This is the first of a series of on line events aimed mainly at PhD students and researchers in their first post-doc. Our goal is to provide a new venue for these young scientists to share their work, get expert feedback and have an opportunity to strengthen scientific relations within the CECAM community.

The event is fully on line and will have two parts. In the first, broadcasted as a Zoom webinar, Prof. Christoph Dellago, University of Vienna, will present a general talk in the area of activated events (title and abstract below). This will be followed by seminars given by two young members of the community to describe their work in the same area. In the second part of the event, we shall move to a virtual poster session hosted in a Gather room where more PhD students and researchers in their first post-doc will present pertinent projects. The session’s speaker and other (surprise) expert guests will join us for this poster session to discuss exciting new science. 

To participate

If you are a PhD student or a post-doc:

Please use the Participate Tab on this page to start the application. You will have to login using your CECAM account to access the application form. If you don't have a CECAM account yet, use the register option on the top right corner of the login page...and welcome to CECAM!

If you are a more senior scientist:

Please contact the organisers and we shall process your registration.

Submission of posters

(Please note that - at least for the time being - we shall accept posters only from PhD students or researchers in their first post-doc)

After your application is accepted, you will be able to submit a poster. In the CECAM page for this event, go to “my participation” tab and click on “Add a poster”, providing in particular title and abstract following the recommended format. Then, please upload the poster file in png or jpg by clicking on “Add a file”. These formats are strict to enable showing of the poster in the Gather session. Please upload your poster as soon as possible to enable a decision from the selection committee - see below.

DEADLINE FOR SUBMISSION: FRIDAY, JANUARY 15 2021

Selection of posters

Posters will be selected by the event organisers with the support of our main speaker and experts who will take place in the poster session. 

Selection of the two talks by PhD or first year postdocs

These contributions, to be broadcasted in the Zoom webinar in the first part of the event, will be selected, after a preliminary screening by the organisers, the main speaker and guest experts, via a lottery from the posters selected for the Gather session. Please indicate in your application if you DO NOT WANT your poster to be considered for this lottery. 

THE DECISION ON THE POSTER AND THE OUTCOME OF THE LOTTERY SELECTION WILL BE COMMUNICATED BY THURSDAY, JANUARY 21 2021

SESSION 1. Title and abstract of talks

Bridging time scales in molecular simulations

Christoph Dellago, Faculty of Physics, University of Vienna

The microscopic dynamics of many condensed matter systems occurring in nature and technology is dominated by rare but important barrier crossing events. The resulting wide ranges of time scales are a challenge for molecular simulation. For instance, a supercooled liquid can exist in a metastable state without freezing for very long times before it eventually crystallizes. In this case, typical waiting times may vastly exceed the time scales accessible to molecular dynamics simulations. Similarly, the time scales of chemical reactions or of biomolecular reoganizations can be many orders of magnitudes longer than those of basic molecular motions. This rare event problem is also related to the problem of finding reaction coordinates, i.e. of identifying important degrees of freedom that capture the mechanism of the process under study. In this talk, I will give an overview of several approaches developed to address these computational problems and illustrate them with various examples including the crystallization of supercooled liquids and cavitation of water under tension. I will conclude with a discussion of some open problems and an outlook to possible future directions.

Training collective variables for enhanced sampling via neural network based discriminant analysis

Luigi Bonati, ETHZ

The design of an appropriate set of collective variables is crucial to the success of several enhanced sampling methods. Here we focus on deriving such variables from information limited to metastable states. We characterize these states with a large set of descriptors and use neural networks to compress this information into a lower-dimensional space, using Fisher's linear discriminant as an objective function [1]. This approach results in an efficient sampling of a variety of rare events, while also identifying the physical descriptors that undergo the most significant changes in the process. We illustrate these features through two applications. The first is the study of an intermolecular aldol reaction characterized by a concerted mechanism, while the second one is the calculation of ligand binding free energies for a set of host-guest systems [2].

References

[1] L. Bonati, V. Rizzi, M. Parrinello, J. Phys. Chem. Lett., 11, 2998-3004 (2020)
[2] V. Rizzi, L. Bonati, N. Ansari, M. Parrinello, Nat Commun, 12, 93 (2021)

Identification of a multi-dimensional reaction coordinate for crystal nucleation in Ni3Al

Yanyan Liang, ICAMS, Ruhr-Universität Bochum

Crystal nucleation during solidification in multi-component alloys is a complex process that comprises competition between various crystalline phases as well as chemical composition and ordering. In this work, we combine transition interface sampling method with extensive committor analysis to investigate the atomistic mechanism during the initial stages of crystallization in bimetallic Ni3Al. The analysis of the path ensemble indicates the existence of multiple reaction channels leading to the formation of face centred cubic (fcc) or body centred cubic (bcc) crystallites. The committor analysis shows that the formation and growth of crystalline clusters and the polymorphs selected in Ni3Al depend explicitly on the interplay between cluster size, crystallinity, and chemical short-range order. In particular, the chemical short-range order exhibits a key role in the stability of the small cluster triggering either continuous growth or shrinkage. In contrast to classical nucleation theory, it is essential to include all three features in a multi-dimensional reaction coordinate to correctly describe the nucleation mechanism in Ni3Al. The identification of a multi-dimensional reaction coordinate is expected to be of key importance for the atomistic characterization of crystal nucleation in complex, multi-component systems.