EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Fast and accurate interatomic potentials are critical for atomistic modeling in materials science, physics and chemistry. Driven by machine learning (ML) recent years have seen rapid progress in the field. In contrast to most ML models, the atomic cluster expansion (ACE) provides a complete representation of the atomic energy, expressed in polynomial multi-atom basis functions. ACE is amenable...

Large-scale atomistic simulations play an important role in the multiscale materials modeling approach. Traditionally, these simulations rely on the classical interatomic potentials. Classical potentials have proven useful for multiple applications thanks to their performance and linear scaling with the system size. However, these potentials often describe chemical behavior of the materials...

Stable and fast ionic conductors for magnesium cathode materials have the prospect of enabling high energy density batteries beyond current Lithium-ion technologies. So far, only a few candidate materials have been identified leading to data only being scarcely available. One of the reasons is the long time it takes to quantify ion conductivity computationally. This limits the development of...

Studying fundamental mechanisms of deformation in metals and alloys requires dependable interatomic potentials because dislocations and cracks are above scales accessible with first-principles calculations. While classical potential forms like the modified embedded atom method (MEAM) have been successfully employed in many cases, non-fcc metals and almost all alloys are not modeled...

I will make the somewhat bold claim that over the past 10 years, a new computational task has been defined and solved for extended material systems: this is the analytic fitting of the Born-Oppenheimer potential energy surface as a function of nuclear coordinates under the assumption of medium-range interactions, out to 5-10 Å. The resulting potentials are reactive, many-body, reach accuracies...

Metal-organic frameworks (MOFs) represent a highly porous class of materials formed by metal nodes connected by organic linkers. Their modular nature enables an almost limitless pool of possible materials leading to a wide range of different applications like gas storage, gas separation or catalysis. Many of the processes occurring during these applications rely on the dissipation of heat....

The generalized-gradient approximation within DFT is a workhorse of computational chemistry especially in modeling metal particles and chemical transformations at their surface. Mixed metal oxides that may be reduced during operation pose a very special challenge to computational methods, as standard DFT methods do no longer provide reliable results. This talk will highlight typical challenges...

Quaternary chalcogenides, $A$Zn$CX_{4}$ with $A$=Cu,Ag, $C$=Si,Ge, and $X$=S,Se, are potential building blocks for the third generation of thin film solar cells. While the prime examples like Cu$_2$ZnSnS$_4$ and Cu$_2$ZnSnSe$_4$ crystallise in the kesterite structure, for the other quaternary chalcogenides different crystal structures can be found, e.g. stannite, wurtz-kesterite, and...

Ab initio databases such as the NOMAD repository or the Materials Project have become a useful and quickly available tool in materials design. However, all these databases consist primarily of T=0K energies, whereas typical experimental conditions for materials design correspond to finite temperatures for which free energies are the relevant quantities. An accurate description of free energies...

Guided design of metallic alloy materials,
such as high entropy alloys (HEA),
necessitates reliable prediction of equilibrium properties of solid
solutions. However, traditional methods based on density functional
theory (DFT) with semi-local exchange correlation (XC) functionals suffer
from systematic errors in the determination of the equilibrium volume,
which in turn leads to errors...

Modern industrial alloys for nuclear energy are complex multicomponent materials with a wide range of concentration of components. Precipitates of secondary phases form during thermal and radiation aging. These precipitates play crucial role in hardening of the materials. Experimental verification of promising candidate alloys is expensive and time-consuming process. Therefore, methods of...

A phase diagram provides a wealth of information, such as coexistence lines, phase stability and phase changes along the thermodynamic variables. It is crucial that an interatomic potential is able to describe significant sections of the phase diagram reliably. The calculation of phase diagrams requires estimating the Helmholtz and Gibbs free energy of the different phases and its variation...

Silver chloride, AgCl, is well known crystalline solid that has been greatly recognized for its photoactive properties for two centuries and as such is intensively researched up to date. It can be prepared in variety of structural forms and morphologies and on various size scales. Intriguingly, no other crystallize phase of silver with chlorine is known [1]. This is quite surprising...

It has been believed that diffusion of a vacancy in metals becomes suppressed by hydrogen because of forming a stable hydrogen-vacancy complex. The fact that excess hydrogen can enhance greatly the self-diffusion of atoms in metals has been usually explained by the appearance of superabundant vacancies, because the vacancy formation energy decreases substantially with increasing H...

In this work, we apply atomistic simulations to consider hydrogen behavior in Fe in presence of the given lattice distortions, namely, defects or lattice expansion/compression due to applied stresses. Simulations are based on two different interatomic potentials describing Fe-H system: the one from Ramasubramaniam et al [1] and the other one developed by the authors of the current work [2]....

