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  • 351.
    Johansson, Magnus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Prilepsky, Jaroslaw E.
    Aston University, Birmingham, UK.
    Derevyanko, Stanislav A.
    Weizmann Institute Science, Rehovot, Israel .
    Strongly localized moving discrete dissipative breather-solitons in Kerr nonlinear media supported by intrinsic gain2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 89, no 4, p. 042912-1-042912-9Article in journal (Refereed)
    Abstract [en]

    We investigate the mobility of nonlinear localized modes in a generalized discrete Ginzburg-Landau-type model, describing a one-dimensional waveguide array in an active Kerr medium with intrinsic, saturable gain and damping. It is shown that exponentially localized, traveling discrete dissipative breather-solitons may exist as stable attractors supported only by intrinsic properties of the medium, i.e., in the absence of any external field or symmetry-breaking perturbations. Through an interplay by the gain and damping effects, the moving soliton may overcome the Peierls-Nabarro barrier, present in the corresponding conservative system, by self-induced time-periodic oscillations of its power (norm) and energy (Hamiltonian), yielding exponential decays to zero with different rates in the forward and backward directions. In certain parameter windows, bistability appears between fast modes with small oscillations and slower, large-oscillation modes. The velocities and the oscillation periods are typically related by lattice commensurability and exhibit period-doubling bifurcations to chaotically walking modes under parameter variations. If the model is augmented by intersite Kerr nonlinearity, thereby reducing the Peierls-Nabarro barrier of the conservative system, the existence regime formoving solitons increases considerably, and a richer scenario appears including Hopf bifurcations to incommensurately moving solutions and phase-locking intervals. Stable moving breathers also survive in the presence of weak disorder.

  • 352.
    Curtsdotter, Alva
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Norberg, Jon
    Department of Systems Ecology, Stockholm University/Stockholm Resilience Centre, Stockholm University, Sweden.
    Åkesson, Anna
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    The strength of interspecific competition modulates the eco-evolutionary response to climate change2014Manuscript (preprint) (Other academic)
    Abstract [en]

    Climate change is predicted to have major implications for global biodiversity. Dispersal and evolution may become crucial for species survival, as species must either adapt or migrate to track the changing climate. However, migration and evolution do not occur in vacuum – the biotic community in which these processes play out may modulate their effect on biodiversity. Here, we use an eco-evolutionary, spatially explicit, multi-species model that allows us to examine the interactive effects of competition, adaptation and dispersal on species richness in plant communities under global warming. We find that there is a larger decline in global species richness when interspecific competition is strong. Furthermore, there is a three-way interaction between interspecific competition, evolution and dispersal that creates a complex pattern of biodiversity responses, in which both evolution and dispersal can either increase or decrease the magnitude of species loss. This interaction arises for at least two reasons: 1) different levels of dispersal, evolution and competition creates differences in local and global community structure before climate change, and 2) competitive interactions determine whether the benefits of dispersal and/or evolution (climate tracking and adaptation) outweighs the risks (competitive exclusion).

  • 353.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gali, Adam
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Theoretical investigation of the single photon emitter carbon antisite-vacancy pair in 4H-SiC2014In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, p. 495-498Conference paper (Refereed)
    Abstract [en]

    Well addressable and controllable point defects in device friendly semiconductors are desired for quantum computational and quantum informational processes. Recently, such defect, an ultra-bright single photon emitter, the carbon antisite - vacancy pair, was experimentally investigated in 4H-SiC. In our theoretical work, based on ab initio calculation and group theory analysis, we provide a deeper understanding of the features of the electronic structures and the luminescence process of this defect.

  • 354.
    Abrikosov, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Nikonov, A. Yu
    Russian Academic Science, Russia .
    Ponomareva, A. V.
    National University of Science and Technology MISiS, Russia .
    Dmitriev, A. I.
    Russian Academic Science, Russia National Research Tomsk State University, Russia .
    Barannikova, S. A.
    Russian Academic Science, Russia National Research Tomsk State University, Russia .
    Theoretical Modeling of Thermodynamic and Mechanical Properties of the Pure Components of Ti and Zr Based Alloys Using the Exact Muffin-Tin Orbitals Method2014In: Russian Physics Journal, ISSN 1064-8887, E-ISSN 1573-9228, Vol. 56, no 9, p. 1030-1038Article in journal (Refereed)
    Abstract [en]

    The exact muffin-tin orbitals (EMTO) method belongs to the third and latest generation of first-principles methods of calculating the electronic structure of materials in the so-called approximation of muffin-tin (MT) orbitals within the framework of the density functional theory. A study has been performed of its applicability for modeling the thermodynamic and mechanical properties of the pure components of Ti and Zr based alloys. The total energies of Ti, Zr, Nb, V, Mo, and Al are calculated in three crystal structures - face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP). For all of these elements and crystal structures, we have calculated the theoretical values of the lattice constants, elastic constants, and equations of state. The stable crystal structures have been determined. In all cases, calculations by the EMTO method predict the correct structure of the ground state. For stable structures we compared the obtained results with experiment and with calculations using full potential methods. We have demonstrated the reliability of the EMTO method and conclude that its further application for effective modeling of the properties of disordered alloys based on Ti and Zr is possible.

  • 355.
    Ivády, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Szasz, Krisztian
    Hungarian Academic Science, Hungary Eotvos Lorand University, Hungary .
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gali, Adam
    Hungarian Academic Science, Hungary Budapest University of Technology and Econ, Hungary .
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Theoretical unification of hybrid-DFT and DFT plus U methods for the treatment of localized orbitals2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 3, p. 035146-Article in journal (Refereed)
    Abstract [en]

    Hybrid functionals serve as a powerful practical tool in different fields of computational physics and quantum chemistry. On the other hand, their applicability for the case of correlated d and f orbitals is still questionable and needs more considerations. In this article we formulate the on-site occupation dependent exchange correlation energy and effective potential of hybrid functionals for localized states and connect them to the on-site correction term of the DFT+ U method. The resultant formula indicates that the screening of the onsite electron repulsion is governed by the ratio of the exact exchange in hybrid functionals. Our derivation provides a theoretical justification for adding a DFT+ U-like on-site potential in hybrid-DFT calculations to resolve issues caused by overscreening of localized states. The resulting scheme, hybrid DFT+ V-w, is tested for chromium impurity in wurtzite AlN and vanadium impurity in 4H-SiC, which are paradigm examples of systems with different degrees of localization between host and impurity orbitals.

  • 356.
    Palumbo, M.
    et al.
    Ruhr University of Bochum, Germany .
    Burton, B.
    NIST, MD 20899 USA .
    Costa e Silva, A.
    EEIMVR UFF, Brazil .
    Fultz, B.
    CALTECH, CA 91125 USA .
    Grabowski, B.
    Max Planck Institute Eisenforsch GmbH, Germany .
    Grimvall, G.
    KTH Royal Institute Technology, Sweden .
    Hallstedt, B.
    Rhein Westfal TH Aachen, Germany .
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Lindahl, B.
    KTH Royal Institute Technology, Sweden .
    Schneider, A.
    Vallourec Deutschland GmbH, Germany .
    Turchi, P. E. A.
    Lawrence Livermore National Lab, CA USA .
    Xiong, W.
    University of Wisconsin, WI 53706 USA .
    Thermodynamic modelling of crystalline unary phases2014In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 251, no 1, p. 14-32Article in journal (Refereed)
    Abstract [en]

    Progress in materials science through thermodynamic modelling may rest crucially on access to a database, such as that developed by Scientific Group Thermodata Europe (SGTE) around 1990. It gives the Gibbs energy G(T) of the elements in the form of series as a function of temperature, i.e. essentially a curve fitting to experimental data. In the light of progress in theoretical understanding and first-principles calculation methods, the possibility for an improved database description of the thermodynamics of the elements has become evident. It is the purpose of this paper to provide a framework for such work. Lattice vibrations, which usually give the major contribution to G(T), are treated in some detail with a discussion of neutron scattering studies of anharmonicity in aluminium, first-principles calculations including ab initio molecular dynamics (AIMD), and the strength and weakness of analytic model representations of data. Similarly, electronic contributions to G(T) are treated on the basis of the density of states N(E) for metals, with emphasis on effects at high T. Further, we consider G(T) below 300K, which is not covered by SGTE. Other parts in the paper discuss metastable and dynamically unstable lattices, G(T) in the region of superheated solids and the requirement on a database in the calculation of phase diagrams. (C) 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

