MATERIALS SCIENCE AND CHEMISTRY

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.

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.

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.

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…

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…

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.

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…

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.

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.

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.

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.

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.

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.

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.

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 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.