MATERIALS SCIENCE AND CHEMISTRY

Leveraging the computing power of HPC systems SuperMUC and SuperMUC-NG hosted at LRZ, researchers of the Munich University of Applied Sciences investigated the piezoelectric properties of ferroelectric hafnia and zirconia, which represent a novel material class based on the fluorite crystal structure. If properly doped, such thin films show large strain effects in field induced phase transitions. A large number of doped supercells were investigated with density functional theory to find the most appropriate dopants.

Metal hydrides have become of great scientific interest as high-temperature superconducting materials at high pressure, with hydrogen-hydrogen interactions suspected as critical in this behavior. Here, nuclear magnetic resonance experiments and electronic structure calculations are combined to explore the compression behavior of FeH and Cu₂H, and results show that within the hydrides a connected hydrogen network forms at significantly larger H-H distances than previously assumed. The network leads to an increased contribution of hydrogen electrons to metallic conduction, and seems to induce a significantly enhanced diffusion of protons.

In this project, the biophysics of Photosynthesis are probed employing high-performance computing. Photosynthesis is based on the Sun light and fuels the metabolic pathways of numerous organisms in our biosphere. However, fluctuations in the light intensity or quality are expected due to the diurnal cycle, or the environmental conditions and could be detrimental to plants. Absorption of light and tunnelling of the associated energy towards the reaction centres of the photosynthetic apparatus are finely-tuned within a well-orchestrated photoprotective mechanism. The atomic-scale details of this mechanism is probed by computational biophysics, with applications on the increase of crop yields and artificial photosynthesis.

To unravel the complexity of the solid state, researchers from the University of Würzburg have mastered very different and complementary methods. Density functional theory in the local density approximation with added dynamical local interactions using the dynamical mean-field approximation has the merit of being material dependent since one can include the chemical constituents of materials. Spacial and temporal fluctuations are crucial to understand e.g. the Iridates, a topic that is explored with the new pseudo-fermion functional renormalization group. Another aspect of this research are realistic quantum Monte Carlo simulations of free standing graphene aiming to elucidate the role of electronic correlations.

The water electrolysis in Proton Exchange Membrane (PEM) cells is fitting plenty of industrial requirements. The main drawback of PEM cells however is the overpotential of the oxygen evolution reaction. In its acidic environment iridium dioxide (IrO₂) is currently the only stable catalyst. Yet the low abundance of iridium makes a reduction of its loading inevitable. One approach to decrease the catalyst loading is the use of nanoparticles. For catalyst optimization a general understanding of shape and surface structure of these nanoparticles is required. In this project a protocol has been developed to generate and simulate IrO₂ nanoparticles based on energies of slab models and to provide insights regarding stability and structure.

Carbon nitride materials have attracted vast interest in the field of photocatalytic water splitting. However, the underlying mechanism is not fully understood. Herein, results are being reported from large-scale first-principles simulations for the specific electron- and proton-transfer processes in the photochemical oxidation of liquid water with heptazine-based photocatalysts. The results reveal that heptazine possesses energy levels that are suitable for the water oxidation reaction. Moreover, the critical role of the solvent in the overall water-splitting cycle is shown. A simple model is developed to describe the water oxidation mechanism.

Ziegler-Natta catalysts are important for industry, but determining exactly how they work is difficult due to their complex nature which involves a number of different active compounds on nano-sized structures. Researchersof the University of Turin led by Dr. Maddalena D’Amore have been using Density Functional Theory (DFT) to try to find out more about these types of systems.

Researchers carried out density functional theory defect calculations of materials relevant in energy applications. They calculated Raman spectra of LiCoO₂ which allow to follow the structural evolution during charging and discharging of this important class of lithium-ion battery cathode materials and to understand what can lead to their failure. Furthermore, the effect of defects forming on a dissolving metastable surface on the (photo)electrocatalytic performance were calculated, and the team worked on novel computational methods applied to defects that will enable DFT calculations of defects with a similar accuracy than state-of-the-art methods, however at a much-reduced computational cost.

In this project, researchers use state of the art fermion quantum Monte Carlo methods to understand emergent collective phenomena in correlated electron system. The scientists define and study theoretical models where topology emerges and leads to novel particles at quantum critical points. The flexibility of their approach also makes it possible to study the physics of magnetic moments in a metallic environment. This could, for instance, enable theoretical experiments for understanding magnetic adatoms on metallic surfaces. In this report, a succinct account of the ALF (Algorithms, Lattice, Fermions) program package, which was developed by the scientists, as well as a summary of selected research projects is provided.

Highly dispersed gold/titania catalysts are widely used for key reactions, notably including the selective oxidation of alcohols in the liquid phase using molecular oxygen. The mechanistic details of this reaction are mostly unknown. Especially the pivotal role of water in stabilizing charge transfer and its actual chemical role in the reaction mechanism is of great interest. In this project, scientists at the Ruhr-Universität Bochum use enhanced sampling ab initio molecular dynamics simulations to elucidate the mechanistic detail of thermally activated liquid-phase methanol oxidation focusing also on the activation of oxygen.

