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  • 1.
    Vorotilo, S.
    et al.
    Natl Univ Sci and Technol MISIS, Russia.
    Sidnov, K.
    Natl Univ Sci and Technol MISIS, Russia; Russian Acad Sci, Russia.
    Mosyagin, I. Yu
    Natl Univ Sci and Technol MISIS, Russia.
    Khvan, A. V
    Natl Univ Sci and Technol MISIS, Russia.
    Levashov, E. A.
    Natl Univ Sci and Technol MISIS, Russia.
    Patsera, E. I
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Ab-initio modeling and experimental investigation of properties of ultra-high temperature solid solutions TaxZr1-xC2019In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 778, p. 480-486Article in journal (Refereed)
    Abstract [en]

    Due to their high melting temperature, high-temperature oxidation resistance and outstanding mechanical properties, TaxZr1-xC solid solutions are promising ultra-high temperature ceramics (UHTC). However, accelerated knowledge-based development of UHTCs solid solutions requires reliable data regarding the properties of the solution phases in the whole interval of concentrations. At present, there are contradictory reports regarding the existence of the miscibility gap in Ta-Zr-C system at temperatures below 900 degrees C. In this work, we carry out ab-initio calculations of the thermodynamic properties of TaxZr1-xC alloys and demonstrate that the solid solutions should not decompose into TaC and ZrC end member compounds. We synthesize single-phase samples of TaxZr1-xC with compositions x = 0.9, 0.8, 0.6, and 0.3 by self-propagating high-temperature synthesis (SHS) and anneal the samples for 40 h. We do not observe any sign of the decomposition of the solid solution during the annealing, corroborating the conclusions obtained by theoretical simulations. (C) 2018 Elsevier B.V. All rights reserved.

    The full text will be freely available from 2020-11-19 15:39
  • 2.
    Jamnig, Andreas
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering. Univ Poitiers, France.
    Sangiovanni, Davide Giuseppe
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Abadias, G.
    Univ Poitiers, France.
    Sarakinos, Kostas
    Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering.
    Atomic-scale diffusion rates during growth of thin metal films on weakly-interacting substrates2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 6640Article in journal (Refereed)
    Abstract [en]

    We use a combined experimental and theoretical approach to study the rates of surface diffusion processes that govern early stages of thin Ag and Cu film morphological evolution on weakly-interacting amorphous carbon substrates. Films are deposited by magnetron sputtering, at temperatures T-S between 298 and 413 K, and vapor arrival rates F in the range 0.08 to 5.38 monolayers/s. By employing in situ and real-time sheet-resistance and wafer-curvature measurements, we determine the nominal film thickness Theta at percolation (Theta(perc)) and continuous film formation (Theta(cont)) transition. Subsequently, we use the scaling behavior of Theta(perc) and Theta(cont) as a function of F and T-s, to estimate, experimentally, the temperature-dependent diffusivity on the substrate surface, from which we calculate Ag and Cu surface migration energy barriers E-D(exp) and attempt frequencies nu(exp)(0). By critically comparing E-D(exp) and nu(exp)(0) with literature data, as well as with results from our ab initio molecular dynamics simulations for single Ag and Cu adatom diffusion on graphite surfaces, we suggest that: (i) E-D(exp) and nu(exp)(0) correspond to diffusion of multiatomic clusters, rather than to diffusion of monomers; and (ii) the mean size of mobile clusters during Ag growth is larger compared to that of Cu. The overall results of this work pave the way for studying growth dynamics in a wide range of technologically-relevant weakly-interacting film/substrate systems-including metals on 2D materials and oxides-which are building blocks in next-generation nanoelectronic, optoelectronic, and catalytic devices.

  • 3.
    Yakimenko, Ivan P.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering.
    Yakymenko, Iryna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Berggren, Karl-Fredrik
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Basic modelling of effects of geometry and magnetic field for quantum wires injecting electrons into a two-dimensional electron reservoir2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 34, article id 345302Article in journal (Refereed)
    Abstract [en]

    High-mobility two-dimensional electron gas (2DEG) which resides at the interface between GaAs and AlGaAs layered semiconductors has been used experimentally and theoretically to study ballistic electron transport. The present paper is motivated by recent experiments in magnetic electron focusing. The proposed device consists of two quantum point contacts (QPCs) serving as electron injector and collector which are placed in the same semiconductor GaAs/AlGaAs heterostructure. Here we focus on a theoretical study of the injection of electrons via a quantum wire/QPC into an open two-dimensional (2D) reservoir. The transport is considered for non-interacting electrons at different transmission regimes using the mode-matching technique. The proposed mode-matching technique has been implemented numerically. Electron flow through the quantum wire with hard-wall rectangular, conical and rounded openings has been studied. We have found for these three cases that the geometry of the opening does not play a crucial role for the electron propagation. When a perpendicular magnetic field is applied the electron paths in the 2D reservoir are curved. We analyse this case both classically and quantum-mechanically. The effect of spin-splitting due to exchange interactions on the electron flow is also considered. The effect is clearly present for realistic choices of device parameters and consistent with observations. The results of this study may be applied in designing magnetic focusing devices and spin separation.

  • 4.
    Silva, Gesiel Gomes
    et al.
    Goias Fed Inst Educ Sci and Technol, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil; Univ Brasilia, Brazil.
    Pereira Junior, Marcelo Lopes
    Univ Brasilia, Brazil.
    de Almeida Fonseca, Antonio Luciano
    Univ Brasilia, Brazil; Univ Brasilia, Brazil.
    de Sousa Junior, Rafael Timoteo
    Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Bipolaron Dynamics in Graphene Nanoribbons2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 2909Article in journal (Refereed)
    Abstract [en]

    Graphene nanoribbons (GNRs) are two-dimensional structures with a rich variety of electronic properties that derive from their semiconducting band gaps. In these materials, charge transport can occur via a hopping process mediated by carriers formed by self-interacting states between the excess charge and local lattice deformations. Here, we use a two-dimensional tight-binding approach to reveal the formation of bipolarons in GNRs. Our results show that the formed bipolarons are dynamically stable even for high electric field strengths when it comes to GNRs. Remarkably, the bipolaron dynamics can occur in acoustic and optical regimes concerning its saturation velocity. The phase transition between these two regimes takes place for a critical field strength in which the bipolaron moves roughly with the speed of sound in the material.

  • 5.
    Tal, Alexey A.
    et al.
    Ecole Polytech Fed Lausanne, Switzerland.
    Posada-Borbon, Alvaro
    Chalmers Univ Technol, Sweden; Chalmers Univ Technol, Sweden.
    Gronbeck, Henrik J.
    Chalmers Univ Technol, Sweden; Chalmers Univ Technol, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Correlation between Ethylene Adsorption Energies and Core-Level Shifts for Pd Nanoclusters2019In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 123, no 4, p. 2544-2548Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations have been used to investigate the adsorption of ethylene on Pd nanoclusters together with shifts in core-level binding energies of Pd atoms bonded to the adsorbate. The adsorption energy is found to correlate with the core-level shifts (CLS), which is consistent with the notion that the core-level binding energy is a measure of differences in cohesion. The correlation between adsorption energies and core-level shifts is found to be stronger than the correlation between adsorption energies and generalized coordination numbers, indicating that descriptors preferably should account for electronic effects explicitly. The advantages of CLS as a descriptor for the screening of adsorption properties is discussed.

    The full text will be freely available from 2019-12-24 10:57
  • 6.
    de Sousa, Leonardo Evaristo
    et al.
    Univ Brasilia, Brazil.
    Bueno, Fernando Teixeira
    Univ Brasilia, Brazil.
    da Silva Filho, Demetrio Antonio
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    de Oliveira Neto, Pedro Henrique
    Univ Brasilia, Brazil.
    Dynamical exciton decay in organic materials: the role of bimolecular recombination2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 4, p. 1711-1716Article in journal (Refereed)
    Abstract [en]

    Excitons play a critical role in light emission when it comes to organic semiconductors. In high exciton concentration regimes, monomolecular and bimolecular routes for exciton recombination can yield different products affecting significantly the materials optical properties. Here, the dynamical decay of excitons is theoretically investigated using a kinetic Monte Carlo approach that addresses singlet exciton diffusion. Our numerical protocol includes two distinct exciton-exciton interaction channels: exciton annihilation and biexciton cascade emission. Our findings reveal that these channels produce different consequences concerning diffusion and spectroscopic properties, being able to explain diverging experimental observations. Importantly, we estimate critical exciton densities for which bimolecular recombination becomes dominant and investigate its effect on average exciton lifetimes and diffusion lengths.

  • 7.
    Pilemalm, Robert
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Effects of high pressure on ScMN2-type (M = V, Nb, Ta) phases studied by density functional theory2019In: RESULTS IN PHYSICS, ISSN 2211-3797, Vol. 13, article id 102293Article in journal (Refereed)
    Abstract [en]

    ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb, but their high-pressure properties have not been studied. Here, we have used first-principles calculations to study their thermodynamic stability, elastic and electronic properties at high-pressure. We have used density functional theory to calculate the formation enthalpy relative to the competing binary phases, electronic density of states and elastic constants (c(ij)), bulk (B), shear (G) and Youngs (E) modulus as the pressure is varied from 0 to 150 GPa. Our results show that when the pressure increases from 0 to 150 GPa, elastic constants, bulk, shear and elastic moduli increase in the range 53-216% for ScTaN2, 72-286% for ScNbN2, and 61-317% for ScVN2.

