97 research outputs found
Comment on `Formation of a Dodecagonal Quasicrystalline Phase in a Simple Monatomic Liquid'
In a recent paper M. Dzugutov, Phys. Rev. Lett. 70 2924 (1993), describes a
molecular dynamics cooling simulation where he obtained a large monatomic
dodecagonal quasicrystal from a melt. The structure was stabilized by a special
potential [Phys. Rev. A46 R2984 (1992)] designed to prevent the nucleation of
simple dense crystal structures. In this comment we will give evidence that the
ground state structure for Dzugutov's potential is an ordinary bcc crystal
Comment on `Universal relation between the Kolmogorov-Sinai entropy and the thermodynamic entropy in simple liquids'
The intriguing relations between Kolmogorov-Sinai entropy and self diffusion
coefficients and the excess (thermodynamic) entropy found by Dzugutov and
collaborators do not appear to hold for hard sphere and hard disks systems.Comment: 1 page revte
The favoured cluster structures of model glass formers
We examine the favoured cluster structures for two new potentials, which both
behave as monatomic model glass-formers in bulk. We find that the oscillations
in the interatomic potential lead to global minima that are non-compact
arrangements of linked 13-atom icosahedra. We find that the structural
properties of the clusters correlate with the glass-forming propensities of the
potentials, and with the fragilities of the corresponding supercooled liquids.Comment: 9 pages, 7 figures; new section added and error in potential
parameters correcte
Decoupling of diffusion from structural relaxation and spatial heterogeneity in a supercooled simple liquid
We report a molecular dynamics simulation of a supercooled simple monatomic
glass-forming liquid. It is found that the onset of the supercooled regime
results in formation of distinct domains of slow diffusion which are confined
to the long-lived icosahedrally structured clusters associated with deeper
minima in the energy landscape. As these domains, possessing a low-dimensional
geometry, grow with cooling and percolate below , the critical temperature
of the mode coupling theory, a sharp slowing down of the structural relaxation
relative to diffusion is observed. It is concluded that this latter anomaly
cannot be accounted for by the spatial variation in atomic mobility; instead,
we explain it as a direct result of the configuration-space constraints imposed
by the transient structural correlations. We also conjecture that the observed
tendency for low-dimensional clustering may be regarded as a possible mechanism
of fragility.Comment: To be published in PR
Simulation of radiation-induced structural transformation in amorphous metals
Molecular-dynamics simulations investigating the radiation-induced structural transformations in metallic glasses are reported. We have studied three models of an equilibrium simple glass, possessing a pronounced icosahedral local order. Two of these are monatomic and one represents the amorphous Ni-P alloy. A detailed analysis of the evolution of the structural damage induced by irradiation is presented. In all the systems, a persistent residual reduction in icosahedral order is observed. An important finding of this study is that the metallic glasses are able to sustain a considerable increase in the number of vacancies which arises as a result of the irradiation-induced structural transformationPeer reviewe
A Structural Model for Octagonal Quasicrystals Derived from Octagonal Symmetry Elements Arising in -Mn Crystallization of a Simple Monatomic Liquid
While performing molecular dynamics simulations of a simple monatomic liquid,
we observed the crystallization of a material displaying octagonal symmetry in
its simulated diffraction pattern. Inspection of the atomic arrangements in the
crystallization product reveals large grains of the beta-Mn structure aligned
along a common 4-fold axis, with 45 degree rotations between neighboring
grains. These 45 degree rotations can be traced to the intercession of a second
crystalline structure fused epitaxially to the beta-Mn domain surfaces, whose
primitive cell has lattice parameters a = b = c = a_{beta-Mn}, alpha = beta =
90 degrees, and gamma = 45 degrees. This secondary phase adopts a structure
which appears to have no known counterpart in the experimental literature, but
can be simply derived from the Cr_3Si and Al_3Zr_4 structure types. We used
these observations as the basis for an atomistic structural model for octagonal
quasicrystals, in which the beta-Mn and the secondary phase structure unit
cells serve as square and rhombic tiles (in projection), respectively. Its
diffraction pattern down the octagonal axis resembles those experimentally
measured. The model is unique in being consistent with high-resolution electron
microscopy images showing square and rhombic units with edge-lengths equal to
that of the beta-Mn unit cell. Energy minimization of this configuration, using
the same pair potential as above, results in an alternative octagonal
quasiperiodic structure with the same tiling but a different atomic decoration
and diffraction pattern.Comment: 25 pages, 10 figure
Evidence for compact cooperatively rearranging regions in a supercooled liquid
We examine structural relaxation in a supercooled glass-forming liquid
simulated by NVE molecular dynamics. Time correlations of the total kinetic
energy fluctuations are used as a comprehensive measure of the system's
approach to the ergodic equilibrium. We find that, under cooling, the total
structural relaxation becomes delayed as compared with the decay of the
component of the intermediate scattering function corresponding to the main
peak of the structure factor. This observation can be explained by collective
movements of particles preserving many-body structural correlations within
compact 3D cooperatively rearranging regions.Comment: 8 pages, 4 figure
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