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  • 951.
    Carlberg, M H
    et al.
    Linköping University, Department of Physics, Chemistry and 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.
    Chirita, Valeriu
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Molecular-dynamics studies of defect generation in epitaxial Mo/W superlattices1996In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 54, no 3, p. 2217-2224Article in journal (Refereed)
    Abstract [en]

    An investigation of defect generation at the interface during growth of epitaxial (100) oriented Mo/W superlattices by ion-assisted deposition has been carried out using molecular-dynamics simulations. The influence of the impact parameter within the irreducible bcc unit cell [001] surface and the incident ion energy on the energy accommodation, the dynamics of energy transfer, and energy dissipation are discussed. A detailed model of the generation of point defects is presented and the influence of materials upon the type and the number of defects as well as the energy accommodation of the superlattice is revealed. It is shown that the behavior of the superlattice as a whole is largely dominated by the material in the surface monolayer.

  • 952.
    Münger, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    NOVOTNY, MA
    Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida .
    MOMENTUM-SPACE MONTE-CARLO RENORMALIZATION-GROUP PROCEDURE1991In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 44, no 9, p. 4314-4325Article in journal (Refereed)
    Abstract [en]

    We implement a momentum-space renormalization-group procedure into the Monte Carlo renormalization-group (MCRG) method. Usually the symmetries of the system must be known and incorporated into the renormalization group, but here we let the renormalization group be given by the Monte Carlo simulation itself This allows the MCRG method to be applicable to systems where the underlying symmetries may not be known, such as in Monte Carlo studies of quantum systems. As a test of this method, we apply it to the study of the two-dimensional square-lattice q-state Potts model, both for integer values of q and for noninteger values of q near q = 4.

  • 953.
    Münger, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    NOVOTNY, MA
    Supercomputer Computations Research Institute, Florida State University, Florida, USA .
    REWEIGHTING IN MONTE-CARLO AND MONTE-CARLO RENORMALIZATION-GROUP STUDIES1991In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 43, no 7, B, p. 5773-5783Article in journal (Refereed)
    Abstract [en]

    A method of reweighting Monte Carlo data to parameters other than the simulated ones is investigated. The method is also extended to include Monte Carlo renormalization-group simulations. Both single and multiple simulation reweighting is used. The models studied are the d = 2 ferromagnetic q = 3 Potts model and the d = 2 antiferromagnetic Ising model. It is shown that the reweighting produces a systematic shift in the height and location of the specific-heat peak. This shift, which without proper care may lead to erroneous results, depends on the simulated and reweighted temperatures and on the number of configurations included in the reweighting. Only for very large numbers of configurations does the shift decrease as the inverse square root of the number of configurations. Within the Monte Carlo renormalization-group study, it is shown that the critical exponents for the Ising model are determined more accurately from a multiple reweighting using one simulation below the critical temperature and one above than from the individual simulations. It is shown that it is more efficient to use two simulations at a time than all of them at once when reweighting multiple simulations.

  • 954.
    BARTKOWIAK, M
    et al.
    University of Trondheim, Norway.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    CHAO, KA
    University of Trondheim, Norway.
    MICNAS, R
    A. Mickiewicz University, Institute of Physics, Poland.
    HIGH - DENSITY EXPANSION FOR ELECTRON-SYSTEMS1990In: APPLICATIONS OF STATISTICAL AND FIELD THEORY METHODS TO CONDENSED MATTER, 1990, Vol. 218Conference paper (Refereed)
  • 955.
    Bartkowiak, M
    et al.
    University of Trondheim, Norway.
    Münger, Peter
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Chao, Kuong-An
    University of Trondheim, Norway.
    High-Density Expansion for the Spinless Fermion Model III: Green-Functions1990In: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 4, no 13, p. 2025-2040Article in journal (Refereed)
    Abstract [en]

    The single-particle electron Green's function and the charge-fluctuation Green's function for the spin-polarized fermion lattice gas are calculated within the framework of the high-density expansion up to the first order in 1/z. Violation of some conditions of consistency of diagrammatic perturbation expansion approximation schemes are discussed. Relations between the Green's functions and corresponding approximate free energy are established. Two kinds of approximations for Green's functions for the charge ordered phase are constructed and applied to determine the band structure of the spinless fermion model. The Green's functions for the nonordered phase are used to study the phase diagram of the model for finite temperatures and arbitrary band filling.