  • 8.
    Ferrari, Alberto
    et al.
    Ruhr Univ Bochum, Germany.
    Sangiovanni, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Rogal, Jutta
    Ruhr Univ Bochum, Germany.
    Drautz, Ralf
    Ruhr Univ Bochum, Germany.
    First-principles characterization of reversible martensitic transformations2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 9, article id 094107Article in journal (Refereed)
    Abstract [en]

    Reversible martensitic transformations (MTs) are the origin of many fascinating phenomena, including the famous shape memory effect. In this work, we present a fully ab initio procedure to characterize MTs in alloys and to assess their reversibility. Specifically, we employ ab initio molecular dynamics data to parametrize a Landau expansion for the free energy of the MT. This analytical expansion makes it possible to determine the stability of the high- and low-temperature phases, to obtain the Ehrenfest order of the MT, and to quantify its free energy barrier and latent heat. We apply our model to the high-temperature shape memory alloy Ti-Ta, for which we observe remarkably small values for the metastability region (the interval of temperatures in which the high-and low-temperature phases are metastable) and for the barrier: these small values are necessary conditions for the reversibility of MTs and distinguish shape memory alloys from other materials.

  • 9.
    Parra-Rivas, Pedro
    et al.
    Univ Libre Bruxelles, Belgium; Univ Leuven, Belgium.
    Gelens, Lendert
    Univ Leuven, Belgium.
    Hansson, Tobias
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Wabnitz, Stefan
    Sapienza Univ Rome, Italy; CNR, Italy.
    Leo, Francois
    Univ Libre Bruxelles, Belgium.
    Frequency comb generation through the locking of domain walls in doubly resonant dispersive optical parametric oscillators2019In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 44, no 8, p. 2004-2007Article in journal (Refereed)
    Abstract [en]

    In this Letter we theoretically investigate the formation of localized temporal dissipative structures, and their corresponding frequency combs in doubly resonant dispersive optical parametric oscillators. We derive a nonlocal mean field model, and show that domain wall locking allows for the formation of stable coherent optical frequency combs. (C) 2019 Optical Society of America

  • 10.
    Laniel, Dominique
    et al.
    Univ Bayreuth, Germany.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Fedotenko, Timofey
    Univ Bayreuth, Germany.
    Ponomareva, Alena V.
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Glazyrin, Konstantin
    DESY, Germany.
    Svitlyk, Volodymyr
    European Synchrotron Radiat Facil, France.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Univ Bayreuth, Germany.
    High Pressure Investigation of the S-N-2 System up to the Megabar Range: Synthesis and Characterization of the SN2 Solid2019In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 58, no 14, p. 9195-9204Article in journal (Refereed)
    Abstract [en]

    Sulfur and nitrogen represent one of the most studied inorganic binary systems at ambient pressure on account of their large wealth of metastable exotic ring-like compounds. Under high pressure conditions, however, their behavior is unknown. Here, sulfur and nitrogen were compressed in a diamond anvil cell up to about 120 GPa and laser-heated at regular pressure intervals in an attempt to stabilize novel sulfur nitrogen compounds. Above 64 GPa, an orthorhombic (space group Pnnm) SN2 compound was synthesized and characterized by single-crystal and powder X-ray diffraction as well as Raman spectroscopy. It is shown to adopt a CaCl2-type structure hence it is isostructural, isomassic, and isoelectronic to CaCl2-type SiO2 comprised of SN6 octahedra. Complementary theoretical calculations were performed to provide further insight into the physicochemical properties of SN2, notably its equation of state, the bonding type between its constitutive elements, and its electronic density of states. This new solid is shown to be metastable down to about 20 GPa, after which it spontaneously decomposes into S and N-2. This investigation shows that despite the many metastable S N compounds existing at ambient conditions, none of them are formed by pressure.

  • 11.
    Bykov, Maxim
    et al.
    Univ Bayreuth, Germany.
    Chariton, Stella
    Univ Bayreuth, Germany.
    Fei, Hongzhan
    Univ Bayreuth, Germany.
    Fedotenko, Timofey
    Univ Bayreuth, Germany.
    Aprilis, Georgios
    Univ Bayreuth, Germany.
    Ponomareva, Alena V
    Natl Univ Sci and Technol MISIS, Russia.
    Tasnadi, Ferenc
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Merle, Benoit
    Friedrich Alexander Univ Erlangen Nurnberg FAU, Germany.
    Feldners, Patrick
    Friedrich Alexander Univ Erlangen Nurnberg FAU, Germany.
    Vogel, Sebastian
    Univ Munich LMU, Germany.
    Schnick, Wolfgang
    Univ Munich LMU, Germany.
    Prakapenka, Vitali B.
    Univ Chicago, IL 60637 USA.
    Greenberg, Eran
    Univ Chicago, IL 60637 USA.
    Hanfland, Michael
    European Synchrotron Radiat Facil, France.
    Pakhomova, Anna
    DESY, Germany.
    Liermann, Hanns-Peter
    DESY, Germany.
    Katsura, Tomoo
    Univ Bayreuth, Germany.
    Dubrovinskaia, Natalia
    Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re-2(N-2)(N)(2) stable at ambient conditions2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 2994Article in journal (Refereed)
    Abstract [en]

    High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K-0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re-2(N-2)(N)(2). Unlike known transition metals pernitrides Re-2(N-2)(N)(2) contains both pernitride N-2(4-) and discrete N3- anions, which explains its exceptional properties. Re-2(N-2)(N)(2) can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH4N3, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re-2(N-2)(N)(2) turned to be at a threshold for superhard materials.

  • 12.
    Davidsson, Joel
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ivády, Viktor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Hungarian Acad Sci, Hungary.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ohshima, Takeshi
    Natl Inst Quantum and Radiol Sci and Technol, Japan.
    Nguyen, Son Tien
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Gali, Adam
    Hungarian Acad Sci, Hungary; Budapest Univ Technol and Econ, Hungary.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Identification of divacancy and silicon vacancy qubits in 6H-SiC2019In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, no 11, article id 112107Article in journal (Refereed)
    Abstract [en]

    Point defects in semiconductors are relevant for use in quantum technologies as room temperature qubits and single photon emitters. Among suggested defects for these applications are the negatively charged silicon vacancy and the neutral divacancy in SiC. The possible nonequivalent configurations of these defects have been identified in 4H-SiC, but for 6H-SiC, the work is still in progress. In this paper, we identify the different configurations of the silicon vacancy and the divacancy defects to each of the V1-V3 and the QL1-QL6 color centers in 6H-SiC, respectively. We accomplish this by comparing the results from ab initio calculations with experimental measurements for the zero-phonon line, hyperfine tensor, and zero-field splitting. Published under license by AIP Publishing.

  • 13.
    Jönsson, Johan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ekholm, Marcus
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    van Smaalen, Sander
    Univ Bayreuth, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Inverse pressure-induced Mott transition in TiPO42019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 24, article id 245132Article in journal (Refereed)
    Abstract [en]

    TiPO4 shows interesting structural and magnetic properties as temperature and pressure are varied, such as a spin-Peierls phase transition and the development of incommensurate modulations of the lattice. Recently, high-pressure experiments for TiPO4 reported two structural phases appearing at high pressures, the so-called phases IV and V [M. Bykov et al., Angew. Chem. Int. Ed. 55, 15053 (2016).]. The latter was shown to include the first example of fivefold O-coordinated P atoms in an inorganic phosphate compound. In this work, we characterize the electronic structure and other physical properties of these phases by means of ab initio calculations and investigate the structural transition. We find that the appearance of phases IV and V coincides with a collapse of the Mott insulating gap and quenching of magnetism in phase III as pressure is applied. Remarkably, our calculations show that in the high-pressure phase V, these features reappear, leading to an antiferromagnetic Mott insulating phase, with robust local moments.

  • 14.
    Belonoshko, Anatoly B.
    et al.
    Royal Inst Technol KTH, Sweden.
    Fu, Jie
    Ningbo Univ, Peoples R China.
    Bryk, Taras
    Natl Acad Sci Ukraine, Ukraine.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Mattesini, Maurizio
    Univ Complutense Madrid, Spain; UCM, Spain.
    Low viscosity of the Earths inner core2019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 2483Article in journal (Refereed)
    Abstract [en]

    The Earths solid inner core is a highly attenuating medium. It consists mainly of iron. The high attenuation of sound wave propagation in the inner core is at odds with the widely accepted paradigm of hexagonal close-packed phase stability under inner core conditions, because sound waves propagate through the hexagonal iron without energy dissipation. Here we show by first-principles molecular dynamics that the body-centered cubic phase of iron, recently demonstrated to be thermodynamically stable under the inner core conditions, is considerably less elastic than the hexagonal phase. Being a crystalline phase, the body-centered cubic phase of iron possesses the viscosity close to that of a liquid iron. The high attenuation of sound in the inner core is due to the unique diffusion characteristic of the body-centered cubic phase. The low viscosity of iron in the inner core enables the convection and resolves a number of controversies.