Hydrogen embrittlement is a fundamental problem in materials science which affects structural materials such as steel. Several mechanisms at the atomic length scale have been proposed, one is hydrogen enhanced decohesion (HEDE), where H accumulates on crystallographic planes and reduces the interplanar cohesion. Grain boundaries could have a significant role in HEDE since they can act as traps...

In ZnO varistors, understanding and controlling the microstructure plays a fundamental role, since the number and character of grain boundaries determines the current-voltage characteristics. In this context the so-called inversion boundaries (IBs), a special class of grain boundaries, are a key to microstructure design. IBs are formed by inverting the ZnO-stacking in the polar [0001]-axis...

Solute segregation at grain boundaries has a profound influence on the properties of
polycrystalline materials. Here, we are using first-principles methods, i.e. Density Functional Theory (DFT), to determine the binding energies of solutes to the Σ5{013}<100> grain boundary in a BCC Ti-25at%Mo alloy. Mo is added as an alloying element in the simulations to stabilize the BCC phase using a...

Grain boundary segregation of Cr, Cu, Mn, Mo, Ni, P and their effects on cohesion in bcc-Fe were studied by means of density functional theory simulation. Four model grain boundaries were considered in our studies: the $\Sigma$3(1$\bar{1}$1)[110], $\Sigma$3(1$\bar{1}$2)[110], $\Sigma$9(2$\bar{2}$1)[110] and $\Sigma$11(3$\bar{3}$2)[110], selected as representatives for "stacking fault",...

Cu is a common metallization material in integrated circuits due to its low resistivity. However, it shows a low adhesion to the dielectric layer and reacts with Si reducing the lifetime of the device. To improve the adhesion and chemical stability, an interlayer such as WTi is needed. The interfacial and mechanical properties of the Cu-WTi system have not been studied in detail and need...

Grain boundary (GB) segregation is a crucial factor for controlled engineering of materials properties like toughness, creep resistance, nanocrystalline stability or electrical conductivity. An important first step to tailor such properties is the knowledge of the segregation and precipitation state resulting from specific production processes including heat treatment steps. This calls for a...

Understanding segregation phenomena is a critical aspect of integrated computational materials design. In this connection, the segregation energies plays a central role and large databases are being created to get a comprehensive overview over materials. With the availability of such databases, machine learning approaches can be used to learn the trends in the periodic table and get...

Cu has been used in a wide variety of applications ranging from power generation and transmission to electronics. Stress-induced voids are amongst the most commonly reported defects in Cu. Since voids are formed by the condensation of vacancies, certain regions within the material like grain boundaries (GBs) have been considered as efficient sinks and thus favorable sites for the void...

Unlike conventional alloys, high entropy alloys (HEAs) contain up to six chemical elements in
nearly equiatomic proportion. Such a composition allows to stabilize solid solutions, exhibiting
in particular impressive mechanical properties and a ‘sluggish’ diffusion. The ternary bcc Zr-Ti-
Nb system is an interesting model HEA; it has a high yield strength and good ductility at...

One of the biggest challenges in the design and operation of nuclear reactors is to achieve a deep understanding of changes in material properties under the extreme conditions of the reactor core. In this context, one of the key safety limiting factors is the impact of severe neutron radiation; a complex, multi-scale problem. In general, accumulation and evolution of atomic-scale defects can...

Diffusion in high entropy alloys (HEAs) has been attracting significant attention in the community of developing advanced HEAs. As vacancies act as one of the most critical vehicles for atom transport, the knowledge of vacancy properties is of great importance for gaining physical insight into the related diffusion mechanisms. Theoretical prediction of vacancy properties in concentrated...

Plastic deformation of metals is a complicated phenomenon that links behaviour of crystal defects with macroscopic change of a sample shape. It is known that one of the basic mechanisms of plasticity is a motion of dislocations under applied stress. In this work, on the example of Mo and Nb, the study of plastic deformation in bcc metals was performed with multi-scale modelling. The...

Understanding the atomic-scale plasticity of bcc transition metal tungsten is crucial for many industrial applications, including components of nuclear fusion reactors that face extreme levels of irradiation. The modeling of dislocations as well as irradiation induced defects, however, remains extremely challenging as it requires simulations of large atomic ensembles with DFT accuracy. In this...

Common polymorph of silver difluoride (AgF2) at ambient pressure has layered antiferromagnetic structure. The phase exhibits numerous structural and electronic similarities with oxocuprate precursors of high-temperature superconductors. The 2D antiferromagnetically (AFM) ordered sheets along with large super-exchange constant possess the same topology as [CuO2] layers in the high-temperature...

Alloying elements segregate to interfaces and reduce their migration rates due to solute drag. Semi-quantitative solute drag models proposed by Cahn, Lücke and Stüwe have been applied successfully to interpret experimental observations of grain boundary migration in the presence of solutes. This allows to extract empirical solute drag parameters such as solute segregation energy and...

