WEB Free energies of segregation: thermodynamic integration at grain boundaries using pyironThursday (27.02.2020) 15:50 - 15:50 Poster Room Part of:
Microstructural evolution in metallic systems is thermodynamically driven by the reduction of free energy in the system. The segregation of solute atoms to grain boundaries thus plays a key role in influencing this evolution, first by reducing the interfacial energy of a boundary through favourable segregation, and second in the form of solute-drag by introducing an energy barrier to further motion of the boundary which hinders coarsening. In this work, we calculate not only the enthalpy of segregation, but rather use thermodynamic integration to compute the free energy of segregation for solutes at grain boundaries in Al as a function of temperature. This allows us to compute the 'defect phase diagram' for a particular boundary by looking at the range of chemical potentials over which a given configuration of solute decoration remains energetically most favourable.
To implement this scheme, we use a cyclic-graph approach inside the pyiron computational framework. Many atomistic simulation algorithms rely on a shared set of common operations; by encoding these operations as vertices inside the cyclic graph, we demonstrate one way that pyiron can be used for rapid prototyping of complex simulation protocols. By building a library of such vertices, the barrier to implementing new algorithms (i.e. graphs) is only the construction of the few vertices unique to that algorithm, and the ordering of the vertices in the graph. We briefly provide other examples of this approach, including quantum mechanical/molecular mechanical coupled calculations, and the finite string method for calculating transition paths.