The influence of a simple semiempirical van der Waals (vdW) correction on the description of dispersive, covalent, and ionic bonds within density functional theory is studied. The correction is based on the asymptotic London form of dispersive forces and a damping function for each pair of atoms. It thus depends solely on the properties of the two atoms irrespective of their environment and is numerically very efficient. The correction is tested in comparison with results obtained using the generalized gradient approximation or the local density approximation for exchange and correlation. The results are also compared with reference values from experiment or quantum chemistry methods. In order to probe the universality and transferability of the semiempirical vdW correction, a range of solids and molecular systems with covalent, heteropolar, and vdW bonds are studied.

The adsorption of adenine on graphite is analyzed from first-principles calculations as a model case for the interaction between organic molecules and chemically inert surfaces. Within density-functional theory we find no chemical bonding due to ionic or covalent interactions, only a very weak attraction at distances beyond the equilibrium position due to the lowering of the kinetic energy of the valence electrons. Electron exchange and correlation effects are much more important for the stabilization of the adsystem. They are modeled by the local density or generalized gradient approximation supplemented by the London dispersion formula for the van der Waals interaction.

We present a numerically efficient approach to solve the Bethe-Salpeter equation for the polarization function. Rather than from the usual eigenvalue representation, the macroscopic polarizability is obtained from the solution of an initial-value problem. This reduces the computational effort considerably and allows for calculating excitonic and local-field effects in optical spectra of complex systems consisting of many atoms. As an example we investigate the optical anisotropy of the monohydride $\mathrm{Si}\mathrm{}\left(001\right)(2\mathrm{}\times 1)$ surface. While excitonic effects influence the surface optical properties considerably, the local-field effect induced changes are minimal.

Oxygen reduction and water oxidation are two key processes in fuel cell applications. The oxidation of water to dioxygen is a 4 H⁺/4 e⁻ process, while oxygen can be fully reduced to water by a 4 e⁻/4 H⁺ process or partially reduced by fewer electrons to reactive oxygen species such as H₂O₂ and O₂⁻. We demonstrate that a novel manganese corrole complex behaves as a bifunctional catalyst for both the electrocatalytic generation of dioxygen as well as the reduction of dioxygen in aqueous media. Furthermore, our combined kinetic, spectroscopic, and electrochemical study of manganese corroles adsorbed on different electrode materials (down to a submolecular level) reveals mechanistic details of the oxygen evolution and reduction processes.