TMTSF2X Salts. Preparation,Structure and Effect of the Anions

The preparation of the TMTSF molecule and some of its properties are reviewed. The preparation of metallic and superconducting TMTSF X salts is described and some structural aspects are discussed, with emphasis of possible order-disorder transitions when X is a non-centrosymmetric anion. Preliminary results for TMTSF₂ TeF₅ which remain conducting to at least 5 K are presented.     

Molecular clusters in two-dimensional surface-confined nanoporous molecular networks: structure, rigidity, and dynamics

The self-assembly of a series of hexadehydrotribenzo[12]annulene (DBA) derivatives has been investigated by scanning tunneling microscopy (STM) at the liquid/solid interface in the absence and presence of nanographene guests. In the absence of appropriate guest molecules, DBA derivatives with short alkoxy chains form two-dimensional (2D) porous honeycomb type patterns, whereas those with long alkoxy chains form predominantly dense-packed linear type patterns. Added nanographene molecules adsorb in the pores of the existing 2D porous honeycomb type patterns or, more interestingly, they even convert the guest-free dense-packed linear-type patterns into guest-containing 2D porous honeycomb type patterns. For the DBA derivative with the longest alkoxy chains (OC20H41), the pore size, which depends on the length of the alkoxy chains, reaches 5.4 nm. Up to a maximum of six nanographene molecules can be hosted in the same cavity for the DBA derivative with the OC20H41 chains. The host matrix changes its structure in order to accommodate the adsorption of the guest clusters. This flexibility arises from the weak intermolecular interactions between interdigitating alkoxy chains holding the honeycomb structure together. Diverse dynamic processes have been observed at the level of the host matrix and the coadsorbed guest molecules.     

Sterically Active Electron Pairs in Lead Sulfide? An Investigation of the Electronic and Vibrational Properties of PbS in the Transition Region Between the Rock Salt and the α-GeTe-Type Modifications

Recently, we have investigated the energy landscape of PbS for many different pressures on the ab initio level by using Hartree-Fock and density functional theory to globally search for possible thermodynamically stable and metastable structures. The perhaps most fascinating observation was that besides the experimentally known modification exhibiting the rock salt structure a second minimum exists close-by on the landscape showing the low-temperature α-GeTe-type structure. In the present study, we investigate the possible reasons for the existence of this metastable modification; in particular we address the question, whether the α-GeTe-type modification might be stabilized (and conversely the rock salt modification destabilized) by steric effects of the non-bonding electron pair.     

Unser tägliches Brot. Zum Erntedank

Bread is regarded as an ultimate “bioproduct without any chemistry.” This is simply not true because chemistry is the basis for the entire bread-manufacturing process from the grain right up to the freshly baked loaf. Its chemical reactions are very complex and we only have a rough idea of what's really going on when kneading the dough and baking the bread. Therefore, attempts of chemists with laboratory but not cuisine experience to produce bread according to scientific principles may lead to more or less edible and digestible products but they cannot compete with the masterpieces of a trained and experienced baker. But that's how it is. Chemistry is necessary for a culinary wonder but sometimes though it is better to let craftspeople with professional experience create the chemical masterpieces and then lean back and simply enjoy things!     

Density functionals and model Hamiltonians: Pillars of many-particle physics

Density-functional theory (DFT) and model Hamiltonians are conceptually distinct approaches to the many-particle problem, which can be developed and applied independently. In practice, however, there are multiple connections between the two. This review focuses on these connections. After some background and introductory material on DFT and on model Hamiltonians, we describe four distinct, but complementary, connections between the two approaches: (i) the use of DFT as input for model Hamiltonians, in order to calculate model parameters such as the Hubbard U and the Heisenberg J. (ii) The use of model Hamiltonians as input for DFT, as in the LDA + U functional. (iii) The use of model Hamiltonians as theoretical laboratories to study aspects of DFT. (iv) The use of special formulations of DFT as computational tools for studying spatially inhomogeneous model Hamiltonians. We mostly focus on this fourth combination, model DFT, and illustrate it for the Hubbard model and the Heisenberg model. Other models that have been treated with DFT, such as the PPP model, the Gaudin–Yang δ$\delta$-gas model, the XXZ chain, variations of the Anderson and Kondo models and Hooke’s atom are also briefly considered. Representative applications of model DFT to electrons in crystal lattices, atoms in optical lattices, entanglement measures, dynamics and transport are described.