FWF - Reliably - Reliably modeling the electronic structure of self-assembled monolayers

Self-assembled monolayers of organic molecules covalently bonded to (noble) metals have been in the focus of multi-disciplinary research for a number of years. Their electronic properties are of particular interest for the use in molecular and organic electronics. Moreover their experimentally well characterized and highly reproducible properties render them ideal test-systems for benchmarking theoretical approaches. In the course of past research efforts a lot has been learned about the fundamental aspects that link the chemical structure of a SAM to its structural and electronic characteristics. However, when trying to predict SAM-properties on a more quantitative level, two main problems arise: In a large number of experimental studies, especially when applying SAMs in devices, one is dealing with non-perfectly ordered layers; moreover, the usually applied simulation method, namely density functional theory (DFT) in the framework of the local density or generalized gradient approximation, suffers from several intrinsic shortcomings. The goal of the present project is to assess and, if possible, correct these two aspects: Using molecular dynamics simulations, we will investigate the impact of temperature on the structural parameters of various SAMs and, more importantly, test the consequences of an incomplete coverage of the metal surface. Moreover, we will study the consequences of imperfections of the metal substrates on the dynamic SAM properties. From the obtained arrangements of the molecules, we will carefully extract test structures for performing electronic-structure calculations, thus, correlating structural imperfections with the resulting electronic properties of the SAM-covered metal. In parallel, we will work on strategies for addressing the main shortcomings of conventional DFT. This includes the application of newly developed correction schemes to account for van der Waals interactions. We will also test approaches to correct for the self-interaction error, excessively benchmark hybrid functionals for the description of metal/organic interfaces and apply post-DFT methods. To account for the well-known band-gap problem of DFT and for the polarization of the metal induced by long-range correlation effects, we will also evaluate computationally far less costly effective approaches. The envisioned research will involve intensive collaborations with international as well as national partners experienced either in the modeling or the experimental investigation of metal/organic interfaces. These will be crucial for a successful completion of the envisioned research program that would be too ambitious to be pursued only in a single group. Additionally, access to high-quality experimental data will allow a thorough validation of the obtained results.