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61

Sep 19, 2013
09/13

by
S. I. Simdyankin; Normand Mousseau; E. R. Hunt

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Stretched exponential distributions and relaxation responses are encountered in a wide range of physical systems such as glasses, polymers and spin glasses. As found recently, this type of behavior occurs also for the distribution function of certain trap time in a number of coupled dynamical systems. We analyze a one-dimensional mathematical model of coupled chaotic oscillators which reproduces an experimental set-up of coupled diode-resonators and identify the necessary ingredients for...

Source: http://arxiv.org/abs/cond-mat/0208487v1

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64

Sep 19, 2013
09/13

by
S. N. Taraskin; S. I. Simdyankin; S. R. Elliott

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It is demonstrated that the width of the uncorrelated atomic-charge distribution in glasses can be extracted from the frequency dependence of the coupling coefficient for the far-infrared absorption measured experimentally by the time-domain terahertz spectroscopy technique. This value for As2S3 glass is found to be 0.12 (e). A density functional theory-based tight-binding molecular dynamics model of As2S3 glass qualitatively supports these findings.

Source: http://arxiv.org/abs/0708.3982v1

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62

Sep 18, 2013
09/13

by
S. I. Simdyankin; S. N. Taraskin; M. Dzugutov; S. R. Elliott

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A structural model of a one-component $\sigma$-phase crystal has been constructed by means of molecular dynamics simulation. The phonon dispersion curves and the vibrational density of states were computed for this model. The dependence of the vibrational properties on the thermodynamical parameters was investigated. The vibrational density of states of the $\sigma$-phase structure is found to be similar to that of a one-component glass with icosahedral local order. On the basis of this...

Source: http://arxiv.org/abs/cond-mat/0002243v1

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44

Sep 17, 2013
09/13

by
S. I. Simdyankin; M. Dzugutov; S. N. Taraskin; S. R. Elliott

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We compare vibrational dynamics in two structurally distinct, simple monatomic model glasses simulated by molecular dynamics: the Lennard-Jones glass with an fcc-related structure and a glass with predominantly icosahedral short-range order. The former, characterised by a single local quasi-periodicity, supports only modes with acoustic behaviour. In the latter, the presence of optic modes and two incommensurate length scales is observed. This pattern of vibrational dynamics is shown to be...

Source: http://arxiv.org/abs/cond-mat/0007373v2

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59

Sep 19, 2013
09/13

by
S. N. Gurbatov; S. I. Simdyankin; E. Aurell; U. Frisch; G. Tóth

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This work is devoted to the decay ofrandom solutions of the unforced Burgers equation in one dimension in the limit of vanishing viscosity. The initial velocity is homogeneous and Gaussian with a spectrum proportional to $k^n$ at small wavenumbers $k$ and falling off quickly at large wavenumbers. In physical space, at sufficiently large distances, there is an ``outer region'', where the velocity correlation function preserves exactly its initial form (a power law) when $n$ is not an even...

Source: http://arxiv.org/abs/physics/9709002v1

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57

Sep 23, 2013
09/13

by
S. I. Simdyankin; S. R. Elliott; Z. Hajnal; T. A. Niehaus; Th. Frauenheim

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We have used a density-functional-based tight-binding method in order to create structural models of the canonical chalcogenide glass, amorphous (a-)As$_2$S$_3$. The models range from one containing defects that are both chemical (homopolar bonds) and topological (valence-alternation pairs) in nature to one that is defect-free (stoichiometric). The structural, vibrational and electronic properties of the simulated models are in good agreement with experimental data where available. The...

Source: http://arxiv.org/abs/cond-mat/0312224v1

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47

Sep 18, 2013
09/13

by
S. I. Simdyankin; M. Elstner; T. A. Niehaus; Th. Frauenheim; S. R. Elliott

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We have studied the influence of alloying copper with amorphous arsenic sulfide on the electronic properties of this material. In our computer-generated models, copper is found in two-fold near-linear and four-fold square-planar configurations, which apparently correspond to Cu(I) and Cu(II) oxidation states. The number of overcoordinated atoms, both arsenic and sulfur, grows with increasing concentration of copper. Overcoordinated sulfur is found in trigonal planar configuration, and...

Source: http://arxiv.org/abs/cond-mat/0504207v1

43
43

Sep 17, 2013
09/13

by
S. I. Simdyankin; S. N. Taraskin; M. Elenius; S. R. Elliott; M. Dzugutov

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We use a local projectional analysis method to investigate the effect of topological disorder on the vibrational dynamics in a model glass simulated by molecular dynamics. Evidence is presented that the vibrational eigenmodes in the glass are generically related to the corresponding eigenmodes of its crystalline counterpart via disorder-induced level-repelling and hybridization effects. It is argued that the effect of topological disorder in the glass on the dynamical matrix can be simulated by...

Source: http://arxiv.org/abs/cond-mat/0108336v3

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38

Sep 22, 2013
09/13

by
S. I. Simdyankin; T. A. Niehaus; G. Natarajan; Th. Frauenheim; S. R. Elliott

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We report on density-functional-based tight-binding (DFTB) simulations of a series of amorphous arsenic sulfide models. In addition to the charged coordination defects previously proposed to exist in chalcogenide glasses, a novel defect pair, [As4]--[S3]+, consisting of a four-fold coordinated arsenic site in a seesaw configuration and a three-fold coordinated sulfur site in a planar trigonal configuration, was found in several models. The valence-alternation pairs S3+-S1- are converted into...

Source: http://arxiv.org/abs/cond-mat/0409441v1

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89

Jul 20, 2013
07/13

by
S. N. Taraskin; S. I. Simdyankin; S. R. Elliott; J. R. Neilson; T. Lo

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Using an analytical theory, experimental terahertz time-domain spectroscopy data and numerical evidence, we demonstrate that the frequency dependence of the absorption coupling coefficient between far-infrared photons and atomic vibrations in disordered materials has the universal functional form, C(omega) = A + B*omega^2, where the material-specific constants A and B are related to the distributions of fluctuating charges obeying global and local charge neutrality, respectively.

Source: http://arxiv.org/abs/cond-mat/0604205v1