ICAMS / Interdisciplinary Centre for Advanced Materials Simulation
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Analysing reaction coordinates and free energies for phase transformations within the reweighted-path ensemble

Date: 27.03.2012
Place: DPG Spring Meeting 2012, Berlin, Germany

Jutta Rogal
Ralf Drautz

Sampling rare events in complex, high dimensional systems, such as crystal nucleation and growth, remains a challenge for computational studies. Employing e.g. classical molecular dynamics simulations to model phase transformations with a sizeable nucleation barrier becomes quickly unfeasible as the system tends to spend most of the time within the stable states while it hardly samples the transition barrier regions of the phase space.

Among other approaches, transition path sampling (TPS) provides a possibility to explore transitions between stable states in rare event systems. One of the key advantages in TPS is that an a priori definition of a reaction coordinate is not required. And by using the underlying physical dynamics the true kinetics of the transition is sampled.

Here we introduce a reweighting scheme for the path ensembles and apply it to a solid-liquid phase transformation in a Lennard‐Jones model system. Once the sampling has been performed, the reweighting allows for the analysis of free energy surfaces and committor projections in an arbitrary order parameter space. The reweighted path ensemble can then be used to optimise non-linear reaction coordinates and extract parameters such as the solid‐liquid interface free energy, which is one of the key quantities governing nucleation and growth during solidification.

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