  • 357.
    Sangiovanni, Davide
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Edström, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Petrov, Ivan
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. University of Illinois, Urbana, USA.
    Greene, Joseph E
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology. University of Illinois, Urbana, USA.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Ti adatom diffusion on TiN(001): Ab initio and classical molecular dynamics simulations2014In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 627, p. 34-41Article in journal (Refereed)
    Abstract [en]

    Ab initio and classical molecular dynamics (AIMD and CMD) simulations reveal that Ti adatoms on TiN(001) surfaces migrate between neighboring fourfold hollow sites primarily along in-plane less than100greater than channels. less than100greater than and less than110greater than single jumps, as well as less than100greater than double jump rates, obtained directly from MD runs as a function of temperature, are used to determine diffusion activation energies Ea, and attempt frequencies A, for the three preferred Ti adatom migration pathways on TiN(001). From transition rates Aexp[-Ea / (k(B)T)], we determine adatom surface distribution probabilities as a function of time, which are used to calculate adatom diffusion coefficients D(T). AIMD and CMD predictions are consistent and complementary. Using CMD, we investigate the effect on the adatom jump rate of varying the phonon wavelength degrees of freedom by progressively increasing the supercell size. We find that long-wavelength phonons significantly contribute to increasing adatom mobilities at temperatures less than= 600 K, but not at higher temperatures. Finally, by directly tracking the Ti adatom mean-square displacement during CMD runs, we find that Ti adatom jumps are highly correlated on TiN(001), an effect that yields lower D-s values (D-s(corr)) than those estimated from uncorrelated transition probabilities. The temperature-dependent diffusion coefficient is D-s(corr) (T) = (4.5 x 10(-4) Cm-2 s(-1)) exp[-0.55 eV / (k(B)T)].

  • 358.
    Klimchitskaya, G. L.
    et al.
    Russian Academic Science, Russia St Petersburg State Polytech University, Russia .
    Mostepanenko, V.M.
    Russian Academic Science, Russia St Petersburg State Polytech University, Russia .
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Two approaches for describing the Casimir interaction in graphene: Density-density correlation function versus polarization tensor2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 12, p. 125407-Article in journal (Refereed)
    Abstract [en]

    A comparison study of theoretical approaches to the description of the Casimir interaction in layered systems including graphene is performed. It is shown that at zero temperature, the approach using the polarization tensor leads to the same results as the approach using the longitudinal density-density correlation function of graphene. An explicit expression for the zero-temperature transverse density-density correlation function of graphene is provided. We further show that the computational results for the Casimir free energy of graphene-graphene and graphene-Au plate interactions at room temperature, obtained using the temperature-dependent polarization tensor, deviate significantly from those using the longitudinal density-density correlation function defined at zero temperature. We derive both the longitudinal and transverse density-density correlation functions of graphene at nonzero temperature. The Casimir free energy in layered structures including graphene, computed using the temperature-dependent correlation functions, is exactly equal to that found using the polarization tensor.

  • 359.
    Elofsson, Viktor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Magnfält, Daniel
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Sarakinos, Kostas
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.
    Unravelling the Physical Mechanisms that Determine Microstructural Evolution of Ultrathin Volmer-Weber Films2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 4, p. 044302-Article in journal (Refereed)
    Abstract [en]

    The initial formation stages (i.e., island nucleation, island growth, and island coalescence) set characteristic length scales during growth of thin films from the vapour phase. They are, thus, decisive for morphological and microstructural features of films and nanostructures. Each of the initial formation stages has previously been well-investigated separately for the case of Volmer-Weber growth, but knowledge on how and to what extent each stage individually and all together affect the microstructural evolution is still lacking. Here we address this question using growth of Ag on SiO2 from pulsed vapour fluxes as a case study. By combining in situ growth monitoring, ex situ imaging and growth simulations we systematically study the growth evolution all the way from nucleation to formation of a continuous film and establish the effect of the vapour flux time domain on the scaling behaviour of characteristic growth transitions (elongation transition, percolation and continuous film formation). Our data reveal a pulsing frequency dependence for the characteristic film growth transitions, where the nominal transition thickness decreases with increasing pulsing frequency up to a certain value after which a steady-state behaviour is observed. The scaling behaviour is shown to result from differences in island sizes and densities, as dictated by the initial film formation stages. These differences are determined solely by the interplay between the characteristics of the vapour flux and time required for island coalescence to be completed. In particular, our data provide evidence that the steady-state scaling regime of the characteristic growth transitions is caused by island growth that hinders coalescence from being completed, leading to a coalescence-free growth regime.

  • 360.
    Hao, Feng
    et al.
    Sandia National Laboratories, Albuquerque, New Mexico, USA.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Mattsson, Ann E.
    Sandia National Laboratories, Albuquerque, New Mexico, USA.
    Using the electron localization function to correct for confinement physics in semi-local density functional theory2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 18, article id 18A536Article in journal (Refereed)
    Abstract [en]

    We have previously proposed that further improved functionals for density functional theory can be constructed based on the Armiento-Mattsson subsystem functional scheme if, in addition to the uniform electron gas and surface models used in the Armiento-Mattsson 2005 functional, a model for the strongly confined electron gas is also added. However, of central importance for this scheme is an index that identifies regions in space where the correction provided by the confined electron gas should be applied. The electron localization function (ELF) is a well-known indicator of strongly localized electrons. We use a model of a confined electron gas based on the harmonic oscillator to show that regions with high ELF directly coincide with regions where common exchange energy functionals have large errors. This suggests that the harmonic oscillator model together with an index based on the ELF provides the crucial ingredients for future improved semi-local functionals. For a practical illustration of how the proposed scheme is intended to work for a physical system we discuss monoclinic cupric oxide, CuO. A thorough discussion of this system leads us to promote the cell geometry of CuO as a useful benchmark for future semi-local functionals. Very high ELF values are found in a shell around the O ions, and take its maximum value along the Cu–O directions. An estimate of the exchange functional error from the effect of electron confinement in these regions suggests a magnitude and sign that could account for the error in cell geometry.

  • 361.
    Shulumba, Nina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Mozafari, Elham
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Steneteg, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Vibrational free energy and phase stability of paramagnetic and antiferromagnetic CrN from ab initio molecular dynamics2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, no 17, p. 174108-Article in journal (Refereed)
    Abstract [en]

    We present a theoretical first-principles method to calculate the free energy of a magnetic system in its high-temperature paramagnetic phase, including vibrational, electronic, and magnetic contributions. The method for calculating free energies is based on ab initio molecular dynamics and combines a treatment of disordered magnetism using disordered local moments molecular dynamics with the temperature-dependent effective potential method to obtain the vibrational contribution to the free energy. We illustrate the applicability of the method by obtaining the anharmonic free energy for the paramagnetic cubic and the antiferromagnetic orthorhombic phases of chromium nitride. The influence of lattice dynamics on the transition between the two phases is demonstrated by constructing the temperature-pressure phase diagram.

  • 362.
    Brodin, G.
    et al.
    Umeå University, Sweden .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Wave Generation in a Warm Magnetized Multi-Component Plasma2014In: Contributions to Plasma Physics, ISSN 0863-1042, E-ISSN 1521-3986, Vol. 54, no 7, p. 623-625Article in journal (Refereed)
    Abstract [en]

    The resonant interaction between three waves propagating perpendicularly to an external magnetic field in a plasma is considered. We present the explicit expressions for the three wave coupling coefficients of a warm multi-component plasma. The results of previous work on the generation of THz radiation by laser plasma interaction are significantly improved.

  • 363.
    Wahlstrand, B
    et al.
    HiQ Mälardalen AB, Arboga, Sweden.
    Yakymenko, Iryna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Wave transport and statistical properties of an open non-Hermitian quantum dot with parity-time symmetry2014In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 89, no 062910Article in journal (Refereed)
    Abstract [en]

    A basic quantum-mechanical model for wave functions and current flow in open quantum dots or billiards is investigated. The model involves non-Hertmitian quantum mechanics, parity-time (PT) symmetry, and PT-symmetry breaking. Attached leads are represented by positive and negative imaginary potentials. Thus probability densities, currents flows, etc., for open quantum dots or billiards may be simulated in this way by solving the Schrödinger equation with a complex potential. Here we consider a nominally open ballistic quantum dot emulated by a planar microwave billiard. Results for probability distributions for densities, currents (Poynting vector), and stress tensor components are presented and compared with predictions based on Gaussian random wave theory. The results are also discussed in view of the corresponding measurements for the analogous microwave cavity. The model is of conceptual as well as of practical and educational interest.

