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Fleck M.,Institute For Festkorperforschung | Huter C.,Institute For Festkorperforschung | Pilipenko D.,Institute For Festkorperforschung | Spatschek R.,Institute For Festkorperforschung | And 2 more authors.
Philosophical Magazine | Year: 2010

We develop a description of diffusion limited growth in solid-solid transformations, which are strongly influenced by elastic effects. Density differences and structural transformations provoke stresses at interfaces, which affect the phase equilibrium conditions. We formulate equations for the interface kinetics similar to dendritic growth and study the growth of a stable phase from a metastable solid in both a channel geometry and in free space. We perform sharp interface calculations based on Green's function methods and phase field simulations, supplemented by analytical investigations. For pure dilatational transformations we find a single growing finger with symmetry breaking at higher driving forces, whereas for shear transformations the emergence of twin structures can be favorable. We predict the steady state shapes and propagation velocities, which can be higher than in conventional dendritic growth.

Reddy N.K.,Catholic University of Leuven | Zhang Z.,Catholic University of Leuven | Lettinga M.P.,Institute for Festkorperforschung | Dhont J.,Institute for Festkorperforschung | Vermant J.,Catholic University of Leuven
AIChE Annual Meeting, Conference Proceedings | Year: 2010

The assembly of rod-like particles by weak attractive inter-actions is important for the properties of several soft biological materials as well as in tailoring the properties of colloidal gels in a variety of applications. Under-standing the link between the physicochemical parameters such as size and aspect ratio, volume fraction, interparticle forces with the resulting microstructure and the rheological response remains however challenging. It is often difficult to obtain a good control over these parameters due to the lack of suitable model systems. In the present work a model rod-like fd-virus particle has been surface modi ed with a thermoreversible polymer poly(N-isoproplyacrlyamide). The repulsive and attractive contributions to the overall interaction potential can be varied indepen-dently by changing the ionic strength and the temperature. The e ects of these changes on the strength and structure of the gel have been studied near the gel transition using a combination of rheological and scattering measurements. The results show that for these thermoreversible 'sticky' rod systems, the variations of the structure in the gelled state are relatively weak, with the gel strength mainly being controlled by the relative magnitudes between the attractive and repulsive contributions and the volume fraction, the anisotropic nature of the electrostatic interactions seems to have a minor effect.

Mazurenko V.V.,Ural State Technical University | Shorikov A.O.,RAS Institute of Metal Physics | Lukoyanov A.V.,RAS Institute of Metal Physics | Kharlov K.,Ural State Technical University | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The LDA+DMFT (local density approximation combined with dynamical mean-field theory) computation scheme has been used to study spectral and magnetic properties of FeSi and Fe1-x Cox Si. Having compared different models, we conclude that a correlated band insulator scenario in contrast to Kondo insulator model agrees well with FeSi band structure and experimental data. Coulomb correlation effects lead to band narrowing of the states near the Fermi level with mass renormalization parameter m *≈.2 in agreement with the results of angle-resolved photoemission spectroscopy. Temperature dependence of spectral functions and magnetic susceptibility calculated in DMFT reproduces transition from nonmagnetic semiconductor to metal with local magnetic moments observed experimentally. Cobalt doping leads to ferromagnetism that has itinerant nature and can be successfully described by the LDA+DMFT method. © 2010 The American Physical Society.

Ono T.,Osaka University | Heide M.,Osaka University | Atodiresei N.,Institute For Festkorperforschung | Baumeister P.,Institute For Festkorperforschung | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We have developed an efficient computational scheme utilizing the real-space finite-difference formalism and the projector augmented-wave (PAW) method to perform precise first-principles electronic-structure simulations based on the density-functional theory for systems containing transition metals with a modest computational effort. By combining the advantages of the time-saving double-grid technique and the Fourier-filtering procedure for the projectors of pseudopotentials, we can overcome the egg box effect in the computations even for first-row elements and transition metals, which is a problem of the real-space finite-difference formalism. In order to demonstrate the potential power in terms of precision and applicability of the present scheme, we have carried out simulations to examine several bulk properties and structural energy differences between different bulk phases of transition metals and have obtained excellent agreement with the results of other precise first-principles methods such as a plane-wave-based PAW method and an all-electron full-potential linearized augmented plane-wave (FLAPW) method. © 2010 The American Physical Society.

Lounis S.,Institute For Festkorperforschung | Lounis S.,University of California at Irvine | Zahn P.,Martin Luther University of Halle Wittenberg | Weismann A.,University of Kiel | And 5 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

A scanning tunneling microscope can be used to visualize in real space effects provided by Fermi surfaces with buried impurities far below substrates acting as local probes. After scattering at buried impurities, anisotropic electronic wave oscillations are observed on the surface as hot spots: The experiments exhibit strongly enhanced intensities in certain directions and much weaker intensities in other directions. A theory describing these features is developed based on the stationary phase approximation for the Friedel oscillations and taking into account the band structure of the host material. It is demonstrated how the Fermi surface of a material, for instance, through Fermi contours' critical points, acts as a mirror focusing electrons that scatter at hidden impurities which allow the projection of parts of the Fermi surface, a quantity defined in reciprocal space, onto real space. © 2011 American Physical Society.

Betzinger M.,Institute For Festkorperforschung | Friedrich C.,Institute For Festkorperforschung | Blugel S.,Institute For Festkorperforschung | Gorling A.,Friedrich - Alexander - University, Erlangen - Nuremberg
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We present a general numerical approach to construct local Kohn-Sham potentials from orbital-dependent functionals within the all-electron full-potential linearized augmented-plane-wave (FLAPW) method, in which core and valence electrons are treated on an equal footing. As a practical example, we present a treatment of the orbital-dependent exact-exchange (EXX) energy and potential. A formulation in terms of a mixed product basis, which is constructed from products of LAPW basis functions, enables a solution of the optimized-effective-potential (OEP) equation with standard numerical algebraic tools and without shape approximations for the resulting potential. We find that the mixed product and LAPW basis sets must be properly balanced to obtain smooth and converged EXX potentials without spurious oscillations. The construction and convergence of the exchange potential are analyzed in detail for diamond. Our all-electron results for C, Si, SiC, Ge, and GaAs semiconductors as well as Ne and Ar noble-gas solids are in very favorable agreement with plane-wave pseudopotential calculations. This confirms the adequacy of the pseudopotential approximation in the context of the EXX-OEP formalism and clarifies a previous contradiction between FLAPW and pseudopotential results. © 2011 American Physical Society.

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