MATERIALS SCIENCE AND CHEMISTRY

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.

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.

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.

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…

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.

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.

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.

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.

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.