  • 364.
    Mendonca, J. T.
    et al.
    Instituto Superior Técnico, Lisboa.
    Onishchenko, O G
    Institute of Physics of the Earth, Moscow, Russia.
    Pokhotelov, O A
    Institute of Physics of the Earth, Moscow, Russia.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Wave-kinetic description of atmospheric turbulence2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 89, p. 125004-Article in journal (Refereed)
    Abstract [en]

    We propose a wave-kinetic description of atmospheric turbulence, where the turbulence spectrum is described as a gas of quasi-particles. We apply this description to the case of zonal structures in the atmosphere, which can be excited by internal gravity wave turbulence. A general expression for the instability growth rates is derived, and the particular example of a nearly mono-kinetic turbulent spectrum is discussed.

  • 365.
    Brodin, G
    et al.
    Umeå University, Sweden .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Alfven wave interactions within the Hall-MHD description2013In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 79, p. 909-911Article in journal (Refereed)
    Abstract [en]

    We show that comparatively simple expressions for the Alfven wave coupling coefficients can be deduced from the well-known Hall-magnetohydrodynamics (MHD) model equations.

  • 366.
    Karimov, A R
    et al.
    Russian Academy of Sciences, Moscow, Russia.
    Yu, M Y
    Zhejiang University, Hangzhou, China .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Asymmetric oscillatory expansion of a cylindrical plasma2013In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 79, no 6, p. 1007-1009Article in journal (Refereed)
    Abstract [en]

    Asymmetric oscillatory expansion of a cylindrical plasma layer into vacuum is investigated analytically by solving the fluid equations of the electrons and ions together with the Maxwell's equations. For the problem considered, it is found that the asymmetrical flow components are strongly affected by the symmetrical components, but not the vice versa.

  • 367.
    Boström, Mathias
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Persson, Clas
    Royal Institute Technology, Sweden .
    Parsons, Drew F.
    Australian National University, Australia .
    Ellingsen, Simen A.
    Norwegian University of Science and Technology, Norway .
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Atmospheric water droplets can catalyse atom pair break-up via surface-induced resonance repulsion2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 101, no 4Article in journal (Refereed)
    Abstract [en]

    We present the theory for a retarded resonance interaction between two identical atoms near a dielectric surface. In free space the resonance interaction between isotropically excited atom pairs is attractive at all atom-atom separations. We illustrate numerically how this interaction between oxygen, sulphur, hydrogen, or nitrogen atom pairs may turn repulsive near water droplets. The results provide evidence of a mechanism causing excited state atom pair breakage to occur in the atmosphere near water droplets.

  • 368. Ohlin, Kjell
    et al.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Att se toner bortom Faradays vågor2013In: Fysikaktuellt, ISSN 0283-9148, no 1, p. 14-16Article in journal (Other (popular science, discussion, etc.))
  • 369.
    Bingham, Robert
    et al.
    STFC Rutherford Appleton Lab, NJ USA .
    Eliasson, Bengt
    Ruhr University of Bochum, Germany .
    Mendonca, Tito
    IST Lisbon, Portugal .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Biographical-Item: Padma Kant Shukla 1950-2013 Obituary in JOURNAL OF PLASMA PHYSICS, vol 79, issue , pp 119-1192013Other (Other academic)
    Abstract [en]

    n/a

  • 370.
    Eliasson, B.
    et al.
    University of Strathclyde, Scotland .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Bingham, R.
    Rutherford Appleton Lab, England .
    Mendonca, J. T.
    Institute Super Tecn, Portugal .
    Biographical-Item: Preface in JOURNAL OF PLASMA PHYSICS, vol 79, issue , pp 981-9812013Other (Other academic)
    Abstract [en]

    n/a

  • 371.
    Yakimenko, Iryna
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tsykunov, V. S.
    Taras Shevchenko National University of Kyiv, Ukraine .
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Bound states, electron localization and spin correlations in low-dimensional GaAs/AlGaAs quantum constrictions2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 7, p. 072201-Article in journal (Refereed)
    Abstract [en]

    We analyze the occurrence of local  magnetization and the effects of electron localization in different models of quantum point contacts (QPCs) using spin-relaxed density functional theory (DFT/LSDA) by means of numerical simulations. In the case of soft confinement potentials the degree of localization is weak and we therefore observe only traces of partial electron localization in the middle of the QPC. In the pinch-off regime there is, however, distinct accumulation at the QPC edges. At the other end, strong confinement potential, low-electron density in the leads and top or implant gates favor electron localization. In such cases one may create a variety of electron configurations from a single localized electron to more complex structures with multiple rows and Wigner lattices.

  • 372.
    Boström, Mathias
    et al.
    Royal Institute of Technology, Stockholm, Sweden, EU.
    Persson, Clas
    University of Oslo, Norway.
    Sernelius, Bo E.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Casimir force between atomically thin gold films2013In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 86, p. 43-46Article in journal (Refereed)
    Abstract [en]

    We have used density functional theory to calculate the anisotropic dielectric functions forultrathin gold sheets (composed of 1, 3, 6, and 15 atomic layers). Such films are important components innano-electromechanical systems. When using correct dielectric functions rather than bulk gold dielectricfunctions we predict an enhanced attractive Casimir-Lifshitz force (at most around 20%) between twoatomically thin gold sheets. For thicker sheets the dielectric properties and the corresponding Casimirforces approach those of gold half-spaces. The magnitude of the corrections that we predict should, withinthe today’s level of accuracy in Casimir force measurements, be clearly detectable.

  • 373.
    Berggren, Karl-Fredrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Yakymenko, Irina I.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    “Correlation and disorder effects on electron transport in modulation-doped semiconductor quantum point contacts” (invited)2013Conference paper (Other academic)
    Abstract [en]

    ABSTRACT We simulate effects of electron localization and quantum correlations in realistic GaAs/AlGaAs quantum point contacts (QPCs) in the presence of randomly distributed donors (1) using spin-relaxed density functional theory (DFT/LSDA). Two different configurations of gates defining the QPCs were studied: a split gate and a top gate in addition to the split gate. In both cases we recover the conventional fluctuation-free parabolic electrostatic potential when the distance between the donor layer and the 2D electron gas exceeds 70 nm.  Hence we also find ballistic phenomena such as integer conductance steps as well as the 0.7 anomaly. The electrostatic potential changes dramatically,however, when the random donors are placed closer to the 2D gas. Electron localization is then increased and conductance fluctuations and resonance peaks appear. At the same time the usual conductance steps vanish. By charging asymmetrically the split gates voltage we have found that conductance fluctuations caused by random donors are shifted while the anomalies caused by interaction effects may remain.  Resonance peaks in the conductance derive from localized states inside within the QPC. The nature of electron localization has been discussed in our previous study (2) where we stress the crucial role of confinement potential on the formation of electron localization. In the present study we have shown that electron localization may be caused by randomly distributed donors and play an important role in electron transport, especially near the pinch-off regime. The results of our numerical simulations agree with recent experimental studies (3). 

     

    (1) J.A. Nixon, J.H. Davies, and H.U Baranger, Phys. Rev. B 43, 12638 (1991) 

    (2) I. I. Yakimenko, V. S. Tsykunov and K.-F. Berggren, J. Phys. Condens. Matter 25, 072201 (2013)

    (3) L.W. Smith, K. J. Thomas, M. Pepper, D. A. Ritchie, I. Farrer, J.P. Griffiths, G.A.C. Jones,  J. of Phys.: Conf. Series  376, 012018,  (2012)

  • 374.
    Vicencio, Rodrigo A.
    et al.
    University of Chile, Chile.
    Johansson, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Discrete flat-band solitons in the kagome lattice2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 6Article in journal (Refereed)
    Abstract [en]

    We consider a model for a two-dimensional kagome lattice with defocusing nonlinearity, and show that families of localized discrete solitons may bifurcate from localized linear modes of the flat band with zero power threshold. Each family of such fundamental nonlinear modes corresponds to a unique configuration in the strong-nonlinearity limit. By choosing well-tuned dynamical perturbations, small-amplitude, strongly localized solutions from different families may be switched into each other, as well as moved between different lattice positions. In a window of small power, the lowest-energy state is a symmetry-broken localized state, which may appear spontaneously.

