| 1. |
- Oppelstrup, Tomas, 1977-, et al.
(författare)
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Anomalous diffusion in supercooled liquids: A long-range localizationin particle trajectories
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131, s. 044510-
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Tidskriftsartikel (refereegranskat)abstract
- A statistical analysis of the geometries of particle trajectories in the supercooled liquid state isreported. The analysis we present here is based on the statistics of the first-passage trajectory length.We examine two structurally different fragile glass-forming liquids simulated by moleculardynamics. In both liquids, the trajectories are found to reveal three distinct diffusion regimes. Ashort-range confinement to the cage of nearest neighbors is followed by a persistent diffusionregime. At a still larger spatial scale, the particle trajectories demonstrate a novel diffusion anomaly:a long-range localization distinct from the short-range localization. This phenomenon can beinterpreted in terms of the potential-energy landscape topography with the local energy minimacoalescing into metabasins—compact domains with low escape probability. We also demonstratethat the persistent diffusion regime can be linked to the exponential decay of the self-part of thevan Hove correlation function.
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| 2. |
- Oppelstrup, Tomas, 1977-, et al.
(författare)
-
First-Passage Kinetic Monte Carlo method
- 2009
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1063-651X .- 1095-3787. ; 80:6, s. 066701-
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Tidskriftsartikel (refereegranskat)abstract
- We present a new effcient method for Monte Carlo simulations of diusion-reaction processes. First introduced by us in [Phys. Rev. Lett., 97:230602, 2006], the new algorithm skips the traditionalsmall diusion hops and propagates the diusing particles over long distances through asequence of super-hops, one particle at a time. By partitioning the simulation space into nonoverlappingprotecting domains each containing only one or two particles, the algorithm factorizesthe N-body problem of collisions among multiple Brownian particles into a set of much simplersingle-body and two-body problems. Ecient propagation of particles inside their protective domainsis enabled through the use of time-dependent Green's functions (propagators) obtained assolutions for the rst-passage statistics of random walks. The resulting Monte Carlo algorithmis event-driven and asynchronous; each Brownian particle propagates inside its own protectivedomain and on its own time clock. The algorithm reproduces the statistics of the underlyingMonte-Carlo model exactly. Extensive numerical examples demonstrate that for an importantclass of diusion-reaction models the new algorithm is effcient at low particle densities, whereother existing algorithms slow down severely.
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| 3. |
- Oppelstrup, Tomas, 1977-
(författare)
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Simulation of relaxation processes in complex condensed matter systems : Algorithmic and physical aspets
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis summarizes interrelated simulation studies of three different physical phenomena. The three topics are: simulation of work hardening of materials using dislocation dynamics, investigation of anomalous diffusion in supercooled liquids using molecular dynamics,and kinetic Monte-Carlo simulation of annealing of radiation damaged materials. All three topics require special algorithms in order to enable physically relevant simulations. The author's contributionconsists of development, implementation, and optimization of these algorithms, as well as interpretation of simulation results.
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