     

  • 956.
    Sernelius, Bo
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Solid State Dioision, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Jin,, Z.-C.
    Physics Department, Chalmers Uniuersity of Technology, Gothenburg, Sweden.
    Hamberg, Ivar
    Physics Department, Chalmers Uniuersity of Technology, Gothenburg, Sweden.
    Granqvist, Claes Göran
    Physics Department, Chalmers Uniuersity of Technology, Gothenburg, Sweden.
    Band-gap tailoring of Zno by means of heavy Al doping1988In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 37, no 17, p. 10244-10248Article in journal (Refereed)
    Abstract [en]

    Films of ZnO:Al were produced by weakly reactive dual-target magnetron sputtering. Optical band gaps, evaluated from spectrophotometric data, were widened in proportion to the Al doping.The widening could be quantitatively reconciled with an effective-mass model for n-doped semiconductors, provided the polar character of ZnO was accounted for.

  • 957.
    Hamberg, Ivar
    et al.
    Physics Department, Chalmers University of Technology, Göteborg, Sweden.
    Granqvist, Claes Göran
    Physics Department, Chalmers University of Technology, Göteborg, Sweden.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Sernelius, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Linköping University, The Institute of Technology.
    Band-gap widening in heavily Sn-daped In2031984In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 30, no 6, p. 3240-3249Article in journal (Refereed)
    Abstract [en]

    Films of pure and Sn-doped semiconducting Inz03 were prepared by reactive e-beam evaporation. The spectral absorption coefficient was evaluated by spectrophotometry in the (2—6)-eV range. The extracted band gap increases with electron density (ne ) approximately as ne 2/3 for ne ≤10-21 cm-3 . This result is interpreted within an effective-mass model for n-doped semiconductors well above the Mott critical density. Because of the high degree of doping, the impurities are ionized and the associated electrons occupy the bottom of the conduction band in the form of an electron gas. The model accounts for a Burstein-Moss shift as well as electron-electron and electron-impurity scattering treated in the random-phase approximation. Experiments and theory were reconciled by assuming a parabolic valence band with an effective mass -0.6m. Earlier work on doped oxide semiconductors are assessed in the light of the present results.

  • 958.
    Liot, Francois
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Hooley, Christopher A.
    Scottish Universities Physics Alliance (SUPA), Shool of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, U.K..
    A Simple Theory of the Invar Effect in Iron-Nickel AlloysManuscript (Other academic)
    Abstract [en]

    Certain alloys of iron and nickel (so-called ‘Invar’ alloys) exhibit almost no thermal expansion over a wide range of temperature. It is clear that this is the result of an anomalous contraction upon heating which counteracts the normal thermal expansion arising from the anharmonicity of lattice variations. This anomalous contraction seems to be related to the alloys’ magnetic properties, since the effect vanishes at a temperature close to the Curie temperature. However, despite many years of intensive research, a widely accepted microscopic theory of the Invar effect in face-centered-cubic Fe-Ni alloys is still lacking. Here we present a simple theory of the Invar effect in these alloys based on Ising magnetism, ab initio total energy calculations, and the Debye-Grüneisen model. We show that this theory accurately reproduces several well known properties of these materials, including Guilaume’s famous plot of the thermal expansion coefficient as a function of the concentration of nickel. Within the same framework, we are able to account in the straightforward way for experimentally observed deviations from Vegard’s law. Our approach supports the idea that the lattice constant is governed by a few parameters, including the fraction of iron-iron nearest-neighbour pairs.

  • 959.
    Eklöf, Anna
    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.
    Kaneryd, Linda
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical 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.
    Can dispersal rescue metacommunities from extinction cascades?Manuscript (preprint) (Other academic)
    Abstract [en]

