(579h) The Influence of Softness on the Stability of Binary Colloidal Crystals

Binary systems of spherical colloids have shown the ability to self-assemble into many more superlattice structures than comparable monodisperse systems. Understanding the nature of the interparticle forces in such self-assembly is critical to target specific structures for self-assembly. When the inter-particle forces are primarily repulsive, the binary hard sphere model has proven useful in understanding the phase behavior of colloids. Here we computationally investigate the influence of “softness”, the steepness of the interaction potential, on the solid phase behavior of particles interacting with a purely repulsive, isotropic pair potential. We determine the ground state phase diagram for our model using a basin-hopping algorithm to optimize candidate structures for low enthalpy. The phase behavior of hard sphere systems is often understood by looking at the packing fraction of different phases; however, we find that a very small amount of softness can change the stable ground state phase of a system away from the densest packing structure. We also find softness increases the stability of many experimentally observed structures. Our results provide further insight into why particular structures self-assemble and will be useful as a reference for experimentalists working with softly repulsive particles.