  • 375.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Drottningen och filosofen - mötet mellan Christina och Descartes2013In: Fysikaktuellt, ISSN 0283-9148, no 3, p. 22-22Article, book review (Other (popular science, discussion, etc.))
  • 376.
    Reeh, S
    et al.
    Rhein Westfal TH Aachen, Germany .
    Kasprzak, M
    Rhein Westfal TH Aachen, Germany .
    Klusmann, C D.
    Rhein Westfal TH Aachen, Germany .
    Stalf, F
    Rhein Westfal TH Aachen, Germany .
    Music, D
    Rhein Westfal TH Aachen, Germany .
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Schneider, J M.
    Rhein Westfal TH Aachen, Germany .
    Elastic properties of fcc Fe-Mn-X (X = Cr, Co, Ni, Cu) alloys studied by the combinatorial thin film approach and ab initio calculations2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 24Article in journal (Refereed)
    Abstract [en]

    The elastic properties of fcc Fe-Mn-X (X = Cr, Co, Ni, Cu) alloys with additions of up to 8 at.% X were studied by combinatorial thin film growth and characterization and by ab initio calculations using the disordered local moments (DLM) approach. The lattice parameter and Youngs modulus values change only marginally with X. The calculations and experiments are in good agreement. We demonstrate that the elastic properties of transition metal alloyed Fe-Mn can be predicted by the DLM model.

  • 377.
    Reeh, S.
    et al.
    Materials Chemistry, RWTH Aachen University, Aachen, Germany.
    Music, D.
    Materials Chemistry, RWTH Aachen University, Aachen, Germany.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Schneider, J. M.
    Materials Chemistry, RWTH Aachen University, Aachen, Germany.
    Elastic properties of fcc Fe-Mn-X (X=Cr, Co, Ni, Cu) alloys from first-principles calculations2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 22Article in journal (Refereed)
    Abstract [en]

    The influence of the valence electron concentration of X in fcc Fe-Mn-X (X=Cr, Co, Ni, Cu) alloys on the elastic and magnetic properties has been studied by means of ab initio calculations for alloy element concentrations of up to 8 at. % X. We observe that Cu increases the bulk-to-shear modulus (B/G) ratio by 19.2%. Simultaneously magnetic moments of Fe and Mn increase strongly. The other alloying elements induce less significant changes in B/G. The trends in B/G may be understood by considering the changes in G induced by the variation in valence electron concentration (VEC). As the VEC is increased, more pronounced metallic bonds are formed, giving rise to smaller shear modulus values. The changes in magnetic moments may be explained by the magnetovolume effect. Alloys with smaller VEC as Fe-Mn exhibit a decrease in local magnetic moments and equilibrium lattice parameters, while alloys with larger VEC as Fe-Mn demonstrate an increase in local magnetic moments and equilibrium lattice parameters. These data provide the basis for the design of Mn-rich steels with enhanced elastic properties.

  • 378.
    Karolewski, Andreas
    et al.
    University of Bayreuth, Germany.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Kümmel, Stephan
    University of Bayreuth, Germany.
    Electronic excitations and the Becke-Johnson potential: The need for and the problem of transforming model potentials to functional derivatives2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 5, p. 052519-1-052519-9Article in journal (Refereed)
    Abstract [en]

    Constructing approximations for the exchange-correlation (xc) potential in density functional theory instead of the energy appears attractive because it may provide for a way of easily incorporating desirable features such as a particle number discontinuity into xc functionals. However, xc potentials that are constructed directly are problematic: An xc potential that is not a priori derived as a functional derivative of some xc energy functional is most likely not a functional derivative of any density functional at all. This severely limits the usefulness of directly constructed xc potentials, e.g., for calculating electronic excitations. For the explicit example of the Becke-Johnson (BJ) potential we discuss defining corresponding energy expressions by density path integrals. We show that taking the functional derivative of these energies does not lead back to potentials that are close to the BJ one, and the new potentials do not share the attractive features of the original BJ expression. With further examples we demonstrate that this is a general finding and not specific to the BJ potential form.

  • 379.
    Pourovskii, L V.
    et al.
    Ecole Polytech, France.
    Miyake, T
    AIST, Japan.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ruban, A V.
    Royal Institute Technology, Sweden.
    Dubrovinsky, L
    University of Bayreuth, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Electronic properties and magnetism of iron at the Earth's inner core conditions2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 11Article in journal (Refereed)
    Abstract [en]

    We employ state-of-the-art ab initio simulations within the dynamical mean-field theory to study three likely phases of iron (hcp, fcc, and bcc) at the Earth's core conditions. We demonstrate that the correction to the electronic free energy due to correlations can be significant for the relative stability of the phases. The strongest effect is observed in bcc Fe, which shows a non-Fermi-liquid behavior, and where a Curie-Weiss behavior of the uniform susceptibility hints at a local magnetic moment still existing at 5800 K and 300 GPa. We predict that all three structures have sufficiently high magnetic susceptibility to stabilize the geodynamo.

  • 380.
    Lindmaa, Alexander
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Lizarraga, R
    University of Austral Chile, Chile.
    Holmstrom, E
    University of Austral Chile, Chile.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Exchange interactions in paramagnetic amorphous and disordered crystalline CrN-based systems2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 5Article in journal (Refereed)
    Abstract [en]

    We present a first principles supercell methodology for the calculation of exchange interactions of magnetic materials with arbitrary degrees of structural and chemical disorder in their high temperature paramagnetic state. It is based on a projection of the total magnetic energy of the system onto local pair clusters, allowing the interactions to vary independently as a response to their local environments. We demonstrate our method by deriving the distance dependent exchange interactions in vibrating crystalline CrN, a Ti0.5Cr0.5N solid solution as well as in amorphous CrN. Our method reveals strong local environment effects in all three systems. In the amorphous case we use the full set of exchange interactions in a search for the noncollinear magnetic ground state.

  • 381.
    Jason, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Johansson, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Existence, dynamics and mobility of Quantum Compactons in an extended Bose-Hubbard model2013Conference paper (Other academic)
    Abstract [en]

    Lattice Compactons, discrete breathers with compact support, were found for a discrete nonlinear Schrödinger (DNLS) equation extended with nearest neighbour intersite nonlinearities, a model originally studied with waveguide arrays in mind. These compactons were shown to exhibit very good mobility if the parameters are tuned close to the compactons stability boundary. The DNLS can also be used to model the behaviour of Bose-Einstein condensates in optical lattices, and the remarkable control over the experiments in this field of research has made it possible to study the quantum mechanics of strongly correlated atoms.

    We will define the concept of a Quantum Lattice Compacton and discuss the existence and dynamics, with special emphasis on mobility, of these in an extended Bose-Hubbard model corresponding to above-mentioned extended DNLS equation in the quantum mechanical limit.

    The compactons is given 'a kick' by means of a phase-gradient and it is shown that the size of this phase is crucial for the mobility of the compactons. For small phase-gradients, corresponding to a slow coherent motion in the classical model, the time-scales of the quantum tunnelings become of the same order as the time-scale of the translational motion and the classical mobility is destroyed by quantum fluctuations. For large phase-gradients, corresponding to rapid classical motion, the classical and quantum time-scales separate so that a mobile, localized coherent quantum state can be translated many sites in the lattice already for small particle numbers of the order of 10.

  • 382.
    Abrikosov, Igor A.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Steneteg, Peter
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Hultberg, Lasse
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Yu Mosyagin, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Department of Theoretical Physics and Quantum Technologies, National Research, Technological University MISiS, Moscow, Russia.
    Lugovskoy, Andrey V.
    Department of Theoretical Physics and Quantum Technologies, National Research, Technological University MISiS, Russia.
    Barannikova, Svetlana A.
    Institute of Strength Physics and Materials Science, Siberian Branch of Russian Academy of Science, Tomsk, Russia; Department of Physics and Engineering, Tomsk State University, Tomsk, Russia.
    Finite Temperature, Magnetic, and Many-Body Effects in Ab Initio Simulations of Alloy Thermodynamics2013In: TMS2013 Supplemental Proceedings, John Wiley & Sons, 2013, p. 617-626Chapter in book (Refereed)
    Abstract [en]

    Ab initio electronic structure theory is known as a useful tool for prediction of materials properties. However, majority of simulations still deal with calculations in the framework of density functional theory with local or semi-local functionals carried out at zero temperature. We present new methodological solution.s, which go beyond this approach and explicitly take finite temperature, magnetic, and many-body effects into account. Considering Ti-based alloys, we discuss !imitations of the quasiharmonic approximation for the treatment of lattice vibrations, and present an accurate and easily extendable method to calculate free ,energies of strongly anharmonic solids. We underline the necessity to going beyond the state-of-the-art techniques for the determination of effective cluster interactions in systems exhibiting mctal-to-insulator transition, and describe a unified cluster expansion approach developed for this class of materials. Finally, we outline a first-principles method, disordered local moments molecular dynamics, for calculations of thermodynamic properties of magnetic alloys, like Cr1-x,.AlxN, in their high-temperature paramagnetic state. Our results unambiguously demonstrate importance of finite temperature effects in theoretical calculations ofthermodynamic properties ofmaterials.