    Climate change and habitat loss are increasingly affecting the structure and dynamics of ecological communities both at the local and regional scale. Changes in the spatial structure of landscapes as well as in the trophic structure of local communities can be expected to have important consequences for the long-term persistence of species in metacommunities. The aim of the present work is to investigate how the spatial structure of the landscape (patch density) and dispersal patterns of species (migration rate and dispersal distance) affect a metacommunities response to local loss of species and to increased mortality of individuals during dispersal. Using a spatially and dynamically explicit metacommunity model we find that the effect of dispersal on metacommunity persistence is two-sided: on the one hand, when dispersal involves no risk, high migration rate significantly reduces the risk of bottom-up extinction cascades following the local removal of a species. The explanation for this is that recolonization rates of the locally removed species increases with increasing migration rate. On the other hand, when dispersal imposes a risk to the dispersing individuals, high migration rate increases extinction risks, especially when dispersal is global (long dispersal distances). Largebodied species with long generation times at the highest trophic level are particularly vulnerable to extinction when dispersal involves a risk. These results suggest that decreasing the mortality risk of dispersing individuals by improving the quality of the habitat matrix might greatly increase the robustness of metacommunities to local loss of species by enhancing recolonizations and rescue effects.

  • 960.
    Adamovic, Dragan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology.
    Chirita, Valeriu
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Hultman, Lars
    Greene, Joe
    Controlled intra- and interlayer mass transport during low-energy Pt(111) homoepitaxyManuscript (Other academic)
  • 961.
    Xie, Mengyao
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Tasnádi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Abrikossov, I. A.
    Linköping University, Department of Physics, Chemistry and Biology. 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.
    Darakchieva, Vanya
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Effect of impurities on the lattice parameters of InNManuscript (preprint) (Other academic)
    Abstract [en]

    We study the effect of the most common impurities and dopants on the lattice parameters of InN by using ab-initio calculations. We have considered both the size and deformation potential effect and report results for H, O, Si andMg. The incorporation of H on interstitial site and substitutional O leads to expansion of the lattice. On the other hand, incorporation of Si or Mg leads to contraction of the lattice. The most pronounced effect is observed for Si. Our results indicate that the increase of the in-plane lattice parameter of Mg doped InN cannot be explained neither by the size nor by the deformation potential effect and suggest that the growth strain is changed in this case.a)Electronic mail: vanya@ifm.liu.se.

  • 962.
    Vekilova, Olga
    et al.
    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.
    Ponomareva, A V
    National University of Science and Technology MISIS, Russia.
    Dubrovinsky, Leonid
    Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Material Physics and Technology at Extreme Conditions, Laboratory of Crystallography, Universität Bayreuth, Bayreuth, Germany.
    Samuel, Henri
    Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Effect of non-uniform stresses on bcc Fe and Fe-Ni alloys at Earth's core conditionsManuscript (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.

  • 963.
    Eklöf, Anna
    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.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology . Linköping University, The Institute of Technology.
    Effects of dispersal on local extinctions in multi-trophic metacommunitiesManuscript (preprint) (Other academic)
    Abstract [en]

    As a result of habitat destruction many ecological communities have a fragmented distribution and are built up of partially isolated local communities connected through dispersal of interacting species. The dynamics of such metacommunities is governed both by local processes (interactions among species coexisting within habitat patches) and regional processes (movement of species among habitat patches). Earlier theoretical work on simple metacommunities have mainly focused on the positive effects of space and dispersal for the coexistence of interacting species and hence for local and regional species diversity. However, it is plausible that dispersal might also pose some kind of risk to the dispersing individuals. Here we explore how such risks might affect the dynamics of metacommunities. We develop spatially and dynamically explicit models to investigate how the trophic structure (connectance) of local communities, the spatial structure of the metacommunity and the dispersal characteristics of species affect species extinction risks. Species extinction risks in these open communities are measured relative to the extinction risks in closed communities (i.e. no dispersal). We show that the introduction of dispersal among initially closed local communities might lead to increased probability of local species extinction. The effects of dispersal depend on migration rate, movement pattern of individuals and the density of patches in the landscape. Specifically, when dispersal involves a risk, high migration rates, global dispersal and low patch density will all lead to increased probability of local species extinctions. Furthermore, the trophic structure of local communities plays a significant role in the response of metacommunities to changes in the regional processes.

