van der Waals interactions of polycyclic aromatic hydrocarbon dimers

Density functional theory is in principle exact and includes also long-range interactions, such as the van der Waals interactions. These are, however, part of the exchange-correlation energy functional that needs to be approximated, and are absent in the local and semilocal standard implementations. Recently a density functional which includes van der Waals interactions for planar systems has been developed, which we show can be extended to provide a treatment of planar molecules. We use this functional to calculate binding distances and energies for dimers of three of the smallest polycyclic aromatic hydrocarbons (PAHs)--naphthalene, anthracene, and pyrene.     

ATR and transmission analysis of pigments by means of far infrared spectroscopy

In the field of FTIR spectroscopy, the far infrared (FIR) spectral region has been so far less investigated than the mid-infrared (MIR), even though it presents great advantages in the characterization of those inorganic compounds, which are inactive in the MIR, such as some art pigments, corrosion products, etc. Furthermore, FIR spectroscopy is complementary to Raman spectroscopy if the fluorescence effects caused by the latter analytical technique are considered. In this paper, ATR in the FIR region is proposed as an alternative method to transmission for the analyses of pigments. This methodology was selected in order to reduce the sample amount needed for analysis, which is a must when examining cultural heritage materials. A selection of pigments have been analyzed in both ATR and transmission mode, and the resulting spectra were compared with each other. To better perform this comparison, an evaluation of the possible effect induced by the thermal treatment needed for the preparation of the polyethylene pellets on the transmission spectra of the samples has been carried out. Therefore, pigments have been analyzed in ATR mode before and after heating them at the same temperature employed for the polyethylene pellet preparation. The results showed that while the heating treatment causes only small changes in the intensity of some bands, the ATR spectra were characterized by differences in both intensity and band shifts towards lower frequencies if compared with those recorded in transmission mode. All pigments' transmission and ATR spectra are presented and discussed, and the ATR method was validated on a real case study. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Quality management in wastewater treatment plants

A quality management system has been designed for process analyses in wastewater plants. The quality management concept consists of a quality manual, quality control charts used together with certified reference materials, and proficiency testing. Certified reference materials have been used to eliminate basic analytical errors. Proficiency testing has been conducted by VKI, the Reference Laboratory for Environmental Chemistry, subcontracted by the Danish Environmental Protection Agency. In the first proficiency test the analytical quality was comparable in general to the quality of routine environmental laboratories. One of the simplified analytical systems resulted, however, in a low recovery of nitrate in wastewater. The COD results reported in the proficiency test were slightly higher than the theoretical values.     

Stacking interactions and the twist of DNA

The importance of stacking interactions for the Twist and stability of DNA is investigated using the fully ab initio van der Waals density functional (vdW-DF). Our results highlight the role that binary interactions between adjacent sets of base pairs play in defining the sequence-dependent Twists observed in high-resolution experiments. Furthermore, they demonstrate that additional stability gained by the presence of thymine is due to methyl interactions with neighboring bases, thus adding to our understanding of the mechanisms that contribute to the relative stability of DNA and RNA. Our mapping of the energy required to twist each of the 10 unique base pair steps should provide valuable information for future studies of nucleic acid stability and dynamics. The method introduced will enable the nonempirical theoretical study of significantly larger pieces of DNA or DNA/amino acid complexes than previously possible.     

Application of van der Waals density functional to an extended system: adsorption of benzene and naphthalene on graphite

It is shown that it is now possible to include van der Waals (vdW) interactions via a nonempirical implementation of density functional (DF) theory to describe the correlation energy in electronic structure calculations on infinite systems of no particular symmetry. The vdW-DF theory [Phys. Rev. Lett. 92, 246401 (2004)] is applied to the adsorption of benzene and naphthalene on an infinite sheet of graphite, as well as the binding between two graphite sheets. A comparison with recent thermal-desorption data [Phys. Rev. B 69, 155406 (2004)] shows great promise for the vdW-DF method.     

Absolute configurations of the histamine liberating sesquiterpene lactones thapsigargin and trilobolide

The absolute configuration of trilobolide and the revised one of thapsigargin classify the compounds as a group of guaianolides previously not found in higher plants.     

van der Waals interaction of simple, parallel polymers

We study the mutual interactions of simple parallel polymers within the framework of density-functional theory (DFT). As the conventional implementations of DFT do not treat the long-range dispersion [van der Waals (vdW)] interactions, we develop a systematic correction scheme for the nonlocal energy contribution of the polymer interaction at the intermediate to the asymptotic separations. We primarily focus on the three polymers, polyethylene, isotactic polypropylene, and isotactic polyvinylchloride, but the scheme presented applies also more generally to other simple polymers. From first-principle calculations we extract the geometrical and electronic structures of the polymers and the local part of their interaction energy, as well as the static electric response. The dynamic electrodynamic response is modeled on the basis of these static calculations, from which the nonlocal vdW interaction of the polymers is extracted.