Ligand Effects in Assembly of Cubic and Spherical Nanocrystals: Applications to Packing of Perovskite Nanocubes

We establish the formula representing cubic nanocrystals (NCs) as hard cubes taking into account the role of the ligands and describe how these results generalize to any other NC shapes. We derive the conditions under which the hard cube representation breaks down and provide explicit expressions for the effective size. We verify the results from the detailed potential of mean force calculations for two nanocubes in different orientations as well as with spherical nanocrystals. Our results explicitly demonstrate the relevance of certain ligand conformations, i.e., vortices, and show that edges and corners provide natural sites for their emergence. We also provide both simulations and experimental results with single component cubic perovskite nanocrystals assembled into simple cubic superlattices, which further corroborate theoretical predictions. In this way, we extend the Orbifold Topological Model (OTM) accounting for the role of ligands beyond spherical nanocrystals and discuss its extension to arbitrary nanocrystal shapes. Our results provide detailed predictions for recent superlattices of perovskite nanocubes and spherical nanocrystals. Problems with existing united atom force fields are discussed.

Automated summary

We develop a formula for representing cubic nanocrystals, considering the influence of ligands, and apply it to generalize to other nanocrystal shapes. We investigate the conditions under which this representation breaks down and determine the effective size. By conducting potential of mean force calculations and experimental studies, we support the relevance of specific ligand conformations and their emergence at edges and corners. Additionally, we present simulations and experimental results on cubic perovskite nanocrystals, further confirming the theoretical predictions. Our findings extend the Orbifold Topological Model beyond spherical nanocrystals and provide detailed predictions for nanocubes and spherical nanocrystals in recent superlattices. We also discuss limitations of existing united atom force fields.