  • 964.
    Asker, Christian
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Belonoshko, A. B.
    Applied Materials Physics, Department of Material Science and Engineering, The Royal Institute of Technology, 10044 Stockholm, Swedent.
    Grimvall, Anders
    Linköping University, Department of Computer and Information Science, Statistics. Linköping University, The Institute of Technology.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Electronic and atomic structure of Mo from high-temperature molecular dynamics simulationsManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    By means of ab initio molecular dynamics (AIMD) simulations we carry out a detailed stdly of the electronic and atomic structure of Mo upon the thermal stabilization of its dynamically unstable face-centered cubic (fcc) phase, Wc calculate how the atomic positions, radial distribution function, and the ei<xtronic density of states of fcc Mo evolve with temperature. The results are compared with those for dynamically stable body-centered cubic (bcc) phase of Mo, as well as with bcc Zr, which is dynamically unstable at T = OK, but (in contrast to fcc Mo) becomes thermodynamically stable at high temperature, In particular, wc emphasize the difference between the local positions of atoms in the simulation boxes at a particular step of AIMD simulation and the average positions, around which the atoms vibrate, and show that the former are solcly responsible for the electronic properties of the material. WE observe that while the average atomic positions in fcc Mo correspond perfectly to the ideal structure at high temperature, the electronic structure of the metal calculated from AIMD differs substantially from the canonical shape of the density of states for the ideal fcc crystaL From a comparison of our results obtained for fcc Mo arid bcc Zr, we advocate the use of the electronic structure calculations, complemented with studies of radial distribution functions, as a sensitive test of a degree of the temperature induced stabilization of phases, which are dynamically unstable at T = OK.

  • 965.
    Vekilova, Olga
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Pourovskii, L. V.
    Centre de Physique Theorique, CNRS, Ecole Polytechnique, Palaiseau, France.
    Abrikosov, Igor
    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.
    Electronic correlations in Fe at Earth's inner core conditions: effect of alloying with NiManuscript (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.

  • 966.
    Fallqvist, Amie
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical 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.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Evidence for B1-cubic SiNx by Aberration-Corrected Analytical STEMManuscript (preprint) (Other academic)
    Abstract [en]

    The crystal structure of epitaxially stabilized SiNx layers on TiN(001) was investigated by analytical aberration corrected electron microscopy. Atomically resolved images of the structure, which were acquired by scanning transmission electron microscopy using high angle annular dark field and annular bright field detectors, are used to identify the B1-cubic structure of SiNx. To corroborate the acquired images, image simulations were performed using candidate structures. Complementary to imaging, spatially resolved electron energy loss spectroscopy of the epitaxial SiNx layers was performed to acquire the symmetry specific nitrogen near edge fine-structure. Finally, full potential calculations performed to determine the near edge structure from candidate crystal structures confirms the existence of B1-cubic SiNx.

  • 967.
    Westwood, Luke
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Kaneryd, Linda
    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.
    Ebenman, Bo
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Biology. Linköping University, The Institute of Technology.
    Keystone patches: upholding diversity in multi-trophic metacommunitiesManuscript (preprint) (Other academic)
    Abstract [en]

    Due to the destruction of their habitat some organisms have an uneven distribution across the landscape. In affected areas a community of interacting organisms may be fragmented into a network of smaller patches connected through dispersal of individuals of the different species. These metacommunities can be modelled with explicit dynamics and spatial structure, with dependence on both local processes (interactions between species within a patch) and global processes (dispersal of individuals between patches). Dispersal between patches is important for the operation of processes like recolonizations and ‘rescue effects’, processes which can counteract local extinctions and hence reduce the risk of global extinctions. Recent studies have applied network theory to real ecological communities, with a wide selection of indices available to characterise either an individual patch or the whole patch network. Certain keystone patches may be the most important in upholding the local or global diversity of a metacommunity and may then be identified by such a network index. A range of network indices were calculated for the patches in a large set of simulated metacommunities and all of the indices identified the keystone patch quality to a certain degree. Some of the indices were consistently better than the others and the dependence of the keystone quality on these indices was at least two times larger than for the others. The quality identified by the indices was of being more important for upholding local rather than global diversity. Many parameters were varied between the different metacommunities and as a result of this the models for identifying keystone patches yielded small R2 values and therefore were not proven to be dependable predictors if applied to particular metacommunities.