  • 383.
    Norrby, Niklas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Lind, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Parakhonskiy, G
    University of Bayreuth, Germany .
    Johansson, M P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Dubrovinsky, L S.
    University of Bayreuth, Germany .
    Dubrovinskaia, N
    University of Bayreuth, Germany .
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    High pressure and high temperature stabilization of cubic AlN in Ti0.60Al0.40N2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 5Article in journal (Refereed)
    Abstract [en]

    In the present work, the decomposition of unstable arc evaporated Ti0.6Al0.4N at elevated temperatures and quasihydrostatic pressures has been studied both experimentally and by first-principles calculations. High pressure and high temperature (HPHT) treatment of the samples was realized using the multi anvil press and diamond anvil cell techniques. The products of the HPHT treatment of Ti0.6Al0.4N were investigated using x-ray diffractometry and transmission electron microscopy. Complimentary calculations show that both hydrostatic pressure and high temperature stabilize the cubic phase of AlN, which is one of the decomposition products of Ti0.6Al0.4N. This is in agreement with the experimental results which in addition suggest that the presence of Ti in the system serves to increase the stability region of the cubic c-AlN phase. The results are industrially important as they show that Ti0.6Al0.4N coatings on cutting inserts do not deteriorate faster under pressure due to the cubic AlN to hexagonal AlN transformation.

  • 384.
    Sergueev, I.
    et al.
    Deutsches Elektronen-Synchrotron, D-22607 Hamburg, Germany.
    Dubrovinsky, Leonid
    Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
    Ekholm, Marcus
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Vekilova, Olga
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Chumakov, A. I.
    European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Zając, M.
    European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Potapkin, V.
    European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Kantor, I.
    European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Bornemann, S.
    Department of Chemistry, Ludwig-Maximilians-Universität München, München, Germany.
    Ebert, H.
    Department of Chemistry, Ludwig-Maximilians-Universität München, München, Germany.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ruffer, R.
    European Synchrotron Radiation Facility (ESRF), P.O. Box 220, F-38043 Grenoble, France.
    Hyperfine Splitting and Room-Temperature Ferromagnetism of Ni at Multimegabar Pressure2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, no 15Article in journal (Refereed)
    Abstract [en]

    Magnetic and elastic properties of Ni metal have been studied up to 260 GPa by nuclear forward scattering of synchrotron radiation with the 67.4 keV Mossbauer transition of Ni-61. The observed magnetic hyperfine splitting confirms the ferromagnetic state of Ni up to 260 GPa, the highest pressure where magnetism in any material has been observed so far. Ab initio calculations reveal that the pressure evolution of the hyperfine field, which features a maximum in the range of 100 to 225 GPa, is a relativistic effect. The Debye energy obtained from the Lamb-Mossbauer factor increases from 33 me V at ambient pressure to 60 me V at 100 GPa. The change of this energy over volume compression is well described by a Gruneisen parameter of 2.09.

  • 385.
    Glazyrin, K.
    et al.
    Bayerisches Geoinstitut, Universität Bayreuth, Germany.
    Pourovskii, L.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Dubrovinsky, L.
    Bayerisches Geoinstitut, Universität Bayreuth, Germany.
    Narygina, O.
    School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.
    McCammon, C.
    Bayerisches Geoinstitut, Universität Bayreuth, Germany.
    Hewener, B.
    Technische Universität Kaiserslautern, Kaiserslautern, Germany.
    Schünemann, V.
    Technische Universität Kaiserslautern, Kaiserslautern, Germany.
    Wolny, J.
    Technische Universität Kaiserslautern, Kaiserslautern, Germany.
    Muffler, K.
    Technische Universität Kaiserslautern, Kaiserslautern, Germany.
    Chumakov, A. I.
    ESRF, Grenoble Cedex, France.
    Crichton, W.
    ESRF, Grenoble Cedex, France.
    Hanfland, M.
    ESRF, Grenoble Cedex, France.
    Prakapenka, V.
    GeoSoilEnviroCARS, University of Chicago, Argonne National Laboratory, USA.
    Tasnádi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Aichhorn, M.
    Centro Atómico Constituyentes, GIyANN, CNEA, San Martin, Buenos Aires, Comisión Nacional de Investigaciones Científicas y Técnicas, Ciudad de Buenos Aires, Argentina.
    Vildosola, V.
    Centro Atómico Constituyentes, GIyANN, CNEA, San Martin, Buenos Aires, Comisión Nacional de Investigaciones Científicas y Técnicas, Ciudad de Buenos Aires, Argentina.
    Ruban, A. V.
    12Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Katsnelson, M. I.
    Radboud University Nijmegen, Institute for Molecules and Materials, Netherlands.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Importance of correlation effects in hcp iron revealed by a pressure-induced electronic topological transition2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 11Article in journal (Refereed)
    Abstract [en]

    We discover that hcp phases of Fe and Fe0.9Ni0.1 undergo an electronic topological transition at pressures of about 40 GPa. This topological change of the Fermi surface manifests itself through anomalous behavior of the Debye sound velocity, c/a lattice parameter ratio, and Mossbauer center shift observed in our experiments. First-principles simulations within the dynamic mean field approach demonstrate that the transition is induced by many-electron effects. It is absent in one-electron calculations and represents a clear signature of correlation effects in hcp Fe. DOI: 10.1103/PhysRevLett.110.117206

  • 386.
    Vekilova, Olga
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Influence of stresses and impurities on thermodynamic and elastic properties of metals and alloys from ab initio theory2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Stresses and impurities may influence elastic properties, phase stability and magnetic behavior of metals and their alloys. A physical understanding of this influence is of great importance to both fundamental science and technological applications. The diverse methods used in this work allowed us to shed light on the various aspects of the problem. In particular, in this work the thermodynamic, magnetic and elastic properties of Fe and Fe-Ni alloys at Earth’s inner core conditions were investigated by means of the ab initio theory. The main features of these calculations are on one side the extreme pressure-temperature conditions; on the other side the strong-correlation effects, which at these conditions may play an unexpected role. That is why I used different approaches, ranging from molecular dynamics to the dynamical mean field theory.

    Interesting possibility for the effect of non-hydrostatic stresses on the stability of the body-centered cubic (bcc) phase of iron was observed. If detected, it could allow for an explanation of striking contradictions in high-pressure experiments. The influence of the alloying with Ni on the stability of Fe was studied. It was shown that the observed reverse of the stability trend under pressure is associated with the suppression of ferromagnetism at conditions of Earth’s inner core.

    The strong correlation effects were observed in Fe3Ni by means of the dynamical mean field theory, revealing that the local environment of iron atoms is crucial for the strength of the on-site electronic correlations.

    There is also an exciting experimental finding of our colleagues indicating that magnetism in pure nickel survives at very high pressures up to 260 GPa, i.e. up to the highest pressure at which magnetism in any material has ever been observed. Our calculations of the pressure dependence of the effective exchange interaction parameter and the hyperfine field support the picture of the ordered ferromagnetic state in Ni at multimegabar pressures.

    Further, hydrogen is believed to be an important light impurity in Earth’s core. Thereupon the hydrogen containing FeOOH was also investigated. The prediction of the effect of symmetrization of the hydrogen bond under pressure was made.

    The universality of applied methods allowed us to study the elastic constants of TiN, which is of high relevance to the industry of cutting tools. The importance of taking into account the finite temperature effects in the calculations of the elastic properties was demonstrated. Another case of practical interest is the Fe-Cr system, a prototype of many industrial steels. For instance, it is used in cooling pipes of pressure vessel reactors. We studied the effect of hydrostatic pressure on the phase stability of Fe-Cr alloys and revealed intriguing differences in the ordering tendencies depending on the Cr concentration and magnetic state of the alloy. We showed how variation of the ordering tendency between the Fe and Cr atoms emerges due to suppression of the local magnetic moment on the Cr atoms.

    Noteworthy, hydrogen is not only the basic material playing fundamental role on and in the Earth, it is also a very promising source of fuel, which does not pollute the environment. In this sense the problem of hydrogen storage in Pd is of separate but related interest and it was theoretically investigated in the present work. The effect of vacancies on the energetically preferable position of hydrogen in the Pd cell was addressed. My theoretical results supported the experimental suggestion of multiple occupation of Pd vacancies by hydrogen.

