Approaches for modeling quantum dots (QDs) at the atomistic level typically approximate QDs as smooth spheres (basic model) or as a collection of pristine crystallographic planes that can be isolated and considered individually (an oversimplification). In reality, modeling wurtzite QDs requires the specification of spatial arrangements of clusters of atoms oftentimes exhibiting irregular and complex surfaces. The presented study exclusively considers wurtzite structures, the most-common structure of the most-common species of QD (CdSe).  Generation of stoichiometric wurtzite nanostructures is typically accomplished by means of isolating atoms from a large lattice falling inside the boundaries of a series spheres with radii approximating the desired size of nanocrystal and having origins defined at points (such as the midpoint of a bond), guaranteeing a 1:1 cluster stoichiometry. This method fails to identify the vast-majority of possible spherical wurtzite structures.  This work seeks to generate and catalogue all stoichiometric wurtzite clusters of atoms that are approximately spherical and maintain the wurtzite structure. Structures can be generated by repetitive addition of binary pairs of the atoms sitting at neighboring positions of a large lattice, to an initial structure. After each binary addition, structures failing to satisfy certain morphological characteristics are removed from the population of structures and not used as initial structures for any subsequent round of binary addition. Large sets containing tens of thousands of structures with radii &lt;13Å can be generated in this way for CdSe wurtzite, a result which can be generalized for the generation of wurtzite nanocrystal structures made of any material (assuming the bond length of that material does not deviate substantially from the CdSe bond length). This result was attained by assessing the spherical nature of the structures and rejecting those which were determined to deviate substantially from ideally spherical. The distribution of the number of structures across the radial range is distinct and appears superficially periodic. This novel and efficient method for generating large sets of unique wurtzite structures can potentially be utilized to model dynamic phenomena such as QD growth because the static set is a time-lapse representation of all the structures that may be formed throughout the growth process, assuming the validity of the morphological boundary conditions.<br/>

Generation and analysis of unique wurtzite quantum dot structures

2019 Spring National Meeting

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