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O: Fachverband Oberflächenphysik

O 6: Organic Molecules on Inorganic Substrates I: Adsorption & Growth

O 6.9: Talk

Monday, March 18, 2024, 12:30–12:45, MA 042

“Organic” ab initio thermodynamics for interfaces: Which corners can we (not) cut? — •Christoph Wachter and Oliver T. Hofmann — Institute of Solid State Physics, Graz University of Technology, Graz, 8010, Austria

Ab initio thermodynamics is a powerful tool to computationally predict the most stable structure under given environmental conditions, i.e. at finite temperature and pressure. In principle, this requires evaluating the free energy for a large number of structures, which is a costly endeavor. To keep the computational cost tractable, the current paradigm is to approximate the free energy and neglect several expensive terms, such as the vibrational zero-point energy, the thermal occupation of vibrations and the configuration entropy.

However, these approximations have been developed with simple inorganic adsorbates in mind. It is a priori unclear whether they also hold true for organic/inorganic interfaces, which feature a rich chemistry. Moreover, several effects can occur in these systems (such as cis-trans isomery) that are hardly present for inorganic adsorbates. In this work, we therefore re-evaluate the most common approximations for three conceptually very different systems: a clearly physisorbed system, a covalently bonded self-assembled monolayer, and an interfaces that undergoes charge-transfer reactions. In an attempt to generalize across the different types of interfaces, we discuss which calculations can generally be skipped in order to allow efficient evaluations of the relative stabilities of different phases.

Keywords: ab initio thermodynamics; surface polymorphism; structure prediction; phase diagrams