IMPRESS

Key challenges that we plan to tackle in the workshop

• Defects and grain boundaries: Which kind of defects need to be accounted for in computational studies? To what extend are defects and their energies relevant for the observed phase? Are defects a frequent mechanism for organic overlayers to reduce strain induced by the substrate lattice?


• Commensurability: Band-structure calculations of interfaces always assume fully commensurate interfaces. Many interfaces, and in particular technologically relevant ones, show point-on-line or point-on-point commensurability, or are fully incommensurate. How can such interfaces be considered within first-principle calculations, without further increasing the already almost intractably large search space?


• Thermodynamics versus kinetics: Monte-Carlo studies notwithstanding, most computational efforts focus on the thermodynamically most stable structure. How can we make sure that an experimentally observed structure is indeed the thermodynamically most stable, and not metastable? Is it possible to define clear target properties that allow computational structure search methods to be geared towards metastable structures?


• Processing conditions: In experiment, the obtained polymorph often depends sensitively on the processing conditions, in particular when solution-based techniques, such as bar meniscus shearing or doctor-blading, is employed. (How) should structure search techniques account for the processing? Since these structures are often not in thermodynamic equilibrium, what is the property that should be optimized? (See previous question)


• Experimental error bars: The analysis of experiments always leaves some room for interpretation, at least in the form of error bars that are inevitably associated with the data. How should structure search techniques account for such error bars?


• Multilayer and morphology: While efficient algorithms exist to predict the structure of bulk materials or for interfaces (i.e., monolayers), strategies to determine the geometry of multilayers or thin films are scarce. What is a good strategy to consider the second, third, etc. layer at the interface? Is it plausible to only consider the first monolayer and neglect the substrate? How to we deal with "cannibalizing" structures, where the first (wetting) layer disappears after deposition of additional material?


• Polymorph identification and retrieval: There is presently no established method to label and uniquely identify a given surface structure. This poses a significant challenge for the comparison between theory and experiment and makes a retrieval of already proposed structure from literature or material databases, such as the Novel Materials Discovery NOMAD laboratory (https://nomad-coe.eu/), almost impossible. Is it possible to develop a sensible, easy to apply labelling scheme to interfaces?