The electronic and optical properties of oxide surfaces and nanoparticles can be tuned by attaching specifically tailored organic molecules. This is employed in molecular electronics or when building dye-sensitized solar cells. Such a chemical functionalization is usually done in solution. In this work, advanced molecular dynamics sampling techniques based on a quantum-chemical description of the atomic interactions are used to obtain a fundamental understanding of the chemical reaction mechanisms at such solid-liquid interfaces. The simulations allow to identify the key reaction intermediates and they provide new insights into the important role of the hydrogen-bond network and the mobility of protons at the interface.

Researchers elucidate the molecular doping of prototypical representatives for the class of molecular semiconductors. As n-type dopants, molecular radicals, closed-shell molecules and metal-organic species are compared. By using the HPC system SuperMUC, they simulate doping-induced states and compare the simulations with ultraviolet photoemission and inverse photoemission spectra. One challenge in the simulations is the necessary accuracy of the computation of the involved energies in the doping process, which requires ab initio approaches. In addition, the disordered material blends include many complex molecules whose charging states and charging energies need to be simulated by taking into account the blend’s dielectric properties and…

Researchers at the Technical University of Munich study surface catalytic processes at a variety of scales, combining several different theoretical methods. They take into account the molecular scale of chemical reactions by first principles calculations of thermodynamic adsorption energies and kinetic reaction barriers. These calculations serve as input for mesoscopic models, which include the statistical interplay between the various chemical reactions and allow to predict macroscopic reaction rates and product selectivities. The work provides new insight into the mechanisms of catalytic reactions and gives important leads how to design improved catalyst materials.

The work horse of chemical industry is heterogeneous catalysis meaning that complex solid materials (catalysts) are used to facilitate chemical reactions, thus reducing production costs. To improve such catalysts in a systematic manner, knowledge of the ongoing reactions is most desirable. One of the key reactions industry performs at large scales is methanol (“wood alcohol”, H₃COH) synthesis from syngas being a mixture of gaseous CO₂, CO, and H₂. Scientists investigated the methanol production which is catalyzed using copper nanoparticles on a zinc oxide support. Based on sophisticated molecular dynamics sampling techniques in conjunction with the large-scale parallel platform SuperMUC at LRZ, they discovered a hitherto unknown complex…

Organisms which live under extreme conditions have established adaptation mechanisms during their evolution. One such mechanism with enables life under kbar pressures in deep sea habitats is an unusually high concentration of a specific molecule in their blood, namely TMAO (trimethylamine N-oxide). Yet, the so-called piezolytic mechanism which counteracts such high pressure effects within cells is not understood. As a first step, scientists investigated the properties of aqueous TMAO solutions at very high pressure compared to ambient conditions and find significant changes in the hydrogen bonding properties.

In an interdisciplinary collaboration, chemists and physicists design and investigate new quantum magnets that can be used as magnetic refrigerant materials for sub-Kelvin cooling. The research group tries to understand the magnetic properties of various molecules starting from assumptions about their pairwise interactions.The key problem, and the reason why supercomputers come into play, results from the quantum nature of the elementary magnetic moments.

Mechanical properties of liquid droplets are highly relevant in materials science and manufacturing. The thermodynamics of liquid droplets are also critical for many applications in energy technology, meteorology, and other fields where nucleation in a supersaturated vapour plays an important role. Using molecular dynamics simulations on SuperMUC, researchers investigated these phenomena to capture the length and time scale dependence of finite-size effects on the properties and the dynamics of nano-dispersed phases.

Scientists of the Department of Theoretical Physics and Astrophysics of the Universität Würzburg are leveraging the computing power of high performance computing system SuperMUC of the LRZ to perform model calculations which are particularly relevant for our understanding of low energy phenomena. These model calculations are essential for computing critical phenomena and associated critical exponents which define universality classes.

Exothermic surface chemical reactions may easily release several electron volts of energy. Fundamental questions regarding the conversion and dissipation of this microscopically sizable amount of energy are critical in e.g. present day energy production and pollution mitigation, and yet in many cases remain unanswered. Scientists of the Technische Universität München promote microscopic understanding through a novel multi-scale approach which, for the first time, allows to model energy dissipation into substrate phonons from first-principles.

Metal-Organic Frameworks (MOFs) are a new class of materials that in the last decade have seen a paramount growth and are expected to have huge impact on the development of next-generation technologies. They consist of inorganic nodes (i.e. a metal ion or a cluster) connected through organic linkers to form a porous 3D framework. The combination of different nodes and linkers makes MOFs very versatile materials with interesting and promising applications in many fields, including: gas adsorption, catalysis, drug delivery, nonlinear optics.

The ability to control and manipulate frictional forces at the nanoscale is extremely important for technology, being closely tied to progress in transportation, manufacturing, energy conversion, and lubricant consumption, impacting on innumerable aspects of our health and environment. In recent years a lot of effort has been devoted to gain control of friction at both the macroscopic and microscopic scale. However, most of the employed techniques cannot be straightforwardly extended to the nanoscale, where a flexible and almost cost-free way to dynamically tune friction forces is still lacking.

Using the vast computing power of GCS system SuperMUC, a team of scientists achieved a new world record with the to date largest molecular dynamics simulation: simulating 4.125*1012 particles on 146,016 cores with one time step taking roughly 40s.