MATERIALS SCIENCE AND CHEMISTRY

Bulk metallic glasses (BMGs) are known to have remarkable mechanical properties, such as high tensile strength, elasticity, and yield strength, which surpass those of many crystalline and polycrystalline metals. These properties make BMGs highly promising candidates for applications requiring materials that can withstand high and complex mechanical stress. However, BMGs have drawbacks; they show strain softening, resulting in localized deformation in the form of shear transformation zones that later lead to the formation of shear bands. This strain-softening characteristic limits their broader application potential, as it can lead to surface defects and, ultimately, fracture.

The efficiency of any opto-electronic device, such as a solar cell, light emitting diode, or photodetector, is intrinsically linked to the nature of the electronic quantum states of the photoactive material. For a deeper understanding and targeted development of new devices, an improved theoretical description of bound electronic excitations, i.e., excitons and trions, is crucial.

The exponential scaling in computational cost when simulating quantum many-body systems poses a significant challenge to their understanding. Variational methods, that approximate the state of the quantum system using an ansatz function, promise to lower that computational cost while making no approximations about the interactions that occur in the system. A novel type of ansatz function, which we explore thoroughly in this project, uses neural networks to approximate the state of the system. As is usual in deep learning, we rely heavily on the use of GPUs during execution, thereby making the use of the JUWELS Booster Module a necessity.

Periodically driven ultracold atomic systems can be used to engineer topologically nontrivial phases, and can give rise to anomalous topological phases with chiral edge modes in the presence of a trivial bulk (AFTI). We have investigated the role of additional quenched disorder and two-particle interactions on this state. Within an exact diagonalization study we have found signatures of the anomalous Floquet Anderson insulator (AFAI) phase within an experimentally realized model by calculating several indicators [1]. It supports quantized charge pumping through chiral edge states, while the bulk states remain completely localized. Moreover, we have developed an efficient new algorithm for calculating higher-order Chern numbers [2].

Although MD is a widely used and accepted method, there is often the need of comparison to experiment to validate the reliability of the findings. The development of supercomputers as well as the optimization of the used simulation code led to enormous changes in the achievable dimensions. Nevertheless, the simulation of an aluminum cube of 1 µm side length would contain about 60 billion atoms. To simulate this for a duration of 1 µs simulated time, with time step 1 fs, it would take 47,248 core years on a Cray XT5 system, based on the 1.49e-6 sec/atom/time step determined at the benchmark on the LAMMPS webpage [2].

Gallium oxide (Ga2O3), a transparent semiconducting oxide with a wide bandgap of around 4.9 eV, has emerged as a promising candidate for future applications in electronics (Schottky barrier diodes, field-effect transistors), optoelectronics (solar- and visible-blind photodetectors, flame detectors, light emitting diodes, touch screens), and sensing systems (gas sensors, nuclear radiation detectors) [2]. The monoclinic β phase is its most stable and studied polymorph. Compared to the bulk properties, research on its surface properties is still sparse. However, these play a crucial role in many processes and applications, such as epitaxial growth and electrical contacts.

Ammonia (NH3) is a versatile compound that finds applications in fertilizer production and fiber manufacturing. The industrial synthesis of ammonia relies on high temperatures and pressures, and requires large amounts of energy while emitting greenhouse gases. A more promising alternative is the electrochemical nitrogen reduction reaction (NRR), which offers a more efficient and environmentally friendly way for ammonia synthesis. Researchers from Technical University of Munich (TUM) have taken this concept further by utilizing artificial-intelligence methods to theoretically design and screen appropriate catalysts for the NRR process. These catalysts, known as single-atom catalysts, play a crucial role in facilitating the reaction.

The project "High performance computational homogenization software for multi-scale problems in solid mechanics" focusses on simulating Advanced High-Strength Steels (AHSS) using computational methods that consider the microscale grain structure. The virtual laboratory relies on high-performance computing and robust numerical methods to predict steel behavior before experimental testing. Computational homogenization reduces the number of degrees of freedom drastically and introduces natural algorithmic parallelism. The scalability of new nonlinear solution methods, as well as the FE^2 software FE2TI was demonstrated under production conditions. A complete virtual Nakajima test was performed leveraging the power of modern supercomputers.

