Statistical Thermodynamics & Molecular Simulations (STMS) Seminar Series
These seminar series are aimed at providing a virtual platform for sharing scientific research in the area of statistical mechanics, molecular simulations, and computational materials science. In recent months, the coronavirus pandemic has stopped all large in-person scientific gatherings, including conferences and department seminars, and it is not clear that the situation will improve any time soon. STMS is aimed at filling this gap, and provide a venue for dissemination of research findings and exchange of ideas in the age of COVID. This model is being currently used by several other scientific communities, and can potentially continue even beyond the pandemic if successful.
Each seminar will be a 60-minute event and will comprise of a long-form (30-minute) talk by a principal investigator or a senior research scientists from academia or industry and a short-form (15-minute) presentation by a graduate student or a postdoc. The remainder of the event will be dedicated to Q&A (10 minutes for the PI, 5 minutes for the student/postdoc). Long-form speakers will be chosen by the STMS Organizing Committee, while we encourage suggestions from the community at large. Student and postdoctoral speakers, however, need to be nominated by their advisors. Seminars will take place on Fridays, from 11 AM-12 PM. During 2021, we expect to hold two seminar per month, at the last two Fridays of each month.This event's talks:
Nucleation in metallic systems - Impact of precursor formation on nucleation rates and mechanisms
Prof. Jutta Rogal (New York University/Freie Universitat Berlin )
Abstract: The initial stages of nucleation and growth during phase transformations are still not fully understood, even for seemingly simple systems, such as solidification in unary metals. Using transition path sampling, we have studied the atomistic mechanisms during homogeneous nucleation in unary FCC and BCC metals as well as binary alloys. 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 mechanisms. Our analysis reveals that the emergence of the crystalline phase is preceded by the formation of pre-structured regions in the liquid that act as precursors.
Extending our study to heterogeneous nucleation, we likewise observe a precursor-mediated crystallization mechanism. Small seeds impact the structural characteristics of the liquid and induce the formation of precursors with specific structural hallmarks. The nucleating ability and polymorph selectivity of these templates is therefore not simply given by lattice mismatch and translational order, but strongly linked to the seed's ability to promote the formation of suitable precursors.
The insight gained on the relationship between structural heterogeneity in the liquid and the nucleation mechanism provides an essential step in controlling template-driven crystallization and polymorph selection.
Speaker Bio: Jutta Rogal is currently a Heisenberg Fellow of the German Research Foundation (DFG) with a research appointment at the Department of Chemistry at New York University, USA, and at the Department of Physics at Freie Universität Berlin, Germany.
She received her doctorate 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, Jutta moved to the University of Amsterdam as a postdoctoral researcher to develop methodological extensions to the transition path sampling approach, before joining the Interdisciplinary Centre for Advanced Materials Simulation (ICAMS) at the Ruhr University Bochum, Germany, as group leader from 2009-2020. In 2016, she 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.
Her research focusses on the development and application of advanced molecular simulation approaches to capture the mechanisms and kinetics of structural phase transformations in molecular and atomic condensed matter systems. This includes the theoretical investigation of the initial stages of nucleation and growth, precipitate formation, and interface dynamics.
Relating energy dissipation to effective interactions and structure formation in cross-linked biopolymers
Dr. Yuqing Qiu (University of Chicago)
Abstract: The actin cytoskeleton serves as a paradigm for molecular assemblies containing active elements that convert chemical energy to mechanical work. Previous work on driven fluids [Tociu et al. PRX 2018] demonstrated that their structure and dynamics can be altered by changing the rates at which they dissipate energy. Here, we extend this concept to biopolymer networks that are cross-linked by molecular motors. Using algorithms for computing large-deviation functions, we sample activity-biased ensembles of biopolymer networks and find a connection between their structures and thermodynamic quantities such as energy dissipation. We consider a system in which molecular motors give rise to effective interactions between actin filaments and drive the formation of either actin asters or bundles depending on the rigidity of motors. We investigate the nature of the transition between asters and bundles and demonstrate that biasing the rate of energy dissipation in a system with fixed motor rigidity has the same effect on structure modulation as tuning the motor rigidity. This work elucidates the relationship between energy dissipation, effective interactions, and pattern formation in active materials with implications for understanding how living systems can exploit dissipation to control the morphologies of their molecular assemblies.
Speaker Bio: Dr. Qiu is a postdoctoral scholar at the University of Chicago. She received B.S. in Chemistry from Zhejiang University in 2012 and Ph.D from the University of Utah in 2018. During her Ph.D, Dr. Qiu investigated ice nucleation efficiency of organic and biological surfaces using theory and simulations. Dr. Qiu’s current research focuses on using tools of non-equilibrium statistical mechanics and simulations to study the emergent behavior of complex systems such as cytoskeletal polymers.