Behrooz Razaznejad

Goldstone tensor modes

In the context of brane solutions of supergravity, we discuss a general method to introduce collective modes of any spin by exploiting a particular way of breaking symmetries. The method is applied to the D3, M2 and M5 branes and we derive explicit expressions for how the zero-modes enter the target space fields, verify normalisability in the transverse directions and derive the corresponding field equations on the brane. In particular, the method provides a clear understanding of scalar, spinor, and rank r tensorial Goldstone modes, chiral as well as non-chiral, and how they arise from the gravity, Rarita-Schwinger, and rank r+1 Kalb-Ramond tensor gauge fields, respectively. Some additional observations concerning the chiral tensor modes on the M5 brane are discussed.

Adiabatic potential-energy surface of O2/Al(111): rare entrance-channel barriers but molecularly chemisorbed state apt for abstraction

Abstract Extensive density-functional calculations of the adiabatic potential-energy hypersurface for O 2 adsorption on the Al(111) surface present (i) an entrance-channel barrier only under some very rare conditions and (ii) a molecularly chemisorbed intermediate state for a non-parallel molecule. The predicted metastable molecular state is stabilized by a Hunds rule spin effect on the very inequivalent oxygen atoms of the non-parallel O 2 in the strong Al-surface field. It provides a source for abstraction, i.e. dissociative decay by emission of one oxygen atom.

Dissociative adsorption of NO upon Al(111): Orientation dependent charge transfer and chemisorption reaction dynamics

The dissociative and abstractive chemisorption dynamics of NO on Al(111) were studied. A higher sticking probability for the N end-on of NO onto Al(111) was measured. In contrast, Auger electron experiments reveal stepped surfaces to be oxygen rich at low coverage after exposure to NO. Density functional theory calculations show (i) a few angstroms from the surface, an N end-on first collision geometry results in electronic structures consistent with charge transfer; (ii) there is stabilization on the surface for N end-on or side-on orientations; (iii) dissociation is enhanced by a partial or full flip of the molecule.

Potential--energy surfaces for excited states in extended systems.

With a simple and physically intuitive method, first-principles calculations of potential-energy surfaces are performed for excited states in a number of illustrative systems, including dimers (H(2) and NaCl) and gas-surface systems [Cl-Na(100) and Cl(2)-Na(100)]. It is based on density-functional theory and is a generalization of the Delta self-consistent field (DeltaSCF) method, where electron-hole pairs are introduced in order to model excited states, corresponding to internal electron transfers in the considered system. The desired excitations are identified by analysis of calculated electron orbitals, local densities of states, and charge densities. For extended systems, where reliable first-principles methods to account for electronically excited states have so far been scarce, our method is very promising. Calculated results, such as the chemiluminescence of halogen molecules impinging on a alkali-metal surface, and the vertical (5 sigma-->2 pi(*)) excitation within the adsorbed CO molecule on the Pd(111) surface, are in working agreement with those of other studies and experiments.

Density-functional bridge between surfaces and interfaces

Interfaces are brought into focus by many materials phenomena, e.g., contacting, materials strength, and wetting. The class of interfaces includes ultra-high-vacuum surfaces, which provide a meeting place for numerous accurate experimental techniques and advanced theory. Such meetings stimulate detailed comparisons on the quantum level between experiment and theory, which develop our theoretical tools and understanding. This creates good positions for broadened applications, e.g., other interfaces, which typically lack adequate experimental tools. Density-functional theory is one key bridge between surfaces and other interfaces. The paper presents some recent typical applications from our group, including brief reports on interface structures (VN/Fe, TiC/Co, TiC/Al 2 O 3 ), dynamic processes at surfaces and interfaces (O 2 /Al(111), scanning-tunneling microscopic spectroscopy and manipulation), adsorption and desorption (CO, N 2 , NO, and O 2 on Al(111)), electronic and magnetic properties at surfaces and interfaces (magnetic effects on TiC/Co, surface state on κ-Al 2 O 3 (001)), and epitaxial growth on surfaces (Al(111) and alike). Similar progress in many worldwide materials groups and networks gives a basis for the ongoing paradigm shift in materials science.

Hard-materials-surface prediction of one-dimensional electron gas

A new and robust one-dimensional electron gas (1DEG) is predicted on the (001) surface of κ-Al 2 O 3 by means of a density-functional-theory (DFT) study. Our first-principles calculations show that this surface is Al terminated, with the Al atoms lying in [100] zigzag lines, and has an excess of electrons due to the charge asymmetry in the bulk κ-Al 2 O 3 . The κ-Al 2 O 3 phase itself is metastable up to 1000 K. To test the robustness of our materials-theory prediction of the 1DEG along the zigzag Al lines, the critical temperature due to a Peierls metal-insulator instability has been estimated to be in the temperature range [0,1] K, using a tight-binding model, where the model parameters are determined with additional DFT calculations. The virtues of both the materials-theory design and the possible 1DEG realization are also discussed.