Field of Expertise: Advanced Material Science | |
Investigating the influence of van der Waals interactions on the adsorption of flat-lying molecules on metallic surfaces Van der Waals (vdW) interactions crucially impact the adsorption of organic molecules on metal surfaces. Their contribution to the overall binding mechanism becomes especially significant in case of flat-lying organic molecules, which are often referred to as being only weakly bound to metallic substrates. To model such systems (semi-)local density-functional-theory (DFT) is frequently used, although it does not include vdW interactions because of their inherent nonlocal character. Therefore, the adsorption geometry often can not be described accurately in this theoretical framework, which makes a reasonable determination of the electronic properties without additional experimental information impossible. We here circumvent this shortcoming of (semi-)local DFT by applying the PBE + vdWsurf [1] approach, which has been shown to strongly improve the modelling of vdW interactions at metal-organic interfaces. Geometry, binding distances and electronic properties of phthalocyanines (PCs) on different noble-metal surfaces and more complex metal-organic interfaces such as three-layer systems [2] and non-planar PCs have been studied on an atomistic level. Building on the excellent agreement with experimental data, we analyse the binding processes in more depth. We find significant vdW contributions for virtually all cases and correspondingly large binding energies for systems commonly thought of as being only weakly coupled to the surface. Our results demonstrate the multitude of interactions responsible for the formation of hybrid metal-organic interfaces and highlight the strong contribution of “weak” vdW interactions. |