2D-Systems: Ground and excited states at surfaces and interface

Total Energy methods

Surface problems, such as the dynamics of molecules on a surface, including catalysed reactions) present a variety of bonding situations and energy barriers, and so test present density-functional theory (DFT) methods to beyond their limits of accuracy. We shall build on current collaborations to develop more accurate methods within DFT (including generalised- Kohn-Sham DFT) and many-body perturbation theory (MBPT).

York and S. Sebastian teams will contribute through developments of the MBPT-GW method; Berlin-FU and Louvain will contribute orbital-dependent functionals, combining the RPA with appropriate TDDFT-XC kernels within the adiabatic connection approach. Milan and Rome will also participate, using GW and Green's Functions Methods. The new methods will describe bonding situations ranging from the van der Waals limit to highly covalent bonding. Van der Waals bonded systems are notoriously difficult in traditional density functional theory.

Surface excited states

Improvements of present state-of-the-art methods for surface excited states:

• going beyond common approximations (e.g., extending the existing tools to spin-polarized systems);
• Developing numerically efficient schemes (i.e. with a favourable size-scaling), in order to allow for the study of large unit cells. Paris, S. Sebastian, Milan, Rome and Berlin-FU will collaborate on the development of new TDDFT Kernels; Rome and Jena will also contribute through the nondiagonal GW method.

Self-assembled structures

Formation of self-assembled structures on surfaces. We will use DFT together with thermodynamics, to investigate structures and the driving forces of the self-assembly. Electronic excitations will be treated using state-of-the-art methods, as well as the improved tools obtained within task C2. Rome, Paris and S. Sebastian will look at the problem of the optical properties, Jena will work on self-assembled nanowires of metal atoms on Si surfaces.

Organic biomolecules on surfaces

Interaction of organic biomolecules with surfaces, using parameter-free theoretical methods (DFT, TDDFT, MBPT). We plan to study atomic structures, electronic excitations, optical properties (RAS), Auger and vibrational spectra. Jena, Rome, York and Milan will study, e.g., DNA bases, molecules like porphyrines, and molecules having an amine group which can act as a hook for the attachment to a surface.

Reactions of small molecules on surfaces, in connection with the new experiments with short-intense lasers, which promote specific chemical reaction (e.g., isomerization, or bonding to specific sites), through transitions to excited-state Born-Oppenheimer surfaces. S. Sebastian, Milan and Berlin-FHI will collaborate through suitable developments of both Green-function techniques and TDDFT. Jena and York will study excited states of simple molecules starting with CO and NO on Si surfaces, and moving on to H2O, CH3Cl and unsaturated cyclic hydrocarbons. Lund will study simple chemisorbed molecules, their vibrational and photoelectron spectra, including shake-up of excitations in the substrate and vibronic shake-up.

Spectral features related to interfaces, in particular to grain boundaries. It requires participation of specialists in the latter field (present in the Paris node), of experts in complex band structure calculations (Louvain), and of specialists of surface optical properties and anisotropy (Rome and Milan). SiO2 and SiHfO4 interfaces with other materials will be studied.

Confinement effects

Goal: to understand the systematic changes in the electronic structure and electronic excitations (e.g. plasmons) when passing from a three-dimensional (bulk) material to a very thin layer. Confinement effects will be studied for selected materials, ranging from those used in semiconductor technology to catalytically active oxides. Multipole plasmons will be studied at Berlin-FHI; Berlin-FU will contribute using TDDFT, Rome will contribute through the GW method, and Milan with the embedding approach for a semi-infinite surface.