Halide perovskites are booming as absorber materials for solar cells: they are cheap and easy to make in the lab while delivering devices with efficiencies of converting the energy of sunlight into electricity. An interesting, more fundamental aspect of these materials regards their atomic motions, which are unusual compared to other solar materials. Researchers at the Technical University of Munich used the power of the JUWELS cluster to investigate the impact of these atomic motions on the absorption of sunlight in halide perovskites. Their findings were intriguing: the strong atomic motions do not hinder but are in actuality a beneficial feature for the efficient collection of sunlight in halide perovskites.

Controlled and reversible opening and forming of chemical bonds allows to switch material properties by light or mechanical load. The controlled change of material properties to enable different functionalities is a promising route to the design of so-called programmable materials that allow the tailored control of materials functions by well-defined external stimuli. A system that can reversibly form and break bonds is the molecule anthracene. Two anthracene molecules can bind together upon stimulation by UV-light. Heating in turn leads to the release of the formed bonds and thus to the regeneration of the initial state. Here we show that mechanical forces considerably accelerate this backreaction and do not lead to irreversible bond…

Using HPC resources at the High-Performance Computing Center Stuttgart, a team led by Prof. Britta Nestler is improving sintering—a common process in advanced manufacturing.

Polymers are a broad class of materials: From nylon and rubber to materials for advanced material design, polymers are long chains of repeating units. Diblock copolymers consist of two halves that repel each other and self-assemble into different phases, creating shapes such as cylinders at the molecular scale. These cylinders arrange as parallel within an individual grain but, on large scales, there are multiple grains that differ in the orientation of their cylinders.

A group of researchers from the Fritz Haber Institute and Aarhus University in Denmark have leveraged the power of the JUWELS supercomputer at the Jülich Supercomputing Centre (JSC) to develop a machine learning algorithm that helps predict how specific molecules bind to the surface of a catalyst. Catalysts play an essential role in many chemical processes, and how specific molecules interact with these materials can influence the efficiency, effectiveness, and safety of chemical reactions at an industrial scale.

Simulations at the atomic level employing supercomputers are a powerful instrument to probe and design new materials or understand better already known ones. Such findings and discoveries could potentially lead to new landscapes regarding the usage of our planet’s resources. Here we present results of our quantum-mechanical simulations investigating the band gap properties of silicon (Si) and germanium (Ge) alloys with cubic and tetragonal symmetries. These alloys’ investigations were inspired by their synthesis using high pressure techniques.

Complex magnetic textures and localized particle-like structures on the nanometer scale such as chiral magnetic skyrmions with non-trivial topological properties are nowadays the most studied objects in the field of nanomagnetism. They offer the promise of new data storage and data processing technologies ranging from racetrack memories to memristive switches for neuromorphic computing. In this project we extend the realm of DFT calculations for magnetic systems to significantly larger setups from the basic description provided by our ab-initio code FLEUR

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.

Understanding the response of silicon and diamond to shear deformation is crucial to improve the performance of nanodevices and low friction coatings. Atomic length scale simulations show that the two materials differ significantly in their amorphization-mediated wear behavior: Externally applied pressure favors the wear of silicon, while it reduces the wear of diamond. For silicon, a shear-induced recrystallization process opposes amorphization. By choosing suitable orientations of two silicon crystals in the sliding contact, the combination of both phase transformations can be exploited to grow silicon crystals with nanoscale precision.

Synthetic or biological amphiphiles self-assemble into spatially modulated structures on the nanoscale with applications ranging from etch masks in semiconductor fabrication, over porous membranes for separation or energy applications, to the compartmentalization of living cells. Often, such systems do not reach thermal equilibrium but, instead, the structures are dictated by processing and kinetic pathways. These molecular simulations provide insight into the correlation between molecular structure and collective dynamics that alter the self-assembly. Two results are being highlighted: (i) the kinetically accessible states in the course of directed self-assembly and (ii) the kinetic pathway of the fusion of two apposing lipid membranes.