    List of papers
    1. Influence of Ni on the lattice stability of Fe-Ni alloys at multimegabar pressures
    Open this publication in new window or tab >>Influence of Ni on the lattice stability of Fe-Ni alloys at multimegabar pressures
    2012 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 86, no 22, p. 224107-Article in journal (Refereed) Published
    Abstract [en]

    The lattice stability trends of the primary candidate for Earths core material, the Fe-Ni alloy, were examined from first principles. We employed the exact muffin-tin orbital method (EMTO) combined with the coherent potential approximation (CPA) for the treatment of alloying effects. It was revealed that high pressure reverses the trend in the relative stabilities of the body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal close-packed (hcp) phases observed at ambient conditions. In the low pressure region the increase of Ni concentration in the Fe-Ni alloy enhances the bcc phase destabilization relative to the more close-packed fcc and hcp phases. However, at 300 GPa (Earths core pressure), the effect of Ni addition is opposite. The reverse of the trend is associated with the suppression of the ferromagnetism of Fe when going from ambient pressures to pressure conditions corresponding to those of Earths core. The first-principles results are explained in the framework of the canonical band model.

    Place, publisher, year, edition, pages
    American Physical Society, 2012
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-86890 (URN)10.1103/PhysRevB.86.224107 (DOI)000312064300001 ()
    Note

    Funding Agencies|Swedish Research Council (VR)|621-2008-55352011-42-59|Goran Gustafsson Foundation for Research in Natural Sciences and Medicine||Swedish Government Strategic Research Area Grant in Materials Science||Functional Materials and VR Linnaeus Grant LiLi-NFM||Swedish Foundation for Strategic Research through the SRL program||Ministry of Education and Science of the Russian Federation|14.B37.21.089014.A18.21.0893|Russian Foundation for Basic Researches|10-02-00-194a|Swedish National Infrastructure for Computing SNIC||

    Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2017-12-06
    2. Effect of non-uniform stresses on bcc Fe and Fe-Ni alloys at Earth's core conditions
    Open this publication in new window or tab >>Effect of non-uniform stresses on bcc Fe and Fe-Ni alloys at Earth's core conditions
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    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Elucidation of Earth's core composition and structure is needed for the understanding of various phenomena, from geodynamics to geomagnetism. Geochemical data suggest that solid Fe alloyed with Ni is Earth's core main constituent, however, the exact content and crystal structure remain unclear. We report the results of ab initio molecular dynamics study of the mechanical stability of the body-centered cubic (bcc) phase of Fe and Fe0.89Ni0.ll. A striking saw-toothed effect in the dependence of stresses on finite distortions is revealed. The calculated region of mechanical stability of the bcc iron under non- hydrostatic stress at Earth's core conditions is narrow, and about 5 GPa stresses should destabilize it. While it is unlikely that stresses in Earth's core are sufficient to mechanically destabilize bcc iron, experimental controversies and puzzling stabilization of diverse phases may be well explained by the observed saw-toothed stress effect. It might be common for different materials close to dynamical instability and has crucial importance for determination of equilibrium phase boundaries.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-97378 (URN)
    Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2013-09-11Bibliographically approved
    3. Electronic correlations in Fe at Earth's inner core conditions: effect of alloying with Ni
    Open this publication in new window or tab >>Electronic correlations in Fe at Earth's inner core conditions: effect of alloying with Ni
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    We have studied the body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal close-packed (hcp) phases of Fe alloyed with 25 at. % of Ni at Earth's core conditions using an ab initio local density approximation + dynamical mean-field theory (LDA+DMFT) approach. The alloys have been modeled by ordered crystal structures based on the bcc, fcc, and hcp unit cells with minimum possible cell size allowing for the proper composition. 0ur calculations demonstrate that the strength of electronic correlations on the Fe 3d shell is highly sensitive to the phase and local environment. In the bcc phase the 3d electrons at the Fe site with Fe only nearest neighbors remain rather strongly correlated even at extreme pressure-temperature conditions, with the local and uniform magnetic  susceptibility exhibiting a Curie-Weiss-like temperature evolution and the quasi-particle lifetime r featuring a non-Fermi-liquid temperature dependence. In contrast, for the corresponding Fe site in the hcp phase we predict a weakly-correlated Fermi-liquid state with a temperature- independent local susceptibility and a quadratic temperature dependence of r. The iron sites with nickel atoms in the local environment exhibit behavior in the range between those two extreme cases, with the strength of correlations gradually increasing along the hcp-fcc- bcc sequence. Further, the inter-site magnetic interactions in the bcc and hcp phases are also strongly affected by the presence of Ni nearest neighbors. The sensitivity to the local environment is related to modifications of the Fe partial density of states due to mixing with Ni 3d-states.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-97380 (URN)
    Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2013-09-11Bibliographically approved
    4. Hyperfine Splitting and Room-Temperature Ferromagnetism of Ni at Multimegabar Pressure
    Open this publication in new window or tab >>Hyperfine Splitting and Room-Temperature Ferromagnetism of Ni at Multimegabar Pressure
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    2013 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, no 15Article in journal (Refereed) Published
    Abstract [en]

    Magnetic and elastic properties of Ni metal have been studied up to 260 GPa by nuclear forward scattering of synchrotron radiation with the 67.4 keV Mossbauer transition of Ni-61. The observed magnetic hyperfine splitting confirms the ferromagnetic state of Ni up to 260 GPa, the highest pressure where magnetism in any material has been observed so far. Ab initio calculations reveal that the pressure evolution of the hyperfine field, which features a maximum in the range of 100 to 225 GPa, is a relativistic effect. The Debye energy obtained from the Lamb-Mossbauer factor increases from 33 me V at ambient pressure to 60 me V at 100 GPa. The change of this energy over volume compression is well described by a Gruneisen parameter of 2.09.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2013
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-97381 (URN)10.1103/PhysRevLett.111.157601 (DOI)000326051100011 ()
    Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2017-12-06Bibliographically approved
    5. Pressure-induced hydrogen bond symmetrization in iron oxyhydroxide
    Open this publication in new window or tab >>Pressure-induced hydrogen bond symmetrization in iron oxyhydroxide
    Show others...
    2013 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, no 17Article in journal (Refereed) Published
    Abstract [en]

    Under high pressures the hydrogen bonds were predicted to transform from a highly asymmetric soft O-H center dot center dot center dot O to a symmetric rigid configuration in which the proton lies midway between the two oxygen atoms. Despite four decades of research on hydroxyl containing compounds, pressure induced hydrogen bond symmetrization remains elusive. Following single crystal x-ray diffraction, Mossbauer and Raman spectroscopy measurements supported by ab initio calculations, we report the H-bonds symmetrization in iron oxyhydroxide, FeOOH, resulting from the Fe3+ high-to-low spin crossover at above 45 GPa.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-97382 (URN)10.1103/PhysRevLett.111.175501 (DOI)000326148500007 ()
    Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2017-12-06Bibliographically approved
    6. First-principles study of vacancy-hydrogen interaction in Pd
    Open this publication in new window or tab >>First-principles study of vacancy-hydrogen interaction in Pd
    2009 (English)In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 80, no 2, p. 024101-Article in journal (Refereed) Published
    Abstract [en]

    Hydrogen absorption in face-centered-cubic palladium is studied from first principles, with particular focus on interaction between hydrogen atoms and vacancies, formation of hydrogen-vacancy complexes, and multiple hydrogen occupancy of a Pd vacancy. Vacancy formation energy in the presence of hydrogen, hydrogen trapping energy, and vacancy formation volume have been calculated and compared to existing experimental data. We show that a vacancy and hydrogen atoms form stable complexes. Further we have studied the process of hydrogen diffusion into the Pd vacancy. We find the energetically preferable position for hydrogen to reside in the palladium unit cell in the presence of a vacancy. The possibility of the multiple hydrogen occupancy (up to six hydrogen atoms) of a monovacancy is elucidated. This theoretical finding supports experimental indication of the appearance of superabundant vacancy complexes in palladium in the presence of hydrogen.

    Keywords
    density functional theory, diffusion, hydrogen, palladium, vacancies (crystal)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-19890 (URN)10.1103/PhysRevB.80.024101 (DOI)
    Note
    Original Publication: Olga Vekilova, D I Bazhanov, Sergey Simak and Igor Abrikosov, First-principles study of vacancy-hydrogen interaction in Pd, 2009, PHYSICAL REVIEW B, (80), 2, 024101. http://dx.doi.org/10.1103/PhysRevB.80.024101 Copyright: American Physical Society http://www.aps.org/ Available from: 2009-08-28 Created: 2009-08-14 Last updated: 2013-09-11Bibliographically approved
    7. Temperature dependence of TiN elastic constants from ab initio molecular dynamics simulations
    Open this publication in new window or tab >>Temperature dependence of TiN elastic constants from ab initio molecular dynamics simulations
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    2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 9Article in journal (Refereed) Published
    Abstract [en]

    Elastic properties of cubic TiN are studied theoretically in a wide temperature interval. First-principles simulations are based on ab initio molecular dynamics (AIMD). Computational efficiency of the method is greatly enhanced by a careful preparation of the initial state of the simulation cell that minimizes or completely removes a need for equilibration and therefore allows for parallel AIMD calculations. Elastic constants C11, C12, and C44 are calculated. A strong dependence on the temperature is predicted, with C11 decreasing by more than 29% at 1800 K as compared to its value obtained at T=0 K. Furthermore, we analyze the effect of temperature on the elastic properties of polycrystalline TiN in terms of the bulk and shear moduli, the Young's modulus and Poisson ratio. We construct sound velocity anisotropy maps, investigate the temperature dependence of elastic anisotropy of TiN, and observe that the material becomes substantially more isotropic at high temperatures. Our results unambiguously demonstrate the importance of taking into account finite temperature effects in theoretical calculations of elastic properties of materials intended for high-temperature applications.

