Reactions at surfaces studied by ab initio dynamics calculations

Due to the development of efficient algorithms and the improvement of computer power it is now possible to map out potential energy surfaces (PES) of reactions at surfaces in great detail. This achievement has been accompanied by an increased effort in the dynamical simulation of processes on surfaces. The paradigm for simple reactions at surfaces -- the dissociation of hydrogen on metal surfaces -- can now be treated fully quantum dynamically in the molecular degrees of freedom from first principles, i.e., without invoking any adjustable parameters. This relatively new field of ab initio dynamics simulations of reactions at surfaces will be reviewed. Mainly the dissociation of hydrogen on clean and adsorbate covered metal surfaces and on semiconductor surfaces will be discussed. In addition, the ab initio molecular dynamics treatment of reactions of hydrogen atoms with hydrogen-passivated semiconductor surfaces and recent achievements in the ab initio description of laser-induced desorption and further developments will be addressed.Comment: 33 pages, 19 figures, submitted to Surf. Sci. Rep. Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Hydrogen dissociation on metal surfaces - a model system for reactions on surfaces

Reactions on surfaces play an important role in many technological applications. Since these processes are often rather complex, one tries to understand single steps of these complicated reactions by investigating simpler system. In particular the hydrogen dissociation on surfaces serves as such a model system. There has been much progress in recent years in the theoretical description of reactions on surfaces by high-dimensional dynamics simulations on potential energy surfaces which are derived from ab initio total energy calculations. In this brief review I will focus on the hydrogen dissociation on the clean and sulfur-covered Pd(100) surface. These calculations established the importance of dynamical concepts like the steering effect. The electronic structure calculations allow furthermore the determination of the factors that determine the reactivity of a particular surface. This will be demonstrated for the poisoning of hydrogen dissociation by sulfur adsorption on the Pd(100) surface. In addition, quantum effects in the dynamics can be assessed by comparing the results of classical with quantum dynamical calculations on the same potential energy surface.Comment: 10 pages, 9 figures, submitted to Appl. Phys. Other related publications can be found at http://www.rz-berlin.mpg.de/th/paper.htm

Scattering of hydrogen molecules from a reactive surface: Strong off-specular and rotationally inelastic diffraction

Six-dimensional quantum dynamical calculations of the scattering of H_2 from a Pd(100) surface using a potential energy surface derived from density-functional theory calculations are presented. Due to the corrugation and anisotropy of the PES strong off-specular and rotationally inelastic diffraction is found. The dependence of the diffraction intensitities on the incident kinetic energy is closely examined. In particular we focus on the quantum oscillations for normal and off-normal incidence.Comment: RevTeX, 5 pages, 5 figures, to appear in Chem. Phys. Let

Seesaw scale, unification, and proton decay

We investigate a simple realistic grand unified theory based on the SU(5) gauge symmetry, which predicts an upper bound on the proton decay lifetime for the channels p→K+ν¯ and p→π+ν¯, i.e., τ(p→K+ν¯)≲3.4×1035 and τ(p→π+ν¯)≲1.7×1034  years, respectively. In this context, the neutrino masses are generated through the type I and type III seesaw mechanisms, and one predicts that the field responsible for type III seesaw must be light with a mass below 500 TeV. We discuss the testability of this theory at current and future proton decay experiments

Dynamical Quantum Processes of Molecular Beams at Surfaces: Dissociative Adsorption of Hydrogen on Metal Surfaces

Due to the improvement of computer power and the development of efficient algorithms it is now possible to combine high-dimensional quantum dynamical calculations of the dissociative adsorption of molecular beams with reliable ab-initio potential energy surfaces (PES). In this brief review two recent examples of such studies of the systems H_2/Cu(111), where adsorption is hindered by a noticeable energy barrier, and H_2/Pd(100), where activated as well as non-activated paths to adsorption exist, are presented. The effect of lateral surface corrugations on the sticking probability in the tunneling and the classical regime and the role of additional parallel momentum are discussed in the context of the H_2/Cu(111) results. For the system H_2/Pd(100) it is shown that the initial decrease of the sticking probability with increasing kinetic energy, which is usually attributed to a precursor mechanism, can be explained by dynamical steering. In addition, the influence of rotation on the adsorption and desorption dynamics is examined.Comment: RevTeX, 22 pages, 6 figure