Focused ion beams can be used to pattern 2D materials and ultimately to create arrays of nanoscale pores in atomically thin membranes for various technologies such as DNA sequencing, water purification and separation of chemical species. Among 2D materials, transition metal dichalcogenides, and specifically, MoS₂, are of particular interest due to their spectacular physical properties, which make them intriguing candidates for various electronic, optical and energy conversion applications. Findings achieved by running large-scale molecular dynamics simulations to study the response of MoS₂ monolayer to cluster ion irradiation suggest new opportunities for the creation of 2D nanoporous membranes with an atomically thin nature.

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.

As most notorious greenhouse gas, CO₂ emissions prevail as high as about 364 million tons carbon with the concentration reaching over 400 ppm in the atmosphere. A drastic reduction of CO₂ is urgently necessary for sustainable growth and to fight climate change. The electrochemical reduction of CO₂ (CO2RR) is a promising approach to utilize renewable electricity to convert CO₂ into chemical energy carriers at ambient conditions and in small-scale decentralized operation. Researchers from Technical University of Munich have employed an active-site screening approach and proposed carbon-rich molybdenum carbides as a promising CO2RR catalyst to produce methanol.

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.

It is well-known that the catalytic properties of metals may extend beyond their melting point. Recently, this has been exploited to grow high-quality 2D materials such as graphene. To improve our understanding of the growth mechanism on liquid metal catalysts, researchers at the Technical University of Munich have employed a multi-scale modelling approach. Here, detailed simulations of various building blocks for the final graphene sheet such as simple hydrocarbons and smaller graphene flakes on solid and liquid Cu surfaces have been carried out. The insights from these simulations were then used to propose a mesoscopic model for the dynamics of graphene growth on molten Cu based on capillary and electrostatic interactions.

Computational fluid dynamics (CFD) simulations play an important role in today’s science and technology. Therefore, it is crucial to validate its underlying methods and models. This can be done by experiments or with molecular dynamics (MD) simulations, but in some cases only the latter are applicable. Since MD simulations follow the motion of each molecule individually, they are computationally very demanding, but they rest on an excellent physical basis. In this project, large systems of several hundred million atoms are considered to study the thermo- and hydrodynamic behavior of fluids during shock wave propagation, droplet coalescence and injection. The results are compared to that of macroscopic numerical methods.

A supramolecular polymer (SMP) has functional groups which interact with each other to form a physical bond. In contrast to chemical bonds, the bond formation in an SMP is reversible and the resulting aggregate morphology in a SMP melt thermally fluctuates. For functional groups allowing only a pairwise association, a ring aggregate is highly important as a ring topologically reduces the mobility of surrounding linear polymers by threading. Using molecular dynamics simulations of SMPs, the effect of ring aggregates on the system relaxation time governing rheological response was investigated. It was shown that the presence of ring aggregates slows down rheological response as measured by a reduction of the so-called entanglement length.

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.

Roughness of many natural and engineered surfaces follows a scaling law called self-affine scaling. In project chka18, the origins of self-affine have been investigated using Molecular Dynamics simulations. It was shown that the self-affine roughness emerges naturally during deformation of initially flat surfaces in different materials.

Within this project, the goal is to study and develop novel approaches to boost the performance of thin film solar cells. For this, 3D optical simulation of the photovoltaic devices is performed by discretizing Maxwell’s equations. A sophisticated light management is important to construct thin-film solar cells with optimal efficiency. The light management is based on suitable nano structures of the different layers and materials with optimized optical properties. The design, development and test of new solar cell prototypes with respect to an optimal light management are time consuming processes. For this reason, suitable models and simulation techniques are required for the analysis of optical properties within thin-film solar cells.

