Low-energy structures of zinc borohydride Zn(BH4_4)2_2

We present a systematic study of the low-energy structures of zinc borohydride, a crystalline material proposed for the hydrogen storage purpose. In addition to the previously proposed structures, many new low-energy structures of zinc borohydride are found by utilizing the minima-hopping method. We identify a new dynamically stable structure which belongs to the $I4_122$ space group as the most stable phase of zinc borohydride at low temperatures. A low transition barrier between $I4_122$ and $P1$, the two lowest-lying phases of zinc borohydride is predicted, implying that a coexistence of low-lying phases of zinc borohydride is possible at ambient conditions. An analysis based on the simulated X-ray diffraction pattern reveals that the $I4_122$ structure exhibits the same major features as the experimentally synthesized zinc borohydride samples.Comment: Version accepted by Phys. Rev. B. Manuscript has 8 pages, 5 figures, 2 tables (with 6 pages, 5 figures, 2 tables in supplemental material

The effect of ionization on the global minima of small and medium sized silicon and magnesium clusters

We re-examine the question of whether the geometrical ground state of neutral and ionized clusters are identical. Using a well defined criterion for being "identical" together, the extensive sampling methods on a potential energy surface calculated by density functional theory, we show that the ground states are in general different. This behavior is to be expected whenever there are metastable configurations which are close in energy to the ground state, but it disagrees with previous studies.Comment: 7 pages, 7 figure

Low-Energy Polymeric Phases of Alanates

Low-energy structures of alanates are currently known to be described by patterns of isolated, nearly ideal tetrahedral [AlH$_4$] anions and metal cations. We discover that the novel polymeric motif recently proposed for LiAlH$_4$ plays a dominant role in a series of alanates, including LiAlH$_4$, NaAlH$_4$, KAlH$_4$, Mg(AlH$_4$)$_2$, Ca(AlH$_4$)$_2$ and Sr(AlH$_4$)$_2$. In particular, most of the low-energy structures discovered for the whole series are characterized by networks of corner-sharing [AlH$_6$] octahedra, forming wires and/or planes throughout the materials. Finally, for Mg(AlH$_4$)$_2$ and Sr(AlH$_4$)$_2$, we identify two polymeric phases to be lowest in energy at low temperatures.Comment: 9 pages, 8 figures, 2 tables, including supplemental materia

Daubechies wavelets as a basis set for density functional pseudopotential calculations

Daubechies wavelets are a powerful systematic basis set for electronic structure calculations because they are orthogonal and localized both in real and Fourier space. We describe in detail how this basis set can be used to obtain a highly efficient and accurate method for density functional electronic structure calculations. An implementation of this method is available in the ABINIT free software package. This code shows high systematic convergence properties, very good performances and an excellent efficiency for parallel calculations.Comment: 15 pages, 11 figure

Aktualisierung und Weiterentwicklung des Praxishandbuches: Bio-Produkte ohne Gentechnik

Was können Landwirte, Verarbeiter und Händler tun, um genetische Verunreinigungen von Lebensmitteln zu vermeiden, und wie können sie bei Schäden Ersatz geltend machen? Bio- und Ohne Gentechnik-Produkte werden unter Verzicht auf den Einsatz von Gentechnik hergestellt. Das Handbuch beschreibt die relevanten biologischen Grundlagen, die rechtliche Situation sowie Eintragspfade und konkrete Maßnahmen zur Vermeidung von Kontaminationen. Kosten und Effizienz von qualitätssichernden Maßnahmen werden beispielhaft dargelegt. Das Handbuch gibt Tipps für die Kommunikation mit Kunden und erläutert, welche Beweise im Schadensfall für eine sichere Durchsetzung gesichert werden sollten. Die zweite Auflage des Handbuchs wurde umfassend aktualisiert. Es wurde erweitert um die Themen Futtermittel, Zusatzstoffe, Saatgut, die Ohne Gentechnik-Kennzeichnung sowie den Bereich der Kartoffel-Produktion. Das Handbuch ist kostenlos und ungekürzt abrufbar unter www.bioxgen.de. Es ist ein Projekt des Bund Ökologische Lebensmittelwirtschaft (BÖLW) und des Forschungsinstitut für Biologischen Landbau (FiBL Deutschland)

The crystal structure of cold compressed graphite

Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as Z-carbon, is formed by pure sp3 bonds and is the only carbon allotrope which provides an excellent match to unexplained features in experimental X-ray diffraction and Raman spectra of graphite under pressure. The transition from graphite to Z-carbon can occur through simple sliding and buckling of graphene sheets. Our calculations predict that Z-carbon is a transparent wide band gap semiconductor with a hardness comparable to diamond.Comment: 4 pages, 5 figure

Gaussian pseudopotentials with nonlinear core corrections for chemical accuracy

During the last decades, density functional theory (DFT) has proven its pivotal role for computational studies in the fields of condensed matter physics and quantum chemistry. Particularly the Kohn-Sham formalism (KS) of DFT has gained enormous popularity as an ab initio method applicable to relatively large systems. An essential ingredient for many large scale implementations of KS-DFT are pseudopotentials which are also frequently denoted as effective core potentials. Adding a non-linear core correction (NLCC) to the well established Dual Space Gaussian type pseudopotentials, new pseudopotentials are constructed for the Perdew Burke Ernzerhof (PBE) functional. These potentials exhibit impressive features of transferability and accuracy of the results, without increasing the hardness of the pseudoatom, and they are benchmarked with respect to highly precise all-electron results of different physical and chemical quantities. The error introduced by pseudopotential approximation is sensibly lower than the one given by any small or medium size Gaussian basis sets in an all-electron calculation. Our results show that, when combined with systematic basis sets, norm-conserving pseudopotential calculations can be as accurate as all-electron calculations

Besoldungs- und Versorgungsstrukturen des Ministeramtes. Eine Untersuchung zu den Ministergesetzen in Bund und Ländern

Erich Schmidt Verlag, Berlin 2000. 228 Seiten, kartoniert, 76,– DMISBN 3-503-05839-7 Was Regierungsmitglieder verdienen, wieviel Übergangsgeld sie erhalten sollen und welche Altersversorgung - diese Fragen sind in Wissenschaft und Öffentlichkeit in den vergangenen Jahren oft, teilweise kontrovers, diskutiert worden. Die Vielfalt der möglichen staatlichen Leistungen deutet auf ein großes Sicherungsbedürfnis hin. In der vorliegenden Arbeit werden erstmals ausführlich die finanziellen Leistungen des Bundes und der Länder sowie deren Rechtsgrundlagen in den Minister- und auch den Abgeordnetengesetzen untersucht. Ziel ist die Beantwortung der Frage, ob sich die derzeitige Ausgestaltung der Vorschriften in den Ministergesetzen über die finanziellen Ansprüche der amtierenden und ehemaligen Regierungsmitglieder mit den Anforderungen des Ministeramtes aus dem Grundgesetz und den Landesverfassungen vereinbaren lässt

Energy Landscape of Fullerene Materials: A Comparison of Boron to Boron Nitride and Carbon

Using the minima hopping global geometry optimization method on the density functional potential energy surface we show that the energy landscape of boron clusters is glasslike. Larger boron clusters have many structures which are lower in energy than the cages. This is in contrast to carbon and boron nitride systems which can be clearly identified as structure seekers. The differences in the potential energy landscape explain why carbon and boron nitride systems are found in nature whereas pure boron fullerenes have not been found. We thus present a methodology which can make predictions on the feasibility of the synthesis of new nanostructures