Pressure induced phase transformations of nanocrystals studied with
transition path sampling simulations
In a series of recent experiments, Alivisatos and coworkers demonstrated
that the pressure-induced transition from the four-coordinate wurtzite
structure to the six-coordinate rocksalt structure in CdSe nanocrystals
is strongly influenced by crystal size. On a molecular time scale, the
transition is a rare event and the resulting long time scales present a
challenge for computer simulations [1]. Using this example, I will
discuss how the transition path sampling methodology provides a
framework to treat systems with widely disparate time scales and, in
particular, to study the mechanism and the kinetics of first order phase
transformations close to experimental conditions [2]. From our
transition path sampling simulation we obtain the preferred
transformation pathway and determine activation enthalpies and volumes,
which permit to make contact to experimental results.
[1] M. Grünwald, E. Rabani, and C. Dellago, "Mechanisms of the wurtzite
to rocksalt transformation in CdSe nanocrystals", Physical Review
Letters 96, 255701 (2006).
[2] M. Grünwald, P. L. Geissler, and C. Dellago, "An efficient
transition path sampling algorithm for nanoparticles under pressure",
Journal of Chemical Physics 127, 154718 (2007).