MARVEL Junior Seminar — November 2016

The MARVEL Junior Seminars aim to intensify interactions between the MARVEL Junior scientists belonging to different research groups located at EPFL. The EPFL community interested in MARVEL research topics is very welcome to attend. We believe that these events will be central for establishing a vibrant community.

Each seminar consists of two presentations of 25 minutes each, allowing to present on a scientific question in depth, each presentation being followed by 10 minutes for discussion. The discussion is facilitated and timed by the chairperson of the day whose mission is to ensure active lively interactions between the audience and the speakers. 

Pizza is served as of 11:45 just outside MED 2 1522 in the MED hall, and after the seminar at 13:30 you are cordially invited for coffee and dessert to continue discussion with the speakers.

MARVEL Junior Seminar Organizing Committee — Ariadni Boziki, Francesco Ambrosio, Fernando Gargiulo, Sandip De, Davide Tiana, Michele Pizzochero, Quang Van Nguyen and Nathalie Jongen

Check the list of the next MARVEL Junior Seminars in 2016-2017 here.

Abstract — Computational exfoliation of all known 3D materials - Nicolas Mounet 

As a first step towards the identification of novel and promising 2D materials, we provide here a large scale first-principles exploration and characterization of such compounds. From a combination of 480,000 non-unique structures harvested from the ICSD [1] and COD [2] databases, three-dimensional crystals are screened systematically by checking the absence of chemical bonds between adjacent layers, identifying close to 6,000 layered systems. Then DFT calculations of the van der Waals interlayer bonding are performed with automatic workflows, after full atomic and cell relaxations. In total, almost 2000 two-dimensional structures are found from this screening and are then classified in prototypes according to their similarity. Finally, the metallic, insulating or magnetic character of the materials obtained is assessed systematically. Thanks to the AiiDA materials' informatics platform [3], and in particular its automatic workflow engine, database structure, sharing capabilities, and pipelines to/from crystallographic repositories, the systematic and reproducible calculation of these properties becomes straightforward, together with seamless accessibility and sharing.

[1] http://www.fizkarlsruhe.com/icsd.htm

[2] S. Grazulis et al, Nucleic Acids Research, 40, D420 (2012).

[3] G. Pizzi, A. Cepellotti, R. Sabatini, N. Marzari and B. Kozinsky, Comp. Mat. Sci. 111, 218 (2016).

Abstract — High-throughput search for topological materials - Gabriel Autès 

Topological materials are materials whose phase is characterized by a topological order. Their non-trivial topology gives rise to many interesting phenomena such as topologically protected surface states or the emergence of exotic quasi-particles.

Many topological phases have been predicted, from the Chern insulator and the symmetry protected Z 2 and crystalline topological insulators, to the recently discovered Dirac and Weyl semimetals. For most of these phases, only a few if any materials are known. In order to identify new candidate materials, we performed a computational high-throughput screening of the band structure topology of compounds in the Inorganic Crystal Structure Database (ICSD), using density functional theory and the Z2Pack package [1].

After an introduction on topological matter and a description of the high-throughput methodology, two examples of predicted topological materials will be presented: the experimentally confirmed quasi one-dimensional Z 2 topological insulator β-Bi 4 I 4 [2] and the robust type-II Weyl semimetals XP 2 (X=Mo,W) [3]. 

[1] D. Gresch, G. Autès, O. V. Yazyev, M. Troyer, D. Vanderbilt, B. A. Bernevig, and A. A. Soluyanov, arxiv:1610.08983.

[2] G. Autès et al., Nature Materials 15, 154 (2016).

[3] G. Autès, D. Gresch, M. Troyer, A. A. Soluyanov, and O. V. Yazyev, Phys. Rev. Lett. 117, 066402 (2016).