SKM 2023 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 14: Development of Computational Methods: Thermodynamics and Local Chemistry, Electronic Structure
MM 14.3: Talk
Tuesday, March 28, 2023, 10:45–11:00, SCH A 251
Extracting free energies from local composition fluctuations in solids: Theoretical background and atomistic simulations — Daniel Bitter1, Marvin Poul2, Guido Schmitz1, and •Sebastian Eich1 — 1Institute of Materials Science, University of Stuttgart, Heisenbergstraße 3, D–70569 Stuttgart, Germany — 2Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, D–40237 Düsseldorf, Germany
While thermodynamic fluctuation theory has been applied to liquids for decades in order to obtain direct thermodynamic information, i.e. Gibbs free energies, from local composition fluctuations, the present work offers an extension for the application in solids. It is demonstrated that composition fluctuations are affected by an additional elastic work term which arises only in solids, thus covering liquids as a special case. The extended fluctuation model is verified through atomistic simulations in an exemplary Cu–Ni embedded-atom system for which Monte Carlo simulations have been carried out in the semi-grandcanonical ensemble at fixed temperature over the entire composition range. Composition fluctuations were monitored in a subvolume over time and statistically evaluated in terms of the variance, demonstrating perfect agreement with the prediction from the extended model. This method has been developed primarily for the application to experimental atom probe data, where three-dimensional chemical information is available with sub-nanometer accuracy, allowing a direct measurement of local composition fluctuations to extract thermodynamic information.