Improving the Applicability of Density Functional Theory Simulations for the Description of Metal-Organic Interfaces
Elisabeth Wruß
Institute of Solid State Physics, Graz University of Technology
13:30 - 14:10 Friday 23 June 2017 SR 05.11 IGAM, Inst.f.Physik KFU Graz

Density functional theory (DFT) is one of the most widely used methods in computational material research, as it provides a good compromise between computational expenses and accuracy. Using standard semi-local DFT, comparably large systems containing several hundred or even thousands of atoms can be simulated, accurately describing many geometric and electronic characteristics. Nonetheless, one has to take into account that the widely used DFT methods contain several approximations and are therefore not fit to describe all properties of a system correctly. Thus it is necessary to choose the method considerately, carefully monitoring observables and occasionally comparing them to experiment. This is especially true for metal-organic interface, where the system size often excludes the use of more advanced (and more expensive) band structure methods.
In my work I investigate several examples of metal-organic interfaces, where “straightforward” simulations run the risk of producing inaccurate results, and in which effects occur that are not obtained in standard semi-local DFT.
For the case of chlorogallium phthalocyanine on Cu(111), I will discuss the interplay of adsorption geometry and electronic properties and show how easily one might misinterpret the processes occurring at the surface. In the case of copper phthalocyanine adsorbed on Ag(111), curious magnetic properties arise, which depend strongly on the used DFT functional.
An additional chapter of my work incorporates the investigation of the charge-transfer properties of metal-organic interfaces, which can be modified by alloying or decoupling the adsorbate from the substrate. While standard semi-local functionals fractionally charge the adsorbed molecules, the use of hybrid DFT functionals leads to different charge transfer properties and so-called integer charge transfer in some specific cases.
These examples highlight the importance of a thoughtful choice of method and careful examination of results as this might lead to a fundamentally different interpretation of the physics of a system.