Metal-organic frameworks (MOFs) are an emerging materials class which, due to their high (nano-)porosity, can be used for numerous applications such as gas separation/capture or encapsulation and release of drugs. Functional devices based on these hybrid materials are becoming increasingly important, calling for a precise knowledge of the materials’ mechanical, thermal, electronic, optical,...

During the last decade, the spin-orbit interaction has played an increasingly crucial role in condensed matter physics, thanks to its relevance as a rich microscopic mechanism from the fundamental point of view and as a driving force for innovative spintronic applications on the technological side. Combined with the global thrust towards miniaturization and with the ubiquitous research in...

Strongly-correlated materials are sometimes defined as systems, where standard formulations of density functional theory do not work any more for a proper description of the electronic properties. We will show in this talk how to incorporate strong correlations in ab-initio calculations via the dynamical mean-field theory. This combination, coined DFT+DMFT, allows to describe Mott insulators...

Two-dimensional (2D) crystals have been attracting enormous research interest owing to their great potential in the future nanoelectronics. In particular, 2D magnetic materials have gained more and more attention recently. Nevertheless, most of the 2D materials are intrinsically non-magnetic, and strategies like impurity doping, defect engineering, etc. are investigated extensively to induce...

The dipole-dipole interaction—a relativistic term in the Breit-Pauli Hamiltonian—is not treated explicitly in non-relativistic spin density functional theory, its influence on the total energy of periodic systems being neglected due the square of the fine structure constant that scales it. This magnetostatic energy contribution may, in magnetically isotropic systems, be negligible, yet it is...

Photopolymers serve as basis for stereolithography, an additive manufacturing process which gains increasing attention due to its high throughput and exceptional spatial resolution. Photopolymers provide high stiffness, strength and heat deflection temperature, but they frequently lack toughness which limits their field of application. A deeper understanding of the structure-property relations...

The growing interest in the development of magnetic cooling devices based on magnetocaloric materials has led to an intensive search for new materials with a more attractive performance to cost ratio. High-throughput (HT) studies, based on first-principles calculations, have the potential to lead the search for new materials. In this approach, relevant systems are identified within a large...

Computational models of metal-organic frameworks (MOFs) have been mostly limited to infinite periodic systems with unit cells of just a few nanometers in diameter because these are, from a computational perspective, relatively easy to simulate through the use of periodic boundary conditions. However, recent experimental evidence on MOFs has demonstrated how their physical properties are...

Electronic properties of graphene are sensitive to its environment and can be altered by adsorption of atomic clusters$^1$$^,$$^2$. These structure serves experimentally to probe the properties of the cluster and to tailor the properties of graphene$^2$$^,$$^3$. This work aims at studying the interaction between graphene and Au$_n$ (n=1-6) cluster using density functional theory calculations....

I will present theoretical approaches for modeling dynamics of molecules on surfaces from first principles. I will cover examples such as scattering and adsorption of CO on metals[1], laser-induced desorption from surfaces[2], and vibrational relaxation on surfaces[3]. The methodology will range from advanced DFT methods such as ab-initio molecular dynamics and density functional perturbation...

Introduction

Artificial ammonia production is mainly based on the Haber-Bosch process, which requires a high energy input to activate the inert and stable nitrogen molecule. Photocatalysis is an alternative for environmentally friendly ammonia production using light, nitrogen and water [1]. Theoretical methods at the atomistic level can provide significant insight into the structure and...

Although zeolites are very important for many industries, their formation is still not fully understood due to the difficult experimental conditions in which formation occurs. On the other hand, theoretical models have been hampered by the troublesome modeling of hydrogen bonds present in the crucial water solvent. Recently, a new synthesis route was proposed whereby the main problems for...

High strength Ni-based superalloys are of great importance for high-temperature industrial applications due to the existence of the ordered L12 Ni$_3$Al phase (γ’ precipitates). The antiphase boundary energy (APBE) associated with the γ’ precipitates determines the mechanical properties when dislocations cut through the precipitates. In this work, the temperature-dependent APBEs of the L12...

Storing methane in clathrates is one of the most promising alternatives for transporting natural gas (NG) as it offers similar gas densities as liquefied and compressed NG while offering lower safety risks. However, the practical use of clathrates is limited given their unfavourable synthesis conditions, with sluggish kinetics and extreme operation factors (low temperatures and high...

Star polymers have been used as model systems to study more complex architectures of industrial relevance. They exhibit rich dynamical response ranging from linear-like to coloidal-like behavior. The key characteristic determining their properties is their penetrability, which is related to their inner structure. Experimental evidence suggests that the penetrability and thus the softness of...