  • 15.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Low-energy paths for octahedral tilting in inorganic halide perovskites2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104105Article in journal (Refereed)
    Abstract [en]

    Instabilities relating to cooperative octahedral tilting is common in materials with perovskite structures, in particular in the subclass of halide perovskites. In this work the energetics of octahedral tilting in the inorganic metal halide perovskites CsPbI3 and CsSnI3 are investigated using first-principles density functional theory calculations. Several low-energy paths between symmetry equivalent variants of the stable orthorhombic (Pnma) perovskite variant are identified and investigated. The results are in favor of the presence of dynamic disorder in the octahedral tilting phase transitions of inorganic halide perovskites. In particular, one specific type of path, corresponding to an out-of-phase "tilt switch," is found to have significantly lower energy barrier than the others, which indicates the existence of a temperature range where the dynamic fluctuations of the octahedra follow only this type of path. This could produce a time averaged structure corresponding to the intermediate tetragonal (P4/mbm) structure observed in experiments. Deficiencies of the commonly employed simple one-dimensional "double-well" potentials in describing the dynamics of the octahedra are pointed out and discussed.

  • 16.
    Krasilnikov, O. M.
    et al.
    NUST MISIS, Russia.
    Lugovskoy, A. V
    NUST MISIS, Russia; Radboud Univ Nijmegen, Netherlands.
    Dikan, V
    NUST MISIS, Russia; CSIC, Spain.
    Belov, M. P.
    NUST MISIS, Russia.
    Vekilov, Yu Kh
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Nonlinear elasticity of epsilon -Fe: The pressure effect2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 18, article id 184101Article in journal (Refereed)
    Abstract [en]

    Description of elasticity of iron at the ultrahigh pressures is a challenging task for physics, with a potential strong impact on other branches of science. In the present work, we calculate the elastic properties of hcp iron in the pressure range of 50-340 GPa beyond the linear elasticity approximation, conventionally assumed in theoretical studies. We define the higher order elastic constants and present expressions for the long-wave acoustic modes Gruneisen parameters of a compressed hcp crystal. We obtain the second and third order elastic constants of the hcp Fe in the considered pressure interval, as well as its Gruneisen parameters for the high-symmetry directions. The latter are directly compared with the Gruneisen parameters derived from the volume dependences of the vibrational frequencies calculated in the quasiharmonic approximation. The obtained results are used for the stability analysis of the hcp phase of iron at high pressures.

  • 17.
    Gautam, Rekha
    et al.
    San Francisco State Univ, CA 94132 USA; Vanderbilt Univ, TN 37240 USA.
    Xiang, Yinxiao
    San Francisco State Univ, CA 94132 USA; Nankai Univ, Peoples R China; Nankai Univ, Peoples R China.
    Lamstein, Josh
    San Francisco State Univ, CA 94132 USA.
    Liang, Yi
    San Francisco State Univ, CA 94132 USA; Guangxi Univ, Peoples R China.
    Bezryadina, Anna
    San Francisco State Univ, CA 94132 USA; Calif State Univ Northridge, CA 91330 USA.
    Liang, Guo
    San Francisco State Univ, CA 94132 USA.
    Hansson, Tobias
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Quebec, Canada.
    Wetzel, Benjamin
    Univ Quebec, Canada; Univ Sussex, England.
    Preece, Daryl
    Univ Calif Irvine, CA USA.
    White, Adam
    San Francisco State Univ, CA 94132 USA.
    Silverman, Matthew
    San Francisco State Univ, CA 94132 USA.
    Kazarian, Susan
    San Francisco State Univ, CA 94132 USA.
    Xu, Jingjun
    Nankai Univ, Peoples R China.
    Morandotti, Roberto
    Univ Quebec, Canada; Univ Elect Sci and Tech China, Peoples R China; ITMO Univ, Russia.
    Chen, Zhigang
    San Francisco State Univ, CA 94132 USA; Nankai Univ, Peoples R China; Nankai Univ, Peoples R China.
    Optical force-induced nonlinearity and self-guiding of light in human red blood cell suspensions2019In: Light: Science & Applications, ISSN 2095-5545, E-ISSN 2047-7538, Vol. 8, article id 31Article in journal (Refereed)
    Abstract [en]

    Osmotic conditions play an important role in the cell properties of human red blood cells (RBCs), which are crucial for the pathological analysis of some blood diseases such as malaria. Over the past decades, numerous efforts have mainly focused on the study of the RBC biomechanical properties that arise from the unique deformability of erythrocytes. Here, we demonstrate nonlinear optical effects from human RBCs suspended in different osmotic solutions. Specifically, we observe self-trapping and scattering-resistant nonlinear propagation of a laser beam through RBC suspensions under all three osmotic conditions, where the strength of the optical nonlinearity increases with osmotic pressure on the cells. This tunable nonlinearity is attributed to optical forces, particularly the forward-scattering and gradient forces. Interestingly, in aged blood samples (with lysed cells), a notably different nonlinear behavior is observed due to the presence of free hemoglobin. We use a theoretical model with an optical force-mediated nonlocal nonlinearity to explain the experimental observations. Our work on light self-guiding through scattering bio-soft-matter may introduce new photonic tools for noninvasive biomedical imaging and medical diagnosis.

  • 18.
    Xu, Bin
    et al.
    Soochow Univ, Peoples R China; Univ Arkansas, AR 72701 USA; Univ Arkansas, AR 72701 USA.
    Hellman, Olle
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bellaiche, L.
    Univ Arkansas, AR 72701 USA.
    Order-disorder transition in the prototypical antiferroelectric PbZrO32019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 2, article id 020102Article in journal (Refereed)
    Abstract [en]

    The prototypical antiferroelectric PbZrO3 has several unsettled questions, such as the nature of the antiferroelectric transition, a possible intermediate phase, and the microscopic origin of the Pbam ground state. Using first-principles calculations, we show that no phonon becomes truly soft at the cubic-to-Pbam transition temperature, and the order-disorder character of this transition is clearly demonstrated based on molecular dynamics simulations and potential energy surfaces. The out-of-phase octahedral tilting is an important degree of freedom, which can collaborate with other phonon distortions and form a complex energy landscape with multiple minima Candidates of the possible intermediate phase are suggested based on the calculated kinetic barriers between energy minima, and the development of a first-principles-based effective Hamiltonian. The use of this latter scheme further reveals that specific bilinear interactions between local dipoles and octahedral tiltings play a major role in the formation of the Pbam ground state, which contrasts with most of the previous explanations.

  • 19.
    Pakhomova, Anna
    et al.
    DESY, Germany.
    Aprilis, Georgios
    Univ Bayreuth, Germany.
    Bykov, Maxim
    Univ Bayreuth, Germany.
    Gorelova, Liudmila
    St Petersburg State Univ, Russia.
    Krivovichev, Sergey S.
    St Petersburg State Univ, Russia; Russian Acad Sci, Russia.
    Belov, Maxim P.
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Dubrovinsky, Leonid
    Univ Bayreuth, Germany.
    Penta- and hexa-coordinated beryllium and phosphorus in high-pressure modifications of CaBe2P2O82019In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 2800Article in journal (Refereed)
    Abstract [en]

    Beryllium oxides have been extensively studied due to their unique chemical properties and important technological applications. Typically, in inorganic compounds beryllium is tetrahedrally coordinated by oxygen atoms. Herein based on results of in situ single crystal X-ray diffraction studies and ab initio calculations we report on the high-pressure behavior of CaBe2P2O8, to the best of our knowledge the first compound showing a step-wise transition of Be coordination from tetrahedral (4) to octahedral (6) through trigonal bipyramidal (5). It is remarkable that the same transformation route is observed for phosphorus. Our theoretical analysis suggests that the sequence of structural transitions of CaBe2P2O8 is associated with the electronic transformation from predominantly molecular orbitals at low pressure to the state with overlapping electronic clouds of anions orbitals.

  • 20.
    Landälv, Ludvig
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering. Sandvik Coromant AB, Stockholm, Sweden.
    Carlström, C-F
    Sandvik Coromant AB, Stockholm, Sweden.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Primetzhofer, D.
    Applied Nuclear Physics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
    Jöesaar, M. J.
    SECO Tools AB, Fagersta, Sweden.
    Ahlgren, M.
    Sandvik Coromant AB, Stockholm, Sweden.
    Göthelid, E.
    Sandvik Coromant AB, Stockholm, Sweden.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731Article in journal (Refereed)
    Abstract [en]

    Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 °C. XRD showed three different crystal structures depending on V-metal fraction in the coating: α-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63–42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure γ-Al2O3. The microstructure changes from large columnar faceted grains for α-V2O3 to smaller equiaxed grains when lowering the vanadium content towards pure γ-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 °C for 42 at.% V and 700 °C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure γ-Al2O3-coating, which transformed to α-Al2O3 after annealing to 1100 °C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.

  • 21.
    Pakornchote, T.
    et al.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Ektarawong, Annop
    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, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Pinsook, U.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Tancharakorn, S.
    Synchrotron Light Res Inst Publ Org, Thailand.
    Busayaporn, W.
    Synchrotron Light Res Inst Publ Org, Thailand.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Thailand; Thailand Ctr Excellence Phys, Thailand.
    Phase stabilities and vibrational analysis of hydrogenated diamondized bilayer graphenes: A first principles investigation2019In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 146, p. 468-475Article in journal (Refereed)
    Abstract [en]

    The phase stabilities as well as some intrinsic properties of hydrogenated diamondized bilayer graphenes, 2-dimensional materials adopting the crystal structure of diamond and of lonsdaleite, are investigated using a first-principles approach. Our simulations demonstrate that hydrogenated diamondized bilayer graphenes are thermodynamically stable with respect to bilayer graphene and hydrogen molecule even at 0 GPa, and additionally they are found to withstand the physical change in structure up to at least 1000 K, ensuring their dynamical and thermal stabilities. The studied hydrogenated diamondized bilayer graphenes are predicted not only to behave as direct and wide band gap semiconductors, but also to have a remarkably high resistance to in-plane plastic deformation induced by indentation as implied by their high in-plane elastic constants comparable to those of diamond and of lonsdaleite. The mechanical stability of the materials is confirmed though the fulfilment of the Born stability criteria. Detailed analysis of phonon vibrational frequencies of hydrogenated diamondized bilayer graphenes reveals possible Raman active and IR active modes, which are found to be distinctly different from those of hydrogenated diamond-like amorphous carbon and defective graphene and thus could be used as a fingerprint for future experimental characterization of the materials. (c) 2019 Elsevier Ltd. All rights reserved.

