MedeA Morphology

By Materials Design, Inc.

MedeA Crystal Morphology From Atomic Arrangement to Crystal Shape At-a-Glance MedeA ®1 Crystal Morphology employs lattice parameters and space-group symmetry as well as information on relative surface stabilities to simulate the morphology of a crystal. Key Benefits • Interactive determination of the morphology • Highly flexible choice of different models of relative surface stabilities When crystals are grown under equilibrium condi-tions, their macroscopic shape or morphology is determined by the minimum of the total surface free energy of the crystal, which in turn is governed by the microscopic interatomic forces. Since the latter are accessible to atomistic simulations, first-principles calculations of morphologies have be-come the method of choice to predict crystal mor-phologies. At the same time, macroscopically observed mor-phologies of crystals and crystallites provide in-sight into the details of materials at the micro-scopic levels. In particular, scanning electron mi-croscopy (SEM) images, as widely employed in the analysis of materials samples, reveal information on the morphology adopted by individual crystal-lites. MedeA Crystal Morphology combines the lattice parameters and space-group-symmetry of a crys-tal with information about the relative energies of low-index crystal faces to simulate the morphol-ogy. As originally proposed by Wulff, the length of a surface normal from a given crystal face to a common point within the crystal interior is pro-portional to its surface energy 2. Indeed, a crys-tal shape constructed in this manner minimizes its surface free energy. The relative stabilities of crystal faces enter via a set of rules proposed by Bravais, Friedel, Donnay and Harker 3,45. Alternatively, computed or mea-sured surface energies can be used. As an example, the morphology of Cr 2O3 is dis-played in the figure below. It is based on lattice parameters and space-group symmetry as pro-vided by MedeA InfoMaticA as well as surface en-ergies reported by Davies et al. 6. As expected, the computed morphology reflects the rhombohedral shape of the corundum structure. Fig. 1: MedeA Crystal Morphology Screenshot: Morphology of Cr 2O3 as based on reported surface energies 6 Key Features • An intuitive user interface for the generation of morphologies using lattice parameters and space-group symmetry as input • Full integration with MedeA InfoMaticA • Uses Wulff construction for morphology generation • Relative surface stabilities are automatically determined from the rules introduced by Bravais, Friedel, Donnay and Harker • Alternatively, computed or measured surface energies can be employed • Morphology files can be saved for later use • Optimal graphical representation of results through a variety of visualization options Fig. 2: The morphology of titanium metal and a nano-scale atomic model, containing 24,840 atoms, constructed using MedeA Crystal Morphology. Model Building MedeA Crystal Morphology provides model con-struction capabilities. For any given crystallite morphology, the MedeA Surface Builder can be invoked through a right-click context menu op-tion, facilitating efficient atomic model construction based on crystallite surfaces. Additionally, nano-scale crystallite atomic models may be constructed using MedeA Crystal Mor-phology. Properties • Morphology of arbitrary crystals Required Modules • MedeA Environment • MedeA Morphology