By applying approaches based on computational chemistry, researchers at the University of Marburg are addressing the challenge of designing functional materials in a novel way. Using computing resources at the High-Performance Computing Center Stuttgart, the scientists under leadership of Dr. Ralf Tonner model phenomena that happen at the atomic and subatomic scale to understand how factors such as molecular structure, electronic properties, chemical bonding, and interactions among atoms affect a material's behaviour.

Project DEFTD is focused on large scale computer simulations of the atomic, electronic and magnetic properties of novel materials for energy applications, first of all, fuel cells transforming chemical energy into electricity, and batteries. Understanding of a role of dopants and defects is a key for prediction of improvement of device performance which is validated later on experimentally. Addressing realistic operational conditions is achieved via combination with ab initio thermodynamics. The state of the art first principles calculations of large and low symmetry are very time consuming and need use of supercomputer technologies as provided at HLRS in Stuttgart.

This group from the Helmholtz-Institute Erlangen-Nürnberg performed simulations, both on a coarse-grained and a molecular level of detail, elucidating how so-called antagonistic salts, consisting of a large anion and a small cation, trigger the spontaneous formation of highly regular, nanometer sized structures in water/oil mixtures. Due to their size difference the small cations accumulate in the water phase while the large anions go to the oil phase. The resulting electrostatic interactions between the phases can lead to long-range ordering.

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.

Studying the mechanochemistry of disulfide systems upon nucleophilic attack is a very rich field where each system requires computing resources and CPU time that can only be provided by very powerful supercomputers such as provided by the Gauss Centre for Supercomputing. Simulations run on JUQUEEN of JSC in the course of this project offered a wealth of surprises and novel insights into mechanochemical reactions. While they resulted in discovering unexpected reaction mechanisms, they - amongst others - brought to light an unknown phenomenon with respect to splitting disulphide bonds in water.

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.

Direct bandgap silicon can be the key to integrate both electronic and optical functionalities on a silicon platform. Despite considerable effort, achieving light emission from group IV semiconductors has remained unattainable until now. Very recently, ab initio calculations combined with experiments could prove that Ge-rich hexagonal crystal phases of Si_xGe_1-x feature a direct bandgap, tunable in a frequency range coinciding with the low loss window for optical fiber communications. Efficient light emission from direct band gap SiGe could also be shown. Further calculations explore how to engineer light emission by strain and alloying.

Granular matter is typically the result of random pattern formation in a solid, like breaking a glass or pulverizing a rock into pieces of variable sizes. Faraday waves are patterns that appear on a fluid that is perturbed by an external drive that oscillates in resonance. Faraday waves aren't random; in contrast to granular matter, these waves are regular, standing, periodic patterns, seen for instance in liquids in a vessel that is shaken. Surprisingly, granulation and Faraday waves can exist in quantum systems too and, even more surprisingly, they can be produced in the same quantum system: in a gas of trapped atoms cooled very close to absolute zero temperature. When the strength of interactions between atoms is modulated, a Faraday…

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 DFG Project SCHM746/154-1 has the objective to investigate strengthening mechanisms in aluminum magnesium alloys using molecular dynamic simulations. Simulating tensile tests in the very short accessible time is leading to high strain rates. These high strain rates together with the limited size of the simulated model is repeatedly leading to retention towards findings by molecular dynamic simulations. To overcome these stigmata, a short insight into two investigations are presented in this project overview, where a good connection between experimentally obtained and simulated results is made.

Being able to handle and manipulate large molecules or other nano-objects in a controlled manner is a central ingredient in many bio- and nanotechnological applications. One increasingly popular approach, e.g., in microfluidic setups, is to use  dielectrophoresis. Here, the nano-objects are exposed to an alternating electric field, which polarizes them. Depending on the polarization, they can then be grabbed and moved around or trapped by an additional field. However, the mechanisms governing the polarization of the objects, which are typically immersed in a salt solution, are very complicated. Simulations allow to disentangle the different processes that contribute to the polarizability and to assess the influence of key factors such as AC…

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.

