Simulation study of the emergence of valency in colloidal crystals using DNA-functionalized particles

The concept of valence electrons is central to chemical bonding theory, which defines how atoms form anisotropic bonding geometries in molecules and crystalline solids. A recent study [Girard et al., Science, vol. 364, pp. 1174, 2019] showed that DNA-functionalized colloidal particles behave similarly when reduced in size and DNA grafting density. In this presentation, we introduce a simulation study of an approach to generating various low symmetry and complex colloidal crystals based upon programmable atom equivalents (PAE, nanoparticles functionalized with many DNA strands) and mobile electron equivalents (EE, small particles functionalized with a low number of DNA strands complementary to the PAEs). We developed a simplified particle model using the HOOMD-Blue MD simulation toolkit, where PAEs and EEs are represented by rigid spherical cores surrounded by soft DNA ligand shell. The finite number of DNA strands on EEs are modeled as spatially uniform anchoring points that can bind to isotropic DNA shells of PAEs. Under appropriate conditions, the spatial distribution of the EEs breaks the symmetry of isotropic PAEs, akin to the anisotropic distribution of valence electrons or coordination sites around a metal atom, leading to a set of well-defined coordination geometries and access to various low symmetry crystalline phases.