Theoretical investigations of novel zinc oxide polytypes and in-depth study of their electronic properties

Zinc oxide is one of the most investigated compounds in materials science, both experimentally and theoretically, while in nature it appears only rarely, as the mineral zincite. Yet there are still many open questions: Is it still possible to observe or synthesize new modifications of zinc oxide? And can we improve the properties of a material that has already been investigated in thousands of studies? What is the connection between zincite, zinc sulfide and zinc oxide, and can we finally explain the controversial mineral matraite? In short, Yes: the answer to these questions is polytypism. We identify a multitude of possible stable polytypes for zinc oxide, and we show that by varying the stacking order, we can fine-tune the electronic properties such as the direct primary and secondary band gaps in zinc oxide without adding dopant atoms

Theoretical modifications of scandium oxychloride in extreme conditions as an example of rare earth compounds

Theoretical modifications of ScOCl at extreme thermodynamic conditions have been identified and are studied as an example of rare earth element (RRE) compounds. Global optimizations with empirical potentials and local optimizations on the ab initio level were performed, leading to the identification of four new structure candidates on the energy landscape that are expected to be relevant under extreme conditions. The structural, as well as electronic properties of these polymorphs, have been investigated and compared with the modifications of the structure under standard conditions. Such theoretical explorations are very important since literature data regarding ScOCl is rather scarce, although ScOCl and the rare-earth elements (REEs) in general have a wide range of applications; for example, scandium is used in solid oxide fuel cells and could be used for potential future applications in photocatalysis or electronic devices, while oxyhalides of transition metals and REEs exhibit interesting magnetic and electronic properties

Data-driven discovery and DFT modeling of Fe4H on the atomistic level

Since their discovery, iron and hydrogen have been two of the most interesting elements in scientific research, with a variety of known and postulated compounds and applications. Of special interest in materials engineering is the stability of such materials, where hydrogen embrittlement has gained particular importance in recent years. Here, we present the results for the Fe-H system. In the past, most of the work on iron hydrides has been focused on hydrogen-rich compounds since they have a variety of interesting properties at extreme conditions (e.g. superconductivity). However, we present the first atomistic study of an iron-rich Fe4H compound which has been predicted using a combination of data mining and quantum mechanical calculations. Novel structures have been discovered in the Fe4H chemical system for possible experimental synthesis at the atomistic level.International Conference on Structural Integrity 2023 (ICSI 2023

DFT study of new hybrid organic-inorganic perovskites: guanidinium-BX3 substituted by B=(Sr2+, Ca2+, Mg2+, Be2+) and X=(Cl-, F-)

Program and book of abstracts / 2nd International Conference on Innovative Materials in Extreme Conditions i. e. (IMEC2024), 20-22 March 2024 Belgrade, Serbia

The presence of superoxide ions and related dioxygen species in zinc oxide—A structural characterization by in situ Raman spectroscopy

Zinc oxide exhibits unique properties that are reflected in a wide variety of applications, particularly in the field of transparent, conductive films. However, less attention has been paid to their color. Here, we present the synthesis of yellow-gray ZnO films at room temperature by femtosecond pulsed laser deposition. In situ Raman investigations of these polycrystalline ZnO films reveal the existence of superoxide ions, O2−, in zinc oxide, which are responsible for the yellow color, and are also detected in ZnO powder and single crystals. In addition, further dioxygen species are identified in the samples, including the O2-molecule. The negative charge excess caused by the dioxygen species creates metallic zinc as a byproduct. Structural analysis reveals an unforced realization of the dioxygen species in the ZnO lattice. Density functional theory (DFT) calculations support the assumed structural displacements as well as the observed, unexpected Raman bands. These results open up completely new insights into the behavior of ZnO

Multifield Ultralight Dark Matter

Ultralight dark matter (ULDM) is usually taken to be a single scalar field. Here we explore the possibility that ULDM consists of $N$ light scalar fields with only gravitational interactions. This configuration is more consistent with the underlying particle physics motivations for these scenarios than a single ultralight field. ULDM halos have a characteristic granular structure that increases stellar velocity dispersion and can be used as observational constraints on ULDM models. In multifield simulations, we find that inside a halo the amplitude of the total density fluctuations decreases as $1/\sqrt{N}$ and that the fields do not become significantly correlated over cosmological timescales. Smoother halos heat stellar orbits less efficiently, reducing the velocity dispersion relative to the single field case and thus weakening the observational constraints on the field mass. Analytically, we show that for $N$ equal-mass fields with mass $m$ the ULDM contribution to the stellar velocity dispersion scales as $1/(N m^3)$. Lighter fields heat the most efficiently and if the smallest mass $m_L$ is significantly below the other field masses the dispersion scales as $1/(N^2 m_L^3)$.Comment: 11 pages, 7 figures, to be submitted to PR

Synthesis, Characterization, and Electronic Properties of ZnO/ZnS Core/Shell Nanostructures Investigated Using a Multidisciplinary Approach

ZnO/ZnS core/shell nanostructures, which are studied for diverse possible applications, ranging from semiconductors, photovoltaics, and light-emitting diodes (LED), to solar cells, infrared detectors, and thermoelectrics, were synthesized and characterized by XRD, HR-(S)TEM, and analytical TEM (EDX and EELS). Moreover, band-gap measurements of the ZnO/ZnS core/shell nanostructures have been performed using UV/Vis DRS. The experimental results were combined with theoretical modeling of ZnO/ZnS (hetero)structures and band structure calculations for ZnO/ZnS systems, yielding more insights into the properties of the nanoparticles. The ab initio calculations were performed using hybrid PBE0 and HSE06 functionals. The synthesized and characterized ZnO/ZnS core/shell materials show a unique three-phase composition, where the ZnO phase is dominant in the core region and, interestingly, the auxiliary ZnS compound occurs in two phases as wurtzite and sphalerite in the shell region. Moreover, theoretical ab initio calculations show advanced semiconducting properties and possible band-gap tuning in such ZnO/ZnS structures

Study of lanthanum fluoride selenides using a combination of crystal structure prediction and DFT calculations with experimental synthesis and characterization

Program and book of abstracts / 2nd International Conference on Innovative Materials in Extreme Conditions i. e. (IMEC2024), 20-22 March 2024 Belgrade, Serbia

Energy Landscapes 2019

This article summarizes the presentations delivered at the Energy Landscapes Conference held in Belgrade, Serbia, from 26 to 30 August 2019. The focus of the conference was on the present state of the art in theoretical energy landscape approaches, and their applications in the fields of chemistry, physics, biology, and materials science in general. The presentations were organized around some of the hot topics, such as applications from spectroscopy to the solid-state, folding and misfolding of proteins, DNA and RNA, multiscale modeling, materials under extreme pressure/temperature conditions, designing landscapes for self-assembly and multifunctional systems, landscapes for machine learning, atomic, molecular, colloidal and nanoalloy clusters