First-principles atomistic computer simulations which make it possible to simulate various materials without any input parameters from the experiment (except for the chemical elements the material consists of) are powerful tools in the modern materials science. Although they require supercomputers, they not only reproduce the structure and properties of the known materials, but also make it possible to predict new ones and describe the behavior of the system under various conditions, e.g., electron irradiation.  In this project, irradiation effects in two-dimensional (2D) inorganic materials were studied with the main focus on transition metal dichalcogenides. The intercalation of Li atoms into bilayer graphene was also addressed.

How fast can information travel in a quantum system? While special relativity yields the speed of light as a strict upper limit, many quantum systems at low energies are in fact described by nonrelativistic quantum theory, which does not contain any fundamental speed limit. Interestingly enough, there is an emergent speed limit in quantum systems with short ranged interactions which is far slower than the speed of light. Fundamental interactions between particles are, however, often of long range, such as dipolar interactions or Coulomb interactions. A very-large scale computational study performed on Hazel Hen revealed that there is no instantaneous information propagation even in the presence of extremely long ranged interactions and that…

One of the most influential chemicals in our daily lives is something many of us will never see: ethylene oxide. This chemical is a critical ingredient in our modern world, used to make everything from the plastic fibers of our clothes to the lubricants in our cars. Virtually all of it is produced by the catalytic reaction of ethylene and oxygen over a silver surface but, while this process has been known since 1931, just how it happens has remained a mystery. Researchers have used high-performance computing to gain new insight into this mystery by identifying the structure of the active catalyst surface and showing how it mediates the reaction of ethylene and oxygen to form ethylene oxide.

Particle-stabilised emulsions have long been studied for their unique properties, which have a number of different industrial applications. Leveraging the petascale computing power of JSC high-performance computing system JUQUEEN, scientists of the Eindhoven University of Technology have been using simulations to investigate these systems, the results of which are now being picked up by experimental groups and realised in practice.

Metallic glasses are very strong and nonetheless elastic, making them appealing for diverse engineering applications. Despite these favourable properties, the failure of metallic glasses sets in directly after the elastic limit, making them brittle. In this project, scientists at the Technische Universität Darmstadt investigate nanostructured metallic glasses as a possible solution to this problem using large-scale molecular dynamics simulations.

“If you want to understand function, study structure” (F. Crick). In the case of carbon, the very different properties of graphite, diamond, and carbon nanotubes can then be traced to different atomic arrangements. The elements provide a fruitful field of study in general. There are fewer than 100 stable elements, and trends can be identified more readily than in alloys with infinitely many compositions. He we describe cluster, amorphous, and liquid phases of the group 15 elements bismuth and antimony using molecular dynamics simulations based on density functional theory.

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…

Simulations have long been an integral part to supplement experiment and theory and became a powerful method to improve the understanding of physical phenomena. Leveraging the phase-field method - an established means for the investigation of the diffusion and phase-transformation-included microstructure evolution during solidification processes in 3D - materials scientists use high-performance computing to study representative volume elements resolving the multiphase microstructure which can be compared with experimental micrographs. Massive-parallel and highly optimized solvers are applied to increase the efficiencies of the simulations in the scientists' pursuit to investigate the directional solidification of binary and ternary eutectic…

Researchers at the University of Paderborn currently focus on the further development of the ring polymer path integral molecular dynamics method, and in particular on the simulation of vibrational spectroscopy methods. Leveraging the petascale computing capabilities of HPC system JUQUEEN, they have improved the current understanding of hydrogen bond cooperation by using a proper basis for its description, namely its energy.

Comprehension of processes in the deep Earth’s interior requires knowledge of the structure and properties of geologically relevant materials at high pressures and high temperatures. In this project, first-principles molecular dynamics simulations are employed to complement experimental efforts to study mainly structurally disordered materials under extreme conditions. For instance, in a recent study the structure of SiO₂ glass was studied up to pressures of more than 1.5 Mbar. Further, the feasibility of predicting element partitioning between melts from first-principles has been explored.

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.

