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Daten sind ein wichtiger Rohstoff des 21. Jahrhunderts. Dies gilt besonders für die Materialwissenschaften. Das Fehlen einer effizienten Infrastruktur zum Datenaustausch hemmt allerdings den Fortschritt des Gebiets. Im Bereich der rechnergestützten Materialwissenschaften wurde in den letzten Jahren mit dem NOMAD CoE (Novel Materials Discovery – Center of Excellence) ein Kulturwandel hin zu einem umfassenden Data Sharing realisiert und der Weg für Big-Data-Analysen geebnet. Dies führt zu neuen Erkenntnissen bis hin zur Entdeckung neuartiger Materialien für technologisch wichtige Anwendungen. Data are an important raw material of the 21st century. This applies in particular to materials science. However, the lack of an efficient data exchange infrastructure is a major obstacle to this area's progress. In the field of computer-aided materials science, the NOMAD CoE (Novel Materials Discovery - Center of Excellence) has brought about a cultural change towards comprehensive data sharing and paved the way for big data analyses. This leads to new insights and even the discovery of new materials for technologically important applications.

Transmission electron microscopy has been a promising candidate for mapping atomic orbitals for a long time. Here, we explore its capabilities by a first-principles approach. For the example of defected graphene, exhibiting either an isolated vacancy or a substitutional nitrogen atom, we show that three different kinds of images are to be expected, depending on the orbital character. To judge the feasibility of visualizing orbitals in a real microscope, the effect of the optics' aberrations is simulated. We demonstrate that, by making use of energy filtering, it should indeed be possible to map atomic orbitals in a state-of-the-art transmission electron microscope.

In-situ monitoring is highly convenient for obtaining profound insight into growth processes. In particular, real time imaging during film formation allows an unambiguous identification of growth modes such as Frank van der Merwe Layer-by-Layer, Stranski–Krastanov or Vollmer–Weber island growth. Here, we discuss the benefits of using Low Energy Electron Microscopy (LEEM) as a tool for the application relevant deposition of para-Sexiphenyl on graphene and Ir{111} substrates. Changes in the growth mode can be identified and interpreted with ease directly from the real time LEEM observations. Examples of all three principal growth modes will be discussed together with a state of the art structure determination. The presented system is a prime candidate for the possible fabrication of thin organic light emitting diodes. It combines an optically active organic semiconductor with the transparent, flexible, and conductive electrode material graphene.

In inorganic epitaxy, intra- and interlayer surface diffusion processes—which are significantly influencing island nucleation and morphology evolution when growing under conditions far from equilibrium—are well understood. Using the rod-like organic molecule para-hexaphenyl, it is demonstrated that experimental and theoretical concepts developed to reveal the underlying atomic diffusion processes for inorganic systems can be applied to understand the growth of crystalline organic films. Here, we focus on the one hand on the determination of step-edge barriers, so-called Ehrlich-Schwoebel barriers, resulting in terraced growth mounds. On the other hand, we explore the island nucleation applying various approaches developed for inorganic systems. Compared to atomic systems, the anisotropy and complexity of the molecular building blocks yield a richer spectrum of diffusion processes resulting in novel phenomena as, e.g., level-dependent step-edge barriers for interlayer diffusion and peculiarities in the size of the critical nucleus.

To understand the link between doping and electronic properties in high temperature superconductors, we report first-principles calculations on the oxygen doping effect for the single layer cuprate HgBa$_2$CuO$_{4+\delta}$. The doping effect is studied both by supercell and single cell virtual crystal type approaches. We find ionic behavior of the dopant atom up to an optimal doping concentration of $\delta=0.22$. The excess oxygen attracts electrons from the CuO$_2$ plane leading to an increase of the hole concentration in this building block. The maximum amount of holes is reached when the oxygen $p$-shell is nearly completely filled. As a consequence the density of states at the Fermi level exhibits a pronounced maximum at the optimal oxygen content. The calculated hole content as a function of doping is in accordance with experimental findings., Comment: 4 pages, 4 figures, comments to sule@mfa.kfki.hu

The electronic structure of SrBi2Ta2O9 (SBT) is investigated from first-principles, within the local density approximation, using the full-potential linearized augmented plane wave (LAPW) method. The results show that, besides the large Ta(5d)-O(2p) hybridization which is a common feature of the ferroelectric perovskites, there is an important hybridization between bismuth and oxygen states. The role played by these two covalent bonds for driving the ferroelectric instability in SBT is investigated., Instituto de Física de Líquidos y Sistemas Biológicos