Nanoparticles with Cubic Symmetry: Classification of Polyhedral Shapes

Abstract

The shape of crystalline nanoparticles (NP) can often be described by polyhedra with flat facet surfaces. Thus, structural studies of polyhedral bodies can help to describe geometric details of NPs. Here we consider compact polyhedra of cubic point symmetry Oh.as simple models. Their surfaces are described by facets with normal vectors along selected directions (a, b, c) together with their symmetry equivalents forming a direction family {abc}. For given {abc} this yields generic polyhedra with up to 48 facets where we focus on polyhedra with facets of {abc} = {100}, {110}, and {111}, suggested for metal NPs with cubic lattices. The resulting generic polyhedra, cubic, rhombohedral, and octahedral, can serve for the description of non-generic polyhedra as intersections of corresponding generic species. Their structural properties are shown to be fully determined by only three structure parameters, facet distances R100, R110, and R111 of three types of facets. This provides a phase diagram to completely classify the corresponding Oh symmetry polyhedra. Structural properties of all polyhedra, such as shape, size, and facet geometries, are discussed in analytical and numerical detail with visualization of characteristic examples. The results may be used for respective nanoparticle simulations but also as a repository assisting the interpretation of structures of real compact nanoparticles observed by experiment.