Laser ablation is a technology which gains more an more importance in drilling, eroding, welding, structuring and marking of all kind of materials. The usage of shorter femtosecond laser pulses promises to improve the quality. Molecular dynamics simulations can contribute to new insights into the not completely comprehended ablation process with these short pulses. Researchers of the University of Stuttgart have developed a program package for the atomistic simulation of laser ablation which can deal with the coupling of the laser light, the heat conduction by the electrons, and the effects of a nascent plasma plume.

A team from the physics department of the Johannes Gutenberg University, Mainz, has investigated nucleation processes and interfacial properties of colloidal crystals. Nucleation is omnipresent in our daily life and describes events as diverse as the formation of rain in clouds, the crystallization of proteins or the growth of nano-particles. The studies undertaken using supercomputers Hazel Hen and Hornet of HLRS Stuttgart contribute towards a more fundamental understanding of these processes and the underlying theoretical foundation.

Ab initio calculations are carried out to study chemical processes and relaxation dynamics of water in its excited states upon photo-excitation. In this project, the researchers discovered an unusual non-grotthus-like proton transfer and a mixed localized and enhanced spin density distribution of solvated electron in water using combined Born-Oppenheimer molecular dynamics and time dependent density functional theory within periodic boundary condition. These investigations led to a deeper understanding of ultra-fast excited-state processes in fluids and are of general importance for physical chemistry of excited-state phenomena.

The properties of water at interfaces such as liquid/vapor and liquid/solid interfaces are relevant to many fundamental processes in atmospheric chemistry as well as in biology such as protein folding and aggregation mechanisms. Leveraging HPC resources available at the HLRS, researchers at the Johannes Gutenberg University in Mainz apply ab initio molecular dynamics simulations (AIMD) in both equilibrium and non-equilibrium conditions, as AIMD simulations are an ideal tool for accurate descriptions of heterogeneous condensed phase systems. By simulating the behaviour of water at the nanoscale, the scientists aim for a better understanding about its properties at the interface.

Nanoscale wires can change from insulators to conductors when struck by a laser pulse. This phase transition occurs extremely fast — as fast as quantum mechanics allows, in fact — something that was previously thought to be impossible on surfaces. Scientists of the University of Paderborn and Duisburg–Essen leveraged the computing power of HPC system Hazel Hen for simulations to explain the physics behind this unexpected discovery.

For the development of new communication and computing technologies, conceptually new materials and device architectures are needed. One pathway of increasing the efficiency of e.g. integrated transistor circuits is to implement photonic functionality to the devices. With the HLRS project “GaPSi”, researchers of the University of Marburg contribute to the developments in designing and producing optically active compound semiconductor materials that can be integrated into conventional silicon-based technology.

Rewritable optical storage media, such as the digital versatile disk (DVD-RW) and Blu-Ray Disc, are based on the extremely rapid and reversible crystallization of amorphous “bits” in thin polycrystalline layers of special alloy materials. The ultimate limit to the speed (and therefore usefulness) of such devices is the speed of crystallization of the amorphous structure, and the nature of the process has been the subject of much speculation. Insight is provided by simulations of crystallization of an amorphous alloy of germanium, antimony, and tellurium (GST) that is widely used as a component of commercial optical memories.

Disulfide bonds are known to stabilize protein structures by imposing covalent cross-links. More recently they have been found to regulate protein activity as well by undergoing chemical reactions themselves. However, the chemistry of disulfide bond cleavage reactions is astonishingly rich and includes also β-elimination reactions in alkaline solution instead of the usual nucleophilic substitution at one of the sulfur atoms. Using HPC system JUQUEEN, an international team of scientists computationally studied both reaction channels as a function of increasingly large mechanical forces.

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.

Long charging times in mobile energy storage devices limit their applicability. Supercapacitors can fill this technological gap, providing quick charging in the range of minutes with the drawback of less energy being stored compared to high-end lithium-ion batteries. Realistic simulations of carbon-based nanoporous electrodes immersed in mixtures of ionic liquids and organic solvents can give insight about the optimal composition of the electrolyte and the molecular mechanisms of the charging process in supercapacitors.