  • 22.
    Monteseguro, V
    et al.
    Univ Valencia, Spain; European Radiat Synchrotron Facil, France.
    Sans, J. A.
    Univ Politecn Valencia, Spain.
    Cuartero, V
    European Radiat Synchrotron Facil, France; Ctr Univ Def Zaragoza, Spain.
    Cova, F.
    European Radiat Synchrotron Facil, France.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Olovsson, Weine
    Linköping University, National Supercomputer Centre (NSC). Linköping University, Faculty of Science & Engineering.
    Popescu, C.
    ALBA CELLS, Spain.
    Pascarelli, S.
    European Radiat Synchrotron Facil, France.
    Garbarino, G.
    European Radiat Synchrotron Facil, France.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Irifune, T.
    Ehime Univ, Japan; Tokyo Inst Technol, Japan.
    Errandonea, D.
    Univ Valencia, Spain.
    Phase stability and electronic structure of iridium metal at the megabar range2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 8940Article in journal (Refereed)
    Abstract [en]

    The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.

  • 23.
    Ektarawong, Annop
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Singapore, Singapore.
    Peng, Y. P.
    Natl Univ Singapore, Singapore.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Phase stability of three-dimensional bulk and two-dimensional monolayer As1-xSbx solid solutions from first principles2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 24, article id 245702Article in journal (Refereed)
    Abstract [en]

    The mixing thermodynamics of both three-dimensional bulk and two-dimensional monolayered alloys of As1-xSbx as a function of alloy composition and temperature are explored using a first-principles cluster-expansion method, combined with canonical Monte-Carlo simulations. We observe that, for the bulk phase, As1-xSbx alloy can exhibit not only chemical ordering of As and Sb atoms at x = 0.5 to form an ordered compound of AsSb stable upon annealing up to T approximate to 475 K, but also a miscibility gap at 475 K less than or similar to T less than or similar to 550 K in which two disordered solid solutions of As1-xSbx of different alloy compositions thermodynamically coexist. At T amp;gt; 550 K, a single-phase solid solution of bulk As1-xSbx is predicted to be stable across the entire composition range. These results clearly explain the existing uncertainties in the alloying behavior of bulk As1-xSbx alloy, as previously reported in the literature, and also found to be in qualitative and quantitative agreement with the experimental observations. Interestingly, the alloying behavior of As1-xSbx is considerably altered, as the dimensionality of the material reduces from the three-dimensional bulk state to the two-dimensional monolayered state-for example, a single-phase solid solution of monolayer As1-xSbx is predicted to be stable over the whole composition range at T amp;gt; 250 K. This distinctly highlights an influence of the reduced dimensionality on the alloying behavior of As1-xSbx.

  • 24.
    Ektarawong, Annop
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Chulalongkorn Univ, Thailand; Natl Univ Singapore, Singapore; Natl Univ Singapore, Singapore; Thailand Ctr Excellence Phys, Thailand.
    Feng, Y. P.
    Natl Univ Singapore, Singapore.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Phase stability of two-dimensional monolayer As1-xPx solid solutions revealed by a first-principles cluster expansion2019In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, no 5, article id 054005Article in journal (Refereed)
    Abstract [en]

    The phase stability of two-dimensional monolayer As1-xPx solid solutions, exhibiting the puckered (alpha phase) and buckled (beta phase) structures are investigated using a first-principles cluster-expansion method. Canonical Monte Carlo simulations, together with harmonic approximation, are performed to capture the influences of thermally induced configurational disorder and lattice vibrations on the phase stability of monolayer As1-xPx. We first demonstrate that, as the temperature approaches 0 K, the monolayer As1-xPx displays a tendency toward phase separation into its constituent elemental phases, and thus no stable ordered structures of As1-xPx, both alpha and beta phases, are predicted to be thermodynamically stable. We further reveal with the inclusion of the lattice vibrational contributions that beta-As1-xPx is thermodynamically favored over alpha-As1-xPx, across the entire composition range even at 0 K and increasingly so at higher temperature, and a continuous series of disordered solid solution of beta-As1-xPx, where 0 amp;lt;= x amp;lt;= 1, is predicted at the temperature above 550 K. These findings not only indicate that the ordered structures of monolayer alpha-As1-xPx, and beta-As1-xPx, frequently studied in the literature, may not exist in nature, but also presumably suggest that monolayer alpha-As1-xPx is metastable with respect to monolayer beta-As1-xPx.

  • 25.
    da Cunha, Wiliam Ferreira
    et al.
    Univ Brasilia, Brazil.
    de Oliveira Neto, Pedro Henrique
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Quasiparticle description of transition metal dichalcogenide nanoribbons2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 3, article id 035405Article in journal (Refereed)
    Abstract [en]

    An effective two-dimensional real-space model is developed to investigate the nature of charge distribution in nanoribbons of transition metal dichalcogenides. Our description is based on a lattice relaxation endowed tight-binding Hamiltonian with spin-orbit and Hubbard interactions, which is parameterized to describe molybdenum disulfide lattices. As our main finding, we observed that electron-phonon coupling induces the creation of quasiparticles such as polarons in the same fashion as observed in conducting polymers and graphene nanoribbons. These similarities suggest that the charge transport in transition metal dichalcogenides can also be mediated by quasiparticles, which is a fundamental aspect concerning the application of these structures in electronics. We determine a range of possible electron-phonon coupling that correctly describes the system and also the critical value where quasiparticle transport is present. Our findings may have profound consequences on the understanding of the transport mechanism of transition metal dichalcogenides nanoribbons.

  • 26.
    Mosyagin, Igor
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISTS, Russia.
    Lugovskoy, A. V.
    NUST MISTS, Russia.
    Krasilnikov, O. M.
    NUST MISTS, Russia; NUST MISTS, Russia.
    Vekilov, Yu. Kh.
    NUST MISTS, Russia; NUST MISTS, Russia.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Reply to the comment by M. Mazdziarz on the article "Ab initio calculations of pressure-dependence of high-order elastic constants using finite deformations approach" [Computer Physics Communications 220 (2017) 20-30]2019In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 235, p. 295-296Article in journal (Other academic)
    Abstract [en]

    Marcin Mazdziarz has published a comment on our recent paper by I. Mosyagin, A.V. Lugovskoy, O.M. Krasilnikov, Yu.Kh. Vekilov, S.I. Simak and L.A. Abrikosov titled "Ab initio calculations of pressure dependence of high-order elastic constants using finite deformations approach" [Computer Physics Communications 220 (2017)2030]. The author states that there are serious fundamental errors and flaws. In this reply we clarify all misunderstanding mentioned in the said comment. (C) 2018 Published by Elsevier B.V.

    The full text will be freely available from 2020-06-19 15:55
  • 27.
    Almyras, Georgios
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering.
    Sangiovanni, Davide Giuseppe
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Sarakinos, Kostas
    Linköping University, Department of Physics, Chemistry and Biology, Nanoscale engineering. Linköping University, Faculty of Science & Engineering.
    Semi-Empirical Force-Field Model For The Ti1-XAlXN (0 ≤ x ≤ 1) System2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 2, article id 215Article in journal (Refereed)
    Abstract [en]

    We present a modified embedded atom method (MEAM) semi-empirical force-field model for the Ti1-xAlxN (0 x 1) alloy system. The MEAM parameters, determined via an adaptive simulated-annealing (ASA) minimization scheme, optimize the models predictions with respect to 0 K equilibrium volumes, elastic constants, cohesive energies, enthalpies of mixing, and point-defect formation energies, for a set of approximate to 40 elemental, binary, and ternary Ti-Al-N structures and configurations. Subsequently, the reliability of the model is thoroughly verified against known finite-temperature thermodynamic and kinetic properties of key binary Ti-N and Al-N phases, as well as properties of Ti1-xAlxN (0 amp;lt; x amp;lt; 1) alloys. The successful outcome of the validation underscores the transferability of our model, opening the way for large-scale molecular dynamics simulations of, e.g., phase evolution, interfacial processes, and mechanical response in Ti-Al-N-based alloys, superlattices, and nanostructures.

  • 28.
    Pereira Junior, Marcelo Lopes
    et al.
    Univ Brasilia, Brazil.
    de Sousa Junior, Rafael Timoteo
    Univ Brasilia, Brazil.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Ribeiro, Luiz Antonio
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Brasilia, Brazil.
    Stationary polaron properties in organic crystalline semiconductors2019In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 21, no 5, p. 2727-2733Article in journal (Refereed)
    Abstract [en]

    Polarons play a crucial role in the charge transport mechanism when it comes to organic molecular crystals. The features of their underlying properties - mostly the ones that directly impact the yield of the net charge mobility - are still not completely understood. Here, a two-dimensional Holstein-Peierls model is employed to numerically describe the stationary polaron properties in organic semiconductors at a molecular scale. Our computational protocol yields model parameters that accurately characterize the formation and stability of polarons in ordered and disordered oligoacene-like crystals. The results show that the interplay between the intramolecular (Holstein) and intermolecular (Peierls) electron-lattice interactions critically impacts the polaron stability. Such an interplay can produce four distinct quasi-particle solutions: free-like electrons, metastable polarons, and small and large polarons. The latter governs the charge transport in organic crystalline semiconductors. Regarding disordered lattices, the model takes into account two modes of static disorder. Interestingly, the results show that intramolecular disorder is always unfavorable to the formation of polarons whereas intermolecular disorder may favor the polaron generation in regimes below a threshold for the electronic transfer integral strength.