  • 968.
    Ullbrand, Jennifer
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Grönhagen, Klara
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Tasnádi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Jansson, Bo
    Seco Tools AB, Fagersta, Sweden.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
    Microstructure evolution of TiAlN-a phase field studyManuscript (preprint) (Other academic)
    Abstract [en]

    In this work the phase field method has been applied to model the spinodal decomposition of TiAlN. Here we have used thermodynamic data from ab initio calculations that takes into account clustering effects, and experimental diffusivity data of TiAlN as an input to the model. The effect of alloy composition on microstructure and stresses, is studied in time and space. In addition, Young’s modulus evolution of the decomposing microstructure is reported. It was found that the microstructure changes from round AlN rich domains in a TiN matrix, to outstretched TiN rich domains in the {100} crystallographic directions in an AlN matrix, as the composition was changed from x=0.3 to x=0.75 in Ti1-xAlxN. The microstructure evolution was observed to undergo different stages. In short; first elongated structures enriched of the majority element in random directions evolve. Thereafter round AlN rich domains evolve, independent of composition studied, and a completely segregated microstructure forms that finally coarsens. The initiation, decomposition, and coarsening rate was found to increase with Al content due to the increase in driving force with Al content. Al rich domains purify fastest, independent of composition studied. The evolving compositional wavelength decreases with Al content resulting in a finer microstructure for alloys rich in Al. During decomposition high local strains and stresses develop, which reach maximum values of 6·10-3 and 12 GPa respectively.

  • 969.
    Kerdsongpanya, Sit
    et al.
    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. Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, USA.
    Sun, Bo
    Department of Mechanical Engineering, National University of Singapore, Block EA, Singapore..
    Koh, Yee Kan
    Department of Mechanical Engineering, National University of Singapore, Block EA, Singapore..
    Van Nong, Ngo
    Dept. of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, Denmark.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Simak, Sergei I.
    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.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Phonon Thermal Conductivity of Scandium Nitride for Thermoelectric Applications from First-Principles CalculationsManuscript (preprint) (Other academic)
    Abstract [en]

    The knowledge of lattice thermal conductivity of materials under realistic conditions is vitally important since most technologies either require either high or low thermal conductivity. Here, we propose a theoretical model for determining lattice thermal conductivity with the effect of microstructure. This is based on ab initio description that includes the temperature dependence of the interatomic force constants, and treats anharmonic lattice vibrations. We choose ScN as a model system, comparing the computational predictions with the experimental data by Time Domain Thermoreflectance (TDTR). Our results show a trend of reduction in lattice thermal conductivity with decreasing grain size, with good agreement between the theoretical model and experimental data. There results suggest a possibility to control thermal conductivity by tailoring the microstructure of ScN. More importantly, we provide a predictive tool for the effect of the microstructure on the lattice thermal conductivity of materials based on first-principles calculations.

  • 970.
    Kaneryd, Linda
    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.
    Eklöf, Anna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical 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.
    Risk of global extinctions in metacommunities exposed to a highly variable environment: local and spatial processesManuscript (preprint) (Other academic)
    Abstract [en]

    Here we analyze how metacommunities (a set of local communities coupled by species dispersal) in spatially explicit landscapes respond to environmental variation. We examine how this response is affected by 1) species richness in the local communities, 2) the degree of correlation in species response to the environmental variation both between species within patches (species correlation) and among patches (spatial correlation) and 3) dispersal pattern of species. We find that the risk of global extinction increases with increasing species richness in the local communities and with decreasing correlation among species in their response to environmental fluctuations. We also show that the pattern of spatial correlation is of great importance; the risk of global extinctions increases with increasing spatial correlation. Moreover, we find that the pattern and rate of dispersal are important; a high migration rate in combination with localized dispersal decrease the risk of global extinctions whereas a global dispersal pattern increases the risk of global extinctions. When dispersal is global the subpopulations of a species become more synchronized which reduces the potential for a patch to become recolonized following extinctions. We also demonstrate the importance of both local and spatial processes when examining the temporal stability of primary production at the scale of metapopulations, local communities and metacommunities.

  • 971.
    Ekholm, Marcus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tasnádi, Ferenc
    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.
    Supercell Calculations of Hyperfine Interactions in Transition-Metal AlloysManuscript (preprint) (Other academic)
    Abstract [en]

    We have performed calculations for the hyperfine field in the disordered Fe0.5Ni0.5 alloy using supercells with up to 864 atoms. The computational scheme is based on exact muffin-tin orbitals and the locally self-consistent Green’s function formalism, which scales linearly with the number of atoms in the supercell. This scheme allows local environment effects, such as chemical and magnetic environment, and short-range order, to be explicitly included. Supercell calculations for Fe-Ni show that while the average fields coincides with that obtained using the coherent potential approximation, there is a significant distribution of the hyperfine fields depending on the local environment. The fields of Fe and Ni show qualitatively different behaviour as a function of the on-site magnetic moment, but scale linearly with the average magnetic moment in the first coordination shell.

