capsids exhibit a complex thermal profile between 82° and 96°, to which DNA melting and capsid denaturation both contribute. In the absence of (unbound) [Mg++], DNA melting shifts to lower temperatures and the two events are resolved. Filled capsids release their DNA at temperatures well below the onset of DNA melting or capsid denaturation. On heating, the internal pressure increases, causing the DNA to exit – probably, via the portal vertex; the capsid, although largely intact, sustains local damage that leads to an earlier onset of thermal denaturation. Filled capsids differ structurally from empty capsids in the curvature of their protein shell, a change attributable to outwards pressure exerted by the DNA. We propose that this transition is sensed by the portal which is embedded in the capsid wall, whereupon the portal's structure and its interactions with terminase, the packaging enzyme, are altered, thus signaling that packaging is at or approaching completion. PMID:19540242

  20. Density functional study of structural and electronic properties of maximum-spin n+1Aun-1Ag clusters

    NASA Astrophysics Data System (ADS)

    Jiang, Zhen-Yi; Hou, Yu-Qin; Lee, Kuo-Hsing; Chu, San-Yan

    The structures and relative stabilities of high-spin n+1Aun-1Ag and nAun-1Ag+ (n = 2-8) clusters have been studied with density functional calculation. We predicted the existence of a number of previously unknown isomers. Our results revealed that all structures of high-spin neutral or cationic Aun-1Ag clusters can be understood as a substitution of an Au atom by an Ag atom in the high-spin neutral or cationic Aun clusters. The properties of mixed gold-silver clusters are strongly sized and structural dependence. The high-spin bimetallic clusters tend to be holding three-dimensional geometry rather than planar form represented in their low-spin situations. Silver atom prefers to occupy those peripheral positions until to n = 8 for high-spin clusters, which is different from its position occupied by light atom in the low-spin situations. Our theoretical calculations indicated that in various high-spin Aun-1Ag neutral and cationic species, 5Au3Ag, 3AuAg and 5Au4Ag+ hold high stability, which can be explained by valence bond theory.