  • 29.
    Gambino, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Structural and magnetic disorder in crystalline materials: a first principles study2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Disorder in crystalline materials can take different forms and originate from different sources. In particular, temperature introduces disorder in any kind of material. This can be observed as the appearance of vacant lattice sites in an otherwise perfect crystal, or as a random distribution of different elements on the same lattice in an alloy; at the same time, if the material is magnetic, temperature induces disorder also on the magnetic degrees of freedom. In this thesis, different levels of disorder associated to structure and magnetism are investigated by means of density functional theory and thermodynamic models.

    I start with diffusion of Ti vacancies in TiN, which is studied by means of nonequilibrium ab initio molecular dynamics using the color diffusion algorithm at different temperatures. The result is an Arrhenius behavior of Ti vacancy jump rates.

    A method to perform structural relaxations in magnetic materials in their hightemperature paramagnetic phase is then developed based on the disordered local moments approach in order to study vacancies, interstitial atoms, and combinations of defects in paramagnetic bcc Fe and B1 CrN, as well as the mixing enthalpy of bcc Fe1−xCrx random alloys. A correction to the energetics of every system due to the relaxation in the disordered magnetic state is observed in all cases.

    Not related to temperature and disorder, but very important for an accurate description of magnetic materials, is the choice of the exchange and correlation functional to be employed in the first principles calculations. We have investigated the performance of a recently developed meta-GGA functional, the strongly constrained and appropriately normed (SCAN) functional, in comparison with the more commonly used LDA and PBE on the ferromagnetic elemental solids bcc Fe, fcc Ni, and hcp Co, and SCAN it is found to give negligible improvements, if not a worsening, in the description of these materials.

    Finally, the coupling between vibrational and magnetic degrees of freedom is discussed by reviewing the literature and proposing an investigation of the influence of vibrations on longitudinal spin fluctuations. These excitations are here studied by means of thermodynamic models based on Landau expansion of the energy in even powers of the magnitude of the local magnetic moments. We find that vibrational and magnetic disorder alter the energy landscapes as a function of moment size also in bcc Fe, which is often considered a Heisenberg system, inducing a more itinerant electron behavior.

    List of papers
    1. Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN
    Open this publication in new window or tab >>Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B1 TiN
    2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 10, article id 104306Article in journal (Refereed) Published
    Abstract [en]

    We use the color diffusion (CD) algorithm in nonequilibrium (accelerated) ab initio molecular dynamics simulations to determine Ti monovacancy jump frequencies in NaCl-structure titanium nitride (TiN), at temperatures ranging from 2200 to 3000 K. Our results showthat theCDmethod extended beyond the linear-fitting rate-versus-force regime [Sangiovanni et al., Phys. Rev. B 93, 094305 (2016)] can efficiently determine metal vacancy migration rates in TiN, despite the low mobilities of lattice defects in this type of ceramic compound. We propose a computational method based on gamma-distribution statistics, which provides unambiguous definition of nonequilibrium and equilibrium (extrapolated) vacancy jump rates with corresponding statistical uncertainties. The acceleration-factor achieved in our implementation of nonequilibrium molecular dynamics increases dramatically for decreasing temperatures from 500 for T close to the melting point T-m, up to 33 000 for T approximate to 0.7 T-m

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2017
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-141712 (URN)10.1103/PhysRevB.96.104306 (DOI)000411076000005 ()
    Note

    Funding Agencies|Swedish Foundation for Strategic Research (SSF) project SRL [10-0026]; Swedish Research Council (VR) [621-2011-4417, 2015-04391, 330-2014-6336]; Swedish Government Strategic Research Area Grant in Materials Science on Advanced Functional Materials [MatLiU 2009-00971]; Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Marie Sklodowska Curie Actions [INCA 600398]; Swedish Foundation for Strategic Research; Stiftelsen Olle Engkvist Byggmastare

    Available from: 2017-10-05 Created: 2017-10-05 Last updated: 2019-06-28
    2. Lattice relaxations in disordered Fe-based materials in the paramagnetic state from first principles
    Open this publication in new window or tab >>Lattice relaxations in disordered Fe-based materials in the paramagnetic state from first principles
    2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 6, article id 064105Article in journal (Refereed) Published
    Abstract [en]

    The first-principles calculation of many material properties, in particular related to defects and disorder, starts with the relaxation of the atomic positions of the system under investigation. This procedure is routine for nonmagnetic and magnetically ordered materials. However, when it comes to magnetically disordered systems, in particular the paramagnetic phase of magnetic materials, it is not clear how the relaxation procedure should be performed or which geometry should be used. Here we propose a method for the structural relaxation of magnetic materials in the paramagnetic regime, in an adiabatic fast-magnetism approximation within the disordered local moment (DLM) picture in the framework of density functional theory. The method is straightforward to implement using any ab initio code that allows for structural relaxations. We illustrate the importance of considering the disordered magnetic state during lattice relaxations by calculating formation energies and geometries for an Fe vacancy and C insterstitial atom in body-centered cubic (bcc) Fe as well as bcc Fe1-xCrx random alloys in the paramagnetic state. In the vacancy case, the nearest neighbors to the vacancy relax toward the vacancy of 0.14 angstrom (-5% of the ideal bcc nearest-neighbor distance), which is twice as large as the relaxation in the ferromagnetic case. The vacancy formation energy calculated in the DLM state on these positions is 1.60 eV, which corresponds to a reduction of about 0.1 eV compared to the formation energy calculated using DLM but on ferromagnetic-relaxed positions. The carbon interstitial formation energy is found to be 0.41 eV when the DLM relaxed positions are used, as compared to 0.59 eV when the FM-relaxed positions are employed. For bcc Fe0.5Cr0.5 alloys, the mixing enthalpy is reduced by 5 meV/atom, or about 10%, when the DLM state relaxation is considered, as compared to positions relaxed in the ferromagnetic state.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2018
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-151199 (URN)10.1103/PhysRevB.98.064105 (DOI)000443139600004 ()
    Note

    Funding Agencies|Swedish Research Council (VR) [2014-6336]; Marie Sklodowska Curie Actions, Cofund [INCA 600398]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFOMatLiU) [2009 00971]; Swedish Foundation for Strategic Research

    Available from: 2018-09-13 Created: 2018-09-13 Last updated: 2019-05-14
    3. Assessing the SCAN functional for itinerant electron ferromagnets
    Open this publication in new window or tab >>Assessing the SCAN functional for itinerant electron ferromagnets
    Show others...
    2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 9, article id 094413Article in journal (Refereed) Published
    Abstract [en]

    Density functional theory is a standard model for condensed-matter theory and computational material science. The accuracy of density functional theory is limited by the accuracy of the employed approximation to the exchange-correlation functional. Recently, the so-called strongly constrained appropriately normed (SCAN) [Sun, Ruzsinszky, and Perdew, Phys. Rev. Lett. 115, 036402 (2015)] functional has received a lot of attention due to promising results for covalent, metallic, ionic, as well as hydrogen- and van der Waals-bonded systems alike. In this work, we focus on assessing the performance of the SCAN functional for itinerant magnets by calculating basic structural and magnetic properties of the transition metals Fe, Co, and Ni. We find that although structural properties of bcc-Fe seem to be in good agreement with experiment, SCAN performs worse than standard local and semilocal functionals for fcc-Ni and hcp-Co. In all three cases, the magnetic moment is significantly overestimated by SCAN, and the 3d states are shifted to lower energies, as compared to experiments.

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2018
    National Category
    Theoretical Chemistry
    Identifiers
    urn:nbn:se:liu:diva-151640 (URN)10.1103/PhysRevB.98.094413 (DOI)000444348500004 ()
    Note

    Funding Agencies|Swedish e-Science Research Centre (SeRC); Swedish Research Council (VR) through the International Career Grant [20146336]; Marie Sklodowska CurieActions, Cofund, Project [INCA 600398]; Swedish Foundation for Strategic Research (SSF) through the Future Research Leaders 6 program; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; competence center FunMat-II - Vinnova [201605156]; Russian Science Foundation [18-12-00492]

    Available from: 2018-09-27 Created: 2018-09-27 Last updated: 2019-05-14
  • 30.
    Mockuté, Aurelija
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Palisaitis, Justinas
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Nedfors, Nils
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Berastegui, P.
    Uppsala Univ, Sweden.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Faculty of Science & Engineering. SKF Res and Technol Dev Ctr, Netherlands.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Näslund, Lars-Åke
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Patscheider, J.
    Evatec AG, Switzerland.
    Jansson, U.
    Uppsala Univ, Sweden.
    Persson, Per O A
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Rosén, Johanna
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Synthesis and characterization of (Ti1-xAlx)B2+Delta thin films from combinatorial magnetron sputtering2019In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 669, p. 181-187Article in journal (Refereed)
    Abstract [en]

    (Ti1-xAlx)B2+Delta films with a lateral composition gradient of x = [0.30-0.66] and Delta = [0.07-1.22] were deposited on an Al2O3 wafer by dual magnetron sputtering at 400 degrees C from sintered TiB2 and AlB2 targets. Composition analysis indicates that higher Ti:Al ratios favor overstoichiometry in B and a reduced incorporation of O. Transmission electron microscopy reveals distinctly different microstructures of Ti- and Al-rich compositions, with formation of characteristic conical growth features for the latter along with a lower degree of crystallinity and significantly less tissue phase from B segregation at the grain boundaries. For Al-rich films, phase separation into Ti- and Al-rich diboride nanometer-size domains is observed and interpreted as surface-initiated spinodal decomposition. The hardness of the films ranges from 14 to 28 GPa, where the higher values were obtained for the Ti-rich regions of the metal boride.