    Place, publisher, year, edition, pages
    American Physical Society, 2013
    National Category
    Natural Sciences Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-78754 (URN)10.1103/PhysRevB.87.094114 (DOI)000316791600001 ()
    Note

    Funding Agencies|Swedish Research Council|621-2008-5535621-2011-4426|Swedish Foundation for Strategic Research (SSF) programs|10-0026|project Designed Multicomponent Coatings (MultiFilms)||Erasmus Mundus doctoral program DocMase||Ministry of Education and Science of the Russian Federation within the framework of Program Research and Pedagogical Personnel for Innovative Russia|14.B37.21.089010.09.2012|

    Available from: 2012-06-20 Created: 2012-06-20 Last updated: 2017-12-07Bibliographically approved
    8. Effect of pressure on phase stability in Fe-Cr alloys
    Open this publication in new window or tab >>Effect of pressure on phase stability in Fe-Cr alloys
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    2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 9, p. 094422-Article in journal (Refereed) Published
    Abstract [en]

    The effect of hydrostatic pressure on the phase stability of Fe-Cr alloys has been studied using ab initio methods. We show that while pressure decreases the tendency toward the phase separation in the paramagnetic state of bcc alloys, in the ferromagnetic state it reduces the alloy stability at low Cr concentration and vice versa, makes the solid solution more stable at higher concentrations. This behavior of the phase stability can be predicted from the deviation of the lattice parameter from Vegards law in bcc Fe-Cr alloys. On the atomic level, the pressure effect can be explained by the suppression of the local magnetic moments on Cr atoms, which gives rise to a decrease of the Fe-Cr magnetic exchange interaction at the first coordination shell and, as a result, to the observed variation of the ordering tendency between the Fe and Cr atoms.

    Place, publisher, year, edition, pages
    American Physical Society, 2011
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-71218 (URN)10.1103/PhysRevB.84.094422 (DOI)000295006300011 ()
    Available from: 2011-10-07 Created: 2011-10-07 Last updated: 2017-12-08
  • 387.
    Zhang, Wenmin
    et al.
    Zhejiang University, Peoples R China .
    Yu, M Y
    Zhejiang University, Peoples R China .
    Karimov, A R
    Russian Academic Science, Russia .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Intense oscillations in the expansion of an inhomogeneous cylindrical electron-positron layer2013In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 88, no 5, p. 055501-Article in journal (Refereed)
    Abstract [en]

    Large amplitude oscillations in the expansion of a cylindrical electron-positron plasma layer are investigated. The cold fluid equations and the Poissons equation are solved non-perturbatively in order to allow for very large amplitude oscillations. It is found that oscillations are self-excited during the expansion and can grow to very large amplitudes as the expansion slows down with time and the plasma density decreases. The kinetic energy of the expansion is thereby converted into that of the oscillations.

  • 388.
    Bingham, Robert
    et al.
    Rutherford Appleton Lab, England .
    Eliasson, Bengt
    Ruhr University of Bochum, Germany .
    Tito Mendonca, Jose
    Institute Super Tecn, Portugal .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ion acceleration by Alfven waves on auroral field lines2013In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 87, no 5Article in journal (Refereed)
    Abstract [en]

    Observations of ion acceleration along auroral field lines at the boundary of the plasma sheet and tail lobe of the Earth show that the energy of the ions increases with decreasing density. The observations can be explained by ion acceleration through Landau resonance with kinetic Alfven waves (KAWs) such that k(A) . v(i) = omega(A), where k(A) is the wave vector, v(i) is the ion resonance velocity and omega(A) is the Alfven wave frequency. The ion resonance velocities are proportional to the Alfven velocity which increases with decreasing density. This is in agreement with the data if the process is occurring at the plasma sheet tail lobe boundary. A quasi-linear theory of ion acceleration by KAWs is presented. These ions propagate both down towards and away from the Earth. The paths of the Freja and Polar satellites indicate that the acceleration takes place between the two satellites, between 1Re and 5Re. The downward propagating ions develop a horseshoe-type of distribution which has a positive slope in the perpendicular direction. This type of distribution can produce intense lower hybrid wave activity, which is also observed. Finally, the filamentation of shear Alfven waves is considered. It may be responsible for large-scale density striations.

  • 389.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Jakten på liv i universum2013In: Fysikaktuellt, ISSN 0283-9148, no 4, p. 26-26Article, book review (Other (popular science, discussion, etc.))
  • 390.
    Bostrom, Mathias
    et al.
    Royal Institute Technology, Sweden University of Oslo, Norway .
    Huang, Dan
    Royal Institute Technology, Sweden .
    Yang, Weihong
    Royal Institute Technology, Sweden .
    Persson, Clas
    Royal Institute Technology, Sweden University of Oslo, Norway University of Oslo, Norway .
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Lithium atom storage in nanoporous cellulose via surface-induced Li-2 breakage2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 104, no 6, p. 63003-Article in journal (Refereed)
    Abstract [en]

    We demonstrate a physical mechanism that enhances a splitting of diatomic Li-2 at cellulose surfaces. The origin of this splitting is a possible surface-induced diatomic-excited-state resonance repulsion. The atomic Li is then free to form either physical or chemical bonds with the cellulose surface and even diffuse into the cellulose layer structure. This allows for an enhanced storage capacity of atomic Li in nanoporous cellulose.

  • 391.
    Lazić, Predrag
    et al.
    Massachusetts Institute of Technology, Cambridge, USA.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Herbert, F W
    Massachusetts Institute of Technology, Cambridge, USA.
    Chakraborty, Rupak
    Massachusetts Institute of Technology, Cambridge, USA.
    Sun, Ruoshi
    Massachusetts Institute of Technology, Cambridge, USA.
    Chan, M K Y
    Argonne National Laboratory, USA.
    Hartman, Katherine
    Massachusetts Institute of Technology, Cambridge, USA.
    Buonassisi, Tonio
    Massachusetts Institute of Technology, Cambridge, USA.
    Yildiz, Bilge
    Massachusetts Institute of Technology, Cambridge, USA.
    Ceder, Gerbrand
    Massachusetts Institute of Technology, Cambridge, USA.
    Low intensity conduction states in FeS2: implications for absorption, open-circuit voltage and surface recombination2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 46, p. 465801-Article in journal (Refereed)
    Abstract [en]

    Pyrite (FeS2), being a promising material for future solar technologies, has so far exhibited in experiments an open-circuit voltage (OCV) of around 0.2 V, which is much lower than the frequently quoted 'accepted' value for the fundamental bandgap of similar to 0.95 eV. Absorption experiments show large subgap absorption, commonly attributed to defects or structural disorder. However, computations using density functional theory with a semi-local functional predict that the bottom of the conduction band consists of a very low intensity sulfur p-band that may be easily overlooked in experiments because of the high intensity onset that appears 0.5 eV higher in energy. The intensity of absorption into the sulfur p-band is found to be of the same magnitude as contributions from defects and disorder. Our findings suggest the need to re-examine the value of the fundamental bandgap of pyrite presently in use in the literature. If the contribution from the p-band has so far been overlooked, the substantially lowered bandgap would partly explain the discrepancy with the OCV. Furthermore, we show that more states appear on the surface within the low energy sulfur p-band, which suggests a mechanism of thermalization into those states that would further prevent extracting electrons at higher energy levels through the surface. Finally, we speculate on whether misidentified states at the conduction band onset may be present in other materials.

  • 392.
    Ingason, Arni Sigurdur
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Mockuté, Aurelija
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Dahlqvist, Martin
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Magnus, F.
    Science Institute, University of Iceland, Reykjavik, Iceland.
    Olafsson, S.
    Science Institute, University of Iceland, Reykjavik, Iceland.
    Arnalds, U. B.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hjörvarsson, B.
    Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Magnetic Self-Organized Atomic Laminate from First Principles and Thin Film Synthesis2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110Article in journal (Refereed)
    Abstract [en]

    he first experimental realization of a magnetic Mn+1AXn (MAX) phase, (Cr0.75Mn0.25)2GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent structural quality. This self-organized atomic laminate is based on the well-known Cr2GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.

