Highlights

Recent experiments have shown that adding palladium (Pd) to the high-entropy alloy CoCrFeNi produces a material that is significantly stronger. In the paper Origin of high strength in the CoCrFeNiPd high-entropy alloy, NCCR MARVEL researchers led by Prof. Bill Curtin, head of EPFL’s Laboratory for Multiscale Materials Modelling, show how a recent parameter-free theory for initial yield strength in random alloys predicts a strength of CoCrFeNiPd that is in good agreement with experimental results. The strengthening is mainly due to the large misfit volume of Pd in CoCrFeNi.

Researchers including Professor Oleg Yazyev, chair of Chair of Computational Condensed Matter Physics at EPFL, and scientist QuanSheng Wu have shown that flat bands are a fundamental feature twisted double bilayer graphene (TDBG) rather than the result of any external fields and have identified a so-called magic angle of 1.3 degrees, at which both electron and hole gaps are maximized. A separate paper, published together with experimental colleagues in China, shows that TDBG is an easily tunable platform for exploring quantum many-body states thanks to vertical displacement fields. The corresponding papers were recently published in Nano Letters and Nature Physics, respectively. 

New collaborative work involving NCCR MARVEL researchers has provided additional insight into the nature of jacutingaite (Pt2HgSe3), a species of platinum-group mineral first discovered in a Brazilian mine in 2008. The new studies show that the material is one of only a few known dual-topological insulators, featuring different surface states that are linked to crystalline symmetries rather than to the topological properties of the 2D monolayer, which is a quantum spin Hall insulator (QSHI). The work has been published in Physical Review Letters and Physical Review Research. 

Heterogeneous catalysts are often preferred in industrial settings because of their robustness and lower operating costs, but homogenous catalysts still dominate when high selectivity is needed—finding superior heterogeneous catalysts has been a challenge. A recent collaboration between the Paul Scherrer Institute's experimental Syncat Group, led by Marco Ranocchiari, and EPFL’s Laboratory of Molecular Simulation, a computational group led by Berend Smit, has shown how micropores in metal-organic frameworks (MOFs) can enhance selectivity to levels that cannot be achieved with existing catalysts. Though the findings have significant potential in the production of aldehydes, the easy experimental protocol and the chemical and structural flexibility of MOFs means that the approach represents a powerful tool for designing selective catalytic heterogeneous processes in the fine chemical industry overall. A paper on the research has just been published in Nature Communications.

NCCR MARVEL researchers at EPFL’s Chair of Computational Condensed Matter Physics (C3MP) and colleagues have developed an artificial neural network (ANN) model that may serve as a basis for solving inverse problems. Their approach reaches the same level of accuracy as the now commonly used maximum entropy (MaxEnt) method for low-noise data, performs significantly better than this standard technique when the noise strength increases, and features a reduction in computational cost by orders of magnitude. The research has just been published in Physical Review Letters.

Michele Simoncelli, a PhD student here at EPFL, together with Andrea Cepellotti, a former EPFL student now at Harvard, and Nicola Marzari, head of EPFL's Theory and Simulation of Materials laboratory as well as director of NCCR MARVEL, have developed a novel set of equations for heat propagation that goes beyond Fourier’s law and explains why and under which conditions heat propagation can become fluid-like, rather than diffusive. These "viscous heat equations'' show how heat conduction is not only governed by thermal conductivity, which was introduced by Fourier in his well-known macroscopic law of heat conduction, but also by another quantity, thermal viscosity. The theory is in striking agreement with pioneering experimental results in graphite published last year and may pave the way for the design of the next generation of more efficient electronic devices. The paper, Generalization of Fourier's law into viscous heat equations, has been published in Physical Review X.  

Wannier90—a computer program for generating maximally-localized Wannier functions and using them in the computation of advanced electronic properties of materials—has become a community code with a wide base of contributors over the last few years. This has resulted in a major new release with novel features described in the paper Wannier90 as a community code: new features and applications, published in Journal of Physics: Condensed Matter.

Though researchers have been looking for solid-state electrolytes that could enhance both the safety and performance of lithium-ion batteries for decades, no thoroughly suitable candidate has yet been found. Computational screening may offer better chances of success than previous methods of investigation, largely led by chemical intuition and experiment, but such methods must also meet certain criteria. In a recent paper published in the journal Energy & Environmental Science, NCCR MARVEL researchers Leonid Kahle, Aris Marcolongo and Nicola Marzari present a suitable computational framework for predicting the diffusion of Li-ions in solid-state materials, show how to employ it in large-scale computational screening and use it to identify new ceramic compounds for further experimental investigation. 

Researchers led by Stefan Goedecker at the University of Basel have developed an algorithm allowing for the rapid identification of entire reaction pathways in complex systems. Applying it to C60 and C20H20, they show that the reaction pathways found contain valuable information on how these molecules can be synthesized. The paper was recently published in Physical Review Letters. 

Chemical engineers led by Berend Smit, MARVEL deputy director and head of the Laboratory of Molecular Simulation at EPFL have designed a material that can capture carbon dioxide from wet flue gases better than some commercial materials. The work has been published in Nature.

In a recently published paper, Relative Abundance of Z2 Topological Order in Exfoliable Two-Dimensional Insulators, researchers from MARVEL director Nicola Marzari’s Laboratory of theory and simulation of materials (THEOS) screened a comprehensive database and identified 13 monolayers that are dynamically stable and potentially exfoliable quantum spin Hall insulators. This highlights a relative abundance of such topological order of around 1%. The paper was published in Nano Letters.

NCCR MARVEL and CCMX, the Competence Centre for Materials Science and Technology, hosted their third annual Materials Science Day on October 8 to present both experimental and modeling approaches to the development of innovative new materials. The event, meant to highlight cutting-edge research and give people a chance to network, drew more than 60 people from industry and academia.