  • 972.
    Hellman, Olle
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical 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.
    Abrikosov, Igor
    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.
    Temperature dependent effective potential method for accurate free energy calculation of solidsManuscript (preprint) (Other academic)
    Abstract [en]

    We have developed a thorough and accurate method of determining anharmonic free energies. The technique is based in ab initio molecular dynamics and map a model Hamiltonian to the fully anharmonic system. We can accurately deal with low-symmetry systems, such as random alloys. The formalism and the numerics are described in great detail. A number of practical examples are given, and favourable results are presented, both with respect to experiment and established techniques.

  • 973.
    Alling, Björn
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Khatibi, Ali
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film 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.
    Eklund, Per
    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.
    Theoretical investigation of cubic B1-like and corundum (Cr1−xAlx)2O3 solid solutionsManuscript (preprint) (Other academic)
    Abstract [en]

    First-principles calculations are employed to investigate the stability and properties of cubic rock-salt like (Cr1−xAlx)2O3 solid solutions, stabilized by metal site vacancies as recently reported experimentally. It is demonstrated that the metal site vacancies can indeed be ordered in a way that gives rise to a favorable coordination of all O atoms in the lattice. B1-like structures with ordered and disordered metal site vacancies are studied for (Cr0.5Al0.5)2O3 and found to a have cubic lattice spacing close to the values reported experimentally, in contrast to fluorite-like and perovskite structures. The obtained B1-like structures are higher in energy than corundum solid solutions for all compositions, but with an energy offset per atom similar to other metastable systems possible to synthesize with physical vapor deposition techniques. The obtained electronic structures show that the B1-like systems are semiconducting although with smaller band gaps than the corundum structure.

  • 974.
    Lind, Hans
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tasnádi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical 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.
    Ti and Cr impurities in cubic and hexagonal AlNManuscript (preprint) (Other academic)
    Abstract [en]

    AlN is a wide band gap semiconductor that is used in many fields, e.g. as electronic material, for piezoelectric applications but also as a component material in high performance hard coating alloys. The stable structure under ambient conditions is a hexagonal wurtzite structure, but it has also been observed in the tetrahedrally bonded cubic zinc-blende structure as well as cubic rock-salt phases that become stable at high pressure. The metastable rock-salt phase of AlN also forms during decomposition processes in hard-coating alloys such as (TiAl)N, (CrAl)N and (TiCrAl)N. Even though thermodynamically unstable, one can expect some amount of Ti and Cr to be present in the c-AlN phase during the decomposition. Still, little study has been done for the dilute (TMAl)N alloys with cubic B1 crystal structure. We study the electronic structure of Ti and Cr impurities in B1 AlN. Because of the limitations of standard local and semi-local approximations within the density functional theory (DFT) in the treatment of wide band gap semiconductors, as well as conventional hybrid functionals for systems consisting of correlated localized and delocalized orbitals, we apply the mHSE+Vw method, which has been developed specifically to dealing with these kind of problems. Simulations are done by means of the supercell technique with single impurities, as well as for the impurity pairs. The effects of different atomic configurations of the TM-impurities on phase stability and magnetic properties of the cubic B1 AlN is studied and compared to the those in hexagonal B4 structures. Our results underline the importance of correlation and magnetic effects for the description of properties of cubic AlN doped with Ti and Cr.

  • 975.
    Hellman, Olle
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Skorodumova, N. V.
    Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Stockholm, Sweden.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
    Tuning ionic conductivity in ceria by volume optimizationManuscript (preprint) (Other academic)
    Abstract [en]

    Effect of volume change on the ionic conductivity in ceria has been studied in the framework of the density functional theory. We show that properly controlling external conditions one can treat the lattice constant of ceria as an adjustable parameter and change the topology of the energy landscape for the oxygen ion diffusion. We reveal the existence of the narrow range of lattice parameters, which optimize the ionic conductivity in ceria.

17181920 951 - 975 of 975
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