    The full text will be freely available from 2020-10-26 15:00
  • 31.
    Filippov, Stanislav
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Stockholm Univ, Sweden.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Haussermann, Ulrich
    Stockholm Univ, Sweden.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Temperature-induced phase transition and Li self-diffusion in Li2C2: A first-principles study2019In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 3, no 2, article id 023602Article in journal (Refereed)
    Abstract [en]

    Lithium carbide, Li2C2, is a fascinating material that combines strong covalent and weak ionic bonding resulting in a wide range of unusual properties. The mechanism of its phase transition from the ground-state orthorhombic (Immm) to the high-temperature cubic (Fm (3) over barm) crystal structure is not well understood and here we elucidate it with help of first-principles calculations. We show that stabilization of the cubic phase is a result of a temperature-induced disorientation of the C-C dumbbells and their further thermal rotations. Due to these rotations rather large deviatoric stress, which is associated with the dumbbell alignment along one of the crystallographic axes, averages out making the cubic structure mechanically stable. At high temperature we observe a type-II superionic transition to a state of high Li self-diffusion involving collective ionic motion mediated by the formation of Frenkel pairs.

  • 32.
    Palonen, H.
    et al.
    Uppsala Univ, Sweden.
    Mukhamedov, B. O.
    Natl Univ Sci and Technol MISIS, Russia.
    Ponomareva, A. V.
    Natl Univ Sci and Technol MISIS, Russia.
    Palsson, G. K.
    Uppsala Univ, Sweden.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Hjorvarsson, B.
    Uppsala Univ, Sweden.
    The magnetization profile induced by the double magnetic proximity effect in an Fe/Fe0.30V0.70 superlattice2019In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 115, no 1, article id 012406Article in journal (Refereed)
    Abstract [en]

    The double magnetic proximity effect (MPE) in an Fe/Fe0.30V0.70 superlattice is studied by a direct measurement of the magnetization profile using polarized neutron reflectivity. The experimental magnetization profile is shown to qualitatively agree with a profile calculated using density functional theory. The profile is divided into a short range interfacial part and a long range tail. The interfacial part is explained by charge transfer and induced magnetization, while the tail is attributed to the inhomogeneous nature of the FeV alloy. The long range tail in the magnetization persists up to 170% above the intrinsic ordering temperature of the FeV alloy. The observed effects can be used to design systems with a direct exchange coupling between layers over long distances through a network of connected atoms. When combined with the recent advances in tuning and switching, the MPE with electric fields and currents, the results can be applied in spintronic devices. Published under license by AIP Publishing.

  • 33.
    Ekholm, Marcus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Univ Bayreuth, Germany.
    Schoenleber, A.
    Univ Bayreuth, Germany.
    van Smaalen, S.
    Univ Bayreuth, Germany.
    The role of magnetic order in VOCl2019In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 31, no 32, article id 325502Article in journal (Refereed)
    Abstract [en]

    VOCl and other transition metal oxychlorides are candidate materials for next-generation rechargeable batteries. We have investigated the influence of the underlying magnetic order on the crystallographic and electronic structure by means of density functional theory. Our study shows that antiferromagnetic ordering explains the observed low-temperature monoclinic distortion of the lattice, which leads to a decreased distance between antiferromagnetically coupled V-V nearest neighbors. We also show that the existence of a local magnetic moment removes the previously suggested degeneracy of the occupied levels, in agreement with experiments. To describe the electronic structure, it turns out crucial to take the correct magnetic ordering into account, especially at elevated temperature.

  • 34.
    Ning, Weihua
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering. Nanjing Tech Univ, Peoples R China.
    Zhao, Xin-Gang
    Jilin Univ, Peoples R China.
    Klarbring, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Bai, Sai
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Ji, Fuxiang
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Wang, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Simak, Sergey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tao, Youtian
    Nanjing Tech Univ, Peoples R China.
    Ren, Xiao-Ming
    Nanjing Tech Univ, Peoples R China.
    Zhang, Lijun
    Jilin Univ, Peoples R China.
    Huang, Wei
    Nanjing Tech Univ, Peoples R China.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Gao, Feng
    Linköping University, Department of Physics, Chemistry and Biology, Biomolecular and Organic Electronics. Linköping University, Faculty of Science & Engineering.
    Thermochromic Lead-Free Halide Double Perovskites2019In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 29, no 10, article id 1807375Article in journal (Refereed)
    Abstract [en]

    Lead-free halide double perovskites with diverse electronic structures and optical responses, as well as superior material stability show great promise for a range of optoelectronic applications. However, their large bandgaps limit their applications in the visible light range such as solar cells. In this work, an efficient temperature-derived bandgap modulation, that is, an exotic fully reversible thermochromism in both single crystals and thin films of Cs2AgBiBr6 double perovskites is demonstrated. Along with the thermochromism, temperature-dependent changes in the bond lengths of Ag Symbol of the Klingon Empire Br (R-Ag Symbol of the Klingon Empire Br) and Bi Symbol of the Klingon Empire Br (R-Bi Symbol of the Klingon Empire Br) are observed. The first-principle molecular dynamics simulations reveal substantial anharmonic fluctuations of the R-Ag Symbol of the Klingon Empire Br and R-Bi Symbol of the Klingon Empire Br at high temperatures. The synergy of anharmonic fluctuations and associated electron-phonon coupling, and the peculiar spin-orbit coupling effect, is responsible for the thermochromism. In addition, the intrinsic bandgap of Cs2AgBiBr6 shows negligible changes after repeated heating/cooling cycles under ambient conditions, indicating excellent thermal and environmental stability. This work demonstrates a stable thermochromic lead-free double perovskite that has great potential in the applications of smart windows and temperature sensors. Moreover, the findings on the structure modulation-induced bandgap narrowing of Cs2AgBiBr6 provide new insights for the further development of optoelectronic devices based on the lead-free halide double perovskites.

  • 35.
    Mukhamedov, B. O.
    et al.
    Natl Univ Sci and Technol MISIS, Russia.
    Saenko, I
    Freiberg Univ Min and Technol, Germany; Russian Acad Sci, Russia.
    Ponomareva, A. V
    Natl Univ Sci and Technol MISIS, Russia.
    Kriegel, M. J.
    Freiberg Univ Min and Technol, Germany.
    Chugreev, A.
    Leibniz Univ Hannover, Germany.
    Udovsky, A.
    Russian Acad Sci, Russia; Natl Res Nucl Univ MEPhl, Russia.
    Fabrichnaya, O.
    Freiberg Univ Min and Technol, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Thermodynamic and physical properties of Zr3Fe and ZrFe2 intermetallic compounds2019In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 109, p. 189-196Article in journal (Refereed)
    Abstract [en]

    Experimental differential scanning calorimetry measurements and ab-initio simulations were carried out to define the heat capacities of Zr3Fe and C15-ZrFe2 compounds from 0 K up to their maximum stability temperatures. Experimental measurements of heat capacity of each compound were performed for the first time in wide range of temperatures. Density functional theory and quasi-harmonic approximation (QHA) were employed to calculate the free energy of the studied systems as a function of volume and temperature. A good agreement was observed between theoretical and experimental heat capacities within validity range of the QHA. This makes it possible to combine theoretical and experimental data to determine the standard entropies of intermetallic compounds.

  • 36.
    Khvan, A. V.
    et al.
    NUST MISIS, Russia.
    Babkina, T.
    Lomonosov Moscow State Univ, Russia.
    Dinsdale, A. T.
    Hampton Thermodynam Ltd, England.
    Uspenskaya, I. A.
    Lomonosov Moscow State Univ, Russia.
    Fartushna, I. V.
    NUST MISIS, Russia.
    Druzhinina, A. I.
    Lomonosov Moscow State Univ, Russia.
    Syzdykova, A. B.
    NUST MISIS, Russia.
    Belov, M. P.
    NUST MISIS, Russia.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. NUST MISIS, Russia.
    Thermodynamic properties of tin: Part I Experimental investigation, ab-initio modelling of alpha-, beta-phase and a thermodynamic description for pure metal in solid and liquid state from 0 K2019In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 65, p. 50-72Article in journal (Refereed)
    Abstract [en]

    Thermodynamic data for crystalline white and grey tin were assessed using an extended Einstein model from 0 K. Ab-initio simulations in the framework of density functional theory (DFT) with the quasiharmonic approximation (QHA) were carried out to define the heat capacities for both phases of tin from 0 K up to room temperatures. Good agreement was observed between theoretical and experimental heat capacities, which makes it possible to combine theoretical and experimental data to determine the standard entropies. Data for the liquid phase were described using a two state model. During the assessment, careful analysis of the experimental data was carried out. In order to fulfil the need for a precise evaluation of S-298(o) we needed to use an additional technique using multiple Einstein functions, which allows the experimental heat capacity and enthalpy data for the solid phase to be approximated accurately from 0 K up to the melting point and to estimate solid phase transition entropy and enthalpy which are difficult to measure due to a high activation barrier. Additional measurements of heat capacity were carried out where existing data were scarce.

