Interface dipoles of organic molecules on Ag(111) in hybrid density-functional theory

We investigate the molecular acceptors 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA), 2,3,5,6-tetra uoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), and 4,5,9,10-pyrenetetraone (PYTON) on Ag(111) using densityfunctional theory. For two groups of the HSE(\alpha, \omega) family of exchange-correlation functionals (\omega = 0 and \omega = 0.2\AA) we study the isolated components as well as the combined systems as a function of the amount of exact-exchange (\alpha). We find that hybrid functionals favour electron transfer to the adsorbate. Comparing to experimental work-function data, we report for (\alpha) ca. 0.25 a notable but small improvement over (semi)local functionals for the interface dipole. Although Kohn-Sham eigenvalues are only approximate representations of ionization energies, incidentally, at this value also the density of states agrees well with the photoelectron spectra. However, increasing (\alpha) to values for which the energy of the lowest unoccupied molecular orbital matches the experimental electron affinity in the gas phase worsens both the interface dipole and the density of states. Our results imply that semi-local DFT calculations may often be adequate for conjugated organic molecules on metal surfaces and that the much more computationally demanding hybrid functionals yield only small improvements.Comment: submitted to New Journal of Physics (2013). More information can be found at http://th.fhi-berlin.mpg.de/site/index.php?n=Publications.Publication

Living history - education for human rights: evaluation of the funding programme "Meeting living witnesses – the lives of former forced labourers" - main outlines; draft report

"How do young people remember the Holocaust after more than 60 years? How can encounters with survivors contribute to an active remembrance? How does living history improve the sustainability of Education for Human Rights? In this context the 'Remembrance and Future'-Fund of the Foundation Remembrance, Responsibility and Future in Berlin asked the Research Group Youth and Europe at the C·A·P in Munich to give strategic advice by evaluating the nearly 2 Million Euro funding programme "Meeting living witnesses – the lives of former forced labourers" (2002-2005). The opinions of over one thousand young people in Germany, over one hundred living witnesses in Europe and almost fifty institutions were considered in the qualitative approach of this evaluation. Getting to know the victims of the Holocaust personally helps especially young people to come to a better understanding of the darkest hours of humanity. One of the greatest opportunities of those encounter programmes lies in making a change in perspective possible. As the results of the evaluation show, bridging the historical gap and deepening the knowledge about the Holocaust are the main benefits of the fund programme. Personal meetings with survivors have a significant effect on the memory culture of young people in Germany, who do not pay much attention to official commemoration ceremonies. At the same time encounter programmes encourage the emotional aspects of learning and promote empathy and self-reflection - a prerequisite for the education of tolerance and democracy among young people in the 21st century. The Draft Report is an English summary of the entire evaluation, which is published in German, see: Eva Feldmann-Wojtachnia/ Oliver Hofmann, 2006: Erinnern, Begegnen, Zukunft gestalten - Evaluation des Förderprogramms 'Begegnungen mit Zeitzeugen - Lebenswege ehemaliger Zwangsarbeiter'; Munich." (author's abstract

Distinguishing between Charge-Transfer Mechanisms at Organic/Inorganic Interfaces Employing Hybrid Functionals

When modeling inorganic/organic interfaces with density functional theory (DFT), the outcome often depends on the chosen functional. Hybrid functionals, which employ a fraction of Hartree–Fock exchange α, tend to give better results than the more commonly applied semilocal functionals, because they remove or at least mitigate the unphysical electron self-interaction. However, the choice of α is not straightforward, as its effect on observables depends on the physical properties of the investigated system, such as the size of the molecule and the polarizability of the substrate. In this contribution, we demonstrate this impact exemplarily for tetrafluoro-1,4-benzoquinone on semiconducting (copper-I-oxide Cu₂O) and metallic (Cu) substrates and explore how the simulated charge transfer depends on α. We determine the value α* that marks the transition point between spurious over-localization and over-delocalization of charges. This allows us to shed light on the interplay between the value of α* and the physical properties of the interface. We find that on the inert semiconducting substrate, α* strongly depends on surface screening. Furthermore, α has a significant impact on the amount of charge transfer and, in particular, the charge localization. Conversely, for the adsorption on Cu, α affects only the amount of transferred charge, but not its localization, which is a consequence of strong hybridization. Finally, we discuss limitations to the predictive power of DFT for modeling charge transfer at inorganic/organic interfaces and explain why the choice of a “correct” amount of Hartree–Fock exchange is difficult, if not impossible. However, we argue why simulations still provide valuable insights into the charge-transfer mechanism at organic/inorganic interfaces and describe how α can be chosen sensibly to simulate any given system

Ermittlung von Zusammenhängen zwischen enzymatischer Aktivität und Krankheiten durch die automatische Analyse wissenschaftlicher Publikationen

Aufgrund des schnellen Wachstums biomedizinischer Daten sowie der assoziierten Literatur wird es auch für Experten zunehmend schwierig, den Überblick über den aktuellen Wissensstand zu behalten. Der Aufbau und die manuelle Erweiterung von Datenbanken ist teuer und zeitaufwändig, kann jedoch durch linguistische Methoden unterstützt werden, welche Erkenntnisse automatisch aus der wissenschaftlichen Literatur extrahieren. Die vorliegende Dissertation stellt eine solche Methode zur Annotation von Enzymklassen mit krankheitsrelevanten Informationen vor. Die Enzymnamen von 3901 Enzymklassen der BRENDA, einer Sammlung von qualitativen und quantitativen Enzymdaten, wurden in einem Textkorpus aus über 100000 Kurzzusammenfassungen der PubMed-Datenbank identifiziert. Phrasen der Kurzzusammenfassungen konnten durch das MetaMap-Programm den Konzepten des UMLS (Unified Medical Language Systems) zugewiesen werden, was eine Identifikation der krankheitsrelevanten Begriffe mittels ihrer semantischen Felder in der UMLS-Ontologie erlaubte. Eine Zuordnung von Enzymklassen zu Krankheitskonzepten erfolgte aufgrund der gemeinsamen Nennung innerhalb eines Satzes. Die Zahl falscher Zuordnung konnte durch den Einsatz verschiedener Filter verringert werden. Verwendet wurden unter anderem die Mindestzahl gemeinsamer Nennungen, die Entfernung von Sätzen mit einer Negation sowie die Klassifikation unbekannter Sätze durch eine Support Vector Machine. Eine Überprüfung der Zuordnungen anhand 1500 manuell annotierter Sätze ergab eine Präzision von 95%, was eine direkte Erweiterung der BRENDA-Datenbank mit den gefundenen Zuordnungen erlaubte