MARVEL Junior Seminar — December 2021

https://epfl.zoom.us/j/68368776745
Password: 1923

The MARVEL Junior Seminars aim to intensify interactions between the MARVEL Junior scientists belonging to different research groups.

Each seminar consists of two presentations of 25 minutes each, allowing to present on a scientific question in depth, followed by time for discussion. The discussion is facilitated and timed by the chair.

MARVEL Junior Seminar Organizing Committee — Michele Kotiuga, Sara Fiore, Stefano Falletta, Kristians Cernevics, Max Veit and Patrick Mayor

Talk 1 — Capturing chemical data to learn “intuitions”

Kevin Maik Jablonka, Berend Smit

Laboratory of Molecular Simulation (LSMO), EPFL

Some of the most interesting phenomena in chemistry are not accessible with theory.

In those cases, machine learning can help—for example, to even learn properties that are not quantum mechanical observables [1] or to predict things for which we do not even know how to set up a simulation [2].

However, in chemistry we have to deal with an additional challenge: We often work in data-sparse regimes and miss crucial data, for example, from failed experiments.
To address these problems, we need efficient ways to explore chemical space, for instance using active learning [4], across different domains and scales, and techniques to easily capture and share chemical data, for example, using electronic lab notebooks [5]

_{[1] Nat. Chem. 2021, 13 (8), 771–777. https://doi.org/10.1038/s41557-021-00717-y.
[2] ChemRxiv 2021. https://10.33774/chemrxiv-2021-322h5.
[3] ChemRxiv 2021. https://10.33774/chemrxiv-2021-h3381-v2
[4] Nat Commun 2021, 12 (1), 2312. https://doi.org/10.1038/s41467-021-22437-0
[5] Chem. Sci. 2021, 12 (10), 3587–3598. https://doi.org/10.1039/D0SC05337F.} 

Talk 2 — Nonlinear transport with Berry-Boltzmann equations and Wannier functions

Stepan S. Tsirkin¹, Xiaoxiong Liu¹, Ivo Souza²

¹ Condensed Matter Theory, University of Zurich (UZH)
² Centro de Fisica de Materiales, San Sebastian, Spain.

There has recently been a huge renewed interest  to the study of currents generated in solids by external electrical and magnetic fields, especially in relation with topology, Berry curvature and Weyl points. The responses of interest include nonlinear anomalous Hall effect, crystal Hall effect, planar Hall effect, unidirectional magnetoresistance and electrical magnetochiral anisotropy among others. In this talk I will overview and systematize  these effects according to their properties with respect to the inversion and time-reversal symmetry, as well as by being  Hall-like (dissipationless) or Ohmic.   Next, I will show how the effects can be systematically described by the Boltzmann equations modified by Berry curvature and intrinsic magnetic moment of Bloch states - the so-called "Berry-Boltzmann" formalism.  Finally, I will address some aspects of ab initio evaluation of such responses within Wannier functions formalism, and how we are implementing it in the WannierBerri code.

Check the list of the next MARVEL Junior Seminars here.