MedeA Microstructure Builder - Build complex grain structures

Creating realistic microstructure models is a prerequisite to understanding materials’ behavior, predicting materials’ properties, and optimizing materials’ performance. Properties such as strength, ductility, conductivity, and reactivity of realistic materials are directly influenced by a materials’ microstructure. By manipulating the microstructure, material performance can be optimized, e.g., the grain size in a polycrystalline material can be tailored to improve its mechanical properties. The MedeA Microstructure Builder can create atomic structures for metals, semiconductors, or ceramics, whereas organic systems are better handled by the MedeA Amorphous Builder module.

The Microstructure Builder generates atomistic grain structures composed of user-specified phases using a Seed & Growth algorithm developed at Materials Design. In this algorithm, seed points are either placed randomly or at user-specified coordinates in the supercell. Each seed point is then used as an origin to grow a grain by placing atoms from that seed point outwards until the grain boundary is reached. The beginning user only needs to specify the components and number of grains per component, where a component is any periodic unit cell. An example is shown in the top panel of the figure below for a Cu-Ag grain structure. The building of the microstructure is carried out interactively, with the resulting structure appearing in the graphical interface when the built is complete.

Examples of atomistic models built with the Microstructure Builder. From top to bottom and left to right: A Cu-Ag multicrystalline grain structure, polycrystalline Li₁₀GeP₂S₁₂, Li, Ge, and P multi-phase grain structure with voids ready to be sintered, and a ZrO₂ nanocrystal.

Several growth parameters can be adjusted by an intermediate user. First, the user can enable and change the default thresholds on interatomic distances. Without such a threshold, atoms from different grains might be placed arbitrarily close to each other at the grain boundary in the Seed & Growth algorithm. Second, the user can specify whether the grains should grow stoichiometrically. In that case, the number of atoms of each species in the grain is proportional to the number of atoms of that species in the unit cell.

Advanced usage allows for the creation of porous microstructures, as seen in the bottom left panel of the figure. The Microstructure Builder can also be used for the generation of interfaces with complex and irregular shapes or nanocrystals of complex shapes, as shown in the bottom right panel of the figure.

The resulting models are fully periodic and can be used directly with the MedeA LAMMPS module. Additionally, the user can further edit the structures in their MedeA client to introduce impurities, vacancies, and interstitial atoms as needed. Voids can be populated in a subsequent step with the MedeA Docking module. We also recommend the MedeA Interface Builder which offers more control over the interface in simpler slab geometries.