Researchers use ab-initio density functional theory (DFT) to unravel the effects of lattice vibrations on the electronic and optical properties of semiconductor nanostructures and how they can influence carrier dynamics in the femtoseconds to tens of picosecond time range. The scientific interest resides in the understanding of fundamental physics and in a reliable assessment of the importance of carrier relaxation, dephasing, and temperature effects, which are relevant for semiconductor nanodevices.

Prebiotic Chemistry is the study of those chemical reactions that could have taken place on the early Earth by which, starting from small molecules like H₂O, NH₃, CO₂, SH₂ or simple amino acids, more complex molecules were formed. This leads eventually to the formation of biomacromolecules as we know them from today's life, for instance proteins, RNA or DNA but also lipids. Advanced computer simulations in conjunction with large-scale HPC facilities and scalable codes allow one to investigate at the very molecular level not only how these reactions could have happened, but more importantly how they are affected by factors like temperature, pressure, or the presence of mineral surfaces to name but a few. 

Light emission in the fireflies is the product of a reaction catalysed by an enzyme named luciferase. The product of this reaction is the oxyluciferin, which in turn emits visible light. Scientists studied the interplay between the structural and absorption properties of oxyluciferins with an unprecedented level of accuracy.

One of the major challenges in understanding silver’s unique ability to catalyze the partial oxidation of ethylene to ethylene oxide is identifying how different forms of oxygen on silver react with ethylene. Using a highly parallelizable open-source DFT code for electronic-structure calculations and materials modeling at the nanoscale, scientists aimed at achieving a realistic picture of the chemistry of ethylene epoxidation.

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.

High performance materials with defined properties are crucial for the development and optimization of existing applications. Especially the possibility of exploiting the advantages of different materials are in focus of the research of high performance alloys as they are needed in applications with high mechanical and thermal requirements, e.g. in automobile, aerospace, and turbines.

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.

The disastrous impact of anthropogenic carbon dioxide (CO₂) emissions on the environment is very well known. The most mature technology for post-combustion CO₂ capture, currently in use in the chemical industry, exploits a cyclic process, in which CO₂ is selectively and reversibly absorbed in an amine (aqueous) solution. However, the operating costs are still too high to allow for large-scale implementation. A large empirical effort is ongoing worldwide primarily to reduce the high energy penalty required for amine regeneration and to increase the rate of CO₂ absorption into the solvent.

Water is called the substance of life: it covers most of the planet, it constitutes the largest fraction of our body, we drink it every day. Water actively participates in most chemical processes in nature, and will be the source of Hydrogen as we transition to clean and renewable energy. Surprisingly, and despite its abundance and importance, water is still poorly understood. In fact, more than 100 anomalous properties of water are known, water ice floating on liquid water being the most eye-catching one. The origin of the complexity is the subtle forces between water molecules, which derive from electrostatic, repulsive, hydrogen bonding, and van der Waals interactions. Getting the balance between these forces right is key for all of soft…

Aluminum alloys are widely used construction materials. A long tradition in metallurgy provides a lot of knowledge concerning the material behavior while different alloying surcharges are added or manufacturing processes are passed through. The strengthening in Aluminum-Copper alloys is based on different mechanisms, which are namely solid solution hardening, precipitate- and grain-boundary-strengthening. To investigate these empirical well known effects on atomistic length scale Molecular Dynamics (MD) simulations are indispensable.

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.

It has been a long-standing goal to understand the quantum physics of interacting quantum many-body systems. From the experimental side, the realization of Bose-Einstein condensates in 1995 provided scientists with such a system that is under almost perfect control: the confinement, the strength of interactions, and even the dimensionality of the Bose-Einstein condensate – a vapor of ultracold bosonic atoms held and cooled with lasers and magnetic fields – can be altered almost at will.

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.

