IMX Seminar Series - Enhanced sampling of atomistic processes during structural phase transformations

Obtaining atomistic insight into the fundamental processes during structural phase transformations and their dynamical evolution up to experimental timescales remains one of the great challenges in materials modelling. In particular, if the mechanisms of the phase transformations are governed by so-called rare events, the timescales of interest will reach far beyond the applicability of regular molecular dynamics simulations. In addition to the timescale problem the simulations provide a vast amount of data within the high-dimensional phase space. A meaningful physical interpretation of these data requires the projection into a low-dimensional space and the identification of suitable reaction coordinates.

In this presentation, I will give an overview of our recent progress in the application of advanced atomistic simulation techniques to capture the dynamical behaviour during phase transformations over a large range of timescales. One of the key results is the analysis of nucleation and growth mechanisms during solidification in metals that can be extracted from transition path sampling simulations. By applying a likelihood maximisation scheme the quality of different reaction coordinates is evaluated which enables us to identify the most important order parameters that characterise the atomistic processes during the initial stages of nucleation and growth.
A second example is the analysis of phase boundary migration during solid-solid transformations in metals between two different crystal structures with semi-coherent interfaces. The transformation proceeds via a collective displacement of atoms in the interface region. The associated effective energy barrier that determines the mobility of the phase boundary results from the characteristic features of the complex energy landscape that the system explores during the transformation.

Bio: Jutta Rogal received her PhD from the Freie Universität Berlin in 2006, carrying out her PhD work on electronic structure calculations for surface catalysis at the Fritz Haber-Institute of the Max Planck Society. For her PhD thesis she was awarded the Otto Hahn Medal of the Max Planck Society and the Ernst-Reuter Preis of the Freie Universität Berlin. In 2007 Dr. Rogal moved to the University of Amsterdam as a postdoctoral researcher to develop methodological extensions to the transition path sampling approach. Since 2009 she is a research group leader at Interdisciplinary Centre for Advanced Materials Simulations (ICAMS) at the Ruhr University Bochum.  Her group focusses on the development and application of advanced atomistic simulation technique to capture the dynamical behaviour of materials on extended timescales.  This includes the investigation of phenomena related to phase transformations such as diffusion, nucleation, and growth. In 2016 Dr. Rogal was awarded a Feodor Lynen Research Fellowship of the Alexander von Humboldt Foundation which she spent at New York University in 2017/18 working on enhanced sampling techniques for high dimensional energy landscapes.