ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

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Solid‐liquid interface free energies and structural phase transformations - atomistic approaches in rare event systems

Date: 30.10.2012
Place: University of California, Berkeley, Berkeley, USA

Jutta Rogal

Solid‐liquid interface free energies and structural phase transformations ‐ Atomistic approaches for rare event systems The solid‐liquid interface free energy is one of the important interfacial properties that govern nucleation and growth during solidification processes. It is extremely difficult to measure experimentally and various theoretical approaches have been developed to extract solid‐liquid interface energies from atomistic simulations.

If the free energy surface (FES) that maps out the transition from a single phase into the coexistence region of the two phases is known, the interface energy can be extracted from the excess energy.[1]

Here, we use the reweighted path ensemble (RPE)[2] to obtain the FES for a solid‐liquid phase transformation in a Lennard‐Jones model system. One of the key advantages of the RPE is that an a priori definition of collective variables is not required. Once the sampling has been performed the RPE allows for a projection of the FES into any arbitrary collective variable space. Furthermore, the RPE can be used to analyse committor projections, identify transition state regions, and optimise non‐linear reaction coordinates to determine important parameters governing the transformation mechanism.

In solid bulk systems the transformation mechanism from one phase into another might involve massive structural rearrangements including concerted multi‐atom processes with sizeable energetic barriers. Due to the rather large energy barriers these processes take place on time scales that are not accessible by regular molecular dynamics.

Here, we employ an adaptive kinetic Monte Carlo (akMC) approach [3] to investigate such processes in complex phases of transition metals. To ensure a proper description of the energetics within these systems we use bond‐order potentials as a basis for our akMC simulations.

[1] S. Angioletti‐Uberti et al., Phys. Rev. B 81, 125416 (2010)
[2] J. Rogal et al., J. Chem. Phys. 133, 174109 (2010)
[3] G. Henkelman et al., J. Chem. Phys. 115, 9657 (2001)

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