In order to initiate chemical reactions, energy must be provided in order to overcome the so-called activation barrier, which separates the reactants from the product of the reaction. This energy can be supplied in different forms such as heat, light, electrical current or as mechanical forces that distort the molecules involved.

Prof. Hannu Häkkinen (University of Jyväskylä, Finland) and his team are employing large-scale time-dependent density functional theory calculations to study absorption of light by 2-3 nm gold and alloyed gold-silver nanoclusters that are defined to the molecular precision, i.e., by exact composition and structure. The project aims at breakthroughs in microscopic understanding of the "birth of a plasmon" in nanoscale noble metal clusters.

Molecular dynamics methods represent most powerful theoretical tools for getting insight in how processes run on the atomic scale. Everything seems to be fairly simple and maybe routine if classical Newtonian mechanics can be used and if (most importantly!) the electronic state of the studied system does not change during the time evolution. However, if the latter is not the case (we speak about non-adiabatic processes in this case), the situation is much more involved and very much more computationally demanding.

Droplets play a crucial role in many fields of science and technology. A fundamental understanding of droplet dynamics is essential for the optimization of technical systems or the better prediction of natural phenomena. Particularly in energy technology, many processes that are associated with droplets occur under extreme conditions of temperature or pressure, e.g. flash boiling in combustion chambers. Such processes are actively being used although striking gaps remain in the essential understanding of droplet dynamics.

Silicon is the most popular semiconductor material in science and industry. It is used for electronic devices with a variety of large-scale applications such as photo-voltaics and computer chips. Up to now, silicon is mainly used in microelectronic applications using its ability for electric conduction. Nevertheless, applications are reaching several physical limits mainly connected with the rapidly decreasing size of electric devices (e.g. transistors). To circumvent the technological bottleneck we are approaching, many ideas were put forward. One idea is to use light instead of electrons for signal transmission combined with the highly developed silicon manufacturing processes.

The challenge of understanding how ice and gas hydrates form, especially at the molecular level, represents one of Nature’s most elusive mysteries. Concretely, such a knowledge of nucleation mechanisms may allow for the development of anti-nucleation agents to prevent the unwanted formation of ice or gas hydrates in gas pipelines, a major industrial goal of ‘flow assurance’. 

In graphene, a two-dimensional material with remarkable properties, electrons move on a honeycomb lattice and exhibit the same energy-momentum dispersion relation as massless Dirac fermions. Because of the two-dimensional character, the Coulomb interaction between electrons is not screened and leads to a strongly correlated system whose collective properties can be very different from that of individual electrons. The study of such systems has a long and fruitful history, and spans research fields as distinct as high-temperature superconductors and biological systems. 

To yield molecular insight into the structure and dynamics of melt chains close to the surface and the resulting property changes of the composite, scientists study a melt of 1,4-polybutadiene.

To study phase separation of colloid-polymer mixtures after a quench into the two phase region in a slit-pore geometry, a team of scientists from the Institute of Physics of the Johannes Gutenberg-Universität Mainz and the Forschungszentrum Jülich employ a multiscale approach, the so-called "multiparticle collision dynamics" method using GCS supercomputers.

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.

The interaction of water with surfaces is of ubiquitous relevance in many different contexts, such as corrosion, electrochemistry, or biological systems, just to name a few. Still, our knowledge of atomistic processes at such interfaces is limited.

Mechanical stress can not only accelerate chemical reactions but also induce novel reaction pathways and possibly novel products. A team of scientists from the Lehrstuhl für Theoretische Chemie at Ruhr-Universität Bochum developed computational machinery to simulate such stressed molecules at the molecular level in the “virtual lab”.

Phase transitions are striking, abrupt transitions in the structure of a substance. Some of them are familiar from everyday experience, for example the freezing of water, or the condensation of vapor to form mist or clouds in the atmosphere.

Chemical processes help create everything from plastic containers to antifreeze to fertilizers. Many products and materials humanity uses daily come from a field only around 100 years old. Through those hundred years, chemical companies pushing the boundaries of science have often had to play a dangerous game of trial and error while experimenting with compounds.