This Week's Discoveries | 26 November 2019
- Tuesday 26 November 2019
Niels Bohrweg 2
2333 CA Leiden
- De Sitterzaal
Beyond the Born-Oppenheimer Static Surface Model for Molecule-Surface Reactions
Paul Spiering (LIC)
Paul is a Ph.D. student in the group of Jörg Meyer and will defend his thesis on 16 December. Paul is interested in non-adiabatic effects that result from molecules interacting with metal surfaces. In particular, his interests are in adapting currently used machine-learning techniques to obtain continuous representations of electronic friction tensors that correctly incorporate symmetry.
Heterogeneous catalysis is one of the cornerstones for the industrial production of fuels and chemicals and thus plays a key role in a sustainable society. In particular, the Haber-Bosch process is one important example of the production of fertilizers. An important and usually rate-determining step for this process is the dissociation of nitrogen molecules (N2) on a metal surface.
In order to better understand and optimize such elementary reaction steps, state-of-the-art electronic structure calculation based on density functional theory have become an invaluable tool. However, up to now, such calculations have commonly relied on the Born-Oppenheimer approximation (BOA), i.e. one of the most fundamental approximation in theoretical chemistry, according to which electrons are assumed to instantaneously follow the motion of nuclei in their ground state.
Here I go beyond this approximation by applying and further developing electronic friction theory, which allows to include the effect of electronic excitations in a metal surface on the nuclear dynamics. For N2 dissociation on a Ru(0001) surface, we find that going beyond the BOA can lead to a reduction of the dissociation probability by a factor of two and more.
This improves the agreement of the theoretical model with the most accurate experimental data that is currently available. With an unambiguous verification by experiments still pending, I discuss potential implications for the reaction of molecules on metal surfaces that are of relevance for heterogeneous catalysis.
Quantifying the emergence of sign language structure
Tessa Verhoef (LIACS)
Tessa is an assistant professor in the Media Technology program at Leiden University. She co-founded the Creative Intelligence Lab (CIL) and conducts research at the intersection of language, cognition, cultural evolution, and computation. After finishing a BSc and MSc in Artificial Intelligence, she obtained her Ph.D. in Language Evolution at the University of Amsterdam. Before joining LIACS she was a postdoc at the University of California, San Diego, where she conducted her NWO Rubicon research at the Center for Research in Language (CRL) and became a Frontiers of Innovation Scholars Program (FISP) fellow at the departments of Communication and Electrical and Computer Engineering.
Besides developing and running studies in the lab, Tessa designs live exhibits to bring scientific questions, experiments and lectures to museums and festivals (most recently featured at Lowlands: https://cil.universiteitleiden.nl/lowlands/).
Gestures produced by users of spoken languages differ from signs produced by users of sign languages in that gestures are more typically ad hoc and idiosyncratic, while signs are more typically conventionalized and shared within a language community. To quantitatively measure how gestures may change over time as a result of the process of conventionalization, work in my lab has used communication game experiments to elicit gestures from participants while using Microsoft Kinect to unobtrusively track the movement of their bodies. We were able to simulate and quantify hallmarks of conventionalization that have been described for sign languages, in the laboratory. For instance, we measured a reduction in the size of the articulatory space and a decrease in the distance traveled by the articulators, while communicative success increased between participants over time. This last summer we collected new data during the music festival Lowlands and I will present a hot off the press first glimpse of what we found there. In concert with video analyses of large datasets, these approaches are opening the door for more direct future comparisons between ad hoc gestures produced in the lab and natural sign languages in the world.