  • 393.
    Gueorguiev Ivanov, Ivan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Gällström, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Leone, Stefano
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Kordina, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Tien Son, Nguyen
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Henry, Anne
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ivády, Viktor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Gali, Adam
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Optical properties of the niobium centre in 4H, 6H, and 15R SiC2013In: SILICON CARBIDE AND RELATED MATERIALS 2012, Trans Tech Publications , 2013, Vol. 740-742, p. 405-408Conference paper (Refereed)
    Abstract [en]

    A set of lines in the photoluminescence spectra of 4H-, 6H-, and 15R-SiC in the near-infrared are attributed to Nb-related defects on the ground of doping experiments conducted with 4H-SiC. A model based on a an exciton bound at the Nb-centre in an asymmetric split vacancy configuration at a hexagonal site is proposed, which explains the structure of the luminescence spectrum and the observed Zeeman splitting of the lines.

  • 394.
    Armiento, Rickard
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Kümmel, Stephan
    Theoretische Physik IV, Universität Bayreuth, Bayreuth, Germany.
    Orbital Localization, Charge Transfer, and Band Gaps in Semilocal Density-Functional Theory2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, no 3, p. 036402-1-036402-5Article in journal (Refereed)
    Abstract [en]

    We derive an exchange energy functional of generalized gradient form with a corresponding potential that changes discontinuously at integer particle numbers. The functional is semilocal, yet incorporates key features that are connected to the derivative discontinuity of Kohn-Sham density-functional theory. We validate our construction for several paradigm systems and explain how it addresses central well-known deficiencies of antecedent semilocal methods, i.e., the description of charge transfer, properly localized orbitals, and band gaps. We find, e.g., an improved shell structure for atoms, eigenvalues that more closely correspond to ionization energies, and an improved description of band structure where localized states are lowered in energy.

  • 395.
    Pokhotelov, O.A.
    et al.
    Institute Phys Earth, Russia .
    Onishchenko, O.G.
    Institute Phys Earth, Russia .
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Physical mechanisms for electron mirror and field swelling modes2013In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 87, no 6, p. 065303-Article in journal (Refereed)
    Abstract [en]

    Ion mirror instability is dominant in planetary and cometary magnetosheaths and other high-beta plasmas where the ions are hotter than the electrons. It is associated with a zero-frequency non-propagating mode with the wave vector nearly perpendicular to the ambient magnetic field. The counterparts of this instability in hot electron plasmas are the field swelling and electron mirror instabilities. A theory for these instabilities was developed more than two decades ago (Basu B and Coppi B 1982 Phys. Rev. Lett. 48 799, 1984 Phys. Fluids 27 1187) within the framework of a fluid model. The connection between the two types of instabilities has been analyzed in (Migliuolo S 1986 J. Geophys. Res. 91 7981). In contrast to these papers, we shall here adopt the standard quasi-hydrodynamic approach that is usually used for the study of mirror instabilities. To analyze the electron mirror and field swelling instabilities, we will only use the perpendicular balance condition and the Liouville theorem. We have found that such a description is easier to understand and gives us increased physical insight into the basic physical features of both these instabilities.

  • 396.
    Eliasson, B
    et al.
    University of Strathclyde, Glasgow, UK.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Bingham, R
    Rutherford Appleton Laboratory, Didcot, UK.
    Mendonca, J T
    Institute Superior Tecnico, Lisboa, Portugal.
    Preface to special issue2013In: Journal of Plasma Physics, ISSN 0022-3778, E-ISSN 1469-7807, Vol. 79, no 6, p. 981-981Article in journal (Other academic)
    Abstract [en]

    This special issue is devoted to the memory of Professor Padma Kant Shukla, who passed away 26 January 2013 on his travel to New Delhi, India to receive the prestigious Hind Rattan (Jewel of India) award. Padma was born in Tulapur, Uttar Pradesh, India, 7 July 1950, where he grew up and got his education. He received a PhD degree in Physics at the Banaras Hindu University, Varanasi, Uttar Pradesh, India, in 1972, under the supervision of late Prof. R. N. Singh, and a second PhD degree in Theoretical Plasma Physics from Umeå University in Sweden in 1975, under the supervision of Prof. Lennart Stenflo. He worked at the Faculty of Physics & Astronomy, Ruhr-University Bochum, Germany since January 1973, where he was a permanent faculty member and Professor of International Affairs, a position that was created for him to honour his international accomplishments and reputation.

  • 397.
    Xu, Weiming M.
    et al.
    School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel.
    Greenberg, Eran
    Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
    Rozenberg, Gregory Kh.
    School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel.
    Pasternak, Moshe P.
    School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel.
    Bykova, Elena
    Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, Germany.
    Boffa-Ballaran, Tiziana
    Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, Germany.
    Dubrovinsky, Leonid
    Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
    Prakapenka, Vitali
    Consortium for Advanced Radiation Sources, University of Chicago, Argonne, USA.
    Hanfland, Michael
    European Synchrotron Radiation Facility (ESRF), Grenoble Cedex, France.
    Vekilova, Olga
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Ruffer, R.
    European Synchrotron Radiation Facility (ESRF), P.O. Box 220, F-38043 Grenoble, France.
    Pressure-induced hydrogen bond symmetrization in iron oxyhydroxide2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, no 17Article in journal (Refereed)
    Abstract [en]

    Under high pressures the hydrogen bonds were predicted to transform from a highly asymmetric soft O-H center dot center dot center dot O to a symmetric rigid configuration in which the proton lies midway between the two oxygen atoms. Despite four decades of research on hydroxyl containing compounds, pressure induced hydrogen bond symmetrization remains elusive. Following single crystal x-ray diffraction, Mossbauer and Raman spectroscopy measurements supported by ab initio calculations, we report the H-bonds symmetrization in iron oxyhydroxide, FeOOH, resulting from the Fe3+ high-to-low spin crossover at above 45 GPa.

  • 398.
    Jason, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Johansson, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Quantum dynamics of lattice states with compact support in an extended Bose-Hubbard model2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 88, no 3, p. 033605-Article in journal (Refereed)
    Abstract [en]

    We study the dynamical properties, with special emphasis on mobility, of quantum lattice compactons (QLCs) in a one-dimensional Bose-Hubbard model extended with pair-correlated hopping. These are quantum counterparts of classical lattice compactons (localized solutions with exact zero amplitude outside a given region) of an extended discrete nonlinear Schrödinger equation, which can be derived in the classical limit from the extended Bose-Hubbard model. While an exact one-site QLC eigenstate corresponds to a classical one-site compacton, the compact support of classical several-site compactons is destroyed by quantum fluctuations. We show that it is possible to reproduce the stability exchange regions of the one-site and two-site localized solutions in the classical model with properly chosen quantum states. Quantum dynamical simulations are performed for two different types of initial conditions: “localized ground states” which are localized wave packets built from superpositions of compactonlike eigenstates, and SU(4) coherent states corresponding to classical two-site compactons. Clear signatures of the mobility of classical lattice compactons are seen, but this crucially depends on the magnitude of the applied phase gradient. For small phase gradients, which classically correspond to a slow coherent motion, the quantum time scale is of the same order as the time scale of the translational motion, and the classical mobility is therefore destroyed by quantum fluctuations. For a large phase instead, corresponding to fast classical motion, the time scales separate so that a mobile, localized, coherent quantum state can be translated many sites for particle numbers already of the order of 10.

  • 399.
    Boström, Mathias
    et al.
    Royal Institute Technology, Sweden.
    Persson, Clas
    Royal Institute Technology, Sweden.
    Ninham, Barry W
    Australian National University, Australia.
    Norman, Patrick
    Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Resonance interaction induced by metal surfaces catalyzes atom-pair breakage2013In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 87, no 4Article in journal (Refereed)
    Abstract [en]

    We present the theory for retarded resonance interaction between two identical atoms at arbitrary positions near a metal surface. The dipole-dipole resonance interaction force that binds isotropically excited atom pairs together in free space may turn repulsive close to an ideal (totally reflecting) metal surface. On the other hand, close to an infinitely permeable surface it may turn more attractive. We illustrate numerically how the dipole-dipole resonance interaction between two oxygen atoms near a metal surface may provide a repulsive energy of the same order of magnitude as the ground-state binding energy of an oxygen molecule. As a complement we also present results from density-functional theory.