    The full text will be freely available from 2021-02-16 11:17
  • 37.
    Pedersen, Henrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Högberg, Hans
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Ektarawong, Annop
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Chulalongkorn Univ, Thailand; Commiss Higher Educ, Thailand.
    Thermodynamic stability of hexagonal and rhombohedral boron nitride under chemical vapor deposition conditions from van der Waals corrected first principles calculations2019In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 37, no 4, article id 040603Article in journal (Refereed)
    Abstract [en]

    Thin films of boron nitride (BN), particularly the sp(2)-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN), are interesting for several electronic applications, given the bandgaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800K and 1000-10000Pa, respectively. In this letter, the authors use the van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. The authors find that r-BN is the stable sp(2)-hybridized phase at CVD conditions, while h-BN is metastable. Thus, their calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

  • 38.
    Pilemalm, Robert
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Pourovskii, Leonid
    Centre de Physique Théorique, Ecole Polytechnique, CNRS, Université Paris-Saclay, Route de Saclay, FR-91128 Palaiseau, France / Collège de France, 11 place Marcelin Berthelot, FR-75005 Paris, France.
    Mosyagin, Igor
    Materials Modeling and Development Laboratory, NUST “MISIS”, RU-119991 Moscow, Russia.
    Simak, Sergei
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Thermodynamic Stability, Thermoelectric, Elastic and Electronic Structure Properties of ScMN2-Type (M = V, Nb, Ta) Phases Studied by ab initio Calculations2019In: Condensed Matter, ISSN 2410-3896, Vol. 4, no 2, article id 36Article in journal (Refereed)
    Abstract [en]

    ScMN2-type (M = V, Nb, Ta) phases are layered materials that have been experimentally reported for M = Ta and Nb, but they have up to now not been much studied. However, based on the properties of binary ScN and its alloys, it is reasonable to expect these phases to be of relevance in a range of applications, including thermoelectrics. Here, we have used first-principles calculations to study their thermodynamic stability, elastic, thermoelectric and electronic properties. We have used density functional theory to calculate lattice parameters, the mixing enthalpy of formation and electronic density of states as well as the thermoelectric properties and elastic constants (cij), bulk (B), shear (G) and Young’s (E) modulus, which were compared with available experimental data. Our results indicate that the considered systems are thermodynamically and elastically stable and that all are semiconductors with small band gaps. All three materials display anisotropic thermoelectric properties and indicate the possibility to tune these properties by doping. In particular, ScVN2, featuring the largest band gap exhibits a particularly large and strongly doping-sensitive Seebeck coefficient.

  • 39.
    Skripnyak, Natalia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ponomareva, A. V.
    Natl Univ Sci and Technol MISIS, Russia.
    Belov, M. P.
    Natl Univ Sci and Technol MISIS, Russia.
    Abrikosov, Igor A.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ab initio calculations of elastic properties of alloys with mechanical instability: Application to BCC Ti-V alloys2018In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 140, p. 357-365Article in journal (Refereed)
    Abstract [en]

    Considering Ti-V alloys with the body-centered cubic crystal lattice, a system with mechanical instability for Tirich alloys, we calculate their elastic properties using Projector Augmented Wave method and the exact muffin tin orbital method in a complete interval of V concentrations. The substitutional disorder is modeled using the special quasi-random structures technique and the coherent potential approximation. The efficiency and accuracy of the simulation techniques is analyzed, and a strategy for efficient high-throughput calculations of elastic properties of disordered alloys is proposed. Dependences of the single crystal elastic moduli on V concentration and a set ofmechanical characteristics of polycrystalline alloys are presented and discussed. The effect of V content on themechanical stabilization of the bcc Ti-V alloys is investigated. In agreement with experiment, we find that titanium-rich alloys are mechanically unstable, however the alloys becomemechanically stablewith increasing content of V in the system. We observe a nonlinear dependence of the alloys Youngs moduli in a vicinity of the mechanical stabilization and suggest that this effect can be used to design alloys with low values of the elastic moduli. (C) 2017 Elsevier Ltd. All rights reserved.

  • 40.
    Sangiovanni, Davide Giuseppe
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.
    Kostov Gueorguiev, Gueorgui
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Kakanakova-Georgieva, Anelia
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Ab initio molecular dynamics of atomic-scale surface reactions: insights into metal organic chemical vapor deposition of AlN on graphene2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 26, p. 17751-17761Article in journal (Refereed)
    Abstract [en]

    Metal organic chemical vapor deposition (MOCVD) of group III nitrides on graphene heterostructures offers new opportunities for the development of flexible optoelectronic devices and for the stabilization of conceptually-new two-dimensional materials. However, the MOCVD of group III nitrides is regulated by an intricate interplay of gas-phase and surface reactions that are beyond the resolution of experimental techniques. We use density-functional ab initio molecular dynamics (AIMD) with van der Waals corrections to identify atomistic pathways and associated electronic mechanisms driving precursor/surface reactions during metal organic vapor phase epitaxy at elevated temperatures of aluminum nitride on graphene, considered here as model case study. The results presented provide plausible interpretations of atomistic and electronic processes responsible for delivery of Al, C adatoms, and C-Al, CHx, AlNH2 admolecules on pristine graphene via precursor/surface reactions. In addition, the simulations reveal C adatom permeation across defect-free graphene, as well as exchange of C monomers with graphene carbon atoms, for which we obtain rates of approximate to 0.3 THz at typical experimental temperatures (1500 K), and extract activation energies Eexca = 0.28 +/- 0.13 eV and attempt frequencies A(exc) = 2.1 (x1.7(+/- 1)) THz via Arrhenius linear regression. The results demonstrate that AIMD simulations enable understanding complex precursor/surface reaction mechanisms, and thus propose AIMD to become an indispensable routine prediction-tool toward more effective exploitation of chemical precursors and better control of MOCVD processes during synthesis of functional materials.

  • 41.
    Stockem, Irina
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Bergman, Anders
    Univ Versailles, France; CEA, France.
    Glensk, Albert
    Max Planck Inst Eisenforsch GmbH, Germany.
    Hickel, Tilmann
    Max Planck Inst Eisenforsch GmbH, Germany.
    Koermann, Fritz
    Max Planck Inst Eisenforsch GmbH, Germany; Delft Univ Technol, Netherlands.
    Grabowski, Blazej
    Max Planck Inst Eisenforsch GmbH, Germany.
    Neugebauer, Joerg
    Max Planck Inst Eisenforsch GmbH, Germany.
    Alling, Björn
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Anomalous Phonon Lifetime Shortening in Paramagnetic CrN Caused by Spin-Lattice Coupling: A Combined Spin and Ab Initio Molecular Dynamics Study2018In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 12, article id 125902Article in journal (Refereed)
    Abstract [en]

    We study the mutual coupling of spin fluctuations and lattice vibrations in paramagnetic CrN by combining atomistic spin dynamics and ab initio molecular dynamics. The two degrees of freedom are dynamically coupled, leading to nonadiabatic effects. Those effects suppress the phonon lifetimes at low temperature compared to an adiabatic approach. The dynamic coupling identified here provides an explanation for the experimentally observed unexpected temperature dependence of the thermal conductivity of magnetic semiconductors above the magnetic ordering temperature.

  • 42.
    Ekholm, Marcus
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Gambino, Davide
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Jönsson, Johan
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tasnadi, Ferenc
    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, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Max Planck Inst Eisenforsch GmbH, Germany.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Univ Sci and Technol MISIS, Russia.
    Assessing the SCAN functional for itinerant electron ferromagnets2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 9, article id 094413Article in journal (Refereed)
    Abstract [en]

    Density functional theory is a standard model for condensed-matter theory and computational material science. The accuracy of density functional theory is limited by the accuracy of the employed approximation to the exchange-correlation functional. Recently, the so-called strongly constrained appropriately normed (SCAN) [Sun, Ruzsinszky, and Perdew, Phys. Rev. Lett. 115, 036402 (2015)] functional has received a lot of attention due to promising results for covalent, metallic, ionic, as well as hydrogen- and van der Waals-bonded systems alike. In this work, we focus on assessing the performance of the SCAN functional for itinerant magnets by calculating basic structural and magnetic properties of the transition metals Fe, Co, and Ni. We find that although structural properties of bcc-Fe seem to be in good agreement with experiment, SCAN performs worse than standard local and semilocal functionals for fcc-Ni and hcp-Co. In all three cases, the magnetic moment is significantly overestimated by SCAN, and the 3d states are shifted to lower energies, as compared to experiments.

  • 43.
    Silverå Ejneby, Malin
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Divison of Neurobiology. Linköping University, Faculty of Medicine and Health Sciences.
    Wu, Xiongyu
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Ottosson, Nina
    Linköping University, Department of Clinical and Experimental Medicine, Divison of Neurobiology. Linköping University, Faculty of Medicine and Health Sciences.
    Münger, E Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Konradsson, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Elinder, Fredrik
    Linköping University, Department of Clinical and Experimental Medicine, Divison of Neurobiology. Linköping University, Faculty of Medicine and Health Sciences.
    Atom-by-atom tuning of the electrostatic potassium-channel modulator dehydroabietic acid2018In: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 150, no 5, p. 731-750Article in journal (Refereed)
    Abstract [en]

    Dehydroabietic acid (DHAA) is a naturally occurring component of pine resin that was recently shown to open voltage-gated potassium (KV) channels. The hydrophobic part of DHAA anchors the compound near the channel’s positively charged voltage sensor in a pocket between the channel and the lipid membrane. The negatively charged carboxyl group exerts an electrostatic effect on the channel’s voltage sensor, leading to the channel opening. In this study, we show that the channel-opening effect increases as the length of the carboxyl-group stalk is extended until a critical length of three atoms is reached. Longer stalks render the compounds noneffective. This critical distance is consistent with a simple electrostatic model in which the charge location depends on the stalk length. By combining an effective anchor with the optimal stalk length, we create a compound that opens the human KV7.2/7.3 (M type) potassium channel at a concentration of 1 µM. These results suggest that a stalk between the anchor and the effector group is a powerful way of increasing the potency of a channel-opening drug.

