ICAMS / Interdisciplinary Centre for Advanced Materials Simulation


Atomistic approaches for rare event systems

Date: 29.04.2013
Place: Materials chemomechanics at the atomic scale: modelling and experiments, CECAM-HQ-EPFL, Lausanne, Switzerland

Jutta Rogal

Modelling the dynamical evolution of systems on the atomistic level over extended time scales is a particular challenging task. If the dynamics are governed by so-called rare events then the time scales of interest go far beyond what can be reached with regular molecular dynamics simulations. Several approaches have been developed to model the dynamics of rare events and the method of choice depends strongly on the investigated problem. In this talk I will discuss three different cases that exemplify the application of various approaches. In the first example the diffusivity of hydrogen in BCC iron in the presence of grain boundaries is investigated. For this highly accurate density-functional theory calculations are combined with a lattice kinetic Monte Carlo approach. From the simulations the distribution of hydrogen as well as the hydrogen mobility can be extracted. The second example discusses atomistic simulations of solid-solid phase transformations. In solid bulk systems the transformation mechanism from one phase into another might involve massive structural rearrangements including concerted multi-atom processes. Here, we employ an adaptive kinetic Monte Carlo approach to investigate such processes at the interface between cubic and topologically close-packed phases in transition metals. The third example shows how solid-liquid interface free energies can be extracted from atomistic simulations. Here, the interface mobility is rather high, but to follow the full transformation from the solid to the liquid phase or vice versa a high nucleation barrier has to be overcome. The dynamical trajectories connecting the solid and liquid state are investigated using transition path sampling. A proper reweighting of the path ensemble allows not only for the extraction of free energy barriers but also for the analysis of dynamical properties and transformation mechanisms.

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