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A series of novel hybrid molecules containing sulfur and nitrogen donor functions simultaneously has been synthesized and characterized. Designed for use in biomimetic coordination chemistry, these molecules are expected to act directly or in specific precursor roles as polyfunctional Lewis bases towards metal-based Lewis acids to form complexes with biological relevance. Their principal architecture is based on aliphatic or aromatic backbones connecting guanidine moieties with sulfur-containing thioether or disulfide portions. Based on acyclic tetramethylguanidino units and their cyclic dimethylethyl-substituted counterparts, a panel of forty-six members of this class of compounds are presented here. The associated denticity extends from bidentate (N/S donor sets) and tridentate (N/N/S donor sets) via tetradentate (N/N/S/S donor sets) to pentadentate (N/N/N/S/S donor sets). Five of these novel systems were structurally characterized and subjected to geometry optimizations using density-functional theory (DFT).

Rare earth induced silicide phases of submonolayer height and 5 × 2 periodicity on the Si(111) surface are investigated by density functional theory and ab initio thermodynamics. The most stable silicide thin film consists of alternating Si Seiwatz and honeycomb chains aligned along the [1\(\overline{1}\) 0] direction, with rare earth atoms in between. This thermodynamically favored model is characterized by a minor band gap reduction compared to bulk Si and explains nicely the measured scanning tunneling microscopy images.

The effect of oxygen impurities and structural imperfections on the coherent on-chain quantum conductance of poly(3-hexylthiophene) is calculated from first principles by solving the scattering problem for molecular structures obtained within density functional theory. It is found that the conductance drops substantially for polymer kinks with curvature radii smaller than 17 A and rotations in excess of about 60∘. Oxidation of thiophene group carbon atoms drastically reduces the conductance, whereas the oxidation of the molecular sulfur barely changes the coherent transport properties. Also isomer defects in the coupling along the chain direction are of minor importance for the intrachain transmission.

The frequency-dependent dielectric function and the second-order polarizability tensor of ferroelectric LiNbO3 are calculated from first principles. The calculations are based on the electronic structure obtained from density-functional theory. The subsequent application of the GW approximation to account for quasiparticle effects and the solution of the Bethe–Salpeter equation yield a dielectric function for the stoichiometric material that slightly overestimates the absorption onset and the oscillator strength in comparison with experimental measurements. Calculations at the level of the independent-particle approximation indicate that these deficiencies are at least partially related to the neglect of intrinsic defects typical for the congruent material. The second-order polarizability calculated within the independent-particle approximation predicts strong nonlinear coefficients for photon energies above 1.5 eV. The comparison with measured data suggests that self-energy effects improve the agreement between experiment and theory. The intrinsic defects of congruent samples reduce the optical nonlinearities, in particular for the 21 and 31 tensor components, further improving the agreement with measured data.

Combining orientation dependent electrically detected magnetic resonance and g tensor calculations based on density functional theory we assign microscopic structures to paramagnetic states involved in spin-dependent recombination at the interface of hydrogenated amorphous silicon crystalline silicon (a-Si:H/c-Si) heterojunction solar cells. We find that (i) the interface exhibits microscopic roughness, (ii) the electronic structure of the interface defects is mainly determined by c-Si, (iii) we identify the microscopic origin of the conduction band tail state in the a-Si:H layer, and (iv) present a detailed recombination mechanism.

The effect of ferroelectric poling on the water adsorption characteristics of lithium niobate Z-cut surfaces is investigated by ab initio calculations. Thereby we model the adsorption of H2O monomers, small water clusters and water thin films. The adsorption configuration and energy are determined as a function of the surface coverage on both the positive and negative LiNbO3(0001) surfaces. Thereby polarization-dependent adsorption energies, geometries and equilibrium coverages are found. The different affinity of water to the two surfaces is explained in terms of different bonding scenarios as well as the electrostatic interactions between the substrate and the polar molecules. Surface phase diagrams for the Z-cuts in equilibrium with water are predicted from atomistic thermodynamics.