  • 44.
    Berggren, Karl-Fredrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Tellander, Felix
    Lund Univ, Sweden.
    Yakymenko, Iryna
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Basic modelling of transport in 2D wave-mechanical nanodots and billiards with balanced gain and loss mediated by complex potentials2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 20, article id 204003Article in journal (Refereed)
    Abstract [en]

    Non-Hermitian quantum mechanics with parity-time (PT) symmetry is presently gaining great interest, especially within the fields of photonics and optics. Here, we give a brief overview of low-dimensional semiconductor nanodevices using the example of a quantum dot with input and output leads, which are mimicked by imaginary potentials for gain and loss, and how wave functions, particle flow, coalescence of levels and associated breaking of PT symmetry may be analysed within such a framework. Special attention is given to the presence of exceptional points and symmetry breaking. Related features for musical string instruments and wolf-notes are outlined briefly with suggestions for further experiments.

  • 45.
    Gradov, O. M.
    et al.
    Russian Acad Sci, Russia.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Basic properties of nonlinear surface charge waves at a plasma boundary2018In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 42-43, p. 3083-3085Article in journal (Refereed)
    Abstract [en]

    The nonlinear properties of surface charges are here analyzed under ideal conditions. We thus deduce a new single equation from the wellknown equations which govern the cold electron plasma motion. Simple formulas that describe the propagation of surface charge perturbations along the plasma boundary are also found. (C) 2018 Elsevier B.V. All rights reserved.

  • 46.
    Lambrix, Patrick
    et al.
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Armiento, Rickard
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Delin, Anna
    School of Science and Engineering (SCI) at the Royal Institute of Technology, KTH, Sweden.
    Li, Huanyu
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Big Semantic Data Processing in the Materials Design Domain2018In: Encyclopedia of Big Data Technologies / [ed] Sherif Sakr and Albert Zomaya, Cham: Springer, 2018Chapter in book (Refereed)
    Abstract [en]

    To speed up the progress in the field of materials design, a number of challenges related to big data need to be addressed. This entry discusses these challenges and shows the semantic technologies that alleviate the problems related to variety, variability, and veracity.

  • 47.
    Ekeroth, Sebastian
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Münger, Peter
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Boyd, Robert
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Ekspong, Joakim
    Umeå Univ, Sweden.
    Wågberg, Thomas
    Umeå Univ, Sweden.
    Edman, Ludvig
    Umeå Univ, Sweden.
    Brenning, Nils
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering. KTH Royal Inst Technol, Sweden.
    Helmersson, Ulf
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Catalytic Nanotruss Structures Realized by Magnetic Self-Assembly in Pulsed Plasma2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 5, p. 3132-3137Article in journal (Refereed)
    Abstract [en]

    Tunable nanostructures that feature a high surface area are firmly attached to a conducting substrate and can be fabricated efficiently over significant areas, which are of interest for a wide variety of applications in, for instance, energy storage and catalysis. We present a novel approach to fabricate Fe nanoparticles using a pulsed-plasma process and their subsequent guidance and self-organization into well-defined nanostructures on a substrate of choice by the use of an external magnetic field. A systematic analysis and study of the growth procedure demonstrate that nondesired nanoparticle agglomeration in the plasma phase is hindered by electrostatic repulsion, that a polydisperse nanoparticle distribution is a consequence of the magnetic collection, and that the formation of highly networked nanotruss structures is a direct result of the polydisperse nanoparticle distribution. The nanoparticles in the nanotruss are strongly connected, and their outer surfaces are covered with a 2 nm layer of iron oxide. A 10 mu m thick nanotruss structure was grown on a lightweight, flexible and conducting carbon-paper substrate, which enabled the efficient production of H-2 gas from water splitting at a low overpotential of 210 mV and at a current density of 10 mA/cm(2).

  • 48.
    Eriksson, Peter
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Tal, Alexey
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Skallberg, Andreas
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Brommesson, Caroline
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Hu, Zhang-Jun
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Boyd, Robert
    Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, Faculty of Science & Engineering.
    Olovsson, Weine
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Fairley, Neal
    Casa Software Ltd, Bay House, Teignmouth, United Kingdom.
    Abrikosov, Igor
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Materials Modeling and Development Laboratory, National University of Science and Technology “MISIS”, Moscow, Russia.
    Zhang, Xuanjun
    Faculty of Health Sciences, University of Macau, Macau, SAR, China.
    Uvdal, Kajsa
    Linköping University, Department of Physics, Chemistry and Biology, Molecular Surface Physics and Nano Science. Linköping University, Faculty of Science & Engineering.
    Cerium oxide nanoparticles with antioxidant capabilities and gadolinium integration for MRI contrast enhancement2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6999Article in journal (Refereed)
    Abstract [en]

    The chelating gadolinium-complex is routinely used as magnetic resonance imaging (MRI) -contrast enhancer. However, several safety issues have recently been reported by FDA and PRAC. There is an urgent need for the next generation of safer MRI-contrast enhancers, with improved local contrast and targeting capabilities. Cerium oxide nanoparticles (CeNPs) are designed with fractions of up to 50% gadolinium to utilize the superior MRI-contrast properties of gadolinium. CeNPs are well-tolerated in vivo and have redox properties making them suitable for biomedical applications, for example scavenging purposes on the tissue-and cellular level and during tumor treatment to reduce in vivo inflammatory processes. Our near edge X-ray absorption fine structure (NEXAFS) studies show that implementation of gadolinium changes the initial co-existence of oxidation states Ce3+ and Ce4+ of cerium, thereby affecting the scavenging properties of the nanoparticles. Based on ab initio electronic structure calculations, we describe the most prominent spectral features for the respective oxidation states. The as-prepared gadolinium-implemented CeNPs are 3-5 nm in size, have r(1)-relaxivities between 7-13 mM(-1) s(-1) and show clear antioxidative properties, all of which means they are promising theranostic agents for use in future biomedical applications.

  • 49.
    Ribeiro, Luiz Antonio
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Monteiro, Fabio Ferreira
    Univ Brasilia, Brazil.
    da Cunha, Wiliam Ferreira
    Univ Florida, FL 32611 USA.
    Magela e Silva, Geraldo
    Univ Brasilia, Brazil.
    Charge Carrier Scattering in Polymers: A New Neutral Coupled Soliton Channel2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 6595Article in journal (Refereed)
    Abstract [en]

    The dynamical scattering of two oppositely charged bipolarons in non-degenerate organic semiconducting lattices is numerically investigated in the framework of a one-dimensional tight-biding-Hubbard model that includes lattice relaxation. Our findings show that it is possible for the bipolaron pair to merge into a state composed of a confined soliton-antisoliton pair, which is characterized by the appearance of states within less than 0.1 eV from the Fermi level. This compound is in a narrow analogy to a meson confining a quark-antiquark pair. Interestingly, solitons are quasi-particles theoretically predicted to arise only in polymer lattices with degenerate ground state: in the general case of nondegenerate ground state polymers, isolated solitons are not allowed.

  • 50.
    Sangiovanni, Davide Giuseppe
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Copper adatom, admolecule transport, and island nucleation on TiN(0 0 1) via ab initio molecular dynamics2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 50, p. 180-189Article in journal (Refereed)
    Abstract [en]

    Density-functional ab initio molecular dynamics (AIMD) simulations are carried out to determine Cu adatom and admolecule transport properties as a function of temperature, as well as atomistic processes leading to formation of Cu/TiN(0 0 1) islands at 350 K. At very low temperatures T ≤ 200 K, Cu adatoms (Cuad) migrate among favored fourfold-hollow surface sites by passing across atop-Ti metastable positions. For increasing temperatures, however, Cuad transport becomes progressively more isotropic, and switches continuously from normal- to super-diffusive with mean-square displacement dependencies on time that alternate between linear and exponential. Despite that, the Cuad diffusivity D can be expressed by a fairly Arrhenius-like behavior D(T) = 8.26(×2±1) × 10−4 cm2 s−1exp[(−0.04 ± 0.01 eV)/(kBT)] over the entire investigated temperature range (100 ≤ T ≤ 1000 K). AIMD simulations also reveal that the condensation of Cu adatoms into Cux>1 adspecies is kinetically hindered by long-range (>5.5 Å) adatom/adatom repulsion. During Cu island nucleation, all Cu atoms occupy atop-N positions indicating favored Cu(0 0 1)/TiN(0 0 1) epitaxial growth. Nevertheless, Cu agglomerates formed by five, or more, atoms tend to arrange in 3D structures, which maximize intracluster bonds while minimizing film/substrate interactions. Results here presented provide insights for understanding the properties of weakly-interacting metal/substrate interface systems in general.

    The